CN108118242A - For the method for thermoforming steel blank - Google Patents

For the method for thermoforming steel blank Download PDF

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Publication number
CN108118242A
CN108118242A CN201711219940.XA CN201711219940A CN108118242A CN 108118242 A CN108118242 A CN 108118242A CN 201711219940 A CN201711219940 A CN 201711219940A CN 108118242 A CN108118242 A CN 108118242A
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temperature
steel
blank
preferable
equal
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托马斯·詹姆斯·泰勒
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Co Ltd Of Tata Steel Britain
Tata Steel UK Ltd
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Co Ltd Of Tata Steel Britain
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    • 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
    • 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
    • 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
    • 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
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—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
    • 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

Abstract

The present invention relates to a kind of products that steel blank is thermoformed into the mechanical performance with enhancing, such as the method for the automobile component with improved ductility and impact flexibility and the thermoformed articles obtained by the method.

Description

For the method for thermoforming steel blank
Technical field
The present invention relates to a kind of product that steel blank is thermoformed into the mechanical performance with enhancing, such as with improvement The method of the automobile component of ductility and impact flexibility and the thermoformed articles obtained by the method.
Background technology
The recent progress obtained in terms of advanced high strength steel (AHSS) and unimach (UHSS) is developed causes vapour Vehicle manufacturer can improve the crash-worthiness of automobile body components, and pass through and reduce specification (down gaug ing) to mitigate weight. However, the AHSS and UHSS of cold forming nevertheless suffer from the limitation of formability, and cold and thermoforming AHSS and UHSS still by To the limitation of ductility and impact flexibility.
In the trial for solving the problems, such as formability, thermoforming is developed and (has been also referred to as drop stamping, pressure is quenched and molding is quenched Fire).It is documented in for the first time GB1490535 suitable for the basic principle of thermoforming technology and steel compositions.
In the typical thermoforming process for using boron steel composition, blank is subjected to stove heat and Austria at 900-950 DEG C Family name's body is transferred to shaping jig from stove, and strikes out required part geometry.The ultimate tensile strength R of blankm< 200MPa, and breaking elongation A>50%.Finally with>The molding of molding blank is quenched into 100- by the average cooldown rate of 30 DEG C/s 200 DEG C, and uniform martensitic microstructure is obtained, while it suffers restraints in shaping jig.Final martensite fraction Usually show yield strength Rp0.2>1100MPa, ultimate tensile strength Rm>1500MPa and breaking elongation A<8%.Drop stamping Boron steel component generally includes to form the anti-intrusion structural body parts of " safe unit ", such as roof column, door beams and insurance Lever reinforcement.The high temperature austenite microscopic structure of flexible relative and ductility allows to reduce specification and loss of weight during shaping, Forming limit is not influenced simultaneously, in addition compared with cold forming, allows partial consolidation, and then increases structural strength and improves processing effect Rate, because reducing engagement/welding.It is several on releasing parts during quenching when higher than ferrite recrystallization temperature profile What constraint and the martensite transfor mation of moulding stress eliminate rebound, generate geometric accuracy.Compared with using cold forming component, most The superhigh intensity martensitic microstructure obtained in terminal part part allows to reduce specification (loss of weight) while improves anti-invasion crash-worthiness.Boron Advantage of the steel in drop stamping application is attributed to (quenching) quenching degree (be attributed to boron add), and then be attributed to can be by relatively low The martensitic microstructure for the superhigh intensity that component (lean) chemical composition obtains.Although however, drop stamping martensite boron steel pair Excellent mechanical performance is provided in anti-invasion crash-worthiness, still, limited ductility, and then the generation of limited toughness is excessively poor Impact energy absorbs crash-worthiness.
It is thus impossible to form the impact energy absorbing structure body component (such as mud guard and longitudinal beam) in " wrinkle area " profit The advantages of with the boron steel of drop stamping and drop stamping technique.Usually for example change induced plasticity (TRIP) by ferritic steel or multi-phase Steels Component as steel cold forming.
In order to meet requirement of the auto industry for lighter but safer vehicle, the steel part with such performance is deposited In lasting demand：Improved mechanical performance, such as improvement tensile strength, ductility for impact energy absorption crash-worthiness And impact flexibility, while excellent formability is shown so that reduction specification is possibly realized, again while showing excellent Dimensional accuracy (minimum or without rebound).
The content of the invention
It is contemplated that find appropriate steel compositions and simultaneous with Ultra-Drawing intensity for being thermoformed into steel blank Have high ductibility and and then excellent impact energy absorb the ameliorative way of the combined shaping product of crash-worthiness, and for routine Thermoforming boron steel and the multi-phase Steels of cold forming do not have disadvantages mentioned above.
It is therefore an object of the present invention to it provides a kind of for steel blank to be thermoformed into the method for product and is suitable for The steel compositions of the method, wherein compared with conventional thermoforming boron steel and cold forming multi-phase Steels, which has excellent Mechanical performance (be used for anti-intrusion crash-worthiness), the ductility of enhancing and and then improved toughness, thus with improved impact energy Amount absorbs crash-worthiness.
It is used to steel blank being thermoformed into for impact energy absorbing structure it is a further object to provide one kind The method of the product of body component compared with conventional cold forming multi-phase Steels, shows minimum rebound or does not spring back, therefore Show improved dimensional accuracy.
It is a further object to provide it is a kind of by steel blank be thermoformed into well can coating product Method.
It is a further object to provide a kind of for steel blank to be thermoformed into the method for product, make reduction specification It is possibly realized with loss of weight, while improves impact energy and absorb crash-worthiness.
According to the present invention, comprise the following steps for steel blank to be thermoformed into the method for product：
(c) steel blank of heating is molded into product in shaping jig, and it quenches from temperature T2 in time period t 3 Fire applies pressure to T3, wherein shaping jig to steel blank；
(d) product is cooled to temperature T4, wherein shaping jig not from temperature T3 in shaping jig in time period t 4 Any pressure is applied to steel blank,
(e) product is quenched into temperature T5, wherein shaping jig pair from temperature T4 in shaping jig in time period t 5 Steel blank applies pressure.
