阅读说明：本技术 一种抗拉强度≥1600MPa级的异型材用钢及生产方法 (Profiled bar steel with tensile strength of more than or equal to 1600MPa and production method thereof ) 是由 葛珍荣 葛锐 冯宗金 于 2021-10-18 设计创作，主要内容包括：一种抗拉强度≥1600MPa级的异型材用钢,其组分及wt%为：C：0.25～0.33％,Si：1.5～2.0％,Mn：2.6～3.2％,P≤0.02％,S≤0.01％,Als：0.01～0.10%,N≤0.005%,Cr不超过1.0％,Ni不超过1.0％,Nb不超过0.05％,V不超过0.5％；工艺：冶炼并铸成板坯；铸坯加热；粗轧；精轧；卷取后空冷；奥氏体化；淬火处理；时效处理；卷取并空冷至室温；再次开卷后平整、分切,辊压成型。本发明通过添加Nb、V,在基体组织中形成Nb/V(C,N),该相在调质热处理的均热阶段起到钉扎作用,阻碍奥氏体的长大,促进形成细化的奥氏体相,并实现在保证屈服强度≥1200MPa、抗拉强度≥1600MPa下,并使延伸率由≤7%提高至≥10%。(The steel for the profiled bar with the tensile strength of more than or equal to 1600MPa comprises the following components in percentage by weight: c: 0.25 to 0.33%, Si: 1.5-2.0%, Mn: 2.6-3.2%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, Als: 0.01-0.10 percent of N, less than or equal to 0.005 percent of N, less than or equal to 1.0 percent of Cr, less than or equal to 1.0 percent of Ni, less than or equal to 0.05 percent of Nb and less than or equal to 0.5 percent of V; the process comprises the following steps: smelting and casting into a plate blank; heating a casting blank; rough rolling; fine rolling; air cooling is carried out after coiling; austenitizing; quenching treatment; aging treatment; coiling and air-cooling to room temperature; and flattening, slitting and roll forming after uncoiling again. According to the invention, Nb and V are added to form Nb/V (C, N) in a matrix structure, the phase plays a pinning role in a soaking stage of quenching and tempering heat treatment, growth of austenite is hindered, formation of a refined austenite phase is promoted, yield strength is guaranteed to be larger than or equal to 1200MPa, tensile strength is larger than or equal to 1600MPa, and elongation is improved to be larger than or equal to 10% from smaller than or equal to 7%.)

1. The steel for the profiled bar with the tensile strength of more than or equal to 1600MPa comprises the following components in percentage by weight: c: 0.25 to 0.33%, Si: 1.5-2.0%, Mn: 2.6-3.2%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, Als: 0.01-0.10 percent of Ni, less than or equal to 0.005 percent of N, less than or equal to 1.0 percent of Cr, less than or equal to 1.0 percent of Ni, less than or equal to 0.05 percent of Nb, less than or equal to 0.5 percent of V, and the balance of Fe and inevitable impurities.

2. A steel for profile shapes with tensile strength more than or equal to 1600MPa level as claimed in claim 1, wherein: the components and the weight percentage content are as follows: c: 0.263 to 0.316%, Si: 1.62-1.85%, Mn: 2.8-3.0%, P is less than or equal to 0.01%, S is less than or equal to 0.005%, Als: 0.01-0.066%, Cr is not more than 0.83%, Ni is not more than 0.85%, Nb is not more than 0.038%, and V is not more than 0.39%.

