CN105026065A - Hot press molding and manufacturing method therefor - Google Patents

Hot press molding and manufacturing method therefor Download PDF

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Publication number
CN105026065A
CN105026065A CN201480009284.9A CN201480009284A CN105026065A CN 105026065 A CN105026065 A CN 105026065A CN 201480009284 A CN201480009284 A CN 201480009284A CN 105026065 A CN105026065 A CN 105026065A
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Prior art keywords
area
temperature
hot forming
shaped region
shaped
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Inventor
内藤纯也
村上俊夫
池田周之
冲田圭介
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0294—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a localised treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • B21D22/208—Deep-drawing by heating the blank or deep-drawing associated with heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2221/00—Treating localised areas of an article

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

The hot press molding comprises: a first forming region exhibiting a metal structure, which contains 80-97 area% of martensite and 3-20 area% of retained austenite, respectively, and in which the residual structure is 5 area% or less; and a second forming region exhibiting a metal structure, which contains 70-97 area% of bainitic ferrite, 27 area% or less of martensite, and 3-20 area% of retained austenite, respectively, and in which the residual structure is 5 area% or less. As a result, hot press moldings, which have at least a region corresponding to a shock-resistant area and a region corresponding to an energy-absorbing area in a single molding and in which a high level of balancing of high strength with elongation according to the respective region can be achieved, are provided without using a welding method.

Description

Hot forming product and manufacture method thereof
Technical field
The present invention relates to a kind of hot forming product and manufacture method thereof, described hot forming product are used to the structural elements of auto parts, can according to the zones of different adjustment intensity in formed products and ductility.More specifically, when relating to the shape becoming to specify by pre-heated steel plate (blank) formed machining, while imparting shape, implement heat treatment, and can obtain meeting the intensity of zones of different and the hot forming product of ductility and the useful method for the manufacture of such hot forming product.
Background technology
As one of countermeasure that the automobile fuel consumption coming from global environmental problems raises, the lightweight of car body is pushed into, and needs the steel plate high strength making automobile use as far as possible.But if the lightweight of automobile and make steel plate high strength, then percentage elongation EL (Elongation) and r value (Lankford value: Lankford value) reduce, and press molding and shape freezing can deteriorations.
In order to solve such problem, hot forming method is adopted in part manufacture, its be by steel plate is heated to specify temperature (such as, become the temperature of austenite phase) and reduce intensity (namely, make shaping easy) after, compare sheet metal with the die forming of comparatively low temperature (such as room temperature), thus while imparting shape, carry out the chilling heat treatment (quenching) of the temperature difference that make use of both, guarantee the intensity after being shaped.
According to such hot forming method, owing to being shaped under low-intensity state, therefore resilience also diminishes (shape freezing is good), and with the addition of the good material of the hardenability of the alloying elements such as Mn, B by using, can obtain by chilling the intensity counting 1500MPa level with tensile strength.It should be noted that, such hot forming method, except pressure sintering, is also called with the various title such as method for hot forming, hot stamping, hot stamped process, die quenching method.
Fig. 1 represents (following for implementing above-mentioned such hot forming, sometimes with " drop stamping " for representative) the schematic illustration that formed of mould, in figure, 1 represents drift, 2 represent punch die, and 3 represent blank holder, and 4 represent steel plate (blank), BHF represents wrinkle resistant pressure-pad-force, rp represents drift shoulder radius, and rd represents punch die shoulder radius, and CL represents gap between drift/punch die.In addition, in these parts, drift 1 and punch die 2 are formed in the following manner, are formed with path 1a, the 2a that cooling medium 5a, 6a (such as water) can be made to pass through in respective inside, by make in these paths by cooling medium 5a, 6a thus make these parts be cooled.
When using such mould to carry out drop stamping (such as, hot deep-draw processing), steel plate (blank) 4 is heated to Ac 3single-phase territory temperature more than transformation temperature and start under the state making it soften be shaped.Namely, under the state that the steel plate 4 being in the condition of high temperature is clipped between punch die 2 and blank holder 3, drift 1 is utilized steel plate 4 to be pressed in the hole of punch die 2 (Fig. 12,2 between) (direction of flechette-type symbol A), while reduce the external diameter of steel plate 4, be configured as the shape corresponding with the profile of drift 1.In addition, by cooling drift 1 and punch die 2 with shaping simultaneously, carry out the heat extraction from steel plate 4 to mould (drift 1 and punch die 2), and keep cooling further at shaping bottom dead centre (when punch head is positioned at most deep: the state shown in Fig. 1) thus implement the quenching of former material (steel plate 4).By implementing such forming process, can obtain the formed products of the good 1500MPa level of dimensional accuracy, and compared with the situation of the part of the equality strength rank that is shaped under cold conditions, can reduce shaping loading, therefore the capacity of press is very just little.
As now widely used drop stamping steel plate, known is former material with 22MnB5 steel.The tensile strength of this steel plate is 1500MPa and percentage elongation is about 6 ~ 8%, is applicable to Impact-resistant member (doing one's utmost during collision not deform, the component do not ruptured).In addition, increase C content, based on 22MnB5 steel, the exploitation carrying out high strength (more than 1500MPa, 1800MPa level) further is also being carried out.
But, steel grade beyond 22MnB5 steel almost cannot be suitable for, present situation controls the intensity of part, percentage elongation (such as, low-intensity: 980MPa level, high-elongation: 20% etc.), expands to the steel grade beyond Impact-resistant member, the research of construction method does not almost carry out by the scope of application.