Inventor can be obtained it has been found that by the way that the blank of heating is molded into product with said sequence with enhancement The combined shaping product of energy.Particularly, compared with using conventional thermoforming boron steel and cold forming multi-phase Steels, which shows excellent Different impact energy absorbs crash-worthiness, and then shows and absorb the reduction specification of crash-worthiness and loss of weight chance based on impact energy.
In common drop stamping technique, steel blank is simply molded into desired geometry, then die quenching To the near-ambient temperature occurred to " complete " transformation of martensite.Therefore, final component shows horse completely or almost completely Family name's body microscopic structure.
It is surprisingly found by the inventors that by from the thermoforming steel removal tool pressure with unique microscopic structure, Ke Yi Die quenching is interrupted within the temperature range of between Ar1 and Ms, and therefore obtains the tool pressure thermoforming of improved mechanical performance Steel part.The product shows mechanical performance, such as tensile strength, the ductility of the enhancing for impact energy absorption crash-worthiness And impact flexibility, while excellent formability is shown so that reduction specification is possibly realized, and shows excellent size Precision (minimum springs back or without rebound).In the context of the present invention, removal tool pressure means removal/opening thermoforming work The punch of tool, but thermoformed articles is remained in mold.Once tool pressure has removed, component is retained in shaping jig In, but without applying tool pressure, therefore temperature range to 200-400 DEG C of the cooldown rate between Ar1 and Ms is relatively slow. In slow air cooling to during 200-400 DEG C, bainite ferrite and retained austenite are generated in microscopic structure.It is extensive Then multiple tool pressure takes out the component to continue die quenching to 100-200 DEG C from instrument.In the context of the present invention In, recovering tool pressure means after punch and slow air cooling is opened, and closes the punch of hot forming tool, right again Thermoformed articles in hot forming tool applies pressure.In this process, we obtain the retained austenites of large volume fraction (rather than forming martensite completely), to provide the microscopic structure of similar TRIP steel in final component.
In step (c), the blank of heating is molded into partially or completely uniform austenite in shaping jig The geometry of the required component of microscopic structure, and at the same time being quenched in the case where applying tool pressure in time period t 3 from temperature T2 To temperature T3.
Temperature T3 is in the chemical specificity Ar1 and Ms temperature ranges of steel compositions.Inventor is it has been found that when T3 is in 400- When in the range of 600 DEG C, good effect has been achieved.When T3 is less than 400 DEG C, atoms permeating rate is relatively low, therefore from shellfish The carbon distribution (partitioning) of family name's body ferrite to austenite reduces.When T3 is higher than 400 DEG C, atoms permeating rate is more Height, and the carbon slave bainite ferrite to austenite of obvious degree is allowed to distribute, to stablize Ovshinsky at ambient temperature Body (so as to retain austenite in final microscopic structure).When T3 be higher than 600 DEG C when, can occur pearlite formed rather than Bainite ferrite and retained austenite.When T3 is when in the range of 400-580 DEG C, better result has been obtained.Advantageously, T3 In the range of 450-550 DEG C.
Time t3 is determined by the quenching rate realized between temperature T2 and temperature T3.It has been found by the present inventors that as t3 etc. When applying the quenching rate of 50 DEG C/more than s when 10s and/or between T2 and T3, good effect has been obtained. Preferably, quenching rate is equal to or more than 100, more preferably equal to or greater than 150, most preferably equal to or greater than 200 DEG C/s.It is less than 50 DEG C/s, austenite can be changed into pearlite and pro-eutectoid ferrite while cooling, so as to prevent the shape in final microscopic structure Into martensite, bainite and retained austenite.Cooldown rate does not have the specific upper limit.Preferably, t3 is equal to or less than 8s, more excellent Choosing is equal to or less than 5s, most preferably equal to or less than 4s.Advantageously, t3 is equal to or less than 2s.
Pass through conductibility of the blank from the heating constrained under tool pressure in shaping jig to shaping jig in itself Heat transfer process and quenching to temperature T3 of the product in shaping jig occurs.Shaping jig may or may not show collection Into cooling duct to enhance conductive heat transfer rate.
In step (d), product occurs from temperature T3 to the Slow cooling of temperature T4, and profiled part is in time period t 4 It rests in shaping jig, but does not apply shaping tool pressure, that is, open/remove punch.While opening/removal punch and Period, the residual heat and latent heat of phase change collected by shaping jig in the quenching from temperature T2 to T3 and formative stage can lead to It crosses convective heat transfer to circulate in profiled part, so as to allow the Slow cooling of thermoformed articles.Only carried out by air cooling Slow cooling from T3 to T4 minimizes cooldown rate by the residual heat in shaping jig, and passes through convective heat transfer Latent heat of phase change is made to circulate in molding component.Therefore, by implementing the pressure or attached of additional heating device after temperature T3 The currently used of heating is unnecessary.During natural air cooling step, the bainite ferrite of carbides-free is formed, And retain austenite.In the context of the present invention, natural air cooling means only through the air of thermoforming working environment Cool down the component of thermoforming.
Temperature T4 can be higher than chemical specificity Ms temperature, the chemistry between chemical specificity Ms and Mf temperature or less than steel Specificity Mf temperature.The preferred temperature range of above three determines the volume fraction of the martensite formed in final quenching.
Inventor also obtains good result it has been found that when T4 is when in the range of 200-400 DEG C.It slowly cools to It can cause austenite decomposition less than 200 DEG C into bainite.Ensure that austenite is retained in most from the temperature rapid quenching higher than 200 DEG C In whole microscopic structure.T4 does not have the specific upper limit.In practice, it will be difficult T4 to be maintained to be higher than 400 DEG C, because at us It is formed before the bainite ferrite of apparent volume fraction, temperature can be fallen below 400 DEG C by natural air cooling.It is preferred that T4 For 300-380 DEG C, more preferable 320-370 DEG C.
