Heat treatment method for improving impact property of 20Cr1Mo1VTiB heat-resistant steel

Abstract

This application discloses a heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel in the field of heat treatment technology, comprising the following steps: S1, normalizing stress relief: heating the forging to 870-890℃, holding for 1-3 hours, and air cooling to room temperature; S2, quenching heating: heating the forging to 1030-1050℃, holding for 1-2 hours; S3, quenching cooling: after holding, removing the forging from the furnace and water cooling to below 100℃; S4, sub-critical quenching: heating the forging to 930-950℃, holding for 1-2 hours; S5, sub-critical quenching cooling: after holding, removing the forging from the furnace and water cooling to below 100℃; S6, high-temperature tempering: heating the forging to 690-710℃, holding for 3-5 hours; S7, tempering cooling: after holding, removing the forging from the furnace and air cooling to room temperature. This solution aims to address the problem of low impact plasticity in 20Cr1Mo1VTiB materials used for forgings in nuclear power and thermal power plants in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, and specifically to a heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel. Background Technology

[0002] 20Cr1Mo1VTiB heat-resistant steel is a commonly used high-temperature bolt steel in thermal power plants, extensively used in the manufacture of fastener bolts for steam turbines and boilers operating below 570℃. It possesses excellent comprehensive performance, relaxation resistance, and high-temperature strength, and has been increasingly replacing the long-used 25Cr2Mo1V steel. This steel improves its creep strength and relaxation resistance by adding carbide stabilizing elements vanadium and titanium, as well as grain boundary strengthening element boron, and also exhibits good impact toughness. The steel is heat-treated using a quenching and tempering process, resulting in a bainitic microstructure after tempering. In recent years, the application of 20Cr1Mo1VTiB bolt steel has expanded to the nuclear power field, where increased safety requirements have placed higher demands on the balance between strength and toughness.

[0003] This steel grade is highly sensitive to changes in heat treatment process parameters. The heat treatment process is the most critical factor affecting the balance of strength and toughness in 20Cr1Mo1VTiB steel. If hot working or heat treatment is not properly controlled, macroscopic coarse grains are easily formed in nuclear and thermal power materials, causing the product to lose toughness and fracture during normal use. Due to the large size of nuclear power products, ensuring both high strength and high impact plasticity of the material has become a major challenge in the nuclear and thermal power fields. Therefore, there is an urgent need for a heat treatment method to improve the impact performance of 20Cr1Mo1VTiB heat-resistant steel. Summary of the Invention

[0004] The present invention aims to provide a processing method for 20Cr1Mo1VTiB heat-resistant steel to solve the problem of low impact plasticity of 20Cr1Mo1VTiB material used in nuclear power and thermal power forgings in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel, comprising the following steps:

[0006] S1, Stress relief by normalizing: Heat the forging to 870-890℃, hold for 1-3 hours, and air cool to room temperature;

[0007] S2, Quenching and Heating: Heat the forging to 1030-1050℃ and hold for 1-2 hours;

[0008] S3, Quenching and Cooling: After the forging is kept at a certain temperature, it is taken out of the furnace and water-cooled to below 100℃;

[0009] S4, Sub-temperature quenching: Heat the forging to 930-950℃ and hold for 1-2 hours;

[0010] S5, Sub-temperature quenching and cooling: After the forging is held at the temperature, it is taken out of the furnace and water-cooled to below 100℃;

[0011] S6, High-temperature tempering: Heat the forging to 690~710℃ and hold for 3~5 hours;

[0012] S7, Tempering and Cooling: After the holding period, remove from the furnace and air cool to room temperature.

[0013] The working principle and beneficial effects of this invention are as follows: This invention first performs normalizing stress relief treatment to refine the grains and homogenize the microstructure. Then, it is quenched at a conventional quenching temperature, followed by sub-temperature quenching at a temperature below the austenitizing temperature to retain a small amount of ferrite. This significantly improves the toughness of the steel, lowers the brittle-cold transition temperature, suppresses reversible temper brittleness, and improves the impact performance of the material. It effectively solves the problem of low impact plasticity of 20Cr1Mo1VTiB material used in thermal and nuclear power plants, improves the -20℃ impact toughness of 20Cr1Mo1VTiB material forgings, and improves the overall mechanical properties of the material.