In medium-sized or above passenger car; during side collision and rearward collision time consider compatibility (compatibility: also protect the function of the other side side during compact car collision); in the part of B post (newel), floor side member, front longitudinal etc., there is the situation making it have resistance to impact position and these two kinds of functions of energy absorption position.In order to make such component, up to now, such as 980MPa level high strength extra-high tension steel and have the high tension steel of the percentage elongation of 440MPa level to carry out laser weld (tailor welded Tailor Welded Blank:TWB), and the method for carrying out cold moudling is main flow.But the exploitation creating the technology of the intensity in part recently with drop stamping is respectively advanced.
Such as, in non-patent literature 1, propose a kind of 22MnB5 steel for drop stamping and carry out laser weld (tailor welded: TWB) with the mould material reaching high strength not yet that carries out quenching, and carry out the method for drop stamping, carry out at high strength side (side, shock-resistant position) tensile strength: 1500MPa (percentage elongation 6 ~ 8%), in the establishment respectively of low-intensity side (side, energy absorption position) tensile strength: 440MPa (percentage elongation more than 12%).From the same viewpoint, it is also proposed the technology that non-patent literature 2 is such.
In the technology of above-mentioned non-patent literature 1,2, in side, energy absorption position, tensile strength is below 600MPa, and percentage elongation is about 12 ~ 18%, but needs in advance to carry out laser weld (tailor welded: TWB), and operation increases and cost is high.In addition, the energy absorption position originally not needing to carry out quenching be heated, not preferred from the viewpoint of heat exhaustion yet.
In addition, as the technology for creating intensity in part respectively, it is also proposed such as non-patent literature 3,4 such technology.The technology of this non-patent literature 3 is come to create respectively by making blank produce temperature difference (distribution) in heating furnace, with 22MnB5 steel for base material, but owing to adding the impact of boron, for the heating of two phase region temperature, the robustness (robustness) of the intensity after quenching is poor, the strength control difficulty of side, energy absorption position, percentage elongation also can only obtain about 15% in addition.
On the other hand, in the technology of non-patent literature 4, by in mould (by the part of the warm mould of heater or use the different material of thermal conductivity) make cooling velocity change thus create respectively, but with 22MnB5 steel for base material, the 22MnB5 steel good for original hardenability does not quench, and carrying out in this way, control this point (mold cools down control) is upper unreasonable.
Prior art document
Non-patent literature
Non-patent literature 1:Klaus Lamprecht, Gunter Deinzer, Anton Stich, JurgenLechler, Thomas Stohr, Marion Merklein, " Thermo-Mechanical Properties ofTailor Welded Blanks in Hot Sheet Metal Forming Processes ", Proc.IDDRG2010,2010.
Non-patent literature 2:Usibor1500P (22MnB5)/1500MPa8%-Ductibor500/550 ~ 700MPa17% [retrieval on April 27th, 2011] network address <http: //www.arcelomittal.com/tailoredblanks/pre/seifware.p1Great T.GreaT.GT
Non-patent literature 3:22MnB5/above Ac 3/ 1500MPa8%-below Ac 3/ Hv190Ferrite/Cementite Rudiger Erhardt and Johannes Boke, " Industrialapplication of hot forming process simulation ", Proc, of 1st Int.Conf.on HotSheet Metal Forming of High-Performance steel, ed.By Steinhoff, K., Oldenburg, M, Steinhoff, and Prakash, B., pp83-88,2008.
Non-patent literature 4:Begona Casas, David Latre, Noemi Rodriguez, and IsaacValls, " Tailor made tool materials for the present and upcoming toolingsolutions in hot sheet metal forming ", Proc, of 1st Int.Conf.on Hot SheetMetal Forming of High-Performance steel, ed.By Steinhoff, K., Oldenburg, M, Steinhoff, and Prakash, B., pp23-35,2008.
Summary of the invention
The problem that invention will solve
The present invention completes in view of the foregoing, its object is to, even if do not apply welding, a kind of hot forming product and the useful method for the manufacture of such hot forming product are also provided, described hot forming product at least have the region being equivalent to shock-resistant position and energy absorption position in single formed products, according to regional, the balance of high strength and percentage elongation can be reached with high level.
For solving the means of problem
The hot forming product of the present invention can reaching above-mentioned purpose are the hot forming product be shaped to sheet metal by hot forming method, it is characterized in that, have display and comprise martensite respectively: 80 ~ 97 area %, retained austenite: 3 ~ 20 area %, remaining set is woven to the 1st shaped region of the metal structure of 5 below area %; Bainite ferrite is comprised respectively: 70 ~ 97 area %, martensite: 27 below area % and retained austenite: 3 ~ 20 area %, remaining set is woven to the 2nd shaped region of the metal structure of 5 below area % with display.
In hot forming product of the present invention, its chemical composition composition does not limit, and include, for example as follows: the 1st shaped region is identical with the 2nd shaped region chemical composition composition, and the steel of each composition range contains the C:0.15 ~ 0.3% (meaning of quality %.Below relate to chemical composition composition all with.), Si:0.5 ~ 3%, Mn:0.5 ~ 2%, below P:0.05% (not containing 0%), below S:0.05% (not containing 0%), Al:0.01 ~ 0.1%, Cr:0.01 ~ 1%, B:0.0002 ~ 0.01%, Ti:[N] × 4 ~ 0.1% [wherein, the content (%) that [N] is N] and N:0.001 ~ 0.01%, surplus is made up of iron and inevitable impurity.
