CN103031493A - 650MPa-level low-Si Cr-containing hot-rolled dual phase steel plate and manufacturing method thereof - Google Patents

Abstract

The invention discloses a 650MPa-level low-Si Cr-containing hot-rolled dual phase steel plate and a manufacturing method thereof. The 650MPa-level low-Si Cr-containing hot-rolled dual phase steel plate comprises the following chemical compositions in pcentage by weight: 0.06-0.15% of C, 0.05-0.5% of Si, 1.0-1.8% of Mn, 0.01-0.08% of Als, 0.3-1.5% of Cr, less than 0.02% of P, less than 0.005% of S and the balance of Fe and inevitable impurities, the steel comprises 80-90% of ferrite and 10-20% of martensite, the elongation percentage is higher than 25%, and the n value is greater than 0.19. The process comprises the following steps of: heating a plate blank at 1200+/-20 DEG C and performing heat preservation for 1-3 hours; performing two-stage controlled rolling, wherein the initial rolling temperature in a recrystallization zone is greater than 1050 DEG C, the initial rolling temperature in a non-recrystallization zone is 900-940 DEG C, and the finish rolling temperature is 820-880 DEG C; after the finish rolling, performing laminar cooling by utilizing successive layers, wherein the cooling rate is 20-40 DEG C/s, the coiling temperature is 530-600 DEG C, and the finished product thickness is 3-10mm. The 650MPa-level low-Si Cr-containing hot-rolled dual phase steel plate has reduced Si, is low in cost and simplified in production process and has excellent mechanical property and forming property.

Description

The low Si of a kind of 650MPa level contains Cr hot rolling biphase plate and manufacture method thereof

Technical field

The invention belongs to technical field of steel rolling, specially refer to the low Si that a kind of tensile strength reaches the 650MPa level and contain Cr hot rolling biphase plate and manufacture method thereof.Dual phase sheet steel of the present invention mainly is applicable to automotive field.

Background technology

In recent years, along with developing rapidly of automotive industry, optimize the advanced manufacturing technology of automobile component and alleviate texture quality and become the focus that each side pays close attention to, particularly owing to fuel and material cost reason and environmental regulation to the strict restriction of motor vehicle emission, the vehicle structure lightweight is seemed becomes more and more important.According to the study, car weight whenever alleviates 10%, can save fuel oil 3%～7%.

The topmost method of lightweight that realizes vehicle structure is to adopt light material.In the automobile making in early days, stamping parts of automobile adopts common soft steel more, and in order to alleviate car weight, people have developed Hi-Stren steel (HSLA), but this material plasticity is low, has caused the impact briquetting difficulty.Compared with common Hi-Stren steel with the dual phase steel that hard phase martensite forms by soft phase ferrite, have more superior mechanical property and forming property, thereby can be widely used in automotive industry.

Each steel mill and research institution have developed a plurality of other hot rolling biphase plates of level at present, but still there is certain defect in it, mainly can be divided into two aspects: the one, contain higher Si element or precious alloy element (such as Mo) in the composition, make steel the problems such as surface quality is relatively poor, composition is higher occur respectively, be difficult to squeeze into the market; Another large defective is that cooling path is complicated after the finish to gauge, causes the performance inconsistency of steel plate larger, and for Si-Mn is hot-rolled dual-phase steel, also exists coiling temperature lower, to problems such as having relatively high expectations of taking-up equipment.These all produce considerable influence to the large-scale production and application of hot rolling biphase plate.

Publication number is to have proposed hot rolling biphase plate and the manufacture method thereof that a kind of tensile strength is the 650MPa level in the patent of CN101717886A, although its cost is lower, it is also relatively simple to roll rear process for cooling, but Si content is higher in its composition, this will cause steel plate surface quality problems to occur, while its coiling temperature lower (being lower than 300 ℃), this requires again taking-up equipment to have the stronger ability of batching, and the ability of batching of traditional hot tandem rolling unit does not reach requirement.Publication number is Similar Problems also to occur in the patent of CN1807670A, CN1807669A and CN101880825A.Publication number is that the producer rule of the hot rolling biphase plate mentioned in the patent of CN1793400A is to adopt the segmentation process for cooling after finish to gauge, and this complicated difficult that will cause process for cooling is with control, thereby has influence on the homogeneity of the final tissue of steel plate and performance.And publication number be the production method of the hot-rolled dual-phase steel mentioned in the patent of CN1970813A except after rolling, adopting the segmentation process for cooling, the Si content in its composition is also higher.