Time t4 is by the remaining heat accumulation and management decision in shaping jig.During time t4, delay with from temperature T3 To temperature T4 non-isothermal bainite transformation occurs for slow cool down, indicates and is changed into bainite ferrite for austenite, from bainite iron The carbon of ferritic to remaining austenite distributes, and the solute concentration of carbon of remaining austenite increases and remaining austenite is steady at ambient temperature Fixedization.Inventor has obtained good effect it has furthermore been found that when t4 is equal to or more than 60s.It, can when t4 is less than 60s It can will form insufficient retained austenite.If t4 is longer than 180 seconds, this will not be beneficial, because must apply pressure Heating is with delay chilling.T4 is preferably in the range of 60-180 seconds, preferably in the range of 100-180 seconds, more preferably in 120- In the range of 180 seconds.Present inventors have further discovered that when the cooldown rate between T3 and T4 is when in the range of 2-10 DEG C/s, Good effect is achieved.Preferably, cooldown rate is in the range of 2-8 DEG C/s.Advantageously, cooldown rate is in 2-5 DEG C/s In the range of.
In step (e), shaping blank is quenched into temperature T5 from temperature T4, wherein during finally temperature T5 is quenched into Austenite can be fully retained or significant volume fraction can be changed into martensite.Retained austenite volume fraction is without spy Fixed lower limit or the upper limit.However, after final quenching, preferably retain not less than 5% in final component, more preferably no less than 10 bodies The austenite of product %.If there is no retained austenite, then the transformation of stress/strain induction is not had during collision accident. It has been found by the present inventors that when there are during 5% or more retained austenite, can realize significantly should during collision accident The transformation of power/strain-induced.Preferably, the retained austenite in thermoformed part is at most 20 volume %.By from instrument Conductive heat transfer effect of the slab constrained under pressure in shaping jig to shaping jig in itself is quenched.Shaping Instrument may or may not show integrated cooling duct to enhance conductive heat transfer rate.
It has been found by the present inventors that when T5 is when in the range of 20 to 200 DEG C, good result is obtained.When T5 is higher than 200 DEG C when, austenite is decomposed into bainite, without being kept under environment temperature.In addition, can higher than 200 DEG C by any shaping Any martensite be tempered, so as to reduce tensile strength.Advantageously, T5 is in the range of 20-100 DEG C.
Time t5 is determined by the quenching rate realized between T4 and T5.Inventor it has been found that when t5 be equal to or less than 8s when, Good result is obtained.When t5 is equal to or less than 4s, better result is realized.Advantageously, t5 is equal to or less than 2s. It has been found by the present inventors that when cooldown rate is at least 50 DEG C/s, good result is had been achieved with.When cooldown rate is at least During 100 DEG C/s, better result can be realized.Advantageously, cooldown rate is at least 150 DEG C/s.
Step c) as described above is necessary for disclosed invention to order e).
For obtain part or uniform austenitic microscopic structure preferred embodiment in, thermoforming step (c) it Before, the method according to the invention comprises the following steps：
(a) steel blank is heated to temperature T1, and by the blank of heating in T1 retention times section t1；
(b) blank of heating is transferred to shaping jig from heating unit optionally in time t2, the base heated therebetween The temperature of material is reduced to temperature T2 from temperature T1；
In the method according to the invention, the intermediate of steel band or sheet material as subsequent step is provided.Mark can be passed through Quasi- casting technique obtains steel band or sheet material.
Steel band or sheet material are cut into steel blank, are then heated to temperature T1 durations t1.It can also use pre- Molding steel blank.Can preforming blank be partly or entirely molded into desired geometry, preferably in environment temperature Lower progress.
Heating unit can be electric furnace or gas furnace, resistive heating device, infrared induction heating unit or it is any other plus Thermal.
Temperature T1 is higher than the chemical specificity Ac1 temperature of steel to form ferrite austenitic microstructure.
In a more preferred embodiment, T1 is higher than chemical specificity Ac3 temperature to generate with the complete of uniform carbon distribution Complete or almost uniform austenitic microstructure.When microscopic structure is uniform austenitic microstructure, formability It improves.
It has been found by the present inventors that when T1 is at least 710 DEG C, good result has been obtained.Preferably, T1 is in 850- In the range of 1150, more preferable 980-1100 DEG C, most preferably 1000-1050 DEG C.
Inventor is it has furthermore been found that can be with combination temperature T1 and sotck thinkness selection retention time t1, described in controlling The austenite grain growth of steel and relevant hardenability.This means compared with relatively low sotck thinkness, in order to needed for obtaining (to It is fixed) austenite grain size, larger sotck thinkness will need longer time t1 and/or higher temperature T1.Time t1 At the end of austenite grain size will influence hardenability, wherein larger austenite grain size (corresponds to smaller Ovshinsky Body boundary surfaces accumulate) quantity of the nucleation site that pro-eutectoid ferrite while cooling is formed is reduced, which thereby enhance hardenability. Then, the degree of hardenability will influence the formation of microstructure evolution, i.e. pro-eutectoid ferrite in cooling procedure.Therefore t1 etc. In or less than 15 minutes.In preferred embodiments, inventor realizes it has been found that when time t1 is equal to or less than 10 minutes Good effect.Advantageously, t1 is 3-5 minutes, to increase the time of technique and energy efficiency.
