阅读说明：本技术 一种低成本热镀锌相变诱导塑性钢及其制备方法 (Low-cost hot-galvanized phase-change induced plasticity steel and preparation method thereof ) 是由 李春诚 刘宏亮 王亚东 王忠东 孙忠斌 高兴昌 冯岗 于 2018-09-06 设计创作，主要内容包括：本发明涉及相变诱导塑性钢领域,具体为一种低成本热镀锌相变诱导塑性钢及其制备方法。按重量百分比含量计,控制钢板的化学成分为C：0.1～0.3％、Si：0.4～2.0％、Mn：1.0～2.5％、P≤0.02％；S≤0.03％、Al≤0.08％,余量为Fe。该方法的工艺流程如下：铁水预处理→转炉冶炼→炉外精炼→连铸→加热→控轧控冷→卷取→酸洗→连续退火→热镀锌→光整→机能检验→包装出厂。采用价格低廉的C-Mn-Si系合金成分设计,不需要加入Cr、Mo等贵重合金元素,通过采用预氧化工艺与合适露点匹配控制,提高含硅TRIP钢可镀性,并通过镀后冷却恰当控制,解决TRIP钢板表面质量和力学性能等技术问题。(The invention relates to the field of phase change induced plasticity steel, in particular to low-cost hot galvanizing phase change induced plasticity steel and a preparation method thereof. According to the weight percentage content, the chemical components of the steel plate are controlled as follows: 0.1 to 0.3%, Si: 0.4-2.0%, Mn: 1.0-2.5% and P is less than or equal to 0.02%; less than or equal to 0.03 percent of S, less than or equal to 0.08 percent of Al and the balance of Fe. The method comprises the following process flows: molten iron pretreatment → converter smelting → external refining → continuous casting → heating → controlled rolling and controlled cooling → coiling → acid cleaning → continuous annealing → hot galvanizing → finishing → functional inspection → packaging and delivery. The method adopts the design of C-Mn-Si series alloy components with low price, does not need to add noble alloy elements such as Cr, Mo and the like, improves the platability of the silicon-containing TRIP steel by adopting a pre-oxidation process and proper dew point matching control, and solves the technical problems of the surface quality, the mechanical property and the like of the TRIP steel plate by properly controlling cooling after plating.)

1. The low-cost hot galvanizing phase transformation induced plasticity steel is characterized in that the chemical components of the steel plate are controlled as follows according to the weight percentage: 0.1 to 0.3%, Si: 0.4-2.0%, Mn: 1.0-2.5%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Al is less than or equal to 0.08%, and the balance is Fe.

2. The low-cost hot-dip galvanized transformation-induced plasticity steel according to claim 1, characterized in that the chemical components of the steel plate are preferably controlled to be C: 0.17 to 0.23%, Si: 1.0-1.5%, Mn: 1.5-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, Al is less than or equal to 0.05%, and the balance is Fe.

3. A preparation method of low-cost hot galvanizing transformation induced plasticity steel according to claim 1 or 2, characterized by comprising the following process flows: molten iron pretreatment → converter smelting → external refining → continuous casting → heating → controlled rolling and controlled cooling → coiling → acid cleaning → continuous annealing → hot galvanizing → finishing → functional inspection → packaging and delivery; wherein the heating temperature in the controlled rolling and controlled cooling process is 1200-1280 ℃, the initial rolling temperature is 1080-1130 ℃, the final rolling temperature is 890-950 ℃, laminar cooling is adopted after rolling, the cooling rate is 20-40 ℃/s, and the coiling temperature is 580-640 ℃.

4. The method for preparing low-cost hot-dip galvanized transformation induced plasticity steel according to claim 3, characterized in that the rolling and cooling control process adopts a reduction rate of not less than 52%.

5. The method for preparing the low-cost hot-dip galvanized phase-change induced plasticity steel according to claim 3, characterized in that the surface quality of the steel plate is ensured by adopting a pre-oxidation process and reasonable control of dew point; wherein, the pre-oxidation process comprises the following steps: by the use of O₂+N₂Atmosphere, O₂The volume content of the catalyst is 1.5-2.0%, the catalyst is pre-oxidized for 8-12 s at 700-800 ℃, and the dew point of the atmosphere is controlled to be-15 to-25 ℃.

