High-strength and high-plasticity steel material as well as preparation method and application thereof

Abstract

The embodiment of the invention relates to a high-strength and high-plasticity steel material and a preparation method and application thereof, and belongs to the technical field of steel and iron materials. The high-strength and high-plasticity steel material disclosed by the embodiment of the invention comprises the following components in percentage by weight: 0.05 to 0.10 percent of C, 0.40 to 0.80 percent of Si, 0.50 to 1.50 percent of Al, 2.00 to 2.50 percent of Mn, 2.00 to 2.50 percent of Cu, 1.00 to 2.00 percent of Ni, 0.10 to 0.25 percent of Mo and 0.05 to 0.15 percent of Nb. The yield strength and the uniform elongation of the steel material are both greatly improved, and a large number of nano Cu clusters appearing in a steel matrix are the reason for greatly improving the yield strength of the steel material; and in addition, the nanometer reverted austenite generated at the steel matrix structure interface provides a high extension effect for the steel material.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of steel materials, and in particular to a high-strength and high-plasticity steel material and a preparation method and application thereof. Background Art

[0002] In order to save energy and reduce greenhouse gas emissions, it is a general trend to improve the quality of steel and reduce the amount of steel used. If the strength and plasticity of steel are doubled, the amount of steel used can be reduced by 3 / 4, which is the famous concept of "one ton of steel = four tons of steel". With the in-depth development of steel material research, many special steels have been born. The concept of the third generation of steel has matured, that is, the steel yield strength is required to be above 700MPa and the plasticity is greater than 20%. The research and development of the third generation of steel has gone through nearly 20 years. The advent of medium manganese steel and high manganese steel has brought the third generation of steel closer and closer to us.

[0003] However, the increase in manganese content in steel often leads to Mn segregation, making it difficult to guarantee the quality of steel and increasing the production cost. On the contrary, by using steel with low manganese content and combining it with a low-carbon, low-alloy multi-component design to give full play to the function of each alloying element, a new type of steel with strength and plasticity that meet the requirements of the third generation of steel can be obtained. Relying on the heat treatment process that has been explored for a long time, the low-manganese multi-component steel is modulated into a high-quality steel with a yield strength of 1000MPa and a plasticity of more than 20%. The preparation process of this type of steel is simple and easy to promote. The heat treatment process is relatively simple and suitable for large-scale heat treatment production in steel mills. Summary of the invention

[0004] In view of this, the embodiments of the present application provide a high-strength and high-plasticity steel material, a preparation method and application thereof, the yield strength and uniform elongation of the steel material are greatly improved, and the large number of nano-Cu clusters appearing in the steel matrix are the reason for the significant improvement in the yield strength of the steel material; in addition, the nano-reverse transformed austenite produced at the interface of the steel matrix structure provides the steel material with a high elongation effect, which can effectively overcome the defects of the above-mentioned prior art.

[0005] A first aspect of an embodiment of the present application provides a high-strength and high-plasticity steel material, the high-strength and high-plasticity steel material comprising the following components in weight percentage: C 0.05-0.10wt.%, Si 0.40-0.80wt.%, Al 0.50-1.50wt.%, Mn 2.00-2.50wt.%, Cu 2.00-2.50wt.%, Ni 1.00-2.00wt.%, Mo 0.10-0.25wt.%, Nb 0.05-0.15wt.%.

[0006] In some embodiments that may include the above embodiments, the high-strength and high-ductility steel material includes the following components in weight percentage: C 0.05wt.%, Si 0.40wt.%, Al 0.50wt.%, Mn 2.00wt.%, Cu 2.00wt.%, Ni1.00wt.%, Mo 0.25wt.%, Nb 0.15wt.%.

[0007] In some embodiments that may include the above embodiments, the high-strength and high-ductility steel material includes the following components in weight percentage: C 0.10wt.%, Si 0.80wt.%, Al 1.50wt.%, Mn 2.50wt.%, Cu 2.50wt.%, Ni2.00wt.%, Mo 0.25wt.%, and Nb 0.15wt.%.

