WO2013042239A1 - 冷間加工用中炭素鋼板及びその製造方法 - Google Patents
冷間加工用中炭素鋼板及びその製造方法 Download PDFInfo
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- 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
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- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
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- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
- Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
- Y10T428/264—Up to 3 mils
- Y10T428/265—1 mil or less
Definitions
- the present invention relates to a medium carbon steel sheet for cold working that is excellent in cold workability and that can increase the strength even in a quenching process with a short heat treatment time typified by induction hardening, and a method for producing the same.
- Medium carbon steel plates are widely used as materials for chains, gears, clutches, saws, blades and the like.
- a process is usually performed in which a material is molded into a predetermined shape and then cured by heat treatment of quenching and tempering.
- the medium carbon steel sheet is required to have both workability and hardenability.
- processing technology has been developed, and a compression method and tensile processing are applied at the same time, and a forming method with a higher degree of processing than before has been adopted.
- Medium carbon steel sheets can withstand severe processing. Sex is required.
- induction hardening In order to respond to the changes in needs as described above, it is soft before cold working and withstands the work during cold working, and hardenability after induction heating (hereinafter referred to as induction hardening). The subsequent quenching was simply called induction hardening.) It was essential to develop a medium carbon steel sheet that was excellent.
- Patent Documents 1 to 4 Conventionally, many investigations have been made on the relationship between workability and induction hardenability of medium carbon steel sheets (see, for example, Patent Documents 1 to 4), but they are excellent in cold workability and 100 ° C./second or more. There seems to be no report of an example where sufficient hardenability can be secured at the heating rate.
- Patent Document 1 discloses a medium / high carbon steel plate made of hypoeutectoid steel with C: 0.1 to 0.8 mass% and S: 0.01 mass% or less.
- carbide is dispersed in ferrite so that the carbide spheroidization rate is 90% or more, and the average carbide particle size is 0.4 to 1.0 ⁇ m.
- the ferrite crystal grain size is adjusted to 20 ⁇ m or more.
- the form of the carbide is properly controlled and the local ductility is improved to improve stretch flangeability.
- both processing characteristics of compression processing and tension processing are improved. Is not considered sufficient.
- Patent Document 2 discloses a high-strength induction hardening steel that is excellent in cold forgeability and excellent in static strength, bending fatigue strength, and rolling contact fatigue strength. In this induction hardening steel, the specific carbide shape necessary for obtaining forgeability is not clearly shown, and specific conditions such as heating temperature and holding time during quenching are not clarified. Further, Patent Document 3 discloses a steel for induction hardening with excellent cold forgeability and a high limit upsetting rate, but specific conditions such as heating temperature and holding time during quenching are clarified. It is not clear whether it is actually excellent in hardenability. Furthermore, Patent Document 4 discloses a high carbon steel pipe excellent in cold workability and induction hardenability.
- This high-carbon steel pipe is suitable for processing methods governed by local ductility such as swaging and pipe expansion, and cold forging such as stamping, drawing, bending, burring, upsetting, ironing, extrusion, etc., which is the object of the present invention. It seems that sex is not enough.
- the cold working targeted by the present invention includes various processes such as punching, drawing, bending, burring, upsetting, ironing, and extrusion, and severe compression and tension are applied during these processes.
- various processes such as punching, drawing, bending, burring, upsetting, ironing, and extrusion, and severe compression and tension are applied during these processes.
- the cold-processed material is often subjected to a quenching process, and in the induction hardening process with a short heat treatment time, the carbide in the material is not sufficiently dissolved during heating, and a stable hardenability is obtained. Is difficult. Therefore, in order to sufficiently dissolve the carbide by induction hardening, it is important to control the form of the carbide of the material. However, it seems that the problems in the case of induction hardening by applying cold working to medium carbon steel sheets are not clear so far.
- the medium carbon steel plate is a steel plate having C of 0.30% to 0.60% and a thickness of 1.6 mm to 20 mm.
- an object of the present invention is to provide a medium carbon steel sheet that is excellent in cold workability and has high quenching ability even in induction hardening, and a method for producing the same. .
- the present inventors have conducted intensive research on methods for achieving the above-mentioned object.
- the hardness during cold working is low and cold workability It was found that a medium carbon steel sheet having sufficient quench hardening ability can be provided even in an induction hardening process with an average heating rate of 100 ° C./second or more.
- the present invention has been made on the basis of the above findings, and the gist thereof is as follows.
- the medium carbon steel sheet for cold working according to one aspect of the present invention is heated at an average heating rate of 100 ° C./second, held at 1000 ° C. for 10 seconds, and at an average cooling rate of 200 ° C./second at room temperature.
- a medium carbon steel sheet for cold working that has a hardness of 500 HV or more and 900 HV or less when induction quenching is performed to rapidly cool to C: 0.30 to 0.60%, Si: 0.06 ⁇ 0.30%, Mn: 0.3 ⁇ 2.0%, P: 0.030% or less, S: 0.0075% or less, Al: 0.005 ⁇ 0.10%, N: 0.001 ⁇ 0.01%, Cr: 0.001 to 0.10%, the balance is Fe and inevitable impurities, the average diameter d of the carbide is 0.6 ⁇ m or less, the spheroidization rate p of the carbide is 70% or more And the average diameter d ⁇ m of the carbide and the spheroidization rate p% of the
- the medium carbon steel sheet for cold working described in the above (1) is in mass%, and Ni: 0.01 to 0.5%, Cu: 0.05 to 0.5%, Mo: 0 .01-0.5%, Nb: 0.01-0.5%, Ti: 0.001-0.05%, V: 0.01-0.5%, Ta: 0.01-0.5 %, B: 0.001 to 0.01%, W: 0.01 to 0.5%, Sn: 0.003 to 0.03%, Sb: 0.003 to 0.03%, As: 0.0. One or more of 003 to 0.03% may be further contained.
- the Cr amount [Cr] and the Mo amount [Mo] satisfy [Cr] + [Mo] / 10 ⁇ 0.10. May be.
- the hardness before cold working may be 120 HV or more and less than 170 HV.
- the three layers of the adhesion layer, the base layer, and the lubricant layer are arranged in the order close to the interface with the medium carbon steel sheet for use, and the adhesion layer has the most component among the three layers due to the silanol bond.
- the base layer contains the most of the heat-resistant resin and the inorganic acid salt among the three layers, and 100 parts by mass of the heat-resistant resin. 0.01 parts by mass or more and 10 parts by mass
- the following inorganic acid salt is included and has a thickness of 0.1 ⁇ m or more and 15 ⁇ m or less
- the lubricant layer contains the lubricant most in the three layers, and is 0.1 ⁇ m or more and 10 ⁇ m or less.
- the ratio of the thickness of the base layer to the thickness of the lubricant layer may be 0.2 or more and 10 or less.
- the inorganic acid salt is selected from the group consisting of phosphate, borate, silicate, molybdate and tungstate. It may be at least one compound.
- the heat-resistant resin is at least one resin selected from the group consisting of a polyimide resin, a polyester resin, an epoxy resin, and a fluororesin. Also good.
- the lubricant is at least one selected from the group consisting of polytetrafluoroethylene, molybdenum disulfide, tungsten disulfide, zinc oxide, and graphite. It may be a seed compound.
- the manufacturing method of the medium carbon steel sheet for cold work which concerns on 1 aspect of this invention keeps the slab which has the component composition as described in said (1) or (2) at 1050 degreeC or more and 1300 degrees C or less.
- a first step to perform after the first step, a second step of performing hot rolling to finish rolling the cast slab at 750 ° C. or more and 1000 ° C. or less to obtain a steel plate; and this second step After the step, a third step of cooling the steel sheet to a first cooling end temperature of 500 ° C. or more and 700 ° C.
- a fifth step of holding the steel sheet as above and the second cooling end temperature less is time is limited to less than 30 hours; after the fifth step, the steel plate, 600 ° C. or higher and A a sixth step of heating to a point c1 to ⁇ 10 ° C. or lower and annealing for 5 hours or more and less than 100 hours.
- the dew point at 400 ° C. or lower is less than ⁇ 20 ° C.
- the dew point at more than 400 ° C. is ⁇ 40. It may be less than ° C. and the hydrogen concentration may be 95% or more.
- a water-soluble silane coupling agent, a water-soluble inorganic acid salt, and a water-soluble heat-resistant material is used.
- An aqueous surface treatment liquid containing a resin and a lubricant is applied to at least one surface of the cold-working medium carbon steel sheet, and the surface treatment liquid is dried to provide the surface on at least one surface of the cold-working medium carbon steel sheet.
- a treatment film may be formed.
- the present invention is low hardness (soft) before cold working, is excellent in both cold working characteristics of compression working and tensile working, and the average heating rate after cold working is 100 ° C./second or more.
- a medium carbon steel sheet for cold working and a method for producing the same which has sufficient quench hardening ability and can achieve high strength even in induction hardening treatment, and achieves both cold workability and induction hardenability. can do.
- the steel sheet of the present embodiment the reason for limitation relating to the component composition of the steel sheet for cold working according to an embodiment of the present invention (hereinafter sometimes referred to as “the steel sheet of the present embodiment”) will be described.
- “%” means “mass%”.
- C 0.30 to 0.60% C is an important element in securing the quenching strength of the steel sheet. Therefore, 0.30% or more of C is added to the steel to ensure the required strength. If the C content is less than 0.30%, the hardenability is lowered and the strength as a high-strength steel sheet for machine structures cannot be obtained, so the lower limit of the C content is 0.30%. If the amount of C exceeds 0.60%, the proportion of carbides acting as a starting point of fracture increases and cold workability decreases, so the upper limit of the amount of C is 0.60%. When it is necessary to ensure hardenability, the lower limit of the C content is preferably 0.35%, more preferably 0.37%, and most preferably 0.40%. . In order to make the form of the carbide easier to control, the upper limit of the C amount is preferably 0.55%, more preferably 0.52%, and 0.50%. Most preferred.
- Si acts as a deoxidizer and is an element effective in improving hardenability while suppressing interfacial delamination between ferrite and carbide during processing. If the Si amount is less than 0.06%, this addition effect cannot be obtained, so the lower limit of the Si amount is 0.06%. On the other hand, if the amount of Si exceeds 0.30%, the crack generation frequency (intragranular crack generation frequency) in the ferrite phase increases due to solid solution strengthening, and the surface properties deteriorate due to scale wrinkles during hot rolling. The upper limit of the amount is 0.30%.
- the lower limit of the Si amount is preferably 0.10%, more preferably 0.13%, and 0.15% Most preferably it is.
- the upper limit of Si amount is 0.26%.
- Mn acts as a deoxidizer and is an effective element for improving hardenability. If the amount of Mn is less than 0.3%, this addition effect cannot be obtained, so the lower limit of the amount of Mn is 0.3%. If the amount of Mn exceeds 2.0%, dissolution of carbides during high-frequency heating is delayed, and the hardenability (quenching hardness) decreases, so the upper limit of the amount of Mn is 2.0%. In order to further improve the hardenability, the lower limit of the Mn amount is preferably 0.5%, more preferably 0.55%, and most preferably 0.65% or 0.73%. preferable. In order to ensure higher induction hardenability, the upper limit of the amount of Mn is preferably 1.6%, more preferably 1.4%, and 1.2% or 1.0%. Most preferably it is.
- P 0.030% or less
- P is a solid solution strengthening element and is an element effective for the strength of a steel sheet.
- the toughness is lowered, so the upper limit of the P content is 0.030%.
- P is an inevitable impurity. Reducing the P amount to less than 0.005% increases the refining cost, so the P amount does not have to be reduced to less than 0.005%.
- the upper limit of the P content is preferably 0.020%.
- the upper limit of the amount of S is 0.0075% or less.
- FIG. 5 shows the relationship between the amount of S and the number of cracks (sulfide starting cracks) on which sulfide acts as a starting point during cold working. As can be seen from FIG. 5, when the S content is 0.0075% or less, the number of cracks at the sulfide starting point is greatly reduced. S is an inevitable impurity. Reducing the S amount to less than 0.0001% greatly increases the refining cost, so the S amount does not have to be reduced to less than 0.0001% or 0.001% or less. Moreover, when it is necessary to ensure higher workability and toughness, the upper limit of the amount of S is preferably 0.007%, and more preferably 0.005%.
- Al acts as a deoxidizer and is an effective element for fixing N. If the Al amount is less than 0.005%, this addition effect cannot be obtained sufficiently, so the lower limit of the Al amount is 0.005%. If the Al content exceeds 0.10%, the above-described addition effect is saturated and surface defects are likely to occur, so the upper limit of the Al content is 0.10%. In order to more sufficiently fix N, the lower limit of the Al content is preferably 0.01%. Moreover, in order to suppress generation
- N 0.001 to 0.01%
- N is an element that forms nitrides. If nitride precipitates during slab bending correction in curved continuous casting, the slab may crack, so the upper limit of the N amount is 0.01%.