6. The method for preparing low-cost hot galvanizing transformation induced plasticity steel according to claim 3, wherein the flow of the continuous annealing furnace comprises the following steps: the process parameters of the heating section → the soaking section → the slow cooling section → the fast cooling section → the balancing section are shown in the following table:

the temperature of the heating section is increased to 820 +/-10 ℃, the temperature of the steel plate is uniformly maintained at 820 +/-10 ℃ in the soaking section, the temperature of the slow cooling section is reduced to 720 +/-10 ℃, the cooling speed is 7-10 ℃/s, the temperature of the fast cooling section is reduced to 420 +/-10 ℃, the cooling speed is 15-30 ℃/s, the temperature of the equalizing section is increased to 460 +/-10 ℃, and the speed in the continuous annealing furnace is 80 +/-10 m/min.

7. The method for preparing low-cost hot-dip galvanized transformation-induced plasticity steel according to claim 3, wherein the hot-dip galvanized steel is put into a zinc pot at the temperature of 460 +/-10 ℃ so that the zinc liquid in the zinc pot reaches 460 +/-10 ℃, and then hot-dip galvanized operation is carried out.

Technical Field

The invention relates to the field of phase change induced plasticity steel, in particular to low-cost hot galvanizing phase change induced plasticity steel and a preparation method thereof.

Background

The transformation induced plasticity steel (TRIP steel) induces martensite nucleation of the retained austenite under the action of plastic deformation through the transformation induced plasticity effect, introduces transformation strengthening and plastic growth, and can improve the strength and the toughness. The steel grade used as the automobile steel plate can reduce the automobile weight, reduce the oil consumption and simultaneously can effectively resist the plastic deformation during the collision, thereby obviously improving the safety level of the automobile. The phase transformation induced plasticity steel can obtain good corrosion resistance by hot galvanizing, and the service life is prolonged.

At present, 590-780 grade hot-galvanized TRIP steel for structural parts and safety parts is already successfully manufactured in a trial mode. 590-780 MPa grade hot-dip galvanized TRIP steel is developed at home and abroad, and 980MPa grade hot-dip galvanized TRIP steel is being developed. However, hot-dip galvanized TRIP steel often has the problems of poor platability, poor coating binding force and the like in production, and lots of researches on the platability of TRIP steel are carried out at home and abroad, but the industrial production is rarely reported.

In order to avoid the problems of surface quality such as galvanization, most of the components of the steel sheet such as the transformation-induced plasticity of galvanization are designed to use high Al instead of or partially replace Si, and because the strength cannot meet the requirements, expensive alloy elements have to be added to improve the strength, and meanwhile, the replacement of Si by Al can improve the platability of TRIP steel, but the high content of Al causes problems in steel making and hot rolling, such as the fact that a continuous casting crystallizer nozzle is easy to block when the content of Al in TRIP steel is too high in the production process. In addition, Al increases the Ac3 transformation temperature, so that the annealing temperature has to be increased, increasing energy consumption. The addition of Si does not need to add expensive alloy elements to compensate for the strength, the comprehensive mechanical property of TRIP steel can be improved, and the problem of how to solve the surface quality of hot galvanizing of high-Si transformation induced plasticity steel becomes a key and difficult point of research.

Disclosure of Invention

In order to solve the technical problems, the invention provides a low-cost hot-dip galvanized phase change induced plasticity steel plate and a preparation method thereof, which adopt the design of low-cost C-Mn-Si alloy components, do not need to add noble alloy elements such as Cr, Mo and the like, improve the platability of silicon-containing TRIP steel by adopting a pre-oxidation process and proper dew point matching control, and solve the technical problems of surface quality, mechanical property and the like of the TRIP steel plate by properly controlling cooling after plating.

The technical scheme of the invention is as follows:

the low-cost hot galvanizing phase change induced plasticity steel comprises the following chemical components in percentage by weight: 0.1 to 0.3%, Si: 0.4-2.0%, Mn: 1.0-2.5%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Al is less than or equal to 0.08%, and the balance is Fe.

The low-cost hot-dip galvanized transformation induced plasticity steel preferably comprises the following chemical components in percentage by weight: 0.17 to 0.23%, Si: 1.0-1.5%, Mn: 1.5-2.0%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, Al is less than or equal to 0.05%, and the balance is Fe.

The preparation method of the low-cost hot galvanizing phase transformation induced plasticity steel comprises the following process flows of: molten iron pretreatment → converter smelting → external refining → continuous casting → heating → controlled rolling and controlled cooling → coiling → acid cleaning → continuous annealing → hot galvanizing → finishing → functional inspection → packaging and delivery; wherein the heating temperature in the controlled rolling and controlled cooling process is 1200-1280 ℃, the initial rolling temperature is 1080-1130 ℃, the final rolling temperature is 890-950 ℃, laminar cooling is adopted after rolling, the cooling rate is 20-40 ℃/s, and the coiling temperature is 580-640 ℃.

