A method for preventing cracks of a valve cover of an oil pump made of 20Cr13 and 30Cr13 stainless steel

Abstract

The application provides a 20Cr13 and 30Cr13 stainless steel material oil pump valve cover anti-crack tempering method. In the tempering process, three process procedures of preheating, quenching and high-temperature tempering are mainly adopted, so that various technical performance indexes stipulated by API are met, and product heat treatment cracks and fracture in the service life are prevented. The tempering process method effect: cracks of the workpiece in the heat treatment and the service life of the product are avoided, and the service performance of the workpiece meets the hardness and mechanical property requirements of the API standard. Since the quenching temperature and the tempering temperature are simultaneously reduced, the tempering energy saving reaches more than 15%, the clean, environment-friendly and safe production requirements are met, and the economic benefits are remarkable.

Description

Technical Field

[0001] This invention relates to the technical field of metal heat treatment, specifically to a method for preventing cracking of valve covers made of 20Cr13 and 30Cr13 stainless steel oil pumps through quenching and tempering. Background Technology

[0002] The valve cover is a major load-bearing component of the oil pump assembly. During operation, it bears the tension of the sucker rod and the axial and radial alternating loads generated by the reciprocating motion of the valve ball. It is made of 20Cr13 and 30Cr13 rolled steel, and after heat treatment, the mechanical properties of the material must meet API specifications: yield strength greater than or equal to 345MPa, hardness 90HRB-23HRC. Its structure mainly consists of inner and outer circular steps, thin walls, and three evenly distributed through-wall oblique holes. This structure is characterized by numerous sharp angles and is a thin-walled, easily cracked, and potentially dangerous metal structural component. The material is low-carbon, high-chromium alloy steel. Due to its high chromium content of 12-14%, after normal quenching heating at 920-980℃ and full austenitization, the internal microstructure undergoes drastic transformation during oil cooling quenching. Furthermore, the thin-walled structure makes it prone to cracking, resulting in visible and micro-cracks after heat treatment, leading to batch scrapping of the product. The product frequently fractures under the alternating loads in oil fields. Because the conventional stainless steel quenching process involves high quenching temperatures, resulting in high quenching hardness, the tempering temperature needs to be increased to 710-750℃ to meet the API standard requirements for hardness and mechanical properties. Summary of the Invention

[0003] The main objective of this invention is to provide a method for preventing cracking of valve covers made of 20Cr13 and 30Cr13 stainless steel oil pumps by tempering, thereby solving the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps: S1. Preheating: Place the oil pump valve cover into the heating furnace and heat it to 620~680℃ and keep it at that temperature; S2. Preheating and cooling: Remove the oil pump valve cover from the heating furnace and place it into the multi-purpose furnace; S3. Quenching and heating: Turn on the multi-purpose furnace heater and control the carbon potential inside the furnace. The carbon potential inside the furnace for 20Cr13 is controlled at 0.16~0.25%, and the carbon potential inside the furnace for 30Cr13 is controlled at 0.26~0.35%. The furnace temperature is heated to 850~880℃ and held at that temperature. S4. Quenching and cooling: Remove the oil pump valve cover from the multi-purpose furnace and quench it in quenching oil for cooling. S5. Tempering heating: Place the quenched oil pump valve cover into a tempering furnace and heat it to 550~610℃ and keep it at that temperature. S6. Tempering and Cooling: Remove the oil pump valve cover from the tempering furnace and place it in the air to cool to room temperature.

[0005] In the preferred embodiment, in step 1, the initial temperature inside the heating furnace is ≤650℃, the heating rate inside the furnace is 150~300℃ / h, and the holding time is 70~100min.

[0006] In the preferred embodiment, in step 2, the initial temperature inside the multi-purpose furnace is 800~850℃, and the oil pump valve cover enters the multi-purpose furnace for quenching and heating.

[0007] In the preferred embodiment, in step 3, the multi-purpose furnace is heated from 800~850℃ at full power to the quenching temperature of 850~880℃, the heating rate inside the furnace is 150~300℃ / h, and the holding time is 50~80min.

[0008] In the preferred embodiment, in step 4, the oil pump valve cover is immersed in quenching oil for quenching and cooling for 5 to 10 minutes.

[0009] In the preferred embodiment, in step 5, the initial temperature inside the tempering furnace is ≤550℃, the heating rate inside the furnace is 150~300℃ / h, and the holding time is 120~180min.