In hot forming product of the present invention, as required, as other element, described steel also containing, for example inferior be also useful: (a) is selected from more than a kind in Cu, Ni and Mo: add up at least a kind in less than 1% (not containing 0%), (b) V and Nb: add up to less than 0.1% (not containing 0%), according to the kind of the element contained, the characteristic of hot forming product is further improved.
The inventive method is shaped by sheet metal being divided into the multiple regions at least comprising the 1st and the 2nd, thus manufacture the method for hot forming product as described above, and its purport is, described sheet metal is heated to Ac 3more than transformation temperature and after the temperature of less than 1000 DEG C, at least for the 1st shaped region and the 2nd shaped region, one reinstates mould carries out punching press thus the cooling and the shaping that start average cooling rate more than 20 DEG C/sec, 1st shaped region terminates to be shaped below the temperature of low 50 DEG C than martensite start temperature, temperature range below the temperature that 2nd shaped region is cooled to start low 100 DEG C of temperature than bainitic transformation and more than martensite start temperature, and the time of staying in described temperature range is set to more than 10 seconds and terminates to be shaped.
Invention effect
According to the present invention, in hot forming method, its condition is suitably controlled by each region according to formed products, the retained austenite of appropriate amount can be made to exist and adjust the metal structure in each region, compared with during the existing 22MnB5 steel of use, the hot forming product that the ductility (remaining ductility) that can realize formed products inherence improves further, in addition, by the combination with heat-treat condition and shaping front spring, can according to the suitable control intensity in each region and percentage elongation.
Accompanying drawing explanation
Fig. 1 is the schematic illustration representing that the mould for implementing hot forming is formed.
Fig. 2 is the schematic illustration of the shaping dies used in embodiment.
Fig. 3 is the schematic illustration of the shape representing the press molding product be shaped in embodiment.
Detailed description of the invention
After sheet metal is heated to the temperature of regulation by the present inventor etc., when carrying out hot forming and manufacture formed products, in order to the difference realizing not only having guaranteed to meet after forming each region requires the intensity of characteristic but also demonstrates the such hot forming product of good ductility (percentage elongation), be studied from various angle.
It found that, when using press molding mould that sheet metal press molding is manufactured hot forming product, if the condition of each shaped region when suitably controlling heating-up temperature and be shaped, the tissue of each shaped region is adjusted according to the mode comprising retained austenite 3 ~ 20 area %, then can realize playing the strength-ductility balanced hot forming product meeting each shaped region, thus complete the present invention.
The range set reason of each tissue (elementary organization) in each shaped region of hot forming product of the present invention is as follows.
(tissue of the 1st shaped region)
By the martensite making the Main Tissues of the 1st shaped region become high strength, the high strength of the specific region in hot forming product can be guaranteed.From this viewpoint, need martensitic Line Integral rate to be set to 80 more than area %.But if this point of rate is more than 97 area %, then the Line Integral rate (retained austenite divides rate) of retained austenite is not enough, and ductility (remaining ductility) reduces.The preferred lower limit of martensite point rate is 83 more than area % (being more preferably 85 more than area %), and preferred upper limit is 95 below area % (being more preferably 93 below area %).
The effect that retained austenite has is phase-changed into martensite in plastic deformation, thus make work hardening rate increase (phase change induction plasticity), and the ductility of formed products is improved.In order to play this effect, need a retained austenite point rate to be set to 3 more than area %.For ductility, retained austenite divides rate The more the better, but in the composition of automotive sheet, the retained austenite that can guarantee is limited, and 20 area about % are the upper limit.The preferred lower limit of retained austenite point rate is 5 more than area % (being more preferably 7 more than area %).
Except above-mentioned tissue, can comprise ferrite, pearlite, bainite etc. as residue tissue, but these tissues and martensitic phase are than being soft tissue, the contribution for intensity is organized low than other, preferably as far as possible few.But, can allow to 5 area %.Residue tissue is more preferably 3 below area %, more preferably 0 area %.
By making the tissue of the 1st shaped region as mentioned above, can be formed intensity (tensile strength TS) for more than 1500MPa and percentage elongation (breaking elongation EL:total elongation) be more than 10% part (such as, the resistance to impact position of auto parts).
(tissue of the 2nd shaped region)
By making the Main Tissues of the 2nd shaped region become high strength and be imbued with the bainite ferrite of ductility, high strength and the high ductibility of hot forming product can be taken into account.From this viewpoint, the Line Integral rate (bainite ferrite point rate) of bainite ferrite needs to be set to 70 more than area %.But if this point of rate is more than 97 area %, then retained austenite divides rate not enough, and ductility (remaining ductility) reduces.The preferred lower limit of bainite ferrite point rate is 75 more than area % (being more preferably 80 more than area %), and preferred upper limit is 95 below area % (being more preferably 90 below area %).
By comprising the martensite of a part of high strength, the high strength of hot forming product can be realized, if but its quantitative change ductility (remaining ductility) reduction at most.From this viewpoint, martensitic Line Integral rate (martensite point rate) needs to be set to 27 below area %.The preferred lower limit of martensite point rate is 5 more than area % (being more preferably 10 more than area %), and preferred upper limit is 20 below area % (being more preferably 15 below area %).
According to the reason same with the 1st shaped region, a retained austenite point rate is set to 3 more than area % and 20 below area %.Retained austenite divides the preferred lower limit of rate also same with the 1st shaped region.
Except above-mentioned tissue, can comprise ferrite, pearlite, bainite etc. as residue tissue, but these tissues and martensitic phase are than being soft tissue, the contribution for intensity is organized low than other, preferably as far as possible few.But, can allow to 5 area %.Residue tissue is more preferably 3 below area %, more preferably 0 area %.