According to the preparation method of the low-cost hot galvanizing phase change induced plasticity steel, the rolling and cooling control process adopts the reduction rate of more than or equal to 52 percent.

The preparation method of the low-cost hot galvanizing phase change induced plasticity steel adopts a pre-oxidation process and reasonable control of dew point to ensure the surface quality of a steel plate; wherein, the pre-oxidation process comprises the following steps: by the use of O₂+N₂Atmosphere, O₂The volume content of the catalyst is 1.5-2.0%, the catalyst is pre-oxidized for 8-12 s at 700-800 ℃, and the dew point of the atmosphere is controlled to be-15 to-25 ℃.

The preparation method of the low-cost hot galvanizing phase transformation induced plasticity steel comprises the following steps of: the process parameters of the heating section → the soaking section → the slow cooling section → the fast cooling section → the balancing section are shown in the following table:

the temperature of the heating section is increased to 820 +/-10 ℃, the temperature of the steel plate is uniformly maintained at 820 +/-10 ℃ in the soaking section, the temperature of the slow cooling section is reduced to 720 +/-10 ℃, the cooling speed is 7-10 ℃/s, the temperature of the fast cooling section is reduced to 420 +/-10 ℃, the cooling speed is 15-30 ℃/s, the temperature of the equalizing section is increased to 460 +/-10 ℃, and the speed in the continuous annealing furnace is 80 +/-10 m/min.

The preparation method of the low-cost hot galvanizing phase change induction plasticity steel comprises the steps of putting hot galvanizing into a zinc pot at the temperature of 460 +/-10 ℃, and carrying out hot galvanizing operation after the temperature of zinc liquid in the zinc pot reaches 460 +/-10 ℃.

The design idea of the invention is as follows:

the design of the invention adopts the traditional C-Mn-Si component design, avoids the problems of ferrite embrittlement caused by high Al content, the deterioration of the strength and ductility of the material, the easy blockage of a water gap in the steelmaking continuous casting process and the like, also avoids the problems that the plasticity, the weldability and the formability of TRIP steel can be reduced due to high P content, does not need additional noble alloy elements Cr, Mo and Ni, and meets the environment-friendly design idea of low cost.

The C element designed by the invention is an austenite stability element, and the price is low; meanwhile, C is also a main strengthening element, so that the content of C is high on the premise of not influencing the welding performance, and the strengthening effect is good. In addition, C improves the content and stability of the retained austenite, so that the plasticity of the steel is better, the retained austenite is subjected to martensite transformation under the action of external force in the forming process of the steel plate, and the strength and the plasticity of the steel are improved.

The Mn element designed by the invention is a strengthening and toughening element and is used as an austenite forming element, and the Mn element can play a role in refining grains and stabilizing residual austenite simultaneously in enlarging an austenite region, reducing the finish rolling temperature and delaying the austenite transformation.

In order to avoid the formation of a dense oxide layer Mn on the surface of the steel sheet₂SiO₄The high-Si hot dip galvanized transformation induced plasticity steel designed by the invention has the advantages that the surface of a substrate is mainly covered by an oxidation/reduction layer containing metal Fe through a pre-oxidation process, the oxidation/reduction layer is divided by a plurality of cavities, the cavities contain a mixture of oxides such as Mn, Si and the like, and the formed oxides are arranged below the oxidation/reduction layer.

In addition, the invention promotes the internal oxidation process by controlling the dew point in the annealing furnace, thereby changing the chemical composition of the surface and improving the platability of the silicon-containing TRIP steel. Therefore, the pre-oxidation process is matched with a proper dew point, and the temperature of the zinc pot, the temperature of the zinc liquid and the production process are reasonably designed at the same time, so that the hot-dip galvanized phase change induced plasticity steel plate with excellent zinc coating adhesion is obtained, the C-Mn-Si TRIP steel obtains good coating adhesion, and the surface quality meets the requirements of related standards.

The invention has the advantages and beneficial effects that:

compared with the prior art, the invention has the advantages that the smelted casting blank can be produced in a continuous annealing line and a hot galvanizing line, the problem of incompatibility of production lines does not exist, the residual casting blank in steel making can be converted into other procedures for production, the production cost is greatly reduced, the cost per ton of steel is reduced by at least 500 yuan, the production control is relatively simple, the process parameters are easy to realize, the surface quality is good, the comprehensive mechanical property is excellent, and the relevant requirements of products are better met.

Drawings

FIG. 1 shows the metallographic structure of a silicon-containing TRIP steel of the present invention.

Detailed Description

The present invention will be explained in further detail below by way of examples and figures.