CN1221680C - Thin steel sheet for automobile excellent in notch fatigue strength and method for production thereof - Google Patents
Thin steel sheet for automobile excellent in notch fatigue strength and method for production thereof Download PDFInfo
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- CN1221680C CN1221680C CNB028054024A CN02805402A CN1221680C CN 1221680 C CN1221680 C CN 1221680C CN B028054024 A CNB028054024 A CN B028054024A CN 02805402 A CN02805402 A CN 02805402A CN 1221680 C CN1221680 C CN 1221680C
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0224—Two or more thermal pretreatments
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
Abstract
The present invention provides a thin steel sheet, for automobile use, excellent in notch-fatigue strength, and a method for producing said steel sheet. Specifically, the present invention is a thin steel sheet for automobile use excellent in notch-fatigue strength, said steel sheet containing, in mass, 0.01 to 0.3% C, 0.01 to 2% Si, 0.05 to 3% Mn, 0.1% or less P, 0.01% or less S and 0.005 to 1% Al, with the balance consisting of Fe and unavoidable impurities, characterized in that, on a plane at an arbitrary depth within 0.5 mm from the surface of said steel sheet in the thickness direction thereof, the average of the ratios of the X-ray diffraction strength in the orientation component group of 100U<011> to 223U<110> to random X-ray diffraction strength is 2 or more and the average of the ratios of the X-ray diffraction strength in the three orientation components of 554U<225>, 111U<112> and 111U<110> to random X-ray diffraction strength is 4 or less and that the thickness of said steel sheet is in the range from 0.5 to 12 mm, and a method for producing said steel sheet by subjecting a steel slab containing aforementioned chemical components to rolling at a total reduction ratio of 25% or more in a temperature range of the Ar3 transformation temperature + 100 DEG C or lower.
Description
Technical field
The present invention relates to the thin steel sheet for automobile and the manufacture method thereof of excellent in notch fatigue strength, particularly relate to and be suitable as the thin steel sheet for automobile and the manufacture method thereof of raw-material, excellent in notch fatigue strength that FATIGUE CRACK GROWTH that blanking (punching) adds the Ministry of worker and welding zone equal stress concentrated part becomes the automobile traveling part parts etc. of problem.
Background technology
In recent years, because the fuel cost raising of automobile etc.,, advancing light metal such as aluminium alloy and high tensile steel plate to be applicable to automobile component so turn to purpose with light weight.But, though light metals such as aluminium alloy have the high advantage of specific tenacity, with steel relatively, price is high significantly, so it is suitable for and is limited to special purposes.So in order to advance the lightweight of automobile in wider scope, an urgent demand is suitable for cheap high tensile steel plate.
Requirement at such high strength, up to now, the exploitation of the steel plate that has both the steel plate of intensity and drawability (deep drawing quality) and baking hardenability is arranged etc. is being carried out in the field of the cold-rolled steel sheet that uses in about 1/4 vehicle body that accounts for car body weight and cladding plate class, helps the lightweight of car body., now, light-weighted object is transferred on about 20% the structural member and running gear member that accounts for car body weight, and the exploitation of the high-strength steel sheet that these members are used becomes the task of top priority.
But high strength generally makes plasticity material behavior deteriorations such as (processibilities), so do not make the material behavior deterioration and how to seek the important elements that high strength becomes the high tensile steel plate exploitation.Particularly as structural member and the running gear member desired characteristic of steel plate, unit elongation much less, shearing and blanking processibility, deburring (burring) processibility, fatigue durability and solidity to corrosion etc. are important, and it is important how making high strength and these balance of properties under higher-dimension.
For example, parts such as suspension system registration arm, by shearing and blanking processing (punching processing), carry out die-cut and perforate after press forming, make parts according to different further welding of member.For such parts, to such an extent as to crackle from shear processing end face and the welding zone near the expansion fatigure failure situation many.That is, the end face of shearing processing and welding zone become the stress concentration portion resemble the breach, and fatigue cracking is by the there expansion.
On the other hand, usually the safe range of stress of material reduces when breach is sharp-pointed., produce the phenomenon that safe range of stress no longer reduces to a certain degree the time when breach is sharp-pointed.This is because the cause of safe range of stress from crackle generation boundary migration to the crack propagation border.When making the material high strength, the border takes place and improves in crackle, but the crack propagation border do not improve, and therefore, the main points of safe range of stress from crackle generation boundary migration to the crack propagation border move to the sharp-pointed side of breach.So even make the material high strength, the reduction of the safe range of stress that breach causes also becomes significantly, the safe range of stress under the sharp-pointed situation of breach can not obtain high-intensity index.That is, when high strength, the susceptibility of breach is uprised.
Now, partly use steel sheet, use the steel plate of 340-440MPa level, but these members are the 590-780MPa level with the desired intensity rank of steel plate, towards further high strength as these automobile travelings.So,, be indispensable even develop the steel plate that also can obtain the index of high strength under the situation that has sharp-pointed breach in order to adapt to these requirements.
The method that makes blanking and shear the processing end face fatigue strength when existing to improve is divided substantially and can be thought there are 2.One is to eliminate at the sharp notch of blanking with burr of shearing the generation of processing end face and so on, has the resistance that also can improve crack propagation even another is such breach.
As the invention that belongs to the former, for example, the spy opens in the flat 5-51695 communique and discloses following technology: make the addition of Si few, reduce tension set by the precipitate of Ti, Nb, V, thereby suppress the generation of burr, improve the fatigue strength under blanking and shearing machining state.In addition, the spy opens flat 5-179346 communique and discloses following technology: limit the upper limit of the volume fraction of bainite by the upper limit of stipulating rolling processing temperature, improve at blanking and shear fatigue strength under the machining state.Te Kaiping 8-13033 communique discloses following technology: stipulate the speed of cooling after rolling, by suppressing martensitic generation, improve at blanking and shear fatigue strength under the machining state.
And, Te Kaiping 8-302446 communique discloses following technology: for the complex tissue steel, the hardness of second phase is defined as ferritic more than 1.3 times, reduces blanking and shear the strain energy that adds man-hour, improve at blanking and shear fatigue strength under the machining state.In addition, the spy opens flat 9-170048 communique and discloses following technology: the length of regulation crystal boundary cementite, and add in blanking and shearing and to reduce burr man-hour, improve at blanking and shear fatigue strength under the machining state.And the spy opens flat 9-202940 communique and discloses following technology: by the parameter of regulation with the addition arrangement of Ti, Nb, Cr, improve blanking, improve the fatigue strength under the blanking state.
On the other hand, as the invention that belongs to the latter, the spy opens flat 6-88161 communique and discloses following technology: will be defined as more than 1.5 the technology that fatigue crack growth rate is reduced in (100) face intensity of the structure parallel with rolling surface on top layer.In addition, the flat 10-147846 communique of Te Kaiping 8-199286 communique and Te Kai discloses following technology: (200) diffracted intensity ratio of the thickness of slab direction that will be measured by X ray is defined as 2.0-15.0, making answer or the ferritic area occupation ratio of recrystallize is 15-40%, thereby fatigue crack growth rate is reduced.
; above-mentioned spy open flat 5-51695 number, spy open flat 5-179346 number, spy open flat 8-13033 number, spy open flat 8-302446 number, the spy opens flat 9-170048 number and special open flat 9-202940 number etc. disclosed in the communique, be reduced in blanking and shear the technology of the breach of burr that the processing end face takes place and so on, the degree of the burr of generation is according to blanking and shear the amount of the leaving a blank (clearance that adds man-hour; The gap) and widely changing, therefore is not the technology that can both be suitable under the condition in any case, has to say so inadequate as the steel plate of excellent in notch fatigue strength.
On the other hand, disclosed in Te Kaiping 6-88161 communique, 8-199286 communique and the 10-147846 communique, control texture improves the technology to the resistance of crack propagation, be that the steel of mainly using with large structures such as building machinery, boats and ships, bridges is the invention of object, not resembling the present invention with the thin steel sheet for automobile is object.
In addition, above-mentioned technology be control mainly from the technology of the said propagation rate of crack in PARIS district during destroying mechanics of the fatigue cracking of welded seam portion expansion, be inadequate as resembling thin steel sheet for automobile exists in the crack propagation district in PARIS district hardly owing to plate thickness approaches the technology of occasion.
In addition, adopt the plane fatigue test method of using as the steel sheet purposes, use the test film shown in Fig. 1 (b) to estimate the invention of notch fatigue characteristic, do not find so far.
Summary of the invention
Therefore, the present invention relates to following technology: for thin steel sheet for automobile, do not add the conditions such as the amount of leaving a blank in man-hour according to blanking and shearing, control texture improves the resistance to crack propagation, processes the fatigue cracking of such breach development thereby improve from blanking and shearing.That is, the objective of the invention is to, the thin steel sheet for automobile of excellent in notch fatigue strength and the manufacture method that can at an easy rate, stably make this steel plate are provided.
The inventor adopts the producing apparatus that usually adopts now, and is being under the theory with the steel-sheet manufacturing process of producing under technical scale, has carried out research with keen determination repeatedly for the raising of the notch fatigue strength of realizing thin steel sheet for automobile.It is new discovery as a result, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's (orientation group) the mean value of the random strength ratio of X ray (random intensity ratio) is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉and the mean value of the random strength ratio of X ray of these 3 orientations is below 4, thickness of slab is that the above 12mm of 0.5mm is following very effective to improving notch fatigue strength, thereby has finished the present invention.
That is, main idea of the present invention is as follows:
(1) a kind of thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
(2) thin steel sheet for automobile of excellent in notch fatigue strength of above-mentioned (1) record is characterized in that, the microstructure of above-mentioned steel plate be the volume fraction maximum mutually for bainite or be the complex tissue of ferrite and bainite.
(3) thin steel sheet for automobile of the excellent in notch fatigue strength of above-mentioned (1) record, it is characterized in that the microstructure of above-mentioned steel plate is that to contain volume fraction be the complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%.
(4) thin steel sheet for automobile of excellent in notch fatigue strength of above-mentioned (1) record is characterized in that, the microstructure of above-mentioned steel plate be the volume fraction maximum be martensitic complex tissue mutually for ferrite, second mutually.
(5) a kind of thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, in quality %, contain C:0.01-0.3%, Si:0.01-2%, Mn:0.05-3%, P :≤0.1%, S :≤0.01%, Al:0.005-1%, the steel plate that remainder is made of Fe and unavoidable impurities, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
(6) thin steel sheet for automobile of the excellent in notch fatigue strength of above-mentioned (5) record, it is characterized in that, in quality %, also further contain Cu:0.2-2%, B:0.0002-0.002%, Ni:0.1-1%, Ca:0.0005-0.002%, REM:0.0005-0.02%, Ti:0.05-0.5%, Nb:0.01-0.5%, Mo:0.05-1%, V:0.02-0.2%, Cr:0.01-1%, more than a kind or 2 kinds of Zr:0.02-0.2%.
(7) thin steel sheet for automobile of the excellent in notch fatigue strength of above-mentioned (5) or (6) record, it is characterized in that the microstructure of above-mentioned steel plate is any following tissue: 1) the volume fraction maximum mutually for bainite or be the complex tissue of ferrite and bainite; 2) containing volume fraction is the complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%; 3) the volume fraction maximum is that ferrite, second is martensitic complex tissue mutually mutually.
(8) a kind of thin steel sheet for automobile of excellent in notch fatigue strength is characterized in that, has implemented zinc-plated to each thin steel sheet for automobile of putting down in writing of (1)-(7).