By making the tissue of the 2nd shaped region as mentioned above, can be formed intensity (tensile strength TS) for more than 1100MPa and percentage elongation (breaking elongation EL) be more than 15% part (such as, the energy absorption position of auto parts).
Formed products of the present invention at least has the 1st shaped region and the 2nd shaped region, but may not be only limitted to two shaped regions, can have the 3rd or the 4th shaped region.When forming such shaped region, can make according to manufacture method described later.
When manufacturing hot forming product of the present invention, sheet metal (chemical composition composition is identical with formed products) is divided into the multiple region at least comprising the 1st and the 2nd and is shaped.Specifically, described sheet metal is heated to Ac 3more than transformation temperature and after the temperature of less than 1000 DEG C, at least for the 1st shaped region and the 2nd shaped region, one reinstates mould punching thus starts cooling and the shaping of average cooling rate more than 20 DEG C/sec, 1st shaped region is (following the temperature of lower than martensite start temperature 50 DEG C, sometimes be designated as " Ms point-50 DEG C ") below terminate be shaped, 2nd shaped region is cooled to the temperature starting low 100 DEG C of temperature than bainitic transformation (following, sometimes be designated as " Bs point-100 DEG C ") temperature range below and more than martensite start temperature (Ms point), and the time of staying in described temperature range be set to more than 10 seconds and terminate to be shaped.The reason of each important document in regulation the method is as follows.It should be noted that, " terminate to be shaped " and refer to, substantially the state of shaping bottom dead centre (punch head is positioned at the moment in most deep: state shown in Fig. 1) is reached, but when mould needs to be cooled to set point of temperature in this condition, be intended to also comprise till leaving mould after mold cools down keeps.
Said method is by being divided at least two shaped regions of steel plate (such as, high strength side region and low-intensity side region), and control manufacturing condition according to regional, can obtain playing the strength-ductility balanced such formed products meeting each region.Manufacturing condition for the formation of each region is described.
(manufacturing condition of the 1st shaped region (high strength side region))
In order to suitably adjust the tissue of hot forming product, heating-up temperature needs to control the scope for regulation.By suitably controlling this heating-up temperature, in cooling procedure thereafter, making it be phase-changed into guarantee the retained austenite of ormal weight, and making the 1st shaped region become the tissue of martensite main body, the tissue desired by can making in final hot forming product.If steel-sheet heating-up temperature is lower than Ac 3transformation temperature, then can not obtain the austenite of q.s when heating, can not guarantee the retained austenite of ormal weight in final tissue (tissue of formed products).In addition, if steel-sheet heating-up temperature is more than 1000 DEG C, then when heating, austenitic particle diameter becomes large, martensite start temperature (Ms point) and martensitic traoformation end temp (Mf point) rise, can not retained austenite be guaranteed when quenching, good formability cannot be reached.Heating-up temperature is preferably (Ac 3transformation temperature+50 DEG C) more than and less than 950 DEG C.
Cooling condition in shaping and shaping end temp need suitably to control according to each region.First, in the steel plate region (sometimes this region being called " the 1st steel plate region ") of the 1st shaped region being equivalent to formed products, need the average cooling rate guaranteeing more than 20 DEG C/sec in mould in shaping, and terminate to be shaped at (Ms point-50 DEG C) following temperature.
For the austenite formed in above-mentioned heating process, generate to both stop the tissues such as ferrite, pearlite and bainite, become again desired tissue (tissue based on martensite), need suitably to control the average cooling rate in shaping and shaping end temp.From this viewpoint, the average cooling rate in shaping is set to more than 20 DEG C/sec, and shaping end temp is set to (Ms point-50 DEG C) below.Particularly with the many steel plate of Si content for object when, by cooling under this condition, the line and staff control of martensite and retained austenite can be become.Average cooling rate in shaping is preferably more than 30 DEG C/sec (being more preferably more than 40 DEG C/sec).
Shaping end temp in 1st steel plate region can to terminate while above-mentioned average cooling rate cool to room temperature to be shaped, also after being cooled to (Ms point-50 DEG C) (preferably to arrive the temperature of Ms point-50 DEG C) below, (2 sections of coolings) can be cooled to less than 200 DEG C with the average cooling rate of less than 20 DEG C/sec.By this refrigerating work procedure additional, the carbon in martensite, to non-transformed austenite multiviscosisty, can make the retained austenite scale of construction increase.These 2 sections cooling time the 2nd section cooling time average cooling rate be preferably less than 10 DEG C/sec (being more preferably less than 5 DEG C/sec).
(manufacturing condition of the 2nd shaped region (low-intensity side region))
On the other hand, in order to suitably control the tissue of the 2nd shaped region in hot forming product, needing is the scope specified by the heating and temperature control in the steel plate region being equivalent to the 2nd shaped region (being sometimes called in this region in " the 2nd steel plate region ").By suitably controlling this heating-up temperature, in cooling procedure thereafter, the retained austenite of ormal weight can be guaranteed and make it be phase-changed into tissue based on bainite ferrite, the tissue desired by making in final hot forming product.If steel-sheet heating-up temperature is lower than Ac 3transformation temperature, then can not obtain the austenite of q.s when heating, can not guarantee the retained austenite of ormal weight in final tissue (tissue of formed products).In addition, if steel-sheet heating-up temperature is more than 1000 DEG C, then same with the 1st steel plate region (preferred temperature range is also same with the 1st steel plate region).
