CN104630622A - High-strength IF steel containing rare earth and preparation method of high-strength IF steel - Google Patents

Abstract

The invention discloses high-strength IF steel containing rare earth and a preparation method of the high-strength IF steel. The IF steel comprises the following chemical components in percentage by weight: not more than 0.006% of C, no more than 0.01% of Si, 1.2-2.0% of Mn, 0.08-0.1% of P, not more than 0.003% of S, not more than 0.003% of O, not more than 0.003% of N, 0.08-0.12% of Nb, 0.02-0.04% of Al, not more than 0.002% of B, not more than 0.02% of Ce and the balance of Fe. The rare earth Ce is added on the basis of the high-strength IF steel, so that on the one hand, the strength is improved by refined crystal particles; on the other hand, relatively much Ce can be dissolved by controlling the O and S contents and selectively adding Nb and Al without Ti, so that the solid-solution rare-earth content reaches 0.0076% to remove crystal boundary segregation of P (solid-solution strengthening element), so that the problem of secondary work brittleness is solved.

Description

A kind of high-strength IF steel containing rare earth and preparation method thereof

Technical field

The present invention relates to high-strength vehicle steel, particularly relate to a kind of high-strength IF steel containing rare earth and preparation method thereof, outside the premium properties having rolled products of ordinary high-strength IF steel, also there is good anti-secondary processing brittleness, therefore have better comprehensive mechanical property and more wide application prospect.

Background technology

Automobile steel to experienced by from rimming steel to aluminium killed steel IF steel up till now, can say that automobile steel there occurs qualitative leap.IF steel is also known as the pure ferritic steel of Ultra-low carbon gap-free atom, it is be developed successfully 1949 the earliest, its ultimate principle adds the elements such as a certain amount of Ti, Nb in ultralow C, N steel, interstitial atom C, N in steel are fixed as carboritride, obtain clean ferrite, thus there is good deep drawability.

Along with people require to improve constantly to automotive performance, consideration particularly in safety, comfortable, oil consumption, this just proposes new requirement to automobile board, mainly comprise following 3 points: high strength (improving safety mark), thin rule (alleviate automobile product deadweight, save material, reduce the consumption of fuel oil, reduce costs), corrosion-resistant (process for treating surface is as galvanized sheet or Alloy Plating zine plate).The automobile board producing more high strength seems particularly important.Because the intensity of common IF steel can not meet the demands far away, therefore by adopting interpolation solution strengthening element P, Mn, Si to improve intensity, but while raising intensity, also create certain problem, first the segregation of P on crystal boundary can be aggravated because schedule of reinforcement is single, cause steel to produce fracture and secondary processing brittleness in post-production process, secondary processing brittleness is a critical defect concerning steel.Herein by the crystal grain thinning of rare earth and the enrichment on crystal boundary, be used for improving or eliminating the grain boundary segregation problem of P, thus solve the secondary processing brittleness problem of steel.Next Si adds the badly damaged quality of coating of membership, so the content of Si will strictly control.And Mn can occur excessively to analyse at surface of steel plate poly-, the oxide compound of precipitation and metallic iron form and corrode microbattery, and in addition measure does not have very large danger to the iron and steel life-span, and this problem can be solved by overlay coating.

Rare earth by the strategic element be described as in the world in new technology revolution, the growth point of hi-tech, the treasure-house of novel material.China is again the country of rare earth reserves first in the world, and how making good use of rare earth has important development strategy to China.

By adding a certain amount of rare earth secondary processing brittleness solving steel in high-strength IF steel, thus improve steel performance, the preparations and applicatio of this novel rare earth-containing high strength IF steel does not also have relevant report.

Summary of the invention

The object of the invention is to the secondary processing brittleness problem caused by P for solving existing high-strength IF steel, providing a kind of high-strength IF steel containing rare earth and preparation method thereof.

A kind of high-strength IF steel chemical component weight percentage ratio containing rare earth of the present invention is: C :≤0.006%, Si :≤0.01%, Mn:1.2% ~ 2.0%, P:0.08% ~ 0.1%, S :≤0.003%, O :≤0.003%, N :≤0.003%, Nb:0.08% ~ 1.2%, Al:0.02% ~ 0.04%, B≤0.002%, Ce :≤0.02%, all the other are Fe.

Production technique is: smelting → hot rolling → cold rolling → annealing; It is characterized in that, adopt vacuum induction furnace smelting.

Controlling Technology parameter is: heating of plate blank is to 1250 DEG C, make complete austenitizing, breaking down temperature is 1200 DEG C, and finishing temperature is 930 DEG C, slab thickness rolls 4mm by 35mmm, hot rolling draft is 85%, and be cooled to 650 DEG C to be incubated 1h and simulate curling, air cooling is to room temperature subsequently, again by 5 passage 80% cold roling reductions, outgoing gauge is 0.8mm, and annealing temperature controls at about 850 DEG C, soaking time 30min.

The invention difference from existing technology is that the present invention achieves following technique effect:

1, the present invention adopts the multiple schedule of reinforcements such as solution strengthening, refined crystalline strengthening and precipitation strength, obtains 440MPa high-strength IF steel.

