CN101956139B - High-strength cold-rolled steel sheet with yield strength level of 700MPa and manufacturing method thereof - Google Patents
High-strength cold-rolled steel sheet with yield strength level of 700MPa and manufacturing method thereof Download PDFInfo
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- CN101956139B CN101956139B CN 201010501953 CN201010501953A CN101956139B CN 101956139 B CN101956139 B CN 101956139B CN 201010501953 CN201010501953 CN 201010501953 CN 201010501953 A CN201010501953 A CN 201010501953A CN 101956139 B CN101956139 B CN 101956139B
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Abstract
The invention provides a high-strength cold-rolled steel sheet with the yield strength level of 700MPa and a manufacturing method thereof. The method comprises a thin stab casting and rolling flow, a cold rolling flow, an annealing flow, a finishing flow and the like. Refined molten steel comprises the following main chemical components: 0.03 to 0.07 weight percent of C, less than or equal to 0.35 weight percent of Si, 0.40 to 2.0 weight percent of Mn, less than or equal to 0.020 weight percent of P, less than or equal to 0.010 weight percent of S, 0.25 to 0.80 weight percent of Cr, 0.06 to 0.25 weight percent of Ti and the balance of Fe and inevitable residual elements. In the annealing process, the steel is annealed in a hood-type annealing furnace in the temperature range of 500 DEG C to an A1 transition point. The manufactured high-strength cold-rolled steel sheet with the yield strength level of 700MPa has the advantages of low alloy element cost, single component, the yield strength of higher than 700MPa, the elongation rate of over 5 percent, high machinability and the like.
Description
Technical field
The present invention relates to a kind of Yield strength 700 MPa grade high strength cold rolled steel plate and preparation method thereof.
Background technology
The lightweight of the vehicles such as automobile is exactly under the prerequisite of the intensity that guarantees automobile and safety performance, the kerb weight of reduce automobile, thus the dynamic property of raising automobile reduces fuel consumption, reduces exhaust pollution; Experiment showed, that car mass reduces half, fuel consumption nearly also can reduce half.
At present, general vehicle structure adopts the high-strength low-alloy steel that adds microalloy element more with cold-rolled steel sheet.The high-strength low-alloy steel of microalloying mostly is soft steel, add Nb, Ti, the microalloy elements such as V, B, these elements at high temperature are solid-solubilized in the matrix of steel at steel plate, subsequently hot rolling and cold rolled annealed in separate out with carbon, nitride Second Phase Particle form, these nano level fine particles can effectively stop grain growth or alligatoring, thereby obtain the tiny weave construction of grain-size, reach the refined crystalline strengthening effect that improves intensity, keeps good unit elongation.
Add chemical ingredients (wt%), process characteristic and finished product kind and the performance of the high-strength steel of microalloy element in table 1 prior art
Continued 1
CN101538681 method of producing high-strength steel with yield strength of 700 MPa, adopt Ti, Nb, V combined microalloying, technique is: sheet blank continuous casting, the strand charging temperature is 950～1050 ℃, Heating temperature is more than or equal to 1150 ℃, 1080～1160 ℃ of tapping temperatures, 820～880 ℃ of finishing temperatures, after the laminar flow cooling, 550～620 ℃ of coiling temperatures.The yield strength scope of the high-strength steel that this invention is produced is at 690MPa～760MPa, and production board thickness is 1.4～9.0mm.Owing to be subject to the restriction of hot rolling unit thickness aspect, the thickness of the steel plate that the employing hot rolling is produced is generally thicker, and along with the raising of armor plate strength, the thickness limit of the hot-rolled steel sheet that can supply also thickens thereupon.In order to adapt to the demand of steel plate attenuate, the high intensity cold steel rolling series of demand exploitation thinner thickness.Simultaneously, the surface quality of hot-rolled steel sheet, dimensional precision and cold-rolled steel sheet differ more, can't replace mutually, therefore do not have comparability.
Publication number CN 101376944A high-strength high-tensile ratio cold-rolled steel sheet and preparation method thereof.In the method, to comprise by weight percentage: C:0.08～0.14.%, Si:0.4～1.0%, Mn:1.2～2.0%, P :≤0.03%, S :≤0.02%, Al:0.02～0.06%, Nb:0.01～0.03%, all the other are Fe and inevitable residual element; And in mentioned component, add again 0.01～0.05%Ti, added expensive alloy element Nb among the present invention, and the compound 0.01～0.05%Ti that added, cost of alloy is high, and the steel plate yield strength rank of simultaneously this invention is the 500MPa level.