[0008] A second aspect of the embodiment of the present application also provides a method for preparing the above-mentioned high-strength and high-plasticity steel material, comprising the following steps:

[0009] Step 1: melt each component into molten steel in a vacuum melting furnace, and then air cool to room temperature to form a steel ingot;

[0010] Step 2, keeping the steel ingot warm at a certain temperature to make the solute in the steel ingot fully homogenized;

[0011] Step 3, hot rolling the steel ingot into a steel plate, and cooling;

[0012] Step 4: performing gradient heat treatment on the steel plate to obtain a high-strength and high-plasticity steel material.

[0013] In some embodiments that may include the above embodiments, in step 2, the steel ingot is kept at a temperature of 1200° C. for 24-48 hours.

[0014] In some embodiments that may include the above embodiments, in step three, the specific conditions of hot rolling are as follows: the initial rolling temperature is 900-940° C., the final rolling temperature is 800-840° C., and the reduction amount each time is 20-40%.

[0015] In some embodiments that may include the above embodiments, in step three, the thickness of the steel plate is 8-15 mm.

[0016] In some embodiments that may include the above embodiments, in step 4, the specific process of the gradient heat treatment is: heating the steel plate to 750-820°C and keeping it warm for 15-60 minutes, and then air cooling it to room temperature; heating the steel plate to 650-720°C again and keeping it warm for 5-60 minutes, and then water cooling it to room temperature.

[0017] Specifically, the steel plate is heated to 650-720℃ again and kept warm for 5-60min, which is the optimal heat treatment temperature slightly higher than the phase transformation point Ac1 temperature. The optimal heat treatment holding time is less than 10min. Too long a holding time will lead to a decrease in steel strength. Keeping warm for less than 10min above the phase transformation Ac1 temperature can form nano-shaped reverse transformation austenite in the matrix, significantly improving the plasticity of the steel. 650-720℃ is the precipitation temperature of the Cu precipitation phase. Short-term heat preservation can obtain a large number of dispersed nano-Cu clusters in the matrix, which will increase the strength of the steel by more than 200MPa.

[0018] In some embodiments that may include the above embodiments, in step three, the cooling is performed by water cooling.

[0019] A third aspect of the embodiments of the present application also provides the application of the above-mentioned high-strength and high-plasticity steel material in automobile parts.

[0020] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0021] 1. In the gradient heat treatment, the steel plate is heated to 680°C again for a short time, so that a large number of dispersed nano-Cu clusters are generated in the steel matrix. The cluster size is between 1-5nm and is coherent with the matrix. The precipitation strengthening effect of the nano-Cu clusters provides a strong strengthening effect, strengthening the steel and improving its yield strength.

[0022] 2. In the gradient heat treatment, the steel plate is heated to 680°C again for a short time, and nano-scale reverse transformation austenite is formed at the interface of the steel matrix. In the process of stress deformation of the steel, the reverse transformation austenite can effectively absorb a large number of dislocations ejected from the interface, reduce the local stress field intensity, and thus delay the appearance of micropores, prolong the necking time, and finally improve the elongation effect of the steel. The nano-reverse transformation austenite enhances the plasticity of the steel;

[0023] 3. In the steel material of the present application, C is used to form reverse austenite and carbides; Si and Al are used to prevent austenite from decomposing during heat treatment and can be dissolved into ferrite to reduce the C content of ferrite; Mn is used to form reverse austenite; Cu forms nanoclusters during heat treatment to strengthen the matrix; Ni is used to promote the formation of reverse austenite and enhance the toughness of steel; Mo and Nb are used to form carbides and prevent the matrix from softening after heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 Figure (a) and (b) are thermal expansion curves of steel materials at different heat treatment stages in Example 1 of the present application, and Figure (c) is a gradient heat treatment process diagram of Example 1 of the present application;

[0026] Figure 2 The stress-strain curves of different heat-treated steel materials of Examples 1-3 and Comparative Example 1 of the present application;

[0027] Figure 3 The reverse transformation austenite structure morphology and structural pattern in the structure of Example 1 of the present application;

[0028] Figure 4 This is a high-resolution image photograph of the nano-Cu precipitation phase in the steel material of Example 1 of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] A first aspect of an embodiment of the present application provides a high-strength and high-plasticity steel material, the high-strength and high-plasticity steel material comprising the following components in weight percentage: C 0.05-0.10wt.%, Si 0.40-0.80wt.%, Al 0.50-1.50wt.%, Mn 2.00-2.50wt.%, Cu 2.00-2.50wt.%, Ni 1.00-2.00wt.%, Mo 0.10-0.25wt.%, Nb 0.05-0.15wt.%.