(9) a kind of method of making the thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, to contain C:0.01-0.3%, Si:0.01-2%, Mn:0.05-3%, P in quality %: S≤0.1%: when≤0.01%, carrying out hot rolling after the steel disc roughing that Al:0.005-1%, remainder are made of Fe and unavoidable impurities, at Ar
3It is finish rolling more than 25% that the thick total draft of steel plate is carried out in humidity province below phase point temperature+100 ℃, the plate face of the most surperficial any degree of depth up to 0.5mm along thickness direction from this steel plate 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
(10) method of the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (9) record is characterized in that, after the above-mentioned finish rolling, with the above speed of cooling cooling of 20 ℃/s, reels under the coiling temperature more than 450 ℃.
(11) method of the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (9) record is characterized in that, after the above-mentioned finish rolling, at Ar
1Phase point temperature is above, Ar
3The following humidity province of phase point temperature stops 1-20 second, thereafter again with the above speed of cooling cooling of 20 ℃/s, is reeling greater than under 350 ℃, coiling temperature less than 450 ℃ humidity provinces.
(12) method of the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (9) record is characterized in that, after the above-mentioned cooling, reels under the coiling temperature below 350 ℃.
(13) method of the thin steel sheet for automobile of each manufacturing excellent in notch fatigue strength of putting down in writing of above-mentioned (9)-(12) is characterized in that, when above-mentioned hot rolling, is lubricated rolling.
(14) method of the thin steel sheet for automobile of each manufacturing excellent in notch fatigue strength of putting down in writing of above-mentioned (9)-(13) is characterized in that, when above-mentioned hot rolling, carries out oxide skin after roughing ends and removes.
(15) a kind of method of making the thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, to contain C:0.01-0.3%, Si:0.01-2%, Mn:0.05-3%, P in quality %: S≤0.1%: when≤0.01%, carrying out hot rolling after the steel disc roughing that Al:0.005-1%, remainder are made of Fe and unavoidable impurities, at Ar
3It is finish rolling more than 25% that the thick total draft of steel plate is carried out in humidity province below phase point temperature+100 ℃, then pickling, again the thick draft of steel plate less than 80% cold rolling after, carry out more than recovery temperature, Ac
3Humidity province below phase point temperature+100 ℃ keeps the answer or the recrystallization annealing of 5-150 second, refrigerative operation, the plate face of the most surperficial any degree of depth up to 0.5mm along thickness direction from this steel plate 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
(16) method of thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (15) record is characterized in that, above-mentioned cold rolling after, carry out at Ac
1Phase point temperature is above, Ac
3Humidity province below phase point temperature+100 ℃ keeps 5-150 second, carries out the thermal treatment of refrigerative operation thereafter.
(17) method of the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (15) record, it is characterized in that, keep 5-150 after second in the said temperature district, carry out with the above speed of cooling of 20 ℃/s be cooled to greater than 350 ℃, less than 450 ℃ humidity provinces, thereafter, keep in this humidity province again 5-600 second, be cooled to the thermal treatment of the operation of the humidity province below 200 ℃ with the 5 ℃/speed of cooling more than the s.
(18) method of the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (15) record, it is characterized in that, keep 5-150 after second in the said temperature district, carry out being cooled to the thermal treatment of the operation of the humidity province below 350 ℃ with the above speed of cooling of 20 ℃/s.
(19) a kind of method of making the thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, in each steel plate of putting down in writing of (11)-(18), also further contain Cu:0.2-2%, B:0.0002-0.002%, Ni:0.1-1%, Ca:0.0005-0.002%, REM:0.0005-0.02%, Ti:0.05-0.5%, Nb:0.01-0.5%, Mo:0.05-1%, V:0.02-0.2%, Cr:0.01-1%, more than a kind or 2 kinds of Zr:0.02-0.2% in quality %.
(20) method of thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (10) or (16) record is characterized in that, the microstructure of above-mentioned steel plate be the volume fraction maximum mutually for bainite or be the complex tissue of ferrite and bainite.
(21) method of the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (11) or (17) record, it is characterized in that the microstructure of above-mentioned steel plate is that to contain volume fraction be the complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%.
(22) method of thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (12) or (18) record is characterized in that, the microstructure of above-mentioned steel plate be the volume fraction maximum be martensitic complex tissue mutually for ferrite, second mutually.
(23) a kind of method of making the thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, behind each hot-rolled steel sheet of putting down in writing or answer or recrystallization annealing plate of making (9)-(22), this steel plate of dipping in zinc-plated bath is implemented zinc-plated to surface of steel plate again.
(24) method of thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of above-mentioned (23) record is characterized in that, above-mentioned zinc-plated after, carry out Alloying Treatment again.
Description of drawings
Fig. 1 is the figure of the shape of explanation fatigue test piece, and wherein (a) represents level and smooth fatigue test piece; (b) indication notch fatigue test piece.
Fig. 2 be 100}＜011 〉～223}＜110〉and orientation group the random strength ratio of X ray mean value and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of these 3 orientations and the pass of notch fatigue strength fasten the result's that preliminary experiment of the present invention is shown figure.
Has embodiment
Fundamental research result of the present invention at first, below is described.
Usually fatigue cracking takes place from the surface.This occasion in the stress concentration portion that has breach and so on is no exception.Even process the occasion that end face exists, under the cyclic loading of the load modes that comprises face excurvation direction, observe fatigue cracking also morely and develop from the surface of steel plate end at blanking or shearing again.So as can be known: even under such situation, steel plate is the most surperficial or also effective to improving notch fatigue strength to the increase of the crack growth resistance of the degree of depth of crystal grain about several.In addition, at the thickness of slab central part,, also be difficult to make crackle to stop even crack growth resistance is increased.So, in the present invention, will be defined as the scope that improves the effective structure of fatigue strength along thickness direction from the most surperficial up to 0.5mm.Preferably arrive 0.1mm.
Investigated plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉and orientation group the random strength ratio of X ray mean value and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of these 3 orientations is to the influence of notch fatigue strength.Used for this reason prepares as follows for the examination material.That is, composition is adjusted into 0.08%C-0.9%Si-1.2%Mn-0.01%P-0.001%S-0.03%Al and the casting sheet of melting at Ar
3Finish hot finishing under the arbitrary temp more than the phase point temperature, make thickness of slab reach 3.5mm, reel then.
For the plate face of obtaining the steel plate that obtains like this along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉and orientation group the random strength ratio of X ray mean value and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations, 1/4W that slave plate is wide or 3/4W position cut into φ 30mm test piece carry out the grinding of three mountains processing from the most surperficial degree of depth up to about 0.05mm, then remove strain and make by chemical grinding or electrolytic polishing.
Moreover, so-called with hkl}＜uvw〉crystalline orientation of expression, the normal direction of display plate face with hkl} is parallel, rolling direction and＜uvw〉parallel.The mensuration of the crystalline orientation that the employing X ray carries out for example, is carried out according to the method for putting down in writing in " new edition power リ テ イ X-ray diffraction will be discussed " (distribution in 1986, Song Cunyuan too youth translates, the ア グ ネ of Co., Ltd.) 274-296 page or leaf.
At this, so-called 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray, be by based on { the 3 dimension structures that the 110} pole graph adopts vector method to calculate, or { 110}, { 100}, { 211}, { the 3 dimension structures of using a plurality of pole graphs (being preferably more than 3) to calculate with Series Expansion Method among the 310} pole graph are obtained the contained main orientation of this orientation group, 100}＜011 〉, 116}＜110 〉, 114}＜110 〉, 113}＜110 〉, 112}＜110 〉, 335}＜110〉and 223}＜110〉X-ray diffraction intensity.
For example, the random strength ratio of the X ray of above-mentioned each crystalline orientation of the latter's method, its former state use (001) [1-10], (116) [1-10], (114) [1-10], (113) [1-10], (112) [1-10], (335) [1-10] of the Φ 2=45 ° section of 3 dimension structures, the intensity of (223) [1-10] to get final product unchangeably.But so-called 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is addition mean value of above-mentioned each orientation.
In the occasion of the intensity that can not obtain above-mentioned whole orientation, also can with 100}＜011 〉, 116}＜110 〉, 114}＜110 〉, 112}＜110 〉, 223}＜110〉and addition of each orientation on average replace.
Secondly, so-called 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations, obtain by the 3 dimension structures of similarly calculating with above-mentioned method and to get final product.
Secondly, in order to investigate the notch fatigue strength of above-mentioned steel plate, 1/4W that slave plate is wide or 3/4W position extract the fatigue test piece of the shape shown in Fig. 1 (b) for the mode on long limit by rolling direction.At this, the fatigue test piece that Fig. 1 (a) is put down in writing is the level and smooth test film of the general fatigue strength that obtains mother metal, and the fatigue test piece that Fig. 1 (b) is put down in writing is for obtaining the notched specimen that notch fatigue strength is made.But, fatigue test piece has been implemented the grinding of three mountains processing from the most surperficial degree of depth up to about 0.05mm.Fatigue test makes electricity consumption oil pressure servo type protracted test machine, and test method is according to JIS Z 2273-1978 and JIS Z 2275-1978.
Investigated 100}＜011 〉～223}＜110〉and orientation group the random strength ratio of X ray mean value and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of X ray random strength ratio of 3 orientations is to the influence of notch fatigue strength, the results are shown in Fig. 2.At this, the numeral in zero is that the safe range of stress that obtained by the fatigue test that the notch fatigue test film that uses shape shown in Fig. 1 (b) carries out is (10
7Time intensity under inferior), as following notch fatigue strength.
100}＜011 〉～223}＜110〉and orientation group the random strength ratio of X ray mean value and 554}＜225 〉, 111}＜112〉and 111}＜110〉strong dependency is arranged between the mean value of the random strength ratio of X ray of 3 orientations and the notch fatigue strength, mean value separately is more than 2 and below 4, demonstrates and improves notch fatigue strength significantly.
The inventor studies the result of these experimental results in great detail, following new discovery is arranged: in order to improve notch fatigue strength, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉and the mean value of the random strength ratio of X ray of 3 orientations is to be very important below 4.
But, breach not only, also in order to improve the fatigue cracking generation resistance under level and smooth, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm, 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 4, and 554}＜225 〉, 111}＜112〉and 111}＜110〉and the mean value of the random strength ratio of X ray of 3 orientations is to be preferred below 2.5.
This mechanism may not be clear and definite, but can be presumed as follows.
Usually, there is the safe range of stress of the situation of sharp notch, according to the crack propagation boundary, promptly, the size of the crack growth resistance that crackle stops decided.FATIGUE CRACK GROWTH be at the bottom of the breach or the small-scale viscous deformation of stress concentration part repeatedly, but crack length is shorter, cause the occasion of its viscous deformation in the scope of the size of crystal grain degree, can infer that the influence of crystallographic slip plane and slip direction is big.So if for crack propagation orientation and crack surface, the crystalline ratio with the high slip plane of crack growth resistance and slip direction is many, then suppresses FATIGUE CRACK GROWTH.
Secondly, the qualification reason of the thickness of slab of steel plate of the present invention is described.
When thickness of slab during less than 0.5mm, irrelevant with the degree of stress concentration, can not satisfy yield condition on a small scale, therefore, to such an extent as to the danger of ductile failure is arranged.In addition, consider that from the viewpoint that crackle stops essential enough plasticity is restrained,, wish to be the thickness of slab more than the 1.2mm at least therefore in order to guarantee plane strain state.
