CN104480397A - 700MPa-grade hot-rolled automobile structure steel and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of steel and iron material engineering, relates to 700MPa-grade hot-rolled automobile structure steel and a preparation method thereof, and particularly relates to the 700MPa-grade hot-rolled automobile structure steel and the preparation method thereof. The 700MPa-grade hot-rolled automobile structure steel comprises the following chemical components in percentage by weight: 0.05%-0.1% of C, 0.30%-0.60% of Si, 0.50%-1.00% of Mn, 0.02%-0.06% of Alt, 0.60%-1.00% of Cr, no more than 0.06% of P, 0.05%-0.10% of Ti, no more than 0.005% of S, no more than 0.006% of N and the balance of Fe and inevitable impurities. On the basis of C-Si-Mn steel components, through addition of Cr, Ti and P, the contents of S and N are strictly controlled; precious micro-alloy elements Nb and V are not added and precious alloys such as Mo and Ni are not added, so that the cost is greatly reduced.

Description

A kind of 700MPa level Hot Rolling Automobile structural steel and preparation method thereof

Technical field

The invention belongs to the technical field of ferrous materials engineering, relate to a kind of high-strength vehicle steel and manufacture method thereof, be specifically related to a kind of 700MPa level Hot Rolling Automobile structural steel and preparation method thereof.

Background technology

Along with being becoming tight energy day, environmental stress increasingly sharpens, and adds constantly perfect to legislative work for protecting environment of the whole world, facilitates automotive technology development center of gravity towards energy-saving and environmental protection and the development of security aspect.Use modern technologies and method to alleviate the weight of component or car load, under the prerequisite of performances such as ensuring safety, realizing energy-saving and emission-reduction consumption reduction target by loss of weight becomes common recognition.

For a long time, many employings alloying when obtaining the steel grade of yield strength at more than 600MPa both at home and abroad, usually realizing by adding the alloying elements such as Mo, Cr, Ni, B, causing the increase of steel product cost; Meanwhile, increasing of alloying element adds steel and smelts and the difficulty of later stage recycling early stage.For these factors, have by adopting the method for adding Ti and Mo to obtain hot-rolling high-strength steel in prior art, but adding Ti and Mo must have certain proportion, the intensity of steel just can reach more than 700MPa.Adding of Mo element, the corresponding cost adding steel, and also its operational path is complicated, needs to batch after held for some time after finish to gauge, the rhythm of production that impact is on-the-spot.At present both at home and abroad high tensile steel plate all adopts the method for adding Nb, V, Ti microalloy element to produce, based on the strengthening mechanism of refined crystalline strengthening or precipitation strength; Some production costs are higher, and what have cannot meet the raising requirement that automobile component propose fatigue property.

Publication number CN101525717A discloses a kind of 700MPa grade Ti micro-alloying Ultrafine Grained Steel and production method thereof, 0.03 ~ 0.07%C, Si < 0.30%, 1.00 ~ 2.10%Mn, P≤0.02%, 0.10-0.14%Ti, S≤0.008%, thin strand continuous casting and rolling production line obtains a kind of high-strength steel of 700MPa level, this steel grade have employed the Composition Design of high manganese height titanium, the large performance of unresolved high titanium steel strength fluctuation is difficult to the problem of stability contorting, especially when titanium content is more than 0.10%, impact property and fatigue property decline more obvious, automobile component cannot be met to requirement that is high tired and high impact property.

Publication number CN 101768698 A discloses a kind of low cost yield strength 700MPa level Micro Alloying process High Strength Steel Plate, it is characterized in that: in mass containing C:0.05 ~ 0.10%; Si:0.1% ~ 0.4%; Mn:1.5 ~ 2.0%; P < 0.015%; S < 0.01%; Cr:0.3 ~ 0.8 %; Ti:0.09 ~ 0.15%; Nb:0.04 ~ 0.08%; N:< 0.005%; O:< 0.002%; All the other are iron Fe and inevitable impurity, produce the high-strength steel of more than 700MPa level, adopt the Composition Design of high manganese chromium alloying, niobium titanium compound in this patent, and its expensive alloying elements addition is comparatively large, and production cost is higher.

Publication number CN101565794A, CN200510100421.2, CN2005110047632.4, CN2005110047633.9, JP11343536 etc. all have employed the Composition Design such as Gao Meng, niobium titanium compound or v n micro alloying and niobium vanadium titanium-combined microalloying, and production cost is all higher.

