阅读说明：本技术 一种1500MPa级超高强度Zn-Cr复合镀层热成型钢的生产方法 (Production method of 1500 MPa-level ultrahigh-strength Zn-Cr composite coating hot-formed steel ) 是由 冯冠文 葛锐 蔡捷 胡宽辉 黄道兵 陈寅 刘永前 于 2021-05-28 设计创作，主要内容包括：本发明公开了一种1500MPa级超高强度Zn-Cr复合镀层热成型钢的生产方法,采用中薄板坯直接轧制超高强度热成形钢,经过电镀Cr+Zn的表面复合镀层,在镀锌前电镀薄镀层Cr,利用Cr高熔点以及耐蚀耐磨性能,既可以减少热冲压过程的表面氧化提高产品耐蚀性能,又可以有效避免微裂纹扩散。本发明针对锌基镀层热成型钢存在的微裂纹问题,提供一种可以避免微裂纹的Zn-Cr复合镀层热成型钢。利用铬熔点高的特征,在热冲压期间形成Zn-Cr合金层,从而避免锌镀层在热冲压过程中出现的LME现象。(The invention discloses a production method of 1500 MPa-level ultrahigh-strength Zn-Cr composite coating hot forming steel, which is characterized in that ultrahigh-strength hot forming steel is directly rolled by adopting a medium-thin slab, a Cr + Zn surface composite coating is electroplated, a thin coating Cr is electroplated before galvanization, and the high melting point and corrosion and wear resistance of Cr are utilized, so that the surface oxidation in the hot stamping process can be reduced, the corrosion resistance of a product is improved, and the micro-crack diffusion can be effectively avoided. The invention provides Zn-Cr composite coating hot forming steel capable of avoiding microcracks, aiming at the problem of microcracks in zinc-based coating hot forming steel. By utilizing the characteristic of high melting point of chromium, a Zn-Cr alloy layer is formed during hot stamping, so that the LME phenomenon of a zinc coating in the hot stamping process is avoided.)

1. A production method of 1500 MPa-level ultrahigh-strength Zn-Cr composite coating hot-forming steel is characterized in that the main technical parameters and indexes of the production method are as follows:

1) smelting composition

2) Production process

Comprises the processes of electric furnace smelting, refining, medium and thin slab continuous casting, casting blank soaking, rolling, laminar cooling, cleaning, chromium electroplating and zinc electroplating;

the superheat degree of tundish molten steel is 15-30 ℃, the thickness of a continuously cast blank is 52-55 mm, the descaling treatment is carried out before the casting blank is fed into a furnace, the feeding temperature of the casting blank is 8500-1050 ℃, the discharging temperature is 1180-1200 ℃, the final rolling temperature in the rolling process is 820-870 ℃, the strip steel is cooled to the required coiling temperature after being finally rolled, the coiling temperature is controlled to be 670 +/-15 ℃, and the thickness of the strip steel is 0.8-2.0 mm;

the strip steel is cleaned and then is electroplated with chromium to obtain 1-2g/m²Electroplating a chromium layer; then electrogalvanizing is carried out to obtain 30-40g/m²The electrogalvanized layer;

and finally, blanking the plate coil into corresponding specifications according to the size of the automobile body part, heating the plate coil to 850-920 ℃ in a heating furnace with a nitrogen protective atmosphere, preserving heat for 3-5 min for austenitizing, then quickly placing the plate coil into a die with a cooling device for stamping and forming, wherein quenching and low-temperature tempering are simultaneously carried out in the forming process, and the quenching and cooling speed is 20-40 ℃/s, so that a lath martensite structure is obtained, and the ultrahigh-strength part is obtained.

2. The method for producing the 1500MPa grade ultra-high strength Zn-Cr composite coated hot-forming steel as claimed in claim 1, wherein: in the production process, the cooling of the strip steel after the final rolling adopts a laminar cooling mode, a water curtain cooling mode or an encryption cooling mode.

3. The method for producing the 1500MPa grade ultra-high strength Zn-Cr composite coated hot-forming steel as claimed in claim 1, wherein: the chromium electroplating process adopts trivalent chromium electroplating, and the components of the electroplating solution are aqueous solution of chromic anhydride and sulfuric acid to provide chromium ions, CrO, in the electroplating solution₃The concentration is controlled to be 180-220g/l, H₂SO₄The concentration is controlled to be 2.5-3.0g/l, the pH value is controlled to be 3.5-4.5, and the current density is 1.5-2A/dm²The temperature of the solution is 20-25 ℃.

