CN1241219A - High-strength steel having high impact energy absorption power and method for mfg. same - Google Patents

Abstract

A high-strength steel sheet to be formed and worked into parts for absorbing striking energy occurring at a collision, for example, front-side members, which exhibits a high absorbing power against striking energy; and a process for the production thereof. The sheet is a high-strength steel sheet exhibiting high dynamic deformation resistance and excellent workability and is characterized in that the microstructure of the finally obtained sheet is a composite one comprising ferrite and/or bainite with either of them being present as the main phase and containing as the third phase another phase containing residual austenite at a volume fraction of 3 to 50 %, that the difference between the quasi-static deformation strength observed when the sheet is subjected to pre-deformation of equivalent strain exceeding 0 % and up to 10 % and then deformed at a strain rate of 5 x 10[-4] to 5 x 10[-3] (1/s) and the dynamic deformation strength (sigma d) observed when the sheet is subjected to the above pre-deformation and then deformed at a strain rate of 5 x 10[2] to 5 x 10[3] (1/s), i.e., sigma d, is 60 MPa or above, and that the work hardening exponent at a strain of 1 to 5 % is 0.080 or above.

Description

High-strength steel and production method thereof with HI high impact energy absorption

Technical field

The present invention relates to have during dynamic deformation the high tensile hot rolled steel sheet and the high strength cooling steel plate of high yielding stress, described steel plate can be as automobile component etc., and the impact energy with by effective absorption collision the time is guaranteed passenger's safety.The present invention also relates to produce the method for this kind steel plate.

Background technology

In recent years, the protection passenger is not subjected to the injury of car collision to be acknowledged as the extremely important aspect of automobile, and, increasing for the expectation of appropriate materials with excellent high-speed deformation drag.For example, by this type of material is used as the preposition member of automobile, then when this material was crushed, the energy of head-on crash just can be absorbed, thereby alleviated the influence of impacting the passenger.

Because the strain rate of the suffered distortion in when collision each position of automobile reaches about 10 ³(1/ second) therefore, need understand its dynamic deformation performance when the high strain rate scope during shock absorbing capability of consideration material.Because simultaneously also must be to such as energy-conservation and reduce CO ₂Discharging, and reduce factor such as vehicle weight and take in, so, the requirement of effective high tensile steel plate is increased.

For example, at CAMP-ISIJ the 9th volume (1996), in the 1112-1115 page or leaf, the inventor to the high-speed deformation properties of high-strength steel sheet can and impact energy absorption characteristic made report, in this article, the inventor points out, and 10 ^-3Static strength during the low strain rate of (1/ second) is compared, about 10 ³Dynamic strength during the high strain rate scope of (1/ second) sharply increases; And the relation of strain rate and resistance to deformation changes according to the strengthening mechanism of material; Compare with other high tensile steel plate, the formability and the shock absorbing capability of TRIP (transformation induced plasticity) steel plate and DP (ferrite/martensite two-phase) steel plate are all very excellent.

In addition, Japanese patent unexamined discloses flat 7-18372 number provides the high tensile steel plate that contains residual austenite with excellent impact resistance to produce the method for this steel plate, increase yielding stress to a kind of by high deformation speed, open so that the method that the shock absorption ability is improved has been done; Yet in order to improve impact absorbency, except the amount of residual austenite, which others of residual austenite should be controlled, and are not confirmed as yet at present.

Therefore, although for when the car collision, the understanding that influences the dynamic deformation performance of the member composition material that impact energy absorbs is being updated, but any performance should improve to greatest extent, to obtain to have the steel that are used for automobile component of more excellent impact energy absorption characteristic, and which kind of criterion to carry out the selection of material according to, still be not very clear at present.The steel that are used for automobile component are shaped by pressing mold and are processed to desired member shape, through after japanning and toasting, are installed in the automobile more usually, and are used for actual impact occasion.Yet still unclear at present is that after this predeformation and baking processing, the strengthening mechanism of which kind of steel is suitable for improving the impact energy receptivity of steel when colliding.

Summary of the invention

An object of the present invention is to provide the high tensile steel plate with HI high impact energy absorption, this steel plate uses as shaping the steel that absorb the parts such as preposition parts of impact energy into such as collision the time, and a kind of method of producing this kind steel plate is provided.At first, the high tensile steel plate with HI high impact energy absorption according to the present invention comprises:

(1). when dynamic deformation, have the high tensile steel plate of high yielding stress, the final microstructure that it is characterized in that described steel plate be a kind of by ferrite and/or bainite with comprise that volume fraction is the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes, ferrite and bainite all can be principal phase (dominant phase) in this tissue, wherein, carrying out equivalent strain is less than or equal to 10% distortion in advance greater than 0% after, again with 5 * 10 ²-5 * 10 ³During the distortion of (1/S) strain rate, the mean value σ dyn (MPa) that equivalent strain is in the yielding stress in the 3-10% scope satisfies inequality: σ dyn 〉=0.766 * TS+250, and TS wherein is not in advance under the texturizing condition, and strain rate is 5 * 10 ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records in the time of (1/S) (MPa), and the work hardening coefficient when dependent variable is 1-5% is at least 0.080, and

(2). according to the high tensile steel plate that has high yielding stress when the dynamic deformation of above-mentioned (1), wherein, the work hardening coefficient when dependent variable is 1-5% and the product of yield strength are at least 40.

Described steel plate further comprises:

(3). when dynamic deformation, have the high tensile steel plate of high yielding stress, the final microstructure of wherein said steel plate be a kind of by ferrite and/or bainite with comprise that volume fraction is the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes, ferrite and bainite all can be principal phase in this tissue, wherein, carry out equivalent strain greater than 0% and be less than or equal to 10% distortion in advance after, with 5 * 10 ²-5 * 10 ³During the distortion of (1/S) strain rate, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfies inequality: σ dyn 〉=0.766 * TS+250, TS in the formula (MPa) be not when being out of shape in advance, 5 * 10 ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records under the strain rate (1/S), value (M) by the average Mn equivalent in solid solution in the residual austenite [C] and the described steel [Mneq=Mn+ (Ni+Cr+Cu+Mo)/2] decision, its definition is M=678-428 * [C]-33Mneq, its value should be at least 70 but be no more than 250, when not being out of shape in advance the volume fraction of residual austenite and carry out equivalent strain be difference between the volume fraction of residual austenite after 5% the distortion in advance be at least residual austenite volume fraction when not being out of shape in advance 30%, work hardening coefficient when dependent variable is 1-5% is 0.080 at least, and the average crystal grain diameter of residual austenite is not more than 5 μ m; The ratio of the average crystal grain diameter of ferrite or bainite is not more than 0.6 in the average crystal grain diameter of residual austenite and the principal phase, and the average crystal grain diameter of principal phase is not more than 10 μ m, preferably is not more than 6 μ m; When martensitic average crystal grain diameter is not more than 10 μ m, and when preferably being not more than 5 μ m, fraction of martensite volume is 3-30%, ferritic volume fraction is at least 40%, yield ratio is not more than 85%, and the product of tensile strength and total unit elongation is at least 20,000.

(4). high tensile steel plate of the present invention contains following composition, by weight percentage: C0.03-0.3%, amount when Si and Al exist respectively or jointly is 0.5-3.0%, and, if necessary, also containing total amount is the Mn that is selected from of 0.5-3.5%, Ni, Cr, one or more elements among Cu and the Mo, surplus person then is the Fe as major components, perhaps, if necessary, be selected from Nb to further interpolation of above-mentioned high tensile steel plate, Ti, V, P, B, the high tensile steel plate that one or more elements among Ca and the REM (rare earth metal) have high yielding stress in the time of can obtaining dynamic deformation, that is wherein added is selected from Nb, the total amount of one or more of Ti and V is no more than 0.3%, and P is no more than 0.3%, B is no more than 0.01%, Ca is 0.0005-0.01%, and REM is 0.005-0.05%, and surplus person is the Fe as major components.

(5). produce according to of the present invention and have the method for the high tensile hot rolled steel sheet of high yielding stress when the dynamic deformation, the microstructure that has the high tensile hot rolled steel sheet of high yielding stress during wherein said dynamic deformation be a kind of by ferrite and/or bainite with comprise that volume fraction is the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes, ferrite and bainite all can be principal phase in this tissue, wherein, carry out equivalent deformation greater than 0% and be less than or equal to 10% distortion in advance after, with 5 * 10 ²-5 * 10 ³During the distortion of (1/S) strain rate, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfies inequality: σ dyn 〉=0.766 * TS+250, TS strain rate when not being out of shape in advance is 5 * 10 in the formula ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records under the condition (1/S) (MPa), and the work hardening coefficient of dependent variable when being 1-5% is at least 0.080, the production method of described steel plate is characterised in that: the continuous casting steel billet with the constituent element composition in above-mentioned (4) is directly delivered to hot rolling by the continuous casting stage, perhaps reheat the back hot rolling, finishing temperature between Ar3-50 ℃ to Ar3+120 ℃ is finished hot rolling, at cooling stages subsequently, after cooling off with 5 ℃/second average cooling rates, described hot rolled strip is batched not being higher than under 500 ℃ the temperature.

(6). have the method described in the method just above-mentioned (5) of high tensile hot rolled steel sheet of high yielding stress when producing dynamic deformation, wherein under the finishing temperature between Ar3-50 ℃ to Ar3+120 ℃, course of hot rolling is controlled, so that metallurgy parameter: A satisfies following inequality (1) and (2), the average cooling rate at runoff table place subsequently is at least 5 ℃/second, and the carrying out of batching should make above-mentioned metallurgy parameter: the relation between A and coiling temperature (CT) satisfies following inequality (3).

9≤LogA≤18????????????????(1)

ΔT≥21×LogA-178??????????(2)

CT≤6×LogA+312????????????(3)

(7). produce according to of the present invention, the method that during dynamic deformation, has the high strength cold rolled steel plate of high yielding stress, described steel plate is the high strength cold rolled steel plate that has high yielding stress during dynamic deformation, its final microstructure be a kind of be the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes by ferrite and/or bainite with containing volume fraction, described ferrite and bainite all can be used as principal phase and exist, wherein, carry out greater than 0% and be less than or equal to the distortion in advance of 10% equivalent strain after, with 5 * 10 ²-5 * 10 ³When strain rate (1/S) was out of shape, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfied inequality, and σ dyn 〉=0.766 * TS+250, the TS in the formula are that strain rate is 5 * 10 under the condition of not being out of shape in advance ^-4-5 * 10 ^-3Maximum stress (MPa) in the time of (1/S) in the measured static tensile test, work hardening coefficient when strain is 1-5% is at least 0.080, the feature of described production method also is: the continuous casting steel billet that will have the constituent element composition of above-mentioned (4) is directly sent to hot rolling by the continuous casting section, carry out hot rolling after perhaps reheating again, the hot-rolled steel sheet that has batched after the hot rolling is carried out pickling, cold rolling more afterwards, and, for obtaining the finished product, in a continuous annealing step steel plate is annealed, annealing time is 10 seconds-3 minutes, and temperature is 0.1 * (Ac ₃-Ac ₁)+Ac1 ℃ to Ac3+50 ℃, afterwards, being cooled to temperature with a cooling rate of 1 to 10 ℃/second is a cooling termination temperature of 550-700 ℃, then, being cooled to temperature with 10 to 200 ℃/second secondary cooling rate again is 150-450 ℃ secondary cooling termination temperature, after this, before being chilled to room temperature, temperature remained on reach 15 seconds to 20 minutes between 150-500 ℃, and, the further feature of described method also is: the cooling conditions after the specific annealing is to handle 10 seconds to 3 minutes at 0.1 * (Ac3-Ac1)+Ac1 ℃ to Ac3+50 ℃ annealing temperature, subsequently, being chilled to temperature with a cooling rate of 1 to 10 ℃/second is 550-720 ℃ secondary cooling starting temperature Tq, afterwards, is cooled to secondary cooling termination temperature Te between Tem-100 ℃ and Tem with 10 to 200 ℃/second secondary speed of cooling again, Tem wherein is by the component and the annealing temperature To decision of steel, afterwards, before being cooled to room temperature, temperature T oa remained on reaching 15 seconds to 20 minutes between Te-50 ℃ and 500 ℃.