Publication number is US20120247606A1, publication date is on October 4th, 2012, name is called the american documentation literature of " a kind of temperature-controlled rolling is without the steel plate of the low molybdenum low-alloy high-strength of accelerating cooling ", it discloses a kind of steel plate of low molybdenum low-alloy content, the essentially consist (in mass percentage wt%) of this steel plate is: C:0.05 ~ 0.07, Mn:1.5 ~ 1.7, Ti:0.01 ~ 0.025; Al:0.02 ~ 0.04; Nb:0.075 ~ 0.1, P≤0.01, S≤0.003, Mo:0.1 ~ 0.2, all the other are Fe and inevitable impurity.The alloying element that Mo and Nb two kinds is comparatively valuable is with the addition of in steel plate disclosed in this patent documentation.

Publication number is US20120247605A1, publication date is on October 4th, 2012, name is called the american documentation literature of " a kind of temperature-controlled rolling without accelerating cooling without molybdenum low-alloy high-strength steel plate ", it discloses a kind of Hi-Stren steel kind not containing molybdenum element.The mass percentage (wt.%) of this steel grade is: C:0.05 ~ 0.09%; Mn:1.70 ~ 1.95%; Ti:0.01 ~ 0.02%; Al:0.02-0.055%; Nb:0.075 ~ 0.1%; P≤0.015%; S≤0.003%; V:0.01 ~ 0.03%; Mo≤0.003%; All the other are Fe and other impurity inevitable.Although patent document does not add Mo element, when adding Nb element, with the addition of again V element.

Publication number is US20100212785A1, publication date is on August 26th, 2010, the american documentation literature that name is called " a kind of Hi-Stren steel and manufacture method thereof with excellent high pressure hydrogen environment degradation property ", it relates to a kind of high-strength low-alloy steel kind, the mass percentage of the chemical element of this steel grade is: C:0.10 ~ 0.20%, Si:0.10 ~ 0.40%, Mn:0.50 ~ 1.20%, Cr:0.20 ~ 0.80%, Cu:0.10 ~ 0.50%, Mo:0.10 ~ 1.00%, V:0.01 ~ 0.10%, B:0.0005 ~ 0.005%, N :≤0.01%, surplus is made up of Fe and inevitable impurity.In this patent, although do not add Nb element, on the basis adding Mo element, also added Cu, the expensive alloying elements such as V.

Consider that high-strength vehicle structural steel is to fatigue property and the higher requirement of impact property and the factor such as with low cost,

The present invention is studied chemical composition proportioning and technique, have devised a kind of 700MPa level high-strength steel and production technique thereof, the product produced is suitable for the processing and manufacturing of automobile component, particularly fatigue property and impact property is had to the parts of high request, meets the requirement of automotive light weight technology development.

Summary of the invention

The object of the invention is to provide a kind of 700MPa level Hot Rolling Automobile structural steel and preparation method thereof for high-strength vehicle structural steel to fatigue property and the higher requirement of impact property and the factor such as with low cost, the present invention is on the basis of C-Si-Mn composition of steel, by adding Cr, Ti and P, strict control S, N content, do not add Nb, the valuable microalloy element of V, also Mo is not added, the precious alloys such as Ni, significantly reduce cost, adopt cooling controlling and rolling controlling process, obtain the high-strength vehicle structural steel of more than tensile strength 700MPa level, it is finally organized as ferrite+bainite structure.This structural steel does not add the elements such as Nb, V, Mo, Ni, and saved production cost, production method is convenient operation also.Structural steel of the present invention can be widely used in the production of automobile structure and stiffener, meets the light-weighted requirement of automotive industry.

Technical scheme of the present invention is: a kind of 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.05 ~ 0.1%, Si 0.30 ~ 0.60%, Mn 0.50 ~ 1.00%, Alt 0.02 ~ 0.06%, Cr 0.60 ~ 1.00%, P≤0.06%, Ti 0.05 ~ 0.10%, S≤0.005%, N≤0.006%, surplus is Fe and inevitable impurity.

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.06 ~ 0.09%, Si 0.30 ~ 0.50%, Mn 0.60 ~ 0.9%, Alt 0.02 ~ 0.06%, Cr 0.70 ~ 0.9%, P 0.03 ~ 0.06%, Ti 0.05 ~ 0.10%, S≤0.005%, N≤0.006%, surplus is Fe and inevitable impurity.

