CN104583445B

CN104583445B - Steel plate

Info

Publication number: CN104583445B
Application number: CN201380044652.9A
Authority: CN
Inventors: 匹田和夫; 玉城朱里; 小嵨启达; 高桥克
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2012-08-28
Filing date: 2013-08-28
Publication date: 2016-10-19
Anticipated expiration: 2033-08-28
Also published as: WO2014034714A1; EP2891727A1; IN2015DN01523A; EP2891727B1; TWI481730B; MX2015002530A; KR101683406B1; US20150225821A1; BR112015004191A2; TW201420776A; ES2707893T3; KR20150038303A; CN104583445A; BR112015004191B1; JP5541428B1; JPWO2014034714A1; PL2891727T3; EP2891727A4

Abstract

The purity of the metal structure of the steel plate of the present invention is less than 0.08%, as the α of Mn degree of segregation be less than 1.6, in thermoforming by less than 5% plastic strain low strain dynamic forming part with by more than 20% plastic strain Large strain forming part described thermoforming after the difference Δ Hv of average hardness be less than 40.

Description

Steel plate

Technical field

The present invention relates to such as hot pressing with thermoforming simultaneously or the most immediately Implement preferred steel plate (thermoforming steel plate) in the purposes of quenching.In more detail, the present invention relates to Even and if such as implement be attended by Large strain molding (be forming part by more than 20% plasticity should Become molding) thermoforming time, also can suppress the strain induced ferrite phase transformation in forming part, in heat The thermoforming steel that after molding, the anisotropy of hardness toughness uniformly, after good-toughness and thermoforming is few Plate.

The application was based on 08 28th, 2012 Japanese Patent Applications 2012-187959 in Japanese publication CLAIM OF PRIORITY, is hereby incorporated its content.

Background technology

In recent years, in the field of automotive sheet, due to the raising or resistance to of the fuel consumption charge of automobile The raising of collision characteristic, the range of application therefore with high-tensile high-strength steel sheet expands.One For as, during steel plate generation high intensity, compressing property can reduce.Therefore, along with high strength steel The application of plate, it becomes difficult to manufacture the goods of complicated shape.Specifically, due to along with the height of steel plate Intensity, ductility reduction, therefore rupture at the position that degree of finish is high, or along with steel plate High intensity, resilience or sidewall warpage increase.As a result of which it is, there is the size of the component processed Precision produces the problems such as deterioration.Therefore, use high intensity, particularly there is the anti-of more than 780MPa The steel plate of tensile strength, utilize and compressing manufacture that to have the goods of complicated shape be very difficult.

If not by compressing but be shaped by roll molding, then for high intensity Steel plate also can carry out processing to a certain degree.But, in roll molding, have and be applicable only to Having the restriction of the processing of the component of same cross-sectional in the longitudinal direction, the degree of freedom of Components Shape is notable Be restricted.

Accordingly, as the technology that the difficult compressing materials such as high-strength steel sheet are pressed, example As patent document 1 discloses that the material being supplied to molding is heated after the thermoforming (example that is shaped Such as hot pressing) technology.This technology is to simultaneously or becoming with molding for soft steel plate before the forming Quench immediately after type, thus guarantee good mouldability when molding, carry out on this basis After molding, obtained the technology of the shaped component with high intensity by quenching.According to this technology, quenching After can obtain the tissue being mainly made up of martensite, with using, there is the tissue that is made up of heterogeneous structure The situation of high-strength steel sheet is compared, and can obtain the shaped component of local deformation ability or good-toughness.

At present, above-mentioned hot pressing promotes the application to the component with more simple shape, from now on Expect the application in the component implementing the strictest molding such as deburring molding.But, in application In time implementing the component of the strictest molding, Large strain forming part can occur strain inducing ferrum element Body phase transformation, has the probability that hardness can reduce partly in component after thermoforming.

In order to suppress this strain induced ferrite phase transformation, in region at higher temperature, carry out thermoforming. But, the high temperatureization of hot-forming temperature can cause the reduction of productivity ratio, the increase of manufacturing cost, surface The deterioration etc. of character, it is dfficult to apply to mass-produced technology.Such as, patent documentation 1 is recorded More than 850 DEG C, implement the content of press process, but have following situation in actual hot pressing: The steel plate being heated to about 900 DEG C in heating furnace etc. is extracted out from heating furnace, transports and put into pressure The period of machine processed, it may occur that temperature is reduced to less than 850 DEG C.This situation is difficult to suppress answering in molding Become induction ferrite transformation.

