CN107735505B

CN107735505B - Steel plate and manufacturing method

Info

Publication number: CN107735505B
Application number: CN201680035011.0A
Authority: CN
Inventors: 匹田和夫; 桥本元仙; 竹田健悟; 高田健
Original assignee: Japanese Style Stock Co
Current assignee: Japanese Style Stock Co
Priority date: 2015-06-17
Filing date: 2016-06-17
Publication date: 2019-10-18
Anticipated expiration: 2036-06-17
Also published as: KR101997382B1; US20180171445A1; EP3312299A4; EP3312299A1; CN107735505A; WO2016204288A1; TWI588270B; TW201708564A; BR112017025756A2; MX2017015266A; KR20180004262A; JP6206601B2; JPWO2016204288A1

Abstract

A kind of steel plate, it is characterized in that, it is the steel plate for improving formability and wearability, with defined at being grouped as, the metal structure of steel plate meet the number of the carbide of ferrite grain boundaries relative to the ratio of the number of the carbide in ferrite crystal grain be more than 1 and ferrite partial size be 5 μm~50 μm, wherein, the Vickers hardness of steel plate is 100HV~170HV.

Description

Steel plate and manufacturing method

Technical field

The present invention relates to steel plate and its manufacturing methods.

Background technique

The automotive parts such as gear, clutch are manufactured via manufacturing procedures such as punching, forging, punch process.Itself plus In work process, for the raising of product property, the reduction of stabilisation, manufacturing cost, it is desirable that improve the carbon as raw material The processability of steel plate.In addition, these components it requires excellent through hardening due to being used after Q-tempering with high intensity Property.

In order to ensure carbon steel sheet processability and ensure harden ability, in the past, give a large amount of motions.

A kind of high carbon steel sheet of excellent tenacity after disclosing processability, harden ability, heat treatment in patent document 1, it is special Sign is, in terms of quality % containing C:0.20~0.45%, Mn:0.40~1.50%, P:0.03% or less, S:0.02% with Under, P+S:0.010% or more, Cr:0.01~0.80%, Ti:0.005~0.050%, B:0.0003~0.0050%, it is remaining Part is made of Fe and inevitable impurity, further containing Sn:0.05% or less, Te:0.05% hereinafter, and Sn+Te Total content be 0.005% or more, by the line and staff control or ferrite of ferrite and pearlite and the mixing group of cementite It knits to be formed.

In patent document 2, disclose a kind of manufacturing method of high-hardenability high-carbon hot-rolled steel sheet, which is characterized in that with Quality % meter containing C:0.2~0.7%, Si:2% or less, Mn:2% or less, P:0.03% or less, S:0.03% or less, The steel that sol.Al:0.08% or less, N:0.01% or less and remainder are made of iron and inevitable impurity, in finish rolling After more than temperature (Ar3 transformation temperature be -20 DEG C) carrying out hot rolling, is more than 120 DEG C/sec in cooling velocity and cooling end temperature is 620 DEG C or less are cooled down, and then, are 600 DEG C or less in coiling temperature and are batched, controlled to be more than with volume fraction It is that 640 DEG C or more and Ac1 transformation temperature or less are annealed in annealing temperature after pickling after the tissue of 20% bainite phase, Spheroidizing tissue is made.

Existing technical literature

Patent document

Patent document 1: No. 4319940 bulletins of Japanese Patent No.

Patent document 2: No. 3879459 bulletins of Japanese Patent No.

Summary of the invention

Problems to be solved by the invention

But the high carbon steel sheet recorded in patent document 1 also uses pearlite with high hardness in raw material tissue, Processability may not be excellent.Do not have to record the specific tissue morphology of excellent in workability in patent document 2.

The present invention in view of conventional art status, and it is an object of the present invention to provide formability and wearability is made to improve, particularly be suitble to In shaping to obtain the steel plate and its manufacturing method of the components such as gear, clutch by heavy wall plate.

Means for solving the problems

It is understood that the steel plate for obtaining being suitable for the raw material of drive component etc. in order to solve above-mentioned problem, only To increase ferritic partial size, by carbide (predominantly carburizing in containing the steel plate for improving C required for harden ability Body) with partial size appropriate progress spheroidizing, reduce pearlitic structrure.This is based on following reason.

The hardness of ferritic phase is low, and ductility is high.Therefore, by increasing it in the tissue using ferrite as main body Partial size, so as to improve raw material formability.

Carbide is due to so as to maintain raw material formability, and assigning by properly dispersing in metal structure Excellent wearability, the special characteristic of rotation fatigue are given, so being to the indispensable tissue of drive component.In addition, in steel plate Carbide be interfere sliding firm particle, by making carbide be present in ferrite grain boundaries, so as to prevent from crossing The propagation of the sliding of crystal crystal boundary, the formation for inhibiting shear band, improve forging, while the formability of steel plate also improves.

But since cementite is hard and crisp tissue, if with the state with ferritic lamellar tissue, that is, pearlite In the presence of then steel can be hardened and become fragile, so must be with spherical presence.If it is considered that the generation of cracking when forging, forging, then Its partial size need to be range appropriate.

However, the manufacturing method for realizing above-mentioned tissue is not disclosed so far.Then, hair of the invention Bright persons have made intensive studies the manufacturing method for realizing above-mentioned tissue.

As a result, it is found that small in order to which the metal structure of the steel plate after batching after hot rolling is formed in piece interlamellar spacing Fine pearlite or tiny ferrite in be dispersed with bainite structure made of cementite, with lower temperature (400 ~550 DEG C) it is batched.By being batched with lower temperature, the cementite being scattered in ferrite also becomes easy ball Shape.Then, as paragraph 1 anneal, by immediately lower than Ac1 point at a temperature of annealing to cementite carry out partly Spheroidizing.Then, anneal as the 2nd section, by temperature between Ac1 point and Ac3 point (so-called ferrite and austenite Two-phase region) under annealing, make ferrite crystal grain a part residual, and make a part occur austenite phase transformation.Thereafter, Remaining ferrite crystal grain is grown by carrying out slow cool down, and makes austenite that ferrite occur as core Phase transformation can be such that cementite is precipitated while obtaining big ferritic phase in crystal boundary, realize above-mentioned tissue.

That is, it is found that with regard to simultaneously meet harden ability and formability steel plate manufacturing method for, even if to hot rolling item Part or annealing conditions etc. are made single effort and are still difficult to realize, by with a so-called coherent process such as hot rolling and annealing operation come Reach optimization, can realize.

The present invention is completed based on above-mentioned opinion, and purport is as follows.