The accompanying drawing summary

Shown in Fig. 1 be TS with when with 5 * 10 ²-5 * 10 ³During the distortion of (1/S) strain rate, the relation of equivalent strain between the difference of the mean value σ dyn of the yielding stress between 3-10% and TS is used for expression according to collision impact energy absorption of the present invention.

Shown in Fig. 2 is the work hardening coefficient of deflection steel plate when being 1-5% and the relation between dynamic energy absorption (J).

Shown in Fig. 3 is relation between the long-pending and dynamic energy absorption (J) of the work hardening coefficient of deflection steel plate when being 1-5% and yield strength.

Fig. 4 a is the skeleton view of used unit (hat sample) in the shock crushing test that carries out for the dynamic energy absorption in the survey sheet 3.

Fig. 4 b is the sectional view of used sample among Fig. 4 a.

Fig. 4 c is the synoptic diagram of shock crushing test method.

Shown in Fig. 5 is according to the relation between Δ T in the hot-rolled step of the present invention and the metallurgy parameter A.

Shown in Fig. 6 is according to the relation between coiling temperature in the hot-rolled step of the present invention and the metallurgy parameter A.

Fig. 7 is the explanation to the annealing cycle in the continuous annealing step according to the present invention.

Shown in Fig. 8 is relation between secondary cooling termination temperature (Te) and overaging temperature (Toa) thereafter in continuous annealing step according to the present invention.

Implement optimal mode of the present invention

By with steel plate bending or compressing, produce the collision impact absorption piece of preposition member such as automobile etc. Processing by this way and after japanning and baking, usually the member of producing is being impacted by car crass. Therefore, just require described steel plate being processed into member and after japanning and baking, having high impact energy absorption characteristic.

Through for many years to high-strength steel sheet as satisfying the research of the impact absorbing member of above-mentioned requirements, the inventor finds, in the steel plate of the member that is used for being processed into this shape, having an amount of retained austenite is the effective ways that a kind of acquisition has the high-strength steel sheet of excellent shock absorbing capability. Particularly, find, when desirable microscopic structure is to be easy to by the ferrite of various substitutional element solution strengthening and/or bainite a kind of comprising, and when containing the complex tissue of the third phase of volume fraction 3-50% retained austenite, just can dynamic deformation show high yield stress, ferrite wherein and bainite all can be used as principal phase and exist, described retained austenite is transformed into hard martensite between deformation phases, in addition, further find, when specific condition is satisfied, have in the compound tissue of steel plate martensite be present in the initial microscopic structure the third mutually in, at this moment, also can obtain during dynamic deformation, to have the high-strength steel sheet of high yield stress.

Through further experiment and the research on as above these find bases, the inventor finds, in advance deflection when being shaped such as the impact absorbing member of preposition member according to the difference at its position sometimes maximum can reach more than 20%, and the equivalent deformation at most of positions is greater than 0 % and is less than or equal to 10%. Therefore, by determining the in advance effect of distortion in the above-mentioned scope, just might estimate the performance of member on the whole after the distortion in advance. Therefore, according to the present invention, select equivalent strain to be less than or equal to the in advance deflection that 10% distortion puts on described member during as member processing greater than 0%.

Shown in Fig. 1 is to be 5 * 10 carrying out strain rate²-5×10 ³During (1/S) distortion, the mean value σ dyn of the yield stress when equivalent strain is 3-10% and the static strength TS of material (, strain rate is 5 * 10^-4-5×10 ^-3Maximum stress TS (MPa) in the static tensile test that records in the time of (1/S)) relation between is used for characterizing according to collision impact energy absorption of the present invention.

Cross section such as the impact absorbing member of preposition member is hat, and by the analysis to this type of deformation of member of in high velocity impact, being broken, the inventor finds, although the maximum strain amount of the distortion of carrying out can reach more than 40%, but in the high speed stress-strain diagram, be equal to or less than in 10% the range of strain and but absorbed total endergonic at least 70%. Therefore, during with dynamic deformation, the yield stress when the high speed deflection is equal to or less than 10% is as the index of weighing high velocity impact energy absorption quality. Particularly, because it is extremely important to be in the dependent variable of 3-10% scope, so this index that is used for the expression impact energy absorption characteristic is 5 * 10 carrying out strain rate exactly²-5×10 ³During (1/S) high-speed tensile deformation, the mean stress σ dyn when equivalent strain is 3-10%.

When being out of shape at a high speed, the mean stress σ dyn when strain is 3-10% generally with not in addition the static stretch intensity of the steel plate processed of in advance distortion or baking (strain rate is 5 * 10^-4-5 ×10 ^-3Maximum stress in the static tensile test that records in the time of (1/S): TS (MPa)) increase and increasing. Therefore, the static stretch intensity (with the strength of materials synonym of static state) of increase steel just directly helps to improve the impact energy absorption characteristic of member. Yet the increase of steel strength can cause its formability that is processed into member to degenerate, thus the member that is difficult to obtain to have required shape. Therefore, identical but the steel that σ dyn is high of preferred tensile strength (TS). Find that also based on this relation, be less than or equal to 10% in advance distortion greater than 0% after, carrying out strain rate is 5 * 10²-5×10 ³During (1/S) distortion, equivalent strain is that the yield stress mean value σ dyn (MPa) of the steel of 3-10% satisfies inequality: during σ dyn-TS 〉=-0.234 * TS+250, the TS in the formula is not in advance under the deformation condition, and strain rate is 5 * 10^-4 -5×10 ^-3Maximum stress TS (MPa) in the static tensile test that records in the time of (1/S), described steel are compared with other steel, has higher impact energy absorption characteristic during as actual components, and, in the situation that does not increase the member gross weight, shock absorbing capability is improved, thereby just might be provided at the high-strength steel sheet that has high yield stress during the dynamic deformation. By the way, because above-mentioned do not wait relational expression σ dyn-TS 〉=-0.234 * TS+250 identical with σ dyn 〉=0.766 * TS+250, so will adopt in the following description inequality σ dyn 〉=0.766 * TS+250.

The inventor also finds, for improving anti-crashworthiness, must increase the work hardening during the in advance processing that the strain hardening coefficient when being 1-5% with strain represents, to improve the initial deformation drag at collision initial point place, and the work hardening during the martensite raising collision deformation of utilization transformation when being out of shape in advance, and increase σ dyn. In other words, carry out aforesaid control by the microscopic structure to steel, can increase the crash-resistant security, so, as shown in Figures 2 and 3, the strain hardening coefficient of steel is at least 0.080, and preferably is at least 0.108, the amassing of strain hardening coefficient when strain is 1-5% and yield strength is at least 40, and preferably is at least 54. Relation between the amassing of the dynamic energy absorption by investigate to be used for characterizing the anti-crashworthiness of automobile component and the strain hardening coefficient of steel plate and yield strength and strain hardening coefficient, can see, when above-mentioned numerical value increases, dynamic energy absorption is just improved, this shows, when the yield strength level is identical, just can make suitable evaluation according to the strain hardening coefficient that characterizes the anti-crashworthiness of automobile component, perhaps in yield strength not simultaneously, this evaluation can and add long-pending the making of sclerosis coefficient according to yield strength.

Adopt the impact grinding test method shown in Fig. 4 a, Fig. 4 b and Fig. 4 c, determine dynamic energy absorption according to following manner. One block plate is processed into sample (R=5mm of fillet place) shown in Fig. 4 b, and the electrode tip radius is the electrode of 5.5mm, electric current be 0.9 times under the condition of spraying electric current (expulsion current), press the spacing of 35mm with in addition spot welding 3 of sample, to make the parts (hat) with the sample 2 between two operative end surface 1, shown in Fig. 4 a, then, 170 ℃ of bakings and japanning process reach 20 minutes after, shown in Fig. 4 c, the weight 4 of about 150Kg falls from the eminence of about 10m, place the described parts on the support 5 that damper 6 is housed to be smashed along its length, just can calculate the work of deformation that displacement is the 0-150mm place by the area among the corresponding load displacement figure, thereby determine dynamic energy absorption.

Strain hardening coefficient when the strain hardening coefficient of the steel plate when calculating strain and be 1-5% by following mode and yield strain are 1-5% and yield strength are long-pending. Particularly, described steel plate is processed into JIS-5 type sample (gauge length: 50mm, the parallel portion width: 25mm), and, carry out tension test take 0.001/ second strain rate and determine yield strength and strain hardening coefficient (strain as 1-5% time n value).

Now the microscopic structure according to steel plate of the present invention is described.

When having an amount of retained austenite to exist in the steel plate, to cause Transformation of Retained Austenite be extremely hard martensite in suffered strain meeting during distortion (shaping), consequently increase strain hardening coefficient, and by the control necking down formability is improved. The amount of suitable retained austenite is preferably 3-50%. Particularly, if the volume fraction of retained austenite is less than 3 %, member after then being shaped can not show excellent work hardening ability when being collided distortion, deformation load can only remain on low-level on, thereby work of deformation is lower, like this, dynamic energy absorption is lower, just can not realize improving the purpose of anti-crashworthiness, and, the effect of nonshrink neck is also not enough, thereby it is long-pending just can not to obtain high tensile strength and breaking elongation. On the other hand, if the volume fraction of retained austenite is higher than 50%, then process the martensite transfor mation of bringing out and when shape processing dependent variable is very little, will concentrate appearance, and, can not look to tensile strength and total percentage elongation are long-pendingly to have what to improve, because the significant sclerosis that occurs during punching out makes reaming extend (hollow extension) than suffering damage on the contrary, even and might described member be shaped, the member after the shaping can not show excellent work hardening ability in when distortion of being collided yet; Above-mentioned residual austenite content scope is determined from this angle just.

Except above-mentioned retained austenite volume fraction was this condition of 3-50%, the average crystal grain diameter that desired another condition is retained austenite should be not more than 5 μ m, and preferably not in 3 μ m. Even being the condition of 3-50%, the retained austenite volume fraction satisfied, but the average crystal grain diameter greater than 5 μ m neither be preferred, small and dispersed in steel distributes because this will hinder retained austenite, thereby has locally suppressed the improvement effect that brought by the performance of retained austenite. And, find, in microscopic structure, the average crystal grain diameter of above-mentioned retained austenite with as the ratio of the average crystal grain diameter of the ferrite of principal phase or bainite less than 0.6, the average crystal grain diameter of principal phase is not more than 10 μ m, and when preferably being not more than 6 μ m, just show excellent anti-crashworthiness and formability.

The present inventor further finds, tensile strength (TS:MPa) is when level is identical, the mean stress when equivalent strain is above-mentioned 3-10%: σ dyn basis steel sheet is processed into that it contains the dissolved carbon content in the residual austenite before the member: [C] (Wt%) with average different variation of Mn equivalent (Mneq) in the steel of Mneq=Mn+ (Ni+Cr+Cu+Mo)/2 expression.The carbon concentration of residual austenite can adopt X-ray diffraction and Mossbauer spectrum analysis to come measuring, for example, can adopt the 60th page of given method in the The Iron and Steel Institute magazine of the 206th phase of nineteen sixty-eight, by using the Alpha-ray X-ray diffraction of Mo K, the integrated reflection intensity that utilizes ferritic (200) face, (211) face and austenitic (200) face, (220) face to reach (311) face calculates the carbon concentration in the residual austenite.Based on the experimental result that the inventor obtained, also find, when be at least 70 and when being not more than 250 by the defined numerical value M of formula M=678-428 * [C]-33 * Mneq, described M value calculates by the dissolved carbon content in the residual austenite [C] with by the definite Mneq of substitutional alloy element that is added in the steel, [C] and Mneq all obtain as stated above, and, the volume fraction of residual austenite when not being out of shape in advance (Vo) with in the difference of volume fraction (V5) of carrying out the residual austenite after equivalent strain is 5% distortion in advance: when { (V0)-(V5) } is at least and is not out of shape in advance 30% o'clock of the residual austenite volume fraction, under the condition of identical static tensile strength (TS), can show higher σ dyn.In this case, when M＞250, the effect that increases owing to the intensity that transformation brought by residual austenite between deformation phases is limited in low strain regions basically, so in fact, member in advance between deformation phases all residual austenites be not fully utilized, and no longer can improve σ dyn when being out of shape at a high speed; Therefore, the upper limit of M is set at 250.In addition, when M less than 70 the time, residual austenite constantly changes between deformation phases, but at low strain regions, the degree of transformation is abundant inadequately, therefore, equivalent strain is that the mean stress σ dyn of 3-10% just remains on low-level, as a result, for static tensile strength TS, σ dyn can not satisfy relational expression σ dyn 〉=0.766 * TS+250; Therefore, the following of M is defined as 70.

