Heat treatment process for large-size 1Cr13 mandrel forgings

Abstract

The invention discloses a heat treatment process of a large-size 1Cr13 mandrel forge piece, which is suitable for the 1Cr13 forge piece with the outer circle diameter of less than or equal to phi 700mm, the temperature difference between the outer surface and the core part of the forge piece is reduced through a multi-step speed-limiting heating mode, and the phenomenon of forge piece cracking caused by overlarge thermal stress in the heating process is avoided. A reasonable quenching cooling mode is adopted, it is guaranteed that even and fine lath-shaped martensite is obtained after the step forge piece with the large cross section difference is quenched, and the risk that the step forge piece with the large cross section difference cracks due to the fact that quenching structure transformation stress is too large is avoided; through a rapid cooling mode, the temper brittleness of the 1Cr13 forge piece in the temperature range of 480-600 DEG C is effectively removed, and the failure phenomenon of intergranular fracture of the forge piece in the using process is avoided; and after tempering and discharging, the final temperature of the forge piece is controlled, so that the residual stress generated by rapid cooling is effectively removed, and the stability of the forge piece is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of metal materials, and particularly relates to a heat treatment process for large-size 1Cr13 mandrel forgings, which not only ensures that forgings with large cross-section differences obtain uniform and good structures and avoids cracking during heating and quenching of the forgings, but also effectively removes high-temperature temper brittleness and residual stress and improves the overall quality of the forgings. Background Art

[0002] 1Cr13 material belongs to martensitic stainless steel, which has high hardness, toughness, good corrosion resistance, thermal strength, cold deformation performance and shock absorption. Therefore, it is generally used to make parts that are resistant to weak corrosive media and bear loads, such as turbine blades, hydraulic press valves, bolts, nuts, etc. It is mainly used for parts that require high toughness, certain stainlessness and withstand impact loads, such as fasteners, thermal cracking anti-sulfur corrosion equipment, etc. It can also be used to make equipment and components that are resistant to weak corrosive media under normal temperature conditions. At present, this material is mainly used to produce forging mandrel products. Since the Cr alloy content of this material is as high as 11.5%~13.5%, and the product is a step forging, the step cross-sectional size difference is large, resulting in more forging times, resulting in coarse and uneven structure. In addition, due to the large cross-sectional difference of the forging, during the heat treatment process, if the conventional direct heating and furnace quenching heat treatment method is used, it is easy to cause the surface and core to crack due to excessive thermal stress and structural stress, and the material has certain high-temperature temper brittleness characteristics. If it is not properly controlled, it is easy to cause the impact toughness of the forging to decrease, and intergranular fracture will occur during use, reducing the service life of the forging and affecting the quality of the forging product. Therefore, in order to improve the quality of 1Cr13 mandrel forging products and form stable batch production, a reasonable heat treatment process method is urgently needed. Patent number: 201610534888.6, patent name: A method for improving the impact performance of 1Cr13, the specific steps disclosed are: placing the material in a medium frequency furnace for refining, the smelting temperature is 1450℃~1460℃, adjusting the content of each element during the smelting process so that its weight ratio meets the design requirements, and casting to obtain an electrode rod; remelting the obtained electrode rod with electroslag to obtain an electroslag ingot; loading the obtained electroslag ingot into a heating furnace, heating it to 1150℃~1170℃, keeping it warm for a certain period of time, and then taking it out of the furnace for forging to make a billet; heat treating the obtained material, including quenching, tempering and stress relief. The gas turbine blade material produced by this application can significantly improve the impact performance of the diaphragm ring, improve the yield rate of the steel ingot, and create considerable production benefits. However, this application still has the problem that excessive thermal stress will lead to cracking, and it cannot guarantee that the forgings will obtain a uniform and consistent structure. During the use of the forgings, there is a phenomenon of intergranular fracture, and the forgings will produce residual stress due to rapid cooling. Summary of the invention

[0003] The object of the present invention is to overcome the deficiencies existing in the prior art and provide a heat treatment process for large-sized 1Cr13 mandrel forgings, which not only ensures that forgings with a large cross-section difference obtain a uniform and good structure, avoids cracking during the heating and quenching processes of the forgings, but also effectively removes high-temperature temper brittleness and residual stress, and improves the overall quality of the forgings.