(1) a kind of steel plate, which is characterized in that the steel plate in terms of quality % containing C:0.10~0.40%, Si:0.01~ 0.30%, Mn:1.00~2.00%, P:0.020% or less, S:0.010% or less, Al:0.001~0.10%, N: 0.010% or less, O:0.020% or less, Cr:0.50% or less, Mo:0.10% or less, Nb:0.10% or less, V:0.10% Below, Cu:0.10% or less, W:0.10% or less, Ta:0.10% or less, Ni:0.10% or less, Sn:0.050% or less, Sb:0.050% or less, As:0.050% or less, Mg:0.050% or less, Ca:0.050% or less, Y:0.050% or less, Zr:0.050% or less, La:0.050% or less and Ce:0.050% hereinafter, remainder be Fe and inevitably it is miscellaneous Matter, wherein the metal structure of above-mentioned steel plate meets: the number of the carbide of ferrite grain boundaries is relative in ferrite crystal grain The ratio of the number of carbide be more than 1, ferrite partial size be 5 μm~50 μm and the area ratio of pearlite be 6% hereinafter, on The Vickers hardness for stating steel plate is 100HV~170HV.

(2) according to the steel plate of above-mentioned (1), which is characterized in that instead of a part of above-mentioned Fe containing Ti:0.10% with 1 kind or 2 kinds in lower and B:0.010% or less.

(3) a kind of manufacturing method of steel plate, which is characterized in that it is the manufacturer for manufacturing the steel plate of above-mentioned (1) or (2) Method, wherein finish rolling is completed in 750 DEG C~850 DEG C of temperature region at the steel billet implementation being grouped as to above-mentioned (1) or (2) Hot rolling and hot rolled steel plate is made, above-mentioned hot rolled steel plate is batched at 400 DEG C~550 DEG C, to the hot rolled steel plate batched Implement pickling, the hot rolled steel plate implementation of pickling is kept 3 hours~60 hours in 650 DEG C~720 DEG C of temperature region Paragraph 1 annealing then keeps hot rolled steel plate implementation 3 hours~50 hours in 725 DEG C~790 DEG C of temperature region 2nd section of annealing, is cooled to 650 DEG C for the hot rolled steel plate after annealing with 1 DEG C/h~30 DEG C/h of cooling velocity.

Invention effect

In accordance with the invention it is possible to provide formability and wearability is excellent, particularly be suitable for shaping by heavy wall plate To the steel plate and its manufacturing method of the components such as gear, clutch.

Specific embodiment

Hereinafter, the present invention is described in detail.Firstly, being carried out to steel plate of the present invention at the restriction reason being grouped as Explanation.Hereinafter, " % " of related ingredient refers to " quality % ".

[C:0.10~0.40%]

C is carbide to be formed in steel, for the reinforcing of steel and the effective element of the miniaturization of ferrite crystal grain.In order to The surface aesthetic for inhibiting the generation of the pears surface in cold working, ensuring to be cold worked component, needs to inhibit the coarse of ferrite partial size When changing, but being lower than 0.10%, the volume fraction of carbide is insufficient, can not inhibit the coarsening of the carbide in box annealing, therefore C is set as 0.10% or more.Preferably 0.12 or more.

On the other hand, if it exceeds 0.40%, then the volume fraction of carbide increases, in instantaneity meeting when loaded load A large amount of to generate the crackle for becoming the starting point destroyed, impact resistance characteristic reduces, therefore C is set as 0.40% or less.Preferably 0.38% or less.

[Si:0.01~0.30%]

Si is the element for working as deoxidier and having an impact to the form of carbide.In order to obtain deoxidation effect Fruit, Si are set as 0.01% or more.Preferably 0.05% or more.

On the other hand, if it exceeds 0.30%, then ferritic ductility reduction, becomes to easily cause in cold working Crackle, cold-workability reduces, therefore Si is set as 0.30% or less.Preferably 0.28% or less.

[Mn:1.00~2.00%]

Mn is the element for improving harden ability, facilitating intensity raising.When lower than 1.00%, quenched intensity and quenching Residual Carbides afterwards ensure to become difficult, therefore Mn is set as 1.00% or more.Preferably 1.09% or more.

On the other hand, if it exceeds 2.00%, then Mn segregation becomes the band-like of extreme, and processability significantly reduces, therefore Mn It is set as 2.00% or less.Preferably 1.91% or less.

[Al:0.001~0.10%]

Al is to work as the deoxidier of steel, make the element of ferrite stabilization.When lower than 0.001%, it is unable to fully Ground obtains additive effect, therefore Al is set as 0.001% or more.Preferably 0.004% or more.

On the other hand, if it exceeds 0.10%, then field trashes are largely generated, cold-workability reduces, therefore Al is set as 0.10% or less.Preferably 0.08% or less.

Element below is impurity, needs to control a certain amount of following.

[P:0.0001~0.020%]

P is the element formed in ferrite grain boundaries segregation, inhibition grain boundary carbide.Although more few the more preferred, but if In refining procedure, P is decreased below 0.0001%, then refining cost can be substantially increased, therefore P be set as 0.0001% with On.Preferably 0.0013% or more.

On the other hand, if it exceeds 0.020%, then the number ratio of grain boundary carbide reduces, and cold-workability reduces, because This P is set as 0.020% or less.Preferably 0.018% or less.

[S:0.0001~0.010%]

S is the impurity element to form the non-metallic inclusions such as MnS.Since non-metallic inclusion can become in cold working The starting point that crackle occurs, therefore the S the few the more preferred, but if S is decreased below 0.0001%, then refining cost can be substantially Rise, therefore S is set as 0.0001% or more.Preferably 0.0012% or more.

On the other hand, if it exceeds 0.010%, then cold-workability reduces, therefore S is set as 0.010% or less.It is preferred that It is 0.007% or less.

[N:0.0001~0.010%]

N is the element for causing ferrite embrittlement and largely containing, more few the more preferred.The content of N can be 0, but If decreasing below 0.0001%, refining cost can be substantially increased, thus substantial lower limit be 0.0001~ 0.0006%.On the other hand, if it exceeds 0.010%, then ferrite embrittlement, cold-workability reduces, therefore N is set as 0.010% or less.Preferably 0.007% or less.

[O:0.0001~0.020%]

O is the element for forming coarse oxide in steel and largely containing, preferably less.The content of O can Think 0, but if decreasing below 0.0001%, then refining cost can be substantially increased, therefore substantial lower limit is 0.0001 ~0.0011%.On the other hand, if it exceeds 0.020%, then coarse oxide is generated in steel, become in cold working The starting point of crackle, therefore O is set as 0.020% or less.Preferably 0.017% or less.

[Sn:0.001~0.050%]

Sn is from steel raw material (waste material) mixed element.Due to leading to the number ratio of grain boundary carbide in cyrystal boundary segregation Reduction, therefore it is more few the more preferred.The content of Sn can be 0, but if decreasing below 0.001%, then refining cost is substantially Increase, therefore substantial lower limit is 0.001~0.002% or more.On the other hand, if it exceeds 0.050%, then ferrite Embrittlement, cold-workability reduces, therefore Sn is set as 0.050% or less.Preferably 0.040% or less.

