Method for improving performance of 35crmo steel and application thereof

Abstract

The application provides a method for improving the performance of 35CrMo steel and application thereof. The method comprises the following steps: 1) heating 35CrMo steel to a first high temperature, carrying out first heat preservation, quenching, and obtaining quenched steel; 2) heating the quenched steel to a second high temperature, carrying out second heat preservation, and air cooling to obtain high-temperature tempered steel; 3) cooling the high-temperature tempered steel to a first low temperature, carrying out third heat preservation, and then increasing the temperature from the first low temperature to a second low temperature, and then decreasing the temperature from the second low temperature to the first low temperature, so as to form a cycle; then increasing the temperature from the first low temperature, and obtaining oscillation cycle cryogenic treated steel; 4) heating the oscillation cycle cryogenic treated steel to a third high temperature, carrying out fourth heat preservation, and air cooling to obtain cold and hot treated 35CrMo steel.

Description

Technical Field

[0001] This invention relates to the field of metal processing, and in particular to a method for improving the mechanical properties and / or dimensional stability of 35CrMo steel. Background Technology

[0002] 35CrMo is a widely used medium-carbon alloy steel. After quenching and tempering, it possesses excellent comprehensive mechanical properties and is widely used in the manufacture of transmission components for vehicles and engines, as well as critical structural components operating under high loads, such as the main shaft of wind turbines. In China, 35CrMo alloy steel is widely used as the main shaft material for locomotive wind turbines, and the heat treatment process typically involves quenching followed by high-temperature tempering. In recent years, the problems of excessive vibration and severe abnormal noise during locomotive wind turbine operation have become increasingly prominent, leading to a high failure rate. Some of these failures are caused by poor machining accuracy, large dispersion, and unreliable geometric tolerances in the components. Furthermore, the reduced dimensional stability of key structural components during long-term operation can also cause abnormal noise. Although current improvements in machining processes can meet design requirements, further improvements to the mechanical properties and dimensional stability of components such as impellers, shafts, end covers, bases, and welded structures still present challenges due to high machining difficulties and high labor and equipment costs. Summary of the Invention

[0003] One aspect of the present invention provides a method for improving the properties of 35CrMo steel, comprising the following steps:

[0004] 1) Heat 35CrMo steel to a first high temperature, hold it at the first temperature, and then quench it to obtain quenched steel.

[0005] 2) Heat the quenched steel to a second high temperature, hold it at the second temperature, and air cool it to obtain high-temperature tempered steel.

[0006] 3) Cool the high-temperature tempered steel to the first low temperature and perform a third heat preservation; raise the temperature from the first low temperature to the second low temperature, and then cool it from the second low temperature to the first low temperature, thus forming a cycle; then raise the temperature from the first low temperature to obtain the oscillating cycle cryogenic treatment steel.

[0007] 4) The steel subjected to oscillating cycle cryogenic treatment is heated to the third high temperature, subjected to the fourth heat preservation, and air cooled to obtain cold and heat treated 35CrMo steel.

[0008] In one specific embodiment, in step 1), the first high temperature is 820 to 880°C, and the first heat preservation time is 1 to 2 hours.

[0009] In one specific embodiment, in step 2), the second high temperature is 520 to 600°C, and the second heat preservation time is 1 to 2 hours.

[0010] In one specific embodiment, in step 3), the first low temperature is -180 to -160°C; the second low temperature is -60 to -100°C.

[0011] In one specific implementation, in step 3), the third heat preservation time is 0.5 to 1 hour.

[0012] In one specific implementation, in step 3), the loop is repeated 10 to 20 times.

[0013] In one specific embodiment, in step 3), the temperature is lowered from the ambient temperature to the first low temperature at a rate of 1 to 3 °C / min; the temperature is raised from the first low temperature to the second low temperature at a rate of 5 to 15 °C / min; the temperature is lowered from the second low temperature to the first low temperature at a rate of 1 to 3 °C / min; and after the cycle, the temperature is raised from the first low temperature at a rate of 2 to 10 °C / min.