- N is an unavoidable impurity. The smaller the amount of N in the steel, the better.
- the lower limit of the amount of N is 0.0010%. In the case of further reducing the refining cost, the lower limit of the N amount is preferably 0.002%.
- the upper limit of the N content is preferably 0.008%, and more preferably 0.006%.
- Cr 0.001 to 0.10% Cr is an element that improves the stability of carbide during high-frequency heating. If the amount of Cr exceeds 0.10% due to the addition of Cr into the steel, the stability of the carbide is greatly increased, the dissolution of the carbide during high-frequency heating is suppressed, and the hardenability is reduced. Therefore, the upper limit of the Cr amount is 0.10%. The lower the Cr content in the steel, the higher the induction hardenability. However, if the Cr content is reduced to 0.001% or less, the refining cost increases greatly, so the lower limit of the Cr content is 0.001%. When increasing the dissolution rate of carbide during high-frequency heating, the upper limit of the Cr content is preferably 0.080%, and more preferably 0.070%. Moreover, when reducing refining cost more, it is preferable that the minimum of the amount of Cr is 0.010%.
- Ni, Cu, and Mo may be added to the steel in the required amount.
- Ni 0.01 to 0.5%
- Ni is an element effective for improving toughness and hardenability. If the amount of Ni is less than 0.01%, this addition effect is not obtained, so the lower limit of the amount of Ni is 0.01%. If the Ni content exceeds 0.5%, the above effect is saturated and the cost increases, so the upper limit of the Ni content is 0.5%. From the viewpoint of strength, the lower limit of the Ni content is preferably 0.05%. From the viewpoint of cost, the upper limit of the Ni amount is preferably 0.3%, more preferably 0.2%, and most preferably 0.15%.
- Cu 0.05 to 0.5%
- Cu is an element effective for ensuring hardenability. If the amount of Cu is less than 0.05%, this addition effect is insufficient, so the lower limit of the amount of Cu is 0.05%. If the amount of Cu exceeds 0.5%, the hardness increases excessively and the cold workability deteriorates, so the upper limit of the amount of Cu is 0.5%. From the viewpoint of strength, the lower limit of the Cu content is preferably 0.08%. From the viewpoint of workability, the upper limit of the Cu content is preferably 0.3%, more preferably 0.2%, and most preferably 0.15%.
- Mo 0.01 to 0.5% Mo is an element effective for improving hardenability. If the amount of Mo is less than 0.01%, this effect of addition is small, so the lower limit of the amount of Mo is 0.01%. When the amount of Mo exceeds 0.5%, a lot of Mo-based carbides are precipitated in the steel. In the induction hardening, the Mo-based carbide is not sufficiently dissolved and the hardenability of the material is lowered, so the upper limit of the Mo amount is 0.5%. When higher hardenability is required, the upper limit of the Mo amount is preferably 0.3%, and more preferably 0.1%.
- Nb, V, Ta, B, and W may be added to the steel in a required amount.
- Nb 0.01 to 0.5%
- Nb is an element that forms carbonitride and is effective in preventing coarsening of crystal grains and improving toughness. If the Nb amount is less than 0.01%, this effect of addition is not sufficiently exhibited, so the lower limit of the Nb amount is 0.01%. If the amount of Nb exceeds 0.5%, the above-mentioned effect of addition is saturated, so the upper limit of the amount of Nb is 0.5%. In order to efficiently use the above addition effect, the Nb content is preferably 0.07 to 0.4%. If necessary, the lower limit of the Nb amount may be limited to 0.09% or 0.14%, and the upper limit may be limited to 0.35% or 0.3%.
- Ti 0.001 to 0.05%
- Ti is added to steel from the viewpoint of N fixation, and contributes to suppression of embrittlement of the slab and stabilization of the material.
- the range of Ti amount is 0.001 to 0.05%.
- the upper limit of the Ti amount is preferably 0.20%, more preferably 0.10%, and most preferably 0.06%.
- V 0.01 to 0.5%
- V is an element that forms carbonitrides and is effective in preventing coarsening of crystal grains and improving toughness. If the amount of V is less than 0.01%, this effect of addition is small, so the lower limit of the amount of V is 0.01%. If the V amount exceeds 0.5%, carbides are generated and the quenching hardness is lowered, so the upper limit of the V amount is 0.5%. In order to efficiently use the above effect, the V amount is preferably 0.07 to 0.2%.
- Ta 0.01 to 0.5% Ta, like Nb and V, is an element that forms carbonitrides and is effective in preventing coarsening of crystal grains and improving toughness. If the amount of Ta is less than 0.01%, this addition effect is small, so the lower limit of the amount of Ta is 0.01%. If the amount of Ta exceeds 0.5%, carbides are generated and the quenching hardness decreases, so the upper limit of the amount of Ta is 0.5%. In order to efficiently use the above effect, the Ta content is preferably 0.07 to 0.2%.
- B 0.001 to 0.01%
- B is an element effective for improving hardenability by adding a small amount. If the amount of B is less than 0.001%, this addition effect is not obtained, so the lower limit of the amount of B is 0.001%. If the amount of B exceeds 0.01%, the castability is reduced, and a B-based compound is generated to reduce toughness. Therefore, the upper limit of the amount of B is 0.01%. When higher hardenability is required, the lower limit of the B amount is preferably 0.003%. Moreover, when it is necessary to suppress the production
- W 0.01-0.5% W is an element effective for strengthening a steel sheet. If the amount of W is less than 0.01%, this addition effect does not appear, so the lower limit of the amount of W is 0.01%. If the W amount exceeds 0.5%, the workability deteriorates, so the upper limit of the W amount is 0.5%. From the viewpoint of strength, the lower limit of the W amount is preferably 0.04%. From the viewpoint of workability, the upper limit of the W amount is preferably 0.2%.
- Sn When scrap is used as a raw material for a steel plate, one or more of Sn, Sb, and As may be inevitably mixed in the steel, but if the amount is 0.03% or less, Does not impair induction hardenability and hardenability. Therefore, one or more of Sn: 0.03% or less, Sb: 0.03% or less, and As: 0.03% or less may be contained in the steel. Usually, each of these components is contained as an impurity in an amount of 0.003% or more.
- the amount of O in the steel sheet is not specified, if the oxide aggregates and coarsens, the cold workability deteriorates, so the amount of O is preferably 0.0025% or less.
- the amount of O is preferably small, but it is technically difficult to reduce the amount of O inevitably contained to less than 0.0001%, so 0.0001% or more of O may be contained. .
- elements such as Zn and Zr are mixed as unavoidable impurities, but the above elements may be mixed into the steel as long as the characteristics of the steel sheet are not impaired. In addition, elements other than Zn and Zr may be mixed in the steel as long as the properties of the steel sheet are not impaired.
- both Cr and Mo suppress the supply (solid solution) of C from the carbide to the parent phase at a high temperature and lower the hardenability. That is, Cr dissolves in cementite, suppresses the solid solution of C from cementite to the parent phase during high-frequency heating, and reduces hardenability. Further, when Mo is excessively contained in the steel, it forms a Mo-based carbide. In this case, the solid solution of C from the Mo-based carbide to the parent phase is suppressed during high-frequency heating, and the hardenability is lowered. Therefore, when Cr and Mo are contained in the steel, it is preferable that the Cr amount [Cr] and the Mo amount [Mo] satisfy the following expression (1).
- the medium carbon steel sheet of the present embodiment includes the above-described basic element, and has at least one selected from the chemical composition including the remaining Fe and inevitable impurities, or the above-described basic element and the above-described selective element. And a chemical composition consisting of the balance Fe and inevitable impurities.
- the average diameter of the carbide is 0.6 ⁇ m or less
- the spheroidization rate of the carbide is 70% or more and less than 90%
- the average diameter d ( ⁇ m) of the carbide and the spheroidization rate p (%) of the carbide are The following formula (2) is satisfied. d ⁇ 0.04 ⁇ p ⁇ 2.6 (2)
- the structure For observation of the structure (carbide), it is preferable to use a scanning electron microscope. Four or more visual fields (regions) containing 500 or more carbides on the tissue observation surface at a magnification of 3000 times are selected, and the area of each carbide contained in the region is measured.
- carbides having an area of 0.01 ⁇ m 2 or less are excluded from the evaluation target.
- the diameter (equivalent circle diameter) when the average area (average area value) of the measured carbides is approximated by a circle is defined as the average diameter (average carbide diameter).
- a carbide having a ratio of the major axis length to the minor axis length (aspect ratio) of each carbide of 3 or more is defined as acicular carbide, and a carbide having this ratio of 1 or more and less than 3 is defined as spherical carbide.
- a value obtained by dividing the number of spherical carbides by the total number of carbides is defined as the spheroidization rate of the carbides.
- the spheroidization rate of the carbide is 70% or more and less than 90%. In the vicinity of the needle-like carbide, stress is likely to be localized at the time of cold working, and is likely to become a starting point of cracking. In particular, when the spheroidization rate is less than 70%, the cold workability deteriorates, so the spheroidization rate of the carbide is 70% or more. Further, when higher cold workability is required, the spheroidization rate of the carbide is preferably 73% or more, and more preferably 75% or more.
- the surface area in contact with the parent phase of steel is smaller than that of acicular carbide, and the carbon emission diffusion path from the carbide to the parent phase is narrow.
- the quench hardening ability in the induction hardening at an average heating rate of 100 ° C./second is not sufficient.
- the spheroidization ratio of the carbide having an area of more than 0.01 ⁇ m 2 may be defined as 70% or more and less than 90%.
- the average diameter d ( ⁇ m) of the carbide and the spheroidization ratio p (%) of the carbide must satisfy the above formula (2). That is, when the spheroidization rate of the carbide is 70% or more and less than 80% and the amount of acicular carbide is large, the absolute value of the major axis length of the acicular carbide affects the cold workability.
- the relationship of the formula (2) is required between the conversion ratio and the average diameter of the carbide. Below, this (2) Formula is demonstrated.
- the cold workability is deeply related to the number of cracks during cold working, and the cold workability is lower as the number of cracks is larger.
- the present inventors can improve cold workability while ensuring induction hardenability by satisfying appropriate predetermined conditions for the average diameter of carbide and the spheroidization rate of carbide. Revealed.
- the hardness before cold working is less than 170 HV, sufficient ductility can be obtained, so that a sufficient molding amount can be ensured during processing.
- the hardness before cold working is preferably less than 165 HV, more preferably less than 160 HV, and most preferably less than 155 HV.
- a technique for achieving both cold workability and induction hardenability of the steel sheet is provided by the present inventors. Is a new finding. Furthermore, the present inventors have found that a steel sheet can be suitably used for cold working by controlling the hardness before cold working to less than 170 HV.
- the quenching hardness after induction quenching is preferably 500 HV or more.
- the wear resistance is improved as the strength of the quenched steel is increased.
- a member such as a clutch plate or a gear for automobile parts is desirably hardened to 500 HV or more in order to obtain wear resistance. If the quenching hardness is too high, the toughness of the quenched portion is extremely lowered, and the function as a member for machine structure may be lost. Therefore, the quenching hardness after induction hardening is preferably 900 HV or less, more preferably 800 HV or less, and most preferably 750 HV or less.
- test conditions for induction hardening in the present invention are as follows: 750 ° C. or higher is raised from room temperature to 1000 ⁇ 20 ° C. at an average heating rate of 100 ⁇ 15 ° C./second, and then 10 ⁇ 0.00 at 1000 ⁇ 20 ° C. The condition is maintained for 5 seconds, and then immediately cooled between 800 ° C. and 400 ° C. to room temperature at an average cooling rate of 200 ⁇ 10 ° C./second.
- a steel sheet having a Vickers hardness of 500 or higher (ie, 500 HV or higher) after induction hardening under these conditions is an object of the present invention.
- the thickness of the steel plate is not particularly limited, but from the viewpoint of workability, it is preferably 20 mm or less or 16 mm or less, more preferably 14 mm or less, and most preferably 12 mm or less or 9 mm or less. . Further, from the viewpoint of strength, it is preferably 1 mm or more or 2 mm or more, more preferably 2.5 mm or more, and most preferably 3 mm or more.
- FIG. 1 shows the influence of the average diameter of carbide and the spheroidization rate of carbide on quenching hardness and cold workability.
- Cold workability was evaluated by a flat plate bending test using a test piece (flat plate bending test piece) having a width of 30 mm and a length of 100 mm.
- a test piece flat plate bending test piece
- compressive stress and tensile stress are applied to the inner surface (inner circumferential surface) and outer surface (outer circumferential surface) of the bent sample (flat plate bending sample), so the cracks on the inner surface side and outer surface side of the sample are evaluated. By doing so, it is possible to simultaneously measure the workability against compressive stress and tensile stress.