The sight of the stable material quality in component after the productivity ratio improving hot pressing, raising molding simultaneously Point sets out, and Patent Document 2 discloses and can omit the material utilizing the heat extraction in compacting tool set to carry out The manufacture method of the excellent hot pressing high strength steel component of the productivity ratio of refrigerating work procedure.Patent documentation 2 Disclosed method is the most excellent invention, but need contain in large quantities in steel Mn, Cr, Cu, Ni etc. have the element of the effect improving hardenability.Therefore, the technology of patent documentation 2 has cost increasing The problem added.It addition, in the component using the technology of patent documentation 2 to manufacture, have a following probability: There is the toughness deterioration caused because of existing various field trashes and because of being mingled with of extending in the rolling direction The anisotropy of the toughness that thing (mainly MnS) causes.Owing to actual component performance is by low toughness The characteristic of side is dominated, therefore when the anisotropy of flexible, it is impossible to play mother originally fully Material characteristic.Such as described in patent documentation 3 by utilizing Ca process to carry out extended field trash Morphology Control, it is possible to reduce the anisotropy of toughness.But, now there is following problem: although tough Property the direction that reduces the most on toughness value improve but field trash amount itself increase in component, therefore Other directivity toughness value reduces.

Prior art literature

Patent documentation

Patent documentation 1: Japanese Unexamined Patent Publication 2002-102980 publication

Patent documentation 2: Japanese Unexamined Patent Publication 2006-213959 publication

Patent documentation 3: Japanese Unexamined Patent Publication 2009-242910 publication

Summary of the invention

The problem that invention is to be solved

As it has been described above, hot pressing in the prior art rests on the structure being applied to have more simple shape Part.Therefore, in view of when being applied to the component implementing the strictest molding such as deburring molding After the thermoforming that strain induced ferrite phase transformation contingent, because of Large strain forming part is caused The hardness of the local of component (through the steel plate of thermoforming process) reduces, the anisotropy of toughness and tough The technical task of the reduction of property value, does not the most inquire into.

Even if it is an object of the invention to provide in above-mentioned problem, i.e. implementing and be attended by Large strain molding Thermoforming time, also can suppress the strain induced ferrite phase transformation in forming part, the hardness after thermoforming The heat one-tenth that uniformly anisotropy of good-toughness after (difference of hardness is little), thermoforming and toughness is little Type steel plate.

For solving the means of problem

The present inventors conducts in-depth research to solve above-mentioned problem.

Result has new discovery: by controlling the chemical composition of steel plate, field trash amount and center segregation, i.e. Just, when implementing the thermoforming being attended by Large strain molding, strain induced ferrite phase transformation can also be suppressed, Can obtain hardness after thermoforming uniformly, the anisotropy of good-toughness and toughness is little after thermoforming heat Molding steel plate.It addition, it is stable that hardness is uniformly referred to as in the following description hardness distribution sometimes.

As follows based on above-mentioned newfound idea of the invention.

(1) steel plate of a mode of the present invention relates to a kind of steel plate, it is characterised in that chemical composition In terms of quality % containing C:0.18%～0.275%, Si:0.02%～0.15%, Mn:1.85%～2.75%, Sol.Al:0.0002%～0.5%, Cr:0.05%～1.00%, B:0.0005%～0.01%, P:0.1% Below, below S:0.0035%, below N:0.01%, Ni:0～0.15%, Cu:0～0.05%, Ti:0～0.1%, Nb:0～0.2%, remainder is Fe and impurity；The purity of metal structure is Less than 0.08%；The α as Mn degree of segregation shown in following formula a is less than 1.6；In thermoforming The low strain dynamic forming part of the plastic strain by less than 5% and the height of the plastic strain by more than 20% The difference Δ Hv of the average hardness after the above-mentioned thermoforming of strain forming part is less than 40.

α=maximum Mn the concentration of quality % (unit of the thickness of slab central part of above-mentioned steel plate be)/(distance Above-mentioned surface of steel plate be the unit of 1/4 depth location of thickness of slab be the average Mn concentration of quality %)

Formula a

(2), in the steel plate described in above-mentioned (1), above-mentioned chemical composition can replace above-mentioned Fe's further A part, containing choosing free Ni:0.02%～0.15% and Cu:0.003%～0.05% in terms of quality % In the group constituted a kind or 2 kinds.

(3) above-mentioned (1) or (2) described in steel plate in, above-mentioned chemical composition can replace further State a part of Fe, in terms of quality % containing choosing free Ti:0.005%～0.1% and Nb:0.005%～ In 0.2% group constituted a kind or 2 kinds.

(4) above-mentioned (1)～(3) according to any one of steel plate in, on the surface of above-mentioned steel plate Can have coating further.

Invention effect

According to the aforesaid way of the present invention, even if being attended by Large strain implementing deburring molding etc. During the thermoforming of type, it is possible to the strain induced ferrite phase transformation of suppression forming part, therefore can obtain in heat The anisotropy after molding with the good-toughness after the distribution of stable hardness, thermoforming and toughness is low Steel plate.This steel plate is such as the machine headed by the car shell structure component of automobile, vehicle to run component etc. The raw material of tool structure component etc. is preferred, and therefore the present invention is industrially the most useful.

