A heat treatment process for 1.4923 forgings

Abstract

This invention relates to a heat treatment process for 1.4923 forgings that achieves the required final heat treatment performance. The invention utilizes stepped heating and annealing to achieve uniform spheroidization of the microstructure, resulting in a well-structured forging blank. Repeated microstructural transformations ensure finer grain size and more uniform microstructure within the forging blank. While guaranteeing the transformation of austenite to martensite under high-temperature cooling, the quenching cooling intensity is reduced, preventing cracking of the forging blank due to excessive internal stress. Compared to conventional heat treatment methods, this process achieves higher strength and toughness in forgings with the same cross-section. The 1.4923 forgings produced according to this invention achieve the required final heat treatment performance.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and specifically relates to a heat treatment process for 1.4923 forgings whose final heat treatment performance meets the standard requirements. Background Technology

[0002] In actual production, 1.4923 material has a high alloy content, characterized by high C, high Cr, and poor thermoplasticity at high temperatures. Therefore, it is prone to forging cracks during forging. To ensure successful forging, multiple high-temperature reheating processes are required when producing forgings from this material. Consequently, the microstructure of the forged billet is relatively coarse. Improper annealing methods after forging can easily produce a network structure, leading to quenching cracks and scrap during subsequent quenching. Furthermore, due to the high alloy content, improper heating and cooling parameters during tempering can also cause problems. This leads to workpiece cracking and uneven microstructure. Therefore, according to conventional production methods, N32 quenching oil is used as the coolant for quenching and cooling 1.4923 material round bars or stepped shafts with an outer diameter of φ300~φ600mm. However, due to the weak cooling strength of N32 quenching oil, it cannot guarantee the quenching effect when producing forgings with high strength and high toughness requirements, resulting in mechanical properties that do not meet the standard requirements. Therefore, in combination with actual production, there is an urgent need for a heat treatment process that can guarantee both the quality of forgings and the high strength and high toughness of large-size forgings. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a heat treatment process for 1.4923 forgings. By using stepped heating and annealing, the microstructure is made uniform and spheroidized, resulting in a good forging structure. Through repeated microstructure transformation, the internal grain size of the forging can be refined and the microstructure can be made uniform. Under the premise of ensuring the transformation of austenite to martensite under high temperature cooling, the quenching cooling intensity is reduced, avoiding cracking of the forging due to excessive internal microstructure stress. Compared with ordinary heat treatment methods, higher strength and toughness can be obtained for forgings with the same cross-section.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a heat treatment process for 1.4923 forgings, the specific process of which is as follows:

[0005] Step 1) Post-forging pretreatment: After forging, place the forging on the rack for air cooling until the surface temperature of the forging is 400℃~600℃. After completing Step 1), load the forging into the box furnace for annealing.

[0006] Step 2) Annealing: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 500℃~600℃ at a rate of ≤10℃ / h~60℃ / h and held for 2h~10h. Then the temperature is increased to 800℃~900℃ at a rate of ≥80℃ / h and held for 5h~20h. After that, the temperature is cooled in the furnace at a rate of ≤30℃ / h to 300℃~450℃ and then air-cooled to room temperature. After completing Step 2), the forging is put into a box furnace for quenching.

[0007] Step 3) Quenching: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 550℃~700℃ at a heating rate of ≤20℃ / h~80℃ / h and held for 3h~10h. Then, the temperature is increased to 850℃~950℃ at a heating rate of ≥80℃ / h and held for 5h~15h. After holding, the forging is taken out of the furnace for quenching and cooling. Before quenching, the forging is pre-cooled for ≤230s. Then, the forging is placed in an aqueous solution for cooling for 40min~100min. The concentration of the aqueous solution is 8%~12%. The liquid temperature is controlled at 25℃~40℃ when quenching begins. Then, the forging is lifted out of the quenching solution and air-cooled for 50s~200s. After air cooling, the forging is placed in the aqueous solution for cooling for 30min~80min. After cooling, the forging is lifted out of the aqueous solution. After completing Step 3), the forging is put into a box furnace for high-temperature tempering.