On the other hand, when thickness of slab surpassed 12mm, the caused fatigue strength reduction of thickness of slab effect (dimensional effect) became remarkable.When thickness of slab surpasses 8mm, in order to realize obtaining, there is pair equipment to apply the anxiety of excessive load-carrying load to improving the hot rolling or the cold rolling condition of the effective structure of notch fatigue strength, therefore wish for below the 8mm.So in the present invention, its thickness of slab is defined as below the above 12mm of 0.5mm.Be preferably below the above 8mm of 1.2mm.
Secondly, the microstructure of steel plate of the present invention is described.
In the present invention, in order to improve the purpose of its notch fatigue strength, do not need to limit especially the microstructure of steel plate, in ferrite that common steel presents, bainite, perlite, martensitic stucture, if can obtain the structure (the random strength ratio of the X ray of the scope of the invention) of the scope of the invention, then can obtain the effect of raising notch fatigue strength of the present invention, therefore, according to other necessary characteristic, the regulation microstructure is for well.But, for specific microstructure, what for example contain volume fraction and be complex tissue that residual austenite below 25% more than 5% and remainder mainly be made of ferrite, bainite or volume fraction maximum is ferrite mutually, second is mainly martensitic complex tissue etc. mutually, can further improve this effect.
Moreover, at this said bainite, also comprise bainite ferrite (bainitic ferrite) and acicular ferrite (acicular ferrite) tissue.If but the crystalline structure such as residual austenite in the complex tissue more than two-phase are not the occasions of the tissue of bcc, organize the random strength ratio of the X ray that by volume divides rate conversion within the scope of the invention beyond it, then can yet.In addition, the perlite that contains thick carbide becomes the generation site of fatigue cracking, the anxiety that has the fatigue strength of making to reduce terrifically, and therefore, the pearlitic volume fraction that comprises thick carbide wishes to be below 15%.Further, in order to ensure good fatigue characteristic, the pearlitic volume fraction that comprises thick carbide wishes to be below 5%.
Moreover, at this, the volume fraction of so-called ferrite, bainite, perlite, martensite and residual austenite, be with the definition of following area branch rate: the test portion that will cut from the wide 1/4W of steel plate plate or 3/4W position grinds at the rolling direction section, use nitric acid ethanol reagent and/or spy to open the disclosed reagent corrosion of flat 5-163590 communique, the face integration rate of the microstructure of the 1/4t of the thickness of slab that the use opticmicroscope is observed under 200-500 multiplying power doubly.But residual austenite can not easily be differentiated sometimes with the mentioned reagent corrosion, therefore also can calculate volume fraction with following gimmick.
That is, austenite is owing to different with the ferrite crystalline structure, so can easily discern on crystallography.So the volume fraction of residual austenite adopts X-ray diffraction method also can obtain experimentally.That is, be to use the K alpha-ray of Mo, obtain the method for its volume fraction from the austenite and the different use following formulas of ferritic plane of reflection intensity easily.
Vγ＝(2/3){100/(0.7×α(211)/γ(220)+1)}+(1/3){100/(0.78×α(211)/γ(311)+1)}
Wherein, α (211), γ (220) and γ (311) are respectively the X ray reflection face intensity of ferrite (α) austenite (γ).
In the present invention, except notch fatigue strength improves, in order to give good deburring processibility, its microstructure be the volume fraction maximum mutually for bainite or be the complex tissue of ferrite and bainite.But allow to comprise inevitable martensite, residual austenite and perlite.In order to obtain good deburring processibility (hole expanding value), the residual austenite and the martensitic volume fraction of total hard are wished less than 5%.In addition, the volume fraction of bainite wishes to be more than 30%.Further, in order to obtain good ductility, the volume fraction of bainite wishes to be below 70%.
In addition, in the present invention, except notch fatigue strength improved, in order to give good ductility, its microstructure was that to contain volume fraction be the complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%.But always allow to comprise inevitable martensite and perlite less than 5%.
Further, in the present invention, except notch fatigue strength improves, in order to give the low yielding ratio that obtains good shape freezing, its microstructure be the volume fraction maximum be martensitic complex tissue mutually for ferrite, second mutually.But always allow to comprise inevitable bainite, residual austenite and perlite less than 5%.Moreover in order to ensure the low yielding ratio below 70%, ferritic volume fraction wishes to be more than 50%.
The qualification reason of chemical ingredients of the present invention then, is described.
C obtains desirable microstructure and essential element.But amount surpasses at 0.3% o'clock, and the processibility deterioration is so be decided to be below 0.3%.In addition, amount surpasses at 0.2% o'clock, and the tendency of weldability deterioration is arranged, and therefore is preferably below 0.2%.On the other hand, when less than 0.01% the time, intensity reduces, so be decided to be more than 0.01%.In addition, in order stably to obtain being used to obtain enough remained austenite contents of good ductility, be preferably more than 0.05%.
Si is effective to improving intensity as the solution strengthening element.In order to obtain desirable intensity, must contain more than 0.01%., when amount surpasses 2%, the processibility deterioration.So the content of Si is decided to be 0.01-2%.
Mn is effective to improving intensity as the solution strengthening element.In order to obtain desirable intensity, must contain more than 0.05%.In addition, beyond Mn, under the situation of the elements such as Ti that fully add the generation that suppresses the thermal crack that S causes,, wish to add the Mn amount that reaches Mn/S 〉=20 by quality %.And Mn is an austenite stabilizer element, and in order stably to obtain being used to obtain enough remained austenite contents of good ductility, its addition wishes to be more than 0.1%.On the other hand, when interpolation surpasses 3%, owing to produce the slab crackle, so be decided to be below 3%.
P is an impurity, and content is low more good more, and when containing when surpassing 0.1%, when bringing bad influence for processibility and weldability, fatigue characteristic also reduce, and therefore are decided to be below 0.1%.
S is an impurity, and content is low more good more, has served as for a long time, and generating and making the A of local ductility and deburring processibility deterioration is inclusion, therefore should do one's utmost to reduce, if but be 0.01% with next be permissible scope.
Al must add more than 0.005% for deoxidation of molten steel, but owing to cause cost to rise, so be defined as 1.0% on it.In addition, when too many amount ground adds, non-metallic inclusion is increased, make the unit elongation deterioration, therefore wish to be below 0.5%.
Cu has the effect of improving fatigue characteristic under solid solution condition, so add as required.But when less than 0.2%, its effect is little, even content surpasses 2%, effect is also saturated.Therefore the content of Cu is decided to be the scope of 0.2-2%.But the coiling temperature is the occasion more than 450 ℃, and content surpasses at 1.2% o'clock, separates out behind coiling, and the processibility of the making anxiety of deterioration is significantly arranged, and therefore wishes to be decided to be below 1.2%.
Therefore the effect of B by having the safe range of stress of making to rise with the compound interpolation of Cu add as required.But during less than 0.0002%, the effect that obtains is insufficient, when interpolation surpasses 0.002%, causes the slab crackle.So the interpolation of B is decided to be 0.0002-0.002%.
The red brittleness that Ni causes in order to prevent to contain Cu is added as required.But during less than 0.1%, its effect is little, surpasses 1% even add, and its effect is also saturated, therefore is decided to be 0.1-1%.
Thereby Ca and REM make the innoxious element of metamorphosis that becomes the destructive starting point, makes the non-metallic inclusion of processibility deterioration.Even but add respectively less than 0.0005%, its effect does not have yet, even Ca add to surpass 0.002%, REM adds and surpasses 0.02%, its effect is also saturated, therefore wishes to add Ca:0.0005-0.002%, REM:0.0005-0.02%.
Further, in order to give intensity, also can add precipitation strength or more than a kind or 2 kinds of solution strengthening element of Ti, Nb, Mo, V, Cr, Zr.But less than is 0.05%, 0.01%, 0.05%, 0.02%, 0.01%, 0.02% o'clock respectively, can not obtain its effect.In addition, surpass 0.5%, 0.5%, 1%, 0.2%, 1%, 0.2% even add respectively, its effect is also saturated.
Moreover it is also passable to contain total Sn, Co, Zn, W, Mg below 1% in the steel that with these is principal constituent., Sn has the anxiety that produces defective when hot rolling, so wish to be below 0.05%.
Secondly, below be described in detail the qualification reason of manufacture method of the present invention.
The present invention can obtain by following method: after the casting, on the hot dip process production line, implement thermal treatment at the state of hot rolling postcooling or the pickling of hot rolling postcooling and cold rolling after annealing or with hot-rolled steel sheet or cold-rolled steel sheet, again these steel plates are implemented surface treatment separately.
In the present invention, be not particularly limited prior to the hot rolled manufacture method.That is, after the melting of blast furnace and electric furnace etc., adopt 2 times various smeltings to carry out the composition adjustment, the feasible component content that achieves the goal, then, except that the casting of common continuous casting, ingot casting method, the method casting of employing thin slab casting etc. gets final product.Even use waste material also can for raw material.In the occasion of the slab that obtains by continuous casting, both can cast under the state of sheet direct sending and give hot rolls at high temperature, also can in process furnace, carry out hot rolling behind the reheat behind the cool to room temperature.
Be not particularly limited about the reheat temperature, but be more than 1400 ℃ the time, squama (scale off) quantitative change that falls is many, and effective rate of utilization reduces, and therefore, the reheat temperature is wished less than 1400 ℃.In addition, on program, damage operation efficiency significantly, so the reheat temperature wishes to be more than 1000 ℃ less than 1000 ℃ heating.
In hot-rolled process, carry out finish rolling after finishing roughing, but the occasion that roughing descales after finishing wishes to satisfy at the percussive pressure P of the high pressure water of surface of steel plate (MPa) * flow L (liter/cm
2The condition of) 〉=0.0025.
Percussive pressure P at the high pressure water of surface of steel plate records and narrates (referring to " iron and steel " 1991, vol.77, No.9, p1450) as described below.
P(MPa)＝5.64×P
0×V/H
2
Wherein, P
0: hydraulic coupling
V (rise/minute): the nozzle flow liquid measure
H (cm): the distance between surface of steel plate and nozzle
Flow is recorded and narrated as described below.
L (liter/cm
2)=V/ (W * v)
Wherein, V (rise/minute): nozzle flow liquid measure
W (cm): each nozzle ejection liquid impacts the width of surface of steel plate
V (cm/ minute): plate passes through speed
The upper limit of percussive pressure P * flow L there is no need definitely especially in order to obtain effect of the present invention, but when the nozzle flow liquid measure increases, produces rough sledding such as nozzle abrasion aggravation, so wish to be below 0.02.
And the maximum height Ry of the steel plate after the finish rolling wishes to be below the 15 μ m (15 μ m Ry, 12.5mm, In 12.5mm).This can be from following as can be known described, that is, for example according to " brief guide of metallic substance Fatigue Design ", Japanese materialogy can compile, 84 pages put down in writing, the fatigue strength of the steel plate of hot rolling or pickling state and the maximum height Ry of surface of steel plate have dependency.In addition, finish rolling is thereafter wished to carry out with interior at 5 seconds in the back regeneration oxide skin that descales in order to prevent.
In addition, after the roughing or continue with it descale after, engage thin slab, finish rolling also can continuously.At this moment, earlier thick silver lap is become web-like, be collected in as required in the cover with heat insulation function, engage also passable once again behind the rewinding.
