CN103290307A - High-strength steel plate with excellent impact resistance and manufacturing method of same - Google Patents
High-strength steel plate with excellent impact resistance and manufacturing method of same Download PDFInfo
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- CN103290307A CN103290307A CN2012100445326A CN201210044532A CN103290307A CN 103290307 A CN103290307 A CN 103290307A CN 2012100445326 A CN2012100445326 A CN 2012100445326A CN 201210044532 A CN201210044532 A CN 201210044532A CN 103290307 A CN103290307 A CN 103290307A
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Abstract
The invention provides a high-strength steel plate with excellent impact resistance in case of no harm to stamping formability and a manufacturing method of the same. The high-strength steel plate is characterized by being composed of the following components in percentage by mass: 0.05-0.20% of C, less than 2.0% of Si, 0.3-3.0% of Mn, less than 0.1% of P, less than 0.1% of Al, and the balance of Fe and inevitable impurities, and has the two phase structures of a martensite phase and the balance of substantially ferritic phase, wherein the volume fraction of the martensite phase is 5-30%; and the ratio Hv(M)/Hv(F) of the hardness Hv(M) of the martensite phase to the hardness Hv(F) of the ferritic phase is 2.4-4.5.
Description
Technical field
The present invention relates to be suitable for automotive component for example with steel plate such, require superior plasticity when the punch process and during to motor-driven vehicle going be high tensile steel plate and the manufacture method thereof that the impact of representative requires the member of superior protective effect shock-resistance with the collision.
Background technology
In recent years, the lightweight of car body mainly reduces thickness of slab and is achieved by improving armor plate strength.For example, there is disclosed method in the Japanese kokai publication sho 57-41849 communique in method as the high strength of in the past realization automobile-use steel plate,, adds the method for solution strengthening elements such as P, Si to carbide forming elements such as Nb, Ti under low C that is.In addition, in Japanese kokai publication sho 60-52528 communique, disclose by the high temperature annealing chilling and made martensitic phase separate out to obtain the method for the superior high tensile steel plate of ductility.
Though these technology have been considered press formability, but for the desired shock-resistant characteristic of the such parts of all side beam, when collision, have the problem with high rate of straining distortion, and the static tensile strength that above-mentioned situation only is based under the low rate of straining is considered.Namely, the intensity of steel plate was to determine according to the static tensile strength under the low rate of straining in the past, when being in this impact conditions of collision accident, when just being out of shape with high rate of straining, the absorption that absorbs by viscous deformation for steel plate can consideration very few, think the steel plate when being out of shape at a high speed absorption can the contribution rate of static strength fix.
Yet, according to the inventor's etc. research as can be known, the absorption of the steel plate when being out of shape at a high speed can the contribution rate of static strength be not to fix, the raising of static strength can not directly make the absorption of the steel plate when being out of shape at a high speed be improved.Fig. 1 be contriver wait when having put dynamic tensile at various steel plates in order with static strength (when the absorption of rate of straining=800s-1) can stretch with static state (and the absorption of rate of straining=0.01s-1) can ratio (quiet moving ratio), recognize that static strength more increases, then absorb and more to descend by quiet moving ratio.As shown in Figure 2, calculate described absorption energy according to the stress-strain curve that obtains by tension test as the absorption energy that reaches the per unit volume of dependent variable=5%.
Need to prove, according to discovering of inventor etc., when estimating the shock-resistance of steel plate, impacting by the actual member that carries out that crushing that the crushing test obtains absorbs can be very high with near the degree of correlation of the work hardening characteristic stress-strain curve that obtains according to the high speed tensile test that utilizes steel plate, the yielding stress, as the value that represents this characteristic, the dependent variable when using stretching reaches the absorption energy of the per unit volume about 5%.
Therefore, realizing under the light-weighted situation by reducing thickness of slab, when only being estimated by static strength, for the distortion of impacting, do not obtain the raising effect of the shock-resistant characteristic of expectation degree, shock-resistant characteristic deficiency.
Shock-resistant characteristic should be under any one situation of low rate of straining distortion and the distortion of high rate of straining absorption during all by distortion can estimate, expectation absorbs can be high.In this case, in order to improve the absorption energy under the low rate of straining, aspect static strength, make steel realize high strength, but consider from the viewpoint of processibility, realizing there is restriction aspect the high strength.Therefore, in order to realize the raising of punch process and shock-resistance, it is essential, under the tensile strength (static strength) that equates, realize the raising of the absorption energy under the high rate of straining distortion, that is to say, the absorption when realizing the distortion of high rate of straining can (dynamically absorb can) absorption during with low rate of straining distortion can (static absorb can) the raising of ratio (quiet moving ratio).