It addition, thermoforming is carried out according to conventional methods.Such as raw steel can be heated to Ac₃ Point above (about 800 DEG C) and Ac₃The temperature of point less than+200 DEG C, carry out more than 0 second and 600 seconds with Under holding, conveyance be pressed to press, carry out the holding of more than 5 seconds in lower dead center. Now, mode of heating can properly select, in the case of instant heating, can carry out electrified regulation or Altofrequency heats.It addition, for generally heating, the stove set to heating-up temperature can be used to heat Deng.Carry out air cooling in the period of conveyance to press, therefore when the time of conveyance is elongated, have Compacting starts the probability causing ferrite transformation, generation to soften before.Therefore, the conveyance time is preferred It it is less than 15 seconds.In order to prevent the rising of mold temperature, the cooling of mould can be carried out.Now, cooling As long as method carries out carrying out the type of cooling as required such as cooling tubing, flowing cold-producing medium in mould ?.

Detailed description of the invention

Steel plate (the sometimes referred to as steel plate of present embodiment) to an embodiment of the invention below Illustrate in greater detail.% relevant with the chemical composition of steel plate in the following description is entirely quality %.

1. chemical composition

(1) C:0.18%～0.275%

C is after improving the hardenability of steel, determining the intensity after quenching and then control thermoforming Local ductility and the important element of toughness.It addition, C is austenite generates element, therefore have Following effects: strain induced ferrite phase transformation during suppression Large strain molding, component after thermoforming In be easily obtained the distribution of stable hardness.But, when C content is less than 0.18%, difficult after quenching To guarantee the tensile strength of more than the 1100MPa as preferred intensity, and, it is impossible to obtain obtain by The effect of the stable hardness distribution that above-mentioned effect brings.On the other hand, when C content is more than 0.275% Time, local ductility and toughness reduce.Therefore, making C content is 0.18%～0.275%.C content Preferred upper limit be 0.26%, the preferred upper limit be 0.24%.

(2) Si:0.02%～0.15%

Si is the element of the oxide skin adaptation after improving thermoforming while improving hardenability.But, When Si content is less than 0.02%, there is the situation that cannot obtain the effect above fully.Therefore, Si is made The lower limit of content is 0.02%.Preferably lower limit is 0.03%.On the other hand, when Si content is more than 0.15% Time, make austenite phase transformation during thermoforming required for heating-up temperature become high temperature significantly.Therefore, have Cost required for causing heat treatment improves or the situation becoming insufficient that quenches because of underheat. It addition, Si is ferrite generating elements, therefore when Si too high levels, then there is following situation: Gao Ying It is prone to occur in strain induced ferrite phase transformation, component after thermoforming hardness partly when becoming type Reduce, stable hardness distribution cannot be obtained.And then, for a large amount of Si contain, have due to Implement wettability when hot-dip processes to reduce and the situation of not plating occurs.Therefore, Si content is upper It is limited to 0.15%.

(3) Mn:1.85%～2.75%

Mn is effective for the intensity of steel after improving the hardenability of steel and stably guaranteeing quenching Element.It addition, Mn is austenite generates element, strain inducing during Large strain molding therefore can be suppressed Ferrite transformation, component after thermoforming are easily obtained stable hardness distribution.But, work as Mn When content is less than 1.85%, there is the situation that cannot fully obtain the effect above.Therefore, Mn content is made Lower limit is 1.85%.On the other hand, when Mn content is more than 2.75%, the effect above is saturated, on the contrary Cause the toughness deterioration after quenching.Therefore, the upper limit making Mn content is 2.75%.Mn content excellent Choose and be limited to 2.5%.

(4) sol.Al:0.0002%～0.5%

Al is that molten steel carries out deoxidation, the element making steel completely change.When sol.Al content is less than 0.0002% Time, deoxidation is insufficient.Therefore, the lower limit making sol.Al content is 0.0002%.And then, Al is also For improving the hardenability of steel plate and stably guaranteeing the intensity after quenching and effective element, therefore may be used Contain energetically.But, even if containing more than 0.5%, not only its effect is saturated but also cause into This increase.Therefore, the upper limit making Al content is 0.5%.

It addition, sol.Al represents acid-solubility Al, its content does not comprise the Al being not dissolved in acid₂O₃ Al amount contained in Deng.

(5) Cr:0.05%～1.00%

Cr is the element of the hardenability improving steel.It addition, Cr is austenite generates element, therefore can press down Strain induced ferrite phase transformation during Large strain molding processed, component after thermoforming are easily obtained steady Fixed hardness distribution.But, when Cr content is less than 0.05%, has and cannot obtain above-mentioned effect fully The situation of fruit.Therefore, the lower limit making Cr content is 0.05%.Preferably lower limit be 0.1%, more preferably Lower limit be 0.2%.On the other hand, when Cr content is more than 1.00%, Cr carbide in steel It is enriched with.Result is, the solid solution of the carbide in heating process when being supplied to thermoforming postpones, Hardenability reduces.Therefore, the upper limit making Cr content is 1.00%.The preferred upper limit of Cr content is 0.8%.

