Process method for eliminating twin-crystal-shaped carbide after forging of 40Cr15Mo2VN

Abstract

The invention discloses a process method for eliminating twin-crystal-shaped carbides after 40Cr15Mo2VN forging, and belongs to the field of heat treatment processing of bearing parts. Decomposing austenite at low temperature; normalizing treatment; forging annealing; and after annealing, the metallographic structure is inspected to have no twin-crystal-shaped carbide, and the hardness meets the requirement. According to the method, carbide particles separated out from a 40Cr15Mo2VN forging structure can be fused into an austenite structure again through high-temperature heating, so that high-temperature deformation recrystallization occurs, an original austenite stubborn grain boundary is destroyed, and the purpose of eliminating twin-crystal-shaped carbide is achieved; austenite in the internal structure is completely decomposed through three times of low-temperature decomposition, and a small amount of residual twin-crystal-shaped carbides are further eliminated. Rapid cooling is carried out after normalizing, twin-crystal-shaped carbides are prevented from being generated again, meanwhile, grains can be refined, and the impact toughness of the material is improved; twin-crystal-shaped carbides generated due to the forging problem are eliminated, the quality of a high-nitrogen stainless steel product is guaranteed, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of heat treatment processing of bearing parts, and in particular relates to a process for eliminating twin-shaped carbides after forging of 40Cr15Mo2VN. Background Art

[0002] The corrosion resistance of bearings made of 40Cr15Mo2VN high nitrogen stainless steel is 10 times that of bearings made of G95Cr18 / G108Cr18Mo high carbon chromium stainless steel. Therefore, under some special working conditions, such as high temperature, high humidity, marine salt spray, etc., bearings made of 40Cr15Mo2VN high nitrogen stainless steel are increasingly widely used.

[0003] There are currently two methods for making bearing parts using 40Cr15Mo2VN high nitrogen stainless steel:

[0004] 1. The outer ring, inner ring and rolling element of the bearing are sampled directly from the raw material (bar) and then machined into shape;

[0005] 2. The outer ring and inner ring of the bearing are made into part blanks by forging, and then annealed and turned into shape. The rolling element is directly sampled from the raw material (bar) and then turned into shape.

[0006] Bearing parts (bearing outer ring and inner ring) with an outer diameter greater than 100mm are generally made by forging to save material costs. However, due to the poor thermal conductivity of 40Cr15Mo2VN high nitrogen stainless steel, high alloy element content, narrow forging temperature range, and great processing difficulty, it is easy to cause coarse forging organization and the presence of twin carbide organization due to equipment problems such as excessive forging temperature and long holding time. Twin carbides have extremely strong heredity and stability, and generally cannot be eliminated by heat treatment methods such as secondary annealing, normalizing or quenching.

[0007] At present, during the forging process of 40Cr15Mo2VN high nitrogen stainless steel bearing parts, if the heating equipment fails in the final heating stage of the material section, such as a sudden power outage, the heating equipment furnace door cannot be opened, the material section slowly cools down in the furnace with the furnace, or the heating equipment fails, the furnace door cannot be opened, the material section is kept at 1110±10℃ for too long, etc., the material section is stored separately after the final forging is completed, and the metallographic structure is inspected after annealing. It will be found that there is a twin carbide structure, and the inspection fails and cannot be further processed. This batch of forgings with twin carbides due to equipment failure can only be scrapped.

[0008] Therefore, a heat treatment process for eliminating twin carbides in 40Cr15Mo2VN after forging was studied to solve the quality problems in the production process and reduce scrap losses. Summary of the invention

[0009] The purpose of the present invention is to solve the above-mentioned technical problems and to provide a process for eliminating twin carbides after forging of 40Cr15Mo2VN.

[0010] A process for eliminating twin carbides after forging 40Cr15Mo2VN is implemented by the following steps:

[0011] 1. High temperature dissolution of carbides:

[0012] The 40Cr15Mo2VN forgings to be processed are placed in a rotary hearth heating furnace one by one for preheating according to the equipment beat setting, and then taken out of the furnace manually and transferred to a high-temperature rotary hearth heating furnace for final heating of the forgings, and then taken out of the furnace manually and transferred to a cooling zone for air cooling until the surface temperature of the forgings is less than 300°C, thus obtaining cooled forgings;

[0013] 2. Low temperature decomposition of austenite:

[0014] The cooled forging is transferred to a box-type annealing furnace for the first low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then transferred to a box-type annealing furnace for the second low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then transferred to a box-type annealing furnace for the third low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then the forging is obtained after low-temperature decomposition;

[0015] 3. Normalizing treatment:

[0016] The forgings after low-temperature decomposition are transferred to a rotary bottom heating furnace for preheating, then manually taken out of the furnace, transferred to a high-temperature rotary bottom heating furnace for final heating of the forgings, then manually taken out of the furnace, transferred to a cooling zone for oil cooling, and thus the forgings are obtained;

[0017] 4. Annealing of forgings:

[0018] The forgings are placed in an annealing furnace and heated to 840-860°C and kept at this temperature for 230-250 minutes, then cooled to 730°C, the isothermal temperature is 720-740°C, the isothermal time is 230-250 minutes, then cooled to 500°C at a rate of 10-15°C / min, then taken out of the furnace and air-cooled to room temperature to obtain annealed forgings;

[0019] V. Inspection:

[0020] The forgings after annealing are inspected. After annealing, there is no twin carbide in the metallographic structure, and the hardness after annealing meets the process requirements. A 40Cr15Mo2VN forging with no twin carbide is obtained. The forging can continue to move and be processed in the next process, thus completing the method described in the present invention.

[0021] Furthermore, the 40Cr15Mo2VN forging to be processed in step 1 is a 40Cr15Mo2VN forging having twin carbides in its structure after forging.

[0022] Furthermore, the protective atmosphere for preheating the forging in step 1 is nitrogen, the temperature is 840°C to 860°C, and the temperature is kept for 25 to 35 minutes after the color is transparent.

[0023] Furthermore, the protective atmosphere for the final heating of the forging in step 1 is nitrogen, the temperature is 1175-1185° C., and the temperature is kept for 55-65 minutes after the color is transparent.

[0024] Furthermore, the conditions of the first low-temperature decomposition, the second low-temperature decomposition and the third low-temperature decomposition in step 2 are: heating at 675-695° C. for 170-190 min.

[0025] Furthermore, the protective atmosphere for preheating the forging in step 3 is nitrogen, the temperature is 840°C to 860°C, and the temperature is kept for 25 to 35 minutes after the color is transparent.

[0026] Furthermore, the protective atmosphere for the final heating of the forging in step 3 is nitrogen, the temperature is 1095-1105° C., and the temperature is kept for 55-65 minutes after the color is transparent.

[0027] Furthermore, in step 3, the oil cooling: the oil temperature is 60-80° C., and the cooling time is 5-10 minutes.

[0028] Advantages of the present invention:

[0029] ① High temperature heating at 1175-1185℃ can make the carbide particles precipitated in the 40Cr15Mo2VN forging structure integrate into the austenite structure again, so as to cause high temperature deformation recrystallization and destroy the original austenite stubborn grain boundaries, thus achieving the purpose of eliminating twin carbides.

[0030] ② Using three low-temperature decomposition processes at 675-695℃, the austenite in the internal structure of the forging can be completely decomposed, and the small amount of residual twin carbides can be further eliminated.

[0031] ③Finally, the normalizing process and rapid cooling are used to prevent the re-generation of twin carbides. At the same time, it can refine the grains and improve the impact toughness of the material.

[0032] ④ Through the new heat treatment process method, the twin carbides caused by forging problems are eliminated, the quality of high nitrogen stainless steel products is guaranteed, and the production cost is reduced.

[0033] The invention is suitable for eliminating twin carbides after forging of 40Cr15Mo2VN. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a 500-fold microstructure diagram of the metallographic structure of the twinned carbide structure of the 40Cr15Mo2VN forging to be treated in the embodiment after forging;

[0035] Figure 2 This is a 500-fold microstructure diagram of the elimination of the twinned carbide structure of 40Cr15Mo2VN after forging in the embodiment. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0037] Specific implementation method 1: This implementation method is a process for eliminating twin carbides after forging 40Cr15Mo2VN, which is implemented by the following steps:

[0038] 1. High temperature dissolution of carbides:

[0039] The 40Cr15Mo2VN forgings to be processed are placed in a rotary hearth heating furnace one by one for preheating according to the equipment beat setting, and then taken out of the furnace manually and transferred to a high-temperature rotary hearth heating furnace for final heating of the forgings, and then taken out of the furnace manually and transferred to a cooling zone for air cooling until the surface temperature of the forgings is less than 300°C, thus obtaining cooled forgings;