[0031] A second aspect of the embodiment of the present application also provides a method for preparing the above-mentioned high-strength and high-plasticity steel material, comprising the following steps:

[0032] Step 1: melt each component into molten steel in a vacuum melting furnace, and then air cool to room temperature to form a steel ingot;

[0033] Step 2, keeping the steel ingot at 1200° C. for 24-48 hours to make the solute of the steel ingot fully homogenized;

[0034] Step 3, hot rolling the steel ingot into a steel plate with a thickness of 8-15 mm, with an initial rolling temperature of 900-940° C., a final rolling temperature of 800-840° C., a reduction of 20-40% each time, and cooling by water cooling;

[0035] Step 4: Perform gradient heat treatment on the steel plate. First, heat the steel plate to 750-820°C and keep it for 15-60 minutes, then air-cool it to room temperature; heat the steel plate to 650-720°C again and keep it for 5-60 minutes, then water-cool it to room temperature to obtain a high-strength and high-plasticity steel material.

[0036] Specifically, the steel plate is heated to 650-720℃ again and kept warm for 5-60min, which is the optimal heat treatment temperature slightly higher than the phase transformation point Ac1 temperature. The optimal heat treatment holding time is less than 10min. Too long a holding time will lead to a decrease in steel strength. Keeping warm for less than 10min above the phase transformation Ac1 temperature can form nano-shaped reverse transformation austenite in the matrix, significantly improving the plasticity of the steel. 650-720℃ is the precipitation temperature of the Cu precipitation phase. Short-term heat preservation can obtain a large number of dispersed nano-Cu clusters in the matrix, which will increase the strength of the steel by more than 200MPa.

[0037] A third aspect of the embodiments of the present application also provides the application of the above-mentioned high-strength and high-plasticity steel material in automobile parts.

[0038] Unless otherwise specified, the experimental methods used in the examples of this application are all conventional methods.

[0039] In the following examples and comparative examples, unless otherwise specified, all raw materials can be obtained by commercial purchase or conventional methods.

[0040] Example 1

[0041] A first aspect of an embodiment of the present application provides a high-strength and high-plasticity steel material, the high-strength and high-plasticity steel material comprising the following components in weight percentage: C 0.05-0.10wt.%, Si 0.40-0.80wt.%, Al 0.50-1.50wt.%, Mn 2.00-2.50wt.%, Cu 2.00-2.50wt.%, Ni 1.00-2.00wt.%, Mo 0.10-0.25wt.%, Nb 0.05-0.15wt.%.

[0042] A second aspect of the embodiment of the present application also provides a method for preparing the above-mentioned high-strength and high-plasticity steel material, comprising the following steps:

[0043] Step 1: melt each component into molten steel in a vacuum melting furnace, and then air cool to room temperature to form a steel ingot;

[0044] Step 2: Keep the steel ingot at 1200°C for 24-48 hours to make the solute of the steel ingot fully homogenized;

[0045] Step 3, hot rolling the steel ingot into a steel plate with a thickness of 8-15 mm, with an initial rolling temperature of 900-940° C., a final rolling temperature of 800-840° C., a reduction of 20-40% each time, and cooling by water cooling;

[0046] Step 4: Perform gradient heat treatment on the steel plate. First, heat the steel plate to 780°C and keep it warm for 30 minutes. The steel plate that has undergone the first heat treatment is recorded as S-30min, and then air-cooled to room temperature; heat the steel plate to 680°C again and keep it warm for 5 minutes, and then water-cooled to room temperature to obtain a high-strength and high-plasticity steel material. The steel plate that has undergone the second heat treatment is recorded as S-30min+5min.