3. A method for producing a profiled bar steel according to claim 1 having a tensile strength of at least 1600MPa, comprising the steps of:

1) smelting and continuously casting into a plate blank;

2) heating a casting blank, and controlling the tapping temperature to 1150-1250 ℃;

3) carrying out rough rolling, and controlling the thickness of the plate blank after rough rolling to be 3.3-4 times of the thickness of a designed finished product;

4) performing finish rolling and rolling to the thickness of a finished product, and controlling the finish rolling temperature to be 850-880 ℃;

5) air cooling to room temperature after conventional coiling;

6) uncoiling and austenitizing, controlling the temperature to be 850-900 ℃, and preserving the heat for 120-180 s at the temperature;

7) quenching treatment is carried out by adopting water or quenching liquid, and the plate blank is cooled to 140-180 ℃ at a cooling speed of not less than 10 ℃/s;

8) carrying out aging treatment, rapidly heating the plate blank to 280-330 ℃ at a speed of not less than 20 ℃/s, and controlling the aging treatment time to be 180-300 s;

9) coiling and air-cooling to room temperature;

10) and after uncoiling again, flattening, slitting and roll forming are sequentially carried out.

4. A method for producing a steel for profile shapes with tensile strength of more than or equal to 1600MPa according to claim 3, characterized in that: the austenitizing temperature is controlled to 868-893 ℃.

5. A method for producing a steel for profile shapes with tensile strength of more than or equal to 1600MPa according to claim 3, characterized in that: the aging treatment temperature is controlled to be 293-323 ℃.

Technical Field

The invention relates to ultrahigh-strength steel for automobiles and buildings and a production method thereof, in particular to steel for manufacturing profiled bars with the tensile strength of more than or equal to 1600MPa and a production method thereof.

Background

In recent years, carbon peaking and carbon neutralization are actively arranged in China, and green low-carbon development is practically promoted. The steel is a base material for modern production and manufacturing, and is also the industry with the largest carbon emission in the existing manufacturing industry; how to lead the green development of the steel industry through the upstream and downstream industry cooperation has important social value. The strength and the application performance of the steel material are optimized and improved, the light weight of the member is realized, the usage amount of the steel material is effectively reduced, and the method is the best way for promoting the carbon peak reaching of the steel material.

The steel profiled bar is widely used for bearing structures of solar photovoltaic brackets, buildings, automobiles, electric power facilities and the like. Because the service working condition and the application environment of the steel are very complex, the steel material is generally required to have good strength and toughness. The steel profile can be classified into rolled profile, hot rolled profile, welded profile, and the like according to the difference of the processing technique. The rolled deformed steel is one of the most widely used deformed steel processing technologies at present, and has the advantages of simple preparation technology, low continuous rolling production cost and the like; however, the currently manufactured steel profiled bars are generally processed by Q235 or Q345 (the tensile strength of the material is less than or equal to 600MPa), and the problems of low material strength, great self-weight and the like exist, so that the application range of the steel profiled bars is limited.

The document with Chinese patent publication No. CN 111519091A discloses a processing technology of high-strength deformed steel, which is completed by the processing of pretreatment, multiple cold-drawing forming and annealing treatment of a steel billet with specific chemical components; the tensile strength of the produced section steel is 621MPa, the yield strength is 523MPa, and the elongation is not expressed.

Chinese patent publication No. CN110343965 discloses a high-strength deformed steel and a preparation method thereof, which is processed by the processes of pretreatment of a steel billet with specific chemical components, isothermal spheroidizing annealing, compression, molding, shaping, quenching and multiple tempering; the tensile strength of the produced profile steel is 966-985 MPa, the yield strength is 966-985 MPa, and the elongation is not expressed.

The production raw material of the high-strength steel is thick steel billet, and the process is complex because the repeated forming and heat treatment are needed; and the strength is still lower, and the research and the promotion are still needed.

Disclosure of Invention

The invention aims to overcome the defects of high strength and elongation rate not exceeding 7 percent in the prior art, and provides the steel for the section and the production method thereof, which can ensure that the elongation rate is not less than 10 percent on the basis of ensuring that the tensile strength is not less than 1600MPa and meet the manufacturing requirements of the section.

The measures for realizing the aim are as follows:

the steel for the profiled bar with the tensile strength of more than or equal to 1600MPa comprises the following components in percentage by weight: c: 0.25 to 0.33%, Si: 1.5-2.0%, Mn: 2.6-3.2%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, Als: 0.01-0.10%, N is less than or equal to 0.005%, Cr: not more than 1.0%, Ni: not more than 1.0%, Nb: not more than 0.05%, V: not more than 0.5%, and the balance of Fe and inevitable impurities.