[0040] 2. Low temperature decomposition of austenite:

[0041] The cooled forging is transferred to a box-type annealing furnace for the first low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then transferred to a box-type annealing furnace for the second low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then transferred to a box-type annealing furnace for the third low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then the forging is obtained after low-temperature decomposition;

[0042] 3. Normalizing treatment:

[0043] The forgings after low-temperature decomposition are transferred to a rotary bottom heating furnace for preheating, then manually taken out of the furnace, transferred to a high-temperature rotary bottom heating furnace for final heating of the forgings, then manually taken out of the furnace, transferred to a cooling zone for oil cooling, and thus the forgings are obtained;

[0044] 4. Annealing of forgings:

[0045] The forgings are placed in an annealing furnace and heated to 840-860°C and kept at this temperature for 230-250 minutes, then cooled to 730°C, the isothermal temperature is 720-740°C, the isothermal time is 230-250 minutes, then cooled to 500°C at a rate of 10-15°C / min, then taken out of the furnace and air-cooled to room temperature to obtain annealed forgings;

[0046] V. Inspection:

[0047] The forgings after annealing are inspected. After annealing, there is no twin carbide in the metallographic structure, and the hardness after annealing meets the process requirements. A 40Cr15Mo2VN forging with no twin carbide is obtained. The forging can continue to move and be processed in the next process, thus completing the method described in the present invention.

[0048] The air cooling described in this embodiment uses a 2KW axial flow fan and an infrared thermometer to detect the surface temperature of the forging.

[0049] The hardness after annealing described in step five of this embodiment meets the process requirements and meets the requirements of ASTM A756-17 "Standard Specification for Stainless Anti-Friction Bearing Steel".

[0050] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the 40Cr15Mo2VN forging to be processed in step 1 is a 40Cr15Mo2VN forging having twin carbides in its structure after forging. Other steps and parameters are the same as those in specific implementation method 1.

[0051] Specific implementation method 3: This implementation method is different from specific implementation method 1 in that the protective atmosphere for preheating the forging in step 1 is nitrogen, the temperature is 840℃~860℃, and the temperature is kept for 25~35min after the color is transparent. Other steps and parameters are the same as those in specific implementation method 1.

[0052] Specific embodiment 4: This embodiment is different from specific embodiment 1 in that the protective atmosphere for the final heating of the forging in step 1 is nitrogen, the temperature is 1175-1185°C, and the temperature is kept for 55-65 minutes after the color is transparent. Other steps and parameters are the same as those in specific embodiment 1.

[0053] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the conditions of the first low-temperature decomposition, the second low-temperature decomposition and the third low-temperature decomposition in step 2 are all heating at 675-695° C. for 170-190 min. The other steps and parameters are the same as those in specific embodiment 4.

[0054] Specific embodiment 6: This embodiment is different from specific embodiment 4 in that the protective atmosphere for preheating the forging in step 3 is nitrogen, the temperature is 840°C to 860°C, and the temperature is kept for 25 to 35 minutes after the color is transparent. Other steps and parameters are the same as those in specific embodiment 4.

[0055] Specific embodiment 7: This embodiment is different from specific embodiment 6 in that the protective atmosphere for the final heating of the forging in step 3 is nitrogen, the temperature is 1095-1105°C, and the temperature is kept for 55-65 minutes after the color is transparent. Other steps and parameters are the same as those of specific embodiment 6.

[0056] Specific implementation eight: This implementation differs from specific implementation one in that the oil cooling in step three: the oil temperature is 60-80° C., and the cooling time is 5-10 minutes. The other steps and parameters are the same as those in specific implementation one.

[0057] Specific embodiment 9: This embodiment is different from specific embodiment 1 in that in step 4, the forging is placed in an annealing furnace and heated to 850°C and kept warm for 240 minutes, then cooled to 730°C, isothermal temperature is 730°C, isothermal time is 240 minutes, and then cooled to 500°C at a rate of 12°C / min. Other steps and parameters are the same as those in specific embodiment 1.

