CN100557058C

CN100557058C - Cold-rolled steel sheet and manufacture method thereof with less anisotropy and high-yield-ratio

Info

Publication number: CN100557058C
Application number: CNB2006800153833A
Authority: CN
Inventors: 尹正凤; 赵雷夏; 郑镇熙; 朴万荣; 陈光根; 韩箱浩; 金成一; 金镐石
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2005-05-03
Filing date: 2006-05-03
Publication date: 2009-11-04
Anticipated expiration: 2026-05-03
Also published as: KR20060115314A; KR100742933B1; KR100723182B1; KR100742943B1; KR20060115315A; US20090126837A1; KR20060115311A; KR20060115635A; TW200702444A; KR20060115312A; KR100742929B1; KR100742944B1; JP2008540826A; KR20060115632A; KR100723164B1; KR20060115310A; JP2008540827A; KR100723216B1; KR20060115630A; KR100742941B1

Abstract

Disclose the compound IF steel of a kind of Nb-Ti, wherein be distributed with the fine throw out that granularity is less than or equal to 2 μ m, as the CuS throw out.Fine precipitate distribution can improve yield strength and reduce the in-plane anisotropy index in the compound IF steel of Nb-Ti.Nano level throw out can form tiny crystal grain.As a result, greater than intragranular amount, this specific character helps not ageing property and cure hardening of room temperature to dissolved carbon at the amount of grain boundary.

Description

Cold-rolled steel sheet and manufacture method thereof with less anisotropy and high-yield-ratio

Technical field

The present invention relates to can be used as the interpolation niobium (Nb) of material of automobile, domestic electronic utensil etc. and no gap (IF) cold-rolled steel sheet of titanium (Ti).More specifically, the present invention relates to the IF cold-rolled steel sheet of high formability, the yield strength of this steel plate improves because being distributed with fine throw out, the invention still further relates to the manufacture method of this IF cold-rolled steel sheet.

Background technology

Generally speaking, the cold-rolled steel sheet that requires to be used for automobile, domestic electronic utensil has good anti-aged at room temperature and cures hardening, and high strength and good formability.

Aging is a kind of strain aging phenomenon, results to be fixed on the sclerosis that tomography causes by dissolved element such as C and N.Because therefore the aging defective that is called " tension strain " that causes guarantees that good anti-aged at room temperature is extremely important.

Cure hardening and refer to because there being dissolved carbon intensity be improved, described dissolved carbon is at press forming, after post coat and drying, and the micro-solid solution figure's who stays carbon.But has the good difficulty that indurative steel plate can overcome the press formability aspect that causes because of high strength of curing.

Can give aluminium (Al)-anti-aged at room temperature of deoxidized steel and cure hardening by carrying out batch annealing.Yet the time that batch annealing prolongs can make the productivity of Al-deoxidized steel descend and at the different sites of steel serious the variation be taken place.In addition, sclerosis (BH) value (yield strength is poor before and after the japanning) of curing of Al-deoxidized steel for 10-20MPa, shows that the raising of yield strength is limited.

In this case,,, annealing continuously then, can form and have good anti-aged at room temperature and cure indurative no gap (IF) steel as Ti and Nb by add forming the element of carbide and nitride.

For example, Japanese Patent Application Publication clear (Sho) 57-041349 has described Ti-base IF steel and by the manganese (Mn) of interpolation 0.4-0.8% and the phosphorus (P) of 0.04-0.12% its intensity is improved.Yet in the IF of utmost point low-carbon (LC) steel, P is because cause the problem of secondary processing embrittlement in the grain boundary segregation.

Flat (Hei) 5-078784 of Japanese Patent Application Publication describes a kind of method that improves intensity, promptly adds greater than 0.9% but the Mn that is no more than 3.0% amount strengthens element as sosoloid.

The open 2003-0052248 of korean patent application describes the method that improves secondary work embrittlement resistance and intensity and workability, promptly adds the Mn of 0.5-2.0%, and aluminium (Al) and boron (B) substitute P.

Flat (Hei) 10-158783 of Japanese Patent Application Publication describes a kind of mode that improves intensity, promptly reduces P content, and uses Mn and Si to strengthen element as sosoloid.According to the content of the disclosure, the consumption of Mn can be the most nearly 0.5%, and Al is 0.1% as its consumption of reductor, and nitrogen (N) is as impurity, and its amount is limited to and is less than or equal to 0.01%.If improve Mn content, then the electroplating characteristic variation.

Flat (Hei) 6-057336 of Japanese Patent Application Publication discloses a kind of method that improves the intensity of IF steel, and the copper (Cu) that promptly adds 0.5-2.5% forms ε-Cu throw out.Obtaining high-intensity IF steel is because there is ε-Cu throw out, but the workability of IF steel descends.

Flat (Hei) 9-227951 peace (Hei) 10-265900 of Japanese Patent Application Publication proposes to improve workability or improves because of using the technology of the surface imperfection that Cu causes by carbide as the nucleus of precipitation carbide.Open according to last patent application, come deposit C uS at the Cu that the IF steel is carried out add during smooth 0.005-0.1%, and the CuS throw out forms the Cu-Ti-C-S throw out as nucleus during hot rolling.In addition, last patent application openly points out during recrystallization, form be parallel to surface of steel plate { 111} planar nucleus quantity increases near the Cu-Ti-C-S throw out, can improve workability like this.Open according to back one patent application, the Cu that adds 0.01-0.05% in the IF steel with the nucleus of this CuS throw out as the precipitation carbide, reduces dissolved carbon (C) amount, thereby improves surface imperfection then to obtain the CuS throw out.According to prior art, because use the CuS first lees when making cold-rolled steel sheet, carbide can be stayed in the product of making.In addition because the amount of the element of the formation emulsion that adds such as Ti and Zr according to atomic wts than the amount of meter greater than sulphur (S), most sulphur (S) and Ti or Zr reaction, rather than react with Cu.

On the other hand, flat (Hei) 6-240365 peace (Hei) 7-216340 of Japanese Patent Application Publication has described the combination that adds Cu and P and has improved the erosion resistance of curing sclerotic type IF steel.Open according to these patent applications, the Cu that adds the 0.05-1.0% amount can guarantee to improve erosion resistance.Yet in fact, the Cu of adding measures more than or equal to 0.2%.