In preferred embodiments, the heating that steel billet in step (a) expects temperature T1 is carried out, and steel blank stays in shaping In instrument.It is this with electrode (so as to provide resistance heating in the shaping jig) application contacted with the steel blank in shaping jig " heating (in pressheating) in press " technology.This adaptability show after temperature T1 and time t1 shaping immediately and It quenches and may not be realized (i.e. time (t2)=0s) from temperature T1 to the cooling of temperature T2.This adaptability allows higher Hardenability and the pro-eutectoid ferrite of the steel compositions for relatively low component is avoided to be formed.Therefore, it is possible to use relatively low component Chemical composition without formed pro-eutectoid ferrite.This is by the economy for improving steel blank, formability, solderability and can coat Property.Furthermore, it is possible to realize shorter time period t 1 and relatively low temperature T1, so as to generate thinner austenite grain size and from The increased carbon of bainite ferrite to austenite distributes rate, and any sacrifice without hardenability.Thinner microscopic structure production Raw improved toughness, again improves process efficiency and economy.
Optionally, in time period t 2 (step (b)) shaping jig is transferred to from heating unit by the blank of heating.Turning It, can be cold from temperature T1 by blank by the effect of natural air cooling and/or any other available cooling means during shifting But temperature T2 is arrived.
The blank of heating can be transferred to from heating unit by Autonomous Robotic System or any other transfer method Shaping jig.
Temperature T2 is preferably above the chemical specificity Ar1 temperature of steel to show austenite-ferrite microscopic structure.More In preferred embodiment, T2 is higher than chemical specificity Ar3 temperature to show uniform austenitic microstructure.As described above, When being molded and quenching beginning, completely or almost completely austenitic microstructure is preferred for optimal formability.
In preferred embodiments, inventor is it has been found that the time t2 of delay or the temperature T2 less than Ar3 allow to form elder generation Eutectoid ferrite, in view of the mechanical performance and properties of product of end article, this is desired, so as to which the surrender for generating relatively low is strong The ratio between degree, higher yield strength and ultimate tensile strength and improved impact energy absorb crash-worthiness.
Inventor also achieves good result it has furthermore been found that when T2 is higher than Ar3 temperature.Particularly, which has Have and the completely or almost completely relevant excellent formability of austenitic microstructure so that can be molded in single stroke non- Often complicated shape.
Time, t2 was determined by transmission method.As described above, resistance heating can eliminate time t2 (t2=0s) in press.From The more conventional robotic delivery system of external heating device to shaping jig usually requires 12 seconds.But in view of burn into technique Efficiency and quenching degree, shorter haulage time are beneficial.
Selection time t2 can also be combined with T1, t1 and T2, to control micro- group of the steel when being molded and quenching beginning The evolution knitted.For example, higher temperature T1 and/or longer time t1 will generate larger austenite grain during time t2 It grows and postpones the formation of pro-eutectoid ferrite.Therefore, it is possible to use shorter time t2 for formed during time t2 to Determine the pro-eutectoid ferrite of degree.In addition, if needing lower temperature T2 (pro-eutectoid ferrite to be allowed to be formed), then necessarily need Longer time t2 is wanted to reach temperature T2.As described above, when being molded and quenching beginning, completely or almost completely austenite is shown Micro-assembly robot is preferred for optimal formability.Present inventors have further discovered that when t2 is equal to or less than 10s, also obtain Good effect.Preferably, t2 is equal to or less than 8s, more preferably equal to or less than 6s.
It is a further object to provide a kind of steel compositions suitable for any method described herein.
According to the present invention, steel blank includes following element in terms of weight % (wt%)：
C：0.05-0.50, preferably 0.15-0.45, most preferably more preferable 0.15-0.35,0.15-0.25.
Mn：0.05-3.00, preferably 1.00-2.50, more preferable 1.00-1.50.
Si:≤ 2.0, preferably≤1.0, more preferable 0.25-0.75, most preferably 0.25-0.50.
Al:≤ 2.0, preferably≤1.0, more preferable 0.25-0.75, most preferably 0.25-0.50.
P:≤ 0.17, preferably≤0.1, more preferable 0.02-0.07, most preferably 0.02-0.05
S:≤ 0.002, preferably≤0.001.
B:≤ 0.01, preferably 0.001-0.005, more preferable 0.003-0.005.
N:≤ 0.01, preferably 0.001-0.005, preferably 0.001-0.003.
Nb:≤ 0.1, preferably 0.02-0.04, more preferable 0.02-0.03.
Ti:≤ 0.1, preferably 0.02-0.04, more preferable 0.02-0.03.
Cr:≤ 1.0, preferably 0.2-0.4, more preferable 0.2-0.3.
And choosing any one kind of them selected from V, Mo, Co, W and other microalloy rare earth elements (REM) or multiple element, total amount Equal to or less than 1.0wt%, remaining is Fe and inevitable impurity.
According to preferred embodiment, steel blank is made of above-mentioned element, in terms of weight % (wt%).
The reason for amount of main composition element, is following (in terms of wt%).
C：0.05-0.50.Carbon content is at least 0.05wt% to provide enough gap solution strengthening, enough hardenabilitys The sufficiently stable property of austenite at ambient temperature, while retain enough low carbon equivalents and be used for motor-driven resistance spot welding technique.It is excellent The carbon content scope of choosing shows a series of products of strength-ductility value scope according to the present invention by providing.It is preferred that carbon contains Amount is in the range of 0.15-0.45.In a more preferred embodiment, carbon is in the range of 0.15-0.35.Advantageously, carbon exists In the range of 0.15-0.25.
Mn：0.05-3.00.Manganese content be at least 0.05 with provide enough displacement solution strengthening, enough hardenabilitys and The sufficiently stable property of austenite at ambient temperature, while the segregation of Mn during casting is minimized, while retain enough low carbon Equivalent is used for motor-driven resistance spot welding technique.Inventor is provided aobvious it has been found that the scope of manganese content is combined with the scope of carbon content The product of some strength-ductility value scope is shown.In preferred embodiments, Mn contents are equal to or less than 2.50.Favorably Ground, manganese is in the range of 1.00-1.50.