For the austenite formed in above-mentioned heating process, organize to stop ferrite, pearlite etc. and generate, and the tissue (tissue based on bainite ferrite) desired by being formed, the average cooling rate in needing suitably control to be shaped and cooling stop temperature.From this viewpoint, need the average cooling rate in being shaped to be set to more than 20 DEG C/sec, cooling stopping temperature being set to (Bs point-100 DEG C) below and more than martensite start temperature (Ms point) (sometimes this temperature range being called " cooling velocity changing temperature ").Average cooling rate is preferably more than 30 DEG C/sec (being more preferably more than 40 DEG C/sec).
By temporarily stopping cooling in above-mentioned temperature range (cooling velocity changing temperature), make it in described temperature range (namely, (Bs point-100 DEG C) below and the above temperature range of martensite start temperature Ms point) stop more than 10 seconds, from overcooling austenite, carry out bainitic transformation and the tissue that can become based on bainite ferrite.The time of staying is now preferably more than 50 seconds (being more preferably more than 100 seconds), if but overstand, then austenite starts to decompose, and can not guarantee retained austenite point rate, is therefore preferably less than 1000 seconds (being more preferably less than 800 seconds).
If within the scope of stop operation said temperature as described above, then can be any one in isothermal maintenance, dull cooling, again heating process.In addition, for the relation of such stop and shaping, in the stage terminating to be shaped in addition stop as described above, also in the midway of terminating to be shaped, operation can be kept within the scope of said temperature.After terminating shaping like this, naturally cool or be cooled to room temperature with suitable cooling velocity.
The control of the average cooling rate in shaping can control the temperature (shown in above-mentioned Fig. 1 cooling medium) of shaping dies by (a), (b) controls the unit of the thermal conductivity of mould etc. and reach (in the cooling in following method too).In addition, in the inventive method, according to each steel plate region, the cooling condition in shaping is different, in single mold, form the control unit such as above-mentioned (a), (b) respectively, the cooling carrying out meeting each steel plate region in single mold controls.
The manufacture method (direct Process) when manufacturing the hot forming product of above-mentioned simple shape as shown in Figure 1 of hot forming product of the present invention can be suitable for certainly, also can be suitable for when the formed products of the shape of manufacture more complicated.But, when complicated part shape, be sometimes difficult to a press molding net shape reaching goods.Under these circumstances, the method (the method is called " indirect processes method ") of carrying out cold-press moulding before hot forming in operation can be adopted.The method is by carrying out cold working and preshaped to approximate shapes to the part being difficult to be shaped, then other parts is carried out to the method for hot forming.According to this method, then, during the part forming such as having 3 places such the jog (mountain portion) of formed products, by cold-press moulding, its 2 place preshaped, then carries out hot forming to the 3rd place.
In the present invention, it is assumed that the hot forming product be made up of high-strength steel sheet, as long as form about the common chemical composition of its steel grade as high-strength steel sheet, but about C, Si, Mn, P, S, Al, Cr, B, Ti and N, adjust to suitable scope and be advisable.From this viewpoint, to limit reason as follows for the preferable range of these chemical compositions and scope thereof.
(C：0.15～0.3％)
C the bainite ferrite making to generate in cooling procedure fine and make the dislocation density in bainite ferrite rise thus make intensity improve on be important element (low-intensity side region).In addition, the intensity of domination martensitic structure is important element (high strength side region).If C content tails off, even then full martensite intensity is also not enough.C is the element closely bound up with hardenability, by making content increase, and the effect of the formation of other tissue that the ferrite in the cooling after performance suppression heating etc. are soft.In addition, guaranteeing it retained austenite is also necessary element.C content lower than 0.15% time, bainitic transformation start temperature Bs rise, the high strength of hot forming product can not be guaranteed.In addition, if C content becomes superfluous and more than 0.3%, then intensity becomes too high, and good ductility can not be obtained.More preferably the lower limit of C content is more than 0.18% (more preferably more than 0.20%), and more preferably the upper limit is less than 0.27% (more preferably less than 0.25%).
(Si：0.5～3％)
Si plays the effect forming retained austenite when quenching.In addition, also play by solution strengthening, make ductility less deterioration and improve the effect of intensity.Si content lower than 0.5% time, can not guarantee specify the retained austenite scale of construction, good ductility can not be obtained.In addition, if Si content is superfluous and more than 3%, then solution strengthening quantitative change is too much, ductility is significantly deteriorated.More preferably the lower limit of Si content is more than 1.15% (more preferably more than 1.20%), and more preferably the upper limit is less than 2.7% (more preferably less than 2.5%).
(Mn：0.5～2％)
Mn is to suppression ferrite, the pearlitic element be formed in once cooling.In addition, be by making (Bs point-100 DEG C) reduce, thus make organization unit's miniaturization of bainite ferrite, or by improving the dislocation density in bainite ferrite, thus the element useful to the intensity improving bainite ferrite.And, be to making stabilization of austenite, making the retained austenite scale of construction increase effective element.In order to play these effects, preferably contain the Mn of more than 0.5%.When only considering characteristic, preferred Mn content is many, but due to alloy add cost increase, be preferably set to less than 2%.In addition, owing to making austenitic intensity significantly improve, the load of hot rolling becomes large, and the manufacture of steel plate becomes difficulty, therefore in productivity ratio, also not preferably containing more than 2%.More preferably the lower limit of Mn content is more than 0.7% (more preferably more than 0.9%), and more preferably the upper limit is less than 1.8% (more preferably less than 1.6%).
