A spheroidizing annealing process for improving carbide network of GCr15 steel

Abstract

This invention relates to the field of heat treatment technology for metallic materials, and discloses a spheroidizing annealing process for improving the carbide network of GCr15 steel. The process includes: S1 furnace preparation stage, S2 heating stage, S3 first-stage holding stage, S4 cooling transition stage, S5 second-stage holding stage, S7 air cooling stage after furnace exit, and S8 quality inspection stage. This process achieves significant improvement in carbide network: by assembling the furnace according to specifications, using stepped heating (40-90℃ / h), and two-stage constant temperature holding (780-820℃ for 4-6h, 700-740℃ for 3.5-5h), the dissolution and spheroidization processes of carbides are precisely controlled, effectively suppressing the continuous precipitation of carbides at grain boundaries. The carbide network level is stably controlled at ≤2.0, the carbide banding level at ≤2.5, the liquid precipitation level at ≤0.5, and the spheroidization structure level reaches 1-4, significantly improving the uniformity of the microstructure.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for metallic materials, specifically to a spheroidizing annealing process for improving the carbide network of GCr15 steel. Background Technology

[0002] High-carbon chromium bearing steel, as a key raw material for core bearing components, directly determines the mechanical properties and service reliability of the product through the morphology and distribution of its carbides. Carbide network is a common core defect in this type of steel, mainly caused by factors such as uncontrolled heating and cooling rates during spheroidizing annealing, improper furnace loading methods, mismatched holding times, and inadequate furnace atmosphere control. This manifests as continuous or semi-continuous precipitation of carbides along austenite grain boundaries, forming a network structure. This defect severely disrupts the integrity of the matrix, leading to uneven hardness and reduced toughness in the steel. During subsequent cold heading, rolling, and service, it easily causes cracks, spalling, and other failures, significantly reducing the bearing's wear resistance and fatigue life, and failing to meet the stringent requirements of high-end bearings in the automotive and construction machinery industries. Existing spheroidizing annealing processes generally suffer from problems such as uneven heating when steel parts of different specifications are mixed, thermal stress caused by excessively rapid heating, incomplete spheroidization of carbides due to insufficient heat preservation, and secondary precipitation of carbides during the cooling stage. Furthermore, they lack sufficient control over decarburization and oxidation, making it difficult to simultaneously achieve synergistic optimization of carbide network refinement, hardness uniformity, and surface quality, thus hindering the quality upgrade and high-end application expansion of high-carbon chromium bearing steel. Summary of the Invention

[0003] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a spheroidizing annealing process for improving the carbide network of GCr15 steel. This process has advantages such as significant improvement in carbide network and solves the problem of uneven heating when mixing steel parts of different specifications.

[0004] (II) Technical Solution To achieve the above-mentioned significant improvement in carbide network, the present invention provides the following technical solution: a spheroidizing annealing process for improving the carbide network of GCr15 steel, comprising the following stages: S1 furnace loading preparation stage, S2 heating stage, S3 first stage heat preservation, S4 cooling transition stage, S5 second stage heat preservation, S7 furnace unloading air cooling stage, and S8 quality inspection stage. The S1 furnace loading preparation stage includes S101 grouping and classifying steel parts by specifications for loading, S102 uniform placement and anti-deformation arrangement of steel parts, and S103 cleaning of impurities on the surface of steel parts. The S2 heating stage includes S201 step heating rate regulation and S202 target temperature heating and temperature difference control. Among them, the first stage of heat preservation in S3 includes the first stage of constant temperature heat preservation for spheroidization preparation in S301 and the timed recording of furnace temperature during the heat preservation process in S302. Among them, the S4 cooling transition stage includes S401 slow cooling to the transition temperature and S402 furnace atmosphere monitoring and decarbonization control. Among them, the second stage of S5 insulation includes the second stage of constant temperature insulation for spheroidization refinement in S501 and the spheroidization trend sampling and detection at the end of the insulation in S502. The S6 cooling stage includes S601 controlled-rate cooling inside the furnace and S602 furnace sealing to prevent oxidation during the cooling process. Among them, the S7 furnace air cooling stage includes S701 furnace air cooling start-up at the target temperature and S702 air cooling process to prevent stacking and scratches. The S8 quality inspection stage includes S801 hardness uniformity testing of steel parts, S802 metallographic testing of carbides and spheroidized structures, S803 compliance testing of decarburized layer depth, and S804 visual and flaw detection of surface defects in steel parts.