2, the present invention utilizes the enrichment of rare earth on crystal boundary and Grain refinement to solve the secondary processing brittleness problem of IF steel.

3, the present invention adopts the Grain refinement of Rare-Earth Ce to make IF steel obtain good fine grained texture in conjunction with later stage hot rolling, cold-rolling treatment.

What use above Composition Design to smelt contains rare earth high-strength IF steel, through rational rolling technology and annealing schedule, can obtain intensity >=440MPa, and have the automobile board of good deep drawability and anti-secondary processing brittleness.

Below in conjunction with accompanying drawing, the invention will be further described.

Accompanying drawing explanation

Fig. 1 is the rolling technology figure that the present invention contains the high-strength IF steel of rare earth;

The micro-organization chart of Fig. 2 to be the annealing time of rare earth-containing high strength IF steel be 500 times of laser co-focusings of 50min.

Embodiment

Below in conjunction with embodiment, to above-mentioned being described in more detail with other technical characteristic and advantage of the present invention.

The determination of C content: general IF steel requires that C content is less than 0.002%.But here I selects 0.006% reason to mainly contain this 2 point.1. production tensile strength to be greater than the steel grade of 390MPa, solid solution strength means be adopted, and C be the most effective solid solution element, so suitably improve C content can improve intensity.2. there is certain C atom to be conducive to the precipitation strength of NbC and to be conducive to that { the continuing of 111} orientation recrystal grain grows up.

The determination of N content: general IF steel requires that N content is less than 0.003%, chooses N content≤0.003 according to standard.

The determination of O, S content: first the rare earth added can react with O, S, in order to the solid solution capacity improving rare earth must control O, S content.Consult reference materials when [S]=0.0018% ~ 0.0026%, in the niobium of [O]=0.0015% ~ 0.0025%, titanium micro-alloyed steel, the rare upper amount of solid solution reaches 76 × 10-6, accounts for 50% of total rare upper amount in steel.Substantially the grain boundary segregation of P, S can be eliminated when rare-earth solid solution capacity reaches 76 × 10-6.So select [O]≤0.003, [S]≤0.003.

P, Mn, Si content is determined: in general, and 340MPa level high-strength IF steel only adds P element, and 390MPa level needs compound to add P, Mn element, and 440MPa level then needs compound to add P, Mn, Si element.But because excessive Si can affect galvanizing process, so the content [Si]≤0.01 reducing Si here (so both can not affect galvanizing process, also certain solution strengthening is served), P is topmost solution strengthening element, Mn provides minimum intensity.

The Main Function of the determination of Nb content: Nb is fixation of C atom, add Nb number depend on C content in steel.When C content is less than 0.003%, the total amount of Ti and Nb is not more than 0.005%, and when C content is at 0.006%-0.01%, Nb content controls between 0.1%-0.15%.Here the content getting Nb is 0.1%.1. only select here to add Nb and do not add Ti major cause and be: first, Ti and P has the effect that identical weakening Fe Grain-boundary Junctions is made a concerted effort, and this can increase the weight of the secondary processing brittleness of P.Secondly, Nb adds the solid solution capacity that can improve rare earth (Re) element.Finally, P can be retained in solid solution state at the Nb of solid solution state, prevent the precipitation of P on crystal boundary.2. tiny NbC particle is separated out, and can improve the intensity of steel.3. the interpolation of Nb can improve the texture of steel, and anisotropy value is low, and have high r mean value, Nb segregates to crystal boundary, can prevent cold working fragility, platability and anti-grinded hardness index better.

What time the determination of Al content: Al acts on 1. Nb below also having except making oxygenant has obvious effect to fixation of C, and bad for fix N effect, and therefore adding appropriate Al has obvious effect (the energy force rate Nb that A1 and N combines is strong) to fixed nitrogen.2. Nb, Al are all conducive to improving rare upper solid solution capacity in steel.3. in coating, the anti-grinded hardness index of aluminium to coating is favourable, but coating not easily alloying and affect the welding property of coating during coating aluminium content height.Here [Al]≤0.04% is selected.

The determination of B content: B element can hinder than crystal boundary fragility, but in view of B element its add-on of side effect to r value aspect must be lacked as much as possible, when adding a small amount of B (content is not more than 0.002%), significantly can reduce the Cold Brittleness Transition Temperature of IF steel, because B element can be separated out fast at grain boundaries and strengthen crystal boundary, B also can suppress P in the segregation of grain boundaries simultaneously.Here select to add [B]≤0.02.

The establishment of Ce content: the interpolation of rare earth not only can improve intensity by crystal grain thinning, also can be eliminated by a small amount of solid solution rare earth or alleviate the segregation of P, solve the secondary processing brittleness of IF steel.By controlling oxygen, sulphur content and rare-earth solid solution capacity ratio, design [Ce]≤0.02%.

Preparation technology:

(1) smelt

Containing in the actual smelting process of rare earth high-strength IF steel, ensure that O, S content is low as far as possible, therefore generally select vacuum induction furnace, also will strictly control other element simultaneously, to ensure the pure of steel.