And common cold rolling high-strength steel adopts the continuous annealing furnace annealing, adopts continuous annealing to produce than being easier to, but also has following shortcoming:
1. continuous annealing furnace investment is large, annealing process is complicated, particularly needs to have the techniques such as quick cooling, and automatization and the operator of production line are required height, the technological operation difficulty.
The continuous annealing line general requirement in batches large, produce continuously, for not having continuous annealing line or be subjected to the steel grade of the restriction of continuous annealing line production dimensions, bell-type annealing can short run, many specifications, many variety production.
CN101135025 preparation method who adopts bell furnace to produce high strength cold-rolled extra-deep drawing sheet steel, this invention has added the microalloy elements such as more Ti, Nb, V, and is rolling after 1100～1250 ℃ of heating, at Ar
3The single-phase austenitic area finish to gauge of above temperature; 73% above rate under the cold rolling; Perhydro or the cover annealing of nitrogen hydrogen, temperature 690-730 ℃; Smooth after the annealing.This invention armor plate strength rank only reaches 390MPa.
For the deficiencies in the prior art, the present invention is by in the situation of adding a small amount of, single, cheap tiny alloying element Ti, by controlled rolling and cooling conditions and bell-type annealing technique, can develop a kind of Yield strength 700 MPa grade high strength cold rolled steel plate, this steel plate satisfies automobile preparation industry fully to the requirement of high-strength steel.
Summary of the invention
One of technical issues that need to address of the present invention are to provide a kind of Yield strength 700 MPa grade high strength cold rolled steel plate, and this Steel Alloy element is cheap, composition is single and yield strength surpasses 700MPa, has simultaneously good processability.
Another technical issues that need to address of the present invention are to provide the preparation method of above-mentioned Yield strength 700 MPa grade high strength cold rolled steel plate.
The technical scheme that solves above-mentioned technical problem of the present invention is as follows:
A kind of method for preparing the Yield strength 700 MPa grade high strength cold rolled steel plate comprises: adopt bar strip continuous casting and rolling flow path, mainly comprise the steps: electric furnace or converter smelting, refining, sheet blank continuous casting, continuously cast bloom soaking, soaking, hot continuous rolling, laminar flow cool off, batch, cold rolling, annealing, finishing;
Wherein, the main chemical compositions of molten steel is after the refining: C:0.03～0.07wt.%, Si :≤0.35wt.%, Mn:0.40～2.0wt.%, P :≤0.020wt.%, S≤0.010wt.%, Cr:0.25～0.80wt.%, Ti:0.06～0.25wt.%, all the other are Fe and inevitable residual element
In the described annealing process, to the temperature range of A1 transition point, described steel are annealed at 500 ℃ in bell type annealing furnace.
Preferably, in the described cold-rolling process, cold roling reduction＞20%; More preferably, described cold roling reduction is 20～40%.
Preferably, described annealing temperature is 570-650 ℃.
Preferably, the processing parameter of bar strip continuous casting and rolling flow path is: 900～1000 ℃ of strand charging temperatures, 1100～1180 ℃ of tapping temperatures, 870～930 ℃ of finishing temperatures, 500～650 ℃ of coiling temperatures; More preferably, described coiling temperature is 580～640 ℃.
Yield strength 700 MPa grade high strength cold rolled steel plate by the aforesaid method preparation provided by the present invention, its microstructure is ferrite, unit elongation is at least 5%.
Preferably, the main chemical compositions of molten steel is after the refining of described Yield strength 700 MPa grade high strength cold rolled steel plate: C:0.04～0.065wt.%, Si :≤0.20wt.%, Mn:0.55～1.3wt.%, P :≤0.020wt.%, S≤0.010wt.%, Cr:0.35～0.60wt.%, Ti:0.07～0.15wt.%.
The function analysis of each chemical ingredients of Yield strength 700 MPa grade high strength cold rolled steel plate of the present invention is as follows:
C: the scope of carbon is 0.03wt.% to 0.07wt.%, add C for strengthening armor plate strength, the content that strengthens C can increase the tensile strength of steel plate, simultaneously with steel in trace element such as the formation TiC precipitate such as Ti intensity is had reinforced effects, but when adding excessive C, the workability of steel and welding property can descend, so the C amount is less than 0.07wt.%.