As for the position of residual austenite because generally be that soft ferrite bears the strain that distortion causes, so with the non-conterminous remaining γ of ferrite mutually (austenite) generally avoid taking place strain, thereby when the about 1-5% of deflection, can not be transformed into martensite; Because the effect of residual austenite can be weakened like this, so preferred residual austenite is adjacent with ferrite.For this reason, require ferritic volume fraction to be at least 40%, and preferably be at least 60%, require average crystal grain diameter (being equivalent to average equivalent circular diameter) to be not more than 10 μ m, and preferably be not more than 6 μ m.As the top explanation of doing, because ferrite is the softest material in the constituent element constituent, therefore, it is the work hardening coefficient of a decision strain when being 1-5% and the important factor of the long-pending and yield ratio of yield strength.Its volume fraction should preferably be in the numerical range of defined.In addition, increase the ferrite volume fraction and make it refinement, can effectively improve the carbon concentration in the austenite that does not change and make it small and dispersed, like this, can cause the martensite that forms by the residual austenite that does not change and remain more refinement of constituent, and can increase volume fraction and the degree of refinement of residual austenite, this will help improving the effect and the formability of crash-resistant security.

Fraction of martensite volume is 3-30%, and requires its average crystal grain diameter (being equivalent to average equivalent circular diameter) to be not more than 10 μ m, and preferably is not more than 6 μ m.Produce movable migration in the main ferrite around of martensite, this helps reducing surrender speed and improves work hardening coefficient, the result, by specified numerical value above satisfying, can further improve anti-crashworthiness effect and formability, thereby make desired performance reach higher level, especially, strain is that work hardening coefficient * strain of 1-5% is higher than 75% yield strength greater than 54.Pass between fraction of martensite volume and average crystal grain diameter is: when low and average crystal grain diameter was big when its volume fraction, role was a locality, thereby can not satisfy above-mentioned performance requriements.As for martensitic position, when martensite and ferrite were non-conterminous, the influence of martensitic movable migration etc. seldom affacted on the ferrite, thereby had just reduced martensitic effect.Therefore, preferred martensite is adjacent with ferrite.

Now chemical constituent element in the high tensile steel plate with above-mentioned microstructure and various performances and their content range are made an explanation.Employed high tensile steel plate according to the present invention contains, by weight percentage: C is 0.03-0.3%, total amount is Si or Al or both sum of 0.5-3.0%, and if necessary, also containing total amount is the Mn that is selected from of 0.5-3.5%, Ni, Cr, one or more elements of Cu and Mo, the rest is Fe as major components, perhaps, if necessary, in above-mentioned high tensile steel plate, further add and be selected from Nb, Ti, V, P, B, one or more elements of Ca and REM, obtain to have the high tensile steel plate of high dynamic deformation drag, wherein be selected from Nb, total addition of one or more elements of Ti and V is not more than 0.3%, P is not more than 0.3%, B is not more than 0.01%, Ca is that 0.0005-0.01% and REM are 0.005-0.05%, the rest is the iron as major components, now these chemical constituent elements and their content (all by weight percentage) is discussed.

C:C be stable austenite under the room temperature the most cheap element and also since the stabilization of austenite effect of its necessity that provides that austenite is able to is residual, thereby, can think that carbon is element the most essential among the present invention.Average carbon content in the steel plate is not only influential to the volume fraction of following the residual austenite that can guarantee of room temperature, and, by during production thermal treatment, increasing the concentration in the austenite that does not change, might improve residual austenite and add the stability in man-hour.Yet, if C content, just can not guarantee that the final volume mark of residual austenite is at least 3% less than 0.03%, so 0.03% is lower limit.On the other hand, when the average C content of steel plate increased, the volume fraction of the residual austenite that can guarantee also increased, and like this, by guaranteeing the volume fraction of residual austenite, has just guaranteed the stability of residual austenite.In addition, if the C too high levels of steel plate, not only the intensity of steel plate can surpass necessary level, thereby damage it in the isochronous formability of punch process, and because the increase of static strength, the increase of dynamic stress can be hindered, and the reduction of weldability can limit the use of described steel plate as member; Therefore, C content on be defined as 0.3%.

Si, Al:Si and Al all are ferrite stabilizers, and are used for increasing ferritic volume fraction, to improve the workability of steel plate.In addition, Si and Al all can stop the formation of cementite, thereby C effectively is enriched in the austenite, and therefore, the interpolation of these elements is essential at room temperature austenite being stabilized in a suitable volume fraction.Except that Al and Si, other element that can suppress cementite generation effect after interpolation comprises P, Cu, Cr, Mo etc.By these elements of suitable interpolation, also can expect similar effect to occur.Yet if Si or Al, perhaps the interpolation total amount of sum of the two is less than 0.5%, and is just insufficient to the restraining effect that cementite produces, and like this, the conduct of being added the major part of the constituent element C of effective stable austenite is wasted with the form of carbide; This or can not guarantee the volume fraction of residual austenite of the presently claimed invention, even or the necessary working condition of residual austenite guaranteed, also can't satisfy the required condition of respective volume mark that obtains; So, will be defined as 0.5% down.In addition, if Si or Al, perhaps the interpolation total amount of sum of the two surpasses 3.0%, may become hard and crisp by the principal phase that ferrite or bainite constituted, this not only hinders the increase of resistance to deformation with the strain rate that increases, and can cause the workability of steel plate and flexible to reduce, and the increase of steel plate cost, and can make required surface treatment properties such as carrying out chemical treatment degenerate greatly; So, will on be defined as 3.0%.In the occasion that especially requires the surface property excellence, as Si≤0.1%, then can avoid occurring the Si exfoliation, then opposite as Si 〉=1.0%, the Si exfoliation can appear on whole surface, and the surface just becomes relatively poor like this.

Mn, Ni, Cr, Cu, Mo:Mn, Ni, Cr, Cu and Mo all are austenite stabilizer element, and are the effective elements of stable austenite under the room temperature.Particularly, when when the weldability angle limits the content of C, an amount of interpolation of these austenite stabilizer element can promote austenitic residual effectively.These elements also have the effect that stops cementite to generate, although the degree of this effect is littler than Al and Si, and these elements help the enrichment of C in austenite.In addition, these elements cause ferrite and the solution strengthening of bainite matrix together with Al and Si, so, also play the effect that increases the yielding stress during the high speed dynamic deformation.Yet, if the total content of one or more of above-mentioned these elements less than 0.5%, so, guarantee that necessary residual austenite will become impossible, and the intensity of steel is lowered also; Like this, just hindered the effort that effectively reduces vehicle weight; So, will be defined as 0.5% down.On the other hand, if the total amount of above-mentioned these elements surpasses 3.5%, then can be hardened by the principal phase that ferrite or bainite constituted, this not only hinders resistance to deformation and increases with the increase of strain rate, and cause the workability of steel plate and flexible to reduce, and increased the cost of steel; Therefore, will on be defined as 3.5%.

When the Nb that is added in case of necessity, Ti or V can be by forming the intensity that carbide, nitride or carbonitride improve steel plate, but, if their total addition levels surpass 0.3%, excessive nitride, carbide or carbonitride will be separated out at the intragranular or crystal boundary place of ferrite or bainite principal phase, thereby become the movable migration source between a high speed deformation phases and make that the high yielding stress of acquisition becomes impossible during dynamic deformation.In addition, the formation of carbide hinders the enrichment of C in residual austenite, and this is the most requisite aspect of the present invention, thereby has wasted C content; So, its upper limit is defined as 0.3%.

When in case of necessity, also can add B or P.B is the effective element of strengthening crystal boundary and improving armor plate strength, still, if add-on surpasses 0.01%, the effect of B will be saturated, and the reinforcement of steel plate can surpass necessary degree, thereby hinders resistance to deformation with the increase of distortion at a high speed, and reduces the workability that it makes member; Therefore, will be defined as 0.01% on it.In addition, P guarantees that steel plate obtains the effective element of high strength and residual austenite, but, if the addition of P is greater than 0.2%, then the cost of steel plate can increase, and the increase of the principal phase resistance to deformation that is made of ferrite or bainite can surpass necessary degree, the result, increase with being out of shape at a high speed with regard to having hindered resistance to deformation, and, caused stress corrosion dehiscence resistant ability and fatigue property and flexible to descend; Therefore, will on be defined as 0.2%.But consider that from preventing the angle that reduces secondary workability, toughness spot weldability and recirculation characteristic the better upper limit is 0.02%.In addition, as for S content, because the existence that is mingled with of sulfide base causes formability (particularly reaming ratio of elongation) with the angle consideration of spot weldability reduction, be limited to 0.01% on comparatively ideal from preventing as inevitable impurity.

The addition of Ca is at least 0.0005%, to improve formability (especially reaming ratio of elongation) by the shape control (spheroidizing) that the sulfide base is mingled with, consider the saturated of its effect and owing to increase the above-mentioned deleterious effect (reducing the reaming ratio of elongation) that is brought that is mingled with, so will be defined as 0.01% on it.In addition, owing to having with Ca, REM similarly acts on, so its addition also is decided to be 0.005-0.05%.

Now, linkage heat rolled steel plate and cold-rolled steel sheet describe in detail according to the production method of high tensile steel plate of the present invention to obtaining.

During dynamic deformation according to the present invention, have in the production method of the high tensile hot rolled steel sheet of high yielding stress and cold-rolled steel sheet, have the continuous casting steel billet that above-mentioned constituent element forms with one and directly send to hot rolling, hot rolling again after perhaps reheating by the continuous casting stage.Except normal continuous casting, can use the hot rolling of steel-sheet continuous casting and employing continuously hot rolling technology (endless rolling) during hot rolling, but, ferritic volume fraction is low and average crystal grain diameter is thicker in the steel sheet microstructure, and preferably the thickness (initial steel billet thickness) at hot rolling input roller end steel plate is at least 25mm.In addition, based on the consideration to the problems referred to above, the roll speed of last passage preferably is at least 500mpm during hot rolling, and more preferably is at least 600mpm.

Especially, during producing high tensile hot rolled steel sheet, hot rolling finishing temperature is preferably Ar ₃-50 ℃ to Ar ₃+ 120 ℃, this temperature range is determined by the chemical constitution of steel plate.When temperature is lower than Ar ₃In the time of-50 ℃, can form the ferrite of distortion, the yielding stress σ dyn of this ferrite during dynamic deformation, work hardening ability during strain 1-5% and formability all not good is when temperature is higher than Ar ₃In the time of+120 ℃, because the microstructure of steel plate is thicker, the result, the yielding stress σ dyn during dynamic deformation, the work hardening abilities during strain 1-5% etc. are also relatively poor, and from the angle of iron scale defective occurring, this temperature range neither be preferred.After steel plate after the hot rolling cools off on runoff table in a manner described, be carried out and batch processing.Average cooling rate herein is at least 5 ℃/second.Determine speed of cooling from the angle of guaranteeing the residual austenite volume fraction.The method of cooling of being taked can be constant cooling rate, or cooling period comprises the combination of the different cooling of a low cooling rate scope.