[0058] The beneficial effects of the present invention are verified by the following examples:

[0059] Example:

[0060] The 32040X / GHV.01 ring forging is heated in a high-temperature rotary bottom heating furnace. After reaching the temperature required by the process, it is in the insulation stage. The workshop is powered off and the furnace door cannot be opened. The material section slowly cools down in the heating furnace. When the temperature drops to 320°C, the workshop power is restored. The batch of material sections is heated, forged, and annealed again according to the current process. After annealing, it is found that twin carbides exist in the structure, and the batch of products is judged to be unqualified. In order to reduce the loss of scrap, a heat treatment process for eliminating twin carbides is carried out. The process method for eliminating twin carbides after forging 40Cr15Mo2VN in the present invention is specially adopted, and the specific implementation is as follows.

[0061] A process for eliminating twin carbides after forging 40Cr15Mo2VN is implemented by the following steps:

[0062] 1. High temperature dissolution of carbides:

[0063] The 40Cr15Mo2VN forgings to be processed are placed in a rotary hearth heating furnace one by one for preheating according to the equipment beat setting, and then taken out of the furnace manually and transferred to a high-temperature rotary hearth heating furnace for final heating of the forgings, and then taken out of the furnace manually and transferred to a cooling zone for air cooling until the surface temperature of the forgings reaches 290°C, and then stopped to obtain cooled forgings;

[0064] 2. Low temperature decomposition of austenite:

[0065] The cooled forging is transferred to a box-type annealing furnace for the first low-temperature decomposition, and then transferred to a cooling zone for air cooling to a forging surface temperature of 295°C, and then transferred to a box-type annealing furnace for the second low-temperature decomposition, and then transferred to a cooling zone for air cooling to a forging surface temperature of 286°C, and then transferred to a box-type annealing furnace for the third low-temperature decomposition, and then transferred to a cooling zone for air cooling to a forging surface temperature of 289°C, and then a low-temperature decomposed forging is obtained;

[0066] 3. Normalizing treatment:

[0067] The forgings after low-temperature decomposition are transferred to a rotary bottom heating furnace for preheating, then manually taken out of the furnace, transferred to a high-temperature rotary bottom heating furnace for final heating of the forgings, then manually taken out of the furnace, transferred to a cooling zone for oil cooling, and thus the forgings are obtained;

[0068] 4. Annealing of forgings:

[0069] The forgings are placed in an annealing furnace and heated to 850°C and kept at this temperature for 240 minutes, then cooled to 730°C, isothermal temperature is 730°C, isothermal time is 240 minutes, then cooled to 500°C at a rate of 12°C / min, then taken out of the furnace and air-cooled to room temperature, to obtain annealed forgings;

[0070] V. Inspection:

[0071] The forgings after annealing are inspected. After annealing, there is no twin carbide in the metallographic structure, and the hardness after annealing meets the process requirements. A 40Cr15Mo2VN forging with no twin carbide is obtained. The forging can continue to move and be processed in the next process, thus completing the method described in the present invention.

[0072] The 40Cr15Mo2VN forging to be treated in step 1 of this embodiment is a 32040X / GHV.01 annular forging having twin carbides in its structure after forging.

[0073] The protective atmosphere for preheating the forging in step 1 of this embodiment is nitrogen, the temperature is 840° C. to 860° C., and the temperature is kept for 30 minutes after the color is transparent.

[0074] In step 1 of this embodiment, the protective atmosphere for the final heating of the forging is nitrogen, the temperature is 1175-1185° C., and the temperature is kept for 60 minutes after the color is transparent.

[0075] The conditions of the first low-temperature decomposition, the second low-temperature decomposition and the third low-temperature decomposition in step 2 of this embodiment are: heating at 675-695° C. for 180 min.

[0076] The protective atmosphere for preheating the forgings in step 3 of this embodiment is nitrogen, the temperature is 840°C to 860°C, and the temperature is kept for 30 minutes after the color is transparent.

[0077] In step 3 of this embodiment, the protective atmosphere for the final heating of the forging is nitrogen, the temperature is 1095-1105°C, and the temperature is kept for 60 minutes after the color is transparent.

[0078] The oil cooling described in step 3 of this embodiment: the oil temperature is 75° C. and the cooling time is 8 minutes.

[0079] The air cooling described in this embodiment uses a 2KW axial flow fan and an infrared thermometer to detect the surface temperature of the forging.

[0080] The hardness after annealing described in step 5 of this embodiment meets the process requirements and complies with the standard requirements of ASTM A756-17 "Standard Specification for Stainless Anti-Friction Bearing Steel".