For finish rolling,, carry out at Ar later half being necessary of its finish rolling in the occasion of making end article as hot-rolled steel sheet
3It is rolling more than 25% that total draft is carried out in humidity province below phase point temperature+100 ℃.At this, so-called Ar
3Phase point temperature for example uses the relation with composition of steel to illustrate simply by following calculating formula.That is,
Ar
3＝910-310×％C+25×％Si-80×％Mn
At Ar
3Total draft of the humidity province below phase point temperature+100 ℃ is less than 25% o'clock, rolling austenitic structure develop deficiently, therefore, after this, no matter implement what kind of cooling, also can not get effect of the present invention.In order more to be strengthened the structure of (sharp), wish at Ar
3Total draft of the humidity province below phase point temperature+100 ℃ is more than 35%.
In addition, the lower limit that carries out total draft and be the rolling humidity province more than 25% is not particularly limited, if but less than Ar
3Phase point temperature, the ferrite residual process tissue of then in rolling, separating out, ductility reduces, and therefore the processibility deterioration is carried out total draft and is the lower limit of the rolling humidity province more than 25% and wish to be Ar
3More than the phase point temperature.But, even this temperature is less than Ar
3Phase point temperature, by the coiling processing of back or the thermal treatment after the processing of reeling, answer or recrystallize proceed to the occasion of certain degree, not limited by this.
In the present invention, be not limited to Ar especially
3The upper limit of total draft of the humidity province below phase point temperature+100 ℃, but this draft always surpasses at 97.5% o'clock, rolling load increases, and must improve the rigidity of roller mill superfluously, produces economically unfavorable, so hope is below 97.5%.
At this, at Ar
3The hot roll during hot rolling of the humidity province below phase point temperature+100 ℃ and the big occasion of friction of steel plate, near surface of steel plate plate face, based on { the crystalline orientation development of 110} face, the notch fatigue strength deterioration, therefore in order to reduce the friction of hot roll and steel plate, implement lubricated as required.
In the present invention, the upper limit of the frictional coefficient of hot roll and steel plate is not particularly limited, but surpasses at 0.2 o'clock, in case the development of the crystalline orientation of 110} face becomes significantly, the notch fatigue strength deterioration, so about at Ar
3At least 1 rolling pass (pass) during the hot rolling of the humidity province below phase point temperature+100 ℃, the frictional coefficient of wishing hot roll and steel plate is below 0.2.More preferably, about at Ar
3Whole rolling passes during the hot rolling of the humidity province below phase point temperature+100 ℃, the frictional coefficient of hot roll and steel plate is below 0.15.
At this, the frictional coefficient of so-called hot roll and steel plate is by advanced rate, rolling load, rolling torque equivalence, the value of obtaining by calculating based on rolling therory.
Do not limit especially about the final rolling pass temperature (FT) of finish rolling, but the final rolling pass temperature (FT) of wishing finish rolling is at Ar
3Finish when phase point temperature is above.This is because in hot rolling, rolling temperature is less than Ar
3During phase point temperature, residual process tissue before rolling or in the ferrite of separating out in rolling, ductility reduces, the cause of processibility deterioration.Even but the final rolling pass temperature (FT) of finish rolling is less than Ar
3Phase point temperature is handled or is handled that the back implements to be used to make it to reply or the heat treated occasion of recrystallize reeling at the coiling of back, not limited by this.
On the other hand, do not set especially, but surpass Ar about the upper limit of final rolling temperature
3During phase point temperature+100 ℃, at Ar
3It is rolling in fact impossible more than 25% that total draft is carried out in humidity province below phase point temperature+100 ℃, and therefore, the upper limit of final rolling temperature wishes to be Ar
3Below phase point temperature+100 ℃.
In the present invention, just in order to improve the purpose of its notch fatigue strength, needn't limit the microstructure of steel plate especially, therefore, after finishing finish rolling, about not definite especially up to the refrigerating work procedure of under the coiling temperature of regulation, reeling, but in order under the coiling temperature of regulation, to reel or in order to control microstructure, to cool off as required.The upper limit of speed of cooling is not particularly limited, but owing to worry the caused slab warping of thermal strain, thus wish speed of cooling be 300 ℃/below the s.And, when this speed of cooling is too fast, can not the controlled chilling finishing temperature, overshoot had the following possibility of coiling temperature of the regulation of being as cold as, therefore, this speed of cooling wish be 150 ℃/below the s.In addition, the lower limit of speed of cooling is not definite especially, but the air cooling speed of not carrying out the refrigerative occasion be 5 ℃/more than the s.
In the present invention, except improving notch fatigue strength, also for the purpose of giving good deburring processibility, being bainite mutually or being the complex tissue of ferrite and bainite of the volume fraction maximum of microstructure, therefore finish finish rolling after, about the operation of under the coiling temperature of stipulating, reeling, beyond the speed of cooling therebetween, do not have special stipulation, but do not make deburring deterioration like that, with with ductility and save as the occasion of target, from Ar
3Transformation temperature is to Ar
1It is also passable second that the humidity province of transformation temperature (ferrite and austenitic two-phase region) stops 1-20.Stop at this is for promoting that at two-phase region ferrite transformation carries out, but during less than 1 second, ferrite transformation at two-phase region is insufficient, therefore can not obtain enough ductility, when surpassing for 20 seconds, generate perlite, the microstructure of the volume fraction maximum of expection can not obtain bainite or be the complex tissue of ferrite and bainite.
In addition, make to stop the 1-20 humidity province in second,, wish to be Ar in order easily to promote ferrite transformation
1Transformation temperature is above below 800 ℃.And the residence time in 1-20 second reduces terrifically in order not make productivity, so wish the second for 1-10.In order to satisfy these conditions, after finish rolling is finished, must arrive this humidity province rapidly with the above speed of cooling of 20 ℃/s again.
The upper limit of speed of cooling does not limit especially, but on the ability of cooling apparatus, 300 ℃/below the s suitable speed of cooling.And, when this speed of cooling is too fast, can not the controlled chilling finishing temperature, overshoot had the Ar of being as cold as
1The possibility that transformation temperature is following, ductility are improved the effect forfeiture, therefore, this speed of cooling wish be 150 ℃/below the s.
Secondly, from this humidity province to coiling temperature (CT), with the above speed of cooling cooling of 20 ℃/s, but generate the bainite of perlite or carbide-containing under less than the speed of cooling of 20 ℃/s, the microstructure of the volume fraction maximum of expection can not obtain bainite or be the complex tissue of ferrite and bainite.Do not limit especially until the upper limit of the speed of cooling of coiling temperature and just can access effect of the present invention, but owing to worry the caused slab warping of thermal strain, thus hope be 300 ℃/below the s.
Again, in the present invention, except improving notch fatigue strength, also for the purpose of giving good ductility, microstructure is to contain the volume fraction complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%, therefore finish the operation after the finish rolling, at first from Ar
3Phase point temperature is to Ar
1The humidity province of phase point temperature (ferrite and austenitic two-phase region) stops 1-20 second.Stop at this is for promoting that at two-phase region ferrite transformation carries out, but during less than 1 second, insufficient so can not obtain enough ductility at the ferrite transformation of two-phase region, when surpassing for 20 seconds, generate perlite, what can not obtain expecting contains the volume fraction microstructure that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%.
Again, make to stop the 1-20 humidity province in second,, wish to be Ar in order easily to promote ferrite transformation
1Phase point temperature is above below 800 ℃.And the residence time in 1-20 second reduces terrifically in order not make productivity, so wish the second for 1-10.In order to satisfy these conditions, after finish rolling is finished, must arrive this humidity province rapidly with the above speed of cooling of 20 ℃/s again.The upper limit of speed of cooling does not limit especially, but on the ability of cooling apparatus, 300 ℃/below the s suitable speed of cooling.And, when this speed of cooling is too fast, can not the controlled chilling finishing temperature, overshoot had the Ar of being as cold as
1The possibility that phase point temperature is following, therefore, this speed of cooling wish be 150 ℃/below the s.
Secondly, from this humidity province to coiling temperature (CT), with the above speed of cooling cooling of 20 ℃/s, but generate the bainite of perlite or carbide-containing under less than the speed of cooling of 20 ℃/s, can not obtain enough residual austenites, what can not get expecting contains the volume fraction microstructure that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%.Do not limit especially until the upper limit of the speed of cooling of coiling temperature and just can access effect of the present invention, but owing to worry the caused slab warping of thermal strain, thus hope be 300 ℃/below the s.
And, in the present invention, except improving notch fatigue strength, also for the purpose of giving to the low yielding ratio that obtains good shape freezing, form microstructure the volume fraction maximum be mainly martensitic complex tissue mutually for ferrite, second mutually, therefore finish the operation after the finish rolling, at first from Ar
3Phase point temperature is to Ar
1The humidity province of phase point temperature (ferrite and austenitic two-phase region) stops 1-20 second.Stop at this is for promoting that at two-phase region ferrite transformation carries out, but during less than 1 second, ferrite transformation at two-phase region is insufficient, therefore can not obtain enough ductility, when surpassing for 20 seconds, generate perlite, the volume fraction maximum that can not obtain expecting be mainly martensitic complex tissue mutually for ferrite, second mutually.
Again, make to stop the 1-20 humidity province in second,, wish to be Ar in order easily to promote ferrite transformation
1Phase point temperature is above below 800 ℃.And, the residence time in 1-20 second, reduce terrifically in order not make productivity, so wish second for 1-10.In order to satisfy these conditions, after finish rolling is finished, must arrive this humidity province rapidly with the above speed of cooling of 20 ℃/s again.The upper limit of speed of cooling does not limit especially, but on the ability of cooling apparatus, 300 ℃/below the s suitable speed of cooling.And, when this speed of cooling is too fast, can not the controlled chilling finishing temperature, overshoot had the Ar of being as cold as
1The possibility that phase point temperature is following, therefore, this speed of cooling wish be 150 ℃/below the s.
Secondly, from this humidity province to coiling temperature (CT), with the above speed of cooling cooling of 20 ℃/s, but under less than the speed of cooling of 20 ℃/s, generate perlite or bainite, can not obtain enough martensite, the ferrite that can not get expecting is that phase, the martensite of volume fraction maximum is the microstructure of second phase.
Do not limit especially until the upper limit of the speed of cooling of coiling temperature and just can access effect of the present invention, but owing to worry the caused slab warping of thermal strain, thus hope be 300 ℃/below the s.
In the present invention, in order to improve the purpose of its notch fatigue strength, do not need to limit especially the microstructure of steel plate just, therefore not definite especially about the upper limit of coiling temperature, but in order to make at Ar
3It is the rolling austenitic structure heredity that obtains more than 25% that total draft is adopted in humidity province below phase point temperature+100 ℃, the coiling temperature T shown in wishing below
0Below reel.But T
0Do not need for below the room temperature.This T
0Be austenite and have the temperature of same free energy with the ferrite of the same composition of austenite and the temperature that on thermodynamics, defines, also consider the influence of the composition beyond the C, use following formula to calculate simply.
T
0＝-650.4×％C+B
At this, B determines as following.
B＝-50.6×Mneq+894.3
At this, so-called Mneq is determined by the quality % that contains element shown in following.
Mneq＝％Mn+0.24×％Ni+0.13×％Si+0.38×％Mo+0.55×％Cr+0.16×％Cu-0.50×％Al-0.45×％Co+0.90×％V
Moreover the quality % of the above-mentioned composition of stipulating among the present invention in addition is to T
0Influence so not big, therefore can ignore at this.
