Heat treatment process of 70 # spring steel

Abstract

The invention discloses a heat treatment process of 70 # spring steel, which comprises the following steps: (1) quenching: putting a spring steel blank sample subjected to rough machining into a heating furnace, heating to 810-850 DEG C, preserving heat for 58-62 minutes, then quenching, and cooling in oil; and (2) tempering: putting the quenched sample into a heating furnace, heating to 460-500 DEG C, preserving heat for 150 + / -5 minutes, then taking out the sample, and cooling in air. The yield strength (larger than or equal to 900 MPa) and the tensile strength (larger than or equal to 1100 MPa) can be remarkably improved through the higher carbon content in the 70 # spring steel and the optimized heat treatment process, and therefore the service life of the steel in the high-stress environment is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of spring steel manufacturing, and in particular relates to a heat treatment process for 70# spring steel. Background Art

[0002] Heat treatment can change the crystal structure and organizational state of steel, thereby adjusting its mechanical properties, such as hardness, strength, toughness, etc. A reasonable heat treatment system can enable spring steel to achieve the required mechanical performance indicators, ensure that the spring can withstand the expected load during operation, and maintain stable performance. The spring will be frequently loaded and unloaded during use, so it needs to have good fatigue resistance and be able to maintain elasticity for a long time. Through a suitable heat treatment system, the fatigue resistance of spring steel can be improved and its service life can be extended. Therefore, it is particularly important to formulate a suitable heat treatment process to ensure that the spring steel has good performance. By studying the phase transition point of 70# spring steel, it is found that the quenching heat treatment temperature of spring steel should be controlled at 810℃~850℃. Selecting oil with a lower cooling rate as the quenching medium can obtain high strength. The tempering temperature should be controlled at 460~500℃.

[0003] Compared with 65# spring steel, the carbon content of 70# spring steel is higher than that of 65# spring steel, generally in the range of 0.68%-0.75%. This will directly affect the hardness and strength of the steel. Due to the increase in carbon content, the temperature range of quenching and tempering needs to be appropriately changed. It is recommended to set the quenching temperature between 810℃ and 850℃, and the tempering temperature between 460 and 500℃ to ensure sufficient hardening and tempering effects. Due to changes in material composition and organizational structure, the holding time has also been appropriately changed, increasing the quenching holding time from 50min to 60min, and the tempering holding time from 120min to 150min to optimize the mechanical properties. Summary of the invention

[0004] The purpose of the present invention is to provide a heat treatment process for 70# spring steel, so that it has good comprehensive mechanical properties, thereby significantly improving the overall life and safety of the spring steel.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention discloses a heat treatment process for 70# spring steel, comprising:

[0007] (1) Quenching: Place the rough-machined spring steel blank sample in a heating furnace, heat it to 810℃~850℃, keep it warm for 58-62min, then quench it and cool it in oil;

[0008] (2) Tempering: Place the quenched sample into a heating furnace, heat it to 460-500°C, keep it warm for 150±5min, then take out the sample and cool it in air.

[0009] Furthermore, during the quenching process, the temperature is kept at room temperature for 60 minutes.

[0010] Furthermore, in the tempering process, the temperature is kept at room temperature for 150 minutes.

[0011] Furthermore, the rough-machined spring steel blank sample was placed in a heating furnace, heated to 810°C, kept warm for 60 minutes, then quenched and cooled in oil; the quenched sample was placed in a heating furnace, heated to 460°C, kept warm for 150 minutes, and then the sample was taken out and cooled in air.

[0012] Furthermore, the rough-machined spring steel blank sample was placed in a heating furnace, heated to 850°C, kept warm for 60 min, then quenched and cooled in oil; the quenched sample was placed in a heating furnace, heated to 500°C, kept warm for 150 min, then the sample was taken out and cooled in air.

[0013] Furthermore, the rough-machined spring steel blank sample was placed in a heating furnace, heated to 830°C, kept warm for 60 minutes, then quenched and cooled in oil; the quenched sample was placed in a heating furnace, heated to 480°C, kept warm for 150 minutes, and then the sample was taken out and cooled in air.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are:

[0015] 1. The higher carbon content and optimized heat treatment process in 70# spring steel can significantly improve the yield strength (satisfying ≥900MPa) and tensile strength (satisfying ≥1100MPa), thereby increasing the service life of the steel in high stress environments.

[0016] The optimized quenching and tempering temperatures can increase the material hardness to ≥220HV, while also having higher fatigue strength to adapt to harsh working environments.

[0017] Through more precise control of temperature and holding time in the heat treatment process, the grain structure of the steel is made more stable and the corrosion resistance is significantly improved. DETAILED DESCRIPTION

[0018] The heat treatment process of the spring steel of the present invention is further described in detail below.

[0019] The steel part in the heat treatment process of the present invention is 70# spring steel, and is carried out according to the following steps:

[0020] (1) Quenching: Place the rough-machined spring steel blank sample in a heating furnace, heat it to 810℃~850℃, keep it warm for 60min, then quench it and cool it in oil;

[0021] (2) Tempering: Place the quenched sample in a heating furnace, heat to 460-500°C, keep warm for 150 minutes, then take out the sample and cool it in air.

[0022] After the heat treatment, the rough-machined blank samples were fine-machined and various performance tests were performed. The test results are shown in Tables 1, 2 and 3. It can be seen from Tables 1, 2 and 3 that all performance indicators are higher than the index requirements, and the performance of the samples after heat treatment is qualified. Compared with the comparative example 65# steel, the mechanical properties, especially the strength and hardness, have been significantly improved.

