CN102409225B - High-strength superfine grain cold rolling IF (Interstitial Free) steel and production method thereof - Google Patents
High-strength superfine grain cold rolling IF (Interstitial Free) steel and production method thereof Download PDFInfo
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Abstract
The invention discloses high-strength superfine grain cold rolling IF (Interstitial Free) steel with tensile strength being larger than or equal to 390 MPa and a production method thereof. The product has good surface quality, formability and secondary processing brittleness resistance, and can be used as a galvanized plate base material. The steel comprises the following components by weight percentage: 0.006%-0.01% of C, 0.004%-0.009% of Si, 1.1%-1.6% of Mn, 0.06% -0.1% of P, less than or equal to 0.01% of S, 0.05%-0.06% of Als, less than or equal to 0.003% of N, 0.1%-0.15% of Nb, 0.0005% -0.0015% of B and the rest Fe and inevitable impurities.
Description
Technical field
The invention belongs to automobile, household electrical appliances are used steel making field, relate to ultra-fine grained cold rolling IF steel plate and production method thereof that a kind of tensile strength is greater than 390MPa.
Background technology
IF (gap-free atom) steel plate has been widely used in automotive industry as third generation Punching Steel.Traditional high-strength IF steel belongs to Solid Solution Strengthened Steel, mainly by add the solution strengthening units such as Mn, P, Si in IF steel, usually improve intensity, simultaneously because C, N atom are completely fixed, atom very close to each other exists, be conducive to texture and first develop in annealing process, so it has again good deep drawability.High-strength IF steel has high strength and deep drawability concurrently, can be processed into the part of complicated shape and improve automobile dent resistance, alleviate vehicle weight, meet the requirement of car safety, loss of weight, energy-saving and environmental protection.
Yet the strengthening mechanism of high tensile steel plate has a lot, mainly comprises: solution strengthening; Precipitation strength; Build up (phase transformation strengthening); Refined crystalline strengthening; Working hardening.Adopt different metallurgical technologies and strengthening mechanism can obtain having the product of different tensile strength and elongation.And, when high-strength IF steel only adopts solution strengthening, owing to lacking grain-boundary strengthening, easily produce secondary processing brittleness; Meanwhile, the Si grievous injury deep drawability in solution strengthening element and the surface quality of coating, make it not be suitable for the complicated exterior panel being shaped.
Comprehensive above-mentioned consideration, the mentality of designing of the high-strength superfine crystalline cold-rolled IF steels product the present invention relates to is to utilize grain refining, precipitation strength in conjunction with original solution strengthening, to form the strengthening mechanism of steel.In this novel high-strength IF steel, carbon content will be high more a lot of than traditional high-strength IF steel, reduce the addition affect the Si of surface quality and expensive solution strengthening elements such as Mo, and add a certain amount of Nb, the carboritride Nb (C, N) the disperse that form how tiny niobium distribute, and these tiny throw outs will contribute to obtain tiny ferrite crystal grain, disperse educt by grain refining intensificatiom and Nb (C, N) obtains high strength.
In addition, cold working fragility is one of major defect of IF steel, be also high-strength IF steel the problem that must solve.Reason is that the multiplex P of high-strength cold rolling IF steel unit usually carries out solution strengthening, and after the C in IF steel, N are fixing by elements such as Ti, Nb, crystal boundary is clean, and P has the tendency that grain boundary segregation occurs, and the P content in the comparable matrix of content exceeds 10 times.There are some researches show, thereby B element can be separated out strengthening crystal boundary fast at grain boundaries, B can also suppress P in the segregation of grain boundaries simultaneously, therefore, adds a small amount of B can significantly reduce the Cold Brittleness Transition Temperature of IF steel.
Usually, the steel plate of grain refining and disperse educt strengthening, yield strength also can rise.But unique in precipitate region (PFZ) owing to comprising in tissue, the yield strength of novel high-strength Ultra-fine Grained IF steel is not only increased, can decline to some extent on the contrary.Product innovation obtains tiny ferrite crystal grain under hot-rolled condition, is conducive to obtain under cold rolling condition { the 111} texture that is conducive to deep drawability.