Silicon, aluminium and phosphorus content prevent precipitation of the carbide in carbon enrichment austenite, so that the Ms temperature of remaining austenite Degree falls below environment temperature and retains austenite at ambient temperature and is possibly realized.Silicon, aluminium and phosphorus content is selected to provide Carbide Precipitation delay, the dynamics of non-isothermal bainite transformation, solderability, can coating, economy and manufacturing capacity and use Conventional steel-making and the optimum balance of sheet material/band processing infrastructure.
Si≤2.0：Silicone content is selected as main Carbide Precipitation delayed-action activator, but is limited to 2.0 maximum, so as to The surface of hot rolling, cold rolling and the coating of obstruction band steel is made to combine the formation minimum of silicate.Silicon is preferably equal to or smaller than 1.0.It is highly preferred that silicon is in the range of 0.25-0.75.In the most preferred embodiment, silicon is in the scope of 0.25-0.50 It is interior.
Al≤2.0：In order to keep solderability and make steel and during casting minimizing " nozzle blockage ", aluminium is limited in 2.0 maximum.Aluminium content is preferably at least 0.25 to increase the dynamics of non-isothermal bainite transformation so that restriction when Between after t4, the austenite of suitable volume fraction can be retained at ambient temperature.Preferably, Al is limited in 1.0 maximum, more It is preferred that aluminium is in the range of 0.25-0.75 weight %.Advantageously, aluminium is in the range of 0.25-0.50.
P≤0.17：Phosphorus content is limited in 0.17 maximum, and there are phosphorus to limit silicon and aluminium content, while still carry Postpone for satisfactory Carbide Precipitation.In preferred embodiments, phosphorus is in the range of 0.02-0.07.Advantageously, phosphorus In the range of 0.02-0.05, acceptable solderability is provided will pass through car gage.
Nb≤0.1：Content of niobium is limited in 0.1 maximum to form niobium carbide precipitate, and then austenite crystal is provided Particle size refines, and which increase the dynamics of non-isothermal bainite transformation.Niobium carbide can also provide precipitation strength.Niobium preferably exists In the range of 0.02-0.04.Advantageously, niobium is in the range of 0.02-0.03.
Ti≤0.1：In order to combine all nitrogen contents, Ti content is limited in 0.1 maximum, and with 3.42:1 Titanium：Nitrogen ratio forms nitridation titanium precipitate, and then Boron contents is made to remain unbonded (for quenching degree) in solid solution, this Outside, there are titanium so that all residual sulfur contents combine, and with titanium：Sulphur 1.5:1 ratio forms vulcanization titanium precipitate.In all nitrogen After having been combined with sulphur, remaining " surplus " titanium will be combined to provide carbonization titanium precipitate with carbon, and then provide precipitation strength.Excellent In the embodiment of choosing, titanium is in the range of 0.02-0.04.Advantageously, titanium is in the range of 0.02-0.03.
Cr≤1.0：Chromium content is limited at most 1.0 to contribute to hot-workability and corrosion resistance.Chromium is preferably in 0.2- In the range of 0.4.Advantageously, chromium is in the range of 0.2-0.3.
B≤0.01：Boron contents are limited in 0.01 maximum to improve hardenability, and and then from temperature T1 to temperature It spends the cooling period of T2 and the formation of pro-eutectoid ferrite is avoided during temperature T3 is quenched into.Boron is preferably in 0.001- In the range of 0.005.Advantageously, boron is in the range of 0.003-0.005.
N≤0.01：Nitrogen content is limited in 0.01 maximum so that boron nitride to be prevented to be precipitated and forms undesirable TiN It minimizes, wherein TiN is no advantage to mechanical performance.N has no significant effect mechanical performance.Nitrogen is preferably in 0.001-0.005 In the range of, more preferably in the range of 0.001-0.003.
S≤0.002.Sulphur is a kind of impurity, and needs to minimize so that harmful non-metallic inclusion minimizes.Therefore, Sulfur content is limited in 0.002 maximum, preferably 0.001 maximum.
Steel band composition can optionally comprising a small amount of one or more alloy elements, such as V, Mo, Co, W or Rare earth element.
Can be no more than the total amount of 1.00 weight % addition V, Mo, Co, W and other microalloy rare earth elements so as to from this It is benefited in the known performance improvement effect of a little elements.
In preferred embodiments, steel microscopic structure composition is to show the ability that stress/strain induces transition effect Multi-phase Steels, preferably TRIP or complex phase (CP) steel.More specifically, steel be it is a kind of be suitable for hot-forming advanced high intensity TBF (TRIP aids in bainite ferrite) steel product, as the boron steel substitute for automobile application.
It is surprisingly found by the inventors that the thermoforming process is applied to class TRIP steel compositions, cause to lure stress/strain (i.e. the bainite ferrite of carbide-containing is not formed and Austria for the ability of the transition effect of hair and TRIP steel microscopic structures evolution principle Family name's body retains) thermoformed articles that combines.The thermoforming TRIP steel part of acquisition is shown in the range of 5 to 20 volume % Significant retained austenite volume fraction and stress/strain induce the ability of transformation.Compared with traditional cold forming TRIP steel, Optimal austenite volume fraction is established after forming process and stress/strain induces transformation ability, therefore it is present in product In, and austenite volume fraction and stress/strain induce transformation ability and are not finished in forming process.This make reduction specification and Loss of weight is possibly realized, while is improved impact energy and absorbed crash-worthiness.
In addition to that mentioned above, compared with traditional drop stamping boron steel, product of the invention shows the machinery significantly improved Performance, it is suitable with traditional TRIP steel before cold forming, and can realize that impact energy absorbs crash-worthiness.