(2) hot rolling

Breaking down temperature is 1200 DEG C, and finishing temperature is 930 DEG C, and slab thickness rolls 4mm by 35mmm, and hot rolling draft is 85%, and be cooled to 650 DEG C to be incubated 1h and simulate curling, air cooling is to room temperature subsequently.

(3) cold rolling

Through 5 passage 80% draught after pickling, outgoing gauge is 0.8mm.Annealing temperature 850 DEG C, soaking time 30min.

Annealing process

Annealing temperature 850 DEG C, soaking time 30min.

1, prepare burden

The present invention is by adding ferrophosphorus (see table 2), ferro-niobium (see table 3), electrolytic manganese, fine aluminium, pure cerium, pure boron and obtain the chemical composition (see table 4) of embodiment on the basis of the pure iron as raw material YT01 (see table 1) of Taiyuan Iron and Steel Co..Wherein the recovery rate of manganese is 95%, and the recovery rate of cerium is 50%, and the recovery rate of boron is 95%, and the recovery rate of other element close to 100%, then takes the other reasonses such as scaling loss into consideration, smelts the actual add-on (see table 5) of 7Kg sample steel.

(1) pure iron as raw material (YT01) of Taiyuan Iron and Steel Co.

The chemical composition (%) of table 1 pure iron as raw material (YT01)

C	Si	Mn	P	S	Al	Cr	Ni	N
									0.0018	0.003	0.012	0.005	0.003	0.01	0.02	0.01	0.0036

(2) ferrophosphorus (nineteen ninety standard specimen)

The chemical composition (%) of table 2 ferrophosphorus

C	Si	Mn	P	S
					0.224	1.87	0.47	17.9	0.0681

(3) ferro-niobium

The chemical composition (%) of table 3 ferro-niobium

Nb	Ta	C	Si	Mn	P	S	Al
								78	0.3	0.03	1.0	0.8	0.04	0.03	3.8

(4) electrolytic manganese (99.9%)

(5) fine aluminium (99.99%)

(6) pure cerium (99.99%)

(7) pure boron (99.9%)

The chemical composition (%) of table 4 embodiment

C	Si	Mn	P	S	O	N	Nb	Al	B	Ce
											0.004	0.01	1.73	0.09	0.002	0.002	0.003	0.11	0.035	0.001	0.019

The actual add-on of table 5 embodiment

Pure iron

Ferrophosphorus

Electrolytic manganese

Ferro-niobium

Fine aluminium

Pure cerium

Pure boron

6790g

37.1g

124g

9g

2g

2.8g

0.1g

The different annealing times of table 6 rare earth-containing high strength of the present invention IF steel are on the impact of steel mechanical property.Can find to select the annealing time of 50min can obtain better mechanical property.

Table 6 is with the impact of annealing time on steel mechanical property

The table 7 rare earth-containing high strength IF steel shock test of rushing agar diffusion method and carrying out.Test temperature is respectively-20 DEG C ,-40 DEG C ,-60 DEG C, with four groups of samples at each temperature, there is top temperature that more than 2 or 2 (>=50%) break for brittle transition temperature.Do not produce according to test-results more than-60 DEG C and break, namely secondary processing brittleness transition temperature <-60 DEG C, meets actual requirement completely.

The shock test record of table 7 hot-rolled sheet

The present invention is compared with similar steel grade, and O, S content controls lower, goes titanium to add niobium, makes content of niobium reach 0.11%, the Rare-Earth Ce then by with the addition of 0.019%, make it have anti-secondary processing brittleness performance more better than similar steel grade.

Above-described embodiment is only be described the preferred embodiment of the present invention; not scope of the present invention is limited; under not departing from the present invention and designing the prerequisite of spirit; the various distortion that those of ordinary skill in the art make technical scheme of the present invention and improvement, all should fall in protection domain that claims of the present invention determines.

Claims (2)

1. the high-strength IF steel containing rare earth, it is characterized in that, chemical component weight percentage ratio is: C :≤0.006%, Si :≤0.01%, Mn:1.2%-2.0%, P:0.08%-0.1%, S :≤0.003%, O :≤0.003%, N :≤0.003%, Nb:0.08%-1.2%, Al:0.02%-0.04%, B≤0.002%, Ce :≤0.02%, all the other are Fe.

2. prepare a method for the high-strength IF steel containing rare earth as claimed in claim 1, comprising: smelting → hot rolling → cold rolling → annealing; It is characterized in that, adopt vacuum induction furnace smelting, Controlling Technology parameter is: heating of plate blank is to 1250 DEG C, make complete austenitizing, breaking down temperature is 1200 DEG C, and finishing temperature is 930 DEG C, and slab thickness rolls 4mm by 35mm, hot rolling draft is 85%, being cooled to 650 DEG C to be incubated 1h simulates curling, and through 5 passage 80% draught after pickling, outgoing gauge is 0.8mm, annealing temperature 850 DEG C, soaking time 30min.