Preferably: c: 0.263 to 0.316%, Si: 1.62-1.85%, Mn: 2.8-3.0%, P is less than or equal to 0.01%, S is less than or equal to 0.005%, Als: 0.01-0.066%, Cr: not more than 0.83%, Ni: not more than 0.85%, Nb: not more than 0.038%, V: not more than 0.39%.

The method for producing the steel for the profiled bar with the tensile strength of more than or equal to 1600MPa comprises the following steps:

1) smelting and continuously casting into a plate blank;

2) heating a casting blank, and controlling the tapping temperature to 1150-1250 ℃;

3) carrying out rough rolling, and controlling the thickness of the plate blank after rough rolling to be 3.3-4 times of the thickness of a designed finished product;

4) performing finish rolling and rolling to the thickness of a finished product, and controlling the finish rolling temperature to be 850-880 ℃;

5) air cooling to room temperature after conventional coiling;

6) uncoiling and austenitizing, controlling the temperature to be 850-900 ℃, and preserving the heat for 120-180 s at the temperature;

7) quenching treatment is carried out by adopting water or quenching liquid, and the plate blank is cooled to 140-180 ℃ at a cooling speed of not less than 10 ℃/s;

8) carrying out aging treatment, rapidly heating the plate blank to 280-330 ℃ at a speed of not less than 20 ℃/s, and controlling the aging treatment time to be 180-300 s;

9) coiling and air-cooling to room temperature;

10) and after uncoiling again, flattening, slitting and roll forming are sequentially carried out.

Preferably: the austenitizing temperature is controlled to 868-893 ℃.

Preferably: the aging treatment temperature is controlled to be 293-323 ℃.

The action and mechanism of each element and main process in the invention

C: carbon is an essential element in steel and is also the most economical and effective strengthening element. The carbon content is designed to be low, and the strength of the material is obviously reduced; however, too high a carbon content lowers the plasticity of the steel and is disadvantageous in weldability. Therefore, in the invention, the carbon percentage content is controlled within the range of 0.25-0.33% of C, and the preferable range is 0.263-0.316% from the aspects of economy and comprehensive performance.

Si: silicon is the most basic element in steel and is one of the most important elements in the steel of the present invention. Si can suppress the precipitation of cementite within a certain temperature range, but has a relatively limited suppression effect on epsilon carbide. Si inhibits cementite precipitation so that carbon atoms diffuse from the martensite into the residual austenite to stabilize the residual austenite. The content of Si is generally not lower than 1.5 percent, otherwise, the function of inhibiting the precipitation of cementite cannot be realized; the content of Si is generally not more than 2.0%, otherwise the steel plate is easy to generate heat cracks during welding, which causes difficulty in application of the steel plate, so the content of Si in the steel is generally controlled to be 1.5-2.0%, and the preferable range is 1.62-1.85%.

Mn: manganese has a solid solution strengthening effect and is one of the most important elements in the steel of the present invention. It is known that Mn is an important element for expanding the austenite phase region, and can reduce the critical quenching rate of steel, stabilize austenite, refine grains, and delay transformation of austenite to pearlite. In the invention, in order to ensure the strength of the steel plate, the Mn content is generally controlled to be more than 2.6 percent, the Mn content is too low, and when the steel plate is subjected to air cooling in the first stage of sectional cooling, the super-cooled austenite is unstable and is easily transformed into a pearlite type structure such as sorbite and the like; meanwhile, the Mn content is generally not more than 3.2%, Mn segregation is likely to occur during steel making, and heat cracking is likely to occur during slab continuous casting. Therefore, the Mn content in the steel is generally controlled to be 2.6-3.2%, and the preferable range is 2.8-3.0%.

P: phosphorus is a harmful element in steel and is easy to cause center segregation of a casting blank. The steel is easy to be deviated to a grain boundary in the subsequent hot continuous rolling heating process, so that the brittleness of the steel is obviously increased. Meanwhile, the content is controlled to be below 0.02 percent based on cost consideration and without influencing the performance of the steel.