Then, hot-rolled steel sheet is batched,, preferably batched herein, can be caused the reduction of residual austenite volume fraction than 500 ℃ of high coiling temperatures at the coiling temperature below 500 ℃ or 500 ℃.In order to obtain martensite, coiling temperature is set in 350 ℃ or following.The above-mentioned condition of batching is for batching the back directly with the steel plate of the hot-rolled steel sheet form supply of material, and for by further cold rolling and for the cold-rolled steel sheet of anneal, above-mentioned these restricted conditions there is no need, because such condition of batching just can realize under common working condition.

According to the present invention, find especially, between the finishing temperature in hot rolling stage, final front mill table temperature and coiling temperature, there is kind of a relation.That is, as shown in Figure 5 and Figure 6, there are the specified conditions of final front mill table temperature and coiling temperature decision mainly by finishing temperature.In other words, promptly course of hot rolling being controlled, is Ar so that work as the hot rolled finishing temperature ₃-50 ℃ to Ar ₃In the time of+120 ℃, metallurgy parameter: A satisfies inequality (1) and (2).Above-mentioned metallurgy parameter: A can be by following The Representation Equation.

A＝ε ^*×exp{(75282-42745×C _eq)/[1.978×(FT+273)]}

In the formula, FT: finishing temperature (℃)

Ceq: carbon equivalent=C+Mneq/6 (%)

Mneq: manganese equivalent=Mn+ (Ni+Cr+Cu+Mo)/2 (%)

ε ^*: the strain rate (S of final pass ^-1) ${\mathrm{\ϵ}}^{*}=(V/\sqrt{R\×h_1})\×(1/\sqrt{r})\×\ln \{1/(1-r)\}$

h ₁: final pass go into the roller thickness of slab

h ₂: final pass go out the roller thickness of slab

r：(h ₁-h ₂)/h ₁

R: roller radius

V: final pass go out roller speed

Δ T: go into roll temperature (during finish to gauge first passage go into roll temperature) during finishing temperature (during finish to gauge final pass go out roll temperature)-finish to gauge

Ar ₃：901-325C％+33Si％-92Mneq

Afterwards, the average cooling rate on the runoff table is 5 ℃/second, and, preferably batch under following condition and carry out, so that metallurgy parameter: A and coiling temperature (CT) satisfy inequality (3).

9≤LogA≤18???????????(1)

ΔT≥21×LogA-178???(2)

CT≤6×LogA+312?????(3)

In above-mentioned inequality (1), consider that from the angle of the generation of remaining γ and microstructure thinning LogA is unacceptable less than 9, and this work hardening ability variation also will make yielding stress σ dyn during the dynamic deformation and 1-5% strain the time.In addition, if LogA greater than 18, then needs huge equipment to reach this purpose.If the condition of inequality (2) is not satisfied, remaining γ will be too stable, like this, although the transformation of remaining γ will take place between deformation phases, but at low strain regions, the degree of this transformation can be insufficient, and, the variation such as work hardening ability when making that yielding stress σ dyn during the dynamic deformation and strain are 1-5%.Shown in inequality (2), the lower limit of Δ T has more mutability with the reduction of LogA.And, consider from the thick degree that increases device size, the volume fraction that reduces residual austenite and microstructure, be limited to 300 ℃ on the preferred Δ T.In addition, if the relation with coiling temperature in the inequality (3) is not satisfied, this will have a negative impact to guaranteeing remaining γ phasor, and, promptly allow to obtain remaining γ phase, the remaining γ that obtains is too stable in institute, although the transformation of remaining γ phase will take place between deformation phases, but this transformation is inadequate at low strain regions, and the work hardening ability can make yielding stress σ dyn and 1-5% strain during the dynamic deformation time etc. degenerates.The lower limit of coiling temperature (CT) has more mutability with the increase of LogA.

By the way, the fraction of martensite volume that began originally was greater than 3% o'clock, and CT can be higher than 350 ℃.Yet for preventing martensitic too much formation, preferred CT is higher than 250 ℃.

After hot rolling and batching, also to carry out the processing of different step to cold-rolled steel sheet according to the present invention, and with 40% or higher compression ratio carry out cold rollingly, afterwards, cold-rolled steel sheet is annealed.The ideal annealing way is to carry out continuous annealing according to the annealing cycle as shown in Figure 7, during for the preparation continuous annealing that the finished product carried out, is 0.1 * (Ac in scope ₃-Ac ₁)+Ac ₁℃ to Ac ₃Under+50 ℃ the temperature T o, annealed 10 seconds to 3 minutes, afterwards, being chilled to scope with a speed of cooling of 1-10 ℃/second is a cooling termination temperature Tq of 550-720 ℃, then, be chilled to secondary cooling termination temperature Te with 10-200 ℃/second secondary speed of cooling again, afterwards, before being chilled to room temperature, kept 15 seconds-20 minutes at temperature T oa.If above-mentioned annealing temperature To is lower than 0.1 * (Ac ₃-Ac ₁)+Ac ₁℃, the temperature Ac in the formula ₁And Ac ₃The chemical group of basis steel sheet assigns to determine (for example, referring to " Iron﹠amp; SteelMaterial Science ": W.C.Leslie, Maruzen, P.273) then too low in the austenitic amount that described annealing temperature obtained, make in final steel plate, can not stably remain with residual austenite; Therefore, 0.1 * (Ac will be defined as under it ₃-Ac ₁)+Ac ₁℃.Equally, even because annealing temperature surpasses Ac ₃In the time of+50 ℃, the performance of steel plate does not have to improve yet and only can cause the increase of cost, so, will be defined as Ac on the annealing temperature ₃+ 50 ℃.Desired annealing time the shortest is 10 seconds under this temperature, and with temperature homogeneous and an amount of austenite of acquisition of guaranteeing steel plate, still, if the time surpasses 3 minutes, then above-mentioned effect reaches capacity, and cost also will increase.

For promoting austenitic transformation to be ferrite and to make C enrichment in the austenite that does not change make stabilization of austenite, once cooling is essential.If speed of cooling is lower than 1 ℃/second, the longer production line of then essential employing, so, consider from the angle of avoiding reducing productivity, will be defined as 1 ℃/second down.On the other hand, if speed of cooling surpasses 10 ℃/second, then ferritic transformation can not fully be carried out, and is difficult to guarantee the residual austenite in the final steel plate, thereby, will on be defined as 10 ℃/second.Carry out if once cool off in the temperature that is lower than 550 ℃, then during cooling have perlite and form, austenite stable element C can not play a role, and therefore, just can not obtain the residual austenite of q.s at last.Equally, if cooling is carried out in the temperature that is not less than 720 ℃, then ferritic transformation is insufficient.

During the cooling of subsequently secondary, must cool off fast with at least 10 ℃/seconds speed of cooling, in order to avoid perlitic transformation during cooling takes place or has the carbide of iron to separate out, but with the cooling rate that is higher than 200 ℃/second cool off can increase equipment burden.Equally, if cooling termination temperature is lower than 150 ℃ when secondary cools off, all residual austenites before cooling all will be transformed into martensite basically, thereby can not guarantee the amount of final necessary residual austenite.On the contrary, if cooling termination temperature is higher than 450 ℃, the yielding stress σ dyn during the then final dynamic deformation can be lowered.

For making austenite residual in the steel plate have room temperature stability, preferably a part of austenitic transformation is become bainite, with the carbon concentration in the further increase austenite.Keep the required temperature of bainite transformation if the secondary cooling termination temperature is lower than, just temperature should be risen to the temperature that should keep.As long as this rate of heating is between between 5 ℃/second and 50 ℃ of seconds, final plate property just can not suffer damage.On the contrary, if the secondary cooling termination temperature is higher than the formation temperature of bainite, as long as force to be chilled to the bainite formation temperature and directly deliver to a heating zone that has been predefined in the temperature that required with 5 ℃/second-200 ℃/second speed of cooling, then the final performance of steel plate will can not suffer damage yet.On the other hand because when steel plate being lower than 150 ℃ or be higher than 500 ℃ of whens insulation, can not guarantee to obtain the residual austenite of q.s, so, the temperature range that is kept is defined as 150-500 ℃.If at 150-500 ℃ temperature hold-time less than 15 seconds, then bainite transformation just can not fully be carried out, thereby can not obtain the amount of final necessary residual austenite, if and the said temperature scope hold-time above 20 minutes, the carbide that then has iron after bainite transformation is separated out or pearlitic transformation, thereby cause the waste that produces the necessary carbon of residual austenite, and, the impossible amount that obtains necessary residual austenite; Therefore, the soaking time scope is set at 15 seconds to 20 minutes.In order to promote bainite transformation, can under a steady temperature, carry out from start to finish in the insulation under 150-500 ℃, perhaps deliberately in the said temperature scope, temperature is changed and do not damage final plate property.

In the present invention, the preferred cooling conditions in annealing back is to be 0.1 * (Ac in scope earlier ₃-Ac ₁)+Ac ₁To Ac ₃+ 50 ℃ annealing temperature was handled 10 seconds-3 minutes, subsequently, being chilled to scope with a speed of cooling of 1-10 ℃/second is 550-720 ℃ secondary cooling starting temperature Tq, afterwards, being chilled to scope with 10-200 ℃/second secondary speed of cooling again is the Tem-100 ℃ of secondary cooling termination temperature Te to Tem, and Tem wherein determines by the constituent element and the annealing temperature To of steel, then, being chilled to before the room temperature, is that temperature T oa between Te-50 ℃ and 500 ℃ kept 15 seconds-20 minutes in scope.In above-mentioned this method, fast cold terminating point temperature T e in the continuous annealing circulation as shown in Figure 8 is expressed as the function of constituent element and annealing temperature To, and, annealing is carried out below a given threshold value, and the scope of overaging temperature T oa is determined by the relation between the temperature T e of itself and fast cold terminating point.

Here, Tem is the beginning temperature that martensitic transformation takes place the residual austenite at fast cold starting point Tq place.That is, Tem is by formula Tem=T ₁-T ₂, perhaps by the temperature value (T that has got rid of the effect of carbon concentration in the austenite ₁) with the temperature value (T of the effect that shows carbon concentration ₂) between difference determine.Herein, T ₁Be the temperature that calculates by the solid solution attitude concentration of element outside the de-carbon, T ₂Be by Ac ₁And Ac ₃The time carbon concentration in the residual austenite temperature that calculates, wherein Ac ₁And Ac ₃Determine that by the component in the steel plate Tq is determined by annealing temperature To.Ceq ^*Carbon equivalent when being illustrated in annealing temperature To in the residual austenite.T ₁=561-33 * { Mn%+ (Ni+Cr+Cu+Mo)/2}T ₂Can be by following Ac ₁, Ac ₃And T ₀Deng expression: Ac ₁=723-0.7 * Mn%-16.9 * Ni%+29.1 * Si%+16.9 * Cr%, Ac ₃=910-203 * (C%) ^1/2-15.2 * Ni%+44.7 * Si%+104 * V%

+31.5×Mo％-30×Mn％-11×Cr％-20×Cu％+70×

P％+40×Al％+400×Ti％，

And annealing temperature To is, when

Ceq ^*＝(Ac ₃-Ac ₁)×C/(To-Ac ₁)+(Mn+Si/4+Ni/7+Cr+Cu

+1.5Mo)/6

Greater than 0.6 o'clock, T ₂=474 * (Ac ₃-Ac ₁) * C/ (To-Ac ₁),

And work as Ceq ^*Be less than or equal at 0.6 o'clock, T ₂=474 * (Ac ₃-Ac ₁) * C/{3 * (Ac ₃-Ac ₁) * C+[(Mn+Si/4+Ni/7+Cr+Cu+1.5Mo)/2-0.85)] * (To-Ac ₁).

In other words, when Te is lower than (Tem-100) ℃, nearly all residual austenite is changed martensite into, thereby just can not obtain the amount of necessary residual austenite, if Te is higher than Tem, then steel plate can soften, thereby just can not obtain by the desired dynamic strength of static strength (TS); Therefore, Tem will be defined as on the Te.Equally, if Te is higher than 500 ℃, the carbide that then produces perlite or iron can cause form residual austenite the waste of requisite carbon, nor may obtain the amount of necessary residual austenite.On the other hand,, just be necessary to use additional cooling apparatus if Toa is lower than Te-50 ℃, and, because the temperature and the difference between steel billet temperature of continuous annealing furnace can make the bigger variation of appearance in the material; Therefore, this temperature is decided to be lower limit.