(below P:0.05% (not containing 0%))
P is the element inevitably comprised in steel, but owing to making degrade ductility, preferred P does one's utmost to reduce.But extreme minimizing causes the increase of steel cost processed, have any problem in manufacture owing to reaching 0%, be therefore preferably less than 0.05% (not containing 0%).More preferably the upper limit of P content is less than 0.045% (more preferably less than 0.040%).
(below S:0.05% (not containing 0%))
S is also same with P is the element inevitably comprised in steel, and owing to making degrade ductility, preferred S does one's utmost to reduce.But extreme minimizing causes the increase of steel cost processed, have any problem in manufacture owing to reaching 0%, be therefore preferably less than 0.05% (not containing 0%).More preferably the upper limit of S content is less than 0.045% (more preferably less than 0.040%).
(Al：0.01～0.1％)
Al is useful as deoxidant element, and is fixed as AlN by the solid solution N existed in steel, useful to the raising of ductility.In order to effectively play such effect, Al content is preferably more than 0.01%.But, if Al content becomes superfluous and more than 0.1%, then Al 2o 3generate superfluously, make degrade ductility.It should be noted that, the more preferably lower limit of Al content is more than 0.013% (more preferably more than 0.015%), and more preferably the upper limit is less than 0.08% (more preferably less than 0.06%).
(Cr：0.01～1％)
Cr has the effect suppressing ferrite transformation, pearlitic transformation, is therefore the formation preventing ferrite and pearlite in cooling, contributes to the element guaranteeing retained austenite.In order to play such effect, preferably contain the Cr of more than 0.01%, but contain to surplus more than 1%, then cost also can rise.In addition, because Cr significantly improves austenitic intensity, the load of hot rolling becomes large, and the manufacture of steel plate becomes difficulty, therefore in productivity ratio, also not preferably containing more than 1%.More preferably the lower limit of Cr content is more than 0.02% (more preferably more than 0.05%), and more preferably the upper limit is less than 0.8% (more preferably less than 0.5%).
(B：0.0002～0.01％)
B has the effect improving hardenability, suppress ferrite transformation, pearlitic transformation, therefore in once cooling after the heating, prevents ferrite, pearlitic formation, contributes to the element guaranteeing bainite ferrite and retained austenite.In order to play such effect, preferably contain the B of more than 0.0002%, but contain to surplus more than 0.01%, effect is also saturated.More preferably the lower limit of B content is more than 0.0003% (more preferably more than 0.0005%), and more preferably the upper limit is less than 0.008% (more preferably less than 0.005%).
(Ti：[N]×4～0.1％)
Ti fix N, maintains B with solid solution condition, thus embodies the improvement effect of hardenability.In order to play such effect, preferred Ti at least contains more than 4 times of the content [N] of N.But if Ti content becomes superfluous and more than 0.1%, then forms TiC in a large number, intensity rises due to precipitation strength, but degrade ductility.More preferably the lower limit of Ti content is more than 0.05% (more preferably more than 0.06%), and more preferably the upper limit is less than 0.09% (more preferably less than 0.08%).
(N：0.001～0.01％)
N is by being fixed as BN by B, thus the element making hardenability improve effect to reduce, and preferably as far as possible reduces, but reduces in actual process and there is boundary, therefore using 0.001% as preferred lower limit.In addition, if N content becomes superfluous, then form thick TiN, this TiN works as the starting point destroyed, and degrade ductility, is therefore set to 0.01% by preferred upper limit.More preferably the upper limit of N content is less than 0.008% (more preferably less than 0.006%).
Basic chemical composition in press molding product of the present invention is described above, and surplus is in fact iron.It should be noted that, " being in fact iron " refers to, also the micro constitutent of the degree of the characteristic not hindering steel of the present invention can be allowed (such as beyond deironing, except Mg, Ca, Sr, Ba, also has the carbide former etc. of REM and Zr, Hf, Ta, W, the Mo etc. such as La), in addition, also can containing the inevitable impurity (such as, O, H etc.) beyond P, S.
In press molding product of the present invention, as required, also be also useful containing, for example lower element: (a) is selected from more than a kind in Cu, Ni and Mo: add up at least a kind in less than 1% (not containing 0%), (b) V and Nb: add up to less than 0.1% (not containing 0%) etc., according to the kind of the element contained, the characteristic of hot forming product is further improved.Reason is limited as follows containing preferable range during these elements and scope thereof.
(being selected from more than a kind in Cu, Ni and Mo: add up to less than 1% (not containing 0%))
Cu, Ni and Mo, owing to suppressing ferrite transformation and pearlitic transformation, in once cooling, prevent ferrite, pearlitic formation, effectively act on guaranteeing of retained austenite.In order to play such effect, preferably containing total more than 0.01%.If only consider characteristic, then preferred content is many, but due to alloy add cost increase, be preferably total less than 1%.In addition, owing to having the effect significantly improving austenitic intensity, the load of hot rolling becomes large, and the manufacture of steel plate becomes difficulty, is therefore also preferably total less than 1% from the viewpoint of manufacturing.More preferably the lower limit of these constituent contents is total more than 0.05% (more preferably more than 0.06%), and more preferably the upper limit is total less than 0.9% (more preferably less than 0.8%).