S sulfur is a very harmful element. Sulfur in steel often exists in the form of sulfide of manganese, and this sulfide inclusion deteriorates toughness of steel and causes anisotropy of properties, so that the lower the sulfur content in steel, the better. The sulfur content in steel is controlled to be less than 0.01% in consideration of the manufacturing cost.

And Als: aluminum is added for deoxidation, and when the content of Als is less than 0.01%, the effect thereof cannot be exerted; on the other hand, since addition of a large amount of aluminum easily forms alumina agglomerates, the aluminum content is controlled in the range of 0.01 to 0.10%, preferably in the range of 0.01 to 0.066%.

N can improve the strength of the steel; however, the bonding force of nitrogen with niobium and titanium is strong, and coarse niobium nitride and titanium nitride particles can be formed in the steel at high temperature, so that the plasticity and toughness of the steel are seriously damaged; in addition, higher nitrogen content increases the amount of micro-alloying elements needed to stabilize the nitrogen element, thereby increasing costs. Therefore, the content of nitrogen should be reduced as much as possible, and nitrogen is controlled to 0.005% or less in the present invention.

Cr: chromium can significantly improve the strength, hardness and wear resistance of steel, but reduces the plasticity and toughness, and increases the risk of slab cracking during continuous casting production after the content of Cr exceeds 1.0%, and the chromium is controlled within 1.0%, preferably not more than 0.83%.

Ni: the nickel can improve the weldability of the steel plate and improve the toughness of the material, and the steel plate has good hardness and toughness by adding a certain content of Ni into high-hardness steel; however, Ni is a noble metal element, and in the present invention, Ni is controlled to be within 1.0%, and preferably Ni is not more than 0.85%.

Nb: niobium is an C, N strengthener forming element. A small amount of niobium is added into the steel to form a certain amount of niobium carbon and nitride, so that austenite grains are prevented from growing and refining, the ultrahigh strength is obtained, and the steel-plastic toughness can be improved. However, excess niobium may combine with C to form coarse carbonitrides, thereby reducing the hardness and strength of the material. Therefore, the total content thereof is controlled to be within a range of not more than 0.05%, preferably not more than 0.038% of Nb.

V: vanadium can improve the hardenability of steel, can be dissolved in ferrite to have a strengthening effect, can form stable carbide, refines grains, and can strengthen the effect of V by N. The method of combining V precipitation strengthening and Ti grain refinement can be used for obtaining larger strengthening effect V. Therefore, V is controlled not to exceed 0.05%, preferably not to exceed 0.39%.

The invention controls the tapping temperature of the casting blank to 1150-1250 ℃ in order to ensure the homogenization of alloy elements of the casting blank, reduce the deformation resistance of the material and facilitate the production and rolling. The tapping temperature is low, which is not beneficial to the homogenization of alloy elements, and the deformation resistance of the material is increased, the load of the rolling mill is large, and the energy consumption is high; the tapping temperature is high, the energy consumption of the heating furnace is high, and the manufacturing cost is improved. Therefore, the heating tapping temperature of the casting blank is generally controlled to be 1150-1250 ℃.

The thickness of the plate blank after rough rolling is controlled to be 3.3-4 times of the thickness of a finished product, and the rolling speed and the production efficiency are improved due to small high-temperature deformation resistance of the plate blank and high reduction rolling; however, the thickness of the rough-rolled plate blank is small, which is not beneficial to the size control of the thickness of the finish-rolled hot-rolled product after finish rolling.

The invention controls the finish rolling temperature to be 830-880 ℃, and the preferred finish rolling temperature is 830-880 ℃, because the finish temperature of rolling deformation has important influence on the structure performance of steel. In order to ensure that the plate blank is rolled in a uniform austenite area so as to obtain a uniform structure and good performance, the finish rolling temperature of finish rolling is required to be controlled to be higher than the starting temperature of ferrite transformation; meanwhile, the higher the finish rolling temperature is, the stronger the tendency of grain focusing growth is, and the coarser the obtained austenite grains are, which will result in the reduction of the strength of the material.