(6) B:0.0005%～0.01%

B is effective element for the intensity after improving the hardenability of steel and stably guaranteeing quenching. But, when B content is less than 0.0005%, have the situation that cannot obtain the effect above fully.Cause This, the lower limit making B content is 0.0005%.On the other hand, when B content is more than 0.01%, on State effect saturated and then cause the toughness in quenching portion to deteriorate.Therefore, the upper limit making B content is 0.01%. The preferred upper limit of B content is 0.005%.

(7) below P:0.1%

The element that P contains typically as impurity.But, due to have improve steel hardenability, And then stably guarantee the effect of intensity of the steel after quenching, therefore can contain energetically.But, work as P When content is more than 0.1%, toughness deteriorates significantly.Therefore, P content is limited to 0.1%.P The preferred upper limit of content is 0.05%.The lower limit of P content is not required to limit especially, but P content Excessively minimizing can cause significant cost to improve.The lower limit that therefore, it can make P content is 0.0002%.

(8) below S:0.0035%

S is the element contained as impurity.It addition, particularly form MnS, become and cause toughness to drop The low anisotropic main cause with toughness.When S content is more than 0.0035%, the deterioration of toughness Become notable, therefore S content is limited to 0.0035%.The lower limit of S content is not required to limit especially Fixed, but the excessive minimizing of S content can cause significant cost to improve, and therefore can make under S content It is limited to 0.0002%.

(9) below N:0.01%

N is the element contained as impurity.When N content is more than 0.01%, formed thick in steel Nitride, make local deformation ability and toughness deteriorate significantly.Therefore, N content is limited to 0.01%.The lower limit of N content is not required to limit especially, but the excessive minimizing of N content can cause Significant cost improves.Therefore, the lower limit of N content can be 0.0002%.N content preferred Lower limit is more than 0.0008%.

In addition to above element, the steel plate of present embodiment also can be containing following arbitrary element. These elements are not required to necessarily contain.Therefore, it is not required to the lower limit of limited content especially, it Lower limit be 0%.

(10) below Ni:0.15%, below Cu:0.05%

Ni and Cu is effective for the intensity after improving the hardenability of steel and stably guaranteeing quenching Element.Therefore, can be containing a kind or 2 kinds of these elements.But, even if exceeding the above-mentioned upper limit Being worth and contain any one element, the effect above is the most saturated and also becomes unfavorable on cost.Therefore, The content of each element is described above.Preferably Ni content is less than 0.10%, Cu content is less than 0.03%. In order to the most reliably obtain the effect above, preferably comprise and select free more than Ni:0.02% and Cu: In more than 0.003% group constituted a kind or 2 kinds.

(11) below Ti:0.1%, below Nb:0.2%

Ti and Nb is that steel plate is being heated to Ac₃Point is above, be supplied to suppression recrystallization during thermoforming, And then form fine carbide, element that suppression grain is grown up, made austenite grain become particulate.Work as Austria When family name's body grain becomes particulate, the toughness of thermoforming component dramatically improves.It addition, for Ti, Generating TiN by being preferentially bonded with the N in steel, the B that suppression causes because of the precipitation of BN disappears Consumption.As a result of which it is, by can improve the hardenability produced by B containing Ti.On obtaining State effect, can be containing a kind or 2 kinds of these elements.But, contain when exceeding above-mentioned higher limit When having any one element, have that the amount of precipitation of TiC or NbC increases, C is consumed, quench after intensity Situation about reducing.Therefore, the content of each element is described above.The upper limit of preferably Ti content is 0.08%, The upper limit of Nb content is 0.15%.It addition, in order to obtain the effect above more reliably, preferably comprise choosing In the group that free more than Ti:0.005% and more than Nb:0.005% is constituted a kind or 2 kinds.

Remainder other than the above is Fe and impurity.Impurity refer to from the raw material such as Ore or slag or The material that person is mixed into from manufacturing environment.

The steel plate of the present invention can be hot rolled steel plate, cold-rolled steel sheet any one, it is also possible to be to hot rolling Steel plate or cold-rolled steel sheet implement annealing hot rolled steel plate or the annealing cold-rolled steel sheet of annealing.

2. metal structure

(1) purity: less than 0.08%

A system, B system and C contained in the steel plate that the purity of present embodiment specifies with JIS G0555 It is that the summation of the algorithm calculations of field trash amount defines.When field trash amount increases, crevasse crack propagation becomes Easily, the anisotropy causing toughness deterioration and toughness adds.Therefore, the upper limit making purity is 0.08%. The preferably upper limit is 0.04%.In the steel plate of present embodiment, the MnS as A system field trash becomes The main anisotropic main cause of reduction toughness.It is therefore especially preferred that A system field trash is 0.06% Below.More preferably A system field trash is less than 0.03%.

Wherein, the preferably low person of purity, but can make from the viewpoint of cost its lower limit be 0.003% or 0.005%.