In view of the above problems, cost of development is low, and adopts the hot rolling biphase plate of simple cooling path and the production of middle warm rolling access method to become current trend.

Summary of the invention

For the Problems Existing that hot rolling biphase plate is produced, the low Si of the 650MPa level of the invention provides a kind of low cost, easily produce, over-all properties is good contains Cr hot rolling biphase plate and manufacture method thereof.

The present invention is that the hot-rolled dual-phase steel composition is as the basis take C-Si-Mn, when reducing Si content, add a certain amount of Cr element, and after rolling, adopt simple cooling path, obtain intensity rank and reach 650MPa, microstructure is ferrite and martensitic dual phase sheet steel.

Chemical ingredients of the present invention is, press mass percent: 0.06%～0.15%C, 0.05%～0.5%Si, 1.0%～1.8%Mn, 0.01%～0.08%Als, 0.3%～1.5%Cr, and limiting P＜0.02%, S＜0.005%, surplus is Fe and inevitable impurity.

Ferrite volume fraction is 80%～90% in the final tissue, and Martensite Volume Fraction is 10%～20%, and the unit elongation of steel plate is higher than 25%, n value greater than 0.19.

The manufacture method that the low Si of 650MPa level of the present invention contains the Cr hot rolling biphase plate may further comprise the steps:

(1) heating process: with heating of plate blank to 1200 ± 20 ℃, soaking time 1-3 hour;

(2) rolling technology: adopt two-stage control rolling, recrystallization zone draft＞60% non-recrystallization district draft＞70%; The recrystallization zone start rolling temperature is greater than 1050 ℃, and non-recrystallization district start rolling temperature is 900～940 ℃, and finishing temperature is 820～880 ℃.

(3) process for cooling: adopt continuous laminar flow cooling after the finish to gauge, rate of cooling is 20～40 ℃/s, and coiling temperature is 530～600 ℃, and finished product thickness is 3～10mm.

Steel plate composition Main Function of the present invention is:

C: mainly be the intensity that forms the martensite of desired number and guarantee steel.Consider weldability etc., require restriction C content below 0.2%, the too low duplex structure that then is difficult to obtain of C, optimized scope is 0.06%～0.15%.

Si: can enlarge the α of Fe-C phasor+γ district, be conducive to keep stability and the circulation ratio of the performances such as dual phase steel intensity, ductility.Si also accelerates carbon to austenitic segregation, and the solid solution carbon in the ferrite is had " removing " and " purification " effect.Yet the Si too high levels makes troubles for hot rolling surface quality and coating.One of principal character of the present invention just is significantly to reduce Si content, thereby improves the surface quality of steel plate, and therefore optimum one-tenth is divided into 0.05%～0.5%.

Mn: be typical austenite stabilizer element, significantly improve the hardening capacity of steel, and play the effect of solution strengthening and refinement ferrite crystal grain, can significantly postpone perlitic transformation and bainite transformation.But the Mn too high levels when postponing perlitic transformation, is also postponed ferritic separating out, and " velocity window " diminished, and Bainite Region moves to right, and makes steel become large to the susceptibility of processing condition.Therefore, selected Mn content is 1.0%～1.80%.

Al: when the critical zone is heated the impact of Austenite Morphology similar to Si, namely Al also impels martensite to be fibrous form, Al can also form AlN and separate out, and plays certain Grain refinement.The optimized scope of Al is 0.01%～0.08%.

P: can make the form generation noticeable change on martensite island, it is little that martensite island size is attenuated, and evenly distribute.Another impact of P is the formation temperature that improves the α phase, enlarges the temperature range that forms the α phase.Add but P is superfluous, then processibility worsens, and therefore is defined as 0.02%. with on it

S: be mingled with by forming the MnS sulfides, become the starting point of crackle and processing characteristics is worsened, so content is more few better, will be defined as 0.005% on it.

Cr: be middle carbide, significantly improve the hardening capacity of steel, can not only strongly postpone perlitic transformation and bainite transformation, and enlarged " batching window ".Though Cr is weak solution strengthening element, can increase and austeniticly cross cold energy power, thereby thinning microstructure, effect is strengthened.Cr can promote that carbon spreads to austenite in addition, and can reduce ferritic yield strength, more is conducive to obtain the dual phase steel of low yield strength.The optimized scope of Cr is 0.3%～1.5%.

