A heat treatment process for grain refinement of C250 maraging steel

Abstract

The present application relates to the field of steel heat treatment technology, and specifically discloses a heat treatment process for refining the grains of C250 maraging steel. The heat treatment process for refining the grains of C250 maraging steel provided in the present application comprises the following steps: first, the C250 maraging steel is kept at a temperature of 945-955°C for 1-1.5 hours and water-cooled to room temperature; then, the C250 maraging steel is kept at a temperature of 925-935°C for 1-1.5 hours and water-cooled to room temperature; then, the C250 maraging steel is kept at a temperature of 895-905°C for 1-1.5 hours and water-cooled to room temperature; finally, the C250 maraging steel is kept at a temperature of 815-825°C for 1-1.5 hours and air-cooled to room temperature. The heat treatment process for refining the grains of C250 maraging steel provided in the present application can fully refine and homogenize the grains of the C250 maraging steel, so that the grains of the C250 maraging steel reach 8-9 levels and have excellent mechanical properties.

Description

Technical Field

[0001] The present application relates to the technical field of steel heat treatment, and in particular to a heat treatment process for refining the grains of C250 maraging steel. Background Art

[0002] C250 maraging steel is an ultra-high-strength steel based on carbon-free or low-carbon martensite, which is hardened by intermetallic compounds through aging treatment. It has the advantages of high strength, high hardness, high toughness, low hardening index, good formability and excellent corrosion resistance. Therefore, it is widely used in aerospace, military industry, petrochemical industry, marine engineering, automobile manufacturing and other fields.

[0003] Research has found that the grain size of maraging steel significantly influences its mechanical properties and service life. Therefore, grain refinement has become the primary method for improving the strength, ductility, and toughness of maraging steel. Traditional methods for grain refinement include solution treatment and deformation treatment. Deformation treatments easily produce texture, which imparts directional properties to the steel, impacting its application in products. Solution treatments, on the other hand, have a very limited effect on grain refinement, often failing to meet the requirements of modern equipment. Furthermore, existing methods for grain refinement of maraging steel remain suboptimal.

[0004] Therefore, a heat treatment process for refining the grains of C250 maraging steel is proposed, which has very important theoretical significance for the wide application of maraging steel. Summary of the Invention

[0005] In order to improve the grain refining effect of C250 maraging steel, the present application provides a heat treatment process for refining the grains of C250 maraging steel.

[0006] In the first aspect, the heat treatment process for refining the grains of C250 maraging steel provided in this application adopts the following technical solutions:

[0007] A heat treatment process for refining the grains of C250 maraging steel comprises the following steps: heat treating the C250 maraging steel according to the following process:

[0008] S1: Keep at 945-955℃ for 1-1.5h, then cool to room temperature with water;

[0009] S2: Keep at 925-935℃ for 1-1.5h, then cool to room temperature with water;

[0010] S3: Keep at 895-905℃ for 1-1.5h, then cool to room temperature with water;

[0011] S4: Keep at 815-825℃ for 1-1.5h, then air cool to room temperature.

[0012] This application utilizes the repeated α-γ transformation of C250 maraging steel during cyclic phase transformation heat treatment, which produces a large number of micro defects in the martensite structure, including dislocations, twins, stacking faults, etc. These micro defects will be inherited into the austenite during the transformation from martensite to austenite, thereby increasing the energy storage capacity of the material. Recrystallization will occur at locations with higher energy in the material, the structure will continue to refine, and the storage energy of the austenite will continue to increase. Therefore, through repeated phase transformation and recrystallization, the austenite grains are fully refined and homogenized.

[0013] In this application, the presence of microscopic defects such as dislocations, twins, and stacking faults can increase the storage energy of the material, and recrystallization mainly nucleates and grows at positions with higher energy; therefore, the presence of these microscopic defects can increase the driving force for recrystallization of the material, causing the structure to continue to fragment and the dislocation density to continue to increase.

[0014] Optionally, the temperature of the S2 process is 930° C. and the holding time is 1 hour.

[0015] Optionally, the temperature of the S3 process is 900° C. and the holding time is 1 hour.

[0016] Optionally, the temperature of the S4 process is 820° C. and the holding time is 1 hour.

[0017] Optionally, the heat treatment process of the C250 maraging steel further comprises aging treatment, specifically comprising the following steps: aging the C250 maraging steel after the S4 process at 475-485° C. for 5-8 hours, and air cooling the steel to room temperature.

[0018] Optionally, the heat treatment process of the C250 maraging steel further includes aging treatment, specifically comprising the following steps: keeping the C250 maraging steel after the S4 process at 475-485° C. for 2-3 hours, and air-cooling to room temperature; then continuing to keep the temperature at 475-485° C. for 2-3 hours, and air-cooling to room temperature.

[0019] In the present application, by performing the above-mentioned two-stage aging treatment on the C250 maraging steel after the cyclic heat treatment, the microstructure of the C250 maraging steel can be further optimized and the fatigue life of the C250 maraging steel can be extended.

[0020] In a second aspect, the present application provides a C250 maraging steel obtained by using the heat treatment process for refining the grains of the C250 maraging steel.

[0021] Optionally, the grain size of the C250 maraging steel is level 8 to 9.

[0022] In summary, this application has the following beneficial effects:

[0023] 1. This application provides a heat treatment process for grain refinement of C250 maraging steel. This process first involves subjecting the maraging steel to a primary phase transformation crystallization at 945-955°C. This process generates a large number of microdefects in the martensite structure, which are then transferred to the austenite. This significantly increases the material's storage energy and strengthens the driving force for recrystallization. Secondary, tertiary, and quaternary phase transformation heat treatments are then performed, resulting in continuous recrystallization and microstructure fragmentation, thereby fully refining and homogenizing the grains of the C250 maraging steel. Therefore, the heat treatment process for grain refinement of C250 maraging steel provided in this application can significantly improve the grain refinement of C250 maraging steel and has significant theoretical significance for the widespread application of maraging steel.

[0024] 2. The heat treatment process for refining the grains of C250 maraging steel provided in this application can refine the grains of C250 maraging steel to levels 8-9. The tensile strength of the C250 maraging steel obtained after aging treatment is greater than 1900 MPa and the fatigue life is greater than 200,000 cycles.

[0025] 3. This application further optimizes the microstructure of the cyclically treated C250 maraging steel by adopting a two-stage aging treatment process, thereby extending the fatigue life of the C250 maraging steel to more than 215,000 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the metallographic structure of C250 maraging steel without cyclic heat treatment;

[0027] Figure 2 This is the metallographic structure diagram of C