A 27SiMn steel and a heat treatment production method after forging

Abstract

The present invention discloses a 27SiMn steel and a heat treatment production method after forging. The 27SiMn steel contains, by weight percentage: 0.24% - 0.32% C, 1.10% - 1.40% Si, 1.10% - 1.40% Mn, 0.030% - 0.035% P, 0.03% - 0.035% S, 0.02% - 0.05% Cu, 0.02% - 0.05% Cr, 0.02% - 0.05% Ni, and the balance is Fe. The heat treatment method includes: (1) forging blank: smelting according to the composition of 27SiMn steel and casting into an ingot, and forging the ingot into a forging blank; (2) quenching: air-cooling the forging blank to 900 - 950 °C and then performing quenching; (3) tempering: air-cooling the forging blank to room temperature. The 27SiMn steel of the present invention has the characteristics of high hardenability, good machinability and excellent processing performance after direct heat treatment after forging.

Description

Technical Field

[0001] The present invention relates to the technical field of steel manufacturing, and particularly to a 27SiMn steel and a heat treatment production method after forging. Background Art

[0002] The 27SiMn steel has relatively high hardenability, with a critical hardening diameter in water reaching 8 - 22 mm, good machinability and excellent processing performance, and is widely used in coal machinery, geological drilling, oil drilling, automotive half shafts, ships, etc.

[0003] Currently, the traditional reheating quenching process is generally adopted for producing 27SiMn steel at home and abroad. When using this process, the workpiece has serious oxidation and decarburization, large workpiece deformation, many processes, a long manufacturing cycle, and high costs. Compared with this, the quenching process after forging omits the reheating process of the workpiece, simplifies the process flow, reduces the production cost, and improves the utilization rate of on-line heat treatment equipment. However, compared with quenching and reheating quenching, the following problems are likely to occur: the surface hardness of the workpiece is slightly lower; the amount of retained austenite in the carburized layer is large; the surface grains are coarse.

[0004] Therefore, the present invention is specifically proposed to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a 27SiMn steel, which contains by weight percentage: 0.24% - 0.32% C, 1.10% - 1.40% Si, 1.10% - 1.40% Mn, 0.030% - 0.035% P, 0.03% - 0.035% S, 0.02% - 0.05% Cu, 0.02% - 0.05% Cr, 0.02% - 0.05% Ni, and the balance is Fe;

[0006] Preferably, the components of the 27SiMn steel are: 0.24% - 0.32% C, 1.10% - 1.40% Si, 1.10% - 1.40% Mn, 0.030% - 0.035% P, 0.035% S, 0.03% Cu, 0.03% Cr, 0.03% Ni, and the balance is Fe;

[0007] Preferably, the components of the 27SiMn steel are 0.32% C, 1.10% Si, 1.10% Mn, 0.035% P, 0.035% S, 0.03% Cu, 0.03% Cr, 0.03% Ni, and the balance is Fe.

[0008] The present invention also provides a heat treatment production method for the 27SiMn steel after forging, and the heat treatment method includes the following steps:

[0009] (1)Forged blank: Smelted and cast into an ingot according to the composition of 27SiMn steel, and the ingot was forged into a forged blank;

[0010] (2)Quenching: The forged blank was air-cooled to 900 - 950 °C and then quenched;

[0011] (3)Tempering: The forged blank was air-cooled to room temperature.

[0012] Preferably, in step (1), the ingot was forged into a forged blank at 1200 - 1250 °C.

[0013] Preferably, after quenching, the forged blank was oil-cooled to 600 - 650 °C at a cooling rate of 10 - 15 °C / s, then water-cooled to 350 - 400 °C, and then oil-cooled to room temperature.

[0014] Preferably, the water-cooling quenching liquid is brine, and the oil-cooling quenching liquid is mineral oil.

[0015] Preferably, the water-cooling rate is controlled at 40 - 50 °C / s.

[0016] Preferably, the oil-cooling rate in step (2) is 10 - 15 °C / s.

[0017] Preferably, the forged blank was held at 570 - 630 °C for 2 - 3 h and then air-cooled to room temperature.

[0018] The beneficial effects of the present invention are:

[0019] Compared with the traditional re-heating quenching process, the quenching process after forging in the present invention omits the re-heating process of the forged blank, simplifies the process flow, reduces the production cost, and improves the utilization rate of on-line heat treatment equipment. In addition, oil-cooling and water-cooling are used for segmented treatment during quenching, with a slow oil-cooling speed and a fast water-cooling speed.

[0020] In the present invention, oil-cooling to 600 - 650 °C first is to avoid excessive cooling speed and generate huge quenching stress; the region between 350 - 650 °C is the most unstable region of supercooled austenite, so water-cooling is carried out; below 350 °C is the martensite transformation region, and oil-cooling is carried out to reduce the tissue stress generated during martensite transformation. The tempering temperature is set at 570 - 630 °C, which is high-temperature tempering, and can improve the problems of low plasticity and low toughness caused by forging.