[Sb:0.001~0.050%]

Sb is in the same manner as Sn from steel raw material (waste material) mixed element.Due to leading to grain boundary carbide in cyrystal boundary segregation Number ratio reduction, therefore it is more few the more preferred.The content of Sb can be 0, but if decreasing below 0.001%, then smart It is smelt and is originally significantly increased, therefore substantial lower limit is 0.001~0.002% or more.On the other hand, if it exceeds 0.050%, then ferrite embrittlement, cold-workability reduces, therefore Sb is set as 0.050% or less.Preferably 0.040% or less.

[As:0.001~0.050%]

As is in the same manner as Sn, Sb from steel raw material (waste material) mixed element.Due to leading to crystal boundary carbon in cyrystal boundary segregation The reduction of the number ratio of compound, thus it is more few the more preferred.The content of As can be 0, but if decreasing below 0.001%, Then refining cost is significantly increased, therefore substantial lower limit is 0.001~0.002% or more.On the other hand, if it exceeds 0.050%, then the number ratio of grain boundary carbide reduces, and cold-workability reduces, therefore As is set as 0.050% or less.It is preferred that It is 0.040% or less.

Steel plate of the present invention is using above-mentioned element as basis, in turn, in order to improve the forging of steel plate, can also contain There is element below.As element below be not in order to obtain effect of the invention necessary to, content can also be with It is 0.

[Cr:0.50% or less]

Cr is the element for improving harden ability, facilitating intensity raising, even and if being to be concentrated on carbide, in austenite Also it will form the element of stable carbide in phase.In order to obtain additive effect, Cr is preferably set to 0.001% or more.It is more excellent It is selected as 0.007% or more.On the other hand, if it exceeds 0.50%, then carbide can stabilize, and in quenching, carbide is molten Solution delay, it is possible to required quenching intensity can not be reached, therefore Cr is set as 0.50% or less.Preferably 0.45% or less.

[Mo:0.10% or less]

Mo is to control effective element to the form of carbide in the same manner as Mn.In order to obtain additive effect, Mo is preferably set It is set to 0.001% or more.More preferably 0.010% or more.On the other hand, if it exceeds 0.10%, then in the face of r value respectively to The opposite sex deteriorates, and cold-workability reduces, therefore Mo is set as 0.10% or less.Preferably 0.08% or less.

[Nb:0.10% or less]

Nb is the effective element of form control to carbide, and is to miniaturize tissue and facilitate toughness raising Element.In order to obtain additive effect, Nb is preferably set to 0.001% or more.More preferably 0.002% or more.Another party Face, if it exceeds 0.10%, then fine Nb carbide is largely precipitated, intensity excessively rises, in addition, of grain boundary carbide Percentage reduces, and cold-workability reduces, therefore Nb is set as 0.10% or less.Preferably 0.08% or less.

[V:0.10% or less]

V is also the effective element of form control in the same manner as Nb to carbide, and is that tissue is made to miniaturize and help In the element that toughness improves.In order to obtain additive effect, V is preferably set to 0.001% or more.More preferably 0.004% with On.On the other hand, if it exceeds 0.10%, then fine V carbide is largely precipitated, intensity excessively rises, in addition, crystal boundary carbon The number ratio of compound reduces, and cold-workability reduces, therefore V is set as 0.10% or less.Preferably 0.08% or less.

[Cu:0.10% or less]

Cu be in ferritic crystal cyrystal boundary segregation and form fine precipitate and facilitate intensity raising member Element.In order to obtain additive effect, Cu is preferably set to 0.001% or more.More preferably 0.005% or more.On the other hand, such as Fruit is more than 0.10%, then generates red brittleness, and the productivity in hot rolling reduces, therefore Cu is set as 0.10% or less.Preferably 0.08% or less.

[W:0.10% or less]

W is also to control effective element to the form of carbide in the same manner as Nb, V.In order to obtain additive effect, W is preferred It is set as 0.001% or more.More preferably 0.003% or more.On the other hand, it if it exceeds 0.10%, is then largely precipitated fine W carbide, intensity excessively rises, in addition, the number ratio of grain boundary carbide reduces, cold-workability is reduced, therefore W is set It is 0.10% or less.Preferably 0.08% or less.

[Ta:0.10% or less]

Ta is also to control effective element to the form of carbide in the same manner as Nb, V, W.In order to obtain additive effect, Ta It is preferably set to 0.001% or more.More preferably 0.005% or more.On the other hand, if it exceeds 0.10%, then a large amount of to be precipitated Fine Ta carbide, intensity excessively rises, in addition, crystal boundary

[Ni:0.10% or less]

Ni is to improve effective element to the toughness of component.In order to obtain additive effect, Ni is preferably set to 0.001% More than.More preferably 0.004% or more.On the other hand, if it exceeds 0.10%, then the number ratio of grain boundary carbide reduces, Cold-workability reduces, therefore Ni is set as 0.10% or less.Preferably 0.08% or less.

[Mg:0.050% or less]

Mg is the element that the form of sulfide can be controlled by micro addition.In order to obtain additive effect, Mg is excellent Choosing is set as 0.0001% or more.More preferably 0.0008% or more.On the other hand, if it exceeds 0.050%, then ferrite Embrittlement, cold-workability reduces, therefore Mg is set as 0.050% or less.Preferably 0.040% or less.

[Ca:0.050% or less]

The element for the form that Ca is and Mg can control sulfide likewise by micro addition.In order to be added Add effect, Ca is preferably set to 0.001% or more.More preferably 0.003% or more.On the other hand, if it exceeds 0.050%, Coarse Ca oxide is then generated, the starting point occurred in cold working as crackle, therefore Ca is set as 0.050% or less.It is excellent It is selected as 0.040% or less.

[Y:0.050% or less]

Y is the element with Mg, Ca form that can control sulfide likewise by micro addition.In order to obtain Additive effect, Y are preferably set to 0.001% or more.More preferably 0.003% or more.On the other hand, if it exceeds 0.050%, then coarse Y oxide is generated, the starting point occurred in cold working as crackle, therefore Y is set as 0.050% Below.Preferably 0.035% or less.

[Zr:0.050% or less]

Zr is the element with Mg, Ca, Y form that can control sulfide likewise by micro addition.In order to obtain Additive effect is obtained, Zr is preferably set to 0.001% or more.More preferably 0.004% or more.On the other hand, if it exceeds 0.050%, then coarse Zr oxide is generated, the starting point occurred in cold working as crackle, therefore Zr is set as 0.050% or less.Preferably 0.045% or less.

[La:0.050% or less]

La be effective element is controlled to the form of sulfide by micro addition, but be also in cyrystal boundary segregation and The element for causing the number ratio of grain boundary carbide to reduce.In order to obtain additive effect, La is preferably set to 0.001% or more. More preferably 0.004% or more.On the other hand, if it exceeds 0.050%, then the number ratio of grain boundary carbide reduces, it is cold plus Work reduces, therefore La is set as 0.050% or less.Preferably 0.045% or less.