Patent CN1492068A has proposed ultralow carbon cold-rolled steel plate and the manufacture method thereof that a kind of tensile strength is the interpolation Nb of 340～440MPa; The crystal grain density variation (PFZ) inner and grain boundaries precipitate of utilizing patent CN1383459A and CN1780928A has designed the cold-rolled steel sheet that tensile strength is greater than 340MPa.Although above-mentioned three kinds of products all have good formability, because they are not very strict to the control of Si constituent content, therefore the surface quality of steel plate will be affected, to zincincation, bring difficulty simultaneously.In addition, although mentioned the improvement effect of B element to secondary processing brittleness in indivedual patent, in embodiment, contain the example of B seldom, illustrate that it can't well utilize this method.Process aspect, in three patents, the annealing type of cooling is not all had to particular requirement, and the present invention is in order better to control and utilize PFZ, has proposed two-stage cooling mode, has obtained good effect.
High-strength superfine crystalline cold-rolled IF steels of the present invention will have that intensity is high, yield tensile ratio is low, plasticity is good and the feature such as anti-secondary processing brittleness is superior, be applicable to the complex-shaped component such as car panel, gusset or collision bumper; Simultaneously owing to not adopting Si as strengthening element, so be suitable as the baseplate material of alloying galvanizing plate.
Summary of the invention
In order to overcome the shortcoming of above-mentioned prior art, the object of the present invention is to provide high-strength superfine crystalline cold-rolled IF steels and the production method thereof of a kind of tensile strength >=390MPa, this product has good surface quality, formability and anti-secondary processing brittleness, can be used as galvanized sheet base material and uses.
Main contents of the present invention are as follows:
The present invention to achieve these goals, utilize grain refining, precipitation strength in conjunction with original solution strengthening the strengthening mechanism as product innovation.In this novel high-strength IF steel, carbon content will be high more a lot of than traditional high-strength IF steel, reduce the addition affect the Si of surface quality and expensive solution strengthening elements such as Mo, and add a certain amount of Nb, the carboritride Nb (C, N) the disperse that form how tiny niobium distribute, and these tiny throw outs will contribute to obtain tiny ferrite crystal grain, disperse educt by grain refining intensificatiom and Nb (C, N) obtains high strength.Unique in precipitate region (PFZ) owing to comprising in tissue, the yield strength of novel high-strength Ultra-fine Grained IF steel is not only increased, can decline to some extent on the contrary.Adding of a small amount of B element will suppress the grain boundary segregation of P, improves the secondary processing brittleness of steel plate.
A kind of high-strength superfine crystalline cold-rolled IF steels, the chemical composition (% by weight) that it is characterized in that steel is C:0.006～0.01, Si:0.004～0.009, Mn:1.1～1.6, P:0.06～0.1, S :≤0.01, Als:0.05～0.06, N :≤0.003, Nb:0.1～0.15, B:0.0005～0.0015, surplus is Fe and inevitable impurity.
C:C and Nb form carbide, are for form the important element of precipitate density different zones with ferrite crystal grain inside near ferrite crystal boundary.When C contains quantity not sufficient, ferrite intracrystalline precipitate density is too low, and armor plate strength declines; During C content overproof, near crystal boundary, precipitate density raises, and steel plate ductility reduces, and easily produces punching press crackle, and shaping surplus is dwindled.Therefore, the present invention requires C content between 0.006～0.01%.
Si:Si does not form carbide in steel, with sosoloid form, be present in ferrite or austenite, the intensity and the cold deformation cementation index that by solution strengthening, improve steel, can add according to intensity rank, also reduces to a certain extent plasticity and the toughness of steel simultaneously.In addition, the equilibrium partial pressure of Si when generating oxide compound is lower than other elements, belong to oxidizable element, after annealing, with oxide form, be enriched in surface of steel plate, thereby worsen the wetting property of steel plate and the tack of zinc plated plate plated layer, the resistance to cracking line and the resistance to separability that reduce galvanneal coating, easily produce the defects such as Pinhole-shaped " plating leakage ".Therefore, along with the increase of Si content, can cause plate surface quality to decline, reduce the plasticity of steel plate simultaneously, therefore the present invention does not adopt Si as main solution strengthening element, require its content to be controlled between 0.004～0.009%.
Mn:Mn is one of main solution strengthening element of the present invention, and it is by making hot-rolled steel sheet grain refining and solution strengthening improve intensity, and does not affect the tack of coating.Mn content is low, and armor plate strength is not enough, Mn too high levels, and Sheet Forming Ability declines, so the present invention controls its content between 1.1～1.6%.