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.08%, Si 0.34%, Mn 0.75%, Alt 0.03%, Cr 0.74%, P 0.045%, Ti 0.078%, S 0.003%, N 0.0033%, surplus is Fe and inevitable impurity.

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.058%, Si 0.35%, Mn 0.63%, Alt 0.034%, Cr 0.69%, P 0.059%, Ti 0.067%, S 0.004%, N.0.0042%, surplus is Fe and inevitable impurity.

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.066%, Si 0.38%, Mn 0.75%, Alt 0.041%, Cr 0.65%, P 0.053%, Ti 0.076%, S 0.002%, N0.0026%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.05 ~ 0.10%, P≤0.06%, Mn 0.50 ~ 1.00%, Si 0.30 ~ 0.60%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 90 ~ 250mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 90 ~ 250mm is heated to 1200 ~ 1300 DEG C by gained thickness, soaking time 1 ~ 3 hour, is then rolled;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1100 ~ 1180 DEG C, finishing temperature 1000 ~ 1100 DEG C, and finish rolling stage start rolling temperature is 980 ~ 1080 DEG C, and finishing temperature is 800 ~ 880 DEG C; Rolling cools after completing;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 650 ~ 700 DEG C with the cooling rate of 50 ~ 100 DEG C/s, air cooling 1 ~

3S, is then cooled to target coiling temperature with the cooling rate of 50 ~ 200 DEG C/s and batches;

(4) coiling technique: coiling temperature is 250 ~ 450 DEG C.

The coiling temperature of described coiling technique is 350 ~ 450 DEG C.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises hot metal pretreatment; Converter smelting; LF process; Continuous casting; Hot continuous rolling; Described hot continuous rolling process is:

(1) heating process: be that the strand of 135mm is heated to 1270 DEG C by gained thickness, soaking time 2 hours, is then rolled;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1170 DEG C, finishing temperature 1090 DEG C, and 3 passes become the intermediate blank of 32mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 880 DEG C; Rolling is carried out after completing

Cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 686 DEG C with the cooling rate of 78 DEG C/S, air cooling 3S, be then cooled to target coiling temperature with the cooling rate of 82 DEG C/S and batch;

(4) coiling technique: coiling temperature is 416 DEG C.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises hot metal pretreatment; Converter smelting; LF process; Continuous casting; Hot continuous rolling; Described hot continuous rolling process is:

(1) heating process: be that the strand of 135mm is heated to 1260 DEG C by gained thickness, soaking time 2.5 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1160 DEG C, finishing temperature 1070 DEG C, and 3 passes become the intermediate blank of 34mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 870 DEG C; Rolling is carried out after completing

Cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 673 DEG C with the cooling rate of 67 DEG C/S, air cooling 2S, be then cooled to target coiling temperature with the cooling rate of 62 DEG C/S and batch;

(4) coiling technique: coiling temperature is 352 DEG C.

Beneficial effect of the present invention is: in the present invention, each alloys producing is as follows: C: the important element improving the intensity of steel, the too low then undercapacity of C content, C content too high welding performance and forming property worsens, and therefore controls 0.05 ~ 0.10%, and preferably 0.06 ~ 0.09%.

Si: deoxidant element, simultaneously in steel, play solution strengthening effect, the too low strengthening effect of content is too weak, and content too great surface quality is restive, therefore controls 0.30 ~ 0.60%, and preferably 0.30 ~ 0.50%.

Mn: improve yield strength and hardening capacity, the too low undercapacity causing body body stability difficult to understand and steel, too high meeting makes the plasticity of steel and weldability decline, and therefore controls 0.50 ~ 1.00%, and preferably 0.60 ~ 0.90%.

S: the impurity element in steel, comparatively large to plasticity and Influence of Fatigue Properties, content is more low better.

P: solution strengthening element, adds appropriate P and can promote ferritic generation and keep intensity and moulding well balanced, therefore control≤0.06%, and preferably 0.03 ~ 0.06%.

Cr: the element improving hardening capacity, be conducive to austenitic stable, too high then ductility deteriorates, too low then hardening capacity reduces, and undercapacity, therefore controls 0.60 ~ 1.00%, and preferably 0.70 ~ 0.90%.

