A heat treatment method for improving comprehensive mechanical properties of SA-194M-Gr.2H material forgings

Abstract

The application discloses a heat treatment method for improving comprehensive mechanical properties of SA-194M-Gr.2H material forgings in the technical field of heat treatment, which comprises the following steps: S1, high-temperature normalizing fine-grain treatment: the forgings are heated to 860-880 DEG C and kept for 1-2 hours; S2, quenching cooling: the forgings are taken out of the furnace and air-cooled to room temperature after the keeping; S3, quenching heating: the forgings are heated to 810-830 DEG C and kept for 1-2 hours; S4, quenching cooling: the forgings are water-cooled after the keeping; S5, medium-temperature tempering: the forgings are heated to 480-560 DEG C and kept for 3.5-4.5 hours; and S6, tempering cooling: the forgings are air-cooled to room temperature after the keeping. The high-temperature normalizing fine-grain treatment is first carried out on the material fastener forgings, then the fastener forgings are heated below the conventional austenitizing temperature for quenching, and therefore, small ferrite structures are uniformly distributed, the toughness of the steel can be significantly improved, the tempering brittleness transition temperature can be reduced, and the tempering brittleness can be reduced.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, specifically to a heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings. Background Technology

[0002] With the development of national nuclear power construction, the design requirements for nuclear-grade fasteners are becoming increasingly stringent, especially in terms of mechanical properties such as hardness and toughness. The comprehensive mechanical properties of fasteners are particularly important, requiring high strength while maintaining high plasticity and toughness. This combination of high strength and high toughness is relatively easy to achieve for alloy steel forgings, but it is a challenge for carbon steel. Since the main component of carbon steel is carbon with virtually no alloying elements, its hardenability is limited and its strength is relatively low. Therefore, maintaining high strength will result in poor plasticity and toughness.

[0003] SA-194M-Gr.2H material belongs to the American standard and is also a carbon steel material. It is mainly used for high-temperature and high-pressure carbon steel nuts. The mechanical properties only require testing the hardness value, which should be 248-352 HB. Currently, a nuclear power plant support platform project uses SA-194M Gr.2H material nuts and washers, which are nuclear safety level 1 forgings. The mechanical properties require a hardness value of 248-301 HB and a low-temperature (-20℃) Akv impact lateral expansion LE ≥ 0.64 mm. However, the existing SA-194M-Gr.2H material cannot simultaneously meet the requirements of high strength and low-temperature impact toughness. Therefore, it is imperative to find a more convenient heat treatment method to improve the comprehensive mechanical properties of fastener forgings. Summary of the Invention

[0004] This invention aims to provide a heat treatment method to improve the comprehensive mechanical properties of SA-194M-Gr.2H material forgings, thereby solving the problem in the prior art that the mechanical properties of SA-194M Gr.2H material fastener forgings for nuclear-grade forgings cannot simultaneously meet the requirements of high strength and hardness and low-temperature impact resistance.

[0005] To address the above problems, the present invention provides the following technical solution:

[0006] A heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings includes the following steps:

[0007] S1. High-temperature normalizing fine grain treatment: Heat the forging to 860-880℃ and hold for 1-2 hours;

[0008] S2. Normalizing and cooling: After the forging is held at room temperature, it is removed from the furnace and air-cooled to room temperature.

[0009] S3. Quenching and heating: Heat the forging to 810-830℃ and hold for 1-2 hours;

[0010] S4. Quenching and cooling: After the forging is held at the temperature, it is removed from the furnace and water-cooled.

[0011] S5. Medium-temperature tempering: Heat the forging to 480-560℃ and hold for 3.5-4.5 hours;

[0012] S6. Tempering and cooling: After the holding period, remove the furnace and air cool to room temperature.