4. The method for producing the 1500MPa grade ultra-high strength Zn-Cr composite coated hot-forming steel as claimed in claim 1, wherein: the electroplating liquid of the electrogalvanizing process comprises an aqueous solution of zinc sulfate, the concentration of the zinc sulfate is controlled at 95g/L, the pH value of the electroplating liquid is controlled at 1.2, and the temperature of the electroplating liquid is 45-55 ℃.

5. The method for producing the 1500MPa grade ultra-high strength Zn-Cr composite coated hot-forming steel as claimed in claim 1, wherein: the ultrahigh-strength part is processed into a tensile sample with a gauge length of 80mm according to the national standard, and a tensile test is carried out according to the national standard, wherein the mechanical property requirements of the product are shown in the following table:

yield strength R_p0.2MPa Tensile strength R_mMPa Elongation A_80mm％ ≥1050 ≥1500 ≥6

。

Technical Field

The invention relates to the technical field of rolling and electroplating processes, in particular to a production method of 1500 MPa-grade ultrahigh-strength Zn-Cr composite coating hot-formed steel.

Background

With the development of the automobile industry and the improvement of laws and regulations of the automobile industry by the nation, the design and manufacture of automobiles gradually develop towards the direction of energy conservation, environmental protection and safety. The design of vehicle body with light weight becomes the mainstream of automobile design at present and for a long time in the future, and the vehicle body weight is greatly reduced while the safety of vehicle body collision is not reduced. The hot forming steel can meet the requirement of automobile body design on ultrahigh strength thinning, can smoothly complete complex deformation without springback, and has high dimensional precision of parts. One of the key steps of the hot forming process is heating the plate to austenitizing, and the oxidation and decarburization phenomena are inevitably generated on the surface of the plate in the heating and stamping processes, so that the precision of parts and the service life of a die are reduced. The hot forming steel with the zinc-based coating, which can realize batch production by utilizing the existing galvanizing unit, can effectively prevent the surface oxidation of parts in the hot stamping process, and has good corrosion resistance in the subsequent use process of the parts. However, the low melting point of the zinc-based plating layer can cause surface microcracks during hot stamping, and the mechanical properties of parts can be affected. In the prior published documents, the research on the process production method of the ultrahigh strength hot forming steel can be consulted at home and abroad with corresponding documents and patents. But the production method of 1500 MPa-level hot forming steel related to the Zn-Cr composite coating is rarely reported. Therefore, the invention needs to invent a production method of 1500 MPa-level ultrahigh-strength Zn-Cr composite coating hot forming steel, and the patent fills the technical blank.

Disclosure of Invention

Based on the defects of the prior art, the technical problem to be solved by the invention is to provide a method for manufacturing steel, which is a Zn-Cr composite zinc-based coating ultrahigh-strength hot-formed automobile plate, the production method of the 1500 MPa-level ultrahigh-strength Zn-Cr composite coating hot forming steel adopts a medium-thin slab to directly roll the ultrahigh-strength hot forming steel, and a Cr + Zn electroplated surface composite coating is formed, electroplating a thin coating Cr before galvanization, utilizing the high melting point (1907 ℃) and the corrosion resistance and wear resistance of the Cr, not only reducing the surface oxidation in the hot stamping process and improving the corrosion resistance of the product, but also effectively avoiding the diffusion of microcracks, mainly being applied to structural members such as an automobile AB column and the like, directly rolling the ultrahigh-strength hot formed steel through a medium-thin slab by the technology, compared with the existing cold-rolled hot formed steel, the manufacturing process is short, and the surface quality and the thickness precision of the product can meet the quality requirements of the cold-rolled product of the same grade. Compared with the existing cold-rolled hot-formed steel with a zinc-based coating, the hot-formed steel has good LME resistance after being subjected to Zn-Cr composite plating.