In addition, the lower value of coiling temperature is just in order to improve the purpose of its notch fatigue strength, therefore do not need to limit especially the microstructure of steel plate, do not need special qualification, but coiled material is when being in the state that water logging drenches for a long time, therefore worry wishes to be more than 50 ℃ by the caused bad order of rust.
In the present invention, except improving notch fatigue strength, also for the purpose of giving good deburring processibility, be bainite mutually or be the complex tissue of ferrite and bainite for the volume fraction maximum that make to form microstructure, when coiling temperature during less than 450 ℃, there is volume ground to generate the anxiety that to think to deleterious residual austenite of deburring or martensite, the complex tissue that is made of the microstructure bainite of volume fraction maximum or ferrite and bainite that can not get expecting, the temperature limit of therefore reeling is decided to be more than 450 ℃.
And, speed of cooling behind the coiling does not limit especially, but add the occasion of the Cu more than 1.2%, Cu separates out behind coiling, processibility deterioration not only, and might lose the Cu that improves the effective solid solution condition of fatigue strength, the speed of cooling after therefore wishing to reel is being decided to be 30 ℃/s till 200 ℃.
In addition, in the present invention, except improving notch fatigue strength, also for the purpose of giving good ductility, making microstructure is to contain volume fraction residual austenite below 25% more than 5%, remainder is mainly by ferrite, the complex tissue that bainite constitutes, when the coiling temperature is more than 450 ℃ the time, generate the bainite of carbide-containing, can not get enough residual austenites, what can not obtain expecting contains volume fraction residual austenite below 25% more than 5%, remainder is mainly by ferrite, the microstructure that bainite constitutes, the temperature limit of therefore reeling is decided to be less than 450 ℃.In addition, the coiling temperature is below 350 ℃ the time, volume ground generates martensite, can not get enough residual austenites, what can not obtain expecting contains the volume fraction microstructure that the residual austenite below 25%, remainder mainly are made of ferrite, bainite more than 5%, and the temperature limit of therefore reeling is decided to be above 350 ℃.
And, speed of cooling behind the coiling does not limit especially, but add the occasion of the Cu more than 1%, Cu separates out behind coiling, processibility deterioration not only, and might lose the Cu that improves the effective solid solution condition of fatigue strength, the speed of cooling after therefore reeling wish till 200 ℃, to be decided to be 30 ℃/more than the s.
And, in the present invention, except improving notch fatigue strength, also for the purpose of giving to the low yielding ratio that obtains good shape freezing, be mainly martensitic complex tissue mutually for ferrite, second mutually for the volume fraction maximum that make to form microstructure, when the coiling temperature surpasses 350 ℃, generate bainite, can not get enough martensite, the ferrite that can not obtain expecting is that phase, the martensite of volume fraction maximum is the microstructure of second phase, and the temperature limit of therefore reeling is decided to be below 350 ℃.In addition, the lower value of coiling temperature does not need special qualification, but coiled material is worried therefore to wish to be more than 50 ℃ by the caused bad order of rust when being in the state that water logging drenches for a long time.
After hot-rolled process is finished, pickling as required, polishing or cold rolling also passable up to draft about 40% of draft below 10% implemented on online thereafter or off-line ground.
Secondly, be the situation of making end article as cold-rolled steel sheet, the hot finishing condition does not limit especially.But, wish at Ar in order to obtain better notch fatigue strength
3Total draft of the humidity province below phase point temperature+100 ℃ is more than 25%.In addition, the final rolling pass temperature (FT) of finish rolling is less than Ar
3Finish also passable under the phase point temperature.Under this occasion, therefore residual process tissue before rolling or in the ferrite of separating out in rolling wishes to make it answer, recrystallize by the coiling processing or the heat treated that continue.
Cold rolling total draft after the pickling that continues is less than 80%.This be because, when cold rolling total draft is 80% when above, { the 111} face or { the X-ray diffraction integration face intensity of 554} face uprises of the crystal face parallel with general cold rolling-recrystallization texture plate face.In addition, hope is below 70%.The lower limit of cold rolling rate does not limit especially and just can obtain effect of the present invention, but for the intensity control of crystalline orientation in suitable scope, hope is more than 3%.
The thermal treatment of cold rolling like this steel plate is prerequisite with the continuous annealing operation.
At first, at Ac
35-150 second is carried out in humidity province below phase point temperature+100 ℃.The upper limit of this thermal treatment temp surpasses Ac
3During phase point temperature+100 ℃, the ferrite that is generated by recrystallize is to austenitic transformation, and by the structure randomization that austenitic crystal grain-growth produces, the ferritic structure that finally obtains is randomization also, and therefore heat treated ceiling temperature is Ac
3Below phase point temperature+100 ℃.
At this, so-called Ac
1Phase point temperature and Ac
3Phase point temperature for example by the calculating formula of record in 273 pages of " レ ス リ one ferrous materials science " (distribution in 1985, the great wild Tian Longyan of Xiong Jing translates, the kind Co., Ltd. of ball), uses the relation with composition of steel to illustrate.
On the other hand, the lower limit of this thermal treatment temp, in order to improve its notch fatigue strength, not needing to limit especially the microstructure of steel plate, also can be more than the recovery temperature therefore, but under the situation less than recovery temperature, worked structure is residual, make plasticity deterioration significantly, therefore, heat treated lower limit temperature is decided to be more than the recovery temperature.In addition, in hold-time of this humidity province during, insufficient for the solid solution fully again for cementite less than 5 seconds, on the other hand, even surpass 150 seconds thermal treatment, not only its effect is saturated, and productivity is reduced, so the hold-time is decided to be 5-150 second.
About cooling conditions thereafter, do not limit especially, but, can carry out following cooling or maintenance under arbitrary temp and cooling as required yet in order to control microstructure.
In the present invention, except improving notch fatigue strength,, form be bainite mutually or be the complex tissue of ferrite and bainite of volume fraction maximum of microstructure also for the purpose of giving good deburring processibility, therefore, the lower limit temperature of its thermal treatment temp is decided to be Ac
1More than the phase point temperature.This lower limit temperature is less than Ac
1The occasion of phase point temperature, the volume fraction maximum that can not obtain expecting mutually for bainite or be the complex tissue of ferrite and bainite.At this,,, its humidity province is decided to be Ac in order to increase ferritic volume fraction not making deburring deterioration and take into account the occasion of ductility so
1The above Ac of phase point temperature
3The humidity province of phase point temperature following (ferrite and austenitic two-phase region).In addition, in order to obtain better deburring, because the volume fraction of bainite is increased, so wish to be Ac
3The above Ac of phase point temperature
3Humidity province below phase point temperature+100 ℃.
Secondly,, do not limit especially in the present invention, but be Ac in above-mentioned thermal treatment temp about refrigerating work procedure
1The above Ac of phase point temperature
3The occasion that phase point temperature is following wishes to be cooled to greater than 350 ℃, T with the above speed of cooling of 20 ℃/s
0The humidity province that temperature is following.This is because when speed of cooling during less than 20 ℃/s, have the volume of falling into ground to contain the anxiety of the constraint of the bainite of carbide or pearlitic transformation.Again, the cooling finishing temperature is below 350 ℃ the time, have volume ground to generate the anxiety that can think to the deleterious martensite of deburring, therefore the complex tissue that is made of the microstructure bainite of volume fraction maximum or ferrite and bainite that can not get expecting wishes above 350 ℃.And, in order to make the structure heredity that obtains before the operation in front, wish to be T
0Below.
At last, the speed of cooling up to finishing temperature of refrigerating work procedure, when be 20 ℃/when s is above, have and in cooling, generate to volume the anxiety that to think to the deleterious martensite of deburring, therefore the complex tissue that is made of the microstructure bainite of volume fraction maximum or ferrite and bainite that can not get expecting wishes for less than 20 ℃/s.Again, when the finishing temperature of refrigerating work procedure surpassed 200 ℃, therefore the anxiety of effective property deterioration wished to be below 200 ℃.Again, about lower limit, because water-cooled or when being in the state that water logging drenches for a long time with the coiled material of the occasion of fog cooling worries that therefore hope is more than 50 ℃ by the caused bad order of rust.
On the other hand, above-mentioned thermal treatment temp is greater than Ac
3Phase point temperature but at Ac
3Under the occasion below phase point temperature+100 ℃, the temperature that is cooled to below 200 ℃ with the above speed of cooling of 20 ℃/s is desirable.This be because, when be 20 ℃/when s is above, the volume of falling into is arranged contain the anxiety of the constraint of the bainite of carbide or pearlitic transformation.Again, when the refrigerative finishing temperature surpassed 200 ℃, therefore the anxiety of effective property deterioration wished to be below 200 ℃.About lower limit, water-cooled or with the occasion of fog cooling is because coiled material when being in the state that water logging drenches for a long time, is worried therefore to wish to be more than 50 ℃ by the caused bad order of rust.
In addition, in the present invention, except improving notch fatigue strength, also for the purpose of giving good ductility, making microstructure is to contain volume fraction residual austenite below 25% more than 5%, remainder is mainly by ferrite, the complex tissue that bainite constitutes, with above-mentioned the same, be more than 450 ℃ the time when the coiling temperature, generate the bainite of carbide-containing, can not get enough residual austenites, what can not obtain expecting contains volume fraction residual austenite below 25% more than 5%, remainder is mainly by ferrite, the microstructure that bainite constitutes is therefore at Ac
1The above Ac of phase point temperature
35-150 second is carried out in humidity province below phase point temperature+100 ℃.At this moment, even in this humidity province, if temperature is low excessively, the occasion of separating out at hot-rolled sheet stage cementite then, cementite is for the spended time too of solid solution again, if temperature is too high, then austenitic volume fraction is excessive, C concentration in the austenite reduces, and is absorbed in constraint (ノ one ズ that volume ground contains the bainite or the pearlitic transformation of carbide easily; Nose) among, be preferred therefore in heating below 850 ℃ more than 780 ℃.Speed of cooling after the maintenance is during less than 20 ℃/s, has the volume of being absorbed in ground to contain the anxiety of the constraint of the bainite of carbide or pearlitic transformation, therefore is decided to be the above speed of cooling of 20 ℃/s.
Secondly, be to promote bainitic transformation to stablize the operation of the residual austenite of necessary amounts, but the cooling finishing temperature is more than 450 ℃ the time, residual austenite is resolved into bainite or the perlite that volume ground contains carbide, and what can not get expecting contains the volume fraction microstructure that the residual austenite below 25%, remainder mainly are made of ferrite, bainite more than 5%.In addition, during less than 350 ℃, the possibility that has martensite volume ground to generate, can not get enough residual austenites, what can not get expecting contains the volume fraction microstructure that the residual austenite below 25%, remainder mainly are made of ferrite, bainite more than 5%, therefore is cooled to surpass 350 ℃ humidity province.
Further, as hold-time in this humidity province, when less than 5 seconds, it is insufficient to be used for the austenitic bainitic transformation of stable residual, unsettled residual austenite is in the cooling that the continues anxiety of martensitic transformation of happening occasionally that ends, and what can not get expecting contains the volume fraction microstructure that the residual austenite below 25%, remainder mainly are made of ferrite, bainite more than 5%.In addition, when surpassing for 600 seconds, bainitic transformation too promotes, can not obtain the stable residual austenite of necessary amounts, and what can not get expecting contains the volume fraction microstructure that the residual austenite below 25%, remainder mainly are made of ferrite, bainite more than 5%.So, be decided to be more than 5 seconds below 600 seconds in the hold-time of this humidity province.