P:P is another main solution strengthening element of the present invention, but it can promote ferrite crystal grain to grow up, and makes hot-rolled sheet grain coarsening, is easy to segregation in grain boundaries simultaneously, worsen plasticity and secondary processing brittleness, so the present invention requires P content between 0.06～0.1%.
S:S exists with sulphided form in steel, is the harmful element in steel plate, is unfavorable for the plasticity of steel plate, therefore the present invention requires its content below 0.01%.
Als:Al is the deoxidant element in steel-making, and can with steel in N form AlN and separate out, alleviate the damaging effect of solid solution N.Als is not enough, and above-mentioned effect is difficult to give full play to, and Als is excessive, can affect the surface quality of steel plate.Therefore the present invention requires its content to be controlled between 0.05～0.06%.
N:N is the harmful element in steel, and too high meeting causes steel plate aging resistance variation.Therefore, the present invention requires N constituent content to be controlled at below 0.003%.
Nb:Nb is combined with C and is formed carbide, is in order to form the important element of precipitate density different zones with crystal grain inside near ferrite crystal boundary.When Nb content is low, the inner precipitate density of ferrite crystal grain is not enough, and when Nb content is high, grain boundaries precipitate density is also high, causes plasticity to decline.Therefore, the Nb content requirement in the present invention is between 0.1～0.15%.
B:B can stop growing up of when annealing ferrite crystal grain, prevents the reduction of unit elongation and r value, thereby B element also can be separated out strengthening crystal boundary fast at grain boundaries simultaneously, and inhibition P, in the segregation of grain boundaries, improves the secondary processing brittleness of steel plate.Because too high B will obviously reduce the plasticity of steel plate, therefore the present invention requires its content to be controlled between 0.0005～0.0015%.
The production method of high-strength superfine crystalline IF steel of the present invention is as follows:
According to mentioned component, smelt, continuous casting becomes slab.
Hot rolling: slab heating temperature is 1150～1250 ℃; Hot rolling start rolling temperature is 1100 ℃, and finishing temperature is 870～910 ℃; Curling temperature is 620～660 ℃.
Pickling and cold rolling: cold rolling draft is controlled between 75～85%.
Continuous annealing: heating rate is 10 ℃/s, Heating temperature is 800～840 ℃, soaking time is 120～160s, slow cooling speed is 15 ℃/s, and slow cooling temperature out is 660～700 ℃, and rapid cooling speed is 35 ℃/s, aging temp is 350 ℃, and aging time is 500～600s.Smooth: smooth draft is 0.4～1.0%.
The invention has the beneficial effects as follows:
(1) in steel plate, ferrite crystal grain is tiny, and crystal grain inside exists, and Nb (C, N) a large amount of, tiny, that disperse distributes separates out, and near crystal boundary, except indivedual larger-size precipitates, along crystal boundary, forms PFZ (without separating out district);
(2) above-mentioned tissue signature causes steel plate when tensile strength improves, and yield strength does not only increase, and can decline to some extent on the contrary, thereby make steel plate have good plasticity;
(3) adding of a small amount of B element, suppress the segregation of P at crystal boundary, improved the anti-secondary processing brittleness of steel plate;
(4) do not use Si as solution strengthening element, improved the surface quality of steel plate, can be as the base material of galvanized sheet.
Accompanying drawing explanation
The metallographic structure figure of Fig. 1 steel plate of the present invention;
Fig. 2 steel plate transmission electron microscope film of the present invention figure.
Embodiment
Below in conjunction with several specific embodiments, super high tensile cold-rolled steel plate of the present invention and manufacture method thereof are described.