(at least a kind in V and Nb: add up to less than 0.1% (not containing 0%))
V and Nb forms fine carbide, has and utilizes pinning effect and make to organize fine effect.In order to play such effect, preferably add up to more than 0.001% containing at least a kind in V and Nb.But, if the content of these elements becomes superfluous, then form thick carbide, become the starting point of destruction, make degrade ductility on the contrary, be therefore preferably total less than 0.1%.More preferably the lower limit of these constituent contents is total more than 0.005% (more preferably more than 0.008%), and more preferably the upper limit is total less than 0.08% (more preferably less than 0.06%).
According to the present invention, by suitably adjusting press molding condition (meeting heating-up temperature and the cooling velocity in each steel plate region), the characteristic such as intensity, percentage elongation of each shaped region in formed products can be controlled, and the hot forming product of high ductibility (remaining ductility) can be obtained.Therefore, even if also can be suitable at the position (such as, requiring shock-resistant characteristic and the component both energy absorption suppression) that hot forming product are up to now difficult to be suitable for, exceedingly useful in the scope of application of expansion hot forming product.In addition, the formed products that the present invention obtains with after cold-press moulding, implement common annealing and carried out organizing compared with the formed products that adjusts, remaining ductility is larger.
Below, more specifically show effect of the present invention by embodiment, but following embodiment does not limit the present invention, carry out design alteration according to the forward and backward purport stated and be all included in technical scope of the present invention.
The application is based on the interests of the Japan patent application 2013-032615 CLAIM OF PRIORITY applied on February 21st, 2013.The full content of the description of No. 2013-032615th, Japan's patent application of application on February 21st, 2013 is quoted in order to reference in this application.
Embodiment
The steel that the chemical composition had described in following table 1 forms are carried out vacuum melting, carries out hot rolling after becoming experiment slab, cool winding afterwards.Carry out cold rolling again and become sheet metal.It should be noted that, the Ac in table 1 3transformation temperature, Ms point and (Bs point-100 DEG C) use following (1) formula ~ (3) formula and try to achieve (being apt to for example, referring to " Lesley's ferrous materials " ball, (1985)).
Ac 3transformation temperature (DEG C)=910-203 × [C] 1/2+ 44.7 × [Si]-30 × [Mn]+700 × [P]+400 × [Al]+400 × [Ti]+104 × [V]-11 × [Cr]+31.5 × [Mo]-20 × [Cu]-15.2 × [Ni] ... (1)
Ms point (DEG C)=550-361 × [C]-39 × [Mn]-10 × [Cu]-17 × [Ni]-20 × [Cr]-5 × [Mo]+30 × [Al] ... (2)
Bs point (DEG C)=830-270 × [C]-90 × [Mn]-37 × [Ni]-70 × [Cr]-83 × [Mo] ... (3)
Wherein, [C], [Si], [Mn], [P], [Al], [Ti], [V], [Cr], [Mo], [Cu] and [Ni] represent the content (quality %) of C, Si, Mn, P, Al, Ti, V, Cr, Mo, Cu and Ni respectively.In addition, when not containing every shown element of above-mentioned (1) formula ~ (3) formula, remove this and calculate.
[table 1]
For obtained steel plate, change the heating-up temperature in each steel plate region, implement shaping, cooling processing.Specifically, the bending die of the hat channel-section steel shape (HAT shape) shown in Fig. 2 is used to carry out press molding.It should be noted that, in Fig. 2,10 represent patrix (being equivalent to drift 1 shown in Fig. 1), and 11 represent counterdie (being equivalent to punch die 2 shown in Fig. 1).In addition, be provided with pad 12 in this shaping dies, apply pressure (pad pressure) (pad pressure is 9800N) according to one side, one side clamps steel plate 4 with patrix 11, and the mode of carrying out press molding is formed.
Heating-up temperature in each steel plate region, average cooling rate are shown in (shaping end temp (calcining temperature) is 200 DEG C in arbitrary region) in following table 2.Plate size when shaping, cooling is 220mm × 500mm (thickness of slab: 1.4mm) (area ratio in the 1st steel plate region and the 2nd steel plate region is 1:1).The shape (key diagram that Fig. 3 (a) schematically shows stereogram, Fig. 3 (b) schematically shows cross section) shown in Figure 3 of the press molding product be shaped.In Fig. 3 (a), 15 represent the 1st steel plate region (being equivalent to the 1st shaped region in formed products), and 16 represent the 2nd steel plate region (being equivalent to the 2nd shaped region in formed products).It should be noted that, " average cooling rate 1 " in the 1st steel plate region shown in table 2 represents the average cooling rate from heating-up temperature to (Ms point-50 DEG C) (shaping end temp) below, and " average cooling rate 2 " in the 1st steel plate region represents from shaping end temp to the average cooling rate of less than 200 DEG C.
[table 2]
For each steel plate having carried out above-mentioned process (heating, be shaped, cooling), carry out the observation (point rate of each tissue) of tensile strength (TS) and percentage elongation (breaking elongation EL), metal structure by following main points.
(tensile strength (TS) and percentage elongation (breaking elongation EL))
Use JIS5 test film to carry out tension test, measure tensile strength (TS), percentage elongation (breaking elongation EL).Now, the rate of straining of tension test: 10mm/ second.In the present invention, a () is in the 1st region, meet tensile strength (TS) for more than 1500MPa and percentage elongation (breaking elongation EL) is more than 10%, and (b) is in the 2nd region, meet tensile strength (TS) for more than 1100MPa and percentage elongation (breaking elongation EL) is more than 15% time, it is qualified to be evaluated as.
(observation (point rate of each tissue) of metal structure)
(1) about the tissue of the martensite in steel plate, ferrite, bainite ferrite, with nital corrosion steel plate, (multiplying power: 1000 times or 2000 times) is observed by scanning electron microscope (Scanning ElectronMicroscope:SEM), distinguish ferrite, bainite ferrite, and try to achieve respective point rate (area occupation ratio).
