Steel billet raw material, forming method of steel billet and forming method of quenching-free high-toughness steel

Abstract

The invention discloses a quenching-free high-toughness steel billet raw material containing carbon, silicon, manganese and other elements, a relatively soft steel billet can be obtained by controlling the cooling speed of the steel billet refined by the quenching-free high-toughness steel billet raw material so as to facilitate plastic processing, finally, the steel billet only needs to be heated to Ac3 line or above and then is subjected to air cooling, and the air cooling speed is controlled, so that the high-toughness steel can be obtained. And annealing and tempering processes are omitted. The method has the remarkable effects that the use of expensive colored elements is reduced, and the production cost is favorably reduced; the quenching process of steel is omitted, but high tensile strength can still be achieved, the process is simplified, and energy consumption is reduced.

Description

Technical Field

[0001] The invention relates to a steel material, in particular to a quench-free high-strength and toughness steel material. Background Art

[0002] When using traditional methods to prepare high-strength and tough martensitic steel with a strength level of 1500MPa (1.5GPa), it can be achieved by adding more alloying elements or performing water quenching and rapid cooling during the heat treatment process. The water quenching and rapid cooling process is more widely used. This process requires the steel billet to be plastically processed, then heated to above the Ac3 temperature to achieve austenitization, and then quickly quenched (generally water quenching, cooling rate greater than 2000℃ / min), and finally tempered at 200℃ for more than half an hour. However, the heat treatment process route for preparing high-strength and tough martensitic steel using quenching technology is relatively complicated, especially the quenching process will produce very large quenching stress, which will cause the steel billet to deform; and this type of steel billet is more prone to corrosion problems after contacting water; at the same time, the quenching process also requires the configuration of corresponding equipment and consumes additional energy.

[0003] However, increasing the tensile strength of steel by adding more and richer alloy elements will undoubtedly significantly increase costs and have poor economic efficiency.

[0004] Therefore, we urgently need a high-strength and tough steel and a forming process with a reasonable alloy element content and that can be exempted from the water quenching step. Summary of the invention

[0005] In order to solve the above technical problems, one of the purposes of the present invention is to provide a quench-free high-strength and tough steel billet raw material, the main points of which are:

[0006] In terms of weight percentage, the steel billet raw material contains:

[0007] C: 0.19%-0.21%, Si: 0.48%-0.52%, Mn: 3.9%-4.1%, P: ≤0.01%, S: ≤0.01%, Al: ≤0.04%, Cr: 0.1%-0.2%, Mo: 0.02%-0.05%, Ti: 0.01%-0.03%, Nb: 0.03%-0.04%, V: 0.02%-0.03%, Cu: 0.1%-0.2%, B: 0.0015%-0.002%, N: 0.01%-0.015%, and the balance of Fe.

[0008] The second object of the present invention is to provide a method for forming a steel billet, the key of which is to carry out the following steps:

[0009] Step 1.1, refining molten steel according to the above steel billet raw materials;

[0010] Step 1.2, casting the molten steel to make a steel billet, and controlling the cooling rate of the steel billet to be less than 100°C / min.

[0011] The third object of the present invention is to provide a method for forming quench-free high-strength and tough steel, the key of which is to follow the following steps:

[0012] Step 2.1, forming a steel billet according to the above method;

[0013] Step 2.2, heat the steel billet to above the Ac3 line, and then cool it in air, controlling the cooling rate to 900-1100°C / min, to obtain high-strength and tough steel that does not require quenching.

[0014] The Ac3 line refers to the temperature at which ferrite completely transforms into austenite when the steel is heated. This line is located above the Ac1 line in the phase diagram and marks the final temperature at which all ferrite in the hypoeutectoid steel transforms into austenite.

[0015] Ac1 line refers to the temperature at which pearlite completely transforms into austenite when steel is heated, also known as the eutectoid line. It is an important reference line in the iron-carbon alloy phase diagram, representing the starting temperature of austenite formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a SEM image of the high-strength and toughness steel of the present invention;

[0017] Figure 2 EBSD diagram of the high-strength and toughness steel of the present invention;

[0018] Figure 3 TEM image of the high-strength and toughness steel of the present invention;

[0019] Figure 4 is a tensile curve diagram of the high-strength and toughness steel of the present invention;

[0020] Figure 5 It is the CCT curve diagram of the high strength and toughness steel of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with embodiments and drawings.