Present inventors have further discovered that the thermoformed articles obtained by the present invention has at least ultimate elongation of 750MPa Intensity (Rm) and/or at least 16% breaking elongation and/or at least R of 20000MPa%m× A products, and in final component It shows that improved impact energy absorbs anti-crash-worthiness, and then shows the potentiality of reduction specification and loss of weight based on crash-worthiness. Preferably, RmIn the range of 750-1500, more preferably in the range of 900-1300, the model most preferably in 900-1150MPa In enclosing.Preferably, breaking elongation is in the range of 16-35, more preferably in the range of 25-35, the scope most preferably in 29-35% It is interior.Preferably, Rm× A products are in the range of 20000-30000MPa%, the scope more preferably in 24000-30000MPa% It is interior, most preferably in the range of 26000-28000MPa%.
According to preferred embodiment, coating is provided to steel band, sheet material, blank, preforming blank or product.To steel band Material, sheet material, blank or preforming blank addition coating can carry out before thermoforming process or after thermoforming process, and And with minimizing the oxidation of steel and/or for final thermoformed part provide the moon when being exposed to oxidizing atmosphere at high temperature The purpose of pole corrosion protection.
In a preferred embodiment, steel band, sheet material, blank, preforming blank or product are coated with zinc base coat, aluminium silicon substrate Coating or organic group coating.
Zinc base coat is the coating of zinc-plated or zinc-plated annealing.Although coating can be applied in various ways, it is preferred that making Galvanizing by dipping is carried out with the GI coatings bath of standard.Other Zn coatings can also be applied.One example is included according to WO 2008102009 Zn alloy coats, particularly by 0.3-4.0 weight %Mg and 0.05 weight %-6.0 weight %Al and optionally The kirsite of one or more other elements of at most 0.2 weight % and inevitable impurity and the zinc of surplus composition applies Coating.The a small amount of of 0.2 weight % can be usually less than from Pb or Sb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr or Bi selection The additional elements of addition.Usually addition Pb, Sn, Bi and Sb is spent with forming zinc.Preferably, the total amount of the additional elements in kirsite At most 0.2%.These a small amount of additional elements for will not be changed in common application with any significance degree the coating or The property of the bath.Preferably, when the Zinc alloy coated middle additional elements in the presence of one or more, each with≤0.02 weight %'s Amount exists, and preferably each exists with the amount of≤0.01 weight %.Usually only add additional elements with prevent in bath with fused zinc Alloy forms scum silica frost or zinc flower is formed in coat.
Article according to the invention shows coat good adhesiveness, after application with good appearance With excellent corrosion resistance.
It is a further object to provide the products obtained by either method as described herein.
According to preferred embodiment, steel sheets or steel band are the steel sheets or band of hot rolling or cold rolling.
It is a further object to provide a kind of polyphase microstructure steel, cause the intensity improved simultaneously and extension Property.By providing above-mentioned steel compositions and passing through the careful control acquisition for applying thermo-mechanical processi method as described above according to this The polyphase microstructure of invention.
Inventor is it has been found that the final microscopic structure of steel includes bainite ferrite, (residual) austenite, optional geneva Body and/or pro-eutectoid ferrite.In preferred embodiments, microscopic structure may further include pro-eutectoid ferrite.According to The present invention determines to induce the ability of transformation and optimization austenite volume fraction for stress/strain after forming process, therefore It is present in product.Austenite volume fraction to the stress/strain for arriving martensite during collision accident for inducing transformation It is optimization, absorbs crash-worthiness so as to generate the impact energy of optimization.If to be different from any other order disclosed herein The step is set, then will not realize desired microstructure evolution.
In a preferred embodiment, final microscopic structure is included in terms of volume fraction (volume %) (amounts to and adds To 100)：
0-75 pro-eutectoid ferrites, preferably up to 30, most preferably 0.
10-30 bainite ferrites, preferably 20-30.
5-20 retained austenites, preferably 10-20.
0-75 martensites, preferably 25-75, most preferably 25-50.
In a more preferred embodiment, final microscopic structure is made of above-mentioned volume fraction (volume %).
Pro-eutectoid ferrite：0-75.There may be pro-eutectoid ferrite.However, it is that the yield strength improved (is bent in purpose Take the ratio between intensity and ultimate tensile strength) in the case of, it is necessary to limit the fraction of pro-eutectoid ferrite.It is surprising It is, using the appropriate balance of other microstructural components (most significantly retained austenite), it is hard still can to obtain high processing Change and tensile ductility.Higher than this limit, final microscopic structure will be free from enough bainite ferrites and/or geneva Body, therefore ultimate tensile strength will be too low.The pro-eutectoid ferrite of big number also leads to low initial yield intensity (low surrender The ratio between intensity and ultimate tensile strength).Preferably, pro-eutectoid ferrite exists with the amount of at most 30 volume %.Advantageously, first altogether Analysis ferrite is 0 volume %.This provides the optimization volume fraction (for ultimate tensile strength) and retained austenite of martensite (transition effect induced for stress/strain), and therefore maximum R is providedm× A products.Additionally it is believed that there is no pro-eutectoids Ferrite, and then it is characterized in showing that the microscopic structure of the microscopical compositon of more like mechanical performance is conducive to edge ductility/hole Expanding ability (HEC).
Bainite ferrite：10-30.Bainite ferrite not only provides intensity, but also it is also to retain austenite that it, which is formed, Prerequisite.During more than the upper limit, it will the martensite of Shortcomings, therefore ultimate tensile strength can be too low, and advising The bainite ferrite more than 30 volume % can not possibly be generated in fixed heat treatment.In the presence of silicon, aluminium and/or phosphorus, bayesian The ferritic carbon for forming driving to austenite phase of body distributes, and makes the carbon enrichment in austenite phase is horizontal to allow at ambient temperature Form (Asia) stable phase.Bainite ferrite also has the advantages that better than the martensite as hardening constituent：It causes to strain less Minute yardstick navigates to softer phase, therefore improves the resistance to fracture compared with dual phase steel.Preferably, bainite ferrite is in 20- In the range of 30, to realize more fully stabilization of austenite.