Embodiment chemical composition is as shown in table 1:
Table 1 chemical composition (wt%)
| Embodiment | C | Si | Mn | P | S | Als | N | Nb | B | Fe |
| 1 | 0.0067 | 0.004 | 1.12 | 0.067 | 0.0031 | 0.058 | 0.0028 | 0.12 | 0.0009 | Surplus |
| 2 | 0.0082 | 0.008 | 1.29 | 0.069 | 0.0038 | 0.053 | 0.0026 | 0.13 | 0.0011 | Surplus |
| 3 | 0.0074 | 0.006 | 1.37 | 0.061 | 0.0025 | 0.056 | 0.0023 | 0.13 | 0.0010 | Surplus |
| 4 | 0.0080 | 0.007 | 1.19 | 0.077 | 0.0034 | 0.055 | 0.0026 | 0.12 | 0.0012 | Surplus |
| 5 | 0.0070 | 0.005 | 1.46 | 0.081 | 0.0036 | 0.053 | 0.0029 | 0.11 | 0.0009 | Surplus |
| 6 | 0.0075 | 0.009 | 1.59 | 0.092 | 0.0028 | 0.057 | 0.0027 | 0.13 | 0.0010 | Surplus |
Embodiment rolling technological parameter is as shown in table 2:
Table 2 rolling technological parameter
Embodiment connect move back and flattening technological parameter as shown in table 3:
Table 3 even moves back and flattening technological parameter
The mechanical property of embodiment product is as shown in table 4:
The mechanical property of table 4 steel plate
| Embodiment | Rp 0.2(MPa) | Rm(MPa) | A(％) | r15 | n |
| 1 | 230 | 410 | 36.5 | 1.75 | 0.27 |
| 2 | 235 | 415 | 36 | 1.7 | 0.25 |
| 3 | 245 | 425 | 36 | 1.65 | 0.26 |
| 4 | 255 | 450 | 35.5 | 1.65 | 0.24 |
| 5 | 260 | 460 | 35 | 1.6 | 0.23 |
| 6 | 270 | 465 | 34 | 1.6 | 0.23 |
Claims (3)
1. a high-strength superfine crystalline cold-rolled IF steels, it is characterized in that: the chemical composition of steel (% by weight) is C:0.006～0.0082, Si:0.004～0.009, Mn:1.1～1.6, P:0.06～0.1, S :≤0.01, Als:0.05～0.06, N :≤0.003, Nb:0.1～0.15, B:0.0005～0.0015, surplus is Fe and inevitable impurity; Described steel plate forms without separating out district PFZ along crystal boundary.
2. a production method for high-strength superfine crystalline cold-rolled IF steels according to claim 1, smelts, and continuous casting becomes hot rolling after slab, it is characterized in that:
A hot rolling: slab heating temperature is 1150～1250 ℃; Hot rolling start rolling temperature is 1100 ℃, and finishing temperature is 870～910 ℃; Curling temperature is 620～660 ℃;
B pickling and cold rolling: cold rolling draft is controlled between 75～85%;
C continuous annealing: heating rate is 10 ℃/s, Heating temperature is 800～840 ℃, soaking time is 120～160s, slow cooling speed is 15 ℃/s, and slow cooling temperature out is 660～700 ℃, and rapid cooling speed is 35 ℃/s, aging temp is 350 ℃, and aging time is 500～600s.
3. the production method of high-strength superfine crystalline cold-rolled IF steels according to claim 2, is characterized in that: smooth after continuous annealing, smooth draft is 0.4～1.0%.
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| CN102747281B (en) * | 2012-07-31 | 2014-10-29 | 首钢总公司 | Production method of batch annealing interstitial-free (IF) steel |
| CN102925796B (en) * | 2012-10-30 | 2014-07-09 | 鞍钢股份有限公司 | Non-alloyed ultra-low carbon structure cold-rolled sheet and production method thereof |
| CN104384228B (en) * | 2014-09-18 | 2016-06-22 | 北京首钢冷轧薄板有限公司 | The process control method and device thereof that produce high-strength IF steel are rolled in a kind of acid |
| CN104630622A (en) * | 2015-01-20 | 2015-05-20 | 内蒙古科技大学 | High-strength IF steel containing rare earth and preparation method of high-strength IF steel |
| CN108203789B (en) * | 2016-12-16 | 2019-11-22 | 宝钢湛江钢铁有限公司 | A kind of high-strength IF steel and its manufacturing method of fine corrosion resistance |
| CN106825100B (en) * | 2017-02-16 | 2018-11-02 | 重庆大学 | A kind of preparation method of High-strength high-plasticity IF steel |
| CN109518085B (en) * | 2018-12-10 | 2021-01-08 | 北京首钢股份有限公司 | Phosphorus-containing high-strength IF steel and method for eliminating surface pockmark defects thereof |
| CN112222189A (en) * | 2020-09-11 | 2021-01-15 | 山东钢铁集团日照有限公司 | Production method of IF cold-rolled steel strip with high surface quality and high strength |
| CN115627414B (en) * | 2022-09-23 | 2023-07-25 | 马鞍山钢铁股份有限公司 | Secondary processing brittleness resistance and excellent surface quality phosphorus-containing IF steel plate and production method thereof |
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