[0004] To achieve the above object of the invention, the present invention adopts the following technical solutions: A heat treatment process for large-sized 1Cr13 mandrel forgings, and the specific process steps are as follows: Step 1), homogenization annealing: Load the forgings into a heating furnace with a furnace temperature of 550°C to 650°C, hold for 2h to 10h, heat up to 850°C to 900°C at a heating rate of 10°C / h to 80°C / h, hold for 5h to 50h, and after the holding is completed, cool in the furnace at a cooling rate of ≤30°C / h to below 300°C and then take out and air-cool to room temperature. After completing Step 1), load the forgings into the heating furnace and perform quenching; Step 2), quenching: Load the forgings into a heating furnace with a furnace temperature of ≤450°C, heat up to 600°C to 700°C at a heating rate of 10°C / h to 100°C / h, hold for 2h to 10h, then heat up to 860°C to 900°C at a heating rate of 10°C / h to 100°C / h, hold for 2h to 10h, and then heat up to 980°C to 1040°C at the full-power heating rate, hold for 2h to 20h and then take out and quench and cool. First, pre-cool in the air for 100s to 300s, and then put the forgings into an N32 quenching oil tank with an initial temperature of 20°C to 70°C and cool for 5min to 200min. During the cooling process, start the compressed air to stir the N32 quenching oil. After cooling, lift the forgings out of the N32 quenching oil tank. After completing Step 2), load the forgings into the heating furnace and perform a high-temperature tempering once; Step 3), high-temperature tempering once: Load the forgings into a heating furnace with a furnace temperature of ≤450°C, heat up to 650°C to 750°C at a heating rate of 10°C / h to 80°C, hold for 5h to 30h, then lift the forgings out of the tempering heating furnace and put them into an N32 quenching oil tank with an initial temperature of 20°C to 70°C and cool until the surface temperature of the forgings is 300°C to 350°C, and then lift the forgings out of the N32 quenching oil tank and air-cool to room temperature. After completing Step 3), load the forgings into the heating furnace and perform a high-temperature tempering twice; Step 4), high-temperature tempering twice: Load the forgings into a heating furnace with a furnace temperature of ≤450°C, heat up to 600°C to 720°C at a heating rate of 10°C / h to 80°C, hold for 5h to 30h, then lift the forgings out of the tempering heating furnace and put them into an N32 quenching oil tank with an initial temperature of 20°C to 70°C and cool until the surface temperature of the forgings is 300°C to 350°C, and then lift the forgings out of the N32 quenching oil tank and air-cool to room temperature.

[0005] The process of the present invention is applicable to round bar-shaped 1Cr13 forgings with an outer diameter ≤ φ700mm. Compared with the prior art, it has the following advantages: 1. By means of multi-step speed-limited heating, the temperature difference between the outer surface and the core of the forging is reduced, avoiding the phenomenon of forging cracking caused by excessive thermal stress during the heating process; 2. By adopting a reasonable quenching and cooling method, not only can uniform and fine lath martensite be obtained after quenching of stepped forgings with a large section difference, but also the risk of cracking of stepped forgings with a large section difference caused by excessive quenching structure transformation stress can be prevented; 3. By means of rapid cooling, the temper brittleness generated by 1Cr13 forgings in the temperature range of 480°C to 600°C is effectively removed, avoiding the failure phenomenon of intergranular fracture during the use of the forgings; 4. After tempering and furnace discharging, by controlling the final temperature of the forging, not only the residual stress generated by rapid cooling is effectively removed, but also the stability of the forging is improved.