[0005] Preferably, the S101 specification grouping and categorizing for furnace loading: the furnace is loaded according to the specifications of the steel parts, with 15-80mm specifications in one group and 80-130mm specifications in another group, to avoid uneven heating caused by mixing different specifications; S102 Steel Parts Evenly Placed and Deformation-Preventing Arrangement: The steel parts are evenly placed on the furnace support with a spacing of 15-35mm to ensure smooth furnace gas flow. At the same time, high-temperature resistant pads are laid under the steel parts to prevent deformation after cooling. S103 steel parts surface impurity cleaning: Before loading into the furnace, clean the surface of the steel parts to remove iron oxide scale, oil stains and impurities to avoid affecting the annealing effect.

[0006] Preferably, the S201 stepped heating rate control adopts a stepped heating method, and the heating rate is controlled at 40-90℃ / h to avoid excessive heating and thermal stress inside the steel parts. S202 target temperature rise and temperature difference control: gradually increase the temperature to 780-820℃, monitor the furnace temperature in real time during the heating process, and control the temperature difference within ±8℃.

[0007] Preferably, the first stage of constant temperature heat preservation spheroidizing preparation in S301 involves maintaining the furnace temperature at 780-820℃ and holding it for 4-6 hours to ensure uniform internal temperature of the steel parts and create conditions for carbide dissolution and spheroidization. S302 Insulation Process Furnace Temperature Timed Recording: Record the furnace temperature every 1.5 hours during the insulation period to ensure that the temperature remains stable within the set range.

[0008] Preferably, the S401 is slowly cooled to the transition temperature: the temperature is slowly reduced at a rate of 30-60℃ / h to 700-740℃, to avoid the carbides from re-precipitating and forming a network due to excessively rapid cooling; S402 Furnace Atmosphere Monitoring and Decarburization Control: During the cooling process, the furnace atmosphere is continuously monitored to maintain a weakly reducing atmosphere and reduce decarburization on the surface of steel parts.

[0009] Preferably, the second stage of constant temperature heat preservation spheroidizing and refining in S501 involves heat preservation at 700-740℃ for 3.5-5 hours to promote full spheroidization of carbides and refine carbide particles. S502 Spheroidization Trend Sampling and Testing at the End of Insulation: Sampling and testing at the end of insulation is conducted to preliminarily determine the spheroidization trend of carbides and ensure the effectiveness of subsequent processes.

[0010] Preferably, the S601 furnace-controlled rate cooling adopts an in-furnace controlled cooling method, with the cooling rate controlled at 20-50℃ / h, gradually decreasing to 80-120℃; S602 Cooling Process: The furnace is sealed during the cooling process to prevent oxidation of the steel parts.

[0011] Preferably, the S701 standard temperature is reached and then the furnace is opened for air cooling start-up: when the furnace temperature drops to 80-120℃, the furnace door is opened and the steel parts are placed in a well-ventilated area to air cool naturally to room temperature. S702 Air Cooling Process Anti-Stacking and Anti-Scratching: During the air cooling process, avoid stacking and squeezing steel parts to prevent surface scratches or deformation.

[0012] Preferably, the S801 steel parts hardness uniformity test involves randomly selecting 3-5 steel parts of different specifications and testing their hardness at 170-230 HBW to ensure uniform hardness. S802 Carbide and Spheroidization Metallographic Detection: Carbide network grade ≤2.0, carbide banding grade ≤2.5, liquid chromatography grade ≤0.5, spheroidization grade 1-4.

[0013] Preferably, the S803 decarburization layer depth compliance test results are: total decarburization layer depth ≤ 1.2% D (D is the diameter of the steel part), and total decarburization layer depth ≤ 0.3% D; Visual inspection and flaw detection of surface defects of S804 steel parts: The surface of the steel parts is inspected by visual inspection or flaw detection. There are no obvious oxide scale, cracks or scratches.

[0014] (III) Beneficial Effects Compared with the prior art, the present invention provides a spheroidizing annealing process for improving the carbide network of GCr15 steel, which has the following beneficial effects: 1. This spheroidizing annealing process improves the carbide network of GCr15 steel. This process achieves significant improvement in carbide network: by assembling furnaces according to specifications, step-wise heating (40-90℃ / h) and two-stage constant temperature holding (780-820℃ for 4-6h, 700-740℃ for 3.5-5h), the dissolution and spheroidization process of carbides are precisely controlled, effectively inhibiting the continuous precipitation of carbides at grain boundaries. The carbide network level is stably controlled at ≤2.0, the carbide banding level is ≤2.5, the liquid precipitation level is ≤0.5, and the spheroidization structure level reaches 1-4, significantly improving the uniformity of the structure.