Summary of the invention
The present invention finishes in view of the above problems, and it provides a kind of the have high tensile steel plate of superior shock-resistance and suitable manufacture method thereof under the situation of not destroying press formability.
Need to prove, steel plate as excellent impact resistance, for example, disclose in castingprocesses at Japanese kokai publication sho 52-86919 communique and to add alloying element in the implant operation of adjusting molten steel and the molten steel in the mold and have and have the inside and outside two-layer high tensile steel plate that specific one-tenth is grouped into, this steel plate is characterised in that, oxide compound by the control weld part is formed the molten metal flow of improving in the weld part generation, thereby realize the raising of nugget (nugget) cohesive force, improve the absorption energy when impacting, but, can not improve the shock-resistant characteristic of steel plate itself, in addition, 2 stratification in the casting process cause production efficiency to descend, thereby have unfavorable factor at economic aspect.
High tensile steel plate of the present invention has composition of steel described later, it is martensitic phase and surplus 2 phase constitution steel plates of ferritic phase in fact, the volume fraction of martensitic phase is 5～30%, and the hardness Hv of martensitic phase (M) and ratio Hv (M)/Hv (F) of the hardness Hv (F) of ferritic phase are 2.4～4.5.
At this, " ferritic phase in fact " refers to, only for containing the carbide precipitate of the carbide generting elements such as Ti, Nb that add as required in ferritic phase or the ferritic phase.
Clear and definite fully for 2 phase constitutions of the steel plate according to the present invention, reason that hardness ratio improves shock-resistant characteristic, but, what can expect is, after controlling the martensite volume fraction in suitable scope, become big by the hardness ratio that makes martensitic phase and ferritic phase, when static deformation, owing to the existence of the movable transposition that occupies most soft ferritic phase and martensite periphery makes yielding stress reduce, thereby guaranteed punch process.On the other hand, when dynamic deformation, the interface of ferritic phase and martensitic phase becomes the obstacle of transposition campaign, thereby the formation of honeycomb (cell) shape transposition structure is postponed, therefore, yielding stress rises significantly, thereby dynamically absorption can obtain enlarging with respect to the raising effect of static state absorption energy, especially, by increasing the hardness ratio of ferritic phase and martensitic phase, the resistance of the transposition campaign on interface barrier effect increases, thereby is the remarkable rising that obtains yielding stress more than 2.4 by making Hv (M)/Hv (F).
The reason that the volume fraction of martensitic phase is limited is can descend shock-resistant characteristic decline if martensite volume less than 5%, then dynamically absorbs.On the other hand, if surpass 30%, then only static absorption can uprise, and not only shock-resistant characteristic descends but also excessive hardization takes place and causes the press formability deterioration.Therefore, the lower limit of martensite volume is made as 5%, and the upper limit is made as 30%.Need to prove that the adjustment of martensite volume can be by adjusting the C amount or adjusting hot rolling or chilling during annealing begins temperature and waits to carry out.
In addition, the reason that ratio Hv (M)/Hv (F) limits of the hardness Hv (M) of martensitic phase and the hardness Hv (F) of ferritic phase is that Hv (M)/Hv (F) is conducive to improve shock-resistant characteristic, if less than 2.4 can't fully improve absorption can quiet moving ratios.In addition, along with the increase of hardness ratio, stretch flanging decline if surpass 4.5, then can't obtain sufficient stretch flanging, thus the press formability deterioration.Therefore, the lower limit of Hv (M)/Hv (F) is made as 2.4, and the upper limit is made as 4.5.Preferably be made as 3.2～4.0.
In addition, for the motor vehicle member, the situation of implementing baking vanish after drawing is a lot.Applying under the situation that this strain aging handles, known have a following situation, and namely when residual when solid solution C is arranged in ferritic phase, namely yielding stress increases sinter-hardened property (BH) to some extent after ageing treatment.