[0008] Step 4) High-temperature tempering: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 550℃~650℃ at a heating rate of ≤20℃ / h~80℃ / h and held for 10h~30h. Then the temperature is slowly reduced to 300℃~350℃ at a cooling rate of ≤20℃ / h~50℃ / h. The forging is then removed from the furnace and air-cooled to room temperature. After completing Step 4), the forging is placed into a box furnace for low-temperature tempering.

[0009] Step 5) Low-temperature tempering: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 500℃~600℃ at a heating rate of ≤20℃ / h~≤80℃ / h and held for 10h~30h. After holding, the forging is taken out of the furnace and air-cooled to room temperature.

[0010] Compared with the prior art, the process of this invention has the following advantages:

[0011] The heat treatment process for 1.4923 forgings according to the present invention can achieve the following positive effects:

[0012] 1. By using stepped heating annealing, the microstructure is made uniformly spheroidized, resulting in a good forging structure.

[0013] 2. Repeated structural transformations can ensure finer grain size and more uniform microstructure within the forged billet.

[0014] 3. While ensuring the transformation of austenite to martensite under high-temperature cooling, reduce the quenching cooling intensity to avoid cracking of the forging billet due to excessive internal structural stress.

[0015] 4. Higher strength and toughness can be obtained in forgings with the same cross-section compared to ordinary heat treatment methods. The 1.4923 forgings produced according to this invention achieve the standard requirements in terms of final heat treatment performance, meet market demands, and improve product delivery rate. Implementation

[0016] A heat treatment process for 1.4923 forgings, the specific process is as follows:

[0017] Step 1) Post-forging pretreatment: After forging, place the forging on the rack for air cooling until the surface temperature of the forging is 400℃~600℃. After completing Step 1), load the forging into the box furnace for annealing.

[0018] Step 2) Annealing: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 500℃~600℃ at a rate of ≤10℃ / h~60℃ / h and held for 2h~10h. Then the temperature is increased to 800℃~900℃ at a rate of ≥80℃ / h and held for 5h~20h. After that, the temperature is cooled in the furnace at a rate of ≤30℃ / h to 300℃~450℃ and then air-cooled to room temperature. After completing Step 2), the forging is put into a box furnace for quenching.

[0019] Step 3) Quenching: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 550℃~700℃ at a heating rate of ≤20℃ / h~80℃ / h and held for 3h~10h. Then, the temperature is increased to 850℃~950℃ at a heating rate of ≥80℃ / h and held for 5h~15h. After holding, the forging is taken out of the furnace for quenching and cooling. Before quenching, the forging is pre-cooled for ≤230s. Then, the forging is placed in an aqueous solution for cooling for 40min~100min. The concentration of the aqueous solution is 8%~12%. The liquid temperature is controlled at 25℃~40℃ when quenching begins. Then, the forging is lifted out of the quenching solution and air-cooled for 50s~200s. After air cooling, the forging is placed in the aqueous solution for cooling for 30min~80min. After cooling, the forging is lifted out of the aqueous solution. After completing Step 3), the forging is put into a box furnace for high-temperature tempering.

[0020] Step 4) High-temperature tempering: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 550℃~650℃ at a heating rate of ≤20℃ / h~80℃ / h and held for 10h~30h. Then the temperature is slowly reduced to 300℃~350℃ at a cooling rate of ≤20℃ / h~50℃ / h. The forging is then removed from the furnace and air-cooled to room temperature. After completing Step 4), the forging is placed into a box furnace for low-temperature tempering.

[0021] Step 5) Low-temperature tempering: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 500℃~600℃ at a heating rate of ≤20℃ / h~≤80℃ / h and held for 10h~30h. After holding, the forging is taken out of the furnace and air-cooled to room temperature.

[0022] Example 1: A heat treatment process for 1.4923 forgings.

[0023] Steel grade: 1.4923;

[0024] Chemical composition: C=0.19%, Si=0.24%, Mn=0.60%, Cr=11.49%, Ni=0.42%.

