A heat treatment method to improve the comprehensive performance of 18Cr2Ni4WA structural steel

Abstract

This invention pertains to the field of heat treatment processing, specifically a heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel. This heat treatment process not only enhances the tensile strength of the material but also simultaneously improves its plasticity, toughness, and other performance indicators, significantly improving product quality, expanding the material's application range, saving raw material costs, and reducing the weight of manufactured parts.

Description

Technical Field

[0001] This invention pertains to the field of heat treatment processing, specifically a heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel. Background Technology

[0002] 18Cr2Ni4WA structural steel is a commonly used metallic material with good fatigue strength, low notch sensitivity, and good low-temperature impact toughness. It is widely used in the manufacture of load-bearing parts such as bolts, shafts, joints, and piston rods. After heat treatment, this material can obtain certain comprehensive properties of strength and toughness. However, the increase in tensile strength is often accompanied by a decrease in plasticity and toughness. Summary of the Invention

[0003] Purpose of the invention: To significantly improve the performance limits of 18Cr2Ni4WA structural steel by adopting a novel heat treatment process.

[0004] This heat treatment process can improve the tensile strength of materials while simultaneously enhancing their plasticity, toughness, and other properties, thereby significantly improving product quality, expanding the range of applications for materials, saving raw material costs, and reducing the weight of manufactured parts.

[0005] Technical solution

[0006] A heat treatment method for improving the overall performance of 18Cr2Ni4WA structural steel includes the following steps:

[0007] Step 1. Carburize the 18Cr2Ni4WA steel;

[0008] Step 2. After carburizing, the carbon content on the surface and in the core is inconsistent. Austenitization treatment is completed at 770℃-830℃ (which is lower than the conventional austenitization temperature), so that the internal and external structures of the material undergo different degrees of structural transformation. From the outside to the inside of the material, the proportion of supercooled austenite decreases and the proportion of ferrite increases.

[0009] Step 3. Perform the first quenching in the temperature range of 180℃-320℃ below the MS point, and hold for 3-10 minutes to determine the proportion of austenite in the microstructure (MS point: the temperature at which austenite transforms into martensite).

[0010] Step 4. After the first quenching at the same suitable temperature, due to the high proportion of austenite content in the supercooled surface, the surface structure consists of a large amount of martensite + some austenite + trace ferrite. From the outside to the inside, the proportion of martensite decreases, the proportion of austenite decreases slightly, and the proportion of ferrite increases.

[0011] Step 5. Select a temperature range of 350℃-450℃ above the MS point for a second quenching. As the carbon element diffuses into the austenite structure, it is stabilized and ultimately retained. The surface structure consists of a large amount of martensite + some austenite + trace ferrite. The austenite, having accepted some carbon element, has improved stability and is ultimately retained.

[0012] Step 6. Select a tempering temperature range of 460-660℃, hold at that temperature for a period of time to perform tempering treatment, complete the stabilization treatment of the microstructure, and the diffuse precipitation of carbides and other microstructures.

[0013] Furthermore, in step 1, the carbon content of the carburized layer is controlled at 0.25%-0.35%.

[0014] Furthermore, in step 2, the inconsistent carbon content on the surface and in the core specifically manifests as a gradient distribution of carbon elements. An increase in C content will lead to a decrease in the austenitizing temperature.

[0015] Furthermore, in step 3, if a significant improvement in ductility and toughness is required, quenching at a higher temperature below the MS point is used to retain more residual austenite structure.

[0016] Furthermore, in step 4, the martensite content is approximately 91%-96%, the austenite content is approximately 2%-7%, and the ferrite content is approximately 1%-2%.

[0017] Furthermore, in step 5, the martensite content is approximately 92%-96.5%, the austenite content is approximately 2%-6.5%, and the ferrite content is approximately 1%-2%.

[0018] Furthermore, the heat preservation time in step 5 is 8-20 minutes.

[0019] Furthermore, it also includes step 7, after which the tensile strength is increased by at least 8% and the ductility and toughness are increased by more than 15%.

[0020] Technical effect

[0021] This invention proposes a novel heat treatment process to enhance the performance of 18Cr2Ni4WA structural steel, resulting in a high-strength, high-ductility, and high-wear-resistance 18Cr2Ni4WA structural steel material. A major advantage of its exceptionally high strength and ductility is that, for the same component design requirements, compared to conventional heat treatment of 18Cr2Ni4WA structural steel, the material thickness can be reduced by more than 20% to meet the strength and other mechanical performance requirements, achieving weight reduction, cost reduction, energy conservation, and emission reduction. Another advantage is that the significant improvement in strength and ductility allows it to replace some medium- and high-alloy steels as a low-alloy steel. Finally, the improved surface wear resistance further expands the application scenarios of this material. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments. The following description represents only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] 18Cr2Ni4WA steel is an excellent carburizing steel. Through the infiltration of carbon, it can maximize the strengthening effect of martensite, the dispersion strengthening effect of carbides and other phases, and the stabilizing effect of austenite. Combined with the adjustment of the content ratio of austenite, ferrite and martensite, it can simultaneously improve the surface wear resistance and the overall tensile strength, ductility and toughness.