[0013] The working principle and beneficial effects of this invention are as follows: Compared with the prior art, this invention first performs high-temperature normalizing and grain refinement treatment, and then quenches at a temperature lower than the conventional quenching temperature and tempers at a medium temperature. That is, by refining the grain of the fastener forging and then quenching it at a temperature lower than the conventional quenching temperature, a uniformly distributed small ferrite structure can be obtained, which can significantly improve the toughness of the steel, reduce the temper brittle transition temperature, and reduce temper brittleness. It effectively solves the problem that the comprehensive mechanical properties of fasteners made of nuclear-grade forging SA-194M Gr.2H material cannot be simultaneously met with high strength and hardness and low low-temperature impact, improves the -20℃ impact toughness of SA-194MGr.2H material fastener forgings (45mm in diameter), and improves the comprehensive mechanical properties of fastener forgings.

[0014] Furthermore, S1, high-temperature normalizing fine grain treatment: heating the forging to 860℃ and holding for 1 hour; S3, quenching and heating: heating the forging to 810℃ and holding for 1 hour; S5, medium-temperature tempering: heating the forging to 480℃ and holding for 3.5 hours.

[0015] Furthermore, S1, high-temperature normalizing fine grain treatment: heating the forging to 870℃ and holding for 1.5h; S3, quenching and heating: heating the forging to 820℃ and holding for 1.5h; S5, medium-temperature tempering: heating the forging to 520℃ and holding for 4h.

[0016] Furthermore, S1, high-temperature normalizing fine grain treatment: heating the forging to 880℃ and holding for 2 hours; S3, quenching and heating: heating the forging to 830℃ and holding for 2 hours; S5, medium-temperature tempering: heating the forging to 560℃ and holding for 4.5 hours.

[0017] Furthermore, S4 is water-cooled to room temperature. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the time and temperature of the heat treatment method of the present invention;

[0019] Figure 2 This is a time-temperature diagram of an embodiment of the present invention;

[0020] Figure 3 This is a time-temperature diagram illustrating conventional heat treatment methods in existing technologies. Detailed Implementation

[0021] The following detailed description illustrates the specific implementation method:

[0022] like Figure 1 As shown, the specific steps of the heat treatment method of the present invention include: heating the furnace to 860-880°C, holding it at that temperature for a certain time, and then air cooling; then heating the furnace to 810-830°C, holding it at that temperature for a certain time, and then water cooling; after water cooling, performing medium-temperature tempering; holding the medium-temperature tempering at that temperature for a certain time; and finally air cooling after removing it from the furnace, thus completing the heat treatment method for fastener forgings made of SA-194M Gr.2H material.

[0023] Example: This example uses fastener forgings made of SA-194M Gr.2H material. The forging specifications are φ45×755 and the material is SA-194M Gr.2H. The chemical composition of the forging is shown in Table 1 below.

[0024] Table 1 Chemical composition of forgings

[0025] C Mn Si P S Cr Ni Mo 0.46 0.67 0.32 0.008 0.002 0.21 0.24 0.06

[0026] Schematic diagram of heat treatment method, time, and temperature, as shown in the figure. Figure 2 As shown, the specific heat treatment method includes the following steps:

[0027] (1) Heating: After 3 hours of heating with the furnace, the thermocouple temperature record reached 860℃ and heat preservation began;

[0028] (2) Heat preservation: Start heat preservation at 860℃ and keep it warm for 90 minutes;

[0029] (3) Normalizing and cooling: After the heat preservation is completed, remove the furnace and air cool to room temperature;

[0030] (4) Quenching and heating: The furnace is heated for 2.0 hours, and the thermocouple temperature record reaches 810℃ and then the heat is maintained.

[0031] (5) Heat preservation: Start heat preservation at 810℃ and keep it warm for 90 minutes;

[0032] (6) Quenching and cooling: After the heat preservation is completed, remove the furnace and cool it with water to below 150℃;

[0033] (7) Medium-temperature tempering: Heat up the furnace for 2 hours, and start holding the thermocouple temperature record when it reaches 500℃ for 245 minutes.

[0034] (8) Tempering and cooling: After the heat preservation is completed, remove the furnace and air cool to room temperature;

[0035] This invention employs high-temperature normalizing for fine grain processing and quenching at a temperature lower than the conventional austenitizing temperature followed by medium-temperature tempering. The mechanical properties of forgings of the same material and specifications after heat treatment are shown in Table 2.