In order to solve the technical problems, the invention provides a production method of 1500 MPa-level ultrahigh-strength Zn-Cr composite coating hot-formed steel, which comprises the following main technical parameters and indexes:

1) smelting composition

2) Production process

Comprises the processes of electric furnace smelting, refining, medium and thin slab continuous casting, casting blank soaking, rolling, laminar cooling, cleaning, chromium electroplating and zinc electroplating;

the superheat degree of tundish molten steel is 15-30 ℃, the thickness of a continuously cast blank is 52-55 mm, the descaling treatment is carried out before the casting blank is fed into a furnace, the feeding temperature of the casting blank is 8500-1050 ℃, the discharging temperature is 1180-1200 ℃, the final rolling temperature in the rolling process is 820-870 ℃, the strip steel is cooled to the required coiling temperature after being finally rolled, the coiling temperature is controlled to be 670 +/-15 ℃, and the thickness of the strip steel is 0.8-2.0 mm;

the strip steel is subjected to a cleaning procedure to remove surface oil stain iron powder and then is subjected to chromium electroplating in a chromium electroplating tank to obtain 1-2g/m²Electroplating a chromium layer; then electrogalvanizing is carried out through an electrogalvanizing bath to obtain 30-40g/m²The electrogalvanized layer;

and finally, blanking the plate coil into corresponding specifications according to the size of the automobile body part, heating the plate coil to 850-920 ℃ in a heating furnace with a nitrogen protective atmosphere, preserving heat for 3-5 min for austenitizing, then quickly placing the plate coil into a die with a cooling device for stamping and forming, wherein quenching and low-temperature tempering are simultaneously carried out in the forming process, and the quenching and cooling speed is 20-40 ℃/s, so that a lath martensite structure is obtained, and the ultrahigh-strength part is obtained.

Preferably, the production method of the 1500 MPa-grade ultrahigh-strength Zn-Cr composite coating hot-forming steel further comprises the following technical characteristics of part or all of the following steps:

as an improvement of the technical scheme, in the production process, the cooling of the strip steel after the final rolling adopts a laminar cooling mode, a water curtain cooling mode or an encryption cooling mode.

3. The method for producing the 1500MPa grade ultra-high strength Zn-Cr composite coated hot-forming steel as claimed in claim 1, wherein: the chromium electroplating process adopts trivalent chromium electroplating, and the components of the electroplating solution are aqueous solution of chromic anhydride and sulfuric acid to provide chromium ions, CrO, in the electroplating solution₃The concentration is controlled to be 180-220g/l, H₂SO₄The concentration is controlled to be 2.5-3.0g/l, the pH value is controlled to be 3.5-4.5, and the current density is 1.5-2A/dm²The temperature of the solution is 20-25 ℃.

As an improvement of the technical scheme, the electroplating solution of the electrogalvanizing process comprises a zinc sulfate aqueous solution, the concentration of zinc sulfate is controlled at 95g/L, the pH value of the electroplating solution is controlled at 1.2, and the temperature of the electroplating solution is 45-55 ℃.

As an improvement of the technical scheme, the ultrahigh-strength part is processed into a gauge length tensile sample (the original gauge length L) of 80mm according to the national standard₀80mm and b 20mm) and performing tensile test according to national standard, wherein the mechanical property requirements of the product are shown in the following table:

yield strength Rp0.2 MPa	Tensile strength Rm MPa	Elongation A80mm％
			≥1050	≥1500	≥6

。

Compared with the prior art, the technical scheme of the invention has the following beneficial effects: the zinc-based coating hot forming steel can effectively prevent the surface oxidation of parts in the hot stamping process. Has good corrosion resistance in the subsequent use process of the part. Due to the low melting point of the zinc-based plating, surface microcracks can result during hot stamping, which can affect the mechanical properties of the part. The invention provides Zn-Cr composite coating hot forming steel capable of avoiding microcracks, aiming at the problem of microcracks in zinc-based coating hot forming steel. By utilizing the characteristic of high melting point of chromium, a Zn-Cr alloy layer is formed during hot stamping, so that the LME phenomenon of a zinc coating in the hot stamping process is avoided.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the contents of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following detailed description is given in conjunction with the preferred embodiments.

Detailed Description

Other aspects, features and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.