[0047] Example 2

[0048] The high-strength and high-plasticity steel material and the preparation method thereof provided in this embodiment can refer to Example 1, except that, in step 4, the steel plate is subjected to a gradient heat treatment, firstly, the steel plate is heated to 780°C and kept warm for 30 minutes, and then air-cooled to room temperature; the steel plate is heated to 680°C again and kept warm for 15 minutes, and then water-cooled to room temperature, to obtain a high-strength and high-plasticity steel material. The steel plate subjected to the second heat treatment is recorded as S-30min+15min.

[0049] Example 3

[0050] The high-strength and high-plasticity steel material and the preparation method thereof provided in this embodiment can refer to Example 1, except that, in step 4, the steel plate is subjected to a gradient heat treatment, firstly, the steel plate is heated to 780°C and kept warm for 30 minutes, and then air-cooled to room temperature; the steel plate is heated to 680°C again and kept warm for 60 minutes, and then water-cooled to room temperature, to obtain a high-strength and high-plasticity steel material. The steel plate subjected to the second heat treatment is recorded as S-30min+60min.

[0051] Comparative Example 1

[0052] A first aspect of an embodiment of the present application provides a high-strength and high-plasticity steel material, the high-strength and high-plasticity steel material comprising the following components in weight percentage: C 0.05-0.10wt.%, Si 0.40-0.80wt.%, Al 0.50-1.50wt.%, Mn 2.00-2.50wt.%, Cu 2.00-2.50wt.%, Ni 1.00-2.00wt.%, Mo 0.10-0.25wt.%, Nb 0.05-0.15wt.%.

[0053] A second aspect of the embodiment of the present application also provides a method for preparing the above-mentioned high-strength and high-plasticity steel material, comprising the following steps:

[0054] Step 1: melt each component into molten steel in a vacuum melting furnace, and then air cool to room temperature to form a steel ingot;

[0055] Step 2, keeping the steel ingot at 1200° C. for 24-48 hours to make the solute of the steel ingot fully homogenized;

[0056] Step 3, hot rolling the steel ingot into a steel plate with a thickness of 8-15 mm, with an initial rolling temperature of 900-940° C., a final rolling temperature of 800-840° C., a reduction of 20-40% each time, and cooling by water cooling;

[0057] Step 4: heat-treat the steel plate by heating the steel plate to 780°C and keeping the temperature for 30 minutes. The heat-treated steel plate is recorded as S-30min, and then air-cooled to room temperature.

[0058] Application Examples

[0059] like Figure 1 As shown, Figure 1 (a) is the thermal expansion curve of the initial rolled plate, which determines that the two-phase region temperatures of the steel plate before gradient heat treatment are 690℃ and 943℃ respectively. Figure 1 (b) is the thermal expansion curve of the steel after the initial rolled plate was water-cooled at 780℃ for half an hour. After this heat treatment, the temperature of the two-phase region of the steel slightly expanded, and the new two-phase region temperature was determined to be between 675℃ and 948℃. Therefore, if Figure 1 (c) The second step heat treatment temperature of the gradient heat treatment is selected to be 680°C, which is slightly higher than 675°C.

[0060] Figure 2 The mechanical property curve in (a) shows that after the second heat treatment, the yield strength of the steel material increased significantly after only a short heat preservation time of 5 minutes. It increased rapidly from 758MPa to 984MPa, an increase of 226MPa ( Figure 2(b)). At the same time, the uniform elongation of S-30min+5min steel reaches 9.56%, which is 83% higher than that of S-30min steel ( Figure 2 (b)). Therefore, the strength and plasticity of S-30min+5min are greatly improved after 5min of heat preservation at 680℃. This effect of improving the overall performance of steel is very significant. As the second step of heat preservation time increases, the yield strength of steel gradually decreases ( Figure 2 (b)). Compare three types of steel: S-30min+5min, S-30min+15min, and S-30min+60min. S-30min+5min steel has achieved outstanding performance improvement. Its yield strength reaches 984MPa, tensile strength reaches 1013MPa, uniform elongation reaches 9.56%, and total elongation reaches 22.5%. S-30min+5min steel has the advantages of high strength and high plasticity, and its heat treatment process is simple, which is convenient for large-scale heat treatment production of steel.