According to the inventor's etc. research as can be known, for steel plate of the present invention, by the solid solution C amount of residual needs in ferrite, compare with the low speed distortion, more remarkable under distortion at a high speed based on the rising of the yielding stress of sinter-hardened generation.Technical scheme 4 described inventions are based on this discovery and finish, except stipulating martensite volume in 2 phase constitutions and the hardness ratio of martensitic phase and ferritic phase, also further the amount of the solid solution C in the ferritic phase is controlled to be 10～30ppm, thereby can not cause yield-point to stretch because of near the importing of the movable transposition the martensitic phase, ageing treatment when as the motor vehicle member, after drawing, carrying out baking vanish, the absorption energy can be further improved, thereby shock-resistant characteristic can be improved.Under the situation of solid solution C amount less than 10ppm, the raising effect that absorbs energy reduces, if surpass 30ppm, yield-point then takes place stretch, thus press formability decline.
[invention effect]
According to high tensile steel plate of the present invention, by making the steel plate tissue become the martensitic phase of specified quantitative and surplus 2 phase constitutions of ferritic phase in fact, and the hardness ratio of 2 phases is defined as prescribed value, thereby can under the situation of not destroying press formability, obtains superior shock-resistant characteristic.In addition, be 10～30ppm by making the solid solution C amount in the ferritic phase, can under the situation that does not produce the yield-point stretching substantially, shock-resistant characteristic be significantly improved.In addition, manufacture method of the present invention is as the industrial process of the high tensile steel plate of excellent impact resistance of the present invention and have superiority.
Description of drawings
Fig. 1 is expression dynamic tensile absorption energy (under the rate of straining 800s-1) and the ratio (quiet moving ratio) of the static absorption energy (under the rate of straining 0.01s-1) that stretches and the graphic representation of the relation of static tensile strength.
Fig. 2 be the expression stress-strain curve with the absorption of the per unit volume that reaches dependent variable=5% can the graphic representation of relation.
Embodiment
Steel plate of the present invention is 2 phase constitutions that ferritic phase constitutes for martensitic phase and the surplus essence by specified amount, the hardness ratio of 2 phases or furthermore the amount of the solid solution C in the ferrite be adjusted to described prescribed value, by chemical ingredients (quality %) is defined as following scope, can under the situation that various characteristicses such as not causing press formability descends, effectively improve shock-resistant characteristic.
Comprise that C:0.05～0.20%, Si:2.0% are following, Mn:0.3～3.0%, below the P:0.1%, below the Al:0.1%, and surplus is made of Fe and unavoidable impurities.
Perhaps, except described basal component, what also further comprise (Mo:1.0% is following, Cr:2.5% following, B:0.002% following) is any more than a kind and/or (Ti, Nb, Zr, V: the total amount is 0.4% below, Cu:2.5% is following, Ni:1.5% is following, below the Ca:0.02%) any more than a kind.
Below, the reason of determinant is described.
C：0.05～0.20％
The amount of C processibility more at least more can be improved, and still, if reduce less than the volume fraction of 0.05% martensitic phase, not only is difficult to guarantee full intensity, and can't obtains to improve significantly the effect of shock absorption energy.On the other hand, surpass 0.20% if add to, then spot weldability, press formability, especially stretch flanging decline.Therefore, the following of addition is limited to 0.05%, on be limited to 0.20%.
Below the Si:2.0%
Si is effectively with the ferrite solution strengthening and for the high strength of steel plate, and also can improve the ductility of steel plate.Therefore, add though need only the intensity that requires to possess according to steel plate, surpass 2.0% if add, then be easy to generate surface spots, so be limited to 2.0% on it.
Mn：0.3～3.0％
The purpose of adding Mn is to strengthen steel plate and improves hardenability.Yet if less than 0.3%, its effect is too small, but if add above 3.0%, not only makes the press formability deterioration but also spot weldability is descended.Therefore, the following of addition is limited to 0.3%, is limited to 3.0% on it.
Below the P:0.1%
Because P improves the intensity of steel plate by solution strengthening, add so need only the intensity that requires to possess according to steel plate.Yet, surpass 0.1% if add, not only the decline because of grain-boundary strength becomes significantly 2 processing embrittlement, but also can cause the decline of shock-resistant characteristic.Therefore, be limited to 0.1% on it.
Below the Al:0.1%
Though add Al as deoxidant element, if add volume, then C is the reason that inclusion increases and become the generation surface spots, but also processibility is reduced, and therefore, is limited to 0.1% on it.