Flat (Hei) 10-280048 peace (Hei) 10-287954 of Japanese Patent Application Publication proposes when reheat and annealing carbon sulfide (Ti-C-S yl) to be dissolved in the carbide, obtaining sosoloid, thereby can obtain to cure sclerosis (BH) value (yield strength of curing front and back is poor) more than or equal to 30MPa in the grain boundary.

According to foregoing disclose, intensity can be by strengthening sosoloid or using ε-Cu throw out to be improved.Use Cu to form ε-Cu throw out and improve erosion resistance.In addition, use the nucleus of Cu as the precipitation carbide.But in these are open, do not mention the anisotropic index that improves in high-yield-ratio (that is yield strength/tensile strength) and the reduction plane.If a kind of tensile strength of IF steel and the ratio of yield strength (being yield tensile ratio) are higher, then can reduce the thickness of this IF steel plate, can effectively reduce weight like this.In addition, if anisotropic index is lower in a kind of plane of IF steel, during processing and after the processing less amount wrinkle and ear (ears) phenomenon can take place respectively.

Summary of the invention

Technical problem

A purpose of some embodiments of the present invention provides the IF cold-rolled steel sheet that adds Nb and Ti, and this steel plate can reach anisotropic index in high-yield-ratio and the low plane.

Another purpose of some embodiments of the present invention provides the method for making this IF cold-rolled steel sheet.

Technical scheme

According to the present invention, a kind of cold-rolled steel sheet is provided, this cold-rolled steel sheet has the composition that comprises following component: % represents according to weight, be less than or equal to Cu, the 0.005-0.08% of 0.01% C, 0.01-0.2% S, be less than or equal to 0.1% Al, be less than or equal to 0.004% N, be less than or equal to Nb, the Ti of 0.005-0.15% of B, the 0.002-0.04% of 0.2% P, 0.0001-0.002%, and the Fe of surplus and other unavoidable impurities, this composition satisfies following relational expression: 1≤(Cu/63.5)/(S ^*/ 32)≤30, S ^*=S-0.8 * (Ti-0.8 * (48/14) * N) * (32/48), this steel plate comprise the CuS throw out that mean particle size is less than or equal to 0.2 μ m.

According to the present invention, a kind of cold-rolled steel sheet is provided, cold-rolled steel sheet has the composition that comprises following component: % represents according to weight, be less than or equal to 0.01% C, the Cu of 0.01-0.2%, the Mn of 0.01-0.3%, the S of 0.005-0.08%, be less than or equal to 0.1% Al, be less than or equal to 0.004% N, be less than or equal to 0.2% P, the B of 0.0001-0.002%, the Nb of 0.002-0.04%, the Ti of 0.005-0.15%, and the Fe of surplus and other unavoidable impurities, wherein, this composition satisfies following relational expression: 1≤(Mn/55+Cu/63.5)/(S ^*/ 32)≤30, and S ^*=S-0.8 * (Ti-0.8 * (48/14) * N) * (32/48), this steel plate comprise (Mn, Cu) the S throw out that mean particle size is less than or equal to 0.2 μ m.

According to the present invention, a kind of cold-rolled steel sheet is provided, this cold-rolled steel sheet has the composition that comprises following component: % represents according to weight, be less than or equal to Cu, the 0.005-0.08% of 0.01% C, 0.01-0.2% S, be less than or equal to 0.1% Al, 0.004-0.02% N, be less than or equal to Nb, the Ti of 0.005-0.15% of B, the 0.002-0.04% of 0.2% P, 0.0001-0.002%, and the Fe of surplus and other unavoidable impurities, wherein, this composition satisfies following relational expression: 1≤(Cu/63.5)/(S ^*/ 32)≤30,1≤(Al/27)/(N ^*/ 14)≤10, S ^*=S-0.8 * (Ti-0.8 * (48/14) * N) * (32/48) and N ^*=N-0.8 * (Ti-0.8 * (48/32) * S) * (14/48), this steel plate comprise CuS and the AlN throw out that mean particle size is less than or equal to 0.2 μ m.

According to the present invention, a kind of cold-rolled steel sheet is provided, this cold-rolled steel sheet has the composition that comprises following component: % represents according to weight, be less than or equal to 0.01% C, 0.01-0.2% Cu, 0.01-0.3% Mn, 0.005-0.08% S, be less than or equal to 0.1% Al, 0.004-0.02% N, be less than or equal to Nb, the Ti of 0.005-0.15% of B, the 0.002-0.04% of 0.2% P, 0.0001-0.002%, and the Fe of surplus and other unavoidable impurities, wherein, this composition satisfies following relational expression: 1≤(Mn/55+Cu/63.5)/(S ^*/ 32)≤30,1≤(Al/27)/(N ^*/ 14)≤10, S ^*=S-0.8 * (Ti-0.8 * (48/14) * N) * (32/48) and N ^*=N-0.8 * (Ti-0.8 * (48/32) * S) * (14/48), this steel plate comprise (Mn, Cu) throw out of S and AlN that mean particle size is less than or equal to 0.2 μ m.

According to the present invention, a kind of cold-rolled steel sheet is provided, this cold-rolled steel sheet has the composition that comprises following component: % represents according to weight, be less than or equal to 0.01% C, be less than or equal to 0.08% S, be less than or equal to 0.1% Al, be less than or equal to 0.004% N, be less than or equal to 0.2% P, the B of 0.0001-0.002%, the Nb of 0.002-0.04%, the Ti of 0.005-0.15%, be selected from following at least a component: the Cu of 0.01-0.2%, the Mn of 0.01-0.3% and the N of 0.004-0.2%, and the Fe of surplus and other unavoidable impurities, wherein, this composition satisfies following relational expression: 1≤(Mn/55+Cu/63.5)/(S ^*/ 32)≤30,1≤(Al/27)/(N ^*/ 14)≤10 (condition is that N content is more than or equal to 0.004%), S ^*=S-0.8 * (Ti-0.8 * (48/14) * N) * (32/48) and N ^*=N-0.8 * (Ti-0.8 * (48/32) * S) * (14/48), steel plate comprise and are selected from (Mn, Cu) at least a in S and the AlN throw out that mean particle size is less than or equal to 0.2 μ m.