[0024] Example 1:

[0025] Sample: Annealed 18Cr2Ni4WA steel bar with diameter φ20*100

[0026] Carburizing parameters: carbon potential 0.39, temperature 820℃, holding time 30min

[0027] Austenitizing parameters: temperature 770℃, holding time 30min

[0028] First quenching parameters: temperature 300℃, holding time 5min

[0029] Second quenching parameters: temperature 410℃, holding time 10min

[0030] Tempering temperature: 570℃, holding time: 90min

[0031] This example demonstrates a significant improvement in ductility and toughness while simultaneously enhancing tensile strength. Microstructure analysis after secondary quenching revealed a surface composition of 92.5% martensite, 6% austenite, and approximately 1.5% ferrite, while the internal composition was primarily 84.2% martensite, 10.2% austenite, and approximately 5.6% ferrite. Mechanical properties after tempering showed a tensile strength Rm of 1179 MPa and an elongation at fracture of 22.7%.

[0032] Example 2:

[0033] Sample: Annealed 18Cr2Ni4WA steel bar with diameter φ20*100

[0034] Carburizing parameters: carbon potential 0.39, temperature 820℃, holding time 30min

[0035] Austenitizing parameters: temperature 820℃, holding time 30min

[0036] First quenching parameters: temperature 200℃, holding time 5min

[0037] Second quenching parameters: temperature 360℃, holding time 10min

[0038] Tempering temperature: 520℃, holding time: 90min

[0039] In this example, while improving ductility and toughness, the tensile strength was significantly increased. Microstructure analysis after secondary quenching revealed that the surface consisted primarily of approximately 94.9% martensite + 4.3% austenite + 0.8% ferrite, while the interior consisted primarily of approximately 89.6% martensite + 3.9% austenite + 6.5% ferrite. Mechanical properties testing after tempering showed a tensile strength Rm = 1388 MPa and an elongation at fracture = 17.5%.

[0040] Example 3:

[0041] Sample: Annealed 18Cr2Ni4WA steel bar with diameter φ20*100

[0042] Carburizing parameters: carbon potential 0.39, temperature 820℃, holding time 30min

[0043] Austenitizing parameters: temperature 850℃, holding time 30min

[0044] First quenching parameters: temperature 25℃, holding time 5min

[0045] Second quenching parameters: temperature 320℃, holding time 10min

[0046] Tempering temperature: 550℃, holding time: 90min

[0047] Compared with the previous two examples, the strength and toughness of this example decreased to varying degrees. After secondary quenching, the microstructure was examined, revealing that the surface consisted mainly of approximately 91.2% martensite + 7.6% carbides + 1.2% ferrite, while the interior consisted mainly of 88.2% martensite + 5.5% carbides + 6.3% ferrite. After tempering, the mechanical properties were tested, showing a tensile strength Rm = 957 MPa and an elongation after fracture of [missing information].

[0048] =13.3%.

[0049] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein. The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel, characterized in that, Includes the following steps: Step 1. Carburize the 18Cr2Ni4WA steel; Step 2. After carburizing, the carbon content on the surface and in the core is inconsistent. Austenitization treatment is completed at 770℃-830℃ to cause different degrees of microstructural transformation in the material. From the outside to the inside, the proportion of supercooled austenite decreases and the proportion of ferrite increases. Step 3. Perform the first quenching in the temperature range of 180℃-320℃ below the MS point, and hold for 3-10 minutes to determine the proportion of austenite in the microstructure. MS point: the temperature at which austenite begins to transform into martensite. Step 4. After the first quenching at the same suitable temperature, due to the high proportion of austenite content in the supercooled surface, the surface structure consists of a large amount of martensite + some austenite + trace ferrite. From the outside to the inside, the proportion of martensite content decreases, the proportion of austenite content decreases slightly, and the proportion of ferrite content increases. Step 5. Select a temperature range of 350℃-450℃ above the MS point for a second quenching. As the carbon element diffuses into the austenite structure, it is stabilized and ultimately retained. The surface structure consists of a large amount of martensite + some austenite + trace ferrite. The austenite has improved its stability by accepting some carbon elements and is ultimately retained. Step 6. Select a tempering temperature range of 460-660℃, hold at that temperature for a period of time to perform tempering treatment, complete the stabilization treatment of the microstructure, and allow the dispersed precipitation of carbide microstructure.

2. The heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 1, characterized in that, In step 1, the carbon content of the carburized layer is controlled between 0.25% and 0.35%.

3. The heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 2, characterized in that, In step 2, the inconsistency in carbon content between the surface and the core is specifically manifested as a gradient distribution of carbon elements. An increase in C content will lead to a decrease in the austenitizing temperature.

4. The heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 3, characterized in that, In step 3, if a significant improvement in ductility and toughness is required, quenching at a higher temperature below the MS point is used to retain more residual austenite structure.

5. A heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 4, characterized in that, In step 4, the martensite content is 91%-96%, the austenite content is 2%-7%, and the ferrite content is 1%-2%.

6. The heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 5, characterized in that, In step 5, the martensite content is 92%-96.5%, the austenite content is 2%-6.5%, and the ferrite content is 1%-2%.

7. A heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 6, characterized in that, The heat preservation time in step 5 is 8-20 minutes.

8. A heat treatment method for improving the comprehensive performance of 18Cr2Ni4WA structural steel according to claim 7, characterized in that, It also includes step 7, after which the tensile strength is increased by at least 8% and the ductility and toughness are increased by more than 15%.