If added by volume, then can cause the material behavior deterioration as S, the N of unavoidable impurities.That is, if S is added by volume, then stretch flanging decline, therefore, preferably its upper limit is advisable with 0.01%.In addition, if N added by volume, then can make room temperature ageing decline and produce yield-point and stretch, therefore, preferably its upper limit is advisable with 0.01%.
Except above basal component, in order to improve hardenability, can add be selected from that Mo:1.0% is following, Cr:2.5% following, B:0.002% in following more than a kind.
Below the Mo:1.0%
Mo is for improving hardenability and realizing that by precipitation strength and build up the high strength of steel plate is effective.Yet, not only cause effect saturated if interpolation surpasses 1.0%, but also can cause ductility to descend, therefore, be limited to 1.0% on it.Preferably, add more than 0.05%.
Below the Cr:2.5%
Cr is for improving hardenability and realizing that by solution strengthening the high strength of steel plate is effective.Yet, if volume adds, not only cause effect saturated but also ductility is descended, therefore, be limited to 2.5% on it.Preferably, add more than 0.05%.
Below the B:0.002%
B still, if volume is added, then can cause ductility to descend, so be limited to 0.002% on it improving hardenability and intensity rising and grain-boundary strengthening by steel plate prevent that 2 processing embrittlement from being effectively.Preferably, add more than 0.0003%.
In addition, can also under the situation that does not hinder effect of the present invention, add in the following element more than a kind.
Ti, Nb, Zr, V: add up to below 0.4%
Ti, Nb, Zr, V are to realizing that by precipitation strength the high strength of steel plate is effective.Yet if too much add, not only effect is saturated, but also ductility is descended, so its upper limit adds up to 0.4%.
Below the Cu:2.5%, below the Ni:1.5%
Cu, Ni are effectively to the high strength by solution strengthening precipitation strength realization steel plate, but also are conducive to improve erosion resistance.Yet, if volume is added, can cause ductility to descend, therefore, be limited on the Cu addition 2.5%, Ni on be limited to 1.5%.Need to prove, adding separately under the situation of Cu, may produce surface spots because addition makes steel plate, but can improve by compound interpolation Ni.
Below the Ca:0.02%
Ca has the effect of the inclusion morphology that improves steel, and also is effective for the processibility of improving steel plate and toughness.Yet if volume is added, the inclusion amount increases, and can cause the cold-workability of steel plate and toughness to descend on the contrary, therefore, is limited to 0.02% on it.
Next, manufacture method of the present invention is described.Manufacture method of the present invention is characterised in that, after the steel with described composition is carried out hot rolling, carry out cold rolling, anneal with 760～920 ℃ soaking temperature then, subsequently, the speed following with 15 ℃/s is cooled to 700～540 ℃ from soaking temperature, then is cooled to normal temperature with the above speed of 100 ℃/s, carry out reheat subsequently and under 150～300 ℃, keep, cool off then.In the process of cooling after reheat keeps, by being cooled to below 100 ℃ with the above speed of 3 ℃/s, thereby can guarantee the solid solution C of specified amount.
In the present invention, though carry out hot rolling, cold rolling getting final product by usual method, but especially for hot rolling, the draft (HR leads) between 1150 ℃～hot precision work temperature of suiting is more than 85% and hot rolling precision work temperature (FT) is more than 830 ℃, coiling temperature (CT) is to carry out under the situation below 600 ℃.Making draft between 1150 ℃～hot precision work temperature is that reason more than 85% is, realizes the granular of hot-rolled sheet tissue.Making hot rolling precision work temperature is that reason more than 830 ℃ is, if be lower than 830 ℃, then can not become trickle hot-rolled sheet tissue uniformly, and this also has influence on the tissue after cold rolled annealed and becomes inhomogeneous tissue, thereby causes the processibility deterioration.In addition, also because sharply becoming big, rolling load meeting is difficult to be rolled.Making coiling temperature is that reason below 600 ℃ is to suppress the growth because of the tissue of hot rolling granular.
In order to carry out recrystallize by the annealing after cold rolling, cold rolling draft is suitably more than 30%.Do not have particular restriction in this case annealing, consider preferred continuous annealing from the viewpoint of production efficiency and quality stability.
Soaking temperature during annealing (ST) is 760～920 ℃.If less than 760 ℃, then can't obtain the martensitic phase of q.s, on the other hand, if surpass 920 ℃, then produce thickization of crystal grain, thereby cause the press formability deterioration.