During relational expression below cold-rolled steel sheet of the present invention satisfies between C, Ti, Nb, N and S content: 0.8≤(Ti ^*/ 48+Nb/93)/(C/12)≤5.0 and Ti ^*=Ti-0.8 * ((48/14) * N+ (48/32) * S), this cold-rolled steel sheet show not ageing property of room temperature.In addition, as solute carbon (Cs) [Cs=(C-Nb * 12/93-Ti that determines by C and Ti content ^** 12/48) * 10000, wherein, T ⁱ*=Ti-0.8 * ((48/14) * N+ (48/32) * S), condition is to work as Ti ^*Less than 0 o'clock, Ti ^*Be defined as 0)) value when being 5-30, cold-rolled steel sheet of the present invention has the hardening of curing.

Depend on the design to forming, the characteristic of cold-rolled steel sheet of the present invention is the soft cold-rolled steel sheet of 280MPa magnitude and more than or equal to the high strength cold rolled steel plate of 340MPa magnitude.

When the P of composition of the present invention content is less than or equal to 0.015%, can make the soft cold-rolled steel sheet of 280MPa magnitude.The sosoloid that also comprises at least a Si of being selected from and Cr when this soft cold-rolled steel sheet strengthens element, or P content can reach the high strength more than or equal to 340MPa when the 0.015-0.2% scope.Only contain P content in the high-strength steel of P preferably at 0.03-0.2%.The Si content of high-strength steel is preferably in the 0.1-0.8% scope.The Cr content of high-strength steel is preferably 0.2-1.2%.When cold-rolled steel sheet of the present invention contained the element of at least a Si of being selected from and Cr, P content can freely be limited to and be less than or equal to 0.2%.

For reaching better workability, cold-rolled steel sheet of the present invention can also contain the Mo of 0.01-0.2 weight %.

According to the present invention, the method for making cold-rolled steel sheet is provided, this method may further comprise the steps: the slab reheat that will satisfy one of described composition is to the temperature that is greater than or equal to 1,100 ℃; Be greater than or equal to Ar ₃Slab to reheat under the final rolling temperature of transformation temperature carries out hot rolling, and the hot rolled steel plate is provided; With the cooling hot-rolled steel plate of 300 ℃/minute speed; Be less than or equal to 700 ℃ temperature with the refrigerative roll of steel plate around; Carry out cold rolling to the steel plate of reeling; And cold-rolled steel sheet carried out continuous annealing.

Best mode

Describe the present invention below in detail.

Granularity is less than or equal to the fine precipitate distribution of 0.2 Xie in cold-rolled steel sheet of the present invention.This sedimentary example comprises the composite precipitation thing of MnS throw out, CuS throw out and MnS and CuS.These throw outs abbreviate " (Mn, Cu) S " as.

The inventor has been found that the yield strength of IF steel improves when fine precipitate distribution is in the IF steel (also abbreviating " the compound IF steel of Nb-Ti " as) of interpolation Nb and Ti, and anisotropic index descends in the plane, therefore reaches the raising workability.Finished the present invention based on these discoveries.Be used for throw out of the present invention and almost do not causing attention aspect the conventional I F steel.Particularly initiatively do not use this throw out from the index aspect consideration of yield strength peace intra-face anisotropy.

Need regulate the component in the compound IF steel of Nb-Ti, to obtain (Mn, Cu) S throw out and/or AlN throw out.If the IF steel contains Ti, Zr and other element, S and N preferably react with Ti and Zr.Since the cold-rolled steel sheet of the present invention compound IF steel that is Nb-Ti, Ti and C, N and S reaction.Therefore, need regulate, make S and N be precipitated as (Mn, Cu) S and AlN form respectively component.

Thus obtained fine throw out can form small grains.The tiny granulometric facies of crystal grain are to having improved the ratio of grain boundary.Therefore, the dissolved carbon amount that exists in the grain boundary is greater than intragranular amount, therefore can reach not ageing property of good room temperature.Can more freely move because be present in intragranular dissolved carbon, be attached to movably tomography, therefore influence aged at room temperature character.On the contrary, near dissolved carbon activation under comparatively high temps (temperature of the processing of for example painting/cure) of settling position (as grain boundary and throw out) segregation, therefore hardening is cured in influence.

The anisotropy of anisotropic index and plasticity has favourable influence in the balance that improves between yield strength, improvement intensity-extension shape, the plane to strengthening because of precipitation to be distributed in fine throw out in the steel plate of the present invention.It is therefore, fine that (Mn, Cu) S throw out and AlN throw out must uniform distribution.According to cold-rolled steel sheet of the present invention, influence speed of cooling specific after composition, preparation condition and the hot rolling between sedimentary components contents, component all to the fine sedimentary very big influence that is distributed with.

The following describes composition component according to cold-rolled steel sheet of the present invention.

Carbon (C) content is preferably limited to and is less than or equal to 0.01%.

Carbon (C) influences the anti-aged at room temperature of cold-rolled steel sheet and cures hardening.When carbon content surpasses 0.01%, need to add expensive reagent N b and Ti and remove residual carbon, this is unfavorable economically and consider it also is undesirable from the formability aspect.When only intention obtains anti-aged at room temperature, preferably keep low carbon content, can reduce the addition of expensive reagent Nb and Ti like this.When intention guarantees requiredly when curing hardening, the preferred carbon amount that adds is more than or equal to 0.001%, more preferably 0.005-0.01%, when carbon content less than 0.005% the time, the amount that needn't increase Nb and Ti also can guarantee anti-aged at room temperature.

Copper (Cu) content is preferably in the 0.01-0.2% scope.

The effect of copper is to form fine CuS throw out, and this throw out can make crystal grain tiny.Copper is by promoting precipitation and reduced anisotropic index in the plane of cold-rolled steel sheet and improved the yield strength of cold-rolled steel sheet.In order to form fine throw out, Cu content must be more than or equal to 0.01%.When Cu content greater than 0.2% the time, obtain thick throw out.Cu content is more preferably in the 0.03-0.2% scope.