[0014] In one specific embodiment, in step 4), the third high temperature is 150 to 220°C, and the fourth heat preservation time is 1 to 2 hours.

[0015] In one specific embodiment, in step 1), the 35CrMo steel material is heated to a first high temperature, held at the first temperature, and then quickly removed and quenched in a 5wt% to 10wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0016] In step 2), the air is cooled to ambient temperature;

[0017] In step 3), after the cycle, the temperature is raised from the first low temperature to the ambient temperature;

[0018] In step 4), the air is cooled to ambient temperature.

[0019] The second invention provides the application of cold- and heat-treated 35CrMo steel obtained by processing according to any of the methods described in the first invention in improving mechanical properties and / or dimensional stability.

[0020] In this invention, the chemical composition of 35CrMo steel is as follows: 0.32wt% to 0.40wt% carbon (C), 0.40wt% to 0.70wt% manganese (Mn), 0.80wt% to 1.10wt% chromium (Cr), 0.17wt% to 0.37wt% silicon (Si), 0.15wt% to 0.25wt% molybdenum (Mo), less than or equal to 0.30wt% nickel (Ni), less than or equal to 0.30wt% copper (Cu), less than or equal to 0.035wt% sulfur (S), less than or equal to 0.035wt% phosphorus (P), and the balance being iron (Fe).

[0021] The beneficial effects of this invention are:

[0022] The method of this invention can improve the mechanical properties and / or dimensional stability of 35CrMo steel, which can further effectively solve the vibration and noise problems during the operation of locomotive fans and reduce the failure rate of fans. Attached Figure Description

[0023] Figure 1 Scanning electron microscope images of the microstructures of Example 3 and Comparative Example 3 are shown. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0025] Example 1

[0026] The steel material used is 35CrMo alloy structural steel, and its chemical composition is as follows (wt.%): carbon content (C) = 0.35, manganese content (Mn) = 0.56, chromium content (Cr) = 0.95, silicon content (Si) = 0.28, molybdenum content (Mo) = 0.20, nickel content (Ni) = 0.25, copper content (Cu) = 0.30, sulfur content (S) = 0.015, phosphorus content (P) = 0.020, and the remainder is iron (Fe).

[0027] 1) Heat 35CrMo steel to 840℃, hold for 1 hour, then quickly remove and quench in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0028] 2) The quenched steel is heated to 550℃ in the furnace and held for 2 hours, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0029] 3) Cool the high-temperature tempered steel from ambient temperature to -180℃ at a rate of 1℃ / min and hold for 1 hour; then heat it from -180℃ to -60℃ at a rate of 10℃ / min, and cool it from -60℃ to -180℃ at a rate of 1 / min, thus forming one cycle, for a total of 15 cycles; then heat it from -180℃ to ambient temperature at a rate of 10℃ / min to obtain the oscillating cycle cryogenic treatment steel.

[0030] 4) The steel subjected to oscillating cycle cryogenic treatment is heated to 200°C in the furnace, held at that temperature for 2 hours, and then air-cooled to ambient temperature to obtain cold and heat treated 35CrMo steel.

[0031] Example 2

[0032] The steel material used is the same as in Example 1.

[0033] 1) Heat 35CrMo steel to 820℃, hold for 1 hour, then quickly remove and quench in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0034] 2) The quenched steel is heated to 520℃ in the furnace and held for 1 hour, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0035] 3) Cool the high-temperature tempered steel from ambient temperature to -160℃ at a rate of 1℃ / min and hold for 0.5h; then heat it from -160℃ to -100℃ at a rate of 5℃ / min, and cool it from -100℃ to -160℃ at a rate of 1 / min, thus forming one cycle, for a total of 10 cycles; then heat it from -160℃ to ambient temperature at a rate of 2℃ / min to obtain the oscillating cycle cryogenic treatment steel.

[0036] 4) The steel subjected to oscillating cycle cryogenic treatment is heated to 150°C in the furnace, held at that temperature for 1 hour, and then air-cooled to ambient temperature to obtain cold and heat treated 35CrMo steel.