After annealing, (chilling begins temperature: scope QT) to 700～540 ℃ from soaking temperature cooling (slow cooling) with the following speed of 15 ℃/s.If be higher than 700 ℃, then the diffusion of the C to the austenite phase becomes insufficient from ferritic phase, can't obtain the martensitic phase of hard, and it is too much that the solid solution C in the ferrite also can become.On the other hand, if be lower than 540 ℃, then separating out of carbide obtains promoting, the martensite minimizing of meeting.In addition, if the speed of cooling of this moment surpasses 15 ℃/s, then with above-mentioned same, the diffusion of the C from from ferritic phase to the austenite phase becomes insufficient, and martensite volume can reduce.
After soaking temperature began to carry out slow cooling, then the purpose that is quenched to normal temperature with the above speed of 100 ℃/s was, prevented that generation because of bainite from causing the minimizing of martensite volume.In case after being cooled to normal temperature, carry out reheat and (the reheat temperature: the purpose that keeps QT) is martenaging martempering is improved ductility, if the reheat temperature is lower than 150 ℃, then ductility can not get improving, and intensity-ductility balance descends at 150～300 ℃.On the other hand, if be higher than 300 ℃, the then softening increase of martensitic phase, thereby the hardness that can't obtain to expect, the result causes the absorption when being out of shape at a high speed to descend.Need to prove, though the hold-time there is not particular restriction, common more than 5 seconds, and consider from the production efficiency aspect and be preferably below 180 seconds.
Speed of cooling after keeping for reheat (speed of cooling that begins from the reheat temperature: CR2), by with 3 ℃/be cooled to more than the s (cooling lower limit temperature) below 100 ℃, thus, can guarantee suitable solid solution C (10～30ppm).Even speed of cooling be 3 ℃/more than the s but the cooling lower limit temperature surpass under 100 ℃ the situation, perhaps under the speed of cooling less than 3 ℃/s, solid solution C reduces, and can't guarantee the solid solution C amount of appropriate amount.
Steel plate of the present invention is not only effective for hot-rolled steel sheet, and also can bring into play its effect to cold-rolled steel sheet, furthermore, also is suitable as the raw sheet of various plated steel sheets such as molten zinc plating.In addition, though manufacture method of the present invention is the manufacture method about cold-rolled steel sheet,, self-evidently be that this manufacture method can also be used as the manufacture method of the raw sheet of various plated steel sheets such as molten zinc plating.
Need to prove, in Japanese kokai publication hei 7-90482 communique, Japanese kokai publication hei 7-188833 communique, put down in writing the superior steel sheet of shock-resistance, be organized as on the 2 phase constitution this point of martensitic phase and ferritic phase identical with the present invention.Yet, the former is necessary composition with Nb, Ti, and by (2Nb+Ti)/C being controlled to be 0.1～0.5 raising that realizes quiet moving ratio, in addition, the latter is by reducing the raising that solid solution C amount in the ferritic phase realizes quiet moving ratio as far as possible, and the two becomes 2.4～4.5 with the ratio of hardness by making martensitic phase and the hardness of ferritic phase, and to realize absorbing the steel plate of the present invention of raising of quiet moving ratio of energy different fully on technological thought.
[embodiment]
(embodiment 1) uses the steel disc of composition shown in table 1 and the table 2, carry out according to usual method hot rolling and cold rolling after anneal, thereby acquisition is by martensitic phase and the steel plate of the thickness of slab 1.2mm that constitutes of 2 phase constitutions of ferritic phase in fact.Annealing is carried out as follows, that is, under 750～900 ℃, carry out after the soaking, be cooled to 700～600 ℃ with the speed of 10 ℃/s, further be cooled to room temperature with the above speed of cooling of 200 ℃/s after the slow cooling, after water-cooled, carry out 200～300 ℃ temper.
[table 1]
[table 2]
At the steel plate that obtains, the hardness Hv (F) of the hardness Hv (M) of the volume fraction % of martensitic phase, martensitic phase and ferritic phase is measured and calculated hardness ratio Hv (M)/Hv (F).About the volume fraction of martensitic phase, according to the rectangular thickness of slab directional profile of rolling direction in, the SEM photo of the tissue of 1/4 position from the surface to the thickness of slab measures.In addition, measured the hardness of each phase with load=5gf by Vickers hardness tester.