Manganese (Mn) content is preferably in the 0.01-0.3% scope.

The effect of manganese is that the sulphur with solid solution figure in the steel is precipitated as the MnS throw out, thereby prevents the red brittleness that causes because of dissolve sulfur (or be called sosoloid strengthen element).Consider from this technological standpoint, generally add a large amount of manganese.The inventor has been found that when reducing manganese content and making sulphur content reach the best, obtains very fine MnS throw out.Based on this discovery, manganese content is restricted to and is less than or equal to 0.3%.In order to guarantee this specific character, manganese content must be more than or equal to 0.01%.When manganese content less than 0.01%, promptly when higher, may produce red brittleness with the residual sulphur content of solid solution figure.When manganese content greater than 0.3% the time, form thick MnS throw out, therefore be difficult to meet the requirements of intensity.Preferred Mn content is 0.01-0.12%.

Sulphur (S) content preferably is restricted to and is less than or equal to 0.08%.

Sulphur (S) and Cu and/or Mn reaction form CuS and MnS throw out respectively.When sulphur content greater than 0.08% the time, the ratio of dissolve sulfur increases.The increase of dissolve sulfur can make the ductility and the obvious variation of formability of steel plate, and increases hot short danger.In order to obtain CuS as much as possible and/or MnS throw out, preferred sulphur content is more than or equal to 0.005%.

Aluminium (Al) content preferably is restricted to and is less than or equal to 0.1%.

Aluminium and nitrogen (N) reaction forms fine AlN throw out, thereby it is aging to prevent fully that dissolved nitrogen from causing.When nitrogen content more than or equal to 0.004% the time, fully form the AlN throw out.Fine AlN precipitate distribution can form small grains and strengthen the yield strength that improves steel plate by precipitating in steel plate.Al content is more preferably in the 0.01-0.1% scope.

Nitrogen (N) content preferably is restricted to and is less than or equal to 0.02%.

When intention was used the AlN throw out, the add-on of nitrogen mostly was 0.02% most.In addition, the control nitrogen content is less than or equal to 0.004%.When nitrogen content less than 0.004% the time, AlN throw out comparatively small amt, so the fine effect of crystal grain and precipitation reinforced effects all can be ignored.On the contrary, when nitrogen content greater than 0.02% the time, also be difficult to guarantee ageing property by using dissolved nitrogen.

Phosphorus (P) content preferably is restricted to and is less than or equal to 0.2%.

Phosphorus is the element that has good sosoloid enhancement and the r-value is slightly reduced.Phosphorus has guaranteed the high strength of steel plate of the present invention, has controlled the precipitation in the steel plate.Desired strength ideal phosphorus content in the steel of 280MPa magnitude is defined as and is less than or equal to 0.015%.Intensity is defined as greater than 0.015% at the desirable phosphorus content of the high-strength steel of 340MPa magnitude but is no more than 0.2%.Phosphorus content surpasses 0.2% and may cause the ductility of steel plate to descend.Therefore, phosphorus content preferably is defined as maximum 0.2%.When adding Si and Cr among the present invention, phosphorus content suitably is controlled at and is less than or equal to 0.2%, to meet the requirements of intensity.

Boron (B) content is preferably in the 0.0001-0.002% scope.

Add boron to prevent the secondary processing embrittlement.Therefore, preferred boron content is more than or equal to 0.0001%.When boron content surpasses 0.002%, the obvious variation of deep-draw ductility of steel plate.

Niobium (Nb) content is preferably in the 0.002-0.04% scope.

The purpose that adds Nb is to guarantee not ageing property and the formability of improving steel plate.Nb is the element that a kind of potential forms carbide, adds niobium in steel, thereby forms the NbC throw out in steel.In addition, the NbC throw out makes the good texturing of steel plate quilt during annealing, and has therefore significantly improved the deep-draw ductility of steel plate.When the Nb content that adds is not more than 0.002%, form very a spot of NbC throw out.Therefore, well texturing of steel plate, like this, the deep-draw ductility of steel plate does not almost improve.On the contrary, when Nb content greater than 0.04% the time, form very a large amount of NbC throw outs.Therefore, reduced the deep-draw ductility and the unit elongation of steel plate, like this, the obvious variation of the formability of steel plate.

Titanium (Ti) content is preferably in the 0.005-0.15% scope.

The purpose that adds titanium is to guarantee not ageing property and the formability of improving steel plate.Ti is the element that a kind of potential forms carbide, adds titanium in steel, thereby forms the TiC throw out in steel.In addition, the TiC throw out makes the dissolved carbon precipitation, to guarantee not aging.When the Ti content that adds less than 0.005% the time, form very a spot of TiC throw out.Therefore, well texturing of steel plate, like this, the deep-draw ductility of steel plate does not almost improve.On the contrary, when the add-on of Ti greater than 0.15% the time, form a large amount of TiC throw outs.Therefore, reduce the tiny usefulness that turns into of crystal grain, caused anisotropic index in the high plane, reduced yield strength, the obvious variation of electroplating characteristic.

(Mn, Cu) S and AlN throw out are adjusted in the content of Mn, Cu, S, Nb, Ti, Al, N and C in the following relational expression restricted portion in order to form.Each component of pointing out in the following relational expression is represented with weight %.

1≤(Cu/63.5)/(S*/32)≤30 (1)

S*＝S-0.8×(Ti-0.8×(48/14)×N)×(32/48) (2)

In the relational expression 1, S* is by relational expression 2 decision, expression with the Ti reaction, afterwards with the sulphur content of Cu reaction.For obtaining fine CuS throw out, the value of preferred (Cu/63.5)/(S*/32) is more than or equal to 1.If value (Cu/63.5)/(S*/32) is greater than 30, the CuS throw out that then distributes thick, this does not wish to take place.For stably forming the CuS throw out that granularity is less than or equal to 0.2 μ m, (Cu/63.5)/value of (S*/32) is preferably in the 1-20 scope, and more preferably 1-9 most preferably is 1-6.