- the bending radius is set to 1 ⁇ 2 of the plate thickness, and the bending angle is set to 90 °.
- the average diameter d of the carbide is 0.6 ⁇ m or less
- the spheroidization rate p of the carbide is 70% or more and less than 90%
- the average diameter d ( ⁇ m) of the carbide and the spheroidization of the carbide In the steel sheet (white circle in FIG. 1) with the rate p (%) satisfying the above formula (2), it was possible to obtain a quenching hardness of 500 HV or higher after induction quenching, and no cracking occurred during processing.
- the spheroidization rate of carbide is 70% or more and less than 80%, and the average diameter d ( ⁇ m) of carbide and the spheroidization rate p (%) of carbide do not satisfy the above formula (2).
- the proportion of carbide acting as a starting point of fracture increased, and cracking occurred during processing.
- a steel plate having an average carbide diameter of more than 0.6 ⁇ m and a spheroidization rate of carbide of 80% or more and less than 90% or a spheroidization rate of carbide of 90% or more black triangle in FIG. 1).
- the quenching hardness was not sufficient.
- the quenching hardness used as a reference is defined as the hardness measured under the following conditions.
- the sample was heated from room temperature to 1000 ° C. at an average heating rate of 100 ° C./second at a frequency of 78 kHz and held for 10 seconds, and immediately subjected to induction quenching to rapidly cool to room temperature at an average cooling rate of 200 ° C./second or more to obtain Vickers hardness.
- This Vickers hardness after induction hardening is the quenching hardness in the present embodiment. The lower the spheroidization rate, the more easily the carbides dissolve, and the quenching hardness tends to increase.
- FIG. 2 shows the relationship between the amount of Si and cold workability (the number of cracks in the carbide interface and grains after cold work).
- the number of cracks in the region of the plate thickness 1/8 to 3/8, 5/8 to 7/8 in the plate thickness section (cross section including the plate thickness direction and the longitudinal direction) of the bending angle portion (maximum curvature portion) of the flat plate bending sample was measured with a scanning electron microscope at a magnification of 3000 times.
- the number of cracks was 20 or less per 1 mm 2, it was judged that the occurrence of cracks due to interfacial peeling during cold working could be suppressed. Therefore, the cold workability was evaluated as “good”. Further, when the number of cracks was more than 20, the cold workability was evaluated as “bad”.
- the cold workability was good in the steel sheet having an Si content of 0.06% or more. Further, the Si amount increased and the number of cracks decreased up to 0.3% Si amount. In this case, cracks were generated by delamination at the interface between ferrite and carbide. Furthermore, when the amount of Si exceeded 0.3%, the amount of Si increased and the number of cracks increased. In this case, cracks occurred in the ferrite phase. Moreover, when the Si amount increased from 0.06% to 0.1%, the decrease rate of the number of cracks was large, and the cold workability was greatly improved. In addition, when the Si amount was 0.15 to 0.26%, the effect of improving the cold workability by Si could be obtained to the maximum. In FIG. 2, a sample having a C content of 0.40 to 0.45% was annealed at 680 ° C. for 30 hours, and then the cold workability described later was evaluated.
- FIG. 3 shows the relationship between [Cr] + [Mo] / 10 and the quenching hardness.
- [Cr] + [Mo] / 10 is less than 0.10, the quenching hardness is further improved. Accordingly, [Cr] + [Mo] / 10 is preferably less than 0.10.
- a sample having a C content of 0.40 to 0.45% was annealed at 680 ° C. for 30 hours and then subjected to the induction hardening described above, and the quenching hardness was measured.
- FIG. 4 shows the relationship between the spheroidization rate of carbide and the number of cracks that originate from carbide during cold working (cracks originating from carbide).
- FIG. 4 when the spheroidization rate of the carbide is less than 70%, the number of cracks rapidly increases.
- FIG. 5 shows the relationship between the amount of S and the number of cracks at the sulfide starting point during cold working. As can be seen from FIG. 5, when the S content is 0.0075% or less, the number of cracks at the sulfide starting point is greatly reduced.
- EDS energy dispersive X-ray spectrometer
- the manufacturing method of this embodiment has a technical idea that combines high-temperature cutting and low-temperature annealing, and a specific example thereof is shown below.
- the manufacturing method shown below is an example, and other methods may be used as long as a necessary structure is obtained.
- the continuous casting slab (slab) of the chemical component of the above embodiment is heated.
- the heating temperature is 1050 ° C. or higher and 1300 ° C. or lower.
- the soaking time is preferably 150 minutes or less, and more preferably 90 minutes or less.
- the soaking time indicates the time from when the slab surface temperature reaches 20 ° C. lower than the target heating temperature until the slab exits the heating furnace. If the heating temperature exceeds 1300 ° C. or the soaking time is excessively long, the surface layer portion of the slab is significantly removed in the heating process, and the hardenability of the steel sheet surface is deteriorated.
- the slab is heated to 1050 ° C.
- the heating temperature is preferably 1280 ° C or lower, more preferably 1240 ° C or lower, and most preferably 1200 ° C or lower.
- the soaking time is more preferably 60 minutes or less. The lower limit of the soaking time is not particularly limited.
- the continuous cast slab may be directly subjected to hot rolling, or may be reheated after cooling and subjected to hot rolling. There is almost no difference in steel plate characteristics between the former and the latter.
- hot rolling either normal hot rolling or continuous hot rolling in which slabs are joined in finish rolling may be employed.
- the end temperature of hot rolling (hot end temperature) is determined from the viewpoints of productivity, sheet thickness accuracy, anisotropy improvement, and surface flaw suppression.
- the hot rolling finish temperature is lower than 750 ° C.
- wrinkles due to seizure frequently occur in finish rolling.
- the hot rolling end temperature is higher than 1000 ° C., the occurrence frequency of wrinkles due to scale increases, resulting in a decrease in product yield and an increase in cost. Therefore, the hot rolling end temperature is 750 to 1000 ° C.
- the steel sheet after hot rolling is subjected to an average cooling rate (first average cooling rate) of 20 ° C./second or more and 50 ° C./second or less immediately after hot rolling at 500 ° C. or more and 700 ° C. or less.
- first average cooling rate 20 ° C./second or more and 50 ° C./second or less immediately after hot rolling at 500 ° C. or more and 700 ° C. or less.
- the cooling temperature is controlled to 500 ° C. or more and 700 ° C. in consideration of the transformation start temperature and transformation end temperature of pearlite.
- the steel sheet is heated to 400 ° C. or more at an average cooling rate (second average cooling rate) of 5 ° C./second or more and 30 ° C./second or less and at least 50 ° C. lower than the first cooling end temperature (that is, , , The difference between the first cooling end temperature and the second cooling end temperature is 50 ° C. or more and a temperature lower than the first cooling end temperature by 50 ° C. or less) and is cooled to a winding temperature (second cooling end temperature). Scrape.
- the lamella spacing of the pearlite produced in the steel sheet can be reduced, and the carbide in the steel sheet after annealing can be made fine.
- the winding is performed at a temperature that is at least 50 ° C. lower than the first cooling end temperature.
- the average cooling rate from the cooling temperature to the coiling temperature is 5 ° C./second or less, a pearlite band accompanying segregation may be generated, or the pearlite lamella spacing may be greatly increased. Therefore, coarse carbides are easily formed after annealing, and the hardenability of the steel sheet may be reduced. Further, when the average cooling rate is 30 ° C./second or more, the pearlite necessary for securing the cementite having the above-mentioned spheroidization ratio may not be generated sufficiently.
- the cooled steel sheet is wound at a winding temperature from 400 ° C. to a temperature that is at least 50 ° C. lower than the first cooling end temperature.
- the coiling temperature is less than 400 ° C., part of the martensitic transformation occurs, and the strength of the steel sheet increases, which may make handling difficult.
- the structure becomes non-uniform, and gauge hunting may occur during cold rolling, resulting in a decrease in yield.
- winding is performed at a temperature exceeding 50 ° C. lower than the first cooling end temperature, as described above, pearlite with a rough lamellar spacing is generated, and the spheroidization rate after annealing is reduced, so that cold working is performed. Sex worsens.
- the steel plate is kept at 400 ° C. or higher and below the second cooling end temperature so that the time during which the wound steel plate (coil) is 400 ° C. or higher is limited to 30 hours or less. Thereafter, the steel sheet is cooled to a temperature of 400 ° C. or lower (for example, room temperature, temperature capable of pickling).
- a temperature of 400 ° C. or lower for example, room temperature, temperature capable of pickling.
- the time during which the steel sheet is 400 ° C. or higher is limited to 30 hours or less during cooling. In these cases, decarburization can be suppressed and a sufficient amount of C on the surface can be secured.
- the time when the steel sheet is 400 ° C.
- the steel sheet is softened and annealed.
- the steel plate is subjected to softening box annealing to improve the workability of the steel plate.
- the steel sheet In the softening box annealing (annealing), the steel sheet is heated from room temperature to an annealing temperature of 600 ° C. or more and A c1 ⁇ 10 ° C. or less and then held for 5 hours or more and less than 100 hours.
- the steel sheet is annealed so that the ferrite grains are coarsened by holding for 5 hours or more and less than 100 hours to soften the steel sheet and the spheroidization rate of the carbide is not increased excessively.
- the annealing temperature is A c1 ⁇ 10 ° C. or higher (particularly, A c1 ° C. or higher)
- the carbide rapidly spheroidizes, and the hardenability is lowered in the subsequent induction hardening.
- the diffusion rate of elements (particularly C) in the steel sheet is optimized, and the spheroidization rate of carbide can be controlled appropriately.
- the hydrogen concentration is 95% or more, the dew point below 400 ° C is less than -20 ° C, and the dew point above 400 ° C is less than -40 ° C.
- the temperature distribution in the coil can be controlled more uniformly, and a decrease in hardenability due to nitrogen penetration can be suppressed. Further, by controlling the dew point below 400 ° C. to below ⁇ 20 ° C. and controlling the dew point above 400 ° C. to below ⁇ 40 ° C., decarburization during annealing can be sufficiently suppressed.
- FIG. 8 shows a flowchart showing an outline of a method for manufacturing a steel sheet for cold working according to the present invention, including the present embodiment and the following modifications.
- a surface treatment film may be formed on the surface of the steel plate of the above embodiment from the viewpoint of lubricity.
- an inclined surface treatment film comprising an adhesion layer that secures adhesion to the base steel sheet, a base layer that retains a lubricant, and a lubricant layer that improves lubricity is provided on the surface of the steel sheet. It is provided and the thickness of each layer is controlled. Therefore, a suitable surface treatment film can be formed on the surface of the steel sheet from the viewpoint of global environmental conservation with a simple treatment process. Further, excellent lubricity, anti-seizure performance and anti-galling performance can be imparted to the steel sheet.
- FIG. 6 is a longitudinal sectional view schematically showing the configuration of the surface-treated steel sheet.
- the surface-treated steel sheet 1 has a steel sheet 10 that is a base, and a surface-treated film (film) 100 formed on at least one surface of the steel sheet 10.
- the steel plate of the above embodiment can be used as it is for the steel plate 10 that is the base of the surface-treated steel plate 1.
- the steel plate of the above embodiment may be plated.
- the steel plate of the said embodiment can be plated using 1 or more types of metals of zinc, nickel, iron, aluminum, titanium, magnesium, chromium, manganese, and tin.
- each component in the film has a concentration gradient in the film thickness direction. Therefore, it is possible to divide the surface treatment film 100 which is an inclined film into three layers. That is, in the surface treatment film 100, three layers are formed in the order of the adhesion layer 110, the base layer 120, and the lubricant layer 130 from the interface between the surface treatment film 100 and the steel plate 10 toward the surface of the surface treatment film 100. ing.
- the “gradient type” in this modification means that the component contained in the surface treatment film 100 has a concentration gradient in the film thickness direction of the film as described above. That is, as main components in the surface treatment film 100, components due to silanol bonds (details will be described later), heat-resistant resins, inorganic acid salts and the like formed between the metal on the surface of the steel sheet 10 as a base. Although there is a lubricant, these components have a concentration gradient in the film thickness direction of the surface treatment film 100. More specifically, the concentration of the lubricant 131 increases from the interface between the surface treatment film 100 and the steel plate 10 toward the surface of the surface treatment film 100, and conversely, the concentrations of the heat resistant resin and the inorganic acid salt decrease.
- the adhesion layer 100, the base layer 120, and the lubricant layer 130 included in the surface treatment film 100 are completely separated to form three layers (components of a certain layer are not present in other layers). Do not mean.