[0037] Example 3

[0038] The steel material used is the same as in Example 1.

[0039] 1) Heat 35CrMo steel to 880℃, hold for 2 hours, then quickly remove and quench in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0040] 2) The quenched steel is heated to 600℃ in the furnace and held for 2 hours, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0041] 3) Cool the high-temperature tempered steel from ambient temperature to -180℃ at a rate of 3℃ / min and hold for 1 hour; then heat it from -180℃ to -60℃ at a rate of 15℃ / min, and cool it from -60℃ to -180℃ at a rate of 3℃ / min, thus forming one cycle, for a total of 20 cycles; then heat it from -180℃ to ambient temperature at a rate of 6℃ / min to obtain the oscillating cycle cryogenic treatment steel.

[0042] 4) The steel subjected to oscillating cycle cryogenic treatment is heated to 220°C in the furnace, held at that temperature for 2 hours, and then air-cooled to ambient temperature to obtain cold and heat treated 35CrMo steel.

[0043] Comparative Example 1

[0044] The steel material used is the same as in Example 1.

[0045] 1) Heat 35CrMo steel to 840℃, hold for 1 hour, then quickly remove and quench in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0046] 2) The quenched steel is heated to 550℃ in the furnace and held for 2 hours, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0047] 3. The high-temperature tempered steel is cooled from ambient temperature to -120℃ at a rate of 1℃ / min and held at that temperature for 1 hour; then, it is heated from -120℃ to -60℃ at a rate of 10℃ / min, and then cooled from -60℃ to -120℃ at a rate of 1 / min, thus forming one cycle, for a total of 15 cycles; then, it is heated from -120℃ to ambient temperature at a rate of 10℃ / min to obtain cryogenically treated steel.

[0048] 4) The cryogenically treated steel is heated to 200°C in the furnace, held for 2 hours, and then air-cooled to ambient temperature to obtain cryogenically treated 35CrMo steel.

[0049] Comparative Example 2

[0050] The steel material used is the same as in Example 1.

[0051] 1) Heat the steel material to 820℃, hold it at that temperature for 1 hour, and then quickly remove it and quench it in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0052] 2) The quenched 35CrMo steel is heated to 520℃ in the furnace and held for 1 hour, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0053] 3) Cool the high-temperature tempered steel from ambient temperature to -100℃ at a rate of 1℃ / min and hold for 0.5h; then cool it from -100℃ to -160℃ at a rate of 5℃ / min, and then heat it from -160℃ to -100℃ at a rate of 1 / min, thus forming one cycle, for a total of 10 cycles; then heat it from -100℃ to ambient temperature at a rate of 2℃ / min to obtain cryogenically treated steel.

[0054] 4) The cryogenically treated steel is heated to 150°C in the furnace, held for 1 hour, and then air-cooled to ambient temperature to obtain cryogenically treated 35CrMo steel.

[0055] Comparative Example 3

[0056] The steel material used is the same as in Example 1.

[0057] 1) Heat 35CrMo steel to 880℃, hold for 2 hours, then quickly remove and quench in an 8% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0058] 2) Cool the quenched steel from ambient temperature to -180℃ at a rate of 3℃ / min and hold for 1 hour; then heat it from -180℃ to -60℃ at a rate of 15℃ / min, and cool it from -60℃ to -180℃ at a rate of 3℃ / min, thus forming one cycle, for a total of 20 cycles; then heat it from -180℃ to ambient temperature at a rate of 6℃ / min to obtain cryogenically treated steel.

[0059] 3) The cryogenically treated steel is heated to 600°C in the furnace and held for 2 hours, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0060] 4) Heat the high-temperature tempered steel to 220°C in the furnace, hold it at that temperature for 2 hours, and then air cool it to ambient temperature to obtain cold and heat treated 35CrMo steel.

[0061] Comparative Example 4

[0062] The steel material used is the same as in Example 1.