Si: silicon is effectively used to deoxidation of molten steel and strengthens sosoloid, but excessive Si can reduce weldability, coating and plastic performance, therefore, but the Si of the amount of the as many as 0.35wt.% of add-on.
Mn: manganese is effectively used to strengthen sosoloid, and very important aspect increase steel strength and hot rolling workability.Yet owing to can form MnS, Mn also can hinder ductility and the workability of steel.A small amount of Mn is favourable for workability, but also can cause steel strength not enough.Therefore, can add the Mn of the amount of 0.40wt.% at least to reach required intensity.On the other hand, Mn is a kind of metallic element of costliness, and excessive Mn can reduce economical efficiency, and harmful to welding and shaping.The Mn that therefore, can add the amount of as many as 2.0wt.%.
P:P can cause the center segregation of steel.Therefore, a large amount of P can reduce weldability and formability.The P that therefore, can add the amount of as many as 0.02wt.%.
S: when when the Mn in the steel is combined, they can form non-metallic inclusion, and are large on mechanical property impact, and therefore, the add-on of S is controlled at as many as 0.01wt.%.
Cr: chromium can improve intensity and hardness and the wear resistance of steel.Chromium adds the high-temperature oxidation resistance that can significantly improve steel in the steel, significantly improves the hardening capacity of steel, improves the anti-temper resistance of steel.When Cr content was lower than 0.25wt.%, it improved the poor-performings such as intensity, and is when being higher than 0.8wt.%, unfavorable to hardening capacity, the delayed fracture of steel.Therefore, the add-on of Cr is controlled at 0.25～0.8wt.%.
Ti: titanium can postpone ferritic recrystallize, and can be combined and precipitated separating out with N with the C of steel, strengthens thus the intensity of steel plate, for obtaining desirable strength, can add the Ti of 0.06～0.25wt.%.
Steel of the present invention contain said components, and all the other components are Fe and inevitable impurity.Especially, choose wantonly and can add alloying element has the steel of good workability with improvement feature, at this, even if in the composition of this cold-rolled steel sheet, added the alloying element of not addressing in the example embodiment of the present invention, the scope of the present invention that also should not be construed as this alloy elements.
The preparation method of Yield strength 700 MPa grade high strength cold rolled steel plate of the present invention, its process characteristic is as follows:
1, rolling technology
The rolling technology flow process is: electric furnace (converter) → concise → continuous casting → cool off → batch → pickling → cold rolling → annealing → finishing directly into process furnace → tandem rolling → laminar flow.
Hot rolling technology adopts Controlled Rolling And Controlled Cooling, especially, adopt higher finishing temperature, be conducive to rolling stability in the course of hot rolling, guarantee the direct motion that good template and thickness deviation control to be conducive to follow-up cold-rolling process, adopt simultaneously more rational coiling temperature, be conducive to obtain tiny TiC precipitate particle; Select lower cold rolling draft to be conducive to reduce the cold rolling drag, reduce cold rolling cost.
2, annealing process
Coil of strip is annealed in bell type annealing furnace, and adopts the continuous annealing furnace annealing with respect to common cold rolling high-strength steel, and the continuous annealing furnace investment is large, annealing process is complicated, particularly needs to have the techniques such as quick cooling, the technological operation difficulty; Adopt simultaneously lower annealing temperature, in relatively low temperature range, carry out bell-type annealing, its tissue remains with the little tissue of part, intensity to material has contribution function, simultaneously the carbon of tiny alloying element Ti, nitride can alligatoring with the stability of proof strength, thereby save the energy and improved annealing efficiency.
These characteristics satisfy the needs of mentioned component system, and can obtain by low temperature bell-type annealing of the present invention, thereby save the energy and improved annealing efficiency.Described low-temperature annealing can make deformed grains partly be retained in the microstructure, is part recrystallized structure.Microstructure of the present invention is ferrite.
According to the present invention, by above-mentioned preparation method obtain the metallographic of 700MPa level cold-rolled steel be tiny ferrite, have the excellent formability energy, yield strength is at least 700MPa, unit elongation is at least 5%.Therefore, this steel plate that has high-intensity high added value can use under needs are resisted the situation of high impact forces.In addition, carry out bell-type annealing in relatively low temperature range, a kind of Yield strength 700 MPa grade high strength cold rolled steel plate of the present invention and cold rolling precipitation strength steel plate of the prior art have notable difference at strengthening principle.
