阅读说明：本技术 抗拉强度1700MPa级热成形钢带及其生产方法 (Hot-formed steel strip with tensile strength of 1700MPa and production method thereof ) 是由 冯晓勇 刘靖宝 刘丽萍 李梦龙 马光宗 毛文文 王朝 石晓伟 史文礼 于 2019-08-30 设计创作，主要内容包括：本发明公开了一种抗拉强度1700MPa级热成形钢带及其生产方法,其成分的质量百分含量为：C 0.25%～0.30%,Mn 1.30%～1.50%,Si 0.20%～0.30%,P≤0.02%,S≤0.006%,Als 0.02%～0.06%,Cr 0.10%～0.20%,Ti 0.03%～0.05%,B 0.002%～0.003%,N≤0.005%,余量为Fe及不可避免的残余元素。本钢带通过对合金元素的优化,不需加入成本较高的Mo、Nb、V元素,并且降低Si、Al的加入量,保证材料具有良好的淬透性,热处理后依然可以获得足够的抗拉强度。本方法通过对成分和工艺进行优化,解决了铸坯元素偏析严重、钢板表面质量、尺寸精度差等问题；所得钢带具有良好的性能均匀性,保证了后期加工的成材率。本方法生产的热轧产品表面质量好、组织性能均匀性稳定、尺寸精度高。(The invention discloses a hot-formed steel strip with 1700 MPa-level tensile strength and a production method thereof, wherein the hot-formed steel strip comprises the following components in percentage by mass: 0.25 to 0.30 percent of C, 1.30 to 1.50 percent of Mn, 0.20 to 0.30 percent of Si, less than or equal to 0.02 percent of P, less than or equal to 0.006 percent of S, 0.02 to 0.06 percent of Als, 0.10 to 0.20 percent of Cr, 0.03 to 0.05 percent of Ti, 0.002 to 0.003 percent of B, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable residual elements. The steel strip does not need to add Mo, Nb and V elements with higher cost through optimizing the alloy elements, reduces the addition amount of Si and Al, ensures that the material has good hardenability, and can still obtain enough tensile strength after heat treatment. The method optimizes the components and the process, and solves the problems of serious casting blank element segregation, poor steel plate surface quality, poor size precision and the like; the obtained steel belt has good performance uniformity, and the yield of post processing is ensured. The hot rolled product produced by the method has good surface quality, stable structural property uniformity and high dimensional precision.)

1. A hot-formed steel strip with tensile strength of 1700MPa is characterized by comprising the following components in percentage by mass: 0.25 to 0.30 percent of C, 1.30 to 1.50 percent of Mn, 0.20 to 0.30 percent of Si, less than or equal to 0.02 percent of P, less than or equal to 0.006 percent of S, 0.02 to 0.06 percent of Als, 0.10 to 0.20 percent of Cr, 0.03 to 0.05 percent of Ti, 0.002 to 0.003 percent of B, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable residual elements.

2. A hot-formed steel strip having a tensile strength of 1700MPa grade according to claim 1 characterised in that: the microstructure of the steel strip is ferrite and pearlite, the thickness of a finished product is 1.5-8.0 mm, and the microstructure of the steel strip after hot forming is martensite.

3. A production method of a hot-formed steel strip with 1700 MPa-level tensile strength is characterized by comprising the following steps: the method comprises the steps of heating, rolling, cooling and coiling the plate blank.

4. A method of producing hot-formed steel strip with a tensile strength of 1700MPa grade according to claim 2, characterised in that: in the rolling procedure, the inlet temperature of finish rolling is 1020-1080 ℃, and the finishing temperature is 840-900 ℃.

5. The method of producing a hot formed steel strip having a tensile strength of 1700MPa grade according to claim 2 wherein the cooling step is: the front section cooling rate is controlled to be less than 40 ℃/s, and the rear section cooling rate is controlled to be less than 20 ℃/s.

6. The method for producing the hot-formed steel strip with the tensile strength of 1700MPa according to claim 3, 4 or 5, wherein the coiling process is carried out at the coiling temperature of 550-650 ℃ and the coiling tension of 38-45N/mm ².