(2) Mn degree of segregation less than α: 1.6

Mn is prone near the thickness of slab central part of steel plate occur segregation when casting.When this center segregation is big Time, the field trash such as MnS concentrates on segregation portion, causes the reduction of toughness and the anisotropic increasing of toughness Add.And then, the martensite generated in segregation portion during due to quenching is hard, and therefore toughness occurs Deterioration.It addition, by the interaction of Mn Yu P, in Mn segregation portion, P segregation also increases, Thus also result in toughness deterioration.Therefore, making the Mn degree of segregation α shown in following formula 1 is less than 1.6. Mn degree of segregation α is preferably close to 1.0 (i.e. not segregations), but from the viewpoint of cost, can make it Lower limit is 1.03 or 1.05.

α=[the maximum Mn concentration (quality %) of thickness of slab central part]/[distance surface is the 1/4 of thickness of slab The average Mn concentration (quality %) of depth location] (formula 1)

3. coating

For the purpose of improving corrosion resistance etc., can be formed on the surface of the thermoforming steel plate of the present invention Coating and make surface treated steel plate.Even if having coating, the effect of present embodiment is also not damaged. Coating can be electrodeposited coating, can also be hot-dip coated.As electrodeposited coating, can exemplify electro-galvanized layer, Electroplating Zn-Ni alloy layer etc..As hot-dip coated, dip galvanized, alloyed hot-dip can be exemplified Zinc coat, hot dip alumin(i)um coating, hot dip galvanizing-Al alloy-layer, hot dip galvanizing-Al-Mg alloy-layer, heat Immersion plating Zn-Al-Mg-Si alloy-layer etc..Plating adhesion amount there is no and limits especially, can be general In the range of.

4. manufacture method

Then, the representational manufacture method of the thermoforming steel plate of the present invention is illustrated.Pass through Use the manufacture method comprising following operation, the steel plate of present embodiment can be readily available.

(1) continuous casting process (S1)

Utilize continuous casting process that the molten steel with above-mentioned chemical composition is made steel disc (slab).At this Continuously in casting process preferably: the temperature that makes liquid steel temperature be high more than 5 DEG C of liquidus temperature of distance and Making the molten steel casting amount of time per unit is less than 6ton/ minute and then real before slab solidifies completely Donor center's segregation reduction processes.

When casting continuously, the casting amount (casting rate) of the time per unit of molten steel was more than 6ton/ minute Time, the MOLTEN STEEL FLOW in casting mold is fast, therefore becomes prone to supplement field trash, increase being mingled with in slab Thing.It addition, when liquid steel temperature is to be less than 5 DEG C apart from liquidus temperature, viscosity rises, field trash becomes Must be difficult to float, field trash amount in steel increases, purity deteriorates (value increase).To molten steel When casting continuously, the temperature more preferably making molten steel is higher more than 8 DEG C than liquidus temperature, casting amount is Less than 5ton/ minute.

Process as center segregation reduction, such as can be by the non-solidification layer before slab is solidified completely Carry out electromagnetic agitation or non-solidification layer pressure etc. and carry out mitigation or the discharge in enrichment portion.

(2) slab homogenizes treatment process (S2)

Segregation reduction after solidifying completely as slab processes, and can carry out by heating of plate blank extremely further 1150 DEG C～1350 DEG C, keep the slab of 10 hours～50 hours to homogenize process.By at above-mentioned bar Carry out slab under part to homogenize process, degree of segregation can be reduced further.It addition, heating-up temperature is excellent Choose be limited to 1300 DEG C, the upper limit of preferred retention time be 30 hours.

(3) hot-rolled process (S3)～refrigerating work procedure (S4)～rolling step (S5)

By by having carried out above-mentioned continuous casting process and having carried out slab as required and homogenize process Operation and the steel disc that obtains implements hot rolling after being heated to 1050 DEG C～1350 DEG C, make steel plate.Will knot The steel plate having restrainted hot rolling keeps 5 seconds～20 seconds in this temperature province.By water-cooled by steel plate after holding It is cooled to 400 DEG C～the temperature province of 700 DEG C.Then, cooled steel plate is wound.

Steel disc has the situation containing non-metallic inclusion, and this non-metallic inclusion is to make to carry out steel plate The toughness of the component after quenching and the reason of local deformability deterioration.Therefore, steel disc is being supplied to During hot rolling, preferably make the solid solution fully of these non-metallic inclusions.Steel disc for above-mentioned chemical composition For, by reaching more than the 1050 DEG C solid solutions promoting above-mentioned non-metallic inclusion when being supplied to hot rolling. It is therefore preferable that the temperature being supplied to the steel disc of hot rolling is more than 1050 DEG C.It addition, be supplied to the steel disc of hot rolling Temperature be more than 1050 DEG C, the steel disc less than 1050 DEG C is heated, reach 1050 DEG C with Upper.