[Ce:0.050% or less]

The element for the form that Ce is and La can control sulfide likewise by micro addition, but be also in crystalline substance Boundary is segregated and the element that causes the number ratio of grain boundary carbide to reduce.In order to obtain additive effect, Ce is preferably set to 0.001% or more.More preferably 0.004% or more.On the other hand, if it exceeds 0.050%, then the number of grain boundary carbide Ratio reduces, and cold-workability reduces, therefore Ce is set as 0.050% or less.Preferably 0.046% or less.

Steel plate of the present invention is Fe and inevitable impurity at the remainder being grouped as.

In addition, a kind or 2 kinds in Ti and B can also be contained instead of a part of above-mentioned Fe.

[Ti:0.10% or less]

Ti is to control the form of carbide effective element, and and tissue is made to miniaturize and facilitate toughness and mention High element.In order to obtain additive effect, Ti is preferably set to 0.001% or more.More preferably 0.005% or more.Another party Face, if it exceeds 0.10%, then coarse Ti oxide is generated, the starting point in cold working as crackle, therefore Ti is set as 0.10% or less.Preferably 0.08% or less.

[B:0.0001~0.010%]

B be improve component heat treatment when harden ability and make microstructure homogenization, facilitate toughness raising element.In order to Additive effect is obtained, B is preferably set to 0.0001% or more.More preferably 0.0006% or more.On the other hand, if it exceeds 0.010%, then coarse B oxide is generated, the starting point in cold working as crackle, therefore B is set as 0.010% or less. Preferably 0.009% or less.

Next, being illustrated to the tissue of steel plate of the invention.

The tissue of steel plate of the present invention is the tissue being substantially made of ferrite and carbide.Carbide in addition to be iron with Carbon compound, that is, cementite (Fe₃C other than), or the Fe atom in cementite is replaced with alloying elements such as Mn, Cr and is obtained Compound, the alloy carbide (M arrived₂₃C₆、M₆C, MC etc. [M:Fe and other metallic elements as alloy addition]).

When being defined shape by steel formability, shear band is formed in the macrostructure of steel plate, near shear band It concentrates and generates sliding deformation.Sliding deformation forms the high area of dislocation density along with the hyperplasia of dislocation near shear band Domain.Along with the increase of the dependent variable assigned to steel plate, sliding deformation is promoted, and dislocation density increases.

In cold forging, implementing equivalent strain is more than 1 to force work.Therefore, for previous steel plate, companion can not be prevented Gap and/or crackle occurs as dislocation density increases, for previous steel plate, the raising of forging is difficult.It is right In the solution of the project, it is effective for inhibiting the formation of shear band when forming.

From the viewpoint of microscopic structure, the formation of shear band can be understood as the sliding generated in some crystal grain The phenomenon that crossing crystal crystal boundary and continuously propagating to adjacent crystal grain.Thus, in order to inhibit the formation of shear band, need to prevent Only cross the propagation of the sliding of crystal crystal boundary.

Carbide in steel plate is the firm particle for interfering sliding, by making carbide be present in ferrite grain boundaries, from And the propagation for the sliding for crossing crystal crystal boundary can be prevented and inhibit the formation of shear band, make it possible that forging improves.Together When, the formability of steel plate also improves.

The formability of steel plate is heavily dependent on the accumulation (accumulation of dislocation) strained into crystal grain, if in crystalline substance Body grain boundaries prevent propagation of the strain to neighboring die, then the dependent variable in crystal grain increases.As a result, work hardening rate increases Greatly, formability improves.

If based on theoretical and principle, then it is assumed that the cold-workability consumingly covering by the carbide of ferrite grain boundaries The influence of rate, it is therefore desirable to measure the coverage rate with high precision.

In order to measure the coverage rate of the carbide in ferrite grain boundaries in three dimensions, in scanning electron microscope It is required for being inside repeated using the serial section SEM observation or three-dimensional EBSP observation of sample cutting and the observation of FIB, This needs huge minute, and the accumulation of technical know-how becomes indispensable.The inventors of the present invention have understood fully this Thing, the conclusion obtained are as follows: general analysis method is not suitable for.

Therefore, evaluation index simple and with high accuracy is explored, as a result, present inventors have discovered that: if Using the number of the carbide of ferrite grain boundaries relative to the number of the carbide in ferrite crystal grain ratio as index, then Cold-workability can be evaluated, if of the number of the carbide of ferrite grain boundaries relative to the carbide in ferrite crystal grain Several ratios is more than 1, then cold-workability significantly improves.

Further, since the buckling of steel plate generated in cold working, fold into, convolution is by with formation of shear bands Caused by strain localization, therefore by making carbide be present in ferrite grain boundaries, so as to mitigate the formation of shear band And strain localization, effectively inhibit buckle, fold into, the generation of convolution.

If the spherical rate of the carbide on crystal crystal boundary is lower than 80%, strains and locally concentrate on rodlike or plate The carbide of shape becomes easy and generates gap and/or crackle, therefore the spherical rate of the carbide on crystal crystal boundary is preferably 80% or more, more preferably 90% or more.

If the average grain diameter of carbide is lower than 0.1 μm, the hardness of steel plate is dramatically increased, and processability reduces, therefore carbon The average grain diameter of compound is preferably 0.1 μm or more.More preferably 0.17 μm or more.On the other hand, if the average grain of carbide Diameter is more than 2.0 μm, then the carbide coarse in cold working becomes starting point and generate cracking, and cold-workability reduces, therefore is carbonized The average grain diameter of object is preferably 2.0 μm or less.More preferably 1.95 μm or less.

The observation of carbide is carried out with scanning electron microscope.Before observation, the sample of structure observation is passed through It is ground using the wet lapping of sand paper and the diamond abrasive grain with 1 μm of average particle size, by viewing surface finishing After work is at mirror surface, tissue is etched using 3% nitric acid-ethanol solution.The multiplying power of observation is that selection can in 3000 times Distinguish the multiplying power of ferrite and carbide.With the multiplying power of selection, 40 μm of 30 μ m at 8 1/4 layer of plate thickness is randomly shot Visual field.

For obtained organization chart picture, the image with three paddy business Co. Ltd. systems (Win ROOF) for representative is used Analysis software measures the area of each carbide contained in the region in detail.It is straight that equivalent circular is found out by the area of each carbide Diameter (=2 × √ (area/3.14)), using its average value as carbide partial size.In addition, the spherical rate of carbide is by carbon Compound is approximately homalographic and the equal ellipse of the moment of inertia, and it is low with the ratio of the maximum length of its right angle orientation to calculate maximum length In 3 elliptical ratio and find out.

