Heat treatment method for improving low-temperature impact property of 12Cr13 martensitic stainless steel

Abstract

The invention discloses a heat treatment method for improving the low-temperature impact performance of 12Cr13 martensitic stainless steel in the technical field of heat treatment. The heat treatment method comprises the following steps that S1, water quenching pretreatment is conducted, specifically, a forge piece is heated to 940-960 DEG C, and heat preservation is conducted for 1-2 h; s2, quenching cooling: after heat preservation of the forge piece is finished, discharging and water-cooling; s3, quenching and heating: heating the forge piece to 830-850 DEG C, and keeping the temperature for 1-2 hours; s4, quenching cooling: discharging and water-cooling the forged piece after heat preservation is finished; s5, high-temperature tempering is conducted, specifically, the forge piece is heated to 600-680 DEG C, and heat preservation is conducted for 3.5-4.5 h; and S6, tempering and cooling, wherein after heat preservation is finished, discharging and air cooling are conducted, and cooling is conducted to the room temperature. According to the method, the material fastener forge piece is subjected to water quenching pretreatment and fine grain treatment, then the fastener forge piece is heated at the temperature lower than the conventional austenitizing temperature for subcritical quenching, a small amount of retained austenite structures are obtained, and the 0 DEG C impact toughness of the 12Cr13 material fastener forge piece is improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment, and in particular to a heat treatment method for improving the low-temperature impact performance of 12Cr13 martensitic stainless steel. Background Art

[0002] With the development of national nuclear power construction, the design requirements for nuclear power fasteners are becoming increasingly higher, especially in terms of mechanical properties, hardness and toughness. The requirements for the comprehensive mechanical properties of fasteners are particularly obvious. It is a major difficulty for ordinary stainless steel to maintain high plasticity while requiring high strength for fasteners.

[0003] 12Cr13 is a martensitic stainless steel, mainly used for the production of high-strength bolts for nuclear power plants. It is required that the steel has high strength after quenching and tempering, and the average value of 0℃ low-temperature impact energy Akv (0℃) is ≥56J, and the single value is ≥40J. Since the steel has high strength requirements and a narrow adjustable range of tempering temperature, the steel currently has a common problem of unqualified or large fluctuations in 0℃ low-temperature impact energy after quenching and tempering, while the strength meets the requirements, which seriously affects the product quality and poses a safety hazard to the safe service of 12Cr13 steel high-strength bolts. Therefore, it is imperative to find a heat treatment method to improve the low-temperature impact performance of 12Cr13. Summary of the invention

[0004] The present invention aims to provide a heat treatment method for improving the low-temperature impact performance of 12Cr13 martensitic stainless steel, so as to solve the problem that the low-temperature impact performance of 12Cr13 material used for nuclear-grade high-strength bolt forgings in the prior art does not meet the requirements. In order to solve the above problems, the present invention provides the following technical solutions: A heat treatment method for improving the low temperature impact performance of 12Cr13 martensitic stainless steel comprises the following steps: S1. Water quenching pretreatment: heat the forging to 940-960°C and keep it warm for 1-2 hours; S2, quenching and cooling: after the forging is finished, it is taken out of the furnace and air-cooled to room temperature; S3, quenching and heating: heat the forging to 830-850℃ and keep it warm for 1-2h; S4, quenching and cooling: after the forging is heat-insulated, it is taken out of the furnace and water-cooled to below 150°C; S5. High temperature tempering: heat the forging to 600-680℃ and keep it warm for 3.5-4.5h; S6. Tempering cooling: After the heat preservation is completed, take out of the furnace and air cool to room temperature.

[0005] The working principle and beneficial effects of the present invention are as follows: Compared with the prior art, the present invention first performs water quenching pretreatment to refine the grains to obtain a uniform structure, and then performs high-temperature tempering after quenching at a temperature lower than the conventional quenching temperature, that is, by performing sub-temperature quenching after the forging is subjected to fine grain treatment, a small amount of residual austenite structure can be obtained, which can significantly improve the toughness of the steel; it effectively solves the problem that the low-temperature impact of 12Cr13 material used for nuclear-grade high-strength bolt forgings does not meet the requirements, improves the 0°C impact toughness of 12Cr13 material fastener forgings, and improves the comprehensive mechanical properties of the fastener forgings.

[0006] Furthermore, the S1, water quenching pretreatment: heating the forging to 940° C. and keeping it warm for 1 hour; S3, quenching heating: heating the forging to 830° C. and keeping it warm for 1 hour; S5, high temperature tempering: heating the forging to 600° C. and keeping it warm for 3.5 hours.

[0007] Furthermore, the S1, water quenching pretreatment: heating the forging to 950° C. and keeping it warm for 1.5 hours; S3, quenching heating: heating the forging to 840° C. and keeping it warm for 1.5 hours; S5, high temperature tempering: heating the forging to 640° C. and keeping it warm for 4 hours.

[0008] Furthermore, the S1, water quenching pretreatment: heating the forging to 960° C. and keeping it warm for 2 hours; S3, quenching heating: heating the forging to 850° C. and keeping it warm for 2 hours; S5, high temperature tempering: heating the forging to 680° C. and keeping it warm for 4.5 hours.

[0009] Furthermore, S2 and S4 are water-cooled to room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a temperature schematic diagram of the heat treatment method of the present invention; Figure 2 This is a time-temperature schematic diagram of an embodiment of the present invention; Figure 3 It is a temperature diagram of general heat treatment method. DETAILED DESCRIPTION

[0011] The following is further described in detail through specific implementation methods: like Figure 1 As shown, the specific steps of the heat treatment method of the present invention include: heating the forging to 940-960°C with the furnace, keeping it warm for a certain period of time and then cooling it with water, then heating it to 830-850°C with the furnace, keeping it warm for a certain period of time and then cooling it with water, performing high-temperature tempering after water cooling, keeping it warm for a certain period of time during high-temperature tempering, and air cooling after taking it out of the furnace, thus completing the heat treatment method of 12Cr13 material fastener forgings.