Form and production method by using above-mentioned steel plate, just might produce the high tensile steel plate that during dynamic deformation, has high yielding stress, the final microstructure that it is characterized in that steel plate be a kind of be the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes by ferrite and/or bainite with containing volume fraction, ferrite in the described tissue and bainite all can be principal phase, wherein, carrying out equivalent strain is less than or equal to 10% distortion in advance greater than 0% after, with 5 * 10 ²-5 * 10 ³During the distortion of (1/S) strain rate, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfies inequality: σ dyn 〉=0.766 * TS+250, the TS in the formula be less than under the texturizing condition in advance, and strain rate is 5 * 10 ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records in the time of (1/S) (MPa), and the work hardening coefficient when strain is 1-5% is at least 0.080.Can be processed into desired any product by process quilts such as annealing, smooth, plating according to high tensile steel plate of the present invention.

Embodiment

Now, the present invention will be described by embodiment.

Embodiment 1

15 kinds of listed in the table 1 steel are heated to 1050-1250 ℃ and carry out hot rolling, cool off and batch under the listed working condition of table 2, to produce hot-rolled steel sheet.As shown in table 3 and 4, the steel plate that satisfies according to composition condition of the present invention and working condition contains the initial residual austenite that volume fraction is 3-50%, and have and be at least 70 and be less than or equal to 250 M value again, described M value is determined by the average Mneq in solid solution in the residual austenite [C] and the steel plate, and the ratio of (volume fraction of the residual austenite after initial residual austenite volume fraction-5% distortion) and the austenitic volume fraction of initial residual shows that greater than 0.3 result described steel plate has suitable stability.According to σ dyn 〉=0.766 * TS+250, work hardening coefficient when being deformed into 1-5% greater than 0.080 and work hardening coefficient when being deformed into 1-5% and yield strength long-pending greater than 40, described as can be known steel plate has excellent anti-crashworthiness, in addition, but described steel has suitable formability and spot weldability again.The chemical composition of table 1 steel

Grade of steel		??1	??2	??3	??4	??5	??6	??7	??8
										Chemical composition (wt%)	C	??0.15	??0.15	??0.15	??0.15	??0.11	??0.16	??0.09	??0.10
Si	??1.45	??1.45	??1.45	??1.45	??1.36	??1.60	??2.10	??2.00
									Mn		??0.99	??0.79	??0.69	??0.79	??1.54	??0.90	??1.20	??1.10
P	??0.012	??0.012	??0.012	??0.012	??0.020	??0.020	??0.009	??0.015
									S		??0.002	??0.005	??0.002	??0.002	??0.003	??0.003	??0.001	??0.002
Al	??0.02	??0.02	??0.02	??0.02	??0.20	??0.01	??0.02	??0.02
									N		??0.003	??0.002	??0.003	??0.002	??0.003	??0.003	??0.002	??0.003
Al+Si	??1.47	??1.47	??1.47	??1.47	??1.56	??1.61	??2.12	??2.02
									Ni			??0.4
Cr			??0.6
									Cu					??0.4
Mo					??0.4
									Nb							??0.04
Ti							??0.06
									V
B
									Ca			??0.004
REM			??0.010
									*1		??0.99	??1.19	??1.29	??1.19	??1.94	??0.90	??1.20	??1.10
Ceq	??0.32	??0.32	??0.32	??0.32	??0.40	??0.31	??0.29	??0.28
									Mneq		??0.99	??0.99	??0.99	??0.99	??1.74	??0.90	??1.20	??1.10
Transition temperature (℃)	Ac1	??755	??750	??768	??757	??746	??760	??771											??769
									Ac3	??868	??868	??871	??866	??879	??875	??932	??904
	Ar3	??809	??809	??809	??809	??750	??819	??831										??833
									Type		??A	??A	??A	??A	??A	??A	??A		??B

A: B of the present invention: this value of data representation that adds horizontal line under the Comparative Examples has exceeded the chemical composition (continuing) of scope of the invention * 1:Mn+Ni+Cr+Cu+Mo table 1 steel

Grade of steel		??9	??10	??11	??12	??13	??14	??15
									Chemical composition (wt%)	C	??0.10	??0.10	??0.15	??0.15	?? 0.35	??0.15	??0.19
Si	??2.00	??2.00	??1.98	??0.01	??1.50	??0.30	??1.10
								Mn		??1.10	??1.10	??1.76	??1.00	??1.90	??1.48	??1.50
P	??0.015	??0.015	??0.016	??0.015	??0.015	??0.010	??0.090
								S		??0.002	??0.002	??0.001	??0.002	??0.003	??0.003	??0.003
Al	??0.02	??0.02	??0.02	??1.70	??0.03	??0.05	??0.04
								N		??0.003	??0.002	??0.002	??0.002	??0.003	??0.003	??0.005
Al+Si	??2.02	??2.02	??2.00	??1.71	??1.53	?? 0.35	??1.14
								Ni
Cr
								Cu
Mo
								Nb
Ti
								V				??0.06
B				??0.001
								Ca
REM
								*1		??1.10	??1.10	??1.76	??1.00	??1.90	??1.48	??1.50
Ceq	??0.28	??0.28	??0.44	??0.32	??0.67	??0.40	??0.44
								Mneq		??1.10	??1.10	??1.76	??1.00	??1.90	??1.48	??1.50
Transition temperature (℃)	Ac1	??769	??769	??762	??713	??746	??716										??739
								Ac3	??904	??904	??875	??871	??802	??803	??834
	Ar3	??833	??833	??756	??761	??662	??726									??738
								Type		??A	??A	??A	??A	??A	??A		??A

A: B of the present invention: this value of data representation that adds horizontal line under the Comparative Examples has exceeded scope of the present invention ^*1:Mn+Ni+Cr+Cu+Mo table 2 working condition

Grade of steel		??1	??2	??3	??4	??5	??6	??7	??8
										Hot-rolled condition	Finishing temperature ℃	??905	??910	??800	??790	??860	??840	??795	?? 960
Steel plate original depth (mm)	??26	??27	??27	??26	??28	??28	??35	??20
									The roll speed of final pass (mpm)		??600	??600	??600	??600	??700	??700	??500	??400
The final thickness of steel plate (mm)	??1.8	??1.8	??1.8	??1.8	??1.4	??1.4	??2.2	??2.2
									Strain rate (ι/second)		??150	??150	??150	??160	??190	??190	??100	??90
Calculation result (log A)	??13.65	??13.60	??14.77	??14.91	??13.50	??14.46	??14.87	??13.15
									ΔT(℃)		??140	??150	??160	??155	??120	??140	??150	??60
The condition of inequality (2)	??○	??○	??○	??○	??○	??○	??○	??×
									Cooling conditions		Average cooling rate (℃/second)	??40	??35	??80	??90	??50	??90	??60	??50
Annotate	?? *1	?? *1
										Batch condition	Coiling temperature (℃)	??390	??250	??390	??260	??350	??380	??370	??505
The condition of inequality (2)	??○	??○	??○	??○	??○	??○	??○	??×

This value of data representation that adds horizontal line down surpasses scope of the present invention ^*Cooling rate is 15 ℃/stopwatch, 2 working conditions (continuing) between 1:750-700 ℃

Grade of steel		??9	??10	??11	??12	??13	??14	??15
									Hot-rolled condition	Finishing temperature (℃)	?? 730	??900	??870	??875	??780	??840	??790
Steel plate original depth (mm)	??26	??25	??26	??28	??30	??32	??55
								The roll speed of final pass (mpm)		??500	??500	??700	??800	??800	??700	??1000
The final thickness of steel plate (mm)	??2.2	??2.2	??1.2	??1.2	??1.2	??1.2	??1.2
								Strain rate (ι/second)		??100	??100	??200	??230	??240	??210	??300
Calculation result (log A)	??15.77	??13.77	??13.07	??14.12	??12.09	??13.78	??14.09
								ΔT(℃)		??170	??130	??110	??135	??100	??125	??150
The condition of inequality (2)	??○	??○	??○	??○	??○	??○	??○
								Cooling conditions		Average cooling rate (℃/second)	??60	??50	??50	??55	??60	??50	??100
Annotate
									Batch condition	Coiling temperature (℃)	?? 510	?? 550	??370	??390	??375	??360	??380
The condition of inequality (2)	?? ×	?? ×	??○	??○	??○	??○	??○

This value of data representation that adds horizontal line down exceeds the microstructure of scope table 3 steel of the present invention

Grade of steel			???1	???2	???3	???4	???5	???6	???7	???8
											Principal phase	Title		Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Bainite
The diameter (μ m) in equivalence garden		??5.2	??5.8	??3.5	??3.0	??4.0	??3.9	??2.7	??11.0
										Ferrite		Volume fraction (%)		??77	??75	??83	??85	??80	??81	??84	??38
Residual austenite	The diameter (μ m) in equivalence garden		??2.6	??2.9	??1.7	??1.8	??2.0	??1.6	??1.6		??5.1
										Crystal grain diameter ratio with principal phase		??0.50	??0.50	??0.49	??0.60	??0.50	??0.41	??0.59	??0.46
	C concentration (%)		??1.20	??1.10	??1.29	??1.30	??1.21	??1.25	??1.25											??1.40
										Volume fraction	Be not out of shape V (0) in advance	??8	??7	??9	??9	??10	??11	??10	?? 2
	V (5) after 5% the distortion in advance	??4	??3	??5	??6	??5	??7	??6	??2
											(V(0)- V(5)}/ V(0)	??0.50	??0.57	??0.44	??0.33	??0.50	??0.36	??0.40	?? 0.00
	Martensite	The diameter (μ m) in equivalence garden		??--	??3.3	??--	??2.6	??3.0	??--											??--	??--
Volume fraction (%)										??0	??18	??0	??6	??5	??0	??0	??0
		Remaining constituent			??B	??--	??B	??--	??B									??B	??B	??B
The M value	The calculation result of M value									??132	??175	??93	??89	??103	??113	??103	?? 43
			Condition		??○	??○	??○	??○	??○									??○	??○	?? ×

This value of data representation that adds horizontal line down exceeds the constituent of scope remainder of the present invention: B=bainite, the microstructure (continuing) of P=pearly-lustre body surface 3 steel

Grade of steel			????9	??10	??11	??12	??13	??14	??15
										Principal phase	Title		Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite
The diameter (μ m) in equivalence garden		Be out of shape	??7.8	??3.3	??5.0	??2.5	??3.0	??2.7
									Ferrite		Volume fraction (%)		??88	??60	??59	??79	??50	??40	??70
Residual austenite	The diameter (μ m) in equivalence garden		??--	??--	??1.9	??2.5	??1.2	??--		??1.6
									Crystal grain diameter ratio with principal phase		??--	??--	??0.58	??0.50	??0.48	??--	??0.59
	C concentration (%)		??--	??--	??1.20	??1.23	??1.01	??--										??1.23
									Volume fraction	Be not out of shape V (0) in advance	?? 0	?? 0	??10	??7	??5	?? 0	??13
	V (5) after 5% the distortion in advance	??0	??0	??6	??4	??3	??0	??7
										(V(0)- V(5)}/ V(0)	??--	??--	??0.40	??0.43	??0.40	???--	??0.46
	Martensite	The diameter (μ m) in equivalence garden		??--	??--	??--	??--	??--										???--	??--
Volume fraction (%)									??0	??0	??0	??0	??0	??0	??0
		Remaining constituent			??P	??P	??B	??B								??B+P	??B+P	??B+P
The M value	The calculation result of M value								??--	??--	??106	??119	??183	??--	??102
			Condition		??--	??--	??○	??○								??○	??--	??○

This value of data representation that adds horizontal line down surpasses the constituent of scope remainder of the present invention: B=bainite, the mechanical property of P=pearly-lustre body surface 4 steel