In addition, from these steel plate interceptings JIS7 test film, carry out tension test with rate of straining=0.01s-1 (static test) and 800s-1 (dynamic testing), test the stress-strain curve that obtains according to static tensile strength and by each, static state and dynamic absorption of obtaining the per unit volume of dependent variable=5% can, and calculate the quiet moving ratio of absorption energy, according to this value shock-resistant characteristic is estimated.
These mensuration, test-results illustrate in table 3 and table 4 in the lump.
[table 3]
(notes) TS: tensile strength, VM: martensite volume fraction, Hv (F): ferrite hardness Hv (M): martensite hardness, Es: static state stretches and absorbs energy Ed: dynamic tensile absorbs energy, λ: hole expansibility, YPE1: yield-point stretches
[table 4]
(notes) TS: tensile strength, VM: martensite volume fraction, Hv (M): martensite hardness, Hv (F): ferrite hardness, Es: the static stretching absorbs energy, Ed: dynamic tensile absorbs energy
As can be known, the C of No.C1 as a comparative example amount is low and outside scope of the present invention during the test portion No.C1 in observing table 3～C5, so the martensite volume fraction becomes very few, represent shock-resistant characteristic absorption can quiet moving ratio be level (with reference to Fig. 1) degree in the past.On the other hand, in the example of C amount for the No.C2～C5 in the scope of the invention, the volume fraction of the martensitic phase that necessitates (5～30%), the quiet moving ratio that absorbs energy is improved, thereby obtains superior shock-resistant characteristic.
When observing influencing of Mn addition according to test portion No.D1～D4 as can be known because the Mn of the No.D1 of comparative example amount is low outside scope of the present invention, so the volume fraction step-down of martensitic phase, thereby shock-resistant characteristic is also bad.
In addition, as can be known, the P of No.E4 as a comparative example amount too much and outside scope of the present invention, therefore, dynamically absorbing can low and shock-resistant characteristic generation deterioration when observing influencing of P addition according to test portion No.E1～E4.
In addition, according to as example, test portion No.H1～H3, I1～I2, J, K1～K2, L1～L2, M1～M2, N1～N2, P1～P2, Q1～Q5 as can be known, add the raising that auxiliary element also can not hinder shock-resistant characteristic with technical scheme 2,3 scope.
(embodiment 2) after the steel disc with the composition shown in the table 5 was heated to 1200～1250 ℃, making the precision work temperature was 840～920 ℃, finished hot rolling with thickness of slab 4.0mm, after batching under 450～600 ℃, was cold rolled to thickness of slab 1.2mm, annealed then.
[table 5]
Annealing conditions is shown in table 6 and table 7,740～910 ℃ of (soaking temperatures: after carrying out 90 seconds soaking ST), (begin the speed of cooling of temperature from the soaking temperature to the chilling: (chilling begins temperature: TQ) CR1) to be cooled to 800～545 ℃ with below the 40 ℃/s, then be cooled to room temperature, remove a part subsequently, reheat to 70～400 ℃ (reheat temperature: QT), and kept 300 seconds, (speed of cooling that begins to cool off from the reheat temperature: speed CR2) is cooled to below 100 ℃ (cooling lower limit temperatures) with 1～10 ℃/s again.In addition, the annealed sheet that obtains is implemented BH and handle (after applying 2% prestrain, carrying out 170 ℃ * 20 minutes ageing treatment).
For the steel plate after the annealing, with (embodiment 1) obtain equally hardness ratio (Hv (M)/Hv (F)), the solid solution C amount of volume fraction % (VM), martensitic phase and the ferritic phase of martensitic phase, in the static tensile test mechanical characteristics, the static absorption can (Es) and dynamically absorb can (Ed) and quiet moving ratio thereof, the steel plate after further handling from BH is obtained dynamic absorption energy and the quiet moving ratio thereof after BH handles.Its result illustrates in table 6, table 7 in the lump.