- the adhesion layer 110 has a role of ensuring adhesion between the surface treatment film 100 and the steel sheet 10 as a base material accompanying cold working and preventing seizure between the surface treatment steel sheet 1 and the mold. Specifically, the adhesion layer 110 is located on the side close to the interface between the surface treatment film 100 and the steel plate 10, and contains the most components due to silanol bonds among the three layers constituting the surface treatment film 100.
- the silanol bond in this modified example is represented by Si—O—X (X is a metal which is a constituent component of the steel sheet (base)) and is formed in the vicinity of the interface between the surface treatment film 100 and the steel sheet 10. .
- This silanol bond is included in the plating when the silane coupling agent contained in the surface treatment liquid for forming the surface treatment film 100 and the metal on the surface of the steel plate 10 (for example, when the steel plate 10 is plated). It is presumed that it corresponds to a covalent bond with an oxide of a metal species (Zn, Al, etc.), which is Fe, which is Fe when the steel plate 10 is not plated.
- silanol bonds is caused by silanol bonds in the film thickness direction of the surface treatment film 100 by a method capable of elemental analysis in the depth direction of the sample (for example, a high frequency glow discharge emission spectroscopic analyzer (high frequency GDS)). It can be confirmed by quantifying each element from the spectral intensity of the component (Si, X, O) element, and direct observation of the sample cross section (for example, using a field emission transmission electron microscope (FE-TEM)). The presence of silanol bonds can also be confirmed from microscopic elemental analysis (for example, analysis method using an energy dispersive X-ray spectrometer (EDS)).
- a method capable of elemental analysis in the depth direction of the sample for example, a high frequency glow discharge emission spectroscopic analyzer (high frequency GDS)
- GDS glow discharge emission spectroscopic analyzer
- the thickness of the adhesion layer 110 needs to be 0.1 nm or more and 100 nm or less. If the thickness of the adhesion layer 110 is less than 0.1 nm, the formation of silanol bonds is insufficient, so that sufficient adhesion between the surface treatment film 100 and the steel sheet 10 cannot be obtained. On the other hand, when the thickness of the adhesion layer 110 exceeds 100 nm, the number of silanol bonds increases so that the internal stress in the adhesion layer 110 increases during the processing of the surface-treated steel sheet 1 and the film becomes brittle. The adhesion between the coating 100 and the steel plate 10 is reduced. From the viewpoint of ensuring the adhesion between the surface treatment film 100 and the steel sheet 10 more reliably, the thickness of the adhesion layer 110 is preferably 0.5 nm or more and 50 nm or less.
- the base layer 120 improves the steel sheet followability during cold working, and imparts hardness and strength against seizure with the mold to the surface-treated steel sheet 1.
- the base layer 120 holds the lubricant 131 and the lubricant layer 130.
- the base layer 120 is positioned as an intermediate layer between the adhesion layer 110 and the lubricant layer 130 and contains the most heat-resistant resin and inorganic acid salt among the three layers constituting the surface treatment film 100. .
- the surface treatment film 100 is formed using an aqueous surface treatment liquid. Therefore, in consideration of the stability of the surface treatment liquid, the inorganic acid salt in this modification is preferably water-soluble. .
- the inorganic acid salt is a salt that is insoluble or hardly soluble in water, for example, if it is a salt that is soluble in an acid, it is not necessary to consider the stability of the surface treatment solution.
- a film containing a salt that is insoluble or hardly soluble in water for example, zinc phosphate is formed. can do.
- phosphates, borates, silicates, sulfates, molybdates, or tungstates can be used alone or in combination as an inorganic acid salt in this modification.
- an inorganic acid salt for example, zinc phosphate, calcium phosphate, sodium sulfate, potassium sulfate, potassium silicate, sodium borate, potassium borate, ammonium borate, potassium molybdate, sodium molybdate, tungsten Potassium acid, sodium tungstate and the like can be used.
- the inorganic acid salt is phosphate, borate and silicic acid. More preferably, it is at least one compound selected from the group consisting of salts.
- the base layer 120 contains a heat resistant resin as a main component.
- the heat-resistant resin in this modification can maintain the film shape at a temperature (for example, a predetermined temperature higher than 200 ° C. and lower than 400 ° C.) that exceeds the ultimate temperature during cold working (approximately 200 ° C.). It preferably has heat resistance.
- the surface treatment film 100 is formed using an aqueous surface treatment liquid. Therefore, in consideration of the stability of the surface treatment liquid, the heat resistant resin in the present modification is preferably water-soluble.
- a polyimide resin for example, a polyester resin, an epoxy resin, a fluorine resin, or the like can be used as the heat-resistant resin in this modification.
- a polyimide resin for example, a polyester resin, an epoxy resin, a fluorine resin, or the like
- a polyimide resin is used as the heat resistant resin.
- the composition of the base layer 120 also affects the composition of the surface-treated steel sheet 1. Therefore, in this modification, the base layer 120 includes a heat-resistant resin as a main component in order to impart processing followability and heat resistance to the surface treatment film 100.
- the content of inorganic components such as phosphate, borate, silicate, molybdate, and tungstate is adjusted to be less than the content of the heat resistant resin.
- the base layer 120 contains an inorganic acid salt of 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the heat resistant resin.
- the content of the inorganic acid salt is less than 0.1 parts by mass, the friction coefficient of the surface treatment film 100 increases and sufficient lubricity cannot be obtained.
- the content of the inorganic acid salt exceeds 100 parts by mass, the performance of the base layer 120 holding the lubricant 131 is not sufficiently exhibited.
- the thickness of the base layer 120 needs to be 0.1 ⁇ m or more and 15 ⁇ m or less.
- the thickness of the base layer 120 is less than 0.1 ⁇ m, the performance of the base layer 120 that holds the lubricant 131 is not sufficiently exhibited.
- the thickness of the base layer 120 exceeds 15 ⁇ m, the thickness of the base layer 120 becomes excessively large, and thus indentation scratches or the like are likely to occur during cold working.
- the thickness of the base layer 120 is preferably 0.5 ⁇ m or more. Further, from the viewpoint of more reliably preventing indentation scratches during processing, the thickness of the base layer 120 is preferably 3 ⁇ m or less.
- the lubricant layer 130 has a role of improving the lubricity of the surface treatment film 100 and reducing the friction coefficient.
- the lubricant layer 120 is located on the side closest to the outermost surface of the surface treatment film 100, and contains the lubricant 131 most of the three layers constituting the surface treatment film 100.
- the lubricant 131 is not particularly limited as long as it can form the surface treatment film 100 having an inclined three-layer structure and can sufficiently improve the lubricity of the surface treatment film 100.
- the lubricant 131 at least one compound selected from the group consisting of polytetrafluoroethylene, molybdenum disulfide, tungsten disulfide, zinc oxide, and graphite can be used.
- the thickness of the lubricant layer 130 needs to be 0.1 ⁇ m or more and 10 ⁇ m or less. If the thickness of the lubricant layer 130 is less than 0.1 ⁇ m, sufficient lubricity cannot be obtained. On the other hand, if the thickness of the lubricant layer 130 exceeds 10 ⁇ m, surplus debris is generated during processing, and this surplus debris adheres to a mold or the like. From the viewpoint of further improving the lubricity, the thickness of the lubricant layer 130 is preferably 1 ⁇ m or more. Further, from the viewpoint of more reliably preventing the generation of excess residue during processing, the thickness of the lubricant layer 130 is preferably 6 ⁇ m or less.
- the ratio of the thickness of the lubricant layer 130 and the base layer 120 is also important. Specifically, the ratio of the thickness of the lubricant layer 130 to the thickness of the base layer 120, that is, (the thickness of the lubricant layer / the thickness of the base layer) needs to be 0.2 or more and 10 or less. When (the thickness of the lubricant layer / the thickness of the base layer) is less than 0.2, the surface treatment film 100 (the entire film) becomes too hard, and thus sufficient lubricity cannot be obtained. On the other hand, if (the thickness of the lubricant layer / the thickness of the base layer) exceeds 10, the retainability of the lubricant 131 is inferior, and the processing followability of the entire film is insufficient.
- the lubricant if the lubricant is polytetrafluoroethylene, it is appropriate to set F as a representative element, and if the lubricant is molybdenum disulfide, set Mo as a representative element. .
- the intensity of the peak corresponding to these representative elements is obtained, and the concentration of each component is calculated for each position in the film thickness direction from the obtained peak intensity.
- the thickness of the lubricant layer 130 is the representative element of the lubricant (for example, F, Mo, W, Zn, C) set as described above in the high-frequency GDS measurement chart from the outermost surface of the surface treatment film 100.
- the distance to the position (depth) in the film thickness direction having a peak intensity that is 1 ⁇ 2 of the maximum value of the peak intensity that is, the interface between the lubricant layer 130 and the base layer 120 coincides with the position in the film thickness direction where the peak intensity of the representative element of the lubricant is 1 ⁇ 2 of the maximum value of the peak intensity.
- the thickness of the adhesion layer 110 is 1 ⁇ 2 of the maximum value of the peak intensity in the representative element (Si) of the component due to the silanol bond in the high-frequency GDS measurement chart from the interface between the surface treatment film 100 and the steel plate 10. It is the distance to the position (depth) in the film thickness direction having the peak intensity. That is, the interface between the adhesion layer 110 and the base layer 120 coincides with the position in the film thickness direction where the peak intensity of the representative element (Si) of the component due to the silanol bond is 1 ⁇ 2 of the maximum value of the peak intensity.
- the thickness of the base layer 120 is such that the peak intensity in the representative element (Si) of the component due to the silanol bond is maximized from a position having a peak intensity that is 1 ⁇ 2 of the maximum peak intensity in the representative element of the lubricant. It is the distance to a position having a peak intensity that is 1 ⁇ 2 of the value.
- the cross section of the surface treatment film 100 is observed with a microscope to obtain the thickness of the entire surface treatment film 100, and the total thickness of the adhesion layer 110 and the lubricant layer 130 obtained above is calculated from the thickness of the entire surface treatment film 100.
- the thickness of the base layer 120 may be obtained by reducing the thickness.
- the thickness of the lubricant layer 130 is obtained using a representative element of an inorganic acid salt (for example, P, B, Si).
- an inorganic acid salt for example, P, B, Si.
- silicate when silicate is used as the inorganic acid salt of the base layer 120, when silicon (Si) is set as a representative element that determines the interface between the base layer 120 and the adhesion layer 110, the silicate (inorganic acid It is difficult to distinguish between Si derived from (salt) and Si derived from components derived from the silanol bond of the adhesion layer 110. Therefore, the thickness of the adhesion layer 110 and the base layer 120 is obtained using carbon (C) derived from the heat resistant resin component of the base layer 120 as a representative element.
- C carbon
- molybdate or tungstate when molybdate or tungstate is used as the inorganic acid salt of the base layer 120, molybdenum (Mo) or tungsten (W) is a representative element that determines the interface between the lubricant layer 130 and the base layer 120. Is set, it is difficult to distinguish between Mo and W derived from inorganic acid salts and Mo and W derived from the lubricant 131. Therefore, the thickness of the base layer 120 and the lubricant layer 130 is obtained using sulfur (S) derived from the lubricant 131 as a representative element.
- S sulfur
- the method for calculating the thickness of each layer (in the case of this modification, the time converted by the sputter rate of SiO 2) sputtering time by the high-frequency GDS from the maximum value of the peak intensity in the representative elements of each component half
- the position having the peak intensity that is, the position in the film thickness direction of the surface treatment film 100 can be obtained.
- the base layer 120 contains 0.01 mass part or more and 10 mass parts or less of inorganic acid salt with respect to 100 mass parts heat resistant resin.
- the method of measuring the mass of the heat resistant resin and inorganic acid salt in the base layer 120 is as follows. The film is ground in the thickness direction with a microtome or the like, and the base layer is cut out. An amount of this film that can be analyzed is collected and then ground in an agate mortar. After measuring the initial weight of the film recovered after pulverization, water is added to dissolve the inorganic acid salt (inorganic compound). After dissolving the inorganic acid salt, the film is sufficiently dried. The film weight after drying is determined as the mass part of the heat-resistant resin, and the difference between the initial weight and the film weight after drying is determined as the mass part of the inorganic acid salt.
- an aqueous surface treatment liquid containing a water-soluble silane coupling agent, a water-soluble inorganic acid salt, a water-soluble heat-resistant resin, and a lubricant is applied to at least one surface of the steel sheet 10 (the steel sheet of the above-described embodiment). After the coating, the surface treatment liquid 100 is dried to form the surface treatment film 100 on at least one surface of the steel plate 10.
- the surface treatment liquid used in the method for producing a surface-treated steel sheet contains a water-soluble silane coupling agent, a water-soluble inorganic acid salt, a water-soluble heat-resistant resin and a lubricant.
- a water-soluble silane coupling agent for a water-soluble silane coupling agent, a water-soluble inorganic acid salt, a water-soluble heat-resistant resin and a lubricant.