[0023] Table 1 Chemical composition of spring steel examples (mass percentage / %)

[0024]

[0025]

[0026] Table 2 Mechanical properties at room temperature after heat treatment

[0027]

[0028] Table 3 Vickers hardness after heat treatment

[0029]

[0030] The heat treatment process of the spring steel of the present invention determines a set of heat treatment systems that can ensure the stable performance of the steel by studying the heat treatment heating system, including the influence of quenching temperature, tempering temperature and holding time on the structure and performance; on the premise of ensuring the structure and performance after heat treatment, the heating temperature range is narrowed, the holding time is reduced, the energy consumption of the heat treatment is reduced, and the efficiency of the heat treatment is improved.

[0031] Embodiment 1:

[0032] The steel part in the heat treatment process of the present invention is 70# spring steel, and is carried out according to the following steps:

[0033] (1) Quenching: Place the rough-machined spring steel blank sample in a heating furnace, heat it to 810°C, keep it at that temperature for 60 minutes, then quench it and cool it in oil;

[0034] (2) Tempering: Place the quenched sample in a heating furnace, heat to 460°C, keep warm for 150 minutes, then take out the sample and cool it in air.

[0035] Embodiment 2:

[0036] The steel part in the heat treatment process of the present invention is 70# spring steel, and is carried out according to the following steps:

[0037] (1) Quenching: Place the rough-machined spring steel blank sample in a heating furnace, heat it to 850°C, keep it warm for 60 minutes, then quench it and cool it in oil;

[0038] (2) Tempering: Place the quenched sample in a heating furnace, heat to 500°C, keep warm for 150 minutes, then take out the sample and cool it in air.

[0039] Embodiment 3:

[0040] The steel part in the heat treatment process of the present invention is 70# spring steel, and is carried out according to the following steps:

[0041] (1) Quenching: Place the rough-machined spring steel blank sample in a heating furnace, heat it to 830°C, keep it at that temperature for 60 minutes, then quench it and cool it in oil;

[0042] (2) Tempering: Place the quenched sample in a heating furnace, heat to 480°C, keep warm for 150 minutes, then take out the sample and cool it in air.

[0043] Compared with 65# spring steel, 70# spring steel has a higher carbon content (usually between 0.68% and 0.75%), and carbon is an important element that determines the hardness and strength of steel. The higher carbon content allows 70# spring steel to form more martensite during the quenching process, thereby significantly improving the hardness and strength of the material. To form a higher proportion of martensite, the quenching temperature needs to be strictly controlled, which allows carbon atoms to be more fully dissolved in austenite and then quickly transformed into martensite during the quenching process.

[0044] The quenching temperature can promote the refinement of austenite grains, thereby improving the comprehensive mechanical properties of steel. In 70# spring steel, appropriately increasing the quenching temperature (for example, between 810℃-850℃) can not only form fine martensite grains, but also effectively improve the yield strength and tensile strength of the material. In contrast, 65# spring steel cannot form such a fine grain structure under the same conditions due to its low carbon content.

[0045] Adjusting the holding time is essential to ensure the uniformity and performance stability of the material. For 70# spring steel, due to its high carbon content, during the quenching and tempering process, a reasonable extension of the holding time can better control the transformation of austenite to martensite and the precipitation of carbides, thereby obtaining a uniform and stable organizational structure. This adjustment can maximize the strength and toughness of the material, while these subtle adjustments have relatively little effect on 65# spring steel, because its carbon content and the amount of martensite formed during quenching are relatively low, resulting in the effect of adjusting the holding time not being as significant as in 70# spring steel.

[0046] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A heat treatment process for 70# spring steel, characterized in that: include: (1) Quenching: Place the rough-machined spring steel blank sample in a heating furnace, heat it to 810℃~850℃, keep it warm for 58-62min, then quench it and cool it in oil; (2) Tempering: Place the quenched sample into a heating furnace, heat it to 460-500°C, keep it warm for 150±5min, then take out the sample and cool it in air.

2. The heat treatment process of 70# spring steel according to claim 1 is characterized in that: During the quenching process, keep warm for 60 minutes.

3. The heat treatment process of 70# spring steel according to claim 1, characterized in that: During the tempering process, keep warm for 150 minutes.

4. The heat treatment process of 70# spring steel according to claim 1, characterized in that: The rough-machined spring steel blank sample is placed in a heating furnace, heated to 810°C, kept warm for 60 minutes, then quenched and cooled in oil; the quenched sample is placed in a heating furnace, heated to 460°C, kept warm for 150 minutes, then taken out and cooled in air.

5. The heat treatment process of 70# spring steel according to claim 1, characterized in that: The rough-machined spring steel blank sample is placed in a heating furnace, heated to 850°C, kept warm for 60 minutes, then quenched and cooled in oil; the quenched sample is placed in a heating furnace, heated to 500°C, kept warm for 150 minutes, then taken out and cooled in air.

6. The heat treatment process of 70# spring steel according to claim 1, characterized in that: The rough-machined spring steel blank sample is placed in a heating furnace, heated to 830°C, kept warm for 60 minutes, then quenched and cooled in oil; the quenched sample is placed in a heating furnace, heated to 480°C, kept warm for 150 minutes, then taken out and cooled in air.

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