[0063] 1) Heat 35CrMo steel to 880℃, hold for 2 hours, then quickly remove and quench in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0064] 2) The quenched steel is heated to 600℃ in the furnace and held for 2 hours, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0065] 3) Cool the high-temperature tempered steel from ambient temperature to -180℃ at a rate of 3℃ / min and hold for 1 hour; then heat it from -180℃ to -60℃ at a rate of 15℃ / min, and cool it from -60℃ to -180℃ at a rate of 3℃ / min, thus forming one cycle, for a total of 5 cycles; then heat it from -180℃ to ambient temperature at a rate of 6℃ / min to obtain cryogenically treated steel.

[0066] 4) The cryogenically treated steel is heated to 220°C in the furnace, held for 2 hours, and then air-cooled to ambient temperature to obtain cryogenically treated 35CrMo steel.

[0067] Comparative Example 5

[0068] The steel material used is the same as in Example 1.

[0069] 1) Heat 35CrMo steel to 880℃, hold for 2 hours, then quickly remove and quench in an 8wt% polyvinyl alcohol aqueous solution to obtain quenched steel.

[0070] 2) The quenched steel is heated to 600℃ in the furnace and held for 2 hours, then taken out and air-cooled to ambient temperature to obtain high-temperature tempered steel.

[0071] 3) Cool the high-temperature tempered steel from ambient temperature to -180℃ at a rate of 3℃ / min and hold for 1 hour; then heat it from -180℃ to -60℃ at a rate of 15℃ / min, and cool it from -60℃ to -180℃ at a rate of 3℃ / min, thus forming one cycle, for a total of 25 cycles; then heat it from -180℃ to ambient temperature at a rate of 6℃ / min to obtain cryogenically treated steel.

[0072] 4) The cryogenically treated steel is heated to 220°C in the furnace, held for 2 hours, and then air-cooled to ambient temperature to obtain cryogenically treated 35CrMo steel.

[0073] Performance testing

[0074] (1) Mechanical property testing

[0075] The room temperature (U-shaped) impact toughness tests of cold- and heat-treated 35CrMo steel in Examples 1 to 3 and Comparative Examples 1 to 5 were performed according to GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method", and the results are shown in Table 1.

[0076] The room temperature tensile strength tests of cold- and heat-treated 35CrMo steel in Examples 1 to 3 and Comparative Examples 1 to 5 were performed according to GB / T 228.1-2010 "Metallic materials - Tensile testing at room temperature - Test method", and the results are shown in Table 1.

[0077] The room temperature hardness tests of cold- and heat-treated 35CrMo steel in Examples 1 to 3 and Comparative Examples 1 to 5 were performed according to GB / T4340.1-2012 "Metallic Materials - Vickers Hardness Test - Test Method", and the results are shown in Table 1.

[0078] (2) Dimensional stability testing

[0079] The circular triangular method developed by the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, was used to test the dimensional stability of steel materials. The influence of the processes in Examples 1-3 and Comparative Examples 1-5 on the dimensional stability of the 35CrMo steel samples was evaluated by measuring the change in the angle of the apex of the circular triangular sample before treatment and the angle of the apex after opening the circular triangular sample after treatment in Examples 1-3 and Comparative Examples 1-5. First, the apex angle of the circular triangular 35CrMo steel sample was measured using a coordinate measuring machine. Then, the circular triangular sample was treated according to the processes in Examples 1-3 and Comparative Examples 1-5. After treatment, the sample was cut along the base of the triangle, leaving the two sides unconstrained. The apex angle was then measured again, and the difference between the second and first measurements (i.e., the angle change) was calculated. The results are shown in Table 1.

[0080] Table 1

[0081] Example 1 145.2 1106.0 357.69 0.0061 Example 2 148.5 1184.5 362.33 0.0052 Example 3 150.6 1202.7 360.50 0.0065 Comparative Example 1 152.0 1074.0 344.59 0.0255 Comparative Example 2 150.0 1076.2 350.32 0.0194 Comparative Example 3 147.7 1022.5 348.20 0.0283 Comparative Example 4 141.5 1080.5 350.52 0.0139 Comparative Example 5 140.8 1006.0 349.27 0.0147

[0082] Note: Dimensional stability is evaluated by the magnitude of the angular change; that is, the smaller the angular change, the better the dimensional stability.