In addition, the influence in order to inhibit the evaluated error generated by noise, is 0.01 μm by area²Carbide below It is excluded from the object of evaluation.The number of carbide present on ferrite grain boundaries is counted, is subtracted by whole carbide numbers The carbide number that goes on crystal boundary and found out the carbide number in ferrite crystal grain.Number based on measurement, has found out ferrite The number ratio of Carbide Phases on crystal boundary for the carbide in ferrite crystal grain.

In the tissue after cold-rolled steel sheet is annealed, by the way that ferrite partial size is set as 5.0 μm or more, so as to Improve cold-workability.If ferrite partial size is lower than 5 μm, hardness increases, and in cold working, becomes easy generation cracking, splits Line, therefore ferrite partial size is set as 5 μm or more.Preferably 7 μm or more.

On the other hand, if it exceeds 50 μm, then the number for the carbide on crystal crystal boundary for inhibiting sliding to propagate is reduced, Cold-workability reduces, therefore ferrite partial size is set as 50 μm or less.Preferably 37 μm or less.

Ferrite partial size is after the viewing surface of sample is ground into mirror surface by above-mentioned grinding method, with 3% nitric acid- Ethanol solution is etched, and the tissue of viewing surface is observed with optical microscopy or scanning electron microscope, to shooting Image application segment method and be measured.

In addition, carbide, that is, cementite of iron be hard and crisp tissue, if with ferritic lamellar tissue, that is, pearly-lustre The state of body exists, then steel, which is hardened, becomes fragile.Therefore, pearlite needs strongly to reduce, in steel plate of the invention, with the area ratio Meter is set as 6% or less.

Pearlite by SEM, optical microphotograph sem observation due to can strictly be discriminated with distinctive lamellar structure Not.By calculating the region of lamellar structure in arbitrary section, so as to find out the area ratio of pearlite.

In turn, by the way that the Vickers hardness of steel plate is set as 100HV~170HV, so as to improve cold-workability.Such as Fruit Vickers hardness be lower than 100HV, then become easy generation in cold working and buckle, thus Vickers hardness be set as 100HV with On.Preferably 110HV or more.

On the other hand, if Vickers hardness is more than 170HV, ductility reduction becomes to be easy to produce interior in cold working Portion's crackle, therefore Vickers hardness is set as 170HV or less.Preferably 168HV or less.

Next, being illustrated to manufacturing method of the present invention.

The basic thought of manufacturing method of the present invention is, using above-mentioned at the steel billet being grouped as, to hot-rolled condition and moves back Fiery condition is consistently managed to carry out the organizational controls of steel plate.

Firstly, by it is required at steel billet made of the molten steel continuously casting being grouped as hot rolling.Casting after continuously casting Base can be directly for hot rolling, again for hot rolling after can also being heated after cooling down for the time being.

It being heated after cooling down steel billet for the time being in the case where for hot rolling, heating temperature is preferably 1000 DEG C~ 1250 DEG C, heating time is preferably 0.5 hour~3 hours.By the steel billet after continuously casting directly for hot rolling the case where Under, the temperature of the steel billet for hot rolling is preferably set to 1000 DEG C~1250 DEG C.

If steel billet temperature or billet heating temperature are more than 1250 DEG C or the heating steel billet time is more than 3 hours, from steel The decarburization on base surface layer becomes significantly, and when heating before carburizing and quenching, the austenite grain on steel plate surface layer is grown singularly, resistance to Impact reduces.Therefore, steel billet temperature or billet heating temperature be preferably 1250 DEG C hereinafter, heating time be preferably 3 hours with Under.More preferably 1200 DEG C or less, 2.5 hours or less.

If steel billet temperature or billet heating temperature are lower than 1000 DEG C or heating time is lower than 0.5 hour, because of casting And microscopic segregation, the gross segregation generated will not be eliminated, the area made of inside steel billet, the alloying elements such as Si, Mn part concentration Domain remaining is got off, and impact resistance reduces.Therefore, steel billet temperature or billet heating temperature are preferably 1000 DEG C or more, heating time Preferably 0.5 hour or more.More preferably 1050 DEG C or more, 1 hour or more.

Finish rolling in hot rolling is completed in 750 DEG C~850 DEG C of temperature region.If final rolling temperature is lower than 750 DEG C, The deformation drag of steel plate increases, and rolling load significantly rises, in addition, roller abrasion loss increases, productivity is reduced, and in order to change It recrystallizes and will not be sufficiently carried out needed for kind plastic anisotropy, therefore final rolling temperature is set as 750 DEG C or more.Promoting Into on this aspect of recrystallization, preferably 770 DEG C or more.

If final rolling temperature is more than 850 DEG C, in the oxidation for keeping steel plate relatively thicker by generation in runout table (ROT) Skin generates scar in surface of steel plate due to the oxide skin, negative being applied with impact after cold forging and carburizing and quenching tempering When lotus, it is easy to generate cracking using scar as starting point, therefore the impact resistance of steel plate reduces.Therefore, final rolling temperature is set as 850 DEG C or less.Preferably 830 DEG C or less.

By the hot rolled steel plate after finish rolling, when ROT is cooled down, cooling velocity is preferably 10 DEG C/sec~100 DEG C/sec. If cooling velocity is lower than 10 DEG C/sec, relatively thicker oxide skin is generated on the way in cooling, can not inhibit the wound due to this The generation of trace, impact resistance reduces, therefore cooling velocity is preferably 10 DEG C/sec or more.More preferably 20 DEG C/sec or more.

If from the surface layer of steel plate until inside is cooled down with the cooling velocity more than 100 DEG C/sec, most surface section It can be cooled excessively, generate the low temperature phase changes tissues such as bainite, martensite.After batching, it will be cooled to room temperature from 100 DEG C When hot rolled steel plate coiled material uncoiling utilizes, fine crack is generated in low temperature phase change tissue.The fine crack be difficult to through pickling and Cold rolling is removed.

Also, if applying impact load to steel plate after cold forging and carburizing and quenching tempering, cracking is with fine crack Starting point and develop, therefore impact resistance reduce.Therefore, in order to inhibit the most surface section in steel plate to generate bainite, martensite etc. Low temperature phase change tissue, cooling velocity are preferably 100 DEG C/sec or less.More preferably 90 DEG C/sec or less.

In addition, above-mentioned cooling velocity refer to the hot rolled steel plate after finish rolling by without water filling section after, from water filling section by During beginning until being cooled to the target temperature batched on ROT until at the time of water is cooling, from each section that fills the water Cooling capacity acquired by cooling equipment, rather than indicate flat until filling the water start time to the temperature that the machine of being taken up batches Equal cooling velocity.

Coiling temperature is set as 400 DEG C~550 DEG C.This is the temperature lower than general coiling temperature, is especially in C In the case that content is high usually without condition.By by the hot rolled steel plate manufactured under the conditions described above in the temperature model Enclose it is interior batched, so as to make steel plate tissue become bayesian made of carbide is dispersed in tiny ferrite Body tissue.