[0014] Further, S1, normalizing stress relief treatment: heat the forging to 870℃ and hold for 1 hour;

[0015] S2, Quenching and Heating: Heat the forging to 1030℃ and hold for 1 hour;

[0016] S4. Sub-temperature quenching: Heat the forging to 930℃ and hold for 1 hour;

[0017] S6. High-temperature tempering: Heat the forging to 690℃ and hold for 3 hours.

[0018] Further, S1, normalizing stress relief treatment: heat the forging to 880℃ and hold for 2 hours;

[0019] S2. Quenching and heating: Heat the forging to 1040℃ and hold for 1.5 hours;

[0020] S4. Sub-temperature quenching: Heat the forging to 940℃ and hold for 1.5 hours;

[0021] S6. High-temperature tempering: Heat the forging to 700℃ and hold for 4 hours.

[0022] Further, S1, normalizing stress relief treatment: heat the forging to 890℃ and hold for 3 hours;

[0023] S2. Quenching and heating: Heat the forging to 1050℃ and hold for 2 hours;

[0024] S4. Sub-temperature quenching: Heat the forging to 950℃ and hold for 2 hours;

[0025] S6. High-temperature tempering: Heat the forging to 710℃ and hold for 5 hours.

[0026] Furthermore, in step S4, the forging is heated to 940°C for sub-temperature quenching, and in steps S3 and S5, after the forging is kept at a certain temperature, it is taken out of the furnace and water-cooled to below 90°C. Attached Figure Description

[0027] Figure 1 This is a temperature diagram illustrating a heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel according to the present invention.

[0028] Figure 2 This is a temperature diagram of Embodiment 1 of the present invention;

[0029] Figure 3 This is a temperature diagram of a heat treatment method in the prior art. Detailed Implementation

[0030] A heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel, with temperature diagrams shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0031] S1, Stress relief by normalizing: Heat the forging to 870-890℃, hold for 1-3 hours, and then air cool to room temperature.

[0032] S2, Quenching and Heating: Heat the forgings that have been air-cooled to room temperature to 1030-1050℃ and hold for 1-2 hours.

[0033] S3, Quenching and Cooling: After the forging is held at room temperature, it is water-cooled to room temperature;

[0034] S4, Sub-temperature quenching: Heat the water-cooled forgings from S3 to 930-950℃ and hold for 1-2 hours.

[0035] S5, Sub-temperature quenching and cooling: After heat preservation, the furnace is cooled by water.

[0036] S6, High-temperature tempering: Finally, heat to 690-710℃ for high-temperature tempering and hold for 3-5 hours.

[0037] S7, after the heat preservation is completed, the steel is removed from the furnace and air-cooled, which is a new method to improve the impact performance of 20Cr1Mo1VTiB heat-resistant steel.

[0038] Example 1: This example uses a 20Cr1Mo1VTiB forging. The forging specifications are φ140*500, the material is 20Cr1Mo1VTiB, and the chemical composition of the forging is shown in Table 1 below.

[0039] Table 1 Chemical composition of forgings

[0040]

[0041] A schematic diagram of the heat treatment method, time, and temperature is attached. Figure 2 As shown, the specific heat treatment method includes the following steps:

[0042] (1) Heating: After 4 hours of heating with the furnace, the thermocouple temperature record reached 870℃ and heat preservation began;

[0043] (2) Heat preservation: Start heat preservation at 870℃ and keep it warm for 60 minutes;

[0044] (3) Normalizing and cooling: After the heat preservation is completed, remove the furnace and air cool to room temperature;

[0045] (4) Quenching and heating: Heat the furnace for 6 hours, and start holding the thermocouple temperature when it reaches 1030℃.

[0046] (5) Heat preservation: Start heat preservation at 1030℃ and keep it warm for 60 minutes;

[0047] (6) Quenching and cooling: After the heat preservation is completed, remove the furnace and cool it with water to below 150℃;

[0048] (7) Sub-temperature quenching and heating: Heat the furnace for 5 hours, and start holding the temperature when the thermocouple temperature reaches 930℃.

[0049] (8) Heat preservation: Start heat preservation at 930℃ and keep it warm for 60 minutes;

[0050] (9) Quenching and cooling: After the heat preservation is completed, remove the furnace and water cool it to below 150℃;

[0051] (10) High-temperature tempering: Heat up the furnace for 4 hours, and when the thermocouple temperature reaches 690℃, start heat preservation for 180 minutes.

[0052] (11) Tempering and cooling: After the heat preservation is completed, remove the furnace and air cool to room temperature;

[0053] This invention employs normalizing stress relief treatment, conventional quenching followed by sub-temperature quenching and high-temperature tempering. The mechanical properties of forgings of the same material and specifications after heat treatment are shown in Table 2.