Grade of steel		??1	??2	??3	??4	??5	??6	??7	??8
										Static tensile test (strain rate=0.001/ second)	TS(MPa)	??625	??810	??640	??780	??680	??655	??645	??655
YS(MPa)	??530	??560	??490	??510	??510	??530	??500	??560
									T.El(％)		??37	??28	??38	??31	??37	??40	??39	??29
N value during strain 1-5%	??0.090	??0.115	??0.105	??0.140	??0.120	??0.100	??0.110	?? 0.070
									YS×n		??48	??64	??51	??71	??61	??53	??55	?? 39
YR(％)	??85	??69	??77	??65	??75	??81	??78	??85
									TS×T.El (MPa)(％)		??23125	??22680	??24320	??24180	??25160	??26200	??25155	??18995
Distortion and BH handle in advance	Deformation method in advance	??c	??C	??L	??C	??C	??C	??C											???C
									Bian Xing equivalent strain % in advance	??5％	??5％	??5％	??3％	??5％	??7％	??5％	???5％
	BH handles	Be	Not	Be	Be	Be	Be	Be										Be
									Dynamic tensile test (strain rate=1000/ second)	σdyn	??760	??901	??769	??878	??810	??801	??776		??701
Expression formula *1	??31.3	??30.5	??28.8	??30.5	??39.1	??49.3	??31.9	?? -50.1
										Other performance	Weldability	Good	Good	Good	Good	Good	Good	Good	Good
d/do	??1.54	??1.36	??1.45	??1.26	??1.40	??1.45	??1.51	??1.51

This value of data representation that adds horizontal line down exceeds scope of the present invention ^*1: σ dyn-(0.766 * T5+250) C=along C to uniaxial extension L=along L to the mechanical property (continuing) of uniaxial extension table 4 steel

Grade of steel		??9	??10	??11	??12	??13	??14	??15
									Static tensile test (strain rate=0.001/)	TS(MPa)	??570	??575	??855	??610	??1005	??653	??650
YS(MPa)	??525	??535	??690	??500	??860	??560	??494
								T.El(％)		??20	??30	??30	??39	??20	??23	??37
N value during strain 1-5%	?? 0.070	?? 0.070	??0.105	??0.105	??0.090	?? 0.070	??0.11
								YS×n		?? 37	?? 37	??72	??53	??77	?? 39	??54
YR(％)	??92	??93	??81	??82	??86	??86	??76
								TS×T.El (MPa)(％)		??11400	??17250	??25650	??23790	??20100	??15019	??24050
Distortion and BH handle in advance	Bian Xing method in advance	??C	??C	??C	??E	??C	??E										??C
								Equivalent strain % when being out of shape in advance	??5％	??5％	??5％	??5％	??5％	??5％	??5％
	BH handles	Be	Be	Be	Be	Be	Be									Be
								The dynamic tensile test (strain rate=1000/sec)	σdyn	??620	??630	??954	??746	??1025	??710		??777
Expression formula *1	?? -66.6	?? -60.5	??49.1	??28.7	??5.2	?? -40.2	??29.1
									Other performance	Weldability	Good	Good	Good	Good	Difference	Good	Good
d/do	??1.20	??1.51	??1.30	??1.52	??1.09	??1.60	??1.40

This value of data representation that adds horizontal line has down exceeded scope of the present invention ^*1: σ dyn-(0.766 * TS+250) C=along C to uniaxial extension E=etc. Biaxially stretched

Embodiment 2

At Ar ₃Or higher temperature, 25 kinds of listed steel carry out complete hot rolling and handle in the his-and-hers watches 5, cool off afterwards again, batch, pickling and cold rolling.Temperature Ac1 and Ac3 are by determining that annealing conditions listed in table 6 heats, cools off and stop (insulation) afterwards, and described steel plate is chilled to room temperature forming of every kind of steel.Shown in Fig. 7 and 8, the steel plate that satisfies working condition of the present invention and form condition has and is at least 70 and be not more than 250 M value, the M value is determined by the average Mneq in solid solution in the residual austenite [C] and the steel plate, work hardening coefficient at least 0.080 when σ dyn 〉=0.076 * TS+250 and 1-5% strain and the work hardening coefficient when being deformed into 1-5% clearly show that with the long-pending result greater than 40 of yield strength all steel all have the anti-crashworthiness of excellence.The chemical composition of table 5 steel

Grade of steel		??16	??17	??18	??19	??20	??21	??22	??23
										Chemical composition (wt%)	C	??0.05	??0.12	??0.20	??0.26	??0.12	??0.12	??0.12	??0.12
Si	??1.20	??1.20	??1.20	??1.20	??2.00	??1.80	??1.20	??1.20
									Mn		??1.50	??1.50	??1.50	??1.50	??0.50	??0.15	??1.00	??0.15
P	??0.010	??0.012	??0.008	??0.007	??0.008	??0.007	??0.013	??0.012
									S		??0.003	??0.005	??0.002	??0.003	??0.003	??0.002	??0.003	??0.005
Al	??0.04	??0.05	??0.04	??0.05	??0.04	??0.03	??0.05	??0.04
									N		??0.003	??0.002	??0.003	??0.002	??0.003	??0.003	??0.002	??0.003
Al+Si	??0.24	??1.25	??1.24	??1.25	??2.04	??1.83	??1.25	??1.24
									Ni						??0.8			??1.5
Cr						??1.8
									Cu								??0.6
Mo								??0.2
									Nb
Ti
									V
B
									*1		??1.50	??1.50	??1.50	??1.50	??1.30	??1.95	??1.60	??1.85
Ceq	??0.30	??0.37	??0.45	??0.51	??0.27	??0.30	??0.34	??0.29
									Mneq		??1.50	??1.50	??1.50	??1.50	??0.90	??1.05	??1.30	??1.00
Transition temperature (℃)	Ac1	??742	??742	??742	??742	??762	??804	??747											??731
									Ac3	??876	??851	??830	??818	??904	??898	??854	??875
	Ar3	??786	??764	??738	??718	??845	??825	??782										??810
									Type		??A	??A	??A	??A	??A	??A	??A		??A

A: B of the present invention: this value of data representation that adds horizontal line under the Comparative Examples has exceeded the chemical composition (continuing) of scope * 1:Mn+Ni+Cr+Cu+Mo table 5 steel of the present invention

Grade of steel		??24	??25	??26	??27	??28	??29	??30	??31
										Chemical composition (wt%)	C	??0.12	??0.10	??0.14	??0.25	??0.15	??0.10	??0.10	??0.10
Si	??1.20	??0.50	??0.01	??1.50	??1.00	??1.20	??1.20	??1.20
									Mn		??1.20	??1.50	??1.50	??2.00	??1.70	??1.50	??1.50	??1.50
P	??0.010	??0.013	??0.012	??0.012	??0.100	??0.008	??0.008	??0.008
									S		??0.003	??0.005	??0.003	??0.005	??0.003	??0.003	??0.003	??0.003
Al	??0.04	??1.20	??1.50	??0.04	??0.05	??0.04	??0.04	??0.04
									N		??0.003	??0.002	??0.002	??0.002	??0.003	??0.003	??0.003	??0.003
Al+Si	??1.24	??1.70	??1.51	??1.54	??1.05	??1.24	??1.24	??1.24
									Ni
Cr	??2.0
									Cu
Mo
									Nb							??0.01		??0.02
Ti							??0.02
									V									??0.01
B				??0.002
									*1		??3.20	??1.50	??1.50	??2.00	??1.70	??1.50	??1.50	??1.50
Ceq	??0.49	??0.35	??0.39	??0.58	??0.43	??0.35	??0.35	??0.35
									Mneq		??2.20	??1.50	??1.50	??2.00	??1.70	??1.50	??1.50	??1.50
Transition temperature (℃)	Ac1	??779	??722	??707	??745	??734	??742	??742											??742
									Ac3	??838	??872	??850	??818	??834	??857	??865	??858
	Ar3	??699	??747	??718	??685	??729	??770	??770										??770
									Type		??A	??A	??A	??A	??B	??A	??A		??A

A: B of the present invention: this value of data representation that adds horizontal line under the Comparative Examples exceeds the chemical composition (continuing) of scope * 1:Mn+Ni+Cr+Cu+Mo table 5 steel of the present invention

Grade of steel		??32	??33	??34	??35	??36	??37	??38	??39	??40
											Chemical composition (wt%)	C	?? 0.02	?? 0.35	??0.12	??0.12	??0.10	??0.12	??0.10	??0.12	??0.12
Si	??1.20	??1.00	?? 0.20	?? 3.50	??1.50	??1.20	??1.20	??1.50	??1.20
										Mn		??1.50	??1.20	??1.50	??1.50	??1.50	??1.50	?? 1.50	?? 0.10	??1.50
P	??0.010	??0.008	??0.010	??0.010	?? 0.250	??0.010	??0.010	??0.010	??0.010
										S		??0.003	??0.003	??0.002	??0.003	??0.003	??0.003	??0.003	??0.002	??0.002
Al	??0.04	??0.05	?? 0.04	??0.05	??0.04	??0.04	??0.04	??0.05	??0.04
										N		??0.003	??0.003	??0.002	??0.003	??0.003	??0.003	??0.003	??0.003	??0.003
Al+Si	??1.24	??1.05	?? 0.24	?? 3.55	??1.54	??1.24	??1.24	??1.55	??1.24
										Ni								?? 1.5	?? 0.2
Cr
										Cu								?? 1.0
Mo
										Nb										?? 0.20
Ti									?? 0.15
										V
B						?? 0.012
										*1		??1.50	??1.20	??1.50	??1.50	??1.50	??1.50	??4.00	??0.30	??1.50
Ceq	??0.27	??0.55	??0.37	??0.37	??0.35	??0.37	??0.56	??0.15	??0.37
										Mneq		??1.50	??1.20	??1.50	??1.50	??1.50	??1.50	??2.75	??0.20	??1.50
Transition temperature (℃)	Ac1	??742	??739	??713	??809	??751	??742	??717	??762												??742
										Ac3	??892	??801	??806	??954	??887	??851	??814	??903	??911
	Ar3	??796	??710	??731	??840	??780	??764	??655	??893											??764
										Type		??B	??B	??B	??B	??B	??B	??B	??B		??B

A: B of the present invention: this value of data representation that adds horizontal line under the Comparative Examples exceeds scope * 1:Mn+Ni+Cr+Cu+Mo table 6 working condition of the present invention

Grade of steel		??16	??17	??18	??19	??20	??21	??22	??23	??24	??25	??26	??27	??28
															Cold rolling condition	Rolling compression ratio (%)	??80	??80	??80	??80	??80	??80	??80	??80	??80	??80	??80	??80	??80
Thickness of slab (mm)	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8
														Annealing conditions		Annealing temperature (To ℃)	??800	??800	??800	??800	??800	??800	??800	??800	??790	??780	??780	??780	??800
Annealing time (second)	??90	??90	??90	??90	??120	??120	??90	??90	??90	??90	??90	??90	??90
															A speed of cooling (℃/second)	??5	??5	??5	???5	???8	???8	??5	??5	??5	??5	??5	??5	??8
Tq ℃ of chilling starting temperature)	??680	??680	??700	??680	??680	??680	??680	??650	??650	??650	??650	??680	??680
															Secondary speed of cooling (℃/second)	??100	??100	??100	??80	??100	??100	??100	??130	??130	??100	??100	??100	?100
Chilling final temperature (Te ℃)	??350	??350	??350	?280	??280	??350	??350	??200	??300	??300	??300	??200	? 400
															Calculation result (T1 ℃)	??512	??512	??512	??512	??531	??526	??518	??528	??488	??512	??512	??495	??505
Calculation result (Ceq *)	??0.41	??0.53	??0.60	?0.64	??0.64	??0.64	??0.56	??0.41	??1.22	??0.53	??0.53	??0.92	??0.55
															Calculation result (T2 ℃)	??138	??147	??144	??161	??214	??116	??139	??310	??300	??166	??179	??248	??134
Calculation result (Tem ℃)	??374	??364	??368	??351	??317	??410	??379	??23.8	??188	??345	??332	??247	??371
															Stopping temperature (Toa ℃)	??350	??350	??350	??400	??400	??400	??350	??300	??350	??400	??400	??350	??400
The residence time (second)	??150	??180	??180	??250	??180	??180	??180	??180	??180	??180	??150	??180	??180