The thin ferrite crystal grain such as axle shape such as grade that is organized as high-temperature zone formation of common cold rolling precipitation strength steel, because ferrite is formed by the high temperature recrystallize, therefore common cold rolling precipitation strength steel is main by microalloy element, can make cold-rolled steel obtain higher intensity although add microalloy element, but only depend on microalloy element produce super-high strength steel (＞700MPa), be difficult to take into account performance and cost.Especially, the strengthening effect of Ti fluctuates easily, be unfavorable for the stable of intensity, and the present invention has solved the large problem of Ti microalloyed steel performance inconsistency effectively by Controlled Rolling And Controlled Cooling and rational bell-type annealing technique.
Although the present invention has also utilized the precipitating reinforcing effect of Ti microalloy element, but the further lifting of intensity mainly relies on the more tiny ferrite crystal grain that lower annealing temperature forms, refined crystalline strengthening can improve intensity and toughness simultaneously, low-temperature annealing can make deformed grains partly be retained in the microstructure simultaneously, have part recrystallized structure in the tissue, therefore there is a large amount of dislocations, the dislocations strengthening successful in the tissue.Therefore, the main strengthening mechanism of cold-rolled steel sheet of the present invention: refined crystalline strengthening+precipitation strength+dislocations strengthening.
Therefore, no matter considering from aspects such as the consumption of strengthening mechanism, alloying element, performance index, steel of the present invention is all different with existing steel grade or have obvious advantage, can satisfy the requirement higher to material of preparation industry.
Yield strength 700 MPa grade high strength cold rolled steel plate of the present invention has the following advantages:
1, the present invention adopts single Ti micro-alloying technology, and the Ti element is abundanter with respect to other micro alloying element resources, price is lower, and product cost is low, competitive power is strong.
2, (C:0.03～0.07wt.%), carbon equivalent is lower than general cold rolling high-strength steel, adds simultaneously the welding property that the Ti microalloy element can improve steel to the invention belongs to soft steel.
3, steel plate of the present invention is conducive to reduce the cold rolling drag, reduces cold rolling cost under less cold roling reduction, bell-type annealing under the lesser temps, and production process control is simple, and yield strength has good processability simultaneously above 700MPa.
4, steel plate of the present invention has solved the Ti micro-alloying technology with the instable problem of volume intensity.
Description of drawings
Fig. 1 is the metallographic structure photo of a kind of Yield strength 700 MPa grade high strength cold rolled steel plate of the present invention.
Embodiment
The present invention will be described below to enumerate specific embodiment.It is pointed out that embodiment only for the invention will be further described, does not represent protection scope of the present invention, nonessential modification and adjustment that other people make according to the present invention still belong to protection scope of the present invention.
The chemical ingredients scope of setting according to the present invention, following embodiment is by following concrete technology flow process: mainly with chemical ingredients C, Si, Mn, S, P and Fe are raw material, carry out electric furnace or converter smelting, refining process to molten steel carry out Alloying Treatment (adding a small amount of Cr, Mn, Ti alloy), sheet blank continuous casting, strand direct heating/soaking, hot continuous rolling, roll rear laminar flow water cooling, batch, the flow process such as pickling, cold rolling, annealing, finishing is prepared from.
In the described annealing process, to the temperature range of A1 transition point, described steel are annealed at 500 ℃ in bell type annealing furnace, and the steel behind the bell-type annealing are not more than 1% finishing amount.Made to the Yield strength 700 MPa grade high strength cold rolled steel plate microstructure of stating be ferrite, unit elongation sees also metallographic structure photo shown in Figure 1 more than or equal to 5%.
Table 2 steel 1-3 of the present invention chemical ingredients
| Embodiment | C | Si | Mn | P | S | Cr | Ti |
| Embodiment 1 | 0.03 | 0.15 | 2.0 | 0.013 | 0.004 | 0.25 | 0.06 |
| Embodiment 2 | 0.07 | 0.35 | 0.40 | 0.009 | 0.002 | 0.55 | 0.08 |
| Embodiment 3 | 0.045 | 0.03 | 0.75 | 0.020 | 0.008 | 0.80 | 0.25 |
| Embodiment 4 | 0.04 | 0.15 | 1.3 | 0.010 | 0.005 | 0.6 | 0.07 |
| Embodiment 5 | 0.05 | 0.20 | 0.8 | 0.011 | 0.004 | 0.4 | 0.10 |
| Embodiment 6 | 0.065 | 0.10 | 0.55 | 0.012 | 0.003 | 0.35 | 0.15 |
The processing parameter of table 3 embodiment of the invention 1-6
The mechanical property of table 4 embodiment of the invention 1-6
As shown in table 4, the embodiment of the invention 1-6 that chemical constitution and working condition satisfy condition of the present invention obtains to be respectively the yield strength of 700MPa at least, at least 5% unit elongation, embodiments of the invention do not ftracture in BENDING PROCESS, therefore can prepare the high strength cold rolled steel plate with workability.