[0061] like Figure 3 As shown in the figure, it can be clearly found that there is nano-reversed austenite in the steel. Reversed austenite can absorb dislocations and transform into martensite during the stress deformation process of the steel. This process reduces the local elastic stress storage energy, delays the nucleation of micropores, and postpones the appearance of necking, thereby improving the uniform elongation of the steel.

[0062] like Figure 4 As shown in the figure, a large number of nano-scale Cu cluster particles with a size between 1-5nm can be clearly seen. These large numbers of dispersed and precipitated nano Cu clusters significantly increase the yield strength of the steel. This is the fundamental reason why the yield strength of S-30min+5min steel can be increased by 226MPa after only 5 minutes of heat preservation.

[0063] In summary, by selecting the type and composition of alloy and using appropriate heat treatment process, the goal of simultaneously improving the strength and plasticity of steel can be achieved.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-strength and high-plasticity steel material, characterized in that: The high-strength and high-plasticity steel material includes the following components in weight percentage: C 0.05-0.10wt.%, Si 0.40-0.80wt.%, Al 0.50-1.50wt.%, Mn 2.00-2.50wt.%, Cu2.00-2.50wt.%, Ni 1.00-2.00wt.%, Mo 0.10-0.25wt.%, and Nb 0.05-0.15wt.%.

2. The high-strength and high-plasticity steel material according to claim 1, characterized in that: The high-strength and high-ductility steel material includes the following components in weight percentage: C 0.05wt.%, Si 0.40wt.%, Al 0.50wt.%, Mn 2.00wt.%, Cu2.00wt.%, Ni 1.00wt.%, Mo 0.25wt.%, and Nb 0.15wt.%.

3. The high-strength and high-plasticity steel material according to claim 1, characterized in that: The high-strength and high-ductility steel material includes the following components in weight percentage: C 0.10wt.%, Si 0.80wt.%, Al 1.50wt.%, Mn 2.50wt.%, Cu2.50wt.%, Ni 2.00wt.%, Mo 0.25wt.%, and Nb 0.15wt.%.

4. A method for preparing a high-strength and high-plasticity steel material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: melt each component into molten steel in a vacuum melting furnace, and then air cool to room temperature to form a steel ingot; Step 2, keeping the steel ingot warm at a certain temperature to make the solute in the steel ingot fully homogenized; Step 3, hot rolling the steel ingot into a steel plate, and cooling; Step 4: performing gradient heat treatment on the steel plate to obtain a high-strength and high-plasticity steel material.

5. The method for preparing a high-strength and high-plasticity steel material according to claim 4, characterized in that: In step 2, the steel ingot is kept at 1200° C. for 24-48 hours.

6. The method for preparing a high-strength and high-plasticity steel material according to claim 4, characterized in that: In step 3, the specific conditions of hot rolling are as follows: the initial rolling temperature is 900-940° C., the final rolling temperature is 800-840° C., and the reduction amount each time is 20-40%.

7. The method for preparing a high-strength and high-plasticity steel material according to claim 4, characterized in that: In step three, the thickness of the steel plate is 8-15 mm.

8. The method for preparing a high-strength and high-plasticity steel material according to claim 4, characterized in that: In step 4, the specific process of the gradient heat treatment is: heating the steel plate to 750-820°C and keeping it warm for 15-60 minutes, then air cooling it to room temperature; heating the steel plate to 650-720°C again and keeping it warm for 5-60 minutes, then water cooling it to room temperature.

9. The method for preparing a high-strength and high-plasticity steel material according to claim 4, characterized in that: In step three, the cooling is performed by water cooling.

10. Application of the high-strength and high-plasticity steel material according to any one of claims 1 to 3 in automobile parts.

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