[0025] S=0.003%, P=0.014%, Mo=0.88%, V0.27;

[0026] Specifications: Φ360 round bar.

[0027] The heat treatment process is as follows:

[0028] Step 1) Post-forging pretreatment: After forging, place the forging on the rack and air cool until the surface temperature of the forging is 450℃.

[0029] Step 2) After Step 1) is completed, the forging is placed into a box furnace for annealing. Annealing: When the forging is put into the furnace, the furnace temperature is 350℃. The temperature is increased to 550℃ at a rate of 50℃ / h and held for 5 hours. Then the temperature is increased to 880℃ at a rate of 100℃ / h and held for 10 hours. After that, the temperature is cooled to 350℃ in the furnace at a rate of 20℃ / h and then air-cooled to room temperature.

[0030] Step 3) After step 2) is completed, the forging is placed in a box furnace for quenching. Quenching: When the forging is put into the furnace, the furnace temperature is 280℃. The temperature is increased to 650℃ at a rate of 50℃ / h and held for 3 hours. Then, the temperature is increased to 900℃ at a rate of 100℃ / h and held for 10 hours. After quenching, the forging is removed from the furnace and cooled. Before quenching, the forging is pre-cooled for 200 seconds. Then, the forging is placed in an aqueous solution for 60 minutes to cool. The concentration of the aqueous solution is 9.3%. The liquid temperature is controlled at 27℃ when quenching begins. Then, the forging is lifted out of the quenching solution and air-cooled for 80 seconds. After air cooling, the forging is placed in the aqueous solution for 40 minutes to cool. After cooling, the forging is lifted out of the aqueous solution.

[0031] Step 4) After step 3) is completed, the forging is placed into a box furnace for high-temperature tempering. High-temperature tempering: When the forging is put into the furnace, the furnace temperature is 300℃. The temperature is increased to 600℃ at a rate of 50℃ / h and held for 12 hours. Then, the temperature is slowly reduced to 350℃ at a rate of 30℃ / h and then removed from the furnace and air-cooled to room temperature.

[0032] Step 5) After step 4) is completed, the forging is placed into a box furnace for low-temperature tempering. Low-temperature tempering: when the forging is put into the furnace, the furnace temperature is 230℃. The temperature is increased to 570℃ at a rate of 50℃ / h and held for 12 hours. After holding, the forging is taken out of the furnace and air-cooled to room temperature.

[0033] The test results after production according to the above heat treatment process are shown in Table 1:

[0034] Table 1 Test Results

[0035] Technical Requirements Yield strength ≥ 700 MPa Tensile strength 850-1050 MPa Elongation ≥10% Shrinkage rate ≥35% Impact energy AKV≥25J Actual testing 740 910 18 51.5 27 / 33 / 28

[0036] After production using the heat treatment process of the 1.4923 forging of this invention, the performance and grain size test results meet the requirements.

[0037] Example 2: A heat treatment process for 1.4923 forgings.

[0038] Steel grade: 1.4923;

[0039] Chemical composition: C=0.18%, Si=0.25%, Mn=0.60%, Cr=11.51%, Ni=0.42%.

[0040] S=0.003%, P=0.014%, Mo=0.87%, V0.27;

[0041] Specifications: Φ360 round bar.

[0042] The heat treatment process is as follows:

[0043] Step 1) Post-forging pretreatment: After forging, place the forging on the rack and air cool until the surface temperature of the forging is 430℃.

[0044] Step 2) After Step 1) is completed, the forging is placed into a box furnace for annealing. Annealing: When the forging is put into the furnace, the furnace temperature is 330℃. The temperature is increased to 550℃ at a rate of 50℃ / h and held for 5 hours. Then the temperature is increased to 880℃ at a rate of 100℃ / h and held for 10 hours. After that, the temperature is cooled in the furnace at a rate of 20℃ / h to 350℃ and then air-cooled to room temperature.