When making its phase transformation in the case of processing austenite after finish rolling, rolling set tissue residue, End article becomes the anisotropic main cause of generation.Therefore, in order to become difficult to understand from recrystallization The phase transformation of family name's body, carries out the guarantor of more than 5 seconds in its temperature province after preferably the rolling at steel plate terminates Hold.In order to carry out the holding of more than 5 seconds in manufacturing circuit, such as in the cooling zone after finish rolling not Carry out water cooling and carry out transporting.

By making coiling temperature be more than 400 DEG C, the ferrite area occupation ratio in metal structure can be improved. When ferrite area occupation ratio height, the intensity of hot rolled steel plate can be suppressed, when carrying out cold rolling in rear operation, Load control or steel plate smooth/strip thickness control becomes easy, manufacture efficiency and improve.It is therefore preferable that winding Temperature is more than 400 DEG C.

On the other hand, by making coiling temperature be less than 700 DEG C, the oxide skin after winding can be suppressed to grow up, The generation of meeting inhibited oxidation skin defect.It addition, the deadweight because of coiled material after winding also can be suppressed to be caused Deformation, the generation of the scratch of the coiled material surface caused because of this deformation can be suppressed.It is therefore preferable that volume It it is less than 700 DEG C around temperature.It addition, above-mentioned deformation is produced by following reason: the most non-phase When there is ferrite transformation after the coiling in change austenite remaining, this non-transformed austenite, ferrite transformation The volumetric expansion that caused and thermal contraction afterwards, thus the winding tension of coiled material can be lost.

(4) pickling process (S6)

For the steel plate after above-mentioned rolling step, pickling can be carried out.Pickling can be according to conventional methods Carry out.Before pickling or after pickling, in order to smooth rectification or promotion oxide skin are peeled off, epidermis can be implemented Dress rolling, does not interferes with the effect of present embodiment.Extensibility when implementing skin-pass is not required to spy Not specifying, for example, 0.3% less than 3.0%.

(5) cold rolling process (S7)

The pickled plate obtained by above-mentioned pickling process also can be implemented as required cold rolling.For cold For rolling method, carry out according to conventional methods.Cold rolling reduction ratio in common scope, In general it is 30%～80%.

(6) annealing operation (S8)

For in the hot rolled steel plate obtained in above-mentioned rolling step (S5) or above-mentioned cold rolling process (S7) For the cold-rolled steel sheet obtained, 700 DEG C～the annealing of 950 DEG C can be implemented as required.

By hot rolled steel plate and cold-rolled steel sheet are implemented to be maintained at the annealing of the temperature province of more than 700 DEG C, The impact of hot-rolled condition can be reduced, the further stabilisation of the characteristic after quenching can be realized.It addition, For cold-rolled steel sheet, recrystallization can be passed through thus steel plate generation softening, before improving thermoforming Processability.Therefore, when hot rolled steel plate or cold-rolled steel sheet are implemented annealing, preferably remain in 700 DEG C with On temperature province.

On the other hand, by making annealing temperature be less than 950 DEG C, can be at the required cost of suppression annealing Guarantee high productivity ratio simultaneously.Further, since the coarse of tissue can be suppressed, the most after quenching Can ensure that the best toughness.Thus, when hot rolled steel plate or cold-rolled steel sheet are implemented annealing, excellent Choosing is maintained at the temperature province of less than 950 DEG C.

After annealing when implementing annealing, cooling is the coldest with the average cooling rate of 3 DEG C/sec～20 DEG C/sec But to 550 DEG C.By making above-mentioned average cooling rate be more than 3 DEG C/sec, thick pearly-lustre can be suppressed Body or the generation of thick cementite, the characteristic after quenching can be improved.It addition, by make above-mentioned averagely Rate of cooling is less than 20 DEG C/sec, it is easy to accomplish the stabilisation of material.

(7) plating process (S9)

When forming coating on surface of steel plate and make coated steel sheet, plating and hot-dip are all according to often Rule method is carried out.In the case of galvanizing by dipping, continuous hot-dipping galvanizing equipment can be used, setting The standby above-mentioned annealing operation of interior enforcement and plating then, the most also can be independent with above-mentioned annealing operation Plating is implemented on ground.Galvanizing by dipping can be implemented Alloying Treatment further and carry out alloyed hot-dip plating Zinc.When implementing Alloying Treatment, preferably making alloying treatment temperature is 480 DEG C～600 DEG C.Pass through Making alloying treatment temperature is more than 480 DEG C, and Alloying Treatment can be suppressed uneven.It addition, by making Alloying treatment temperature is less than 600 DEG C, can guarantee high production while suppression manufacturing cost Rate.After galvanizing by dipping, in order to carry out smooth rectification, skin-pass can be implemented as required.For For the extensibility of skin-pass, carry out according to conventional methods.

Field trash amount in this steel plate and degree of segregation operation before hot rolling are determined, substantially in heat Essentially without change before and after molding.Therefore, as long as the chemical composition of the steel plate before thermoforming, being mingled with Thing amount (purity) and degree of segregation meet the scope of present embodiment, then manufactured by hot pressing afterwards Hot pressing component meets the scope of present embodiment similarly.