[0022] Embodiment 1-3:

[0023] A quench-free high-strength and tough steel billet raw material, in terms of weight percentage, the elements contained in the billet raw material are shown in Table 1:

[0024] Table 1. Weight percentage of elements in steel billet raw materials of Examples 1-3

[0025] element Example 1 Example 2 Example 3 C 0.19％ 0.21％ 0.19％ Si 0.48％ 0.52％ 0.51％ Mn 4.1％ 3.9％ 4.05％ P 0.01％ 0.01％ 0.008％ S 0.01％ 0.01％ 0.01％ Al 0.04％ 0.04％ 0.031％ Cr 0.1％ 0.2％ 0.15％ Mo 0.02％ 0.05％ 0.03％ Ti 0.03％ 0.01％ 0.02％ Nb 0.04％ 0.03％ 0.035％ V 0.03％ 0.032％ 0.025％ Cu 0.1％ 0.2％ 0.15％ B 0.0015％ 0.002％ 0.0016％ N 0.01％ 0.015％ 0.011％ Fe margin margin margin

[0026] Embodiment 4:

[0027] A method for forming a steel billet is carried out according to the following steps:

[0028] Step 1.1, refining molten steel using the steel billet raw material described in Example 3;

[0029] Step 1.2, casting the molten steel to make a steel billet, and controlling the cooling rate of the steel billet to be less than 100°C / min;

[0030] According to the requirements, the steel billet in step 1.2 can be a steel plate, a steel coil or a steel ingot.

[0031] Embodiment 5:

[0032] A method for forming quench-free high-strength and tough steel is carried out according to the following steps:

[0033] Step 2.1, manufacturing a steel billet according to the method of Example 4;

[0034] Step 2.2, heat the steel billet to above the Ac3 line, and then cool it in air, controlling the cooling rate to 900-1100°C / min, to obtain high-strength and tough steel that does not require quenching.

[0035] In step 2.2, the steel billet may be subjected to plastic processing, and there are two specific plastic processing methods.

[0036] The first method is: pre-plastic processing the steel billet to obtain a target product billet, then heating the target product billet to above the Ac3 line for 5-30 minutes, and finally air cooling.

[0037] The second method is: heating the steel billet to above the Ac3 line and maintaining it for 5-30 minutes, performing plastic processing during this period to obtain a target product billet, and then placing the target product billet in the air for cooling.

[0038] When high-strength and toughness steel is applied to automobile parts, the steel billet is preferably a steel coil, and the target product billet is an automobile part such as an automobile suspension.

[0039] The high-strength and tough steel obtained in step 2.2 of Example 5 was analyzed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Figure 1 , 2 , 3. From Figure 1 , 2 , 3 It can be seen that the corresponding high-strength and toughness steel has a uniform structure, mainly martensite structure.

[0040] The high-strength and tough steel obtained in step 2.2 of Example 5 was subjected to mechanical tensile tests (3 times), and the tensile curves obtained are shown in FIG. Figure 4 .from Figure 4 It can be seen that the tensile results of the corresponding high-strength and toughness steel after multiple (3 times) tensile tests are consistent, with the tensile strength reaching more than 1500 MPa and the elongation reaching about 8%.

[0041] Using JmatPro software, the composition of the high-strength and tough steel obtained in step 2.2 of Example 5 was simulated to obtain the CCT curve. The results are shown in Figure 5 .from Figure 5 It can be seen that the steel with this alloy composition is very close to the bainite phase line at a cooling rate of 1000℃ / min. Therefore, it is believed that when the steel plate after forging or rolling is naturally cooled in the air at a rate of about 1000℃ / min, the calculation results can be used to determine that a high-strength martensitic structure can be obtained.

[0042] Embodiment 6:

[0043] A galvanizing process for steel is carried out according to the following steps: the steel is immersed in a zinc solution at 500-600°C for 5 minutes for hot-dip galvanizing to improve the corrosion resistance of the steel.

[0044] The high-strength and tough steel obtained in step 2.2 of Example 5 and the quenched 22MnB5 carbon steel were respectively subjected to hot-dip galvanizing; the tensile strength of the two after hot-dip galvanizing was tested, and the results showed that:

[0045] The high-strength and tough steel obtained in step 2.2 of Example 5 has a tensile strength of >1350 MPa after hot-dip galvanizing, and the decomposition degree of the martensite structure is relatively small;

[0046] However, after hot-dip galvanizing, the tensile strength of quenched 22MnB5 carbon steel is less than 1000MPa; the degree of decomposition of the martensitic structure is relatively large.