At last, the speed of cooling that ends up to cooling is during less than 5 ℃/s, the too promoted possibility of bainitic transformation is arranged in cooling, can not obtain the stable residual austenite of necessary amounts, what can not get expecting contains the volume fraction microstructure that the residual austenite below 25%, remainder mainly are made of ferrite, bainite more than 5%.So, be decided to be 5 ℃/more than the s.
In addition, when the cooling finishing temperature surpassed 200 ℃, therefore the anxiety of effective property deterioration was decided to be below 200 ℃.Lower limit about the cooling finishing temperature does not limit especially, but water-cooled or with the occasion of fog cooling, when coiled material is in the state that water logging drenches for a long time, worries that therefore hope is more than 50 ℃ by the caused bad order of rust.
And, in the present invention, except improving notch fatigue strength, also for the purpose of giving to the low yielding ratio that obtains good shape freezing, be mainly martensitic complex tissue mutually for ferrite, second mutually for the volume fraction maximum that make to form microstructure, therefore, with above-mentioned the same, at Ac
1The above Ac of phase point temperature
35-150 second is carried out in humidity province below phase point temperature+100 ℃.At this moment, even in this humidity province, if temperature is low excessively, the occasion of separating out at hot-rolled sheet stage cementite then, cementite is for the spended time too of solid solution again, if temperature is too high, then austenitic volume fraction is excessive, C concentration in the austenite reduces, is absorbed in easily among the constraint that contains the bainite of carbide or pearlitic transformation in volume ground, and be preferred therefore in heating below 850 ℃ more than 780 ℃.
Speed of cooling after the maintenance is during less than 20 ℃/s, has the volume of being absorbed in ground to contain the anxiety of the constraint of the bainite of carbide or pearlitic transformation, therefore is decided to be the above speed of cooling of 20 ℃/s.When the cooling finishing temperature surpassed 200 ℃, therefore the anxiety of effective property deterioration was decided to be below 200 ℃.The cooling finishing temperature is when surpassing 350 ℃, and the ferrite that can not get expecting is that phase, the martensite of volume fraction maximum is the microstructure of second phase, therefore is cooled to the humidity province below 350 ℃.Lower limit about the finishing temperature of refrigerating work procedure does not limit especially, but water-cooled or with the occasion of fog cooling, when coiled material is in the state that water logging drenches for a long time, worries that therefore hope is more than 50 ℃ by the caused bad order of rust.
And, thereafter, also can implement dress rolling as required.
Implement zinc-platedly for the cold-rolled steel sheet after the hot-rolled steel sheet after the pickling or above-mentioned recrystallization annealing are finished, in zinc-plated bath, flood, as required also can Alloying Treatment.
Embodiment
(embodiment 1)
1 illustrate further the present invention by the following examples.
The A-L steel converter melting that will have the chemical ingredients shown in the table 1, behind the continuous casting, reheat, after roughing, and then reach the thickness of slab of 1.2-5.5mm by finish rolling after, reel.Expression about the chemical constitution in the table is quality %.
Secondly table 2 illustrates the details of creating conditions.At this, " SRT " represents slab heating temperature; " FT " represents final rolling pass final rolling temperature, and so-called " rolling rate " is illustrated in Ar
3The total amount of the draft of the humidity province below phase point temperature+100 ℃.Wherein, the occasion that the back is rolled in cold rolling process does not have the limit of such restriction, so be designated as "-".In addition, " lubricating " expression has or not at Ar
3Humidity province below phase point temperature+100 ℃ lubricated.
And, so-called " coiling ", coiling temperature (CT) is if be T
0Below just be designated as " zero ", surpassing T
0Situation under, be designated as " * ".But the occasion of cold-rolled steel sheet does not need special qualification as creating conditions, and therefore is designated as "-".
Secondly, for a part, carry out pickling, cold rolling, annealing after the hot rolling.Thickness of slab is 0.7-2.3mm.At this, so-called " cold rolling rate " is total cold rolling rate; " time " is annealing time; So-called " annealing ", recovery temperature is above if annealing temperature is included in, Ar
3Humidity province below phase point temperature+100 ℃ then is designated as " zero ", if not in this humidity province then be designated as " * ".Moreover, about steel L, after the roughing at percussive pressure 2.7MPa, 0.001 liter/cm of flow
2Condition under implement to descale.On the other hand, in the above-mentioned steel plate, implemented zinc-plated about steel G and steel F-5.
The tension test of the hot-rolled sheet that obtains like this is at first to be processed into No. 5 test films of JIS Z 2201 records for the examination material, carries out according to the test method of JIS Z 2241 records.Table 2 illustrates yield strength (σ Y), tensile strength (σ B), tension set (E1) in the lump.
And, 1/4W that slave plate is wide or 3/4W position cut into φ 30mm test piece carry out the grinding of three mountains processing from the degree of depth of top layer up to about 0.05mm, then remove strain and make by chemical grinding or electrolytic polishing.Carry out the mensuration of X-ray diffraction intensity according to the method for putting down in writing in " new edition カ リ テ イ X-ray diffraction will be discussed " (distribution in 1986, Song Cunyuan too youth translates, the ア グ ネ of Co., Ltd.) 274-296 page or leaf.
At this, so-called 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray, be by based on { the 3 dimension structures that the 110} pole graph adopts vector method to calculate, or { 110}, { 100}, { 211}, { the 3 dimension structures of using a plurality of pole graphs (being preferably more than 3) to calculate with Series Expansion Method among the 310} pole graph are obtained the contained main orientation of this orientation group, 100}＜011 〉, 116}＜110 〉, 114}＜110 〉, 113}＜110 〉, 112}＜110 〉, 335}＜110〉and 223}＜110〉X-ray diffraction intensity.
For example, the random strength ratio of the X ray of above-mentioned each crystalline orientation of the latter's method, its former state use (001) [1-10], (116) [1-10], (114) [1-10], (113) [1-10], (112) [1-10], (335) [1-10] of the Φ 2=45 ° section of 3 dimension structures, the intensity of (223) [1-10] to get final product unchangeably.But so-called 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is addition mean value of above-mentioned each orientation.
In the occasion of the intensity that can not obtain above-mentioned whole orientation, also can with 100}＜011 〉, 116}＜110 〉, 114}＜110 〉, 112}＜110 〉, 223}＜110〉and addition mean value of each orientation replace.
Secondly, so-called 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations, obtain by the 3 dimension structures of similarly calculating with above-mentioned method and to get final product.
In table 2, among the random strength ratio of X ray, so-called " strength ratio 1 " be 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray, so-called " strength ratio 2 " be 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations.
Secondly, in order to investigate the notch fatigue strength of above-mentioned steel plate, 1/4W that slave plate is wide or 3/4W position extract the fatigue test piece of the shape shown in Fig. 1 (b) by rolling direction for the mode on long limit, use for fatigue test.Wherein, the degree of depth of fatigue test piece about from top layer to 0.05mm implemented the grinding of three mountains processing.Fatigue test makes electricity consumption oil pressure servo type protracted test machine, and test method is according to JIS Z 2273-1978 and JIS Z 2275-1978.Table 2 illustrates the notch fatigue limit (σ Wk), notch fatigue limit in the lump than (σ Wk/ σ B).
Following of the present invention is steel A, E, F-1, F-2, F-5, G, H, I, J, K, these 11 kinds of steel of L, can obtain the thin steel sheet for automobile of excellent in notch fatigue strength, the feature of this steel plate is: the composition of steel that contains specified amount, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.Thereby the limit of fatigue ratio of the steel in the past of the method evaluation of employing the present invention record exceeds 0.2-0.3.
Steel beyond above-mentioned because of following reason outside scope of the present invention.
That is, therefore the C content of steel B can not get enough intensity (σ B) outside scope of the present invention.Therefore the P content of steel C can not get enough notch fatigue strengths (σ Wk/ σ B) outside scope of the present invention.Therefore the S content of steel D can not get enough unit elongation (E1) outside scope of the present invention.Steel F-3 at Ar
3Therefore total draft of the humidity province below phase point temperature+100 ℃ can not get the structure as the object of the invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).
The finish rolling finishing temperature (FT) of steel F-4 is outside scope of the present invention, and therefore the coiling temperature can not get the structure as the object of the invention also outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).Therefore the cold rolling rate of steel F-6 can not get structure of the present invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).Therefore the annealing temperature of steel F-7 can not get the structure as purpose of the present invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).Therefore the annealing time of steel F-8 can not get structure of the present invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).
(embodiment 2)
Two kinds of steel of G, H reheat under the Heating temperature shown in the table 3 that will have the chemical ingredients shown in the table 1, after roughing, and then reach the thickness of slab of 1.2-5.5mm by finish rolling after, reel.In addition, as shown in table 3 like that, about several steel after roughing at percussive pressure 2.7MPa, 0.001 liter/cm of flow
2Condition under implement to descale.
Table 3 illustrates the details of creating conditions.At this, " SRT " represents slab heating temperature; " FT " represents final rolling pass final rolling temperature, and so-called " rolling rate " is illustrated in Ar
3The total amount of the draft of the humidity province below phase point temperature+100 ℃.Wherein, the occasion that the back is rolled in cold rolling process does not have the limit of such restriction, so be designated as "-".In addition, " lubricating " expression has or not at Ar
3Humidity province below phase point temperature+100 ℃ lubricated.And, so-called " CT ", expression coiling temperature.But the occasion of cold-rolled steel sheet does not need special qualification as creating conditions, and therefore is designated as "-".Secondly, for a part, carry out pickling, cold rolling, thermal treatment after the hot rolling.Thickness of slab is 0.7-2.3mm.So-called " cold rolling rate " is total cold rolling rate; So-called " ST " is thermal treatment temp; " time " is heat treatment time.Moreover several in the above-mentioned steel plate implement zinc-plated.
The hot-rolled sheet that obtains like this and the tension test of cold-reduced sheet are adopted with above-mentioned same method and are implemented.
Table 4 illustrates yield strength (σ Y), tensile strength (σ B), tension set (E1) and yield ratio (YR, strength-ductility balanced (σ B * E1)).On the other hand, about deburring processibility (hole extendability), estimate according to the hole expanding test method of the Japanese iron and steel specification JFST1001-1996 of alliance record.Table 4 illustrates the hole rate of spread (λ).
And, also be shown in table 4 about microstructure.At this, so-called other, be meant the tissue beyond ferrite that perlite and/or table 4 individually illustrate, bainite, residual austenite, the martensite.In the microstructure of steel plate, so-called ferrite, bainite, residual austenite, perlite, martensitic volume fraction, with the definition of following area branch rate: the test portion that will cut from the wide 1/4W of steel plate plate or 3/4W position grinds at the rolling direction section, use nitric acid ethanol reagent and/or spy to open the disclosed reagent etching of flat 5-163590 communique, the face integration rate of the microstructure of the 1/4t of the thickness of slab that the use opticmicroscope is observed under 200-500 multiplying power doubly.
On the other hand, austenite is owing to different with the ferrite crystalline structure, so can easily discern on crystallography.So the volume fraction of residual austenite adopts X-ray diffraction method also can obtain experimentally.That is, adopt K alpha-ray, obtain the method for its volume fraction from the austenite and the different use following formulas of ferritic plane of reflection intensity easily via Mo.
Vγ＝(2/3){100/(0.7×α(211)/γ(220)+1)}+(1/3){100/(0.78×α(211)/γ(311)+1)}
Wherein, α (211), γ (220) and γ (311) are respectively the X ray reflection face intensity of ferrite (α) austenite (γ).Even the volume fraction of residual austenite uses any method of observation by light microscope and X-ray diffraction method all to obtain value unanimous on the whole, therefore also can use arbitrary measured value.