Martensite：0-75.Martensite may be formed during the last rapid quenching of thermoforming process.Work as martensitic volume When fraction is equal to or less than 75 volume %, the optimization balance of ultimate tensile strength and ductility is obtained.It is completely absent martensite It is favourable for maximum ductility, wherein microscopic structure is by complete pro-eutectoid ferrite, bainite ferrite and/or retained austenite Family name's body is formed.By the abundant carbon enrichment of the austenite during bainite ferrite/retained austenite is formed, can realize completely There is no martensites so that the martensite start temperature of residue/retained austenite falls below environment temperature, therefore heat into During last rapid quenching during type, no austenite is changed into martensite.Martensite is preferably 25-75.Advantageously, horse Family name's body is in the range of 25-50.
Retained austenite：5-20.Metastable retained austenite fraction ensures the balance combination of intensity and ductility.Part The transition effect that ground is induced by stress/strain, retained austenite enhancing ductility, this shows as increasing with work hardening index Higher plastic strain is added to, the increase of the uniform elongation and breaking elongation observed.During less than 5 volume %, it will not realize The aspiration level of ductility according to the present invention and/or uniform elongation.The upper limit is set by composition.Preferably, retained austenite Body is in the range of 10-20.
All or part of basis can be carried out in the controlled inert atmosphere of hydrogen, nitrogen, argon or any other inert gas The method of the present invention, to prevent the oxidation of the steel and/or decarburization.
Preferably by punching press/pressing operation carry out it is according to the present invention blank is molded into required part geometry, Wherein punch and mold of the shaping jig with represents that the steel is located in cooperation before punch and mold closing/cooperation Between punch and mold, so as to by the required part geometry of the steel punching press/be pressed into.However, current method is also fitted It is molded for other forming methods such as roller.
In addition to the advantages described above, the product manufactured by the thermoforming process is characterized in that Ultra-Drawing intensity, answers Miscellaneous shape shows minimum or without rebound, and realizes that high yield strength increases, for spray painting.Based on this A little advantages can obtain the excellent impact property of steel part.
For using the final products of the present invention, that is, show that retained austenite and stress/strain induce transformation The hot stamping part of ability (being attributed to air cooled non-isothermal bainite transformation), can be used as the component of automotive body structure, Referred to as white body (BiW), for absorption ability for impact energy.Except automobile BIW is applied, product of the invention can be also used for needing In the other application for wanting absorption ability for impact energy.
Description of the drawings
The TRIP800 CR steel bands that it is 1.2mm using the specification of thermoforming process according to the present invention that Fig. 1, which is shown, The Time-temperature cycle.
Fig. 2 is the amplifier section in the Time-temperature cycle of Fig. 1, shows and stove is opened under T1 and is opened under temperature T5 Process cycle between shaping jig.
Fig. 3 is the amplifier section in the Time-temperature cycle of Fig. 1, shows and shaping work is opened under temperature T4 and temperature T5 Process cycle between tool.
Fig. 4 a-c show the scanning of the final thermoformed articles of thermoforming TRIP800 CR steel part according to the present invention Electron micrograph.
Ac1：The temperature of austenite is initially formed during heating.
Ac3：During heating, the temperature at the end of ferrite changes to austenite.
Ar3：During cooling, austenite starts to transform to ferritic temperature.
Ar1：During cooling, the temperature that austenite terminates to ferrite+cementite transformation.
Ms：During cooling, austenite starts to transform to the temperature of martensite.
Mf：During cooling, the temperature that austenite terminates to martensite transfor mation.
It can be tested by swellability measurement and determine above-mentioned critical phase transition temperature.
Specific embodiment
Refer to the attached drawing is illustrated into the present invention by following non-limiting examples.
The TRIP800 steel bands for the cold rolling that specification is 1.2mm are provided by conventional and known method.Steel band is with weight Amount % meters contain：C：0.186；Mn：1.330；Si：1.670；P：0.008；Al：0.131；N：0.004；Nb：0.001；Ti： 0.014；Cr：0.026, surplus is Fe and inevitable impurity.Steel band is heated under 1006 DEG C (T1), is kept in T1 194.4 seconds (t1), and in 11.3 seconds (t2) hot forming tool is transferred to from stove.During transfer, it is cold by exposure to air But, steel band is cooled to 820 DEG C (T2).Steel band is put into the hot forming tool with temperature T2, while in 0.2 second (t 3) drop stamping and die quenching are to 451 DEG C (T3) in.Under temperature T3, the punch of hot forming tool, i.e. shaping jig are opened not Apply pressure, and slowly cooled to 350 DEG C (T4) in 53.2 seconds (t4).It has been recognised by the inventors that as shown in figure 3, temperature T3's Temperature rise is attributable to latent heat (martensite and/or the bainite ferrite shape of overturning (upset) and/or the phase transformation of thermocouple Into).Under 350 DEG C (T4), shaping jig is again switched off, the product of thermoforming is quenched to 100 DEG C in 6.8 seconds (t5) (T5).In temperature T5, shaping jig is opened.Fig. 4 is shown closes the instrument for the second time at 350 DEG C, observes cooldown rate Delay (inflection point in cooling curve).It has been recognised by the inventors that delay may be due to the overturning of thermocouple and/or due to forming horse Latent heat of phase change caused by family name's body.
Table 1 gives the temperature value T1, T2, T3, T4 and T5 (being represented with DEG C) during process according to the invention, table 2 Give time period t 1, t2, t 3, t4 and t5 (using the second to represent).