If coiling temperature is lower than 400 DEG C, the austenite phase of non-phase transformation becomes harder martensite before batching, It when the uncoiling of hot rolled steel plate coiled material utilizes, is cracked on the surface layer of hot rolled steel plate, impact resistance reduces.

Further more, when from austenite to ferritic recrystallization, since recrystallization driving force is small, recrystallization iron element The orientation of body crystal grain becomes the influence being consumingly orientated by austenite grain, and the randomization of texture becomes difficult.Therefore, it rolls up Temperature is taken to be set as 400 DEG C or more.Preferably 430 DEG C or more.

If coiling temperature is more than 550 DEG C, the biggish pearlite of piece interlamellar spacing is generated, generates the high phase of thermal stability When thick acicular carbide.The acicular carbide also remains after 2 sections of annealing.It is needle-shaped with this in the forming such as cold forging of steel plate Carbide generates cracking as starting point.

In addition, when ferrite is by austenite recrystallization, on the contrary, recrystallization driving force becomes excessive, in such case Under, it can also become the recrystallization ferrite crystal grain for being strongly depend on austenite grain orientation, the randomization of texture can not be carried out. Therefore, coiling temperature is set as 550 DEG C or less.Preferably 520 DEG C or less.

Hot rolled steel plate coiled material uncoiling is utilized, after implementing pickling, implements 2 sections kept in 2 temperature regions The annealing (2 sections of annealing) of step type.By implementing 2 sections of annealing to hot rolled steel plate, to control the stability of carbide, promote The generation of carbide at ferrite grain boundaries.

If implementing cold rolling, ferrite crystal grain miniaturization, therefore steel plate to the steel plate after pickling before annealing Become difficult to softening.Therefore, in the present invention, before the anneal implement cold rolling be it is undesirable, preferably after pickling not into Row cold rolling is implemented to make annealing treatment.

Paragraph 1 annealing is at 650~720 DEG C, preferably in A_c1It is carried out in point temperature region below.By the annealing, from And make carbide coarsening, part spherical, and make alloying element concentration in carbide, improve the thermostabilization of carbide Property.

In paragraph 1 annealing, the heating speed (hereinafter referred to as " paragraph 1 heating speed ") until annealing temperature is set It is set to 30 DEG C/h~150 DEG C/h.If paragraph 1 heating speed is lower than 30 DEG C/h, heating needs the time, produces Rate reduces, therefore paragraph 1 heating speed is set as 3 DEG C/h or more.Preferably 10 DEG C/h or more.

On the other hand, if paragraph 1 heating speed is more than 150 DEG C/h, in hot rolled steel plate coiled material peripheral part with Internal temperature difference increases, and generates the scar as caused by thermal expansion difference, burns and glue, forms bumps in surface of steel plate.Cold forging etc. at When shape, which becomes starting point and generates cracking, and forging reduces, the impact resistance after formability and carburizing and quenching tempering drops It is low, therefore paragraph 1 heating speed is set as 150 DEG C/h or less.Preferably 130 DEG C/h or less.

Annealing temperature (hereinafter referred to as " paragraph 1 annealing temperature ") in paragraph 1 annealing is set as 650 DEG C~720 DEG C.Such as Fruit paragraph 1 annealing temperature is lower than 650 DEG C, then the stabilisation of carbide is insufficient, in the 2nd section of annealing, remains in carbide It is become difficult in austenite.Therefore, paragraph 1 annealing temperature is set as 650 DEG C or more.Preferably 670 DEG C or more.

On the other hand, it if paragraph 1 annealing temperature is more than 720 DEG C, is generated before the stability of carbide rises difficult to understand Family name's body, the control of above-mentioned tissue change becomes difficult, therefore paragraph 1 annealing temperature is set as 720 DEG C or less.Preferably 700 DEG C with Under.

Annealing time (hereinafter referred to as " paragraph 1 annealing time ") in paragraph 1 annealing is set as 3 hours~60 hours.Such as Fruit paragraph 1 annealing time is lower than 3 hours, then the stabilisation of carbide is insufficient, in the 2nd section of annealing, remains in carbide It is become difficult in austenite.Therefore, paragraph 1 annealing time is set as 3 hours or more.Preferably 5 hours or more.

On the other hand, if paragraph 1 annealing time is more than 60 hours, it fail to predict the further steady of carbide Fixedization, and then productivity reduces, therefore paragraph 1 annealing time is set as 60 hours or less.Preferably 55 hours or less.

Then, 725~790 DEG C, preferably A are warming up to_c1Point~A₃The temperature region of point, gives birth to austenite in the tissue At.At this point, the carbide in fine ferrite crystal grain dissolves in austenite, but annealed by paragraph 1 so that coarsening Carbide is remaining in austenite.

In the case where carrying out cooling without the 2nd section of annealing, ferrite partial size will not become larger, and be unable to get reason The tissue thought.

Heating speed (hereinafter referred to as " the 2nd section of heating speed ") until the annealing temperature that the 2nd section is annealed is set as 1 DEG C/h~80 DEG C/h.In the 2nd section of annealing, austenite is generated by ferrite grain boundaries and is grown.At this point, by slowing down Heating speed until annealing temperature is formed to inhibit the karyogenesis of austenite by the slow cool down after annealing In tissue, the crystal boundary coverage rate for improving carbide is possibly realized.

Therefore, the 2nd section of heating speed is preferably relatively slow, but if being lower than 1 DEG C/h, then heating needs the time, productivity It reduces, therefore the 2nd section of heating speed is set as 1 DEG C/h or more.Preferably 10 DEG C/h or more.

If the 2nd section of heating speed is more than 80 DEG C/h, in hot rolled steel plate coiled material, peripheral part and internal temperature Difference increases, and generates due to the scar of larger thermal expansion difference as caused by phase transformation, burns and glue, forms bumps in surface of steel plate.Cold When forging, cracking is generated by starting point of the bumps, forging and formability reduce, in addition, the impact resistance after carburizing and quenching tempering Property also reduces, therefore the 2nd section of heating speed is set as 80 DEG C/h or less.Preferably 70 DEG C/h or less.

Annealing temperature (hereinafter referred to as " the 2nd section of annealing temperature ") in 2nd section of annealing is set as 725 DEG C~790 DEG C.Such as The 2nd section of annealing temperature of fruit is lower than 725 DEG C, then the production quantity of austenite tails off, and after the cooling after the 2nd section of annealing, ferrite is brilliant The number of carbide at boundary is reduced, in addition, ferrite partial size becomes smaller.Therefore, the 2nd section of annealing temperature be set as 725 DEG C with On.Preferably 735 DEG C or more.

On the other hand, if the 2nd section of annealing temperature is more than 790 DEG C, so that carbide is remained in austenite and become difficult, The control of tissue change becomes difficult, therefore the 2nd section of annealing temperature is set as 790 DEG C or less.Preferably 770 DEG C or less.