Among the present invention, in order to reduce Si to the impact of surface of steel plate, adopted low Si Composition Design, but Si has very large promoter action to ferrite content, reduce Si content, the deficiency that probably causes ferrite content in the final tissue of steel plate, this just needs to formulate rational rolling technology to remedy its impact.During hot rolling, carry out larger distortion in the austenite recrystallization district, thereby make austenite generation recrystallize crystal grain thinning, then obtain enough Strain Accumulation by larger distortion in the non-recrystallization district, after rolling, adopt simultaneously continuous laminar flow cooling technology that ferrite crystal grain is separated out in a large number fast, thereby ferritic content is guaranteed, and has simplified process for cooling.And if in higher temperature range, batch, then must guarantee austenitic stability, except technologic adjustment, it is necessary adding suitable austenitizing stable element, so has added the Cr element of proper content among the present invention.In a word, reasonable component design and cooperatively interacting of cooling controlling and rolling controlling process are the keys that the present invention is achieved.

650MPa level dual phase sheet steel beneficial effect of the present invention is:

Because Si content is lower in the composition of the present invention, has reduced the impact of Si on surface of steel plate, only add a certain amount of Cr element in the composition simultaneously, in order to guarantee austenitic stability, get the cost of type hot-rolled dual-phase steel with warm rolling in the tradition and compare greatly reduction; Owing to roll the continuous process for cooling of rear employing, and unconventional complicated segmentation process for cooling is simplified production process, is easy to carry out; Simultaneously, warm rolling is got in adopting after the cooling, has reduced the requirement to taking-up equipment; Roll the continuous process for cooling of rear employing and also improved on the steel plate length direction stability of tissue and performance, avoided cooling off owing to segmentation tissue and the performance inequality of the steel plate that brings; Compare with the dual phase steel of prior art and to have more superior mechanical property and forming property.

Embodiment

Inventive embodiments is as follows: will be by mass percent: 0.06%～0.15%C, 0.05%～0.5%Si, 1.0%～1.8%Mn, 0.01%～0.08%Als, 0.3%～1.5%Cr, and restriction P＜0.02%, S＜0.005%, surplus is that the thickness of Fe and inevitable impurity is that the test base of 60mm is heated to 1200 ± 20 ℃, be incubated after 2 hours and carry out the controlled rolling of two stages at Φ 500 two-roller reversible formula hot rolling units, the recrystallization zone draft is＞60%, and non-recrystallization district draft is＞70%; The recrystallization zone start rolling temperature is greater than 1050 ℃, and non-recrystallization district start rolling temperature is 900～940 ℃, and finishing temperature is 820～880 ℃.Adopt continuously cooling after the finish to gauge, rate of cooling is 20～40 ℃/s, and coiling temperature is 530～600 ℃, and finished product thickness is 3～10mm.

Below by several most preferred embodiments of the present invention technique effect of the present invention is described.The Microstructure and properties of its concrete composition, temperature schedule and steel plate sees Table 1-3.

The chemical ingredients (wt, %) of table 1 embodiment of the invention

The temperature schedule of table 2 embodiment of the invention

The tissue of table 3 embodiment of the invention and mechanical property parameters

Claims (3)

1. the low Si of 650MPa level contains the Cr hot rolling biphase plate, it is characterized in that, chemical ingredients is, press mass percent: 0.06%～0.15%C, 0.05%～0.5%Si, 1.0%～1.8%Mn, 0.01%～0.08%Als, 0.3%～1.5%Cr, and limiting P＜0.02%, S＜0.005%, surplus is Fe and inevitable impurity.

2. the low Si of a kind of 650MPa level according to claim 1 contains the Cr hot rolling biphase plate, it is characterized in that ferrite volume fraction is 80%～90% in the final tissue of steel, Martensite Volume Fraction is 10%～20%, the unit elongation of steel plate is higher than 25%, n value greater than 0.19.

3. one kind is used for the manufacture method that the low Si of a kind of 650MPa level claimed in claim 1 contains the Cr hot rolling biphase plate, it is characterized in that, adopts the slab of claim 1 composition, may further comprise the steps:

(1) heating process: with heating of plate blank to 1200 ± 20 ℃, soaking time 1-3 hour;

(2) rolling technology: adopt two-stage control rolling, the recrystallization zone draft is＞60%, and non-recrystallization district draft is＞70%; The recrystallization zone start rolling temperature is greater than 1050 ℃, and non-recrystallization district start rolling temperature is 900～940 ℃, and finishing temperature is 820～880 ℃;

(3) process for cooling: adopt continuous laminar flow cooling after the finish to gauge, rate of cooling is 20～40 ℃/s, and coiling temperature is 530～600 ℃, and finished product thickness is 3～10mm.