[0081] The twin carbide structure of the 40Cr15Mo2VN forging to be processed after forging is as follows Figure 1 As shown; the method of eliminating twin carbides in this embodiment is used to test the forgings after annealing, and the results are as follows Figure 2 As shown, there is no twin carbide in the metallographic structure after annealing.

[0082] In step 1 of this embodiment, the forging is heated at a high temperature of 1175-1185°C, so that the carbide particles precipitated in the structure can be integrated into the austenite structure again, thereby causing high-temperature deformation recrystallization and destroying the original austenite stubborn grain boundaries, thereby achieving the purpose of eliminating twin carbides.

[0083] By using three low-temperature decomposition processes at 675-695°C, the austenite in the internal structure of the forging can be completely decomposed, and the small amount of residual twin carbides can be further eliminated.

[0084] Finally, the normalizing process and rapid cooling are used to prevent the re-production of twin carbides. At the same time, it can refine the grains and improve the impact toughness of the material.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for eliminating twin carbides after forging 40Cr15Mo2VN, characterized in that It is implemented as follows:

1. High temperature dissolution of carbides: The 40Cr15Mo2VN forgings to be processed are placed in a rotary hearth heating furnace one by one for preheating according to the equipment beat setting, and then taken out of the furnace manually and transferred to a high-temperature rotary hearth heating furnace for final heating of the forgings, and then taken out of the furnace manually and transferred to a cooling zone for air cooling until the surface temperature of the forgings is less than 300°C, thus obtaining cooled forgings; 2. Low temperature decomposition of austenite: The cooled forging is transferred to a box-type annealing furnace for the first low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then transferred to a box-type annealing furnace for the second low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then transferred to a box-type annealing furnace for the third low-temperature decomposition, and then transferred to a cooling zone for air cooling until the surface temperature of the forging is less than 300°C, and then the forging is obtained after low-temperature decomposition; 3. Normalizing treatment: The forgings after low-temperature decomposition are transferred to a rotary bottom heating furnace for preheating, then manually taken out of the furnace, transferred to a high-temperature rotary bottom heating furnace for final heating of the forgings, then manually taken out of the furnace, transferred to a cooling zone for oil cooling, and thus the forgings are obtained; 4. Annealing of forgings: The forgings are placed in an annealing furnace and heated to 840-860°C and kept at this temperature for 230-250 minutes, then cooled to 730°C, the isothermal temperature is 720-740°C, the isothermal time is 230-250 minutes, then cooled to 500°C at a rate of 10-15°C / min, then taken out of the furnace and air-cooled to room temperature to obtain annealed forgings; V. Inspection: The forgings after annealing are inspected. After annealing, there is no twin carbide in the metallographic structure, and the hardness after annealing meets the process requirements. A 40Cr15Mo2VN forging with no twin carbide is obtained. The forging can continue to move and be processed in the next process, thus completing the method described in the present invention.

2. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The 40Cr15Mo2VN forging to be treated in step 1 is a 40Cr15Mo2VN forging having twin carbides in its structure after forging.

3. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The protective atmosphere for preheating the forging in step 1 is nitrogen, the temperature is 840°C to 860°C, and the temperature is kept for 25 to 35 minutes after the color is transparent.

4. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The protective atmosphere for the final heating of the forging in step 1 is nitrogen, the temperature is 1175-1185° C., and the temperature is kept for 55-65 minutes after the color is transparent.

5. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The conditions of the first low-temperature decomposition, the second low-temperature decomposition and the third low-temperature decomposition in step 2 are: heating at 675-695° C. for 170-190 min.

6. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The protective atmosphere for preheating the forging in step 3 is nitrogen, the temperature is 840°C to 860°C, and the temperature is kept for 25 to 35 minutes after the color is transparent.

7. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The protective atmosphere for the final heating of the forging in step 3 is nitrogen, the temperature is 1095-1105°C, and the temperature is kept for 55-65 minutes after the color is transparent.

8. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that The oil cooling described in step 3: the oil temperature is 60-80°C and the cooling time is 5-10 minutes.

9. A process for eliminating twin carbides after forging 40Cr15Mo2VN according to claim 1, characterized in that In step 4, the forging is placed in an annealing furnace and heated to 850°C and kept warm for 240 minutes, then cooled to 730°C with the furnace, the isothermal temperature is 730°C, the isothermal time is 240 minutes, and then cooled to 500°C at a rate of 12°C / min.

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