[0021] The present invention uses quenching after forging to obtain fine acicular martensite + a small amount of ferrite, and tempering treatment can precipitate carbides to obtain fine tempered sorbite + a small amount of ferrite, reducing internal stress and increasing the toughness of the material, and finally obtaining 27SiMn steel with good comprehensive mechanical properties. Brief Description of the Drawings

[0022] Figure 1This is the quenched metallographic structure diagram of a 27SiMn steel of the present invention;

[0023] Figure 2 This is the tempered metallographic structure diagram of a 27SiMn steel of the present invention. Specific embodiments

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present invention.

[0025] A 27SiMn steel of the present invention has components of C, Si, Mn, P, S, Cu, Cr, Ni, and Fe, and the weight percentages are shown in Table 1 as follows:

[0026] Table 1

[0027]

[0028]

[0029] An embodiment of the present invention is: directly performing heat treatment on the 27SiMn steel after forging, and the heat treatment method includes the following steps:

[0030] (1) Forged billet: According to the composition of 27SiMn steel, smelt and pour it into an ingot, and forge the ingot into a forged billet;

[0031] (2) Quenching: Air-cool the forged billet to 900 - 950 °C and then perform quenching;

[0032] (3) Tempering: Air-cool the forged billet to room temperature.

[0033] Another embodiment of the present invention: Forge the poured ingot into a forged billet at 1200 - 1250 °C.

[0034] Another embodiment of the present invention: After quenching the forged billet, oil-cool it to 600 - 650 °C, with a cooling rate of 10 - 15 °C / s, then water-cool it to 350 - 400 °C, and then oil-cool it to room temperature.

[0035] Among them, the water-cooling quenching liquid is brine, the oil-cooling quenching liquid is mineral oil, the water-cooling rate is controlled at 40 - 50 °C / s, and the oil-cooling rate is 10 - 15 °C / s.

[0036] Another embodiment of the present invention: During the tempering process, the forged billet is held at 570 - 630 °C for 2 - 3 h and then air-cooled to room temperature.

[0037] Tensile tests and impact tests were carried out on the 100-mm-thick steel material obtained by the heat treatment method of directly performing heat treatment on 27SiMn steel after forging according to the above embodiments, and mechanical property tests were conducted. As shown in Table 2:

[0038] Table 2

[0039]

[0040]

[0041]

[0042] The present invention utilizes quenching after forging to obtain fine acicular martensite + a small amount of ferrite. Tempering treatment can precipitate carbides to obtain fine tempered sorbite + a small amount of ferrite, reduce internal stress, increase the toughness of the material, and finally obtain 27SiMn steel with good comprehensive mechanical properties. Among them, the best comprehensive performance is obtained with the composition of 0.32% C, 1.10% Si, 1.10% Mn, 0.035% P, 0.035% S, 0.03% Cu, 0.03% Cr, 0.03% Ni, and the balance being Fe. Figure 1 and Figure 2 are the quenching and tempering metallographic structures of the steel obtained from this composition.

[0043] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A heat treatment production method for 27SiMn steel after forging, characterized in that: The following steps are involved: (1) Forging billet: According to the composition of 27SiMn steel, it is smelted and cast into an ingot, and the ingot is forged into a forging billet; (2) Quenching: The forging blank is air-cooled to 900-950°C and then quenched. It is first oil-cooled to 600-650°C at a cooling rate of 10-15°C / s, then water-cooled to 350-400°C at a cooling rate of 40-50°C / s, and then oil-cooled to room temperature at a cooling rate of 10-15°C / s. (3) Tempering: The forging blank is kept at 570-630°C for 2-3 hours and then air-cooled to room temperature.

2. The heat treatment production method for 27SiMn steel after forging according to claim 1 is characterized in that: The ingot in step (1) is forged into a forging blank at 1200-1250°C.

3. The heat treatment production method for 27SiMn steel after forging according to claim 1 is characterized in that: The water-cooled quenching liquid is salt water, and the oil-cooled quenching liquid is mineral oil.

4. A 27SiMn steel produced by the heat treatment method according to any one of claims 1 to 3, characterized in that: By weight percentage, it contains: 0.24%~0.32% C, 1.10%~1.40% Si, 1.10%~1.40% Mn, 0.03%~0.035%P, 0.03%~0.035%S, 0.02%~0.05%Cu, 0.02%~0.05%Cr, 0.02%~0.05%Ni, and the balance is Fe.

5. The 27SiMn steel composition according to claim 4 is: 0.24%-0.32% C, 1.10%-1.40% Si, 1.10%-1.40% Mn, 0.030%-0.035% P, 0.035% S, 0.03% Cu, 0.03% Cr, 0.03% Ni, and the balance is Fe.

6. The 27SiMn steel according to claim 5 has a composition of 0.32% C, 1.10% Si, 1.10% Mn, 0.035% P, 0.035% S, 0.03% Cu, 0.03% Cr, 0.03% Ni, and the balance is Fe.

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