[0054] Table 2 - Mechanical property values ​​of the examples

[0055]

[0056] Comparative Example: Forgings made of 20Cr1Mo1VTiB material with the same specifications as in Example 1 were used, and the general heat treatment method is shown in the appendix. Figure 3 The specific heat treatment method includes the following steps:

[0057] (1) Quenching and heating: Heat up the furnace for 6 hours, and start holding the thermocouple temperature when it reaches 1030℃.

[0058] (2) Heat preservation: Start heat preservation at 1030℃ and keep it warm for 60 minutes;

[0059] (3) Quenching and cooling: After the heat preservation is completed, the furnace is removed and water-cooled to below 150℃;

[0060] (4) High-temperature tempering: Heat up the furnace for 4 hours, and start heat preservation when the thermocouple temperature reaches 700℃ for 180 minutes.

[0061] (5) Tempering and cooling: After the heat preservation is completed, remove the furnace and air cool it to room temperature;

[0062] The mechanical properties of forgings after heat treatment using general heat treatment methods are shown in Table 3:

[0063] Table 3 - Comparative Mechanical Properties

[0064]

[0065] As can be seen from Tables 2 and 3, the strength of the forgings in the examples meets the requirements, and the impact values ​​are much higher than those in the comparative examples.

[0066] In the examples, the impact values ​​at -20℃ were 168 / 161 / 158 and 184 / 145 / 200, which are significantly higher than the impact values ​​under the same experimental conditions in the comparative example, and the overall mechanical properties are also very good. Therefore, the stress-relieving treatment of 20Cr1Mo1VTiB forgings, followed by conventional quenching, sub-temperature quenching, and high-temperature tempering, can meet the low-temperature impact requirements and has good results.

[0067] For those skilled in the art, various modifications and improvements can be made without departing from the technical concept of this invention, and these should also be considered within the scope of protection of this invention. These modifications and improvements will not affect the effectiveness of the implementation of this invention or the practicality of the patent.

Claims

1. A heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel, characterized in that: Includes the following steps: S1, Stress relief by normalizing: Heat the forging to 870-890℃, hold for 1-3 hours, and air cool to room temperature; S2, Quenching and Heating: Heat the forging to 1030-1050℃ and hold for 1-2 hours; S3, Quenching and Cooling: After the forging is kept at a certain temperature, it is taken out of the furnace and water-cooled to below 100℃; S4, Sub-temperature quenching: Heat the forging to 930-950℃ and hold for 1-2 hours; S5, Sub-temperature quenching and cooling: After the forging is held at the temperature, it is taken out of the furnace and water-cooled to below 100℃; S6, High-temperature tempering: Heat the forging to 690~710℃ and hold for 3~5 hours; S7, Tempering and Cooling: After the holding period, remove from the furnace and air cool to room temperature.

2. The heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel according to claim 1, characterized in that: S1, normalizing stress relief treatment: heat the forging to 870℃ and hold for 1 hour; S2, Quenching and Heating: Heat the forging to 1030℃ and hold for 1 hour; S4. Sub-temperature quenching: Heat the forging to 930℃ and hold for 1 hour; S6. High-temperature tempering: Heat the forging to 690℃ and hold for 3 hours.

3. The heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel according to claim 1, characterized in that: S1, normalizing stress relief treatment: heat the forging to 880℃ and hold for 2 hours; S2. Quenching and heating: Heat the forging to 1040℃ and hold for 1.5 hours; S4. Sub-temperature quenching: Heat the forging to 940℃ and hold for 1.5 hours; S6. High-temperature tempering: Heat the forging to 700℃ and hold for 4 hours.

4. The heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel according to claim 1, characterized in that: S1. Stress relief treatment: Heat the forging to 890℃ and hold for 3 hours; S2. Quenching and heating: Heat the forging to 1050℃ and hold for 2 hours; S4. Sub-temperature quenching: Heat the forging to 950℃ and hold for 2 hours; S6. High-temperature tempering: Heat the forging to 710℃ and hold for 5 hours.

5. The heat treatment method for improving the impact properties of 20Cr1Mo1VTiB heat-resistant steel according to claim 1, characterized in that: In step S4, the forging is heated to 940°C for sub-temperature quenching. In steps S3 and S5, after the forging is kept at a certain temperature, it is taken out of the furnace and water-cooled to below 90°C.

Images