- the water-soluble silane coupling agent is not particularly limited, and may be a known silane coupling agent.
- this water-soluble silane coupling agent 3-aminopropyltrimethoxysilane, N-2- (aminomethyl) -3-aminopropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycid Xylpropyltriethoxysilane or the like can be used.
- various additives may be added to the surface treatment liquid.
- the surface treatment liquid used in the method for producing the surface-treated steel sheet includes a leveling agent, a water-soluble solvent, a metal stabilizer, an etching inhibitor, and a regulator that improve the coating properties as long as the effects of the present modification are not impaired.
- a leveling agent a nonionic or cationic surfactant can be used.
- the leveling agent include polyethylene oxide, polypropylene oxide adduct, and acetylene glycol compound.
- water-soluble solvents examples include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol and propylene glycol, cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether, esters such as ethyl acetate and butyl acetate, acetone And ketones such as methyl ethyl ketone and methyl isobutyl ketone.
- the metal stabilizer include chelate compounds such as EDTA and DTPA.
- the etching inhibitor include amine compounds such as ethylenediamine, triethylenepentamine, guanidine and pyrimidine.
- amine compounds having two or more amino groups in one molecule are used as metal stabilizers. Therefore, it is more preferable to use such an amine compound as an etching inhibitor.
- the pH adjuster include organic acids such as acetic acid and lactic acid, inorganic acids such as hydrofluoric acid, ammonium salts and amines.
- a surface treatment liquid used in a method for producing a surface-treated steel sheet can be prepared by uniformly dissolving or dispersing the above-described components in water.
- a method for applying the surface treatment liquid to the steel sheet 10 for example, a method of immersing the steel sheet 10 in the surface treatment liquid can be used. In this case, it is necessary to heat the steel plate 10 in advance to a temperature higher than the temperature of the surface treatment liquid, or to dry it with warm air during drying. Specifically, for example, the steel plate 10 is immersed in warm water at about 80 ° C. for about 1 minute, then immersed in a surface treatment solution at a temperature of 40 ° C. to 60 ° C. for about 1 second, and then dried at room temperature for about 2 minutes. Let By such a method, the inclined surface treatment film 100 having a three-layer structure including the adhesion layer 110, the base layer 120, and the lubricant layer 130 can be formed.
- the film thickness of each layer constituting the surface treatment film 100 is the coating amount of the surface treatment liquid, the concentration of each component in the surface treatment liquid, the reactivity between the surface treatment liquid and the steel plate 10 as the substrate, and the hydrophilicity of the surface treatment liquid. / By appropriately controlling the hydrophobicity, the film thickness can be adjusted to the range described above.
- the temperature of the solid-liquid interface is high and the temperature of the gas-liquid interface is low. Therefore, a temperature difference is generated in the thin film, water as a solvent is volatilized, and a minute convection is generated in the thin film.
- a thin film formed by applying a normal temperature surface treatment liquid to the normal temperature steel sheet 10 is dried with warm air, the temperature at the gas-liquid interface increases, the surface tension at the gas-liquid interface decreases, In order to mitigate the change and the change in surface tension, minute convection occurs in the thin film.
- the surface treatment liquid is a component having a high affinity for air (for example, a lubricant) and a component having a high affinity for metal or water (for example, an inorganic acid). Salt and heat-resistant resin). Thereafter, water gradually evaporates and the surface treatment liquid becomes a film, and an inclined film having a concentration gradient of each component is formed.
- the silane coupling agent has a high affinity with the metal on the surface of the steel plate 10, and thus diffuses in the vicinity of the steel plate 10 in the thin film. Thereafter, the silane coupling agent that has reached the vicinity of the steel plate 10 is shared with a metal oxide existing on the surface of the steel plate 10 (for example, zinc oxide when the steel plate 10 is galvanized). It is considered that a bond is formed and a silanol bond represented by Si—O—X is formed. Thus, when a silanol bond is formed in the vicinity of the steel plate 10, the adhesion between the surface treatment film 100 and the steel plate 10 is remarkably improved, so that seizure and galling are prevented.
- a surface treatment that imparts lubricity to the surface of a steel sheet that is normally subjected to cold working such as cold working.
- a phosphate treatment bonding treatment in which a phosphate film made of a phosphate compound (zinc phosphate, manganese phosphate, calcium phosphate, iron phosphate, etc.) is conventionally formed on the surface of the steel sheet. )It has been known.
- the steel sheet treated with phosphate has relatively high anti-seizure performance and anti-galling performance.
- cold steel sheets for cold work must be subjected to more severe plastic working as the transition from cold forging to machining fields with large shape deformation such as hot forging and cutting. Is required.
- a composite film in which a layer made of metal soap (for example, sodium stearate) is laminated on a phosphate film has been widely used. This composite film has excellent anti-seizure performance and anti-galling performance even under severe friction conditions with a high surface pressure press during cold working.
- this lubrication treatment involves many complicated processes such as a cleaning process and a reaction process in which a metal soap and a phosphate film are reacted (a process control such as a process liquid management and a temperature control during the reaction is also necessary). There is a problem that productivity is reduced because a processing step is required and batch processing is required. Further, the lubrication treatment using the composite film has problems such as waste liquid treatment that occurs during the treatment, which is not preferable from the viewpoint of environmental protection.
- the surface-treated steel sheet can be manufactured by a suitable method from the viewpoint of global environment conservation with a simple treatment process and has excellent lubricity. Therefore, with the recent environmental measures as a background, the processing method can be shifted from a processing field having a large shape deformation, such as hot forging, which consumes a large amount of energy, or cutting that generates a large amount of material loss, to cold processing.
- a processing field having a large shape deformation such as hot forging, which consumes a large amount of energy, or cutting that generates a large amount of material loss, to cold processing.
- a processing field having a large shape deformation such as hot forging, which consumes a large amount of energy, or cutting that generates a large amount of material loss
- the conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Not.
- the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
- Steels having the composition shown in Table 1 were melted, hot rolled, and annealed to produce steel sheets having different hardness, carbide diameter and carbide spheroidization ratio, and cold workability and induction hardening hardness were investigated. Below, the manufacturing method of this steel plate is demonstrated.
- a steel ingot (slab) having a sheet thickness of 150 mm was hot-rolled so as to obtain a hot-rolled steel sheet having a sheet thickness of 6 mm under the condition that the rolling end temperature was 870 ° C. after being held at 1220 ° C. for 2 hours. Thereafter, the hot-rolled steel sheet is cooled to the first cooling temperature at the first average cooling rate shown in Tables 2 to 7, and then to the second cooling temperature at the second average cooling rate shown in Tables 2 to 7.
- a surface layer of 2.0 mm and a back layer of 2.0 mm were cut from each of the obtained hot-rolled steel sheets in the thickness direction to obtain a sample having a thickness of 2 mm (corresponding to steel Nos. A, B, C, K, and L). .
- a surface layer of 0.5 mm and a back layer of 0.5 mm are cut from each hot-rolled steel plate under the same production conditions, and a plate thickness of 5 mm (corresponding to steel No. D, E, M, N, O, P, Q). A sample was obtained.
- a steel ingot having a thickness of 150 mm melted in a vacuum atmosphere is kept hot at 1240 ° C. for 1.5 hours so that a hot-rolled steel sheet having a thickness of 16 mm is obtained at a rolling end temperature of 920 degrees.
- Rolled Thereafter, the steel sheet was cooled to the first cooling temperature at the first average cooling rate shown in Tables 2 to 7, and then cooled to the second cooling temperature at the second average cooling rate shown in Tables 2 to 7. After winding, it was air-cooled. Moreover, it confirmed that it was 30 hours or less from 550 degreeC to 400 degreeC.
- a surface layer of 3.5 mm and a back layer of 3.5 mm were cut from each of the above hot-rolled steel plates to obtain a sample having a plate thickness of 9 mm (corresponding to steel Nos. F, G, R, U, and V). Moreover, 2.0 mm of the front and back layers was cut from a hot-rolled steel sheet having the same production conditions to obtain a sheet thickness of 12 mm (corresponding to steel Nos. H, W, X, and Y). Furthermore, a hot-rolled steel sheet having a thickness of 16 mm (corresponding to steel Nos. I, J, Z, AA, and AB) not subjected to cutting was also used as a sample.
- the Ac1 temperature of each sample was measured by a thermal expansion test.
- this thermal expansion test when heating at an average heating rate of 30 ° C./hr close to the actual box annealing furnace, the temperature at which austenite transformation started was determined as the Ac1 temperature.
- Each sample (corresponding to steel Nos. A to AB) was 3 hours at 680 ° C. (corresponding to Table 2), 30 hr at 680 ° C. (corresponding to Table 3), and 30 hr at 700 ° C. (corresponding to Table 4) in a 95% hydrogen atmosphere. ), 740 ° C. for 10 hr (corresponding to Table 5), 700 ° C. for 90 hr (corresponding to Table 6), and 700 ° C. for 60 hr (corresponding to Table 7).
- the furnace cooling was carried out after completion of holding (annealing).
- the sample annealed at 740 ° C. was cooled to 700 ° C. at an average cooling rate of 2 ° C./second after holding, and then cooled in the furnace.
- samples annealed at 680 ° C. for 3 hours are shown in Table 2, and are shown in FIG.
- the samples of A-1 to AB-1 are steel No. It is made from a sample having a chemical composition of A to AB.
- each sample (steel plates No. A-1 to AB-6) was heated from room temperature to 1000 ⁇ 20 ° C.
- the number of cracks in the region of the plate thickness 1/8 to 3/8 and 5/8 to 7/8 in the plate thickness cross section at the corner was measured with a scanning electron microscope at a magnification of 3000 times.
- the number of cracks was 20 or less per 1 mm 2, it was judged that the occurrence of cracks due to interfacial peeling during cold working could be suppressed. Therefore, the cold workability was evaluated as “good”. Further, when the number of cracks was more than 20, the cold workability was evaluated as “bad”.
- the steel plate No. in A-1 to AB-1 the annealing time was short and the spheroidization of the carbide was less than 70%, so the cold workability was not sufficient. Further, in Table 5, the steel plate No. In A-4 to AB-4, the spheroidization rate of the carbide exceeded 90%, and the induction hardening and curing ability was not sufficient. Steel plate No. in Table 4 In D-3 and F-3, since the first average cooling rate exceeded 50 ° C./second, carbide with a spheroidization rate of 90% or more was generated from bainite in the hot-rolled steel sheet, and induction hardening and hardening ability was sufficient. It was not. Furthermore, the steel plate Nos.
- a surface treatment film (a medium carbon steel sheet for cold working having a surface film) that can be suitably used for cold working will be described more specifically with reference to examples.
- the obtained hot-rolled steel sheet was annealed at 700 ° C. for 30 hours in a 95% hydrogen atmosphere, and then cooled in the furnace.
- the surface treatment liquids a to q were applied to the annealed hot-rolled steel sheet (annealed steel sheet) with a paint # 3 bar (paint bar).
- the film thickness of the surface treatment film was controlled by the concentration of the surface treatment solution.
- the annealed steel sheet to which the surface treatment liquid was applied was dried in a 300 ° C. hot air drying oven under conditions where the ultimate plate temperature was 150 ° C. It air-cooled after drying and produced the surface-treated steel plate.
- a hardened sample having a thickness of 8 mm, a plate width of 15 mm, and a plate length of 100 mm was taken from the annealed steel plate before surface treatment, and the temperature was raised from room temperature to 1000 ° C. at an average heating rate of 100 ° C./second at a frequency of 78 kHz. Thereafter, the temperature was maintained at 1000 ° C. for 10 s, immediately cooled to room temperature at an average cooling rate of 200 ° C./second or more, and the Vickers hardness (quenching hardness) of the quenched material was measured.
- the film thickness of the obtained surface-treated steel sheet was measured using high frequency GDS. Specifically, from the outermost surface of the surface treatment film, in the high-frequency GDS measurement chart, in the film thickness direction having a peak intensity that is 1 ⁇ 2 of the maximum value of the peak intensity of representative elements (Mo, C, etc.) of the lubricant. The distance to the position (depth) was measured to determine the thickness of the lubricant layer.
- the film thickness direction having a peak intensity that is 1 ⁇ 2 of the maximum value of the peak intensity in the representative element (Si) of the component due to the silanol bond in the high-frequency GDS measurement chart The distance to the position (depth) was measured, and the thickness of the adhesion layer was determined. Furthermore, from the position having the peak intensity that is 1/2 of the maximum value of the peak intensity in the representative element (Mo) of the lubricant, 1 / of the maximum value of the peak intensity in the representative element (Si) of the component due to the silanol bond. The distance to a position having a peak intensity of 2 was measured (calculated), and the thickness of the base layer was determined.