Annealing time (the 2nd section of annealing time) in 2nd section of annealing was set as 3 hours more than or lower than 50 hours.If 2nd section of annealing time is lower than 3 hours, then the production quantity of austenite is few, also, the dissolution of the carbide in ferrite crystal grain is not It can be sufficiently carried out, become difficult the number increase of the carbide of ferrite grain boundaries, in addition, ferrite partial size becomes smaller.Cause This, the 2nd section of annealing time is set as 3 hours or more.Preferably 5 hours or more.

On the other hand, if the 2nd section of annealing time is more than 50 hours, remaining in carbide in austenite becomes tired Difficulty, in addition, manufacturing cost also increases, therefore the 2nd section of annealing time is set to be lower than 50 hours.Preferably 40 hours or less.

After 2 sections of annealing, steel plate is cooled to 650 DEG C with 1 DEG C/h~30 DEG C/h of cooling velocity.

The austenite generated in the 2nd section of annealing is subjected to slow cool down by using slow cool down, thus mutually becoming ferrite While carbon atom be adsorbed on the carbide remained in austenite, carbide and austenite cover ferrite grain boundaries, finally The tissue that carbide is largely present in ferrite grain boundaries can be become.

For this purpose, cooling velocity is preferably relatively slow, but if being lower than 1 DEG C/h, then required time increase, productivity are cooled down It reduces, therefore cooling velocity is set as 1 DEG C/h or more.Preferably 10 DEG C/h or more.

On the other hand, if cooling velocity is more than 30 DEG C/h, austenite phase becomes pearlite, and the hardness of steel plate increases Add, forging reduces, in addition, the impact resistance after carburizing and quenching tempering reduces, therefore cooling velocity is set as 30 DEG C/h Below.Preferably 20 DEG C/h or less.

In turn, it will be cooled to 650 DEG C of steel plate to be cooled to room temperature.Cooling velocity at this time is simultaneously not limited.

Atmosphere in 2 sections of annealing is not particularly limited to specific atmosphere.For example, it may be the atmosphere of 95% or more nitrogen, Any atmosphere in the atmosphere of 95% or more hydrogen, air atmosphere.

As described above, according to the present invention hot-rolled condition and annealing conditions consistently manage to carry out The manufacturing method of the organizational controls of steel plate can be manufactured and be had excellent formability when being combined with drawing, thickening the cold forging of forming and right The excellent steel plate of harden ability needed for the raising of impact resistance after carburizing and quenching tempering.

Embodiment

Next, being illustrated to embodiment, but the level of embodiment is to confirm exploitativeness and effect of the invention Fruit and the example of condition used, the present invention is not limited to the condition examples.The present invention can use various conditions, Reach the purpose of the present invention without departing from purport of the invention.

For the evaluation of cold-workability, by plate thickness be 3mm annealed condition JIS5 tension test sheet acquired for materials Lai Tension test is carried out, is evaluated with rolling direction at 0 ° of direction and with the percentage of total elongation in rolling direction direction in 90 °, Both direction is the difference of the percentage of total elongation of 35% or more and all directions | Δ EL | to add in 4% situation below depending on thinking cold Work is superior.

It is 1.5mm by annealed condition material removal to the plate thickness that plate thickness is 3mm, in vacuum for the evaluation of harden ability The holding that 880 DEG C × 10 minutes are carried out in atmosphere, is quenched with 30 DEG C/sec of cooling velocity, if a point rate for martensite is 60% or more, then depending on thinking that harden ability is superior.

(embodiment 1)

After being heated 1.8 hours at 1240 DEG C shown in table 1 at the continuously casting slab (steel ingot) being grouped as, supply It in hot rolling, after terminating smart hot rolling at 890 DEG C, is batched at 510 DEG C, has manufactured the coils of hot rolled that plate thickness is 3.0mm. Pickling is carried out to coils of hot rolled, coils of hot rolled is packed into box annealing furnace, is -5% nitrogen of 95% hydrogen by control climate, from room Temperature is heated to 705 DEG C, is kept for 36 hours at 705 DEG C and makes the temperature distribution homogenization in coils of hot rolled, is then heated to It 760 DEG C, is maintained at 760 DEG C 10 hours.

Then, 650 DEG C are cooled to 10 DEG C/h of cooling velocity, then, are furnace-cooled to room temperature, have made evaluating characteristics Sample.In addition, the tissue of sample is determined by above-mentioned method.

Table 1

Vickers hardness to manufactured sample, the number of the carbide on ferrite grain boundaries are shown relative to iron in table 2 Ratio, pearlite the area ratio, cold-workability, the harden ability of the number of carbide in ferritic crystal grain are determined or evaluate Result.

Table 2

As shown in table 2, B-1, E-1, F-1, H-1, J-1, K-1, L-1, M-1, N-1, P-1, R- of invention steel 1, T-1, W-1, X-1, Y-1, Z-1, AB-1 and AC-1 are equal are as follows: the number of the carbide of ferrite grain boundaries is relative to ferrite crystalline substance The ratio of the number of the carbide of intragranular is more than 1, and Vickers hardness is 170HV hereinafter, cold-workability and harden ability are excellent.

In contrast, the C amount for comparing steel G-1 is high, and cold-workability reduces.Compare steel O-1 due to Mo amount and Cr amount height, carbon The stability of compound is high, therefore carbide does not dissolve in quenching, and austenite production quantity is few, and harden ability is inferior.

Compare steel Q-1 and AD-1 since the amount of Si, Al are high, A3 point is high, therefore austenite production quantity is few in quenching, quenches Permeability is inferior.The S amount of comparative example U-1 is high, coarse MnS is generated in steel, cold-workability is low.The Mn amount of Comparative examples A A-1 is low, Harden ability is inferior.

The final rolling temperature of the hot rolling of Comparative Example I -1 is low, and productivity reduces.The final rolling temperature of the hot rolling of Comparative Example D -1 is high, Oxide skin scar is generated in surface of steel plate.The coiling temperature of the hot rolling of comparative example C-1 and S-1 is low, bainite, martensite etc. Low temperature phase change tissue becomes more and brittle, frequently cracks when the uncoiling of coils of hot rolled utilizes, and productivity reduces.

The coiling temperature of the hot rolling of Comparative examples A -1 and V-1 is high, and the relatively thicker pearl of sheet gap is generated in hot rolling microstructure Body of light and the high acicular coarse carbide of thermal stability, the carbide also remain in steel plate after 2 sections of steps are annealed, Cold-workability reduces.