Alt: deoxidant element, can reduce the oxide inclusion in steel and pure steel, is conducive to the forming property improving steel plate; Too high levels will cause ductility deteriorates, therefore control 0.02 ~ 0.06%.

The 700MPa level Hot Rolling Automobile structural steel that the present invention produces, yield strength >=650MPa, tensile strength >=700MPa, unit elongation >=16%, there is higher intensity, plastotype and plasticity, the use properties such as good extensibility, weldability, clod wash, is suitable for the processing and manufacturing of the trolley parts such as automobile frame, structural part and stiffener, meets the demand for development of automotive light weight technology.Be particularly suitable for the automobile structure of requirement high strength and high fatigue property and the process for processing of stiffener.

Embodiment

Below by embodiment, the present invention will be described in detail.

Embodiment 1

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.08%, Si 0.34%, Mn 0.75%, Alt 0.03%, Cr 0.74%, P 0.045%, Ti 0.078%, S 0.003%, N 0.0033%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.08%, P 0.045%, Mn 0.75%, Si 0.34%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 135mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 135mm is heated to 1260 DEG C by gained thickness, soaking time 2 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1180 DEG C, finishing temperature 1100 DEG C, and 3 passes become the intermediate blank of 32mm, and finish rolling stage start rolling temperature is 1070 DEG C, and finishing temperature is 880 DEG C; Rolling completes laggard

Row cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 692 DEG C with the cooling rate of 79 DEG C/S, air cooling 1s, be then cooled to target coiling temperature with the cooling rate of 136 DEG C/S and batch;

(4) coiling technique: coiling temperature is 392 DEG C, gained steel plate finished product thickness 1.8mm.

The yield strength of this embodiment 1 resulting structures steel is 692MPa, and tensile strength is 758MPa, and unit elongation is 18%.

Embodiment 2

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.058%, Si 0.35%, Mn 0.63%, Alt 0.034%, Cr 0.69%, P 0.059%, Ti 0.067%, S 0.004%, N0.0042%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.058%, P 0.059%, Mn 0.63%, Si 0.35%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 135mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 135mm is heated to 1270 DEG C by gained thickness, soaking time 2 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1170 DEG C, finishing temperature 1090 DEG C, and 3 passes become the intermediate blank of 32mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 880 DEG C; Rolling is carried out after completing

Cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 686 DEG C with the cooling rate of 78 DEG C/S, air cooling 3s, be then cooled to target coiling temperature with the cooling rate of 82 DEG C/S and batch;

(4) coiling technique: coiling temperature is 416 DEG C.Gained steel plate finished product thickness 2mm.

The yield strength of this embodiment 2 resulting structures steel is 689MPa, and tensile strength is 773MPa, and unit elongation is 17%.

Embodiment 3

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.066%, Si 0.38%, Mn 0.75%, Alt 0.041%, Cr 0.65%, P 0.053%, Ti 0.076%, S 0.002%, N0.0026%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.066%, P 0.053%, Mn 0.75%, Si 0.38%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 135mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 135mm is heated to 1260 DEG C by gained thickness, soaking time 2.5 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1160 DEG C, finishing temperature 1070 DEG C, and 3 passes become the intermediate blank of 34mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 870 DEG C; Rolling completes laggard

Row cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 673 DEG C with the cooling rate of 67 DEG C/S, air cooling 2s, be then cooled to target coiling temperature with the cooling rate of 62 DEG C/S and batch;

(4) coiling technique: coiling temperature is 352 DEG C.Gained steel plate finished product thickness 4mm.

The yield strength of this embodiment 3 resulting structures steel is 672MPa, and tensile strength is 757MPa, and unit elongation is 19%.

Embodiment 4

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.073%, Si 0.48%, Mn 0.76%, Alt 0.031%, Cr 0.72%, P 0.043%, Ti 0.056%, S 0.003%, N0.0029%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.073%, P 0.043%, Mn 0.76%, Si 0.48%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 135mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 135mm is heated to 1250 DEG C by gained thickness, soaking time 2 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1160 DEG C, finishing temperature 1060 DEG C, and 3 passes become the intermediate blank of 34mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 860 DEG C; Rolling is carried out after completing

Cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 667 DEG C with the cooling rate of 61 DEG C/S, air cooling 2s, be then cooled to target coiling temperature with the cooling rate of 67 DEG C/S and batch;

(4) coiling technique: coiling temperature is 376 DEG C.Gained steel plate finished product thickness 5mm.