1≤(Mn/55+Cu/63.5)/(S*/32)≤30 (3)

(Mn, Cu) the S throw out is relevant, obtains relational expression 3 by add Mn content in relational expression 1 with formation for relational expression 3.(value (Mn/55+Cu/63.5)/(S*/32) must be more than or equal to 1 for Mn, Cu) S throw out in order effectively to form.When the value of relational expression 3 greater than 30 the time, form thick (Mn, Cu) S throw out.For stably form granularity be less than or equal to 0.2 μ m ((Cu/63.5)/value of (S*/32) is more preferably in the 1-20 scope, more preferably 1-9 most preferably is 1-6 for Mn, Cu) S throw out.When Mn and Cu add fashionablely together, the total amount of Mn and Cu is preferably 0.05-0.4%.The reason that the total amount of Mn and Cu is limited is fine (Mn, Cu) S throw out in order to obtain.

1≤(Al/27)/(N*/14)≤10 (4)

N*＝N-0.8×(Ti-0.8×(48/32)×S)×(14/48) (5)

Relational expression 4 with form fine (Mn, Cu) the S throw out is relevant, in the relational expression 4, N* is by relational expression 5 decisions, expression with the Ti reaction, afterwards with the N content of Al reaction.In order to obtain fine AlN throw out, (Al/27)/(N ^*/ 14) value is in the 1-10 scope.In order to obtain effective AlN precipitation, (Al/27)/(N ^*/ 14) value must be more than or equal to 1.If (Al/27)/(N ^*/ 14) value then forms thick AlN throw out greater than 10., therefore cause the workability of difference and low yield strength.(Al/27)/(N ^*/ 14) value is preferably in the 1-6 scope.

The component of cold-rolled steel sheet of the present invention can make up in a different manner according to the throw out kind that will obtain.For example, a kind of cold-rolled steel sheet provided by the invention, this cold-rolled steel sheet has the composition that comprises following component: % represents according to weight, be less than or equal to 0.01% C, be less than or equal to 0.08% S, be less than or equal to 0.1% Al, be less than or equal to 0.004% N, be less than or equal to 0.2% P, the B of 0.0001-0.002%, the Nb of 0.002-0.04%, the Ti of 0.005-0.15%, at least a Cu that is selected from following component: 0.01-0.2%, the Mn of 0.01-0.3% and the N of 0.004-0.2%, and the Fe of surplus and other unavoidable impurities, wherein, form and satisfy following relational expression: 1≤(Mn/55+Cu/63.5)/(S*/32)≤30,1≤(Al/27)/(N*/14)≤10 (prerequisite is that N content is more than or equal to 0.004%), S ^*=S-0.8 * (Ti-0.8 * (48/14) * N) * (32/48) and N ^*=N-0.8 * (Ti-0.8 * (48/32) * S) * (14/48), and steel plate comprises at least a throw out that is selected from following throw out: MnS, CuS, MnS and AlN, and described sedimentary mean particle size is less than or equal to 0.2 μ m.That is, one or more components that are selected from the N of the Mn of Cu, 0.01-0.3% of 0.01-0.2% and 0.004-0.2% produce (Mn, Cu) the sedimentary various combinations of S and AlN that granularities are not more than 0.2 μ m.

In the steel plate of the present invention, carbon deposition is NbC and TiC form.Therefore, the anti-aged at room temperature of steel plate and cure the influence that hardening is subjected to the situation of dissolved carbon does not form NbC and TiC throw out under this situation.Consider these requirements, most preferably the content of Nb, Ti and C satisfies following relational expression.

0.8≤(Ti*/48+Nb/93)/(C/12)≤5.0 (6)

Ti*＝Ti-0.8×((48/14)×N+(48/32)×S) (7)

Relational expression 6 and formation NbC and TiC precipitation are with removal solid solution figure's carbon, thereby ageing property is relevant to reach room temperature.In the relational expression 6, Ti* is by relational expression 7 decision, and expression N and S reaction are afterwards with the content of the titanium of C reaction.

When (value of Ti*/48+Nb/93)/(C/12) is difficult to guarantee not ageing property of room temperature less than 0.8 the time.On the contrary, when (value of Ti*/48+Nb/93)/(C/12) is greater than 5 the time, and the Nb and the Ti amount that remain in the steel with the solid solution figure are bigger, can make the ductility variation of steel.When intention obtains room temperature not during aging not guaranteeing to cure under the hardening condition, preferably carbon content is defined as to be less than or equal to 0.005%.Though carbon content greater than 0.005%, still can obtain not aging of room temperature when satisfying relational expression 6, NbC and TiC precipitation capacity increase, and therefore make the workability deteriorates of steel plate.

Cs＝(C-Nb×12/93-Ti*×12/48)×10000 (8)

(condition be when Ti* less than 0 the time, Ti* is defined as 0.)

Relational expression 8 with reach that to cure hardening relevant.Cs represents with ppm in relational expression 8, and representative is not precipitated as the content of the dissolved carbon of NbC and TiC form.In order to obtain the high sclerosis value of curing, the Cs value must be more than or equal to 5ppm.If the Cs value surpasses 30ppm, the content of dissolved carbon increases, and makes to be difficult to obtain not aging of room temperature.

Fine throw out preferably can be evenly distributed in the composition of the present invention.Sedimentary mean particle size preferably is less than or equal to 0.2 μ m.The research of carrying out according to the inventor, when sedimentary mean particle size during greater than 0.2 μ m, anisotropic index is low in the low and plane of the intensity of steel plate.In addition, be less than or equal to the precipitate distribution of 0.2 μ m in of the present invention the composition by a large amount of mean particle sizes.Though the sedimentary quantity that distributes is had no particular limits, and the throw out that a greater number is arranged is more favourable.The sedimentary quantity that distributes is preferably greater than or equals 1 * 10 ⁵/ mm ², more preferably greater than or equal 1 * 10 ⁶/ mm ², most preferably more than or equal to 1 * 10 ⁷/ mm ²By increasing sedimentary quantity, improve plasticity-anisotropic index and reduced anisotropic index in the plane, the result has significantly improved workability.There is restriction in the raising of workability, and this is known, because anisotropic index improves with plasticity-anisotropic index increase in the plane.It should be noted that when the throw out quantity that distributes in the steel plate of the present invention increased, the plasticity of steel plate-anisotropic index improved, and anisotropic index descends in the plane of steel plate.The present invention wherein forms fine sedimentary steel plate and satisfies yield tensile ratio (yield strength/tensile strength) more than or equal to 0.58 requirement.