Embodiment

In test converter, the steel with the chemical composition shown in table 1 is carried out melting, uses test Casting continuously is implemented with continuous casting machine.As shown in table 2, to when casting in continuous casting process Casting rate and molten steel heating-up temperature poor (liquid steel temperature-liquidus temperature) carried out various change. It addition, in Solidification Process in Continuous Slab Casting, carried out electromagnetic agitation.And then, in slab finally solidification portion, By in constriction continuous casting machine up and down to roll interval non-solidification layer pressure (extrusion), enter Go the discharge in center segregation portion.As a comparison, a part be also made for not carrying out electromagnetic agitation and/or The slab of extrusion (center segregation reduction process).Afterwards, at 1300 DEG C, carried out the plate of 20 hours Base homogenizes process.A part eliminates slab and homogenizes process.The slab using so making is carried out Hot rolling, carries out afterwards cooling down, winding, has obtained the hot rolled steel plate that thickness of slab is 5.0mm or 2.9mm. Hot-rolled condition now be the heating-up temperature of slab be 1250 DEG C, rolling starts temperature and is 1150 DEG C, rolls End temp processed is 900 DEG C, coiling temperature is 650 DEG C.Hot rolling be implemented by multi-pass rolling and Rolling has carried out the holding of 10 seconds after terminating.Cooling after hot rolling is carried out by water-cooled.In order to Relatively, a part keeps.

It addition, the test casting continuously that casting rate uses in actual production equipment and the present embodiment In machine, the size of equipment is different.Therefore, table 2 recorded in view of size factor, be converted into The value of the casting rate of actual production equipment.It addition, the molten steel heating-up temperature difference in table 2 refers to molten steel Temperature deducts the value after liquidus temperature.

According to conventional methods the hot rolled steel plate of gained is implemented pickling processes and be made for pickled plate.Right For the pickled plate that thickness of slab is 5.0mm, cold rolling by implementing, it is made for the cold-rolled steel of 2.9mm Plate.The hot rolled steel plate of a part is implemented plating.The cold-rolled steel sheet of a part is set in continuous annealing Standby middle enforcement full annealed (annealing temperature be 800 DEG C, annealing time be 60 seconds), and then to it In a part implement electrogalvanizing later.Further, to hot rolled steel plate and a part for cold-rolled steel sheet Annealing (annealing temperature be 800 DEG C, annealing time be 60 seconds) is implemented in continuous hot-dipping galvanizing equipment And galvanizing by dipping.It is 460 DEG C, part enforcement 20 at 540 DEG C by the temperature making galvanizing by dipping bathe The Alloying Treatment of second, thus obtained hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel plate.

The steel plate manufactured is implemented hot pressing molding as material to be tested, use hot pressing assay device. Will be with billet size: 150mm is square, punching aperture: 36mm (gap 10%) is punched Steel plate in heating furnace, be heated to surface of steel plate temperature to 900 DEG C, keep at this temperature 4 minutes it After, take out from heating furnace.Afterwards, it is cooled to 750 DEG C by letting cool, in the time arriving 750 DEG C Point implements hot deburring molding, maintains 1 minute in lower dead center.The following institute of hot deburring condition of molding State.

Perforating machine shape: circular cone,

Perforating machine diameter: 60mm,

Pressing speed: the 40mm/ second,

Cooling after molding is to be carried out by the mould cooling kept in lower dead center 1 minute.

For the cross section parallel with the rolling direction of the steel plate through hot pressing, utilize Vickers Determine deburring portion (the Large strain forming part of the plastic strain by more than 20%) and flange part (is moulded Property dependent variable is the low strain dynamic forming part of less than 5%) the hardness of 1/4 depth location of thickness of slab in cross section. Measure load for 98kN.Assay method is on the basis of JIS Z2244.In identical thickness of slab position with 200 μm intervals are moved while implementing this hardness measurement of 5 times altogether.Try to achieve and each component is obtained The meansigma methods of 5 Vickers hardness numbers obtained, as average hardness (Hv).Try to achieve the flat of deburring portion All differences (Δ Hv=[flange part Hv]-[deburring portion Hv]) of the average hardness of hardness and flange part, The situation that Δ Hv is less than 40 is judged to that hardness is qualified.The survey result of hardness is shown in table 3.

Wherein, dependent variable be the thickness of slab of each position measuring processed steel plate, by the thickness of slab after processing Try to achieve relative to the decrement of the thickness of slab before processing.

It addition, using manufactured steel plate as material to be tested, to toughness value (absolute value of toughness) and The anisotropy of toughness is investigated.