Technical Field

The invention relates to hot stamping forming steel, in particular to hot stamping steel strip with 1700 MPa-level tensile strength and a production method thereof.

Background

At present, hot stamping formed steel is generally applied to the production of components such as automobile A columns, B columns, bumpers, roof frames, underbody frames, door impact bars and the like. The forming process of the hot stamping formed steel is that a plate is heated to a complete austenitizing state, is quickly transferred to a die with a uniform cooling system for high-speed stamping forming, and is simultaneously subjected to cooling quenching treatment to obtain an ultrahigh-strength steel part with a uniform martensite structure; the method has the advantages that the formability of the high-temperature steel is good, complex components can be formed by stamping, the influence of springback is eliminated, the precision of parts is high, and the quality is good.

Along with the continuous promotion of the requirements on the light weight and the safety of the automobile, the requirements on the anti-collision beam for the automobile are higher and higher, the steel strip is required to have enough strength after heat treatment, and meanwhile, the processing and forming characteristics of the steel strip also require the steel strip to have good performance uniformity before heat treatment, so that the yield loss in the processing link is avoided.

Disclosure of Invention

The invention aims to solve the technical problem of providing a hot-formed steel strip with 1700 MPa-level tensile strength, low cost and uniform mechanical property; the invention also provides a production method of the hot-formed steel strip with the tensile strength of 1700 MPa.

In order to solve the technical problems, the invention comprises the following components in percentage by mass: 0.25 to 0.30 percent of C, 1.30 to 1.50 percent of Mn, 0.20 to 0.30 percent of Si, less than or equal to 0.02 percent of P, less than or equal to 0.006 percent of S, 0.02 to 0.06 percent of Als, 0.10 to 0.20 percent of Cr, 0.03 to 0.05 percent of Ti, 0.002 to 0.003 percent of B, less than or equal to 0.005 percent of N, and the balance of Fe and inevitable residual elements.

The microstructure of the steel strip is ferrite and pearlite, the thickness of a finished product is 1.5-8.0 mm, and the microstructure of the hot-formed steel strip is martensite.

The method comprises the working procedures of heating, rolling, cooling and coiling the plate blank; the components and the mass percentage of the slab are as described above.

In the rolling procedure of the method, the inlet temperature of finish rolling is 1020-1080 ℃, and the finishing temperature is 840-900 ℃.

The cooling process of the method comprises the following steps: the front section cooling rate is controlled to be less than 40 ℃/s, and the rear section cooling rate is controlled to be less than 20 ℃/s.

The method comprises the coiling process, wherein the coiling temperature is 550-650 ℃, and the coiling tension is ² of 38-45N/mm.

The hot formed steel substrate was processed into a standard tensile specimen, and heat treatment (hot stamping) was performed: austenitizing at 850-930 ℃, keeping the temperature for 3-20 min, and then water quenching to room temperature; the tempering temperature is 120-250 ℃, and the heat preservation time is 10-30 minutes. And (3) performing performance test on the heat-treated sample, wherein the tensile strength of the quenched sample is 1.7-2.0 GPa, and the structure of the quenched sample is full martensite. As can be seen, the ultra-high strength of the hot forming steel strip which is not less than 1700MPa can be obtained after the hot forming process.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: according to the invention, through optimization of alloy elements, Mo, Nb and V with higher cost are not required to be added, the addition amount of Si and Al is reduced, the material is ensured to have good hardenability, and sufficient tensile strength can be obtained after heat treatment.

By optimizing the components and the process, the method solves the problems of serious casting blank element segregation, poor surface quality and dimensional accuracy of the steel plate and the like; the obtained steel belt has good performance uniformity, and the yield of post processing is ensured. The hot-rolled product produced by the method has good surface quality, stable uniformity of structure performance and high dimensional precision, and has important significance for realizing light weight and safety of automobiles.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a photograph of a hot rolled structure of a hot formed steel substrate according to the present invention;

FIG. 2 is a photograph of the structure of a hot formed steel strip after heat treatment according to the present invention.