- the representative elements of the lubricant layer (lubricant component) and the base layer (inorganic acid salt component) and the representative elements of the base layer (inorganic acid salt component) and the adhesion layer (component due to silanol bonds) are the same. In order to avoid this, measurement was performed using other non-overlapping elements as representative elements.
- the thicknesses of the lubricant layer and the base layer were determined using the peak intensities of the representative elements (P, Si, Mo, W) of the inorganic acid salt.
- the flat bead mold one set of a mold having a length of 40 mm, a width of 60 mm and a thickness of 30 mm, polished with emery paper having a material of SKD11 and a surface of # 1000 was prepared. Next, the sample was sandwiched between the above molds, pressed by 1000 kg with an air cylinder, and the sample was pulled out with a tensile testing machine. About the sample after drawing, the intensity
- this spike height is used to evaluate, and when the spike height is less than 12.5 mm, “bad”, when the spike height is 12.5 mm or more and 13.5 mm or less, “ The case where the spike height was over 13.5 mm was evaluated as “excellent”.
- the evaluation of “good” corresponds to the performance of a sample produced by forming a conventional composite film (chemical conversion reaction / soap treatment) on the same steel sheet.
- Table 10 shows the measurement results of the thickness of each layer and the evaluation results of film adhesion and workability performed as described above.
- the present invention plays an important role in greatly expanding the use of medium carbon steel sheets using induction hardening, and is highly applicable in the steel product manufacturing industry.
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Abstract
Description
また、特許文献2には、冷鍛性に優れ、かつ静的強度や曲げ疲労強度および転がり接触疲労強度に優れた高強度高周波焼入れ用鋼が開示されている。この高周波焼入れ用鋼では、鍛造性を得るために必要な具体的な炭化物の形状が明示されておらず、焼入れ時の加熱温度や保持時間等の具体的な条件も明確にされていない。
また、特許文献3には、冷間鍛造性に優れ、限界据込率の高い高周波焼入れ用鋼が開示されているが、焼入れ時の加熱温度や保持時間等の具体的な条件は明確にされておらず実際に焼入れ性に優れるか明確でない。
更に、特許文献4には、冷間加工性と高周波焼入れ性とに優れた高炭素鋼管が開示されている。この高炭素鋼管は、スウェージングや拡管などの局部延性に支配される加工法に適しており、本発明の対象とする打抜き、絞り、曲げ、バーリング、据込み、しごき、押出し等の冷間鍛造性が十分ではないと考えられる。
また、冷間加工された素材は、焼入れ処理が施されることが多く、熱処理時間が短い高周波焼入れ処理においては、加熱中に素材中の炭化物が十分に溶解せず、安定した焼入れ性を得ることが困難である。したがって、高周波焼入れによって十分に炭化物を溶解させるためには、素材の炭化物の形態制御が重要である。
しかしながら、中炭素鋼板に冷間加工を適用して、高周波焼入れを行う場合の問題点がこれまでのところ明確でないように思われる。
なお、本発明において、中炭素鋼板は、Cが0.30%以上かつ0.60%以下であって、板厚が1.6mm以上かつ20mm以下の鋼板を示す。
(3)上記(2)に記載の冷間加工用中炭素鋼板では、Cr量[Cr]と、Mo量[Mo]とが、[Cr]+[Mo]/10<0.10を満足してもよい。
(4)上記(1)または(2)に記載の冷間加工用中炭素鋼板では、冷間加工前の硬度が120HV以上かつ170HV未満であってもよい。
(7)上記(5)に記載の冷間加工用中炭素鋼板では、前記耐熱樹脂が、ポリイミド樹脂、ポリエステル樹脂、エポキシ樹脂及びフッ素樹脂からなる群より選択される少なくとも1種の樹脂であってもよい。
(8)上記(5)に記載の冷間加工用中炭素鋼板では、前記潤滑剤が、ポリテトラフルオロエチレン、二硫化モリブデン、二硫化タングステン、酸化亜鉛およびグラファイトからなる群より選択される少なくとも1種の化合物であってもよい。
(11)上記(9)または(10)に記載の冷間加工用中炭素鋼板の製造方法では、前記第6の工程の後に、水溶性シランカップリング剤、水溶性無機酸塩、水溶性耐熱樹脂および潤滑剤を含む水系の表面処理液を前記冷間加工用中炭素鋼板の少なくとも片面に塗布し、前記表面処理液を乾燥させて、前記冷間加工用中炭素鋼板の少なくとも片面に前記表面処理皮膜を形成してもよい。
Cは、鋼板の焼入れ強度を確保するうえで重要な元素である。そのため、鋼中にCを0.30%以上添加し、所要の強度を確保する。C量が0.30%未満では、焼入れ性が低下し、機械構造用高強度鋼板としての強度が得られないので、C量の下限は0.30%である。C量が0.60%を超えると、破壊の起点として作用する炭化物の割合が増加し冷間加工性が低下するため、C量の上限は0.60%である。より焼入れ性を確保する必要がある場合には、C量の下限が、0.35%であることが好ましく、0.37%であることがより好ましく、0.40%であることが最も好ましい。また、炭化物の形態をより制御しやすくする場合には、C量の上限が、0.55%であることが好ましく、0.52%であることがより好ましく、0.50%であることが最も好ましい。
Siは、脱酸剤として作用し、加工時におけるフェライトと炭化物との間の界面剥離を抑えるとともに、焼入れ性の向上に有効な元素である。Si量が0.06%未満では、この添加効果が得られないので、Si量の下限は0.06%である。一方、Si量が0.30%を超えると、固溶強化によってフェライト相における亀裂発生頻度(粒内亀裂発生頻度)が増加し、熱間圧延時のスケール疵によって表面性状が劣化するので、Si量の上限は0.30%である。フェライトと炭化物との間の界面における剥離をより低減する場合には、Si量の下限が、0.10%であることが好ましく、0.13%であることがより好ましく、0.15%であることが最も好ましい。また、フェライト相での亀裂(粒内亀裂)の発生をより低減する場合には、Si量の上限が、0.26%であることが好ましい。
Mnは、脱酸剤として作用し、焼入れ性の向上に有効な元素である。Mn量が0.3%未満では、この添加効果が得られないので、Mn量の下限は0.3%である。Mn量が2.0%を超えると、高周波加熱時の炭化物の溶解が遅れ、焼入れ性(焼入れ硬度)が低下するので、Mn量の上限は2.0%である。より焼入れ性を高める場合には、Mn量の下限が、0.5%であることが好ましく、0.55%であることがより好ましく、0.65%又は0.73%であることが最も好ましい。また、より高周波焼入れ性を確保する場合には、Mn量の上限が、1.6%であることが好ましく、1.4%であることがより好ましく、1.2%又は1.0%であることが最も好ましい。
Pは、固溶強化元素であり、鋼板の強度に有効な元素である。鋼中にPが過剰に含有されると、靭性が低下するので、P量の上限は0.030%である。Pは、不可避的不純物である。P量を0.005%未満に低減すると、精錬コストが上昇するので、P量を0.005%未満に低減しなくてもよい。より靭性を必要とする場合には、P量の上限が0.020%であることが好ましい。
Sは、非金属介在物(硫化物)を形成し、加工性及び熱処理後の靭性を低下させる原因になるので、S量の上限は0.0075%以下である。図5に、S量と冷間加工時に硫化物が起点として作用する亀裂(硫化物起点の亀裂)の数との関係を示す。この図5から分かるように、S量が0.0075%以下であると、硫化物起点の亀裂数が大きく低下する。また、Sは、不可避的不純物である。S量を0.0001%未満に低減すると、精錬コストが大幅に上昇するので、S量を0.0001%未満又は0.001%以下に低減しなくてもよい。また、より高い加工性及び靭性を確保する必要がある場合には、S量の上限は、0.007%であることが好ましく、0.005%であることがより好ましい。
Alは、脱酸剤として作用し、Nの固定に有効な元素である。Al量が0.005%未満では、この添加効果が十分に得られないので、Al量の下限は0.005%である。Al量が0.10%を超えると、上記添加効果が飽和し、表面疵が発生し易くなるので、Al量の上限は0.10%である。より十分にNを固定するためには、Al量の下限が0.01%であることが好ましい。また、表面疵の発生をより確実に抑えるためには、Al量の上限を0.07%又は0.05%としてもよい。
Nは、窒化物を形成する元素である。湾曲型連続鋳造における鋳片曲げ矯正時に窒化物が析出すると、鋳片が割れることがあるので、N量の上限は0.01%である。Nは、不可避的不純物である。鋼中のN量は少ないほど好ましいが、N量を0.0010%未満に低減すると、精錬コストが増加するので、N量の下限は0.0010%である。精錬コストをより低減する場合には、N量の下限が0.002%であることが好ましい。窒化物の発生または粗大化をより抑える必要がある場合には、N量の上限が、0.008%であることが好ましく、0.006%であることがより好ましい。
Crは、高周波加熱時の炭化物の安定性を高める元素である。鋼中へのCrの添加によってCr量が0.10%を超えると、炭化物の安定性を大きく高め、高周波加熱時の炭化物の溶解を抑制し、焼入れ性を低下させる。そのため、Cr量の上限は、0.10%である。鋼中のCr量が少ないほど高周波焼入れ性が高まるが、Cr量を0.001%以下に低減すると、精錬コストが大きく増加するため、Cr量の下限は0.001%である。高周波加熱時の炭化物の溶解速度をより増加させる場合には、Cr量の上限が、0.080%であることが好ましく、0.070%であることがより好ましい。また、精錬コストをより低減する場合には、Cr量の下限が、0.010%であることが好ましい。
Niは、靭性及び焼入れ性の向上に有効な元素である。Ni量が0.01%未満では、この添加効果がないので、Ni量の下限は0.01%である。Ni量が0.5%を超えると、上記効果が飽和し、コストが増加するので、Ni量の上限は0.5%である。強度の観点からは、Ni量の下限が0.05%であることが好ましい。また、コストの観点からは、Ni量の上限が0.3%であることが好ましく、0.2%であることがより好ましく、0.15%であることが最も好ましい。
Cuは、焼入性の確保に有効な元素である。Cu量が0.05%未満では、この添加効果が不十分であるので、Cu量の下限は0.05%である。Cu量が0.5%を超えると、硬さが増加し過ぎ、冷間加工性が劣化するので、Cu量の上限は0.5%である。強度の観点からは、Cu量の下限が0.08%であることが好ましい。また、加工性の観点からは、Cu量の上限が0.3%であることが好ましく、0.2%であることがより好ましく、0.15%であることが最も好ましい。