The yield strength of this embodiment 4 resulting structures steel is 666MPa, and tensile strength is 746MPa, and unit elongation is 20%.

Embodiment 5

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.084%, Si 0.40%, Mn 0.87%, Alt 0.043%, Cr 0.77%, P 0.036%, Ti 0.092%, S 0.001%, N0.0034%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.084%, P 0.036%, Mn 0.87%, Si 0.40%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 135mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 135mm is heated to 1250 DEG C by gained thickness, soaking time 2 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1180 DEG C, finishing temperature 1060 DEG C, and 3 passes become the intermediate blank of 38mm, and finish rolling stage start rolling temperature is 1030 DEG C, and finishing temperature is 840 DEG C; Rolling is carried out after completing

Cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 671 DEG C with the cooling rate of 58 DEG C/S, air cooling 1s, be then cooled to target coiling temperature with the cooling rate of 57 DEG C/S and batch;

(4) coiling technique: coiling temperature is 346 DEG C.Gained steel plate finished product thickness 6mm.

The yield strength of this embodiment 5 resulting structures steel is 662MPa, and tensile strength is 741MPa, and unit elongation is 18.5%.

Embodiment 6

Described 700MPa level Hot Rolling Automobile structural steel, comprise the chemical composition of following weight percent: C 0.095%, Si 0.45%, Mn 0.92%, Alt 0.028%, Cr 0.88%, P 0.052%, Ti 0.088%, S 0.001%, N0.0045%, surplus is Fe and inevitable impurity.

The preparation method of described 700MPa level Hot Rolling Automobile structural steel, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.095%, P 0.052%, Mn 0.92%, Si 0.45%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 150mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 150mm is heated to 1240 DEG C by gained thickness, soaking time 2.5 hours, then carries out

Rolling;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1130 DEG C, finishing temperature 1030 DEG C, and 3 passes become the intermediate blank of 45mm, and finish rolling stage start rolling temperature is 990 DEG C, and finishing temperature is 820 DEG C; Rolling is carried out after completing

Cooling;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 656 DEG C with the cooling rate of 52 DEG C/S, air cooling 1s, be then cooled to target coiling temperature with the cooling rate of 56 DEG C/S and batch;

(4) coiling technique: coiling temperature is 307 DEG C.Gained steel plate finished product thickness 8mm.

The yield strength of this embodiment 6 resulting structures steel is 656MPa, and tensile strength is 738MPa, and unit elongation is 17.5%.

A kind of 700MPa level Hot Rolling Automobile structural steel cost of the present invention is lower, forming property and excellent weldability, be suitable for the processing and manufacturing of automobile component, particularly fatigue property and impact property are had to the parts of high request, manufacture method of the present invention is workable, be easy to realize suitability for industrialized production, there is higher application value.

Claims (9)

1. a 700MPa level Hot Rolling Automobile structural steel, it is characterized in that, comprise the chemical composition of following weight percent: C 0.05 ~ 0.1%, Si 0.30 ~ 0.60%, Mn 0.50 ~ 1.00%, Alt 0.02 ~ 0.06%, Cr 0.60 ~ 1.00%, P≤0.06%, Ti 0.05 ~ 0.10%, S≤0.005%, N≤0.006%, surplus is Fe and inevitable impurity.

2. 700MPa level Hot Rolling Automobile structural steel according to claim 1, it is characterized in that, comprise the chemical composition of following weight percent: C 0.06 ~ 0.09%, Si 0.30 ~ 0.50%, Mn 0.60 ~ 0.9%, Alt 0.02 ~ 0.06%, Cr 0.70 ~ 0.9%, P 0.03 ~ 0.06%, Ti 0.05 ~ 0.10%, S≤0.005%, N≤0.006%, surplus is Fe and inevitable impurity.

3. 700MPa level Hot Rolling Automobile structural steel according to claim 1, it is characterized in that, comprise the chemical composition of following weight percent: C 0.08%, Si 0.34%, Mn 0.75%, Alt 0.03%, Cr 0.74%, P 0.045%, Ti 0.078%, S 0.003%, N 0.0033%, surplus is Fe and inevitable impurity.