(notes) HR leads: draft, FT between 1150 ℃～hot precision work temperature: hot rolling precision work temperature, CT: coiling temperature, ST: soaking temperature, QT: chilling begins temperature
CR1: the speed of cooling, the QT that from the soaking temperature to the chilling, begin temperature: reheat temperature, CR2: the speed of cooling, the VM that begin from the reheat temperature: martensite volume fraction
Hv (M): martensite hardness, Hv (F): ferrite hardness, TS: tensile strength, E1: stretching, Es: static energy, the Ed of absorbing: dynamically absorb energy
According to table 6 and table 7, the test portion of example has obtained good punch process, shock-resistant characteristic.Test portion No.E3, Z2, AD2 have obtained enough shock-resistance before BH handles, it is the example of technical scheme 1.Yet, because the speed of cooling that begins to cool off from the reheat temperature is slow, thus solid solution C quantity not sufficient, thus do not satisfy the important document of technical scheme 4, therefore, the raising effect of the shock-resistance after BH handles descends slightly.
With respect to this handle because as a comparative example test portion No.A1, A4, C2 and C4 carry out reheat after annealing, cooling, the reheat temperature QT when perhaps reheat is handled is inappropriate, therefore, punch process or absorb can raising descend to some extent.In addition, the chilling of the No.B1 of comparative example begins temperature T Q height, and the martensite volume fraction increases, therefore, and punch process decline.
In addition, because as a comparative example test portion No.G2, G3 are fast from the speed of cooling CR1 that the annealing soaking temperature begins, thus the martensite volume fraction that can't obtain to expect, thus shock-resistance descends to some extent.
In addition, because the composition of steel of test portion No.D, the F of comparative example is not within the scope of the present invention, so martensite volume fraction step-down, shock-resistance descends.Furthermore, because that the P quantitative change of the No.M of comparative example gets is too high, can step-down so dynamically absorb, shock-resistance descends.On the other hand, from as the test portion No.N～Y of example as can be known, even add Mo, Cr, the auxiliary elements such as Ti, Nb of specified amount, also can not hinder the raising of shock-resistant characteristic.
Need to prove, self-evidently be, in the manufacturing of steel plate of the present invention, can't help the restriction of creating conditions of the above embodiments 1, embodiment 2.In addition, steel plate of the present invention is suitable as the raw steel of automotive component, can realize lightweight under the situation that does not reduce its crashworthiness, still self-evident is to be not limited to this purposes, and it is applicable to the various member steel plates that require shock-resistant characteristic.
Claims (8)
1. the high tensile steel plate that shock-resistance is superior is characterized in that,
In quality %, contain that C:0.05～0.20%, Si:2.0% are following, Mn:0.3～3.0%, P:0.1% are following, below the Al:0.1%, surplus is made of Fe and unavoidable impurities, have the martensitic phase of volume fraction 5～30% and surplus 2 phase constitutions of ferritic phase in fact, the hardness of martensitic phase is 2.4～4.5 with the ratio of the hardness of ferritic phase.
2. the superior high tensile steel plate of shock-resistance according to claim 1 is characterized in that,
Except the described composition of claim 1, contain also that Mo:1.0% is following, Cr:2.5% following, B:0.002% more than one in following.
3. the superior high tensile steel plate of shock-resistance according to claim 1 and 2 is characterized in that,
Except claim 1 or 2 described compositions, also contain Ti, Nb, Zr, V: add up to below 0.4%, Cu:2.5% is following, Ni:1.5% following, Ca:0.02% more than one in following.
4. the superior high tensile steel plate of shock-resistance according to claim 1 and 2 is characterized in that,
Solid solution C amount in the ferritic phase is 10～30ppm.
5. the superior high tensile steel plate of shock-resistance according to claim 3 is characterized in that,
Solid solution C amount in the ferritic phase is 10～30ppm.
6. the manufacture method of the high tensile steel plate that a shock-resistance is superior is characterized in that,
After the steel with any described composition in the claim 1～3 is carried out hot rolling, carry out cold rolling, be cooled to 700～540 ℃ with the following speed of cooling of 15 ℃/s from the annealing soaking temperature then, then be cooled to normal temperature with the above speed of cooling of 100 ℃/s, carry out reheat then and under 150～300 ℃, keep, cool off subsequently.
7. the manufacture method of the high tensile steel plate that shock-resistance according to claim 6 is superior is characterized in that,
After keeping under 150～300 ℃, the speed of cooling above with 3 ℃/s is cooled to below 100 ℃.
8. according to the manufacture method of the superior high tensile steel plate of claim 6 or 7 described shock-resistance, it is characterized in that,
In hot rolling, make that draft between 1150 ℃～hot precision work temperature is more than 85%, hot rolling precision work temperature is more than 830 ℃, coiling temperature is below 600 ℃.
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