Examples

Base material

The steel plate is designed by adopting MnB components: c: 0.21 to 0.25, Si: 0.26 to 0.30, Mn: 1.0 to 1.3, P: less than or equal to 0.010, S: 0.005 or less, Als: 0.015 to 0.060, Cr: 0.25 to 0.30, Ti: 0.026-0.030, B: 0.003 to 0.004, Nb: 0.026-0.030, V: 0.026-0.030, N: less than or equal to 0.005

A manufacturing method of 1500 MPa-level Zn-Cr composite coating ultrahigh-strength hot formed steel with a thin specification of 0.8-2.0 mm directly rolled by a medium-thin slab mainly comprises the steps of smelting in an electric furnace or a converter, refining, medium-thin slab continuous casting, casting blank soaking, rolling, laminar cooling, coiling, chromium electroplating and zinc electroplating, austenitizing by heating, and stamping, forming and quenching by a die.

The superheat degree of the tundish molten steel is 15-30 ℃;

the thickness of a casting blank for continuously casting the medium and thin slabs is 52-55 mm, and the drawing speed is 3.7-7.0 m/s;

descaling the casting blank continuously cast by the medium thin slab before entering the furnace;

controlling the soaking furnace to be in a weak oxidation atmosphere, wherein the residual oxygen in the furnace is 0.5-5.0%;

the charging temperature of the casting blank is 850-1050 ℃, and the discharging temperature is 1180-1200 ℃;

and the rolling pass reduction distribution in the rolling process is a first pass: 52-63%, and the second pass is: 50-60%, last pass: 10-16%; controlling the rolling speed to be 8-12 m/s;

the descaling process in the rolling process comprises high-pressure water descaling before entering a rolling mill, wherein the pressure of the descaling water is 280-420 bar; removing scale by medium-pressure water between F1 and F2, wherein the pressure of the scale removing water is 200-280 bar;

the finish rolling temperature in the rolling process is 820-870 ℃, the strip steel is cooled to the required coiling temperature after finish rolling by adopting a laminar cooling, water curtain cooling or encryption cooling mode, the coiling temperature is controlled to be 670 +/-15 ℃, the thickness of the strip steel finished product is 0.8-2.0 mm, and a supporting roller is adopted for lubrication in the rolling process;

the band steel is washed by alkali, scrubbed, degreased and rinsed, and then enters an electro-chromic plating bath, trivalent chromium is adopted for electroplating, the main components are chromic anhydride and sulfuric acid, and chromium ions, CrO, in the plating solution are provided₃The concentration is controlled to be 180-220g/l, H₂SO₄The concentration is controlled to be 2.5-3.0g/l, the pH value is controlled to be 3.5-4.5, and the current density is 1.5-2A/dm²The solution temperature is 20-25 ℃ to obtain 1-2g/m²The electroplated chromium layer. Then passing through an electrogalvanizing bath, the main component is zinc sulfate, the concentration of the zinc sulfate is controlled at 95g/L, the PH value of the plating solution is controlled at 1.2, the temperature of the plating solution is 45-55 ℃, and 30-40g/m is obtained²The electroplated zinc layer.

And (3) uncoiling and blanking a plated steel coil, then austenitizing the steel coil, keeping the austenitizing temperature at 850-920 ℃, and performing die stamping forming quenching after heat preservation for 3-5 min.

The obtained ultrahigh-strength part is processed into a gauge length tensile sample (the original gauge length L) of 80mm according to the national standard₀80mm and b 20mm) and performing tensile test according to national standard, wherein the mechanical property requirements of the product are shown in the following table:

yield strength Rp0.2 MPa	Tensile strength Rm MPa	Elongation A80mm％
			≥1050	≥1500	≥6

。

Compared with the prior art, the technical scheme of the invention has the following beneficial effects: the zinc-based coating hot forming steel can effectively prevent the surface oxidation of parts in the hot stamping process. Has good corrosion resistance in the subsequent use process of the part. Due to the low melting point of the zinc-based plating, surface microcracks can result during hot stamping, which can affect the mechanical properties of the part. The invention provides Zn-Cr composite coating hot forming steel capable of avoiding microcracks, aiming at the problem of microcracks in zinc-based coating hot forming steel. By utilizing the characteristic of high melting point of chromium, a Zn-Cr alloy layer is formed during hot stamping, so that the LME phenomenon of a zinc coating in the hot stamping process is avoided.

The raw materials listed in the invention, the upper and lower limits and interval values of the raw materials of the invention, and the upper and lower limits and interval values of the process parameters (such as temperature, time and the like) can all realize the invention, and the examples are not listed.

While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.