When steel plate of the present invention was applied to high tensile steel plate, the sosoloid that described steel plate can also contain at least a P of being selected from, Si and Cr strengthened element.The front has illustrated the adjection of P, therefore omits the explanation to them.

Silicon (Si) content is preferably in the 0.1-0.8% scope.

Si is the element with sosoloid enhancement, and unit elongation is slightly descended.Si has guaranteed the high strength of steel plate of the present invention, has controlled the precipitation in the steel plate.Have only when Si content more than or equal to 0.1% the time, just can guarantee high strength.Yet, when Si content greater than 0.8% the time, the ductility variation of steel plate.

Chromium (Cr) content is preferably in the 0.2-1.2% scope.

Cr is the element with sosoloid enhancement, and Cr has reduced the secondary processing embrittlement temperature, and has reduced ageing index because of the carbide that forms Cr.Cr has guaranteed the high strength of steel plate of the present invention, has controlled the precipitation in the steel plate, and has the effect that reduces anisotropic index in the steel plate plane.Have only when Cr content more than or equal to 0.2% the time, could guarantee high strength.Yet, when Cr content surpasses 1.2%, the ductility variation of steel plate.

Cold-rolled steel sheet of the present invention also contains molybdenum (Mo).

Molybdenum in the cold-rolled steel sheet of the present invention (Mo) content is preferably in the 0.01-0.2% scope.

Mo adds with element, can improve the plasticity-anisotropic index of steel plate.Have only when molybdenum content is not less than 0.01%, could improve the plasticity-anisotropic index of steel plate.Yet when molybdenum content surpassed 0.2%, plasticity-anisotropic index no longer improved, and has hot short danger.

Make cold-rolled steel sheet

Below, referring to the method for following preferred implementation explanation manufacturing cold-rolled steel sheet of the present invention.Embodiments of the present invention can be carried out various modifications, and these are revised all within the scope of the present invention.

The inventive method is characterised in that, satisfying steel that steel defined above one of form can be by carrying out hot rolling and cold rolling, forms the throw out that mean particle size is less than or equal to 0.2 μ m and handle in the steel plate of cold rolling back.Sedimentary mean particle size in the cold-rolled steel sheet is subjected to the influence that steel are formed design and treatment condition, as reheat temperature and coiling temperature.Particularly, the speed of cooling after the hot rolling directly has influence on sedimentary mean particle size.

Hot-rolled condition

Among the present invention, the steel that satisfy one of composition defined above are carried out reheat, carry out hot rolling then.The reheat temperature is preferably and is greater than or equal to 1,100 ℃.During to the temperature that is lower than 1,100 ℃, the first lees that forms during continuous casting can not dissolve fully and be residual with the steel reheat.First lees even after hot rolling, still keep residual.

Preferably be not less than Ar ₃Carry out hot rolling under the final rolling temperature of transformation temperature.When final rolling temperature is lower than Ar ₃During transformation temperature, produce rolling particle (rolled grain), they can make workability deteriorates and make strength degradation.

Cooling is preferably carried out with the speed more than or equal to 300 ℃/minute before reeling but after hot rolling.Though the composition of component is controlled to form fine throw out, and when cooling off down less than 300 ℃/minute, the sedimentary mean particle size of formation is greater than 0.2 μ m.That is, improve the many nucleus of generation with speed of cooling, so throw out becomes more and more thinner.Reduce because sedimentary granularity raises with speed of cooling, therefore needn't limit the upper limit of speed of cooling.But when speed of cooling during greater than 1,000 ℃/minute, the effect that reduces the throw out granularity no longer is significantly improved.Therefore, speed of cooling is preferably at 300-1000 ℃/minute.

(winding) condition of coiling

After the hot rolling, reel being no more than under 700 ℃ of temperature.When the coiling temperature was higher than 700 ℃, the throw out of formation was too thick, therefore was difficult to guarantee high strength.

Cold rolling condition

Steel carry out cold rolling with the draft (reduction rate) of 50-90%.Because cold rolling draft less than 50% o'clock, causes producing small number of crystal nucleus behind annealing recrystallization, hypertrophy makes the grain coarsening by annealing recrystallization to crystal grain by annealing, causes intensity and formability to descend.The cooling draft produces too much a large amount of nucleus simultaneously greater than causing improving formability at 90% o'clock, and therefore, the crystal grain by annealing recrystallization becomes too thin, makes the ductility variation of steel like this.

Continuous annealing

The continuous annealing temperature plays an important role to the mechanical properties of determining the finished product.According to the present invention, continuous annealing is preferably carried out under 700-900 ℃ of temperature.When continuous annealing was carried out under being lower than 700 ℃ temperature, recrystallization was incomplete, therefore can not guarantee the ductility that requires.On the contrary, when continuous annealing is carried out under being higher than 900 ℃ of temperature, the grain coarsening of recrystallization, so the intensity variation of steel.Keep continuous annealing and finish recrystallization up to steel.The recrystallization of steel is finished in more than or equal to 10 second time.Continuous annealing was preferably carried out 10 seconds to 30 minutes.

Implement mode of the present invention

Illustrate in greater detail the present invention referring to the following examples.

According to ASTM E-8 standard method of test, estimate the mechanical properties of the steel plate of making in following examples.Particularly, each steel plate is carried out machining, make standard model.Use tensile strength meter (obtaining with 6025 models) to measure yield strength, tensile strength, unit elongation, plasticity-anisotropic index (r from INSTRON Company _mValue) peaceful intra-face anisotropy index (Δ r value) and ageing index.Plasticity-anisotropic index r _mPeace intra-face anisotropy index (Δ r value) adopts following equation to calculate respectively: r _m=(r ₀+ 2r ₄₅+ r ₉₀)/4 and Δ r=(r ₀-2r ₄₅+ r ₉₀)/2.

The ageing index of steel plate is defined as by each sample is annealed, and carries out 1.0% skin rolling then and in 100 ℃ of yield point elongation rates of carrying out measuring after the thermal treatment in 2 hours.Sclerosis (BH) value of curing of standard model is measured in the following manner, applies 2% strain on each sample, and the strained sample was in 170 ℃ of annealing 20 minutes.Measure the yield strength of annealing back sample.The BH value calculates by deducting the yield strength value that records before the annealing by the yield strength value that records after the annealing.