[0010] This invention provides a method for preventing cracking in valve covers of 20Cr13 and 30Cr13 stainless steel oil pumps through quenching and tempering. The quenching and tempering process mainly employs three heat treatment processes: preheating, quenching, and high-temperature tempering. This meets all the technical performance indicators specified by API, preventing heat treatment cracks and fractures within the product's service life. It avoids cracking of the workpiece during heat treatment and its service life, and ensures that the workpiece's performance meets the hardness and mechanical property requirements of API standards. Because the quenching and tempering temperatures are simultaneously reduced, energy savings of over 15% are achieved during the quenching and tempering process, meeting clean, environmentally friendly, and safe production requirements with significant economic benefits. Attached Figure Description

[0011] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a flowchart of the anti-crack quenching and tempering process for the valve cover of the 30Cr13 stainless steel oil pump of the present invention. Figure 2 This is a flow chart of the anti-crack quenching and tempering process for the valve cover of the 20Cr13 stainless steel oil pump of the present invention. Figure 3 This is another process flow diagram of the anti-crack quenching and tempering of the 30Cr13 stainless steel oil pump valve cover of the present invention. Detailed Implementation

[0012] Example 1 This embodiment provides a method for preventing cracking of the valve cover of a 30Cr13 stainless steel oil pump through quenching and tempering. Figure 1 As shown, the specific steps are as follows: Step P1, Preheating Place the oil pump valve cover into a heating furnace with a furnace temperature of 400℃, preheat it to 620℃ at a heating rate of 150-300℃ / h, and hold it for 70 minutes. Step P2, Preheating and Cooling The workpiece is taken out of the furnace and placed into the heating chamber of the multi-purpose furnace, where the furnace temperature is preheated to 800℃. Step P3, quenching and heating Turn on the heating equipment in the rear chamber of the multi-purpose furnace. The temperature of the quenching furnace is increased from 800℃ to 850℃ at a heating rate of 150-300℃ / h. During the quenching heating process, the carbon potential of the furnace is controlled to be 0.26% for 30Cr13. The quenching holding time is 50min. Step P4, quenching and cooling Open the agitator of the rapid quenching oil tank in the front chamber of the multi-purpose furnace. In a carbon protective atmosphere, the part is quickly transferred from the rear chamber heating furnace to the rapid quenching oil in the front chamber by the robot inside the multi-purpose furnace. The quenching cooling time is 5 minutes. The temperature of the oil pump valve cover is 20℃ at the end of quenching. Step P5, tempering The quenched oil pump valve cover was placed directly into a heating furnace at 150℃ without any cleaning. It was then tempered at a heating rate of 150-300℃ / h to 550℃, and the tempering holding time was 120min. Step P6, tempering and cooling After the tempering process is completed, the parts are quickly transferred out of the tempering furnace by a robotic arm, and the workpieces are placed in the air to cool to room temperature.

[0013] Test results after quenching and tempering: yield strength equals 545 MPa, hardness is 22 HRC. The workpiece is qualified and has no cracks.

[0014] Example 2 This embodiment provides a method for preventing cracking of the valve cover of a 20Cr13 stainless steel oil pump through quenching and tempering. Figure 2 As shown, the specific steps are as follows: Step P1, Preheating Place the oil pump valve cover into a heating furnace with a furnace temperature of 450℃, preheat it to 680℃ at full furnace power, and keep it warm for 100 minutes. Step P2, Preheating and Cooling After the workpiece is removed from the furnace, it enters the heating zone of the multi-purpose furnace. The furnace temperature is preheated to 850℃. Step P3, quenching and heating Turn on the heating equipment in the rear chamber of the multi-purpose furnace. The temperature of the quenching furnace is increased from 850℃ to 850℃ at a heating rate of 150-300℃ / h. During the quenching process, the carbon potential of the furnace is controlled to be 0.16% for 20Cr13. The quenching holding time is 80min. Step P4, quenching and cooling Open the agitator of the rapid quenching oil tank in the front chamber of the multi-purpose furnace. In the protective atmosphere inside the furnace, the part is quickly transferred from the rear chamber heating furnace to the rapid quenching oil in the front chamber by the robot inside the multi-purpose furnace. The quenching and cooling time is 10 minutes. The temperature of the oil pump valve cover is 50℃ at the end of quenching. Step P5, tempering The quenched oil pump valve cover was placed directly into a heating furnace at a temperature of 250℃ without any cleaning. The tempering operation was carried out at a heating rate of 150-300℃ / h to 580℃, and the tempering holding time was 180min. Step P6, tempering and cooling After the tempering process is completed, the parts are quickly transferred out of the tempering furnace by a robotic arm, and the workpieces are placed in the air to cool to room temperature.

[0015] Test results after quenching and tempering: yield strength equals 375 MPa, hardness is 95 HRB. The workpiece is qualified and has no cracks.