Detailed Description

The hot-formed steel strip with the tensile strength of 1700MPa and the production method thereof comprise the working procedures of molten iron pretreatment, converter smelting, LF refining, slab continuous casting, slab heating, rolling, cooling and coiling; the processes of the respective steps are as follows.

(1) Pretreating molten iron: after the magnesium powder is sprayed into the ladle, the slag is fished out by a slag fishing device, the surface layer of the molten iron has no slag, and S of the molten iron entering the furnace is less than or equal to 0.003 wt%.

(2) Smelting in a converter: the alkalinity of the final slag is 3.3-3.7; the control components of the end point molten steel are less than or equal to 0.010wt%, P is less than or equal to 0.012wt%, and the end point temperature is 1660-1700 ℃; the tapping time is more than or equal to 3 minutes, the slag discharge amount is strictly controlled, and the tapping is fully alloyed.

(3) LF refining: fully slagging when entering the station, heating by power transmission, alloying and adjusting components, wherein the temperature of leaving the station is 1575-1600 ℃.

(4) Slab continuous casting: the superheat degree of the molten steel of the tundish is 20-30 ℃; the tundish adopts a slag stopping wall and a slag stopping weir, the baking temperature of the tundish is more than or equal to 1100 ℃, and the baking time is more than or equal to 3 hours; the tundish uses a carbon-free magnesium refractory, an aluminum-carbon argon blowing upper nozzle, an argon blowing stopper rod and an immersion nozzle; the carbon-free low-silicon covering agent is used, the special covering slag is used for the crystallizer, the secondary cooling adopts a weak cooling mode, and the pulling speed is controlled to be 1.2-1.3 m/min.

(5) A slab heating process: a heat accumulating type stepping heating furnace is adopted, the heating temperature of a continuous casting billet is 1230-1270 ℃, the standing time is 120-180 min, and the discharging temperature is more than 1200 ℃.

(6) A rolling procedure: the inlet temperature of finish rolling is 1020-1080 ℃, and the finish rolling temperature is 840-900 ℃.

(7) A cooling process: and the cooling section after rolling adopts a slow cooling mode, the cooling speed of the front section is controlled to be less than 40 ℃/s, the cooling speed of the rear section is controlled to be less than 20 ℃/s, and the steel is cooled to the coiling temperature. The front-stage cooling is that the cooling of the strip steel starts from the initial end of a cooling area and is performed by adding and subtracting a header along the rolling direction; the back section cooling is to add or subtract headers from the tail end of the cooling area in the direction opposite to the traveling direction of the strip steel.

(8) And a coiling step, wherein the coiling temperature is 550-650 ℃, the coiling tension is 38-45N/mm ², and the hot forming steel substrate can be obtained after coiling.

(9) and (3) performance detection: sampling the obtained hot forming steel substrate for detection: taking a standard tensile sample and a hardness sample along the width direction and the length direction of the hot rolled steel strip, and carrying out performance test; the results of the comparative tests are as follows: the deviation of tensile strength is less than or equal to 60MPa, the deviation of yield strength is less than or equal to 60MPa, and the deviation of HRC hardness is between 5 and 8; the uniformity of mechanical properties is good. Therefore, the hot-formed steel substrate obtained by the method has good performance uniformity after longitudinal shearing and stripping.

(10) The hot formed steel substrate was processed into a standard tensile specimen, and heat treatment (hot stamping) was performed: austenitizing at 850-930 ℃, keeping the temperature for 3-20 min, and then water quenching to room temperature; the tempering temperature is 120-250 ℃, and the heat preservation time is 10-30 minutes. And (3) performing performance test on the heat-treated sample, wherein the tensile strength of the quenched sample is 1.7-2.0 GPa, and the structure of the quenched sample is full martensite. As can be seen, the ultra-high strength of the hot forming steel strip which is not less than 1700MPa can be obtained after the hot forming process.

The hot-rolled structure of the hot-formed steel substrate obtained by the method is shown in figure 1, and the structure is ferrite plus pearlite; the structure of the hot-formed steel substrate after heat treatment is shown in FIG. 2, and the structure is martensite.