The present invention controls the austenitizing temperature to 850-900 ℃ to ensure the material to be fully austenitized. The temperature is too low, and the material cannot realize complete austenitization; too high a temperature will result in coarse austenite grains, directly affecting the material properties.

The cooling speed of the invention is not lower than 10 ℃/s to cool the high-temperature plate blank to 140-180 ℃ so as to directly transform most of austenite into martensite, thereby obtaining higher material strength. The cooling speed is too low, and the austenite structure is easy to be cooled and transformed into other structures except martensite, thereby directly influencing the strength of the material. The temperature is too high after the cooling is finished, the martensite structure fraction obtained by cooling is lower, and the material strength is lower; the temperature is too low at the end of cooling, the fraction of martensite structure obtained by cooling is higher, and the toughness and the elongation of the material are reduced.

The cooled plate is rapidly heated to 280-330 ℃ for isothermal partition aging treatment, so that C elements in supersaturated martensite are promoted to diffuse into untransformed austenite, the stability of retained austenite is improved, and 5-10% of retained austenite is obtained at room temperature, so that the material has good toughness and plasticity.

Compared with the prior art, Nb and V are added to form Nb/V (C, N) with a certain size in a matrix structure, the phase plays a pinning role in a soaking stage of a quenching and tempering heat treatment process, growth of austenite is hindered, a refined austenite phase is promoted to be formed, yield strength is guaranteed to be larger than or equal to 1200MPa, tensile strength is larger than or equal to 1600MPa, the limited elongation rate is not more than 7% and is improved to be not less than 10%, and the requirement of the steel for the section is met.

Drawings

FIG. 1 is a typical metallographic structure of an ultra-high strength steel plate according to the present invention;

description of the drawings: the metallographic structure is martensite + retained austenite.

Detailed Description

The present invention is described in detail below:

table 1 is a list of values of the components of each example and comparative example of the present invention;

table 2 shows the values of the process parameters of the examples and comparative examples of the present invention;

table 3 is a table of the results of testing the performance of each example and comparative example of the present invention.

The preparation method comprises the following steps:

1) smelting and continuously casting into a plate blank;

2) heating a casting blank, and controlling the tapping temperature to 1150-1250 ℃;

3) carrying out rough rolling, and controlling the thickness of the plate blank after rough rolling to be 3.3-4 times of the thickness of a designed finished product;

4) performing finish rolling and rolling to the thickness of a finished product, and controlling the finish rolling temperature to be 850-880 ℃;

5) air cooling to room temperature after conventional coiling;

6) uncoiling and austenitizing, controlling the temperature to be 850-900 ℃, and preserving the heat for 120-180 s at the temperature;

7) quenching treatment is carried out by adopting water or quenching liquid, and the plate blank is cooled to 140-180 ℃ at a cooling speed of not less than 10 ℃/s;

8) carrying out aging treatment, rapidly heating the plate blank to 280-330 ℃ at a speed of not less than 20 ℃/s, and controlling the aging treatment time to be 180-300 s;

9) coiling and air-cooling to room temperature;

10) and after uncoiling again, flattening, slitting and roll forming are sequentially carried out.

TABLE 1 tabulated (wt%) chemical composition values for each example of the invention and comparative example

TABLE 2 tabulation of values of main process parameters for each example of the invention and comparative example

TABLE 3 results of testing the properties of the inventive and comparative examples

As can be seen from Table 3, the ultrahigh strength cold rolled steel sheet for the section bar produced by the alloy composition design and the related process has yield strength of more than or equal to 1200MPa, tensile strength of more than or equal to 1600MPa and elongation (A)₅₀) The steel has the advantages of not less than 10 percent, good processing formability and weldability, and can meet the use requirements of cold-rolled ultrahigh-strength steel for profiles such as photovoltaic brackets, building profiles, logistics brackets and the like.

The present embodiments are merely preferred examples, and are not intended to limit the scope of the present invention.