[0015] 2. The improved spheroidizing annealing process for GCr15 steel with improved carbide network structure significantly enhances hardness uniformity: through uniform placement, strict control of furnace temperature difference (within ±8℃), and constant temperature control throughout the process, the hardness of the steel parts is stabilized at 170-230HBW, and the hardness difference between different specifications and different parts is significantly reduced, avoiding the processing difficulties caused by excessively high or low local hardness, and providing a good foundation for subsequent cold heading and grinding processes.

[0016] 3. The improved spheroidizing annealing process for GCr15 steel with improved carbide network structure achieves precise control over decarburization and oxidation: through monitoring the weak reducing atmosphere in the furnace, sealing protection during the cooling process, and precise temperature control, decarburization and oxidation on the surface of the steel parts are effectively reduced. The total depth of the decarburized layer is ≤1.2% D (D is the diameter of the steel part), and the depth of the entire decarburized layer is ≤0.3% D. There is no obvious oxide scale on the surface, thus avoiding the adverse effects of decarburization-induced surface hardness reduction and oxidation defects on service performance.

[0017] 4. The improved spheroidizing annealing process for GCr15 steel with carbide network structure achieves optimization of deformation and surface quality: high-temperature resistant pads are laid during furnace loading, and stacking and squeezing are avoided during air cooling. Combined with full-process cleanliness control (surface impurity cleaning), the deformation of steel parts is significantly reduced, and the surface is free of cracks and scratches. Processing requirements can be met without additional grinding, thereby improving production efficiency and reducing costs.