(2) rate (area occupation ratio) is divided about the retained austenite in steel plate, after being ground to the thickness of 1/4 of steel plate, after carrying out chemical grinding, measure (such as, ISJJInt.Vol.33. (1933) by X-ray diffraction method, No.7, P.776).
(3) about the area occupation ratio of martensite (martensite of as-quenched), the corrosion of leper reagent is carried out to steel plate, the line and staff control being observed martensite using the contrast of white as as-quenched and retained austenite by SEM measures area occupation ratio, therefrom deduct the retained austenite point rate of being tried to achieve by X-ray diffraction, calculate the martensite point rate of as-quenched.
The measurement result of the metal structure in each region of formed products is shown in following table 3, the mechanical property in each region of formed products is shown in following table 4.
[table 3]
[table 4]
Can be analyzed as follows by these results.Test N o.2,4 are the embodiments meeting the important document specified in the present invention, knownly can obtain the strength-ductility balanced formed products reaching each region with high-performance.
On the other hand, test No.1,3,5,6 is the comparative examples not meeting a certain important document specified in the present invention, a certain deterioration in characteristics.Namely, the time of staying of (Bs-100 DEG C) ~ Ms point of test No.1 in the 2nd steel plate region is short, in the tissue in the 2nd region in formed products, point rate of bainite ferrite is few, and martensitic point of rate becomes many, can only obtain low elongation (breaking elongation EL) in the 2nd region.
Cooling velocity changing temperature in the 2nd steel plate region of test No.3 is suitable, but it is short in the time of staying of (Bs-100 DEG C) ~ Ms point, in the tissue in the 2nd region in formed products, point rate of bainite ferrite can guarantee appropriate amount, but because the retained austenite scale of construction is few, low elongation (breaking elongation EL) can only be obtained in the 2nd region.
Cooling velocity changing temperature in the 2nd steel plate region of test No.5 is high, forms ferrite and can not guarantee bainite ferrite amount, therefore low and can only obtain low elongation (breaking elongation EL) in the 2nd field strength.Test No.6 due to the Si content in composition of steel few, even if therefore cooling condition is suitable, also can not generate the retained austenite scale of construction in arbitrary region of formed products, low elongation (breaking elongation EL) (the intensity also step-down in the 2nd region) can only be obtained.
Utilizability in industry
Press molding product of the present invention have display and comprise martensite respectively: 80 ~ 97 area %, retained austenite: 3 ~ 20 area %, and remaining set is woven to the 1st shaped region of the metal structure of 5 below area %; Bainite ferrite is comprised respectively: 70 ~ 97 area %, martensite: 27 below area % and retained austenite: 3 ~ 20 area %, remaining set is woven to the 2nd shaped region of the metal structure of 5 below area % with display.Thus, even if do not apply welding, also at least there is in single formed products the region being equivalent to shock-resistant position and energy absorption position, according to regional, the balance of high strength and percentage elongation can be reached with high level.
Symbol description
1 drift
2 punch dies
3 blank holders
4 steel plates (blank)

Claims (5)

1. hot forming product, it is characterized in that, it is the hot forming product be shaped to sheet metal by hot forming method, there is the 1st shaped region and the 2nd shaped region, wherein, described 1st shaped region shows below metal structure, comprise martensite respectively: 80 ~ 97 area %, retained austenite: 3 ~ 20 area %, remaining set is woven to 5 below area %, described 2nd shaped region shows below metal structure, comprise bainite ferrite respectively: 70 ~ 97 area %, martensite: 27 below area % and retained austenite: 3 ~ 20 area %, remaining set is woven to 5 below area %.
2. hot forming product according to claim 1, wherein, the 1st shaped region is identical with the chemical composition composition of the 2nd shaped region, and the steel of each composition range contains in mass % respectively:
C：0.15～0.3％、
Si：0.5～3％、
Mn：0.5～2％、
Below P:0.05% and containing 0%,
Below S:0.05% and containing 0%,
Al：0.01～0.1％、
Cr：0.01～1％、
B：0.0002～0.01％、
Ti:[N] × 4 ~ 0.1%, wherein, the content % that [N] is N,
And N:0.001 ~ 0.01%,
Surplus is made up of iron and inevitable impurity.
3. hot forming product according to claim 2, wherein, described steel also containing add up to less than 1% using quality % and containing 0% be selected from Cu, Ni and Mo more than a kind as other element.
4. the hot forming product according to Claims 2 or 3, wherein, described steel also containing using quality % add up to less than 0.1% and containing 0% V and Nb at least a kind as other element.
5. a manufacture method for hot forming product, is characterized in that, it is shaped by sheet metal being divided into the multiple regions at least comprising the 1st and the 2nd, thus the method for hot forming product according to any one of manufacturing claims 1 ~ 3,
Described sheet metal is heated to Ac 3more than transformation temperature and after the temperature of less than 1000 DEG C,
At least for the 1st shaped region and the 2nd shaped region, one reinstates mould carries out punching press thus the cooling and the shaping that start average cooling rate more than 20 DEG C/sec,
1st shaped region terminates to be shaped below the temperature of low 50 DEG C than martensite start temperature, temperature range below the temperature that 2nd shaped region is cooled to start low 100 DEG C of temperature than bainitic transformation and more than martensite start temperature, and the time of staying in described temperature range is set to more than 10 seconds and terminates to be shaped.
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