[0012] Embodiment: This embodiment uses 12Cr13 material fastener forgings, forging specifications: φ80×900 material: 12Cr13, forging chemical composition see Table 1 below. Table 1 Forging chemical composition

[0013] Heat treatment method time and temperature diagram Figure 2 As shown, the specific heat treatment method includes the following steps: (1) Heating: After the forging is heated up with the furnace for 3.5 hours, the thermocouple temperature reaches 960°C and then insulation begins; (2) Insulation: Start at 960°C and keep warm for 90 minutes; (3) Water quenching pretreatment cooling: After the insulation is completed, the furnace is taken out of the furnace and water-cooled to below 150°C; (4) Quenching temperature rise: Heat up with the furnace for 2.0 hours, and start keeping warm when the thermocouple temperature reaches 840℃; (5) Insulation: Start at 840°C and keep warm for 90 minutes; (6) Quenching and cooling: After the heat preservation is completed, the furnace is taken out of the furnace and water-cooled to below 150°C; (7) High temperature tempering: Heat up with the furnace for 2 hours. When the thermocouple temperature reaches 650°C, keep warm for 245 minutes.

[0014] (8) Tempering cooling: After the heat preservation is completed, the furnace is taken out and air-cooled to room temperature; The present invention adopts water quenching pretreatment and high temperature tempering after sub-temperature quenching. The mechanical properties of forgings of the same material and specification after heat treatment are shown in Table 2: Table 2 - Mechanical properties of the examples

[0015] Comparative Example: Using 12Cr13 material fastener forgings with the same specifications as in Example 1, the general heat treatment method is shown in Figure 3 The specific heat treatment method includes the following steps: (1) Quenching temperature rise: Heat up with the furnace for 2.0 hours, and start keeping warm when the thermocouple temperature reaches 960℃; (2) Insulation: Start at 960°C and keep warm for 90 minutes; (3) Quenching and cooling: After the heat preservation is completed, the furnace is taken out of the furnace and water-cooled to below 150°C; (4) High temperature tempering: Heat up with the furnace for 2 hours. When the thermocouple temperature reaches 600℃ and 680℃, keep warm for 245 minutes.

[0016] (5) Tempering cooling: After the heat preservation is completed, the furnace is taken out and air-cooled to room temperature; General heat treatment method The mechanical properties of forgings after heat treatment are shown in Table 3: Table 3 - Mechanical properties of comparative examples

[0017] It can be seen from Table 2 and Table 3 that the impact and strength of the forgings in the embodiment meet the requirements, and R m and Akv values ​​are much higher than those of the control group.

[0018] The low temperature 0℃ impact Akv (125; 121; 118) and Akv (112; 105; 101) in the embodiment are much higher than the 0℃ impact under the same experimental conditions in the comparative example, the impact toughness is increased by nearly 1 times, and the overall strength is also higher than that in the comparative example. Therefore, the 12Cr13 material fastener forging can achieve high strength and low temperature impact requirements by water quenching and grain refinement treatment and sub-temperature quenching and high temperature tempering, and has good effects.

[0019] For those skilled in the art, multiple variations and improvements can be made without departing from the technical concept of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A heat treatment method for improving the low temperature impact performance of 12Cr13 martensitic stainless steel, characterized in that: The following steps are involved: S1. Water quenching pretreatment: heat the forging to 940-960°C and keep it warm for 1-2 hours; S2, quenching and cooling: after the forging is heat-insulated, it is taken out of the furnace and water-cooled to below 150°C; S3, quenching and heating: heat the forging to 830-850℃ and keep it warm for 1-2h; S4, quenching and cooling: after the forging is heat-insulated, it is taken out of the furnace and water-cooled to below 150°C; S5. High temperature tempering: heat the forging to 600-680℃ and keep it warm for 3.5-4.5h; S6. Tempering cooling: After the heat preservation is completed, take out of the furnace and air cool to room temperature.

2. The heat treatment method for improving the low temperature impact performance of 12Cr13 martensitic stainless steel according to claim 1, characterized in that: The S1, water quenching pretreatment: heating the forging to 940°C and keeping it warm for 1 hour; S3, quenching heating: heating the forging to 830°C and keeping it warm for 1 hour; S5, high temperature tempering: heating the forging to 600°C and keeping it warm for 3.5 hours.

3. The heat treatment method for improving the low temperature impact performance of 12Cr13 martensitic stainless steel according to claim 1, characterized in that: S1, water quenching pretreatment: heating the forging to 950°C and keeping it warm for 1.5 hours; S3, quenching heating: heating the forging to 840°C and keeping it warm for 1.5 hours; S5. High temperature tempering: Heat the forging to 640℃ and keep it warm for 4h.

4. The heat treatment method for improving the low temperature impact performance of 12Cr13 martensitic stainless steel according to claim 1, characterized in that: The S1, water quenching pretreatment: heating the forging to 960°C and keeping it warm for 2 hours; S3, quenching heating: heating the forging to 850°C and keeping it warm for 2 hours; S5, high temperature tempering: heating the forging to 680°C and keeping it warm for 4.5 hours.

5. The heat treatment method for improving the low temperature impact performance of 12Cr13 martensitic stainless steel according to any one of claims 1 to 4, characterized in that: The S2 and S4 are water-cooled to room temperature.

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