This value of data representation that adds horizontal line down exceeds scope table 6 working condition of the present invention (continuing)

Grade of steel		??29	??30	??31	??32	??33	??34	??35	??36	??37	??38	??39	??40
														Cold rolling condition	Rolling compression ratio (%)	??68	??68	??68	??80	??80	??80	??80	??80	??80	??70	??70	??70
Thickness of slab (mm)	??1.2	??1.2	??1.2	??0.8	??0.8	??0.8	??0.8	??0.8	??0.8	??1.2	??1.2	??1.2
													Annealing conditions		Annealing temperature (To ℃)	??780	??780	??780	??800	??760	??780	??850	??800	??800	??780	??800	??800
Annealing time (second)	??90	??90	??90	??90	??90	??90	??90	??90	??90	??90	??90	??90
														A speed of cooling (℃/second)	??8	??5	??5	??5	??5	??5	??5	??5	??5	??5	???5	???5
Tq ℃ of chilling starting temperature)	??680	??630	??680	??680	??680	??680	??680	??680	??680	??630	??680	??680
														Secondary speed of cooling (℃/second)	??100	??150	??100	??100	??100	??100	??100	??100	??100	??100	??100	??100
Chilling final temperature (Te ℃)	??350	??320	??350	??350	?? 300	??300	??300	??300	??300	??350	??250	??300
														Calculation result (T1 ℃)	??512	??512	??512	??512	??521	??512	??512	??512	??512	??470	??554	??512
Calculation result (Ceq *)	??0.60	??0.62	??0.60	??0.35	??1.29	??0.42	??0.82	??0.59	??0.52	??0.66	??0.53	??0.65
														Calculation result (T2 ℃)	??143	??153	??144	??120	??495	??186	??200	??143	??147	??73	??285	??165
Calculation result (Tem ℃)	??369	??359	??368	??392	??26	??326	??311	??369	??364	??398	??270	??346
														Stopping temperature (Toa ℃)	??330	??320	??400	??400	??300	??350	??300	??350	??400	??400	??400	??400
The residence time (second)	??180	??180	??180	??180	??180	??180	??150	??180	??180	??180	??180	??180

Grade of steel			??16	??17	??18	??19	????20	????21	??22	??23	??24	??25	??26	??27	??28
																Principal phase	Title		Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	The plain part of iron	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Bainite	Ferrite
The diameter (μ m) in equivalence garden		??7.2	??6.4	??5.3	??5.5	??8.1	??6.9	??5.1	??5.5	??5.1	??7.1	??5.3	??3.8	??5.3
															Ferrite		Volume fraction (%)		??85	??65	??48	??41	??80	??55	??69	??82	??55	??73	??66	??41	??55
Residual austenite	The diameter (μ m) in equivalence garden		??2.8	??2.6	??1.9	??1.2	??2.8	??2.8	??2.9	??2.1	??1.3	??1.8	??1.9	??1.2		??1.3
															Ratio with the crystal grain diameter of principal phase		??0.39	??0.41	??0.36	??0.22	??0.35	??0.41	??0.57	??0.38	??0.25	??0.25	??0.36	??0.32	??0.25
	C concentration (%)		??1.29	??1.19	??1.21	??1.16	??1.08	??1.10	??1.28	??1.03	??1.04	??1.17	??1.16	??1.05																??1.48
															Volume fraction	The preceding V (0) of distortion in advance	??4	??10	??15	??20	???9	??10	??8	??12	??10	??7	??10	??21	??11
	V (5) after 5% the distortion in advance	??2	??5	??8	??7	???3	??3	??3	??4	??3	??3	??4	??8	??8
																{V(0)- V(5))/V(0)	??0.50	??0.50	??0.47	??0.65	??0.67	??0.70	??0.63	??0.67	??0.70	??0.57	??0.60	??0.62	0.27
	Martensite	The diameter (μ m) in equivalence garden		??1.6	??1.3	??--	??2.5	??3.2	??3.1	??1.9	??2.8	??3.1	??3.3	??2.6																??4.2	??1.6
Volume fraction (%)															??1	??1	??0	??5	??3	??4	??1	??6	??4	??4	??4	??15	??1
		Remaining constituent			??B	??B	??B	??B	??B	??B	??B	??B	??B	??B														??B	??B	??B
The M value	The calculation result of M value														??77	??177	??113	??132	??185	??171	??89	??206	??160	??129	??131	??164	?? -12
			Condition		??○	??○	??○	??○	??○	??○	??○	??○	??○	??○														??○	??○	??×

This value of data representation that adds horizontal line down exceeds scope of the present invention

Grade of steel			??29	??30	??31	??32	??33	????34	??35	??36	??37	??38	??39	??40
															Principal phase	Title		Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Ferrite	Bainite
The diameter (μ m) in equivalence garden		??6.8	??7.1	??6.6	?10.9	??4.1	??6.2	??5.5	??6.8	??5.9	??4.8	?10.4	??5.9
														Ferrite		Volume fraction (%)		??71	??70	??73	??92	??25	??70	??55	??66	??58	??32	??80	??65
Residual austenite	The diameter (μ m) in equivalence garden		??2.5	??2.7	??2.6	??--	??2.8	??--	??2.1	??2.6	??2.1	??1.2	??--		??1.9
														Ratio with the crystal grain diameter of principal phase		??0.37	??0.38	??0.39	??--	??0.68	??--	??0.38	??0.38	??0.36	??0.25	??--	??0.32
	C concentration (%)		??1.10	??1.23	??1.19	??--	??1.42	??--	??1.38	??1.41	??1.33	??1.35	??--															??1.42
														Volume fraction	The preceding V (0) of distortion in advance	??8	??7	??7	?? 0	??18	?? 0	??8	??7	??7	??6	?? 0	??6
	V (5) after 5% the distortion in advance	??3	??3	??3	?? 0	??15	?? 0	??6	??5	??5	??5	?? 0	??5
															(V(0)- V(5))/V(0)	??0.63	??0.57	??0.57	?? --	?? 0.17	?? --	?? 0.25	?? 0.29	?? 0.29	?? 0.17	??? --	?? 0.17
	Martensite	The diameter (μ m) in equivalence garden		??2.9	??4.1	??2.9	??--	??4.2	??2.9	??3.1	??2.7	??3.6	??3.6															???--	??3.8
Volume fraction (%)														??4	??2	??4	??0	??26	??6	??2	??5	??3	??3	??0	??6
		Remaining constituent			??B	??B	??B	??B	??B+P	??B	??B	??B	??B													??B	??B	??B
The M value	The calculation result of M value													??159	??101	??120	?? --	?? 31	?? --	?? 38	?? 25	?? 59	?? 9	?? --	?? 21
			Condition		??○	??○	???○	??×	??×	??×	??×	??×	??×													??×	??×	??×

This value of data representation that adds horizontal line down exceeds the mechanical property of scope table 8 steel of the present invention

Grade of steel		??16	??17	??18	??19	??20	??21	??22	??23	??24	??25	??26	??27	??28
															Static tensile test (strain rate=0.001/ second)	TS(MPa)	??576	??653	??812	??936	??681	??669	??637	??732	??748	??597	??619	??1176	??752
YS(MPa)	??397	??477	??609	??552	??463	??435	??452	??447	??471	??406	??402	??635	??647
														T.El(％)		??43	??35	??31	??25	??33	??34	??35	??32	??30	??37	??35	??23	??32
N value during 1～5% strain	??0.117	??0.107	??0.095	??0.095	??0.105	??0.112	??0.116	??0.112	??0.103	??0.122	??0.116	??0.092	??0.122
														YS×n		??47	??51	??58	??52	??49	??49	??52	??50	??49	??50	??47	??58	??79
YR(％)	??0.69	??0.73	??0.75	??0.59	??0.68	??0.65	??0.71	??0.61	??0.63	??0.68	??0.65	??0.54	??0.86
														TS×T.El (MPa)(％)		??24768	??22855	??25172	??23400	??22473	??22746	??22295	??23424	??22440	??22089	??21665	??27048	??24064
Distortion and BH handle in advance	Bian Xing method in advance	??C	??C	??L	??C	??C	??C	??C	??C	??E	??C	??L	??C																??C
														Equivalent strain when being out of shape in advance	??5	??5	??10	??5	??5	??3	??5	??5	??10	??5	??5	??1	??5
	BH handles	Be	Not	Be	Be	Be	Be	Be	Be	Not	Be	Not	Be															Be
														Dynamic tensile test (strain rate=1000/ second	σdyn	??712	??771	??890	??986	??823	??815	??761	??842	??849	??742	??765	??1162		??801
Expression formula *1	??20.8	??20.8	??18.0	??19.0	??51.4	??52.5	??23.1	??31.3	??26.0	??34.7	??40.8	??11.2	-25.0
															Weldability		Good	Good	Good	Good	Good	Good	Good	Good	Good	Good	Good	Good	Good

This value of data representation that adds horizontal line down exceeds scope of the present invention ^*1: σ dyn-(0.766 * TS+250) C=along C to uniaxial extension L=along L to the mechanical property (continuing) of Biaxially stretched table 8 steel such as uniaxial extension E=

Grade of steel		??29	??30	??31	??32	???33	???34	??35	???36	???37	???38	???39	???40
														Static tensile test (strain rate=0.001/ second)	TS(MPa)	??667	??679	??703	??502	??1156	??570	??865	??849	??716	??916	??515	??756
YS(MPa)	??420	??475	??464	??437	??694	??353	??675	??501	??437	??641	??453	??514
													T.El(％)		??35	??34	??30	??31	??17	??25	??31	??32	??34	??22	??32	??26
N value during 1～5% strain	??0.118	??0.112	??0.126	??0.144	0.079	??0.141	0.079	0.077	??0.086	??0.132	??0.164	??0.142
													YS×n		??50	??53	??58	??63	??55	??50	??53	?? 39	?? 38	??85	??74	??73
YR(％)	??0.63	??0.70	??0.66	??0.87	??0.60	??0.62	??0.78	??0.59	??0.61	??0.70	?? 0.88	??0.68
													TS×T.El (MPa)(％)		??23345	??23086	??21090	15562	19652	14250	??26815	??27168	??24344	??20152	16480	19656
Distortion and BH handle in advance	Deformation method in advance	??C	??E	??C	??C	??C	??C	??C	??C	??C	??C	??C															??C
													Equivalent strain when being out of shape in advance (%)	??5	??5	??5	??5	??5	??5	??5	??5	??5	??5	??5	??5
	BH handles	Not	Be	Be	Be	Be	Be	Be	Be	Be	Be	Be														Be
													Dynamic tensile test (strain rate=1000/ second)	σdyn	??806	??792	??810	??592	??1026	??632	??867	??855	??768	??901	??598		??789
Expression formula * 1	??45.1	??21.9	??21.5	-42.5	-109.5	??-54.6	-45.6	-45.3	-30.5	-50.7	-46.5	-40.1
														Weldability		Good	Good	Good	Good	Difference	Good	Good	Good	Good	Difference	Good	Good

This value of data representation that adds horizontal line down exceeds scope * 1 of the present invention: σ dyn-(0.766 * TS+250) C=along C to uniaxial extension E=etc. Biaxially stretched

Adopt following method that microstructure is estimated.

Examine with a kind of nital and Japanese patent application and to disclose that disclosed reagent corrodes the cross section of steel sheet rolling direction among the clear 59-219473, then, debate not the measurement of the observation of present position and average crystal grain diameter (equivalent garden diameter) and volume fraction by what 1000 times opticmicroscopes carried out ferrite, bainite, martensite and remaining tissue.

Corrode the cross section of rolling direction with disclosed reagent among the flat 3-351209 of Japanese patent application, then, determine the average equivalent garden diameter of residual austenite again with 1000 times opticmicroscope, it is definite that the residual austenite present position also adopts same Photomicrograph to observe.