(embodiment 2)

In order to investigate the influence of annealing conditions, 1.8 will be heated at 1240 DEG C at the steel billet being grouped as shown in table 1 After hour, for hot rolling, after terminating smart hot rolling at 820 DEG C, 520 DEG C are cooled to 45 DEG C/sec of cooling velocity on ROT, It is batched at 510 DEG C, the coils of hot rolled that manufacture plate thickness is 3.0mm implements 2 sections of steps with annealing conditions shown in table 3 The box annealing of type has made the sample that plate thickness is 3.0mm.

Shown in table 3 the carbide diameter to manufactured sample, ferrite partial size, Vickers hardness, on ferrite grain boundaries Carbide number relative to the ratio of number of the carbide in ferrite crystal grain, pearlite the area ratio, cold-workability, The result that harden ability is determined or evaluates.

Table 3

As shown in table 3, B-2, C-2, E-2, F-2, H-2, I-2, J-2, K-2, M-2, N-2, R- of invention steel 2, S-2, V-2, Z-2 and AC-2 are equal are as follows: the number of the carbide of ferrite grain boundaries is relative to the carbide in ferrite crystal grain The ratio of number is more than 1, and Vickers hardness is 170HV hereinafter, cold-workability and harden ability are excellent.

In contrast, the C amount for comparing steel G-1 is high, and cold-workability reduces.Mo amount and the Cr amount for comparing steel O-1 are high, cold to add Work reduces.In addition, the stability due to carbide is high, in quenching, carbide does not dissolve, austenite production quantity Few, harden ability is inferior.

Compare steel Q-1 since Si amount is high, ferritic hardness is high, therefore processability reduces.In addition, since A3 point is high, because In quenching, austenite production quantity is few for this, and harden ability is inferior.Compare steel AD-1 since Al amount is high, A3 point is high, therefore in quenching Austenite production quantity is few, and harden ability is inferior.The S amount for comparing steel U-1 is high, and coarse MnS is generated in steel, and cold-workability reduces. The Mn amount for comparing steel AA-1 is low, and harden ability is inferior.

Compare box annealing of the steel T-2 due to 2 sections of step types paragraph 1 annealing when holding temperature it is low, Ac1 temperature with Under carbide coarsening processing it is insufficient, the heat stability of carbide is insufficient, thus the 2nd section annealing when remaining Carbide is reduced, and can not inhibit pearlitic transformation in the tissue after slow cool down, and cold-workability reduces.

Holding temperature when comparing the paragraph 1 annealing of the box annealing of 2 sections of step types of steel A-2 is high, generates in annealing Austenite can not improve the stability of carbide, and in the 2nd section of annealing, the carbide of remaining is reduced, the tissue after slow cool down In can not inhibit pearlitic transformation, cold-workability reduces.

Compare box annealing of the steel L-2 due to 2 sections of step types paragraph 1 annealing when retention time it is short, Ac1 temperature with Under carbide coarsening processing it is insufficient, the heat stability of carbide is insufficient, thus the 2nd section annealing when remaining Carbide is reduced, and can not inhibit pearlitic transformation in the tissue after slow cool down, and cold-workability reduces.

Retention time when comparing paragraph 1 annealing when 2 sections of steps annealing of steel W-2 is long, and productivity reduces.Compare steel For X-2 since holding temperature when the 2nd section when 2 sections of steps are annealed is annealed is low, the production quantity of austenite is few and can not increase crystal boundary The number ratio of the carbide at place, therefore cold-workability reduces.

Holding temperature when comparing the 2nd section of annealing of box annealing of the steel AB-2 due to 2 sections of step types is high, promotes carbonization The dissolution of object, therefore the carbide of remaining is reduced, and can not inhibit pearlitic transformation, Cold Forging in the tissue after slow cool down Property reduce.

Holding temperature when comparing the 2nd section of annealing of the box annealing of 2 sections of step types of steel P-2 is low, the generation of austenite Amount is few, can not increase the number ratio of the carbide at ferrite grain boundaries, and cold-workability reduces.Compare steel Y-2 since 2 sections walk Retention time when the 2nd section of annealing of the box annealing of rapid type is long, promotes the dissolution of carbide, therefore the carbide of remaining subtracts It is few, pearlitic transformation can not be inhibited in the tissue after slow cool down, Cold Forging reduces.

Compare cooling velocity of the steel D-2 from the end of the 2nd section of annealing of the box annealing of 2 sections of step types until 650 DEG C Greatly, cause pearlitic transformation while cooling, cold-workability reduces.

Industrial availability

As described above, in accordance with the invention it is possible to manufacture and provide formability and the excellent steel plate of wearability.The present invention Steel plate due to be suitable for as manufactured via manufacturing procedures such as punching, bending, punch process automotive part, cutter, The steel plate of the raw material of other mechanical parts, therefore the utilizability of the present invention industrially is high.

Claims

1. a kind of steel plate, which is characterized in that the steel plate is contained in terms of quality %:

C:0.10~0.40%,

Si:0.01~0.30%,

Mn:1.09~2.00%,

P:0.020% or less,

S:0.010% or less,

Al:0.001~0.10%,

N:0.010% or less,

O:0.020% or less,

Cr:0.50% or less,

Mo:0.10% or less,

Nb:0.10% or less,

V:0.10% or less,

Cu:0.10% or less,

W:0.10% or less,

Ta:0.10% or less,

Ni:0.10% or less,

Sn:0.050% or less,

Sb:0.050% or less,

As:0.050% or less,

Mg:0.050% or less,

Ca:0.050% or less,

Y:0.050% or less,

Zr:0.050% or less,

La:0.050% or less,

Ce:0.050% hereinafter,

Remainder be Fe and inevitable impurity,

Wherein, the metal structure of the steel plate meets:

The number of the carbide of ferrite grain boundaries is more than 1 relative to the ratio of the number of the carbide in ferrite crystal grain,

Ferrite partial size is 5 μm~50 μm, and

The area ratio of pearlite be 6% hereinafter,

The Vickers hardness of the steel plate is 100HV~170HV.

2. steel plate according to claim 1, which is characterized in that instead of a part of the Fe containing Ti:0.10% with 1 kind or 2 kinds in lower and B:0.010% or less.

3. a kind of manufacturing method of steel plate, which is characterized in that it is the manufacturing method of steel plate described in manufacturing claims 1 or 2,

Wherein, implement to complete in 750 DEG C~850 DEG C of temperature region at the steel billet being grouped as to of any of claims 1 or 2 The hot rolling of finish rolling and hot rolled steel plate is made,

The hot rolled steel plate is batched at 400 DEG C~550 DEG C,

Pickling is implemented to the hot rolled steel plate batched,

3 hours~60 hours paragraph 1 are kept in 650 DEG C~720 DEG C of temperature region to the hot rolled steel plate implementation of pickling Annealing, then,

Hot rolled steel plate is implemented to be kept for the 2nd section of 3 hours~50 hours anneal in 725 DEG C~790 DEG C of temperature region,

Hot rolled steel plate after annealing is cooled to 650 DEG C with 1 DEG C/h~30 DEG C/h of cooling velocity.