[0036] Table 2 - Mechanical property values ​​of the examples

[0037]

[0038] Comparative Example: Fastener forgings made of SA-194MGr.2H material with the same specifications as in Example 1 were used. The general heat treatment method is described in [link to example]. Figure 3 The specific heat treatment method includes the following steps:

[0039] (1) Quenching and heating: The furnace is heated for 2.0 hours, and the thermocouple temperature record reaches 810℃ and then the heat is maintained.

[0040] (2) Heat preservation: Start heat preservation at 840℃ and keep it warm for 90 minutes; Heat preservation: Start heat preservation at 860℃ and keep it warm for 90 minutes;

[0041] (3) Quenching and cooling: After the heat preservation is completed, the furnace is removed and water-cooled to below 150℃;

[0042] (4) Medium-temperature tempering: Heat up the furnace for 2 hours, and start holding the thermocouple temperature record when it reaches 500℃ and 550℃ for 245 minutes.

[0043] (5) Tempering and cooling: After the heat preservation is completed, remove the furnace and air cool it to room temperature;

[0044] The mechanical properties of forgings after heat treatment using general heat treatment methods are shown in Table 3:

[0045] Table 3 - Comparative Mechanical Properties

[0046]

[0047] As can be seen from Tables 2 and 3, the hardness of the forgings in the embodiments meets the requirements, and R P0.2 R m The value is much higher than the comparative figure.

[0048] In the examples, the impact lateral expansion LE under Akv (70, 66, 64) was 0.92, 1.03, and 0.93; the impact lateral expansion LE under Akv (61, 50, 66) was 0.80, 0.67, and 1.00, which are much higher than the impact lateral expansion LE under the same experimental conditions in the comparative example. The impact toughness is improved by nearly 1.5 times, and the comprehensive mechanical properties are also very good. Therefore, the fastener forgings made of SA-194M Gr.2H material can achieve high strength and hardness and low temperature impact requirements by high-temperature normalizing fine-grain treatment and quenching below the conventional austenitizing temperature followed by medium-temperature tempering, with good results.

[0049] For those skilled in the art, numerous modifications and improvements can be made without departing from the inventive 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 invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings, characterized in that, S1. High-temperature normalizing fine grain treatment: Heat the forging to 860-880℃ and hold for 1-2 hours; S2. Quenching and cooling: After the forging is held at the temperature, it is taken out of the furnace and air-cooled to room temperature; S3. Quenching and heating: Heat the forging to 810-830℃ and hold for 1-2 hours; S4. Quenching and cooling: After the forging is kept at the heat, it is taken out of the furnace and water-cooled to below 150℃; S5. Medium-temperature tempering: Heat the forging to 480-560℃ and hold for 3.5-4.5 hours; S6. Tempering and cooling: After the holding period, remove the furnace and air cool to room temperature; The chemical composition of the SA-194M Gr.2H material forgings, by mass percentage, includes: C: 0.46%, Mn: 0.67%, Si: 0.32%, P: 0.008%, S: 0.002%, Cr: 0.21%, Ni: 0.24%, Mo: 0.06%.

2. The heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings according to claim 1, characterized in that: S1, High-temperature normalizing and fine-grain treatment: heating the forging to 860℃ and holding for 1 hour; S3, Quenching and heating: heating the forging to 810℃ and holding for 1 hour; S5, Medium-temperature tempering: heating the forging to 480℃ and holding for 3.5 hours.

3. The heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings according to claim 2, characterized in that: S1, High-temperature normalizing and fine-grain treatment: Heat the forging to 870℃ and hold for 1.5h; S3, Quenching and heating: Heat the forging to 820℃ and hold for 1.5h; S5, Medium-temperature tempering: Heat the forging to 520℃ and hold for 4h.

4. The heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings according to claim 3, characterized in that: S1, High-temperature normalizing and fine-grain treatment: heating the forging to 880℃ and holding for 2 hours; S3, Quenching and heating: heating the forging to 830℃ and holding for 2 hours; S5, Medium-temperature tempering: heating the forging to 560℃ and holding for 4.5 hours.

5. The heat treatment method for improving the comprehensive mechanical properties of SA-194M-Gr.2H material forgings according to any one of claims 1 to 4, characterized in that: The S4 is water-cooled to room temperature.

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