Each processing parameter of embodiment 4-6 integrated optimization, technology controlling and process is simple, with low cost, final resulting product performance not only satisfy the demand of intensity, the stable 720-800MPa that is controlled at of yield strength, specific elongation steadily is controlled at more than 11% simultaneously, and comparatively ideal processability is arranged in the use procedure of material.
Claims (6)
1. method for preparing the Yield strength 700 MPa grade high strength cold rolled steel plate, it is characterized in that, comprise: adopt bar strip continuous casting and rolling flow path, mainly comprise the steps: electric furnace or converter smelting, refining, sheet blank continuous casting, continuously cast bloom soaking, hot continuous rolling, laminar flow cool off, batch, cold rolling, annealing, finishing;
Wherein, the main chemical compositions of molten steel is after the refining: C:0.03～0.07wt.%, Si :≤0.35wt.%, Mn:0.40～2.0wt.%, P :≤0.020wt.%, S≤0.010wt.%, Cr:0.25～0.80wt.%, Ti:0.06～0.25wt.%, and all the other are Fe and inevitable residual element;
In the described annealing process, at 500 ℃ to A
1Described steel are annealed in bell type annealing furnace;
In the described cold-rolling process, 20%＜cold roling reduction≤40%.
2. the method for preparing the Yield strength 700 MPa grade high strength cold rolled steel plate according to claim 1 is characterized in that, described annealing temperature is 570-650 ℃.
3. each described method for preparing the Yield strength 700 MPa grade high strength cold rolled steel plate according to claim 1-2, it is characterized in that the processing parameter of described bar strip continuous casting and rolling flow path is: 900～1000 ℃ of strand charging temperatures, 1100～1180 ℃ of tapping temperatures, 870～930 ℃ of finishing temperatures, 500～650 ℃ of coiling temperatures.
4. the method for preparing the Yield strength 700 MPa grade high strength cold rolled steel plate according to claim 3 is characterized in that, 580～640 ℃ of described coiling temperatures.
5. Yield strength 700 MPa grade high strength cold rolled steel plate by each described method preparation of claim 1-4, its microstructure is ferrite, unit elongation is at least 5%.
6. Yield strength 700 MPa grade high strength cold rolled steel plate according to claim 5, it is characterized in that the main chemical compositions of molten steel is after the described refining: C:0.04～0.065wt.%, Si :≤0.20wt.%, Mn:0.55～1.3wt.%, P :≤0.020wt.%, S≤0.010wt.%, Cr:0.35～0.60wt.%, Ti:0.07～0.15wt.%.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1962099A (en) * | 2006-11-10 | 2007-05-16 | 广州珠江钢铁有限责任公司 | Method for manufacturing 700MPa high-strength weathering steel based on thin slab continuous casting and rolling flow by use of Ti microalloying process |
| CN101285156A (en) * | 2008-06-05 | 2008-10-15 | 广州珠江钢铁有限责任公司 | 700MPa grade composite strengthening bainite steel and method for preparing same |
| CN101343677A (en) * | 2008-09-01 | 2009-01-14 | 湖南华菱涟源钢铁有限公司 | Process for manufacturing low-silicon low-carbon deep punching/drawing steel |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1962099A (en) * | 2006-11-10 | 2007-05-16 | 广州珠江钢铁有限责任公司 | Method for manufacturing 700MPa high-strength weathering steel based on thin slab continuous casting and rolling flow by use of Ti microalloying process |
| CN101285156A (en) * | 2008-06-05 | 2008-10-15 | 广州珠江钢铁有限责任公司 | 700MPa grade composite strengthening bainite steel and method for preparing same |
| CN101343677A (en) * | 2008-09-01 | 2009-01-14 | 湖南华菱涟源钢铁有限公司 | Process for manufacturing low-silicon low-carbon deep punching/drawing steel |
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