Moは、焼入れ性の向上に有効な元素である。Mo量が0.01%未満では、この添加効果が小さいので、Mo量の下限は0.01%である。Mo量が0.5%を超えると、鋼中にMo系の炭化物が多く析出する。高周波焼入れでは、Mo系の炭化物が十分に溶解せず、素材の焼入れ性が低下するため、Mo量の上限は0.5%である。より高い焼入れ性が必要である場合には、Mo量の上限が、0.3%であることが好ましく、0.1%であることがより好ましい。
Nbは、炭窒化物を形成し、結晶粒の粗大化防止及び靭性改善に有効な元素である。Nb量が0.01%未満では、この添加効果が充分に発現しないので、Nb量の下限は0.01%である。Nb量が0.5%を超えると、上記添加効果が飽和するので、Nb量の上限は0.5%である。上記添加効果を効率良く利用するためには、Nb量が、0.07~0.4%であることが好ましい。必要に応じて、Nb量の下限を0.09%又は0.14%に、上限を0.35%又は0.3%に制限してもよい。
Tiは、N固定の観点から鋼中に添加され、鋳片の脆化抑制及び材質の安定化に寄与する。Tiを鋼中に添加してTi量が0.05%を超えると、この効果が飽和し、Ti量が0.001%以下では、この効果が得られない。そのため、Ti量の範囲は、0.001~0.05%である。上記効果を効率良く利用するためには、Ti量の上限が、0.20%であることが好ましい、0.10%であることがより好ましく、0.06%であることが最も好ましい。
Vは、Nbと同様に、炭窒化物を形成し、結晶粒の粗大化防止及び靭性改善に有効な元素である。V量が0.01%未満では、この添加効果が小さいので、V量の下限は0.01%である。V量が0.5%を超えると、炭化物が生成し焼入れ硬度が低下するので、V量の上限は0.5%である。上記効果を効率良く利用するためには、V量が、0.07~0.2%であることが好ましい。
Taは、Nb、Vと同様に、炭窒化物を形成し、結晶粒の粗大化防止及び靭性改善に有効な元素である。Ta量が0.01%未満では、この添加効果が小さいので、Ta量の下限は0.01%である。Ta量が0.5%を超えると、炭化物が生成し焼入れ硬度が低下するので、Ta量の上限は0.5%である。上記効果を効率良く利用するためには、Ta量が、0.07~0.2%であることが好ましい。
Bは、微量の添加で、焼入性を高めるのに有効な元素である。B量が0.001%未満では、この添加効果がないので、B量の下限は0.001%である。B量が0.01%を超えると、鋳造性が低下し、B系化合物が生成して靭性が低下するので、B量の上限は0.01%である。より高い焼入れ性が必要とされる場合には、B量の下限が、0.003%であることが好ましい。また、B系化合物の生成を抑える必要がある場合には、B量の上限が、0.007%であることが好ましく、0.005%であることがより好ましい。
Wは、鋼板の強化に有効な元素である。W量が0.01%未満では、この添加効果が発現しないので、W量の下限は0.01%である。W量が0.5%を超えると、加工性が低下するので、W量の上限は0.5%である。強度の観点からは、W量の下限が0.04%であることが好ましい。加工性の観点からは、W量の上限が0.2%であることが好ましい。
[Cr]+[Mo]/10<0.10 ・・・(1)
以上のように、本実施形態の中炭素鋼板は、上述の基本元素を含み、残部Fe及び不可避的不純物からなる化学組成、または、上述の基本元素と、上述の選択元素から選択される少なくとも1種とを含み、残部Fe及び不可避的不純物からなる化学組成を有する。
すなわち、炭化物の平均径が0.6μm以下であり、炭化物の球状化率が70%以上かつ90%未満であり、炭化物の平均径d(μm)と炭化物の球状化率p(%)とが、下記式(2)を満足する。
d≦0.04×p-2.6 ・・・(2)
冷間加工性は、冷間加工時の亀裂数と深い関係があり、亀裂数が多いほど冷間加工性が低い。冷間加工時の亀裂は、加工により導入された転位の絡み合いや転位のカッティングにより生じたボイド(原子空孔)を核として発生すると考えられる。したがって、加工歪の集中を抑えることにより冷間加工性を確保することができる。
炭化物が針状であると、短軸長と長軸長との間の寸法差が大きく、針状の炭化物の長軸方向の端部(長軸端部)に応力が集中し、この長軸端部の応力場と短軸方向の端部(短軸端部)の応力場との間の応力差が大きくなる。この応力場の不均一性を解消するため、転位(歪)が導入される。このため、冷間加工時には、針状炭化物の近傍でボイドが多数生成し、亀裂が発生すると考えられる。一方、炭化物が球状であると、短軸長と長軸長との間の寸法差が小さく、応力場の不均一性が少ないため、炭化物の近傍に転位(歪)が局在化しにくくなり、亀裂の発生が抑制されると考えられる。
また、炭化物のアスペクト比だけではなく、針状炭化物の長軸長の絶対値も長軸端部の応力集中に影響を及ぼす。長軸長が大きいほど、長軸端部での応力集中が高くなるため、転位(歪)が発生しやすくなる。このため、冷間加工性を確保するためには、炭化物の球状化率が高くない場合(針状炭化物が多い場合)に、炭化物の平均径を小さくする必要がある。すなわち、炭化物の球状化率が70%以上かつ80%未満である場合に、炭化物の平均径d(μm)と炭化物の球状化率p(%)とが、上記(2)式を満足する必要がある。
このように、本発明者らは、炭化物の平均径と炭化物の球状化率とについて適切な所定の条件を満足させることにより、高周波焼入れ性を確保しながら冷間加工性を高めることができることを明らかにした。
冷間加工前の硬度が170HV未満であれば、十分な延性が得られるため、加工時に十分な成形量を確保することができる。より大きな成形量を確保するためには、冷間加工前の硬度が、165HV未満であることが好ましく、160HV未満であることがさらに好ましく、155HV未満であることが最も好ましい。鋼板が軟質な程、延性が改善し厳しい加工にも鋼板が耐えうるが、打抜き加工時のダレが発生しやすくなる。そのため、冷間加工前の硬度が、120HV以上であることが好ましい。近年、打ち抜きと曲げと絞り加工とを一体化した冷間加工技術も普及しつつあり、そのような製造工程の一体化に応じて、適切に冷間加工前の硬度を制御することが望ましい。
また、図5に、S量と冷間加工時の硫化物起点の亀裂数との関係を示す。この図5から分かるように、S量が0.0075%以下であると、硫化物起点の亀裂数が大きく低下する。
なお、硫化物起因の亀裂と炭化物起因の亀裂とを判別するために、走査型電子顕微鏡に付属のエネルギー分散型X線分光器(EDS)を使用した。
上記の冷却された鋼板を酸洗し、表面を清浄化した後、鋼板に軟質化焼鈍を施す。本実施形態では、鋼板に軟質化箱焼鈍を施し、鋼板の加工性を向上させている。
なお、本明細書及び上記図面において、実質的に同一の機能構成を有する構成要素については、同一の符号を付することにより重複説明を省略する。
まず、図6を参照しながら、本変形例に係る鋼板(以下、「表面処理鋼板」という。)の構成について説明する。図6は、表面処理鋼板の構成を模式的に示す縦断面図である。
表面処理鋼板1の素地である鋼板10には、上記実施形態の鋼板をそのまま用いることができる。しかしながら、上記実施形態の鋼板にめっきを施しても良い。例えば、上記実施形態の鋼板に、亜鉛、ニッケル、鉄、アルミニウム、チタン、マグネシウム、クロム、マンガン、スズの1種以上の金属を使用しためっきを施すことができる。
表面処理皮膜100では、この皮膜中の各成分が膜厚方向に濃度勾配を有している。そのため、傾斜型皮膜である表面処理皮膜100を3層に区分することが可能である。すなわち、この表面処理皮膜100では、表面処理皮膜100と鋼板10との界面から表面処理皮膜100の表面に向かって、密着層110、ベース層120、潤滑剤層130の順に3つの層が形成されている。
密着層110は、冷間加工に伴う表面処理皮膜100と素地である鋼板10との密着性を確保し、表面処理鋼板1と金型との焼き付きを防止する役割を有する。具体的に、密着層110は、表面処理皮膜100と鋼板10との界面に近い側に位置し、シラノール結合に起因する成分を、表面処理皮膜100を構成する3層のうちで最も多く含む。
ベース層120は、冷間加工時における鋼板追従性を向上させ、金型との焼き付きに対する硬さおよび強度を表面処理鋼板1に付与する。また、このベース層120は、潤滑剤131及び潤滑剤層130を保持する。具体的には、ベース層120は、密着層110と潤滑剤層130との間に中間層として位置し、表面処理皮膜100を構成する3層のうちで耐熱樹脂および無機酸塩を最も多く含む。
潤滑剤層130は、表面処理皮膜100の潤滑性を向上させ、摩擦係数を低減する役割を有する。具体的に、潤滑剤層120は、表面処理皮膜100の最表面に近い側に位置し、潤滑剤131を、表面処理皮膜100を構成する3層のうちで最も多く含む。
以上説明したように、本変形例に係る表面処理鋼板1では、鋼板10に近い側の密着層110、皮膜表面に近い側の潤滑剤層130、これらの間のベース層120の3つの層を存在させることが重要である。これらの層のうち、いずれの層が欠けても、本変形例で意図している冷間加工に耐え得る潤滑性を発揮することが難しい。また、密着層110、ベース層120、潤滑剤層130の各層の厚みが上述した範囲内でない場合にも、本変形例で意図している冷間加工に耐え得る潤滑性を発揮することが難しい。従って、本変形例では、密着層110、ベース層120、潤滑剤層130の各層が形成されているかどうかを確認する方法、および、これら各層の厚みを測定する方法も重要である。
まず、潤滑剤層130の厚みは、表面処理皮膜100の最表面から、高周波GDSの測定チャートにおいて、上述したように設定した潤滑剤の代表元素(例えば、F、Mo、W、Zn、C)におけるピーク強度の最大値の1/2であるピーク強度を有する膜厚方向の位置(深さ)までの距離である。すなわち、潤滑剤層130とベース層120との界面は、潤滑剤の代表元素のピーク強度がピーク強度の最大値の1/2になる膜厚方向の位置と一致する。
以上、表面処理鋼板の構成について詳細に説明した。続いて、このような構成を有する表面処理鋼板の製造方法について説明する。
表面処理鋼板の製造方法に用いる表面処理液は、水溶性シランカップリング剤、水溶性無機酸塩、水溶性耐熱樹脂および潤滑剤を含むが、無機酸塩、耐熱樹脂および潤滑剤の詳細については、上述したので、ここでは説明を省略する。
上記表面処理液の鋼板10への塗布方法として、例えば、鋼板10を表面処理液中に浸漬させる方法等を用いることができる。この場合、鋼板10を予め表面処理液の温度より高い温度に加温しておくか、乾燥の際に温風で乾燥させることが必要である。具体的には、例えば、鋼板10を80℃程度の温水中に1分程度浸漬した後、40℃~60℃の温度の表面処理液に1秒程度浸漬し、その後、室温で2分程度乾燥させる。このような方法によって、密着層110、ベース層120および潤滑剤層130からなる3層構造の傾斜型の表面処理皮膜100を形成することができる。
表面処理皮膜100を構成する各層の膜厚は、表面処理液の塗布量、表面処理液中の各成分の濃度、表面処理液と素地である鋼板10との反応性、表面処理液の親水性/疎水性を適宜制御することにより、上述したような膜厚の範囲になるように調整することができる。
以上のように、水溶性シランカップリング剤、水溶性無機酸塩、水溶性耐熱樹脂および潤滑剤を水に溶解または分散させた表面処理液を鋼板10に塗布した後乾燥させることにより、傾斜型の表面処理皮膜100が形成される理由を、本発明者らは、以下のように推定している。まず、上記のように鋼板10を予め表面処理液の温度より高い温度に加温しておくと、鋼板10の温度が表面処理液の温度より高いので、表面処理液が鋼板10の上に塗布されて形成された薄膜内では、固液界面の温度が高く、気液界面の温度が低い。そのため、薄膜内に温度差が生じ、溶媒である水が揮発して、薄膜内に微小な対流が起きる。また、常温の鋼板10に常温の表面処理液を塗布して形成された薄膜を温風により乾燥する場合には、気液界面の温度が高くなり、気液界面における表面張力が低下し、温度変化と表面張力変化とを緩和するため、薄膜内に微小な対流が起こる。上記のいずれの塗布乾燥方法の場合も、対流が起こるとともに、表面処理液が、空気との親和力の高い成分(例えば、潤滑剤)と、金属や水との親和力の高い成分(例えば、無機酸塩や耐熱樹脂)とに分離する。その後、徐々に水が揮発して表面処理液が膜状になり、各成分の濃度勾配を有する傾斜型の皮膜が形成される。
なお、冷間加工では、鋼板と金型との間の摩擦により、鋼板と金型との接触部分の温度が比較的高く(概ね300℃以上)なる。そのため、何も表面処理を施していない鋼板を冷間加工すると、鋼板と金型との間の潤滑性が十分でない場合には、鋼板と金型との間に焼き付きやカジリを生じやすくなる。この場合には、金型が局所的に破損したり、急激な摩耗が生じたりすることがあるため、金型の寿命が著しく短縮する場合もある。
板厚150mmの鋼塊(鋳片)を、1220℃で2hr保持後、圧延終了温度が870℃の条件で、板厚6mmの熱延鋼板が得られるように熱間圧延した。その後、この熱延鋼板を、表2~7に示す第一の平均冷却速度で第一の冷却温度まで冷却した後、表2~7に示す第二の平均冷却速度で第二の冷却温度まで冷却し、巻取った後空冷した。また、550℃から400℃まで30時間以下であることを確認した。
得られた各熱延鋼板から板厚方向に表層2.0mm、裏層2.0mmを切削し、板厚2mm(鋼No.A、B、C、K、Lに対応)のサンプルを得た。また、同様の製造条件の各熱延鋼板から表層0.5mm、裏層0.5mmを切削し、板厚5mm(鋼No.D、E、M、N、O、P、Qに対応)のサンプルを得た。
