阅读说明：本技术 一种钢板及其生产方法 (Steel plate and production method thereof ) 是由 齐建群 杜明山 杜雁冰 孟凡月 范博 王海龙 于航 于 2021-07-21 设计创作，主要内容包括：本发明一种钢板及其生产方法,钢板的化学成分及其质量百分含量为：C：0.06～0.09%,Mn：1.00～1.50%,Si：0.30～0.50%,S≤0.025%,P≤0.025%,Al：0.030～0.050%,Ti：0.01～0.05%,N≤0.0050%,余量为铁和不可避免的杂质元素。采用连续退火炉进行退火,均温段温度780～810℃,快冷开始温度640～660℃,快冷终止温度270～290℃,终冷段结束温度90～110℃。淬火后可实现与相近强度级别的热成形钢材料匹配焊接,达到汽车零部件强度梯度分布的特点。(The invention relates to a steel plate and a production method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: c: 0.06-0.09%, Mn: 1.00-1.50%, Si: 0.30-0.50%, S is less than or equal to 0.025%, P is less than or equal to 0.025%, Al: 0.030 to 0.050%, Ti: 0.01-0.05%, N is less than or equal to 0.0050%, and the balance of iron and inevitable impurity elements. And annealing by adopting a continuous annealing furnace, wherein the temperature of the temperature equalizing section is 780-810 ℃, the quick cooling starting temperature is 640-660 ℃, the quick cooling ending temperature is 270-290 ℃, and the ending temperature of the final cooling section is 90-110 ℃. After quenching, the hot forming steel can be matched and welded with hot forming steel materials with similar strength levels, and the characteristic of gradient distribution of strength of automobile parts is achieved.)

1. The steel plate is characterized by comprising the following chemical components in percentage by mass: c: 0.06% -0.09%, Mn: 1.00% -1.50%, Si: 0.30-0.50%, S is less than or equal to 0.025%, P is less than or equal to 0.025%, Al: 0.030-0.050%, Ti: 0.01 to 0.05 percent of the total weight of the alloy, less than or equal to 0.0050 percent of N and the balance of iron and inevitable impurity elements.

2. A steel sheet according to claim 1, wherein S is contained in an amount of 0.005% by mass or less.

3. The production method of the steel plate according to claims 1 and 2, which comprises an annealing process, a leveling process and a hot forming process in sequence, wherein the annealing process adopts a continuous annealing furnace for annealing, and the whole annealing furnace consists of a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an overaging section, a final cooling section and water quenching equipment, and is characterized in that the temperature of the uniform cooling section is 780-810 ℃, the temperature of the fast cooling start is 640-660 ℃, the temperature of the fast cooling end is 270-290 ℃, and the temperature of the final cooling end is 90-110 ℃.

4. A method for producing a steel sheet as claimed in claim 3 wherein the annealing step is carried out at a temperature of 30 to 40 ℃ after water quenching.

5. The method for producing a steel sheet as claimed in claim 3, wherein the leveling step is performed at an elongation set value of 0.8 to 1.2% and a rolling force control of 4000 to 8000 KN.

6. The method for producing a steel sheet as claimed in claim 3, wherein the hot forming step has a quenching cooling rate of not less than 30 ℃/s.

7. The method for producing a steel sheet according to claim 3, wherein the annealing step is carried out at a process speed of 65 to 160 m/min.

8. A method of producing a steel sheet according to any one of claims 3 to 7, wherein the steel sheet is produced to a thickness of 0.7 to 2.5 mm.

Technical Field

The invention belongs to the technical field of steel plate rolling and heat treatment, and particularly relates to an 800 MPa-grade steel plate and a production method thereof.

Background

An important way to realize the lightweight of the automobile is to use high-strength steel, but with the improvement of the strength, the forming performance of the steel plate is obviously reduced, the steel plate is easy to crack by direct processing, and the hot stamping forming process well solves the problem. The hot stamping forming process is an advanced manufacturing technology which combines plastic forming and heat treatment of a steel plate and is specially used for forming the ultrahigh strength boron steel, and the strength of automobile parts manufactured by adopting the hot stamping process can reach 2 GPa.