And, according to carrying out mensuration, the fatigue test of X-ray diffraction intensity with above-mentioned the same method.
In addition, fatigue test is according to carrying out with above-mentioned the same method.Table 4 shows the notch fatigue limit (σ Wk), notch fatigue limit than (σ Wk/ σ B).
Following of the present invention is steel g-1, g-2, g-3, g-5, g-6, g-7, h-1, h-2, these 9 kinds of steel of h-3, can obtain the thin steel sheet for automobile of excellent in notch fatigue strength, the feature of this steel plate is: the composition of steel that contains specified amount, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉and the mean value of the random strength ratio of X ray of 3 orientations is below 4, and thickness of slab is below the above 12mm of 0.5mm, and, be the volume fraction maximum mutually for bainite, it perhaps is the complex tissue of ferrite and bainite, perhaps contain volume fraction residual austenite below 25% more than 5%, remainder is mainly by ferrite, the complex tissue that bainite constitutes, perhaps the volume fraction maximum is ferrite mutually, second is martensitic complex tissue mutually.So, than 20-30%, can see the difference of having a mind to respect to the limit of fatigue of the past steel that adopts method of the present invention to estimate.
Steel beyond above-mentioned because of following reason outside scope of the present invention.
That is the finish rolling finishing temperature (FT) of steel g-4 and, at Ar
3Therefore total draft of the humidity province below phase point temperature+100 ℃ can not get the structure as the object of the invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).Therefore the cold rolling rate of steel g-8 can not get the structure as the object of the invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).The finish rolling finishing temperature (FT) of steel h-4 and at Ar
3Therefore total draft of the humidity province below phase point temperature+100 ℃ can not get the structure as the object of the invention outside scope of the present invention, can not get enough notch fatigue strengths (σ Wk/ σ B).
Table 1
Table 2
| Create conditions | The random strength ratio of X ray | Mechanical properties | Fatigue characteristic | ||||||||||||||
| Hot-rolled process | Cold rolling, annealing operation | ||||||||||||||||
| Steel | Distinguish | SRT (℃) | FT (℃) | Rolling rate (%) | Lubricated | Reel | Cold rolling rate (%) | Annealing | Time (s) | Strength ratio 1 | Strength ratio 2 | σY (MPa) | σB (MPa) | E1 (％) | σWk (MPa) | σWk/σB (％) | Remarks |
| A | Hot rolling | 1250 | 880 | 42 | Do not have | ○ | - | - | - | 5.8 | 0.7 | 221 | 311 | 47 | 100 | 32 | The present invention |
| B | Hot rolling | 1250 | 890 | 30 | Have | ○ | - | - | - | 1.3 | 6.1 | 161 | 281 | 56 | 75 | 27 | Comparative steel |
| C | Hot rolling | 1200 | 880 | 30 | Do not have | ○ | - | - | - | 0.8 | 1.3 | 220 | 369 | 42 | 90 | 24 | Comparative steel |
| D | Hot rolling | 1200 | 880 | 30 | Do not have | ○ | - | - | - | 1.2 | 0.9 | 195 | 306 | 44 | 75 | 25 | Comparative steel |
| E | Hot rolling | 1150 | 870 | 42 | Do not have | ○ | - | - | - | 8.1 | 1.8 | 422 | 637 | 29 | 230 | 36 | The present invention |
| F-1 | Hot rolling | 1200 | 870 | 42 | Do not have | ○ | - | - | - | 7.2 | 2.1 | 438 | 668 | 28 | 230 | 34 | The present invention |
| F-2 | Hot rolling | 1200 | 870 | 42 | Have | ○ | - | - | - | 8.3 | 1.4 | 423 | 655 | 29 | 240 | 37 | The present invention |
| F-3 | Hot rolling | 1300 | 950 | 0 | Do not have | ○ | - | - | - | 1.8 | 1.5 | 431 | 660 | 28 | 150 | 23 | Comparative steel |
| F-4 | Hot rolling | 1300 | 970 | 0 | Do not have | × | - | - | - | 1.8 | 1.7 | 400 | 622 | 32 | 150 | 24 | Comparative steel |
| F-5 | Cold rolling | 1200 | 860 | - | Have | - | 65 | ○ | 90 | 4.2 | 2.3 | 418 | 671 | 28 | 240 | 36 | The present invention |
| F-6 | Cold rolling | 1200 | 860 | - | Have | - | 80 | ○ | 90 | 2.8 | 4.2 | 433 | 667 | 28 | 150 | 22 | Comparative steel |
| F-7 | Cold rolling | 1200 | 860 | - | Have | - | 65 | × | 90 | 1.7 | 2.6 | 552 | 721 | 20 | 150 | 21 | Comparative steel |
| F-8 | Cold rolling | 1200 | 860 | - | Have | - | 65 | ○ | 2 | 1.8 | 2.2 | 570 | 710 | 21 | 150 | 21 | Comparative steel |
| G | Hot rolling | 1150 | 870 | 71 | Do not have | ○ | - | - | - | 8.5 | 0.8 | 441 | 661 | 30 | 235 | 36 | The present invention |
| H | Hot rolling | 1250 | 870 | 30 | Have | ○ | - | - | - | 8.7 | 0.9 | 776 | 986 | 16 | 340 | 34 | The present invention |
| I | Hot rolling | 1200 | 870 | 42 | Do not have | ○ | - | - | - | 6.7 | 2.0 | 404 | 638 | 27 | 220 | 34 | The present invention |
| J | Hot rolling | 1200 | 870 | 71 | Do not have | ○ | - | - | - | 5.9 | 2.1 | 431 | 623 | 26 | 220 | 35 | The present invention |
| K | Hot rolling | 1200 | 870 | 71 | Do not have | ○ | - | - | - | 7.8 | 1.0 | 425 | 627 | 30 | 220 | 35 | The present invention |
| L | Hot rolling | 1150 | 790 | 71 | Do not have | ○ | - | - | - | 11.0 | 1.4 | 401 | 588 | 25 | 210 | 36 | The present invention |
Table 3
| Create conditions | The random strength ratio of X ray | |||||||||||||||||
| Hot-rolled process | Cold rolling, heat treatment step | |||||||||||||||||
| Steel | Distinguish | SRT (℃) | FT (℃) | Ar 3+100 (℃) | Rolling rate (%) | Lubricated | CT (℃) | T 0 (℃) | Rolling rate (%) | Ac 1 (℃) | ST (℃) | Ac 3+100 (℃) | Time 1 (s) | OA (℃) | Time 2 (s) | CR (℃/s) | Strength ratio 1 | Strength ratio 2 |
| g-1 | Hot rolling | 1150 | 870 | 916 | 71 | Have | 50 | 782 | - | - | - | - | - | - | - | - | 8.2 | 1.1 |
| g-2 | Hot rolling | 1150 | 870 | 916 | 71 | Have | 400 | 782 | - | - | - | - | - | - | - | - | 8.0 | 1.0 |
| g-3 | Hot rolling | 1150 | 890 | 916 | 42 | Have | 600 | 782 | - | - | - | - | - | - | - | - | 8.4 | 0.9 |
| g-4 | Hot rolling | 1250 | 930 | 916 | 0 | Do not have | 600 | 782 | - | - | - | - | - | - | - | - | 1.8 | 1.5 |
| g-5 | Cold rolling | 1150 | 870 | - | - | Have | - | - | 65 | 730 | 800 | 982 | 90 | - | - | 5 | 4.4 | 2.2 |
| g-6 | Cold rolling | 1150 | 870 | - | - | Have | - | - | 65 | 730 | 800 | 982 | - | 400 | 180 | 30 | 4.6 | 2.4 |
| g-7 | Cold rolling | 1150 | 870 | - | - | Have | - | - | 65 | 730 | 800 | 982 | 90 | - | - | 30 | 4.8 | 2.6 |
| g-8 | Cold rolling | 1150 | 870 | - | - | Do not have | - | - | 80 | 730 | 800 | 982 | 90 | - | - | 5 | 2.6 | 4.3 |
| h-1 | Hot rolling | 1230 | 860 | 879 | 30 | Have | 50 | 727 | - | - | - | - | - | - | - | - | 8.6 | 1.2 |
| h-2 | Hot rolling | 1230 | 860 | 879 | 30 | Have | 400 | 727 | - | - | - | - | - | - | - | - | 8.5 | 0.9 |
| h-3 | Hot rolling | 1230 | 860 | 879 | 30 | Have | 600 | 727 | - | - | - | - | - | - | - | - | 8.4 | 1.3 |
| h-4 | Hot rolling | 1230 | 930 | 879 | 0 | Do not have | 730 | 727 | - | - | - | - | - | - | - | - | 1.8 | 2.1 |
Table 4
| Microstructure | Mechanical properties | Fatigue characteristic | |||||||||||
| Ferrite (%) | Bainite (%) | Martensite (%) | Residual austenite (%) | Other (%) | σY (MPa) | σB (MPa) | E1 (％) | λ (％) | σB×E1 (MPa*％) | YR(％) | σWk (MPa) | σWk/σB (％) | Remarks |
| 85 | 0 | 13 | 2 | 0 | 470 | 772 | 26 | 52 | 20072 | 61 | 2g0 | 36 | The present invention |
| 80 | 8 | 0 | 12 | 0 | 512 | 646 | 37 | 67 | 23902 | 79 | 220 | 34 | The present invention |
| 67 | 30 | 0 | 0 | 3 | 478 | 576 | 27 | 130 | 15552 | 83 | 190 | 33 | The present invention |
| 65 | 35 | 0 | 0 | 0 | 502 | 588 | 28 | 141 | 16464 | 85 | 120 | 20 | Comparative steel |
| 70 | 28 | 0 | 0 | 2 | 482 | 584 | 25 | 87 | 14600 | 83 | 190 | 33 | The present invention |
| 79 | 10 | 0 | 11 | 0 | 480 | 660 | 36 | 50 | 23760 | 73 | 230 | 35 | The present invention |
| 87 | 0 | 10 | 3 | 0 | 444 | 731 | 26 | 42 | 19006 | 61 | 270 | 37 | The present invention |
| 50 | 45 | 0 | 2 | 3 | 495 | 591 | 25 | 76 | 14775 | 84 | 135 | 23 | Comparative steel |
| 67 | 5 | 21 | 4 | 3 | 613 | 991 | 21 | 18 | 20811 | 62 | 330 | 33 | The present invention |
| 63 | 15 | 3 | 17 | 2 | 694 | 902 | 27 | 26 | 24354 | 77 | 285 | 32 | The present invention |
| 35 | 55 | 3 | 4 | 3 | 670 | 823 | 18 | 76 | 14814 | 81 | 255 | 31 | The present invention |
| 30 | 63 | 0 | 3 | 4 | 673 | 796 | 20 | 70 | 15920 | 85 | 180 | 23 | Comparative steel |
As detailed above, the present invention relates to the thin steel sheet for automobile and the manufacture method thereof of excellent in notch fatigue strength, by using these steel sheets, can expect to add the significantly improvement of notch fatigue strength of one of key property that automobile traveling part parts that the FATIGUE CRACK GROWTH of the Ministry of worker and welding zone equal stress concentrated part becomes problem etc. require the member of weather resistance from blanking, therefore, the present invention is the high invention of industrial value.