4. 700MPa level Hot Rolling Automobile structural steel according to claim 1, it is characterized in that, comprise the chemical composition of following weight percent: C 0.058%, Si 0.35%, Mn 0.63%, Alt 0.034%, Cr 0.69%, P 0.059%, Ti 0.067%, S 0.004%, N 0.0042%, surplus is Fe and inevitable impurity.

5. 700MPa level Hot Rolling Automobile structural steel according to claim 1, it is characterized in that, comprise the chemical composition of following weight percent: C 0.066%, Si 0.38%, Mn 0.75%, Alt 0.041%, Cr 0.65%, P 0.053%, Ti 0.076%, S 0.002%, N 0.0026%, surplus is Fe and inevitable impurity.

6. a preparation method for 700MPa level Hot Rolling Automobile structural steel according to any one of claim 1 to 5, comprises the following steps: first molten iron is through KR desulfurization process; Then smelt through converter routine, the weight percent content controlling molten steel terminal C, P, Mn, Si is respectively: C 0.05 ~ 0.10%, P≤0.06%, Mn 0.50 ~ 1.00%, Si 0.30 ~ 0.60%; Carry out feeding after LF process calcium line again to carry out denaturing treatment to inclusion and control the soft blow time being not less than 10 minutes, the strand that last continuous casting becomes 90 ~ 250mm thick, strand obtains 700MPa level Hot Rolling Automobile structural steel through hot continuous rolling; Wherein said hot continuous rolling comprises following technique:

(1) heating process: be that the strand of 90 ~ 250mm is heated to 1200 ~ 1300 DEG C by gained thickness, soaking time 1 ~ 3 hour, is then rolled;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1100 ~ 1180 DEG C, finishing temperature 1000 ~ 1100 DEG C, and finish rolling stage start rolling temperature is 980 ~ 1080 DEG C, and finishing temperature is 800 ~ 880 DEG C; Rolling cools after completing;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 650 ~ 700 DEG C with the cooling rate of 50 ~ 100 DEG C/s, air cooling 1 ~ 3S, be then cooled to target coiling temperature with the cooling rate of 50 ~ 200 DEG C/s and batch;

(4) coiling technique: coiling temperature is 250 ~ 450 DEG C.

7. the preparation method of 700MPa level Hot Rolling Automobile structural steel according to claim 6, it is characterized in that, the coiling temperature of described coiling technique is 350 ~ 450 DEG C.

8. the preparation method of 700MPa level Hot Rolling Automobile structural steel according to claim 6, is characterized in that, comprise hot metal pretreatment; Converter smelting; LF process; Continuous casting; Hot continuous rolling; Described hot continuous rolling process is:

(1) heating process: be that the strand of 135mm is heated to 1270 DEG C by gained thickness, soaking time 2 hours, is then rolled;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1170 DEG C, finishing temperature 1090 DEG C, and 3 passes become the intermediate blank of 32mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 880 DEG C; Rolling cools after completing;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 686 DEG C with the cooling rate of 78 DEG C/S, air cooling 3S, be then cooled to target coiling temperature with the cooling rate of 82 DEG C/S and batch;

(4) coiling technique: coiling temperature is 416 DEG C.

9. the preparation method of 700MPa level Hot Rolling Automobile structural steel according to claim 6, is characterized in that, comprise hot metal pretreatment; Converter smelting; LF process; Continuous casting; Hot continuous rolling; Described hot continuous rolling process is:

(1) heating process: be that the strand of 135mm is heated to 1260 DEG C by gained thickness, soaking time 2.5 hours, is then rolled;

(2) rolling technology: adopt two-stage control rolling, wherein rough rolling step single pass draft >=20%, total reduction is >=70%, and finish rolling stage draft is >=75%; Rough rolling step start rolling temperature is 1160 DEG C, finishing temperature 1070 DEG C, and 3 passes become the intermediate blank of 34mm, and finish rolling stage start rolling temperature is 1060 DEG C, and finishing temperature is 870 DEG C; Rolling cools after completing;

(3) process for cooling: adopt cooling speed change cooling technique, be cooled to 673 DEG C with the cooling rate of 67 DEG C/S, air cooling 2S, be then cooled to target coiling temperature with the cooling rate of 62 DEG C/S and batch;

(4) coiling technique: coiling temperature is 352 DEG C.