[0083] (3) Microstructural characterization

[0084] The microstructure of the cold- and hot-treated 35CrMo steel materials of each embodiment and comparative example was observed using a scanning electron microscope (Hitachi SU1510). The microstructure of the cold- and hot-treated 35CrMo steel materials of Example 3 and Comparative Example 3 is as follows: Figure 1 As shown.

[0085] from Figure 1 As can be seen, the microstructure of the cold-treated 35CrMo steel in Example 3 consists of tempered martensite and carbides, meaning that the quenched martensite decomposes during high-temperature tempering, precipitating a large number of dispersed carbides. Compared with Comparative Example 3, Example 3 shows an increase in tempered martensite laths, indicating that high-temperature tempering promotes martensite formation during subsequent cryogenic treatment. The increased martensite leads to a higher local dislocation density, providing more nucleation sites for carbide precipitation. Therefore, the white carbide particles in Example 3 are more concentrated than in Comparative Example 3, indicating that high-temperature tempering before cryogenic treatment promotes the precipitation of carbide particles in the microstructure, thereby improving the mechanical properties of 35CrMo steel. Furthermore, high-temperature tempering before cryogenic treatment allows for a greater release of quenching thermal stress; therefore, the smaller angle change in Example 3 indicates improved dimensional stability of the 35CrMo steel.

[0086] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. A method for improving the properties of 35CrMo steel, comprising the following steps: 1) Heat 35CrMo steel to a first high temperature, hold it at the first temperature, and then quench it to obtain quenched steel. 2) Heat the quenched steel to a second high temperature, hold it at the second temperature, and air cool it to obtain high-temperature tempered steel; 3) Cool the high-temperature tempered steel to the first low temperature and perform a third heat preservation; raise the temperature from the first low temperature to the second low temperature, and then cool it from the second low temperature to the first low temperature, thus forming a cycle; then raise the temperature from the first low temperature to obtain the oscillating cycle cryogenic treatment steel. 4) The steel subjected to oscillating cycle cryogenic treatment is heated to the third high temperature, subjected to the fourth heat preservation, and air cooled to obtain cold and heat treated 35CrMo steel; In step 3), the first low temperature is -180 to -160°C; the second low temperature is -60 to -100°C. The cycle is repeated 10 to 20 times.

2. The method according to claim 1, characterized in that, In step 1), the first high temperature is 820 to 880°C, and the first heat preservation time is 1 to 2 hours.

3. The method according to claim 1, characterized in that, In step 2), the second high temperature is 520 to 600°C, and the second heat preservation time is 1 to 2 hours.

4. The method according to claim 1, characterized in that, In step 3), the third heat preservation time is 0.5 to 1 hour.

5. The method according to claim 1, characterized in that, In step 3), the temperature is lowered from the ambient temperature to the first low temperature at a rate of 1 to 3 °C / min; the temperature is raised from the first low temperature to the second low temperature at a rate of 5 to 15 °C / min; the temperature is lowered from the second low temperature to the first low temperature at a rate of 1 to 3 °C / min; and after the cycle, the temperature is raised from the first low temperature at a rate of 2 to 10 °C / min.

6. The method according to claim 1, characterized in that, In step 4), the third high temperature is 150 to 220°C, and the fourth heat preservation time is 1 to 2 hours.

7. The method according to claim 1, characterized in that, In step 1), the 35CrMo steel material is heated to a first high temperature, held at the first temperature, and then quickly removed and quenched in a 5wt% to 10wt% polyvinyl alcohol aqueous solution to obtain quenched steel. In step 2), the air is cooled to ambient temperature; In step 3), after the cycle, the temperature is raised from the first low temperature to the ambient temperature; In step 4), the air is cooled to ambient temperature.

8. The application of cold- and heat-treated 35CrMo steel obtained by the method according to any one of claims 1 to 7 in improving mechanical properties and / or dimensional stability.

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