同様に、真空雰囲気下で溶製した板厚150mmの鋼塊を、1240℃で1.5hr保持後、圧延終了温度920度の条件で、板厚16mmの熱延鋼板が得られるように熱間圧延した。その後、この鋼板を、表2~7に示す第一の平均冷却速度で第一の冷却温度まで冷却した後、表2~7に示す第二の平均冷却速度で第二の冷却温度まで冷却し、巻取った後空冷した。また、550℃から400℃まで30時間以下であることを確認した。
上記の各熱延鋼板から表層3.5mm、裏層3.5mmを切削し、板厚9mm(鋼No.F、G、R、U、Vに対応)のサンプルを得た。また、同様の製造条件の熱延鋼板から表裏層の2.0mmを切削し、板厚12mm(鋼No.H、W、X、Yに対応)を得た。さらに、切削を施さない板厚16mm(鋼No.I、J、Z、AA、ABに対応)の熱延鋼板もサンプルとして用いた。
各サンプル(鋼No.A~ABに対応)を水素95%雰囲気下でそれぞれ、680℃で3hr(表2に対応)、680℃で30hr(表3に対応)、700℃で30hr(表4に対応)、740℃で10hr(表5に対応)、700℃で90hr(表6に対応)、700℃で60hr(表7に対応)の6つの条件で焼鈍した。680℃及び700℃で焼鈍されたサンプルについては、保定(焼鈍)完了後炉冷した。740℃で焼鈍されたサンプルについては、保定完了後、700℃まで2℃/秒の平均冷却速度で冷却し、その後炉冷した。なお、例えば、680℃で3hr焼鈍されたサンプル(鋼板No.A-1~AB-1)は、表2中に示され、鋼板No.A-1~AB-1のサンプルは、それぞれ、鋼No.A~ABの化学組成を有するサンプルから作製されている。
高周波焼入れ試験では、各サンプル(鋼板No.A-1~AB-6)を、周波数78kHzにて750℃以上を100±15℃/秒の平均加熱速度で室温から1000±20℃まで昇温後、1000±20℃で10±0.5s保持し、すぐさま800℃から400℃の間を200±10℃/秒の平均冷却速度で室温まで急冷し、焼入れ材のビッカース硬度(焼入れ硬度)を測定した。また、各サンプルから幅30mm、長さ100mmの平板曲げ試験片を作製し、曲げ半径を板厚の1/2、曲げ角度を90°の条件にて曲げ試験を実施し、平板曲げサンプルの曲げ角部(最大曲率部)の板厚断面において板厚1/8~3/8、5/8~7/8の領域の亀裂数を走査型電子顕微鏡にて倍率3000倍で測定した。上記の亀裂数が1mm2あたり20個以内である場合、冷間加工時における界面剥離に起因する亀裂発生が抑えられると判断できるため、冷間加工性が“良好”であると評価した。また、亀裂数が20個超である場合、冷間加工性が“不良”であると評価した。なお、これらの亀裂を種類(セメンタイト起点の亀裂、硫化物起点の亀裂、粒内亀裂)毎に分類して集計した。セメンタイト起点の亀裂と硫化物起点の亀裂とを区別するために、走査型電子顕微鏡に付属のエネルギー分散型X線分光器(EDS)を使用した。また、平均炭化物径及び炭化物の球状化率については、上述した方法で測定した。
まず、下記の表8に示す成分を含有した表面処理液(薬剤)a~qを調製した。なお、表8中で、無機酸塩として硝酸亜鉛とリン酸との組み合わせを使用している理由は、リン酸亜鉛が水に極めて溶けにくく、酸に溶解するためである。このように、水に可溶性の硝酸亜鉛とリン酸とを組み合わせることにより、水に難溶性のリン酸亜鉛を生成し、表面処理液中に存在させることができる。
次に、上記のようにして調製した表面処理液a~qを用いて、以下の方法により、傾斜型の3層構造の表面処理皮膜が板の両面に形成された表面処理鋼板(No.1~29)を製造した(下記表10を参照)。
なお、表面処理を施す前の焼鈍鋼板から、板厚8mm×板幅15mm×板長100mmの焼入れサンプルを採取し、周波数78kHzにて100℃/秒の平均加熱速度で室温から1000℃まで昇温後、1000℃で10s保持し、すぐさま200℃/秒以上の平均冷却速度で室温まで急冷し、焼入れ材のビッカース硬度(焼入れ硬度)を測定した。さらに、焼鈍鋼板の平均炭化物径及び炭化物の球状化率について、上述した方法で測定した。その結果、平均炭化物径が0.31μm、球状化率が85.7%、高周波焼入れ後の硬度が638.7HVであることを確認した。
得られた表面処理鋼板に対して、高周波GDSを用いて膜厚の測定を行った。詳細には、表面処理皮膜の最表面から、高周波GDSの測定チャートにおいて、潤滑剤の代表元素(Mo、Cなど)におけるピーク強度の最大値の1/2であるピーク強度を有する膜厚方向の位置(深さ)までの距離を測定し、潤滑剤層の厚みを決定した。また、表面処理皮膜と鋼板との界面から、高周波GDSの測定チャートにおいて、シラノール結合に起因する成分の代表元素(Si)におけるピーク強度の最大値の1/2であるピーク強度を有する膜厚方向の位置(深さ)までの距離を測定し、密着層の厚みを決定した。さらに、潤滑剤の代表元素(Mo)におけるピーク強度の最大値の1/2であるピーク強度を有する位置から、シラノール結合に起因する成分の代表元素(Si)におけるピーク強度の最大値の1/2であるピーク強度を有する位置までの距離を測定(計算)し、ベース層の厚みを決定した。また、潤滑剤層(潤滑剤成分)とベース層(無機酸塩成分)の代表元素、および、ベース層(無機酸塩成分)と密着層(シラノール結合に起因する成分)の代表元素が同じにならないように、重複しない他の元素を代表元素として用いて測定した。
さらに、下記に示す評価方法および評価基準により、上記のように製造された表面処理鋼板の皮膜密着性および加工性を評価した。
平ビード金型を用いた引抜き摺動試験にて皮膜密着性を評価した。この引抜き摺動試験では、サイズ30×200mmでエッジの剪断バリを除去した試験片(サンプル)を表面処理鋼板から採取して使用した。なお、サンプルに対して摺動試験を行う前に、蛍光X線分析装置にて皮膜中の主な構成元素の強度(試験前強度)を測定した。
スパイク試験にて加工性を評価した。このスパイク試験では、まず、図7Aに示すロート状の内面形状を有するダイ3の上に、表面処理鋼板から作製された円柱状のスパイク試験片1A(図7Bに示す加工前のスパイク試験片1A)を載せる。この後、図7Aに示すプレート2を介してスパイク試験片1Aに対して荷重を掛け、スパイク試験片1Aを、ダイ3内に押し込んで、図7Bに示す加工後のスパイク試験片1Bの形状に成型する。このような方法で、ダイ形状に従うスパイクを形成し、この際のスパイク高さ(mm)により潤滑性を評価した。従って、スパイク高さが高くなるほど潤滑性が優れている。なお、スパイク試験の条件については、特開平5-7969号公報に開示された方法に準じた。
Claims (11)
- 100℃/秒の平均加熱速度で昇温後、1000℃で10秒保持し、200℃/秒の平均冷却速度で室温まで急冷する高周波焼入れを行った場合に硬度が500HV以上かつ900HV以下になる冷間加工用中炭素鋼板であって、
質量%で、
C:0.30~0.60%、
Si:0.06~0.30%、
Mn:0.3~2.0%、
P:0.030%以下、
S:0.0075%以下、
Al:0.005~0.10%、
N:0.001~0.01%、
Cr:0.001~0.10%
を含有し、残部がFe及び不可避的不純物からなり、炭化物の平均径dが0.6μm以下、炭化物の球状化率pが70%以上かつ90%未満であり、前記炭化物の平均径dμmと前記炭化物の球状化率p%とがd≦0.04×p-2.6を満足する
ことを特徴とする冷間加工用中炭素鋼板。 - 質量%で、さらに、
Ni:0.01~0.5%、
Cu:0.05~0.5%、
Mo:0.01~0.5%、
Nb:0.01~0.5%、
Ti:0.001~0.05%、
V:0.01~0.5%、
Ta:0.01~0.5%、
B:0.001~0.01%、
W:0.01~0.5%、
Sn:0.003~0.03%、
Sb:0.003~0.03%、
As:0.003~0.03%
の1種以上をさらに含有することを特徴とする請求項1に記載の冷間加工用中炭素鋼板。 - Cr量[Cr]と、Mo量[Mo]とが、[Cr]+[Mo]/10<0.10を満足することを特徴とする請求項2に記載の冷間加工用中炭素鋼板。
- 冷間加工前の硬度が120HV以上かつ170HV未満であることを特徴とする請求項1または2に記載の冷間加工用中炭素鋼板。
- 少なくとも片面に、金属成分Xを含むSi-O-Xで表されるシラノール結合に起因する成分、耐熱樹脂、無機酸塩および潤滑剤の各成分を含む表面処理皮膜をさらに有し、
この表面処理皮膜が、膜厚方向に前記各成分の濃度勾配を有し、かつ前記表面処理皮膜と前記冷間加工用中炭素鋼板との界面に近い順に、密着層とベース層と潤滑剤層との3つの層を有し、
前記密着層が、前記シラノール結合に起因する成分を前記3つの層の中で最も多く含み、0.1nm以上かつ100nm以下の厚みを有し 、
前記ベース層が、前記耐熱樹脂および前記無機酸塩を前記3つの層の中で最も多く含み、かつ、100質量部の前記耐熱樹脂に対して0.01質量部以上かつ10質量部以下の前記無機酸塩を含み、0.1μm以上かつ15μm以下の厚みを有し、
前記潤滑剤層が、前記潤滑剤を前記3つの層の中で最も多く含み、0.1μm以上かつ10μm以下の厚みを有し、
前記潤滑剤層の厚みに対する前記ベース層の厚みの比が、0.2以上かつ10以下である
ことを特徴とする請求項1または2に記載の冷間加工用中炭素鋼板。 - 前記無機酸塩が、リン酸塩、ホウ酸塩、ケイ酸塩、モリブデン酸塩およびタングステン酸塩からなる群より選択される少なくとも1種の化合物であることを特徴とする請求項5に記載の冷間加工用中炭素鋼板。
- 前記耐熱樹脂が、ポリイミド樹脂、ポリエステル樹脂、エポキシ樹脂及びフッ素樹脂からなる群より選択される少なくとも1種の樹脂であることを特徴とする請求項5に記載の冷間加工用中炭素鋼板。
- 前記潤滑剤が、ポリテトラフルオロエチレン、二硫化モリブデン、二硫化タングステン、酸化亜鉛およびグラファイトからなる群より選択される少なくとも1種の化合物であることを特徴とする請求項5に記載の冷間加工用中炭素鋼板。
- 請求項1または請求項2に記載の成分組成を有する鋳片を、1050℃以上かつ1300℃以下に保持する第1の工程と;
この第1の工程後、前記鋳片に対して750℃以上かつ1000℃以下で圧延を終了する熱間圧延を行い、鋼板を得る第2の工程と;
この第2の工程後、前記鋼板を、20℃/秒以上かつ50℃/秒以下の第一の平均冷却速度で500℃以上かつ700℃以下の第一の冷却終了温度まで冷却する第3の工程と;
この第3の工程後、前記鋼板を、5℃/秒以上かつ30℃/秒以下の第二の平均冷却速度で400℃以上かつ前記第一の冷却終了温度より50℃低い温度以下の第二の冷却終了温度まで冷却し、巻取る第4の工程と;
この第4の工程後、400℃以上かつ前記第二の冷却終了温度以下である時間が30時間以下に制限されるように前記鋼板を保持する第5の工程と;
この第5の工程後、前記鋼板を、600℃以上かつAc1点-10℃以下まで加熱し、5時間以上かつ100時間未満保持して焼鈍を行う第6の工程と;
を含むことを特徴とする冷間加工用中炭素鋼板の製造方法。 - 前記第6の工程では、400℃以下での露点が-20℃未満、400℃超での露点が-40℃未満であり、かつ、水素濃度が95%以上であることを特徴とする請求項9に記載の冷間加工用中炭素鋼板の製造方法。
- 前記第6の工程の後に、水溶性シランカップリング剤、水溶性無機酸塩、水溶性耐熱樹脂および潤滑剤を含む水系の表面処理液を前記冷間加工用中炭素鋼板の少なくとも片面に塗布し、前記表面処理液を乾燥させて、前記冷間加工用中炭素鋼板の少なくとも片面に前記表面処理皮膜を形成することを特徴とする請求項9または10に記載の冷間加工用中炭素鋼板の製造方法。
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KR (1) | KR101591208B1 (ja) |
CN (1) | CN103797146B (ja) |
CA (1) | CA2848028C (ja) |
WO (1) | WO2013042239A1 (ja) |
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Also Published As
Publication number | Publication date |
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JP5048168B1 (ja) | 2012-10-17 |
KR101591208B1 (ko) | 2016-02-02 |
CA2848028C (en) | 2016-10-18 |
KR20140048329A (ko) | 2014-04-23 |
CN103797146B (zh) | 2015-12-09 |
JPWO2013042239A1 (ja) | 2015-03-26 |
CN103797146A (zh) | 2014-05-14 |
CA2848028A1 (en) | 2013-03-28 |
US9840750B2 (en) | 2017-12-12 |
US20140212660A1 (en) | 2014-07-31 |
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