Claims (20)
1. the thin steel sheet for automobile of an excellent in notch fatigue strength, this steel plate contains C:0.01-0.3% in quality %, Si:0.01-2%, Mn:0.05-3%, P :≤0.1%, S :≤0.01%, Al:0.005-1%, remainder is made of Fe and unavoidable impurities, it is characterized in that, plate face along thickness direction from the most surperficial any degree of depth up to 0.5mm 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
2. according to the thin steel sheet for automobile of the excellent in notch fatigue strength of claim 1 record, it is characterized in that, in quality %, also further contain Cu:0.2-2%, B:0.0002-0.002%, Ni:0.1-1%, Ca:0.0005-0.002%, REM:0.0005-0.02%, Ti:0.05-0.5%, Nb:0.01-0.5%, Mo:0.05-1%, V:0.02-0.2%, Cr:0.01-1%, more than a kind or 2 kinds of Zr:0.02-0.2%.
3. according to the thin steel sheet for automobile of excellent in notch fatigue strength of claim 1 or 2 records, it is characterized in that the microstructure of above-mentioned steel plate is any following tissue: 1) the volume fraction maximum mutually for bainite or be the complex tissue of ferrite and bainite; 2) containing volume fraction is the complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%; With 3) the volume fraction maximum be that ferrite, second is mutually for martensitic complex tissue mutually.
4. the thin steel sheet for automobile of an excellent in notch fatigue strength is characterized in that, is to carry out zinc-plated making by each thin steel sheet for automobile put down in writing to claim 1-3.
5. a method of making the thin steel sheet for automobile of the described excellent in notch fatigue strength of claim 1 is characterized in that, after the steel disc roughing that will be made of the described component of claim 1, when carrying out hot rolling, at Ar
3It is finish rolling more than 25% that the thick total draft of steel plate is carried out in humidity province below phase point temperature+100 ℃, the plate face of the most surperficial any degree of depth up to 0.5mm along thickness direction from this steel plate 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
6. according to the method for the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 5 record, it is characterized in that, after the above-mentioned finish rolling,, under the coiling temperature more than 450 ℃, reel with the above speed of cooling cooling of 20 ℃/s.
7. according to the method for the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 5 record, it is characterized in that, after the above-mentioned finish rolling, at Ar
1Phase point temperature is above, Ar
3The following humidity province of phase point temperature stops 1-20 second, thereafter again with the above speed of cooling cooling of 20 ℃/s, greater than 350 ℃ and be no more than under 450 ℃ the coiling temperature of humidity province and reel.
8. according to the method for the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 5 record, it is characterized in that, after the above-mentioned cooling, under the coiling temperature below 350 ℃, reel.
9. according to the method for the thin steel sheet for automobile of each manufacturing excellent in notch fatigue strength of putting down in writing of claim 5-8, it is characterized in that, when above-mentioned hot rolling, be lubricated rolling.
10. according to the method for the thin steel sheet for automobile of each manufacturing excellent in notch fatigue strength of putting down in writing of claim 5-8, it is characterized in that, when above-mentioned hot rolling, carry out oxide skin after roughing ends and remove.
11. a method of making the thin steel sheet for automobile of the described excellent in notch fatigue strength of claim 1 is characterized in that, will be by after the described steel disc roughing of claim 1, at Ar
3It is finish rolling more than 25% that the thick total draft of steel plate is carried out in humidity province below phase point temperature+100 ℃, then pickling, again the thick draft of steel plate less than 80% cold rolling after, carry out more than recovery temperature, Ac
3Humidity province below phase point temperature+100 ℃ keeps the answer or the recrystallization annealing of 5-150 second, refrigerative operation, the plate face of the most surperficial any degree of depth up to 0.5mm along thickness direction from this steel plate 100}＜011 〉～223}＜110〉orientation group's the mean value of the random strength ratio of X ray is more than 2, and 554}＜225 〉, 111}＜112〉and 111}＜110〉mean value of the random strength ratio of X ray of 3 orientations is below 4, thickness of slab is below the above 12mm of 0.5mm.
12. the method according to the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 11 record is characterized in that, above-mentioned cold rolling after, carry out at Ac
1Phase point temperature is above, Ac
3Humidity province below phase point temperature+100 ℃ keeps 5-150 second, carries out the thermal treatment of refrigerative operation thereafter.
13. method according to the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 11 record, it is characterized in that, keep 5-150 after second in the said temperature district, carry out being cooled to greater than 350 ℃ and less than 450 ℃ humidity province with the above speed of cooling of 20 ℃/s, thereafter, keep in this humidity province again 5-600 second, be cooled to the thermal treatment of the operation of the humidity province below 200 ℃ with the 5 ℃/speed of cooling more than the s.
14. method according to the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 11 record, it is characterized in that, keep 5-150 after second in the said temperature district, carry out being cooled to the thermal treatment of the operation of the humidity province below 350 ℃ with the above speed of cooling of 20 ℃/s.
15. method of making the thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, in claim 5 or 11 steel plates of being put down in writing, also further contain Cu:0.2-2%, B:0.0002-0.002%, Ni:0.1-1%, Ca:0.0005-0.002%, REM:0.0005-0.02%, Ti:0.05-0.5%, Nb:0.01-0.5%, Mo:0.05-1%, V:0.02-0.2%, Cr:0.01-1%, more than a kind or 2 kinds of Zr:0.02-0.2% in quality %.
16. the method for thin steel sheet for automobile according to the manufacturing excellent in notch fatigue strength of claim 6 or 12 records is characterized in that, the microstructure of above-mentioned steel plate be the volume fraction maximum mutually for bainite or be the complex tissue of ferrite and bainite.
17. the method for thin steel sheet for automobile according to the manufacturing excellent in notch fatigue strength of claim 7 or 13 records, it is characterized in that the microstructure of above-mentioned steel plate is that to contain volume fraction be the complex tissue that the residual austenite below 25% and remainder mainly are made of ferrite, bainite more than 5%.
18. according to Claim 8 or the method for thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of 14 records, it is characterized in that, the microstructure of above-mentioned steel plate be the volume fraction maximum be martensitic complex tissue mutually for ferrite, second mutually.
19. method of making the thin steel sheet for automobile of excellent in notch fatigue strength, it is characterized in that, after making claim 5 or 11 hot-rolled steel sheets of being put down in writing or answer or recrystallization annealing plate, this steel plate of dipping in zinc-plated bath is implemented zinc-plated to surface of steel plate again.
20. the method according to the thin steel sheet for automobile of the manufacturing excellent in notch fatigue strength of claim 19 record is characterized in that, above-mentioned zinc-plated after, carry out Alloying Treatment again.
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|---|---|---|---|
| JP049012/2001 | 2001-02-23 | ||
| JP2001049012 | 2001-02-23 | ||
| JP2001247306A JP3927384B2 (en) | 2001-02-23 | 2001-08-16 | Thin steel sheet for automobiles with excellent notch fatigue strength and method for producing the same |
| JP247306/2001 | 2001-08-16 |
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| CN1492938A CN1492938A (en) | 2004-04-28 |
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| US (1) | US20040069382A1 (en) |
| EP (1) | EP1362930A4 (en) |
| JP (1) | JP3927384B2 (en) |
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| TWI248977B (en) * | 2003-06-26 | 2006-02-11 | Nippon Steel Corp | High-strength hot-rolled steel sheet excellent in shape fixability and method of producing the same |
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| JPS59100214A (en) * | 1982-11-29 | 1984-06-09 | Nippon Kokan Kk <Nkk> | Production of thick walled high tension steel |
| JP2952624B2 (en) * | 1991-05-30 | 1999-09-27 | 新日本製鐵株式会社 | High yield ratio type hot rolled high strength steel sheet excellent in formability and spot weldability and its manufacturing method and high yield ratio type hot rolled high strength steel sheet excellent in formability and its manufacturing method |
| JP3219820B2 (en) * | 1991-12-27 | 2001-10-15 | 川崎製鉄株式会社 | Low yield ratio high strength hot rolled steel sheet and method for producing the same |
| KR940702231A (en) * | 1992-06-22 | 1994-07-28 | 미노루 다나까 | COLD ROLLED STEEL SHEET AND HOT DIP AINC-COATED COLD ROLLED STEEL SHEET HAVING EXCELLENT BAKE HARDENABILITY, NON-AGING PROPERTIES AND FORMABILITY, AND PROCESS FOR PRODUCING SAME) |
| US5470529A (en) * | 1994-03-08 | 1995-11-28 | Sumitomo Metal Industries, Ltd. | High tensile strength steel sheet having improved formability |
| JP3039842B2 (en) * | 1994-12-26 | 2000-05-08 | 川崎製鉄株式会社 | Hot-rolled and cold-rolled steel sheets for automobiles having excellent impact resistance and methods for producing them |
| BE1010142A6 (en) * | 1996-04-16 | 1998-01-06 | Centre Rech Metallurgique | Method for producing a hot rolled strip steel high strength. |
| JPH1060527A (en) * | 1996-08-21 | 1998-03-03 | Sumitomo Metal Ind Ltd | Production of steel having high young's modulus |
| EP0969112B2 (en) * | 1997-03-17 | 2017-03-08 | Nippon Steel & Sumitomo Metal Corporation | A method of producing dual-phase high-strength steel sheets having high impact energy absorption properties |
| EP1026278B2 (en) * | 1998-07-27 | 2014-04-30 | Nippon Steel & Sumitomo Metal Corporation | Use of a ferritic steel sheet having excellent shape fixability and manufacturing method thereof |
| JP3417878B2 (en) * | 1999-07-02 | 2003-06-16 | 株式会社神戸製鋼所 | High-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue properties and its manufacturing method |
| JP4060997B2 (en) * | 1999-08-27 | 2008-03-12 | 新日本製鐵株式会社 | High-strength cold-rolled steel sheet and high-strength galvanized cold-rolled steel sheet excellent in bendability and deep drawability and manufacturing method thereof |
| WO2001081640A1 (en) * | 2000-04-21 | 2001-11-01 | Nippon Steel Corporation | Steel plate having excellent burring workability together with high fatigue strength, and method for producing the same |
| US6733601B2 (en) * | 2001-01-18 | 2004-05-11 | Jfe Steel Corporation | Ferritic stainless steel sheet with excellent workability |
-
2001
- 2001-08-16 JP JP2001247306A patent/JP3927384B2/en not_active Expired - Fee Related
-
2002
- 2002-02-20 KR KR1020037010529A patent/KR100572762B1/en active IP Right Grant
- 2002-02-20 EP EP02700640A patent/EP1362930A4/en not_active Withdrawn
- 2002-02-20 US US10/468,945 patent/US20040069382A1/en not_active Abandoned
- 2002-02-20 WO PCT/JP2002/001498 patent/WO2002066697A1/en not_active Application Discontinuation
- 2002-02-20 CA CA002438393A patent/CA2438393A1/en not_active Abandoned
- 2002-02-20 CN CNB028054024A patent/CN1221680C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CN1492938A (en) | 2004-04-28 |
| EP1362930A4 (en) | 2004-11-24 |
| EP1362930A1 (en) | 2003-11-19 |
| CA2438393A1 (en) | 2002-08-29 |
| JP3927384B2 (en) | 2007-06-06 |
| KR20030077018A (en) | 2003-09-29 |
| JP2002322533A (en) | 2002-11-08 |
| KR100572762B1 (en) | 2006-04-24 |
| US20040069382A1 (en) | 2004-04-15 |
| WO2002066697A1 (en) | 2002-08-29 |
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