[0016] Example 3 This embodiment provides a method for preventing cracking of the valve cover of a 30Cr13 stainless steel oil pump through quenching and tempering. Figure 3 As shown, the specific steps are as follows: Step P1, Preheating Place the oil pump valve cover into a heating furnace with a furnace temperature of 150℃, and preheat it to 650℃ at a heating rate of 150-300℃ / h, with a preheating holding time of 85min. Step P2, Preheating and Cooling The workpiece is taken out of the furnace and put into a multi-purpose furnace, where the furnace temperature is raised to 825℃; Step P3, quenching and heating Turn on the multi-purpose furnace heating equipment, and raise the furnace temperature from 825℃ to 865℃ at a heating rate of 150-300℃ / h. Control the carbon potential of the furnace to 0.305% for 30Cr13, and the quenching and holding time is 65min. Step P4, quenching and cooling Turn on the agitator of the rapid quenching oil tank in the multi-purpose furnace. In the protective atmosphere inside the furnace, the workpiece is quickly transferred from the rear heating furnace to the rapid quenching oil in the front chamber for cooling by the robot inside the multi-purpose furnace. The quenching and cooling time is 7.5 minutes. The temperature of the oil pump valve cover is 35℃ at the end of quenching. Step P5, tempering The quenched oil pump valve cover was placed in a heating furnace at 150℃ without any cleaning and heated to 565℃ at a heating rate of 150-300℃ / h, and then tempered and held for 150 minutes. Step P6, tempering and cooling After the tempering process is completed, the parts are quickly transferred out of the tempering furnace by a robotic arm, and the workpieces are placed in the air to cool to room temperature.

[0017] Test results after quenching and tempering: yield strength equals 405 MPa, hardness is 20 HRC. The workpiece is qualified and has no cracks.

[0018] As can be seen from Examples 1-3, the present invention provides a method for preventing cracking of valve covers of oil pumps made of 20Cr13 and 30Cr13 stainless steel. The tempering process mainly adopts three processes: preheating, quenching, and high-temperature tempering, which meets the various technical performance indicators specified by API and prevents heat treatment cracks and fractures within the service life of the product.

[0019] Preheating process: The workpiece is put into the furnace at a temperature lower than the preheating temperature, and heated at a rate of 150-300℃ / h and kept at that temperature.

[0020] Quenching process: The process involves heating at a rate of 150-300℃ / h, incomplete austenitization through sub-temperature quenching, controlling the in-furnace carbon potential during the austenitization process based on the carbon content of the material, and quenching the workpiece in rapid oil quenching. This process yields a large amount of lath martensite and a small amount of acicular martensite. Quenching further refines the grains, and the quenching hardness reaches the material's moderately hardened state, with a quenching hardness of 45-55 HRC.

[0021] Tempering process: High-temperature tempering is adopted. The furnace is put into the furnace below the tempering temperature, heated at a rate of 150-300℃ / h, held at high temperature, and immediately cooled in air after being taken out of the furnace. This process yields a refined tempered sorbite structure with a tempering hardness of 90HRB-23HRC. The sampled mechanical properties meet the requirement that the yield strength is greater than or equal to 345MPa.

[0022] The effects of tempering: It prevents cracks in workpieces during heat treatment and product lifespan, and ensures that workpiece performance meets the hardness and mechanical property requirements of API standards. Because it simultaneously reduces quenching and tempering temperatures, tempering achieves energy savings of over 15%, meeting clean, environmentally friendly, and safe production requirements with significant economic benefits.

[0023] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preventing cracking of valve covers made of 20Cr13 and 30Cr13 stainless steel in oil pumps, characterized in that: Includes the following steps: S1. Preheating: Place the oil pump valve cover into the heating furnace and heat it to 620~680℃ and keep it at that temperature for 70~100min; the heating rate in the heating furnace is 150~300℃ / h; S2. Transfer: Remove the oil pump valve cover from the heating furnace and place it into the multi-purpose furnace; S3. Quenching and Heating: Turn on the multi-purpose furnace heater and control the carbon potential inside the furnace. The carbon potential inside the furnace for 20Cr13 should be controlled at 0.16~0.25%, and the carbon potential inside the furnace for 30Cr13 should be controlled at 0.26~0.35%. The temperature inside the multi-purpose furnace should be heated to 850~880℃ and held for 50~80 minutes. The heating rate inside the multi-purpose furnace should be 150~300℃ / h. S4. Quenching and cooling: Remove the oil pump valve cover from the multi-purpose furnace and cool it in quenching oil for 5-10 minutes. S5. Tempering heating: Place the oil pump valve cover into the tempering furnace and heat it to 550~610℃ and hold it for 120~180min; the heating rate in the tempering furnace is 150~300℃ / h. S6. Tempering and Cooling: Remove the oil pump valve cover from the tempering furnace and place it in the air to cool to room temperature.

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