[0018] 5. The improved spheroidizing annealing process for GCr15 steel carbide network enhances product service reliability by optimizing carbide morphology, achieving uniform hardness, controlled decarburization and oxidation, and ensuring qualified surface quality. This process simultaneously improves the wear resistance, toughness, and fatigue resistance of steel parts, effectively reducing the risk of cracking and failure during subsequent processing and service. It meets the stringent requirements of high-end bearings for raw materials and broadens the application scenarios of high-carbon chromium bearing steel. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] This solution provides a technical approach, specifically a spheroidizing annealing process for improving the carbide network in GCr15 steel, comprising the following steps: S1 Furnace Loading Preparation Stage: S101 Specification Grouping and Furnace Loading: The furnace is loaded according to the specifications of the steel parts. The 15-80mm specifications are grouped into one group, and the 80-130mm specifications are grouped into another group to avoid uneven heating caused by mixing different specifications. S102 Steel Parts Evenly Placed and Deformation-Preventing Arrangement: The steel parts are evenly placed on the furnace support with a spacing of 15-35mm to ensure smooth furnace gas flow. At the same time, high-temperature resistant pads are laid under the steel parts to prevent deformation after cooling. S103 steel parts surface impurity cleaning: Before loading into the furnace, clean the surface of the steel parts to remove iron oxide scale, oil stains and impurities to avoid affecting the annealing effect; S2 heating stage: S201 Stepped heating rate control: The stepped heating method is adopted, and the heating rate is controlled at 40-90℃ / h to avoid excessive heating and thermal stress inside the steel parts. S202 target temperature rise and temperature difference control: gradually rise to 780-820℃, monitor the furnace temperature in real time during the heating process, and control the temperature difference within ±8℃; S3 first stage insulation: S301 First Stage Constant Temperature Insulation Spheroidizing Preparation: Maintain furnace temperature at 780-820℃, holding time 4-6h, to ensure uniform internal temperature of steel parts and create conditions for carbide dissolution and spheroidization. S302 Insulation Process Furnace Temperature Timed Recording: Record the furnace temperature every 1.5 hours during the insulation period to ensure that the temperature remains stable within the set range; S4 cooling transition phase: S401 slowly cools down to the transition temperature: slowly cool down at a rate of 30-60℃ / h to 700-740℃ to avoid excessive cooling causing carbides to re-precipitate and form a network; S402 Furnace Atmosphere Monitoring and Decarburization Control: During the cooling process, the furnace atmosphere is continuously monitored to maintain a weakly reducing atmosphere and reduce decarburization on the surface of steel parts; S5 Second Stage Insulation: S501 Second Stage Constant Temperature Insulation Spheroidization and Refinement: Insulation at 700-740℃ for 3.5-5 hours to promote full spheroidization of carbides and refine carbide particles; S502 Spheroidization Trend Sampling and Testing at the End of Insulation: Sampling and testing are conducted at the end of insulation to preliminarily determine the spheroidization trend of carbides and ensure the effect of subsequent processes. S6 Cooling Phase: S601 Controllable rate cooling in furnace: The furnace-controlled cooling method is adopted, and the cooling rate is controlled at 20-50℃ / h, gradually decreasing to 80-120℃; S602 Cooling Process: The furnace is sealed during the cooling process to prevent oxidation of the steel parts. S7 air cooling stage after being taken out of the oven: S701 Standard Temperature Out-of-Furnace Air Cooling Start-up: When the furnace temperature drops to 80-120℃, open the furnace door to take out the steel parts and place them in a well-ventilated area to air cool to room temperature. S702 Air Cooling Process Anti-Stacking and Anti-Scratch: Avoid stacking and squeezing steel parts during air cooling to prevent surface scratches or deformation; S8 Quality Inspection Stage: S801 steel parts hardness uniformity test: Randomly select 3-5 steel parts of different specifications and test the hardness of 170-230HBW to ensure uniform hardness. S802 Carbide and Spheroidization Metallographic Detection: Carbide network grade ≤2.0, carbide banding grade ≤2.5, liquid chromatography grade ≤0.5, spheroidization grade 1-4; S803 Decarburization Layer Depth Compliance Test: Total decarburization layer depth ≤ 1.2% D (D is the diameter of the steel part), total decarburization layer depth ≤ 0.3% D; S804 steel parts surface defect visual and flaw detection: The surface of the steel parts is inspected visually or by flaw detection. There are no obvious oxide scale, cracks or scratches. Furthermore, this process achieves significant improvement in carbide network structure: by assembling furnaces according to specifications, step-wise heating (40-90℃ / h), and two-stage constant temperature holding (780-820℃ for 4-6h, 700-740℃ for 3.5-5h), the dissolution and spheroidization processes of carbides are precisely controlled, effectively inhibiting the continuous precipitation of carbides at grain boundaries. The carbide network level is stably controlled at ≤2.0, the carbide banding level is ≤2.5, the liquid precipitation level is ≤0.5, and the spheroidization structure level reaches 1-4, significantly improving the uniformity of the structure. Furthermore, this process significantly improves the uniformity of hardness: with uniform placement, strict control of furnace temperature difference (within ±8℃) and constant temperature control throughout the process, the hardness of steel parts is stabilized at 170-230HBW, and the hardness difference between different specifications and different parts is significantly reduced, avoiding the processing difficulties caused by excessively high or low local hardness, and providing a good foundation for subsequent cold heading and grinding processes. Furthermore, this process achieves precise control over decarburization and oxidation: through monitoring the weak reducing atmosphere in the furnace, sealing and protecting the cooling process, and precise temperature control, it effectively reduces decarburization and oxidation on the surface of steel parts. The total depth of the decarburized layer is ≤1.2% D (D is the diameter of the steel part), the depth of the entire decarburized layer is ≤0.3% D, and there is no obvious oxide scale on the surface, thus avoiding the adverse effects of decarburization-induced surface hardness reduction and oxidation defects on service performance. Furthermore, this process achieves optimization of deformation and surface quality: high-temperature resistant pads are laid during furnace loading, and stacking and squeezing are avoided during the air cooling process. Combined with full-process cleanliness control (surface impurity cleaning), the deformation of steel parts is significantly reduced, and there are no cracks or scratches on the surface. Processing requirements can be met without additional grinding, thereby improving production efficiency and reducing costs. Furthermore, this process achieves improved product reliability during service: the combined effects of optimized carbide morphology, uniform hardness, controlled decarburization and oxidation, and qualified surface quality simultaneously enhance the wear resistance, toughness, and fatigue resistance of steel parts, effectively reducing the risk of cracking and failure during subsequent processing and service. It can meet the stringent requirements of high-end bearings for raw materials and broaden the application scenarios of high-carbon chromium bearing steel.

[0021] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A spheroidizing annealing process for improving the carbide network in GCr15 steel, comprising: S1 furnace loading preparation stage, S2 heating stage, S3 first stage holding stage, S4 cooling transition stage, S5 second stage holding stage, S7 furnace unloading air cooling stage, and S8 quality inspection stage, characterized in that: The S1 furnace loading preparation stage includes S101 grouping and classifying the steel parts for loading, S102 evenly placing and anti-deformation arrangement of the steel parts, and S103 cleaning the surface impurities of the steel parts. The S2 heating stage includes S201 step heating rate regulation and S202 target temperature heating and temperature difference control. Among them, the first stage of heat preservation in S3 includes the first stage of constant temperature heat preservation for spheroidization preparation in S301 and the timed recording of furnace temperature during the heat preservation process in S302. Among them, the S4 cooling transition stage includes S401 slow cooling to the transition temperature and S402 furnace atmosphere monitoring and decarbonization control. Among them, the second stage of S5 insulation includes the second stage of constant temperature insulation for spheroidization refinement in S501 and the spheroidization trend sampling and detection at the end of the insulation in S502. The S6 cooling stage includes S601 controlled-rate cooling inside the furnace and S602 furnace sealing to prevent oxidation during the cooling process. Among them, the S7 furnace air cooling stage includes S701 furnace air cooling start-up at the target temperature and S702 air cooling process to prevent stacking and scratches. The S8 quality inspection stage includes S801 hardness uniformity testing of steel parts, S802 metallographic testing of carbides and spheroidized structures, S803 compliance testing of decarburized layer depth, and S804 visual and flaw detection of surface defects in steel parts.

2. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S101 specification is grouped and categorized for furnace loading: the furnace is loaded according to the specifications of the steel parts, with 15-80mm specifications in one group and 80-130mm specifications in another group, to avoid uneven heating caused by mixing different specifications. S102 Steel Parts Evenly Placed and Deformation-Preventing Arrangement: The steel parts are evenly placed on the furnace support with a spacing of 15-35mm to ensure smooth furnace gas flow. At the same time, high-temperature resistant pads are laid under the steel parts to prevent deformation after cooling. S103 steel parts surface impurity cleaning: Before loading into the furnace, clean the surface of the steel parts to remove iron oxide scale, oil stains and impurities to avoid affecting the annealing effect.

3. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S201 stepped heating rate control: adopts a stepped heating method, and controls the heating rate at 40-90℃ / h to avoid excessive heating that could cause thermal stress inside the steel parts. S202 target temperature rise and temperature difference control: gradually increase the temperature to 780-820℃, monitor the furnace temperature in real time during the heating process, and control the temperature difference within ±8℃.

4. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The first stage of constant temperature insulation spheroidizing preparation of S301: maintain the furnace temperature at 780-820℃, and the insulation time is 4-6h to ensure uniform internal temperature of the steel parts and create conditions for carbide dissolution and spheroidization. S302 Insulation Process Furnace Temperature Timed Recording: Record the furnace temperature every 1.5 hours during the insulation period to ensure that the temperature remains stable within the set range.

5. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S401 is slowly cooled to the transition temperature: the temperature is slowly reduced at a rate of 30-60℃ / h to 700-740℃, to avoid the carbides from re-precipitating and forming a network due to excessively rapid cooling; S402 Furnace Atmosphere Monitoring and Decarburization Control: During the cooling process, the furnace atmosphere is continuously monitored to maintain a weakly reducing atmosphere and reduce decarburization on the surface of steel parts.

6. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The second stage of constant temperature heat preservation spheroidization and refinement of S501 involves heat preservation at 700-740℃ for 3.5-5 hours to promote full spheroidization of carbides and refine carbide particles. S502 Spheroidization Trend Sampling and Testing at the End of Insulation: Sampling and testing at the end of insulation is conducted to preliminarily determine the spheroidization trend of carbides and ensure the effectiveness of subsequent processes.

7. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S601 furnace-controlled rate cooling method adopts an in-furnace controlled cooling method, with the cooling rate controlled at 20-50℃ / h, gradually decreasing to 80-120℃. S602 Cooling Process: The furnace is sealed during the cooling process to prevent oxidation of the steel parts.

8. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S701 standard temperature for furnace exit and air cooling start-up: When the furnace temperature drops to 80-120℃, open the furnace door to take out the steel parts and place them in a well-ventilated area to air cool to room temperature. S702 Air Cooling Process Anti-Stacking and Anti-Scratching: During the air cooling process, avoid stacking and squeezing steel parts to prevent surface scratches or deformation.

9. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S801 steel parts hardness uniformity test: randomly select 3-5 steel parts of different specifications and test the hardness of 170-230 HBW to ensure uniform hardness. S802 Carbide and Spheroidization Metallographic Detection: Carbide network grade ≤2.0, carbide banding grade ≤2.5, liquid chromatography grade ≤0.5, spheroidization grade 1-4.

10. The spheroidizing annealing process for improving the carbide network of GCr15 steel according to claim 1, characterized in that: The S803 decarburization layer depth compliance test results are as follows: total decarburization layer depth ≤ 1.2% D (D is the diameter of the steel part), and total decarburization layer depth ≤ 0.3% D. Visual inspection and flaw detection of surface defects of S804 steel parts: The surface of the steel parts is inspected by visual inspection or flaw detection. There are no obvious oxide scale, cracks or scratches.