[0045] Step 3) After step 2) is completed, the forging is placed in a box furnace for quenching. Quenching: When the forging is put into the furnace, the furnace temperature is 270℃. The temperature is increased to 650℃ at a rate of 50℃ / h and held for 3 hours. Then, the temperature is increased to 900℃ at a rate of 100℃ / h and held for 10 hours. After quenching, the forging is removed from the furnace and cooled. Before quenching, the forging is pre-cooled for 200 seconds. Then, the forging is placed in an aqueous solution for 60 minutes to cool. The concentration of the aqueous solution is 9.3%. The liquid temperature is controlled at 27℃ when quenching begins. Then, the forging is lifted out of the quenching solution and air-cooled for 80 seconds. After air cooling, the forging is placed in the aqueous solution for 40 minutes to cool. After cooling, the forging is lifted out of the aqueous solution.

[0046] Step 4) After step 3) is completed, the forging is placed into a box furnace for high-temperature tempering. High-temperature tempering: When the forging is put into the furnace, the furnace temperature is 310℃. The temperature is increased to 600℃ at a rate of 50℃ / h and held for 12 hours. Then, the temperature is slowly reduced to 350℃ at a rate of 30℃ / h and then removed from the furnace and air-cooled to room temperature.

[0047] Step 5) After step 4) is completed, the forging is placed into a box furnace for low-temperature tempering. Low-temperature tempering: when the forging is put into the furnace, the furnace temperature is 260℃. The temperature is increased to 570℃ at a rate of 50℃ / h and held for 12 hours. After holding, the forging is taken out of the furnace and air-cooled to room temperature.

[0048] The test results after production according to the above heat treatment process are shown in Table 1:

[0049] Table 1 Test Results

[0050] Technical Requirements Yield strength ≥ 700 MPa Tensile strength 850-1050 MPa Elongation ≥10% Shrinkage rate ≥35% Impact energy AKV≥25J Actual testing 800 920 17 59.5 26 / 30 / 28

[0051] After production using the heat treatment process of the 1.4923 forging of this invention, the performance and grain size test results meet the requirements.

Claims

1. A heat treatment process for 1.4923 forgings, characterized in that: The specific process is as follows: Step 1) Post-forging pretreatment: After forging, place the forging on the rack for air cooling until the surface temperature of the forging is 400℃~600℃. After completing Step 1), load the forging into the box furnace for annealing. Step 2) Annealing: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 500℃~600℃ at a rate of 10℃ / h~60℃ / h and held for 2h~10h. Then the temperature is increased to 800℃~900℃ at a rate of ≥80℃ / h and held for 5h~20h. After that, the temperature is cooled in the furnace at a rate of ≤30℃ / h to 300℃~450℃. The forging is then air-cooled to room temperature. After completing Step 2), the forging is placed into a box furnace for quenching. Step 3) Quenching: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 550℃~700℃ at a rate of 20℃ / h~80℃ / h and held for 3h~10h. Then, the temperature is increased to 850℃~950℃ at a rate of ≥80℃ / h and held for 5h~15h. After holding, the forging is taken out of the furnace for quenching and cooling. Before quenching, the forging is pre-cooled for ≤230s. Then, the forging is placed in an aqueous solution for 40min~100min. The concentration of the aqueous solution is 8%~12%. The liquid temperature is controlled at 25℃~40℃ when quenching begins. Then, the forging is lifted out of the quenching solution and air-cooled for 50s~200s. After air cooling, the forging is placed in the aqueous solution for 30min~80min. After cooling, the forging is lifted out of the aqueous solution. After completing Step 3), the forging is put into a box furnace for high-temperature tempering. Step 4) High-temperature tempering: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 550℃~650℃ at a rate of 20℃ / h~80℃ / h and held for 10h~30h. Then the temperature is slowly reduced to 300℃~350℃ at a rate of 20℃ / h~50℃ / h. The forging is then removed from the furnace and air-cooled to room temperature. After completing Step 4), the forging is put into a box furnace for low-temperature tempering. Step 5) Low-temperature tempering: When the forging is put into the furnace, the furnace temperature is ≤450℃. The temperature is increased to 500℃~600℃ at a rate of 20℃ / h~80℃ / h and held for 10h~30h. After holding, the forging is taken out of the furnace and air-cooled to room temperature.