Although the hot forming technology is widely applied to manufacturing of automobile parts, the hot forming technology has the characteristics of poor weldability, poor toughness and the like, and other auxiliary parts must be introduced during design to meet the requirements of collision laws and regulations on safety and energy absorption during application. Many improved thermoforming techniques have been used, such as die zone quenching, patch thermoforming, differential plate thermoforming, dissimilar material laser tailor-welding thermoforming, etc. The heterogeneous laser tailor-welding hot forming method is a process method which adopts different materials to perform laser tailor-welding and obtains different performance partitions after hot forming, and has the advantages of stable performance of a soft area, realization of the effect of a poor thick plate, fundamental improvement of weldability of the soft area and the like.

Disclosure of Invention

The technical problem solved by the invention is as follows: the steel plate and the production method thereof are provided, the defects that the material transition gradient of a soft and hard area is large, the material difference is large, the forming flow stress needs to be matched again and the like in the laser tailor-welding hot forming of dissimilar materials are overcome, the matched welding with the hot forming steel material with similar strength level is realized, and the strength gradient distribution of automobile parts is achieved.

In order to solve the problems, the invention provides a steel plate which comprises the following chemical components in percentage by mass: c: 0.06% -0.09%, Mn: 1.00% -1.50%, Si: 0.30-0.50%, S is less than or equal to 0.025%, P is less than or equal to 0.025%, Al: 0.030-0.050%, Ti: 0.01 to 0.05 percent of the total weight of the alloy, less than or equal to 0.0050 percent of N and the balance of iron and inevitable impurity elements.

Preferably, the mass percentage of S in the steel plate is less than or equal to 0.005 percent.

The production method of the steel plate sequentially comprises an annealing process, a leveling process and a hot forming process, wherein the annealing process adopts a continuous annealing furnace for annealing, the whole annealing furnace consists of a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an overaging section, a final cooling section and water quenching equipment, the temperature of the soaking section is 780-810 ℃, the temperature of the fast cooling start temperature is 640-660 ℃, the temperature of the fast cooling end temperature is 270-290 ℃, and the temperature of the final cooling end temperature is 90-110 ℃.

Further, in the annealing process, the temperature of the steel plate after water quenching is 30-40 ℃.

Further, in the leveling process, the set value of the elongation is 0.8-1.2%, and the rolling force is controlled to be 4000-8000 KN.

Furthermore, in the hot forming process, the quenching cooling rate is more than or equal to 30 ℃/s.

Further, the process speed of the annealing process is 65-160 m/min.

Furthermore, the thickness of the produced steel plate is 0.7-2.5 mm.

The invention adopts the component design concept of adopting low-carbon, low-manganese and high-silicon components and adding low-alloy titanium, and adopts low-carbon components to ensure the welding performance of the material; boron alloy is not added, so that the defects of plasticity and toughness caused by over high hardenability are avoided; the addition of trace titanium element can further refine austenite grains and martensite lath structures, thereby ensuring that the steel plate still has better toughness while keeping high strength to the maximum extent.

C. The reasons for setting the contents of the elements Si, Mn and Ti are as follows:

c: carbon is the most basic element in steel and is also one of the main factors affecting yield strength and tensile strength. Meanwhile, carbon also has an important influence on the welding performance of the material. Generally, the higher the carbon content in the steel, the higher the yield strength and tensile strength, and the lower the weldability. In order to ensure that the hot-formed steel plate with the tensile strength of 800MPa is obtained, the carbon content at least reaches over 0.06 percent under the condition of adopting Mn, Si and microalloy element Ti, otherwise, the tensile strength of the hot-formed plate is difficult to meet the requirement. On the other hand, if the carbon content is too high and exceeds 0.09%, the welding property of the plate material will be affected, thereby reducing the use value of the material. Therefore, the influence of carbon on the strength and the welding performance is comprehensively considered, and the carbon content in the steel is controlled to be 0.06% -0.09%.