[0047] Embodiment 7:

[0048] A method for forming an automobile suspension is carried out according to the following steps:

[0049] First, a steel billet is manufactured according to the method of Example 4. The steel billet is a steel coil obtained by continuous casting and rolling. The cooling rate of the steel coil is controlled to be less than 100° C. / min. The tensile strength of the steel coil is detected to be about 600 MPa.

[0050] Secondly, the steel coils are processed into pipes, thin plates, sheet metal parts and other parts corresponding to the automobile suspension and welded;

[0051] Finally, the welded automobile suspension is heated to above the Ac3 line and maintained for 10 minutes, and then placed in the air for cooling, and the cooling rate during cooling is controlled to be 950-1050℃ / min, so as to obtain a high-strength and tough automobile suspension that does not require quenching.

[0052] Beneficial effects: The solution of the present invention has the following effects:

[0053] ①. Except for C, Mn and Si, the total amount of other trace alloying elements in steel is ≤0.3%, avoiding adding too many alloying elements, especially reducing the use of expensive non-ferrous elements, which helps to reduce production costs;

[0054] ② The quenching process of steel is eliminated, but its tensile strength can still reach 1500MPa, which simplifies the process and reduces energy consumption;

[0055] ③. The material can be formed in a relatively soft state, which reduces the difficulty of processing;

[0056] ④. Multiple parts can be heat treated at the same time with good consistency;

[0057] ⑤. The carbon equivalent is relatively low, which can improve welding performance;

[0058] ⑥Hot-dip galvanizing will not significantly reduce the tensile strength of steel after heat treatment.

[0059] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Under the guidance of the present invention, ordinary technicians in this field can make various similar expressions without violating the purpose and claims of the present invention, and such changes all fall within the scope of protection of the present invention.

Claims

1. A quench-free high-strength and tough steel billet raw material, characterized in that: In terms of weight percentage, the steel billet raw material contains: C: 0.19%-0.21%, Si: 0.48%-0.52%, Mn: 3.9%-4.1%, P: ≤0.01%, S: ≤0.01%, Al: ≤0.04%, Cr: 0.1%-0.2%, Mo: 0.02%-0.05%, Ti: 0.01%-0.03%, Nb: 0.03%-0.04%, V: 0.02%-0.03%, Cu: 0.1%-0.2%, B: 0.0015%-0.002%, N: 0.01%-0.015%, and the balance of Fe.

2. The quench-free high-strength and tough steel billet raw material according to claim 1, characterized in that: In the step 1, the steel billet raw material contains, by weight percentage: C: 0.19%, Si: 0.51%, Mn: 4.05%, P: ≤0.01%, S: ≤0.01%, Al: ≤0.04%, Cr: 0.15%, Mo: 0.03%, Ti: 0.02%, Nb: 0.035%, V: 0.025%, Cu: 0.15%, B: 0.0016%, N: 0.011%, and the balance of Fe.

3. A method for forming a steel billet, characterized in that Follow these steps: Step 1.1, refining molten steel using the steel billet raw material according to any one of claims 1 or 2; Step 1.2, casting the molten steel to make a steel billet, and controlling the cooling rate of the steel billet to be less than 100°C / min.

4. A method for forming a steel billet according to claim 3, characterized in that: In the step 1.2, the steel billet is a steel ingot, a steel plate or a steel coil.

5. A method for forming non-quenching high-strength and tough steel, characterized in that Follow these steps: Step 2.1, forming a steel billet according to the method of claim 3 or 4; Step 2.2, heat the steel billet to above the Ac3 line, and then cool it in air, controlling the cooling rate to 900-1100°C / min, to obtain high-strength and tough steel that does not require quenching.

6. The method for forming a quench-free high-strength and tough steel according to claim 5, characterized in that: In the step 2.2, the steel billet is pre-plastic processed to obtain a target product billet, and then the target product billet is heated to above the Ac3 line, and finally air-cooled.

7. The method for forming a quench-free high-strength and tough steel according to claim 5, characterized in that: In the step 2.2, the steel billet is heated to above the Ac3 line and plastically processed to obtain a target product billet, and then the target product billet is air-cooled.

8. The method for forming a quench-free high-strength and tough steel according to claim 6, characterized in that: In the step 2.2, the steel billet is a steel coil, and the target product billet is an automobile part.

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