[0006] The overall quality of the 1Cr13 forgings produced according to the present invention is improved, meeting the market use requirements. Specific embodiments

[0007] Example 1: A heat treatment process for a large-sized 1Cr13 mandrel forging, steel grade: 1Cr13, chemical composition: C = 0.12%, Si = 0.43%, Mn = 0.68%, Cr = 12.41%, Ni = 0.09%, S = 0.002%, P = 0.015%; specification: Φ300*Φ390*Φ645*Φ350*3500mm; the heat treatment process is as follows: Step 1), homogenization annealing: Load the forging into a heating furnace with a furnace temperature of 600°C, hold for 3h, heat up to 860°C at a heating rate of 80°C / h, hold for 15h, and then cool with the furnace at a cooling rate of 30°C / h to below 291°C and discharge the furnace for air cooling until it reaches room temperature; Step 2), prepare for quenching after step 1) is executed: Load the forging into a heating furnace with a furnace temperature of 268°C, heat up to 620°C at a heating rate of 80°C / h, hold for 3h, then heat up to 880°C at a heating rate of 80°C / h, hold for 2h, and then heat up to 1020°C at the full power heating rate, hold for 14h and then discharge the furnace for quenching and cooling. First, pre-cool in the air for 160s, and then put the forging into an N32 quenching oil tank with an initial temperature of 35°C for cooling for 65min. During the cooling process, start the compressed air to stir the N32 quenching oil, and after cooling, lift the forging out of the N32 quenching oil tank; Step 3): After step 2) is executed, prepare to perform a high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 305°C, raise the temperature to 677°C at a heating rate of 80°C / h, hold for 30 h, then lift the forging out of the tempering heating furnace and put it into an N32 quenching oil tank with an initial temperature of 39°C to cool until the surface temperature of the forging reaches 315°C. Then lift the forging out of the N32 quenching oil tank and perform air cooling until it reaches room temperature. Step 4): After step 3) is executed, prepare to perform a second high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 289°C, raise the temperature to 650°C at a heating rate of 80°C / h, hold for 28 h, then lift the forging out of the tempering heating furnace and put it into an N32 quenching oil tank with an initial temperature of 36.5°C to cool until the surface temperature of the forging reaches 331°C. Then lift the forging out of the N32 quenching oil tank and perform air cooling until it reaches room temperature.

[0008] Table 1 Test Results Technical requirements σs≥345 σb≥540 δ5≥22 Ψ≥55 Aku≥78 Surface hardness 200 - 230 HB Actual detection 530 690 24 72 145 / 86 203 / 203 / 200 After being produced by the heat treatment process method of a large-sized 1Cr13 mandrel forging of the present invention, the test results such as mechanical properties and surface hardness are qualified and meet the technical requirements of customers.

[0009] Example 2: A heat treatment process for a large-sized 1Cr13 mandrel forging, steel grade: 1Cr13, Chemical composition: C = 0.12%, Si = 0.44%, Mn = 0.65%, Cr = 12.43%, Ni = 0.09%, S = 0.003%, P = 0.014%; Specification: Φ300*Φ440*Φ645*Φ350*3500 mm; The heat treatment process is as follows: Step 1): Homogenization annealing: Load the forging into a heating furnace with a furnace temperature of 600°C, hold for 3 h, raise the temperature to 860°C at a heating rate of 80°C / h, hold for 15 h, and then cool it in the furnace at a cooling rate of 30°C / h until it is below 293°C and then take it out of the furnace for air cooling until it reaches room temperature. Step 2): After step 1) is executed, prepare to perform quenching: Load the forging into a heating furnace with a furnace temperature of 265°C, raise the temperature to 620°C at a heating rate of 80°C / h, hold for 3 h, then raise the temperature to 880°C at a heating rate of 80°C / h, hold for 2 h, and then raise the temperature to 1020°C at a full-power heating rate, hold for 14 h and then take it out of the furnace for quenching and cooling. First, pre-cool it in the air for 163 s, and then put the forging into an N32 quenching oil tank with an initial temperature of 33°C to cool for 65 min. During the cooling process, turn on the compressed air to stir the N32 quenching oil. After cooling, lift the forging out of the N32 quenching oil tank. Step 3), after step 2) is executed, prepare to perform a high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 275 °C, and raise the temperature to 675 °C at a heating rate of 80 °C / h. After holding for 30 h, lift the forging out of the tempering heating furnace and place it in an N32 quenching oil tank with an initial temperature of 36 °C to cool until the surface temperature of the forging reaches 332 °C. Then lift the forging out of the N32 quenching oil tank and perform air cooling until it reaches room temperature; Step 4), after step 3) is executed, prepare to perform a second high-temperature tempering: Load the forging into a heating furnace with a furnace temperature of 339 °C, and raise the temperature to 650 °C at a heating rate of 80 °C / h. After holding for 28 h, lift the forging out of the tempering heating furnace and place it in an N32 quenching oil tank with an initial temperature of 40 °C to cool until the surface temperature of the forging reaches 343 °C. Then lift the forging out of the N32 quenching oil tank and perform air cooling until it reaches room temperature.