Embodiment 1

At first, prepare plate slab according to the composition shown in the following table.Plate slab is carried out reheat and smart hot rolling, the hot rolled steel plate is provided.This hot-rolled steel sheet cools off with 400 ℃ of/minute speed, reels in 650 ℃, and the draft with 75% carries out cold rolling, carries out continuous annealing then, makes cold-rolled steel sheet.At this moment, carry out smart hot rolling in 910 ℃, this temperature is higher than Ar ₃Transformation temperature by with 10 ℃ of/second speed hot-rolled steel sheet being heated to 830 ℃ and keep carrying out continuous annealing in 40 seconds, makes final cold-rolled steel sheet.

Table 1

Table 2

Table 3

^*Annotate:

The YS=yield strength, TS=tensile strength, E1=unit elongation, r _m=plasticity-anisotropic index, anisotropic index in the Δ r=plane, AI=ageing index, the embrittlement of SWE=secondary processing, IS=steel of the present invention, CS=comparative example steel

Embodiment 2

Table 4

Table 5

Table 6

^*Annotate:

The YS=yield strength, TS=tensile strength, E1=unit elongation, r _m=plasticity-anisotropic index, anisotropic index in the Δ r=plane, the embrittlement of SWE=secondary processing, AI=ageing index, IS=steel of the present invention, CS=comparative example steel

Embodiment 3

At first, prepare plate slab according to the composition shown in the following table.Plate slab is carried out reheat and smart hot rolling, the hot rolled steel plate is provided.This hot-rolled steel sheet cools off with 400 ℃ of/minute speed, reels in 650 ℃, and the draft with 75% carries out cold rolling, carries out continuous annealing then, makes cold-rolled steel sheet.At this moment, carry out smart hot rolling in 910 ℃, this temperature is higher than Ar ₃Transformation temperature by with 10 ℃ of/second speed hot-rolled steel sheet being heated to 830 ℃ and keep carrying out continuous annealing in 40 seconds, makes final cold-rolled steel sheet

Table 7

Table 8

Table 9

^*Annotate:

Embodiment 4

Table 10

Table 11

Table 12

^*Annotate:

Embodiment 5

Table 13

Table 14

Table 15

^*Annotate:

Embodiment 6

Table 16

Table 17

Table 18

^*Annotate:

Embodiment 7

Table 19

Table 20

Table 21

^*Annotate:

Embodiment 8

Table 22

Table 23

Table 24

^*Annotate:

Embodiment 9

Table 25

Table 26

Table 27

^*Annotate:

Embodiment 10

Table 28

Table 29

Table 30

^*Annotate:

Embodiment 11

Table 31

Table 32

Table 33

^*Annotate:

Embodiment 12

Table 34

Table 35

Table 36

^*Annotate:

Embodiment 13

Table 37

Table 38

Table 39

^*Annotate:

Embodiment 14

Table 40

Table 41

Table 42

^*Annotate:

Preferred implementation of the present invention is not construed as limiting the invention, and just is used for illustration purpose.Have with the substantially the same formation of the technical spirit of the present invention of claims definition and any embodiment of essentially identical operating effect and all be included within the technical scope of the present invention.

Commercial Application

Can be understood by top description, according to cold rolling steel plate of the present invention, fine precipitate distribution is at Nb-Ti In the compound IF steel, so that form tiny crystal grain, the result has reduced in the plane respectively to different by strengthening precipitation Sex index has also improved surrender intensity.

Claims

1. A cold-rolled steel sheet having excellent formability and a high yield ratio, said cold-rolled steel sheet having a composition comprising, by weight: 0.01% or less of C, 0.01-0.2% of Cu , 0.005-0.08% of S, less than or equal to 0.1% of Al, less than or equal to 0.004% of N, less than or equal to 0.2% of P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% Ti, and the balance of Fe and other unavoidable impurities,

Wherein, the composition satisfies the following relationship:

1≤(Cu/63.5)/(S ^* /32)≤30,

S ^* =S-0.8×(Ti-0.8×(48/14)×N)×(32/48),

The steel plate contains CuS precipitates with an average particle size of less than or equal to 0.2 μm.

2. The cold-rolled steel sheet according to claim 1, wherein the composition further includes 0.01-0.3% Mn, and satisfies the following relationship: 1≤(Mn/55+Cu/63.5)/(S ^* / 32) ≤ 30, the steel plate contains (Mn, Cu)S precipitates with an average particle size less than or equal to 0.2 μm.

3. The cold-rolled steel sheet according to claim 1, characterized in that the N content is 0.004-0.02%, and the composition satisfies the following relationship:

1≤(Al/27)/(N ^* /14)≤10,

N ^* =N-0.8×(Ti-0.8×(48/32)×S)×(14/48),

The steel sheet contains AlN precipitates with an average particle size of 0.2 μm or less.

4. The cold-rolled steel sheet according to claim 1, wherein the composition further comprises 0.01-0.3% of Mn and 0.004-0.02% of N, and satisfies the following relationship:

1≤(Mn/55+Cu/63.5)/(S ^* /32)≤30,

1≤(Al/27)/(N ^* /14)≤10,

N ^* =N-0.8×(Ti-0.8×(48/32)×S)×(14/48),

The steel sheet contains (Mn, Cu)S precipitates and AlN precipitates with an average particle size of 0.2 μm or less.

5. The cold-rolled steel sheet according to any one of claims 1 to 4, wherein the content of C, Ti, Nb, N and S satisfies the following relationship:

0.8≤(Ti ^* /48+Nb/93)/(C/12)≤5.0,

Ti ^* =Ti-0.8×((48/14×N+(48/32)×S).

6. The cold rolled steel sheet according to claim 5, characterized in that the C content is less than or equal to 0.005%.

7. The cold-rolled steel sheet according to any one of claims 1 to 4, characterized in that the solute carbon (Cs) determined by C and Ti content is 5-30, Cs=(C-Nb×12/93- Ti ^* ×12/48)×10000, where Ti ^* =Ti-0.8×((48/14)×N+(48/32)×S), provided that Ti ^* is defined as 0 when Ti ^* is less than 0.