Si: silicon is the most basic element in steel, has a solid solution strengthening effect on ferrite, and has a certain effect on improving the mechanical property of the plate. The residual silicon content in steel is usually below 0.60%. If the content of silicon is too high, the welding performance is damaged, and if the content of silicon is controlled to be less than 0.30%, the smelting cost is additionally increased. Therefore, the content of silicon is controlled to be 0.30-0.50%.

Mn: manganese is the most basic element in steel and is also one of the important alloying elements used in the present invention. Manganese stabilizes austenite and reduces the critical quenching speed of steel, thereby improving the hardenability of the material. In the invention, in order to improve the hardenability and further ensure the required strength of the material after hot forming treatment, the manganese content should be at least more than 1.00%. Meanwhile, if the manganese content exceeds 2.00%, the risk of slab cracking will be significantly increased. Therefore, on the basis of meeting the performance requirement, the manganese content is controlled to be 1.00-1.50% in consideration of cost factors.

Ti: titanium is one of the important alloying elements employed in the present invention. Titanium has the functions of refining grains and improving toughness, but if the content of titanium element is too high, the number of coarse carbide and nitride inclusions is increased, thereby affecting the comprehensive mechanical properties. Therefore, the titanium content should be controlled to be 0.01-0.05%.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

1) the low-carbon, low-manganese and high-silicon low-alloy titanium is adopted, and the cost is low;

2) the boron alloy is not added, the niobium-titanium composite strengthening design is not adopted, and the steel-making and hot rolling production operation is easy to realize;

3) after annealing and flattening, the yield strength of the plate is more than or equal to 350MPa, the tensile strength is more than or equal to 500MPa, and the elongation A_50mm≥15%；

4) After the plate is treated by the hot forming process, the microstructure mainly comprises ferrite and martensite, the yield strength is more than or equal to 500MPa, the tensile strength is more than or equal to 800MPa, and the elongation A_50mmNot less than 10 percent, can be used in the field of automobile steel with higher requirements on plasticity and strength;

5) after quenching, the hot forming steel material can be matched and welded with hot forming steel materials with similar strength levels, and the characteristic of strength gradient distribution of automobile parts is achieved, so that the requirements of collision laws and regulations on laser tailor-welded hot forming parts on safety and energy absorption are met, the characteristics of small transition gradient and strength gradient distribution of a soft and hard area are achieved, the good hot forming processing performance is met, and the uniform deformation capability of the laser tailor-welded hot forming parts is improved.

Drawings

FIG. 1 is a 500-fold photograph of a typical microstructure of the steel sheet of example 1 after annealing and flattening.

FIG. 2 is a 1000-fold photograph of a typical microstructure of the annealed and flattened steel sheet of example 1.

FIG. 3 is a 500-fold photograph of a typical microstructure of the steel sheet of example 1 after quenching.

FIG. 4 is a 1000-fold photograph of a typical microstructure of the steel sheet of example 1 after quenching.

FIG. 5 is a schematic view of the temperature control of the annealing process of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Examples 1 to 6

The chemical compositions and the mass percentage contents of the steel plates in the embodiments 1 to 6 are shown in table 1, the production process sequentially comprises an annealing process, a leveling process and a hot forming process, the annealing process adopts a continuous annealing furnace for annealing, the whole annealing furnace consists of a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an overaging section, a final cooling section and water quenching equipment, the temperature of the soaking section, the temperature of the fast cooling start temperature, the temperature of the fast cooling end, the temperature of the final cooling end, the temperature of the steel plates after water quenching and the process speed are shown in table 2, the leveling process, the set value of the elongation and the rolling force are shown in table 2, and the hot forming process and the quenching cooling rate are shown in table 2. The thickness of the produced steel sheet is shown in Table 2.

TABLE 1

TABLE 2

Mechanical properties of the steel sheets after annealing, flattening and quenching in the hot forming process of examples 1-6 were sampled and examined. The tensile strength, yield strength and elongation A of the steel plate after flattening_50mmThe results of the test are shown in Table 3. Tensile strength, yield strength and elongation A of steel plate quenched in hot forming procedure_50mmThe results of the test are shown in Table 3.

TABLE 3

Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.