Table 1
T1 T2 T3 T4 T5
1006 820 451 350 100
Table 2
t1 t2 t3 t4 t5
194.2 11.3 0.2 53.6 6.8
Fig. 4 a-c show the scanning electron microscope (SEM) obtained using 6100 scanning electron microscope of JEOL JSM Image.Sample is prepared by standard metallographic preparation procedure, is included in 2% nital and etches.Fig. 4 a show the overall situation The schematic diagram of microscopic structure.Fig. 4 b and 4c show the finer section of the microscopic structure under higher magnifying power.Fig. 4 b and 4c show Pro-eutectoid ferrite matrix and martensite dispersion (being annotated in such as figure) are gone out.It is considered as retained austenite that Fig. 4 b, which are also shown, The part of dispersion, and Fig. 4 c also show be considered as bainite ferrite dispersion part.SEM image confirms that class is more The microscopic structure of phase TRIP steel.

Claims (15)

1. a kind of method that steel blank is thermoformed into product, comprises the following steps：
(c) steel blank of heating is molded into product in hot forming tool, while it quenches from temperature T2 in time period t 3 Fire applies pressure to temperature T3, wherein hot forming tool to steel blank,
(d) product in hot forming tool is cooled to temperature T4, wherein hot forming tool not from temperature T3 in time period t 4 Any pressure is applied to steel blank,
(e) product in hot forming tool is quenched into temperature T5, wherein hot forming tool pair from temperature T4 in time period t 5 Steel blank applies pressure.
2. the method according to claim 1, wherein T4 are at 200-400 DEG C, preferably 300-380 DEG C, more preferable 320-370 DEG C of model In enclosing.
3. method according to claim 1 or 2, wherein time period t 4 are equal to or more than 60s, more excellent preferably in 60-180s Select 100-180s, in the range of most preferably 120-180s and/or the cooldown rate wherein between temperature T3 and T4 2-10 DEG C/ S, preferably 2-8 DEG C/s, in the range of more preferable 2-5 DEG C/s.
4. method as claimed in one of claims 1-3, wherein T5 are in the range of 20-200, preferably 20-100 DEG C.
5. according to the described method of any one of claim 1-4, wherein time period t 5 is equal to or less than 8s, preferably equal to or small In 4s, more preferably equal to or less than 2s and/or the quenching rate wherein between temperature T4 and T5 are equal to or more than 50 DEG C/s, excellent Choosing is equal to or more than 100 DEG C/s, more preferably equal to or greater than 150 DEG C/s.
6. according to the method any one of claim 1-5, before thermoforming step c), step is further included：
(a) steel blank is heated to temperature T1, and by the blank of heating in T1 retention times section t1；
(b) blank of heating is optionally transferred to shaping jig in time t2, the temperature of the blank heated therebetween is from temperature T1 is reduced to temperature T2.
7. according to the method described in claim 6, wherein T1 is at least 730 DEG C, preferably at 850-1150 DEG C, 980- is more preferably In the range of 1100 DEG C, most preferably 1000-1050 DEG C and/or wherein time period t 1 is equal to or less than 15 minutes, preferably 3-5 Minute.
8. according to the described method of any one of claim 1-7, which part or all preforming steel blank.
9. according to the method any one of claim 1-8, wherein the blank, preforming blank or product are provided with zinc The coating or organic group coating of base coating or aluminium silicon substrate or be designed as during thermoforming reduce oxidation and/or decarburization it is any Other coatings.
10. according to the method described in claim 9, wherein described zinc base coat is comprising 0.5-3.8 weight %Al, 0.5-3.0 Weight %Mg, optionally at most one or more additional elements of 0.2 weight %, inevitable impurity, surplus zinc coating.
11. according to the method any one of claim 1-10, wherein the steel blank is included in terms of weight % (wt%) Following element：
C：0.05-0.50, preferably 0.15-0.45, most preferably more preferable 0.15-0.35,0.15-0.25；
Mn：0.05-3.00, preferably 1.00-2.50, more preferable 1.00-1.50；
Si:≤ 2.0, preferably≤1.0, more preferable 0.25-0.75, most preferably 0.25-0.50；
Al:≤ 2.0, preferably≤1.0, more preferable 0.25-0.75, most preferably 0.25-0.50；
P:≤ 0.17, preferably≤0.1, more preferable 0.02-0.07, most preferably 0.02-0.05；
S:≤ 0.002, preferably≤0.001；
B:≤ 0.01, preferably 0.001-0.005, more preferable 0.003-0.005；
N:≤ 0.01, preferably 0.001-0.005, preferably 0.001-0.003；
Nb:≤ 0.1, preferably 0.02-0.04, more preferable 0.02-0.03；
Ti:≤ 0.1, preferably 0.02-0.04, more preferable 0.02-0.03；
Cr:≤ 1.0, preferably 0.2-0.4, more preferable 0.2-0.3；
And choosing any one kind of them selected from V, Mo, Co, W and other microalloy rare earth elements (REM) or multiple element, total amount are equal to Or less than 1.0wt%, remaining is Fe and inevitable impurity.
12. the steel part obtained by the method according to any one of claim 1-11, wherein steel part have extremely Few 750MPa, preferably 750-1500, the ultimate tensile strength R of more preferable 900-1300, most preferably 900-1150MPam。
13. steel part according to claim 12, wherein the steel part has in 16-35%, more preferable 25-35, most It is preferred that breaking elongation and/or wherein R in the range of 29-35%m× A products are in 20000-30000MPa%, more preferably In the range of 24000-30000MPa%, most preferably 26000-28000MPa%.
14. the steel part according to claim 12 or 13, wherein the microscopic structure of the steel part includes at least 5 volume % Retained austenite.
15. according to the steel part any one of claim 12-14, wherein the microscopic structure of the steel part is with volume integral Number meter (volume %) includes (adding up to 100)：
0-75 pro-eutectoid ferrites, preferably up to 30, most preferably 0,
10-30 bainite ferrites, preferably 20-30,
5-20 austenites, preferably 10-20,
0-75 martensites, preferably 25-75, most preferably 25-50.
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CN113528973A (en) * 2021-06-16 2021-10-22 首钢集团有限公司 Production method of high-plasticity hot-forming steel

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