[0010] Table 2 Test Results Technical requirements σs≥345 σb≥540 δ5≥22 Ψ≥55 Aku≥78 Surface hardness 200 - 230 HB Actual detection 530 695 23 71 79 / 87 215 / 206 / 203 After being produced by the heat treatment process method of a large-sized 1Cr13 mandrel forging of the present invention, the test results such as mechanical properties and surface hardness are qualified and meet the technical requirements of customers.

Claims

1. A heat treatment process for a large-sized 1Cr13 mandrel forging, characterized in that: The specific process steps are as follows: Step 1), homogenizing annealing: Load the forging into a heating furnace with a furnace temperature of 550°C to 650°C, hold for 2h to 10h, heat up to 850°C to 900°C at a heating rate of 10°C / h to 80°C / h, hold for 5h to 50h, and after the holding is completed, cool with the furnace to below 300°C at a cooling rate of ≤30°C / h and then take out and air-cool to room temperature. After completing Step 1), load the forging into the heating furnace and perform quenching; Step 2), quenching: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat up to 600°C to 700°C at a heating rate of 10°C / h to 100°C / h, hold for 2h to 10h, then heat up to 860°C to 900°C at a heating rate of 10°C / h to 100°C / h, hold for 2h to 10h, and then heat up to 980°C to 1040°C at the full-power heating rate, hold for 2h to 20h and then take out for quenching and cooling. First, pre-cool in the air for 100s to 300s, and then put the forging into an N32 quenching oil tank with an initial temperature of 20°C to 70°C and cool for 5min to 200min. During the cooling process, start the compressed air to stir the N32 quenching oil. After cooling, lift the forging out of the N32 quenching oil tank. After completing Step 2), load the forging into the heating furnace and perform a high-temperature tempering once; Step 3), high-temperature tempering once: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat up to 650°C to 750°C at a heating rate of 10°C / h to 80°C / h, hold for 5h to 30h and then lift the forging out of the tempering heating furnace and put it into an N32 quenching oil tank with an initial temperature of 20°C to 70°C and cool until the surface temperature of the forging is 300°C to 350°C, and then lift the forging out of the N32 quenching oil tank and air-cool to room temperature. After completing Step 3), load the forging into the heating furnace and perform a high-temperature tempering twice; Step 4), high-temperature tempering twice: Load the forging into a heating furnace with a furnace temperature of ≤450°C, heat up to 600°C to 720°C at a heating rate of 10°C / h to 80°C / h, hold for 5h to 30h and then lift the forging out of the tempering heating furnace and put it into an N32 quenching oil tank with an initial temperature of 20°C to 70°C and cool until the surface temperature of the forging is 300°C to 350°C, and then lift the forging out of the N32 quenching oil tank and air-cool to room temperature.

2. The heat treatment process of a large-sized 1Cr13 mandrel forging according to claim 1, characterized in that: Applicable to 1Cr13 forgings with an outer diameter of ≤φ700mm.