Adopt Mo-K α X-ray analysis, go out the volume fraction (V γ: with per-cent is unit) of residual austenite according to following Equation for Calculating.

Vγ＝(2/3){100/(0.7×α(211)/γ(220)+1)}+(1/3){100/(0.78×α(211)/γ(311)+1)}

In the formula, α (211), γ (220), α (211) and γ (311) represent the peak pole strength.

Use Cu-K α X-ray analysis, lattice parameter (unit: dust) determine that by the reflection angle of austenitic (200) face, (220) face and (311) face the carbon concentration in the residual austenite (C γ: with per-cent is unit) then goes out according to following Equation for Calculating.

C γ=(lattice parameter-3.572)/0.033

Adopt the evaluation of carrying out performance in the following method.

According to JIS5 (gauge length: 50mm, average portion width: 25mm), carry out tension test with 0.001/ second strain rate, by determining tensile strength (TS), yield strength (YS), total unit elongation (T.EL) and work hardening coefficient (the n value during the 1-5% strain), calculate YS * work hardening coefficient, yield ratio (YR=YS/TS * 100) and TS * T.EL.

From carrot-free limit, enlarge with of the punching of one 30 ° tapered punch a 20mm, and the counter bore diameter (d) when determining that crackle runs through thickness of slab (d0, reaming 20mm) is stretched than (d/d0), measures its outer hemming performance according to this with initial counter bore diameter.

Using the electrode of electrode head radius as 5 times of the square roots of steel plate thickness, is 0.9 times of welding one spot welding sample under the condition of spraying electric current at electric current, if described spot-welding sample is being peeled off fracture with a chisel when disrumpent feelings, but then the judgement spot weldability is defective.

Industrial usability

As mentioned above, the present invention might provide high tensile hot rolled steel sheet and cold-rolled steel sheet take a kind of economy and stable mode as automobile, anti-crashworthiness and the formability of the inaccessiable excellence of institute before described steel plate provides, the result has just significantly expanded use object and the condition of high-strength steel sheet.

Claims (14)

1. high tensile steel plate that during dynamic deformation, has high yielding stress, it is characterized in that the final microstructure of described steel plate be a kind of be the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes by ferrite and/or bainite with containing volume fraction, in this tissue, ferrite and bainite all can be principal phase, wherein with greater than 0% and be less than or equal to 10% equivalent strain and be out of shape in advance after, with 5 * 10 ²-5 * 10 ³During the strain rate of (1/ second) distortion, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfies inequality: σ dyn 〉=0.766 * TS+250, and the TS in the formula (MPa) is not in advance under the texturizing condition, and strain rate is 5 * 10 ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records when (1/ second), and the work hardening coefficient when strain is 1-5% is at least 0.080.

2. high tensile steel plate that has high yielding stress during dynamic deformation according to claim 1, wherein, work hardening coefficient and yield strength are during the 1-5% strain long-pendingly is at least 40.

3. high tensile steel plate that during dynamic deformation, has high yielding stress, it is characterized in that the final microstructure of described steel plate be a kind of be the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes by ferrite and/or bainite with containing volume fraction, ferrite and bainite all can be principal phase in this tissue, wherein carry out equivalent strain greater than 0% and be less than or equal to 10% distortion in advance again after, with 5 * 10 ²-5 * 10 ³During the strain rate of (1/ second) distortion, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfies inequality: σ dyn 〉=0.776 * TS+250, and TS in the formula (MPa) is not in advance under the texturizing condition, and strain rate is 5 * 10 ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records when (1/ second), average Mn equivalent { the M value that Mneq=Mn+ (Ni+Cr+Cu+Mo)/2} determines by solid solution in the residual austenite [C] and steel, its definition is M=678-428 * [C]-33Mneq, described M value should be at least 70 and be not more than 250 again, the volume fraction of residual austenite when not being out of shape in advance with carry out equivalent strain be the difference of residual austenite volume fraction after 5% the distortion in advance should be at least residual austenite volume fraction when not being out of shape in advance 30%, and the work hardening coefficient when strain is 1-5% is at least 0.080.

4. one kind according to each the steel plate among the claim 1-3, and the average crystal grain diameter of wherein said residual austenite is not more than 5 microns; The ratio of the average crystal grain diameter of described residual austenite and the average crystal grain diameter of ferrite in the principal phase or bainite is not more than 0.6, and the average crystal grain diameter of principal phase is not more than 10 microns, preferably is not more than 6 microns.

5. one kind according to each steel plate among the claim 1-4, and wherein, fraction of martensite volume is 3-30%, and described martensitic average crystal grain directly is not more than 10 microns, and preferably is not more than 5 microns.

6. one kind according to each steel plate among the claim 1-5, and wherein ferritic volume fraction is at least 40%.

7. one kind according to each steel plate among the claim 1-6, and wherein, yield ratio is no more than 85%, and tensile strength and breaking elongation are long-pendingly to be at least 20,000.

8. one kind according to each steel plate among the claim 1-7, it also contains, by weight percentage, the C of 0.03-0.3%, total amount be the Si of 0.5-3.0% or Al or both sums, and if necessary, also contain total amount and be one or more elements among Mn, Ni, Cr, Cu and the Mo of being selected from of 0.5-3.5%, the rest is Fe as main ingredient.

9. steel plate according to Claim 8, if necessary, it can further contain, by weight percentage, be selected from one or more elements among Nb, Ti, V, P and the B, the total amount that wherein is selected from one or more elements among Nb, Ti and the V is no more than 0.3%, P be no more than 0.3% and B be no more than 0.01%.

10. one kind according to each steel plate among the claim 1-9, and if necessary, it can further contain, by weight percentage, and the Ca of 0.0005-0.01% and the REM of 0.005-0.05% (rare earth metal).

11. a production has the method for the high tensile hot rolled steel sheet of high yielding stress during dynamic deformation, the microstructure of wherein said hot-rolled steel sheet be a kind of be the compound microstructure that the third mixture mutually of 3-50% residual austenite constitutes by ferrite and/or bainite with containing volume fraction, ferrite and bainite all can be principal phase in this tissue, wherein carry out equivalent strain greater than 0% and be less than or equal to 10% distortion in advance again after, with 5 * 10 ²-5 * 10 ³When the strain rate of (1/ second) was out of shape, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfied inequality: σ dyn 〉=0.766 * TS+250, the TS in the formula (MPa) are that strain rate is 5 * 10 under the condition of not being out of shape in advance ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records when (1/ second), and, work hardening coefficient when strain is 1-5% is at least 0.080, described production method is characterised in that: a continuous casting steel billet contains, by weight percentage, the C of 0.03-0.3%, total amount is Si or Al or the sum of the two of 0.5-3.0%, and if necessary, also containing total amount is the Mn that is selected from of 0.5-3.5%, Ni, Cr, one or more elements of Cu and Mo, and it is as further necessary, also contain and be selected from Nb, Ti, V, P, B, one or more elements among Ca and the REM, wherein be selected from Nb, the total amount of one or more elements among Ti and the V is not more than 0.3%, and P is not more than 0.3%, and B is not more than 0.01%, Ca is that 0.0005-0.01% and REM are 0.005-0.05%, surplus person is the Fe as main ingredient, described continuous casting steel billet is directly sent to hot rolling by the continuous casting stage or reheat after hot rolling again, hot rolling is at Ar ₃-50 ℃ to Ar ₃Finish under+120 ℃ the finishing temperature, after the hot rolling, cool off, afterwards, batch described steel plate in the temperature that is not higher than 500 ℃ with 5 ℃/second average cooling temperatures.

12. according to the method for claim 11, wherein, at Ar ₃-50 ℃ to Ar ₃Carry out hot rolling under+120 ℃ the hot rolling finishing temperature, so that metallurgy parameter: A satisfies following inequality (1) and (2), subsequently, average cooling rate in runoff table is at least 5 ℃/second, and, coiling process is controlled, so that described metallurgy parameter: the relation between A and coiling temperature (CT) satisfies following inequality (3):

9≤LogA≤18???????????????????(1)

ΔT≥21×LogA-178?????????????(2)

CT≤6×LogA+312???????????????(3)

13. a production has the method for the high strength cold rolled steel plate of high yielding stress during dynamic deformation, the microstructure of wherein said cold-rolled steel sheet be a kind of be the compound microstructure that the third mixture mutually of the residual austenite of 3-50% constitutes by ferrite and/or bainite with containing volume fraction, ferrite and bainite all can be principal phase in this tissue, wherein carry out equivalent strain greater than 0% and be less than or equal to 10% distortion in advance again after, with 5 * 10 ²-5 * 10 ³When the strain rate of (1/ second) was out of shape, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfied inequality: σ dyn 〉=0.766 * TS+250, the TS in the formula (MPa) are that strain rate is 5 * 10 under the condition of not being out of shape in advance ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records when (1/ second), and, work hardening coefficient when strain is 1-5% is at least 0.080, described cold-rolled steel sheet production method is characterised in that: a kind of continuous casting steel billet contains, by weight percentage, the C of 0.03-0.3%, total amount is Si or Al or the sum of the two of 0.5-3.0%, and if necessary, also containing total amount is the Mn that is selected from of 0.5-3.5%, Ni, Cr, one or more elements among Cu and the Mo, in addition, as further necessity, then also contain and be selected from Nb, Ti, V, P, B, one or more elements among Ca and the REM, wherein be selected from Nb, the total amount of one or more elements among Ti and the V is for being not more than 0.3%, P is not more than 0.3%, B is not more than 0.01%, Ca is that 0.0005-0.01% and REM are 0.005-0.05%, surplus person is the Fe as main ingredient, described continuous casting steel billet is directly sent to hot rolling by the continuous casting stage, hot rolling again after perhaps reheating is carried out pickling to the hot-rolled steel sheet that is batched after the hot rolling, and then cold rolling, for during producing the continuous annealing that the finished product carried out, be 0.1 * (Ac in scope ₃-Ac ₁)+Ac ₁℃ to Ac ₃Annealing is 10 seconds-3 minutes under+50 ℃ the temperature, then, it with a speed of cooling scope of being cooled to of 1-10 ℃/second a cooling termination temperature of 550-720 ℃, afterwards, it with 10-200 ℃/second the secondary speed of cooling scope of being cooled to 150-450 ℃ secondary cooling termination temperature, after this, before being chilled to room temperature, insulation is 15 seconds-20 minutes under the temperature of 150-500.

14. have the method for the high strength cold rolled steel plate of high yielding stress during the production dynamic deformation according to claim 13, the microstructure of wherein said cold-rolled steel sheet be a kind of be the compound microstructure that the third mixture mutually of 3-50% residual austenite constitutes by ferrite and/or bainite with containing volume fraction, ferrite and bainite all can be principal phase in this tissue, wherein carry out equivalent strain greater than 0% and be less than or equal to 10% distortion in advance again after, with 5 * 10 ²-5 * 10 ³When the strain rate of (1/ second) was out of shape, the mean value σ dyn (MPa) of the yielding stress when equivalent strain is 3-10% satisfied inequality: σ dyn 〉=0.766 * TS+250, the TS in the formula (MPa) are that strain rate is 5 * 10 under the condition of not being out of shape in advance ^-4-5 * 10 ^-3Maximum stress in the static tensile test that records when (1/ second), and, work hardening coefficient when strain is 1-5% is at least 0.080, and described production method is characterised in that: during in for the production continuous annealing step that the finished product carried out, in 0.1 * (Ac ₃-Ac ₁)+Ac ₁℃ to Ac ₃Under+50 ℃ the temperature, annealed 10 seconds-3 minutes, subsequently, with a speed of cooling scope of being cooled to of 1-10 ℃/second is 550-720 ℃ secondary cooling starting temperature Tq, afterwards, is the Tem-100 ℃ of secondary cooling termination temperature Te to Tem with 10-200 ℃/second the secondary speed of cooling scope of being cooled to, temperature value Tem-100 wherein ℃ by steel form and annealing temperature To determines, then, before being chilled to room temperature, be incubated 15 seconds-20 minutes down in Te-50 ℃ to 500 ℃ temperature T oa.

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