Investigation is carried out according to following getting.First, by the steel plate of above-mentioned 2.9mm in heating furnace It is heated to surface of steel plate temperature and reaches 900 DEG C, after keeping 4 minutes at this temperature, from heating furnace Take out.Then, it is cooled to 750 DEG C by letting cool, uses flat plate mold at the time point arriving 750 DEG C Clamp from upper and lower, maintain 1 minute.Afterwards, the table back side from material to be tested is ground, It is made for the thickness of 2.5mm.Become to roll right angle orientation with rolling direction according to the length direction of sample Mode acquires Charpy-type test sample.Now, breach is the V breach of the 2mm degree of depth.Test Temperature is room temperature, has carried out impact test on the basis of JISZ 2242.The impact value of rolling direction (is inhaled Receive energy/sectional area) with rolling right angle orientation impact value be used for anisotropic index.

Show the result in table 3.The result of test is if when the impact value of length rolling direction is 70J/cm²Above and impact value ratio is more than 0.65, then it is judged to that characteristic is good.

The purity of steel plate is investigated on the basis of JIS G0555.For the steel plate of each test number, At 5, cut out material to be tested, in the position of 1/8,1/4,1/2,3/4 and the 7/8 of thickness of slab, make Purity has been investigated with point count.In the result of each thickness of slab position, using numerical value maximum for Reinheitszahl as The purity of this material to be tested.Purity is A system, B system and the summation of C system field trash.

Mn degree of segregation is to utilize EPMA to try to achieve by carrying out the composition surface analysis of Mn.To respectively The steel plate of test number, cuts out material to be tested at 5, the 1/4 of thickness of slab, the position of 1/2 with The multiplying power of 500 times measures 10 visual fields, have employed the meansigma methods of the Mn degree of segregation of each visual field.

In test number 16～19,21,22, it is all flat with the flange part as low strain dynamic variant part All hardness is compared, and the average hardness as the deburring portion of Large strain variant part significantly decreases, Δ Hv Value be up to 41～99.Its reason is, because of the strain induced ferrite phase caused by deburring processing Become, deburring portion there occurs softening.Now, the hardness of manufactured heat product is the most different, The intensity of products formed will not become identical, partly become low-intensity, therefore damage as goods can By property.

It addition, in test number 4,8,10,12,15,18,20,23,24, chemical composition, Purity or degree of segregation are departing from the scope of the present invention, and therefore rolling direction impact value and/or impact value ratio are not Fully.

On the other hand, have the steel plate of chemical composition of the present invention either with or without cold rolling process, with or without moving back How are firer's sequence and plating kind, and Δ Hv is-4～24, the average hardness of flange part and deburring The difference of the average degree in portion is little, Large strain molding time hardness and the excellent in stability of intensity.

It addition, the anisotropy for the toughness after hot rolling and toughness is also shown for sufficiently being worth.

Operational feasibility in industry

Even if deburring molding etc. implemented by the steel plate of the present invention is attended by the thermoforming of Large strain molding Time, also can suppress the strain induced ferrite phase transformation in forming part, therefore can obtain and have after thermoforming Have stable hardness to be distributed, steel plate that the anisotropy of good-toughness after thermoforming, toughness is low.Should Steel plate is such as the mechanical realization structure headed by the car shell structure component of automobile, vehicle to run component etc. The raw materials such as part are preferred, and therefore the present invention is industrially the most useful.

Claims

1. a steel plate, it is characterised in that

Chemical composition contains in terms of quality %

C:0.18%～0.275%,

Si:0.02%～0.15%,

Mn:1.85%～2.75%,

Sol.Al:0.0002%～0.5%,

Cr:0.05%～1.00%,

B:0.0005%～0.01%,

Below P:0.1%,

Below S:0.0035%,

Below N:0.01%,

Ni:0～0.15%,

Cu:0～0.05%,

Ti:0～0.1%,

Nb:0～0.2%,

Remainder is Fe and impurity；

The purity of metal structure is less than 0.08%；

The α as Mn degree of segregation shown in following formula 1 is less than 1.6；

In thermoforming by less than 5% plastic strain low strain dynamic forming part with by more than 20% Plastic strain Large strain forming part described thermoforming after the difference Δ Hv of average hardness be 40 with Under,

A system, B system and C system field trash contained in the steel plate that described purity JIS G0555 specifies The summation of the algorithm calculations of amount defines,

α=maximum Mn the concentration of quality % (unit of the thickness of slab central part of described steel plate be)/(distance Described surface of steel plate be the unit of 1/4 depth location of thickness of slab be the average Mn concentration of quality %) formula 1。

Steel plate the most according to claim 1, it is characterised in that described chemical composition further with In the quality % meter group containing choosing free Ni:0.02%～0.15% and Cu:0.003%～0.05% composition 1 kind or 2 kinds with replace described Fe a part.

3. according to the steel plate described in claim 1 or claim 2, it is characterised in that described chemistry Composition contains choosing free Ti:0.005%～0.1% and Nb:0.005%～0.2% further in terms of quality % In the group constituted a kind or 2 kinds is to replace a part of described Fe.

Steel plate the most according to claim 1 and 2, it is characterised in that on the surface of described steel plate On there is coating further.

Steel plate the most according to claim 3, it is characterised in that enterprising on the surface of described steel plate One step has coating.