8. The cold-rolled steel sheet according to claim 7, characterized in that the C content is 0.001-0.01%.

9. The cold-rolled steel sheet according to any one of claims 1 to 4, characterized in that the cold-rolled steel sheet satisfies a yield strength ratio (yield strength/tensile strength) greater than or equal to 0.58.

10. The cold-rolled steel sheet according to any one of claims 1 to 4, characterized in that the amount of the precipitate is greater than or equal to 1×10 ⁶ /mm ² .

11. The cold-rolled steel sheet according to any one of claims 1 to 4, characterized in that the P content is less than or equal to 0.015%.

12. The cold-rolled steel sheet according to any one of claims 1 to 4, characterized in that the P content is 0.03-0.2%.

13. The cold-rolled steel sheet according to any one of claims 1 to 4, wherein the composition further comprises one or two groups selected from 0.1-0.8% Si and 0.2-1.2% Cr point.

14. The cold-rolled steel sheet according to any one of claims 1 to 4, characterized in that said composition further comprises 0.01-0.2% of Mo.

15. The cold-rolled steel sheet according to claim 13, wherein said composition further comprises 0.01-0.2% of Mo.

16. The cold-rolled steel sheet according to claim 2 or 4, characterized in that the total amount of Mn and Cu is 0.05-0.4%.

17. The cold-rolled steel sheet according to claim 2 or 4, characterized in that the Mn content is 0.01-0.12%.

18. The cold-rolled steel sheet according to claim 2 or 4, characterized in that the value of (Mn/55+Cu/63.5)/(S ^* /32) is 1-9.

19. The cold-rolled steel sheet according to claim 3 or 4, characterized in that the value of (Al/27)/(N ^* /14) is 1-6.

20. A method of manufacturing a cold-rolled steel sheet with excellent formability and high yield ratio, the method comprising the steps of:

Reheating a steel slab to a temperature greater than or equal to 1100° C., said steel slab having a composition comprising, by weight, less than or equal to 0.01% C, 0.01-0.2% Cu, 0.005-0.08% S, Al less than or equal to 0.1%, N less than or equal to 0.004%, P less than or equal to 0.2%, B 0.0001-0.002%, Nb 0.002-0.04%, Ti 0.005-0.15%, and the balance Fe and other unavoidable impurities, the composition satisfies the following relationship: 1≤(Cu/63.5)/(S ^* /32)≤30, S ^* =S-0.8×(Ti-0.8×(48/14) ×N)×(32/48);

hot-rolling the reheated steel slab at a finish rolling temperature higher than or equal to the _Ar3 transformation point to obtain a hot-rolled steel plate;

cooling the hot-rolled steel sheet at a rate greater than or equal to 300°C/min;

coiling the cooled steel sheet at a temperature lower than or equal to 700°C;

cold rolling the coiled steel sheet;

Continuous annealing is performed on the cold-rolled steel sheet, the cold-rolled steel sheet including CuS precipitates with an average particle size of 0.2 μm or less.

21. The method according to claim 20, wherein the composition further comprises 0.01-0.3% Mn, and satisfies the following relationship: 1≤(Mn/55+Cu/63.5)/(S ^* /32) ≤30, the steel plate contains (Mn, Cu)S precipitates with an average particle size less than or equal to 0.2 μm.

22. The method according to claim 20, characterized in that the N content is 0.004-0.02%, and the composition satisfies the following relationship:

1≤(Al/27)/(N ^* /14)≤10,

N ^* =N-0.8×(Ti-0.8×(48/32)×S)×(14/48),

23. The method according to claim 20, wherein the composition further comprises 0.01-0.3% of Mn, and the N content is 0.004-0.02%, and the composition satisfies the following relational formula:

1≤(Mn/55+Cu/63.5)/(S ^* /32)≤30,

1≤(Al/27)/(N ^* /14)≤10,

N ^* =N-0.8×(Ti-0.8×(48/32)×S)×(14/48),

24. The method according to any one of claims 20 to 23, characterized in that the content of C, Ti, Nb, N and S satisfies the following relationship:

0.8≤(Ti ^* /48+(Nb/93)/(C/12)≤5.0,

Ti ^* =Ti-0.8×((48/14)×N+(48/32)×S).

25. The method of claim 24, wherein the C content is less than or equal to 0.005%.

26. The method according to any one of claims 20 to 23, characterized in that the solute carbon (Cs) determined by C and Ti content is 5-30, Cs=(C-Nb×12/93-Ti ^* ×12/48)×10000, where Ti ^* =Ti−0.8×((48/14)×N+(48/32)×S), provided that Ti ^* is defined as 0 when Ti ^* is less than 0.

27. The method according to claim 26, characterized in that the C content is 0.001-0.01%.

28. The method according to any one of claims 20 to 23, characterized in that the cold-rolled steel sheet satisfies a yield ratio (yield strength/tensile strength) greater than or equal to 0.58.

29. A method as claimed in any one of claims 20 to 23, characterized in that the amount of precipitate is greater than or equal to 1 x ¹⁰⁶ / ^mm2 .

30. A method as claimed in any one of claims 20 to 23, characterized in that the P content is less than or equal to 0.015%.

31. A method as claimed in any one of claims 20 to 23, characterized in that the P content is 0.03-0.2%.

32. The method according to any one of claims 20 to 23, characterized in that the composition further comprises one or two components selected from 0.1-0.8% Si and 0.2-1.2% Cr.

33. A method as claimed in any one of claims 20 to 23, characterized in that the composition further comprises 0.01-0.2% Mo.

34. The method of claim 32, wherein said composition further comprises 0.01-0.2% Mo.

35. The method according to claim 21 or 23, characterized in that the total amount of Mn and Cu is 0.08-0.4%.

36. The method according to claim 21 or 23, characterized in that the Mn content is 0.01-0.12%.

37. The method according to claim 21 or 23, characterized in that the value of (Mn/55+Cu/63.5)/(S ^* /32) is 1-9.

38. The method according to claim 22 or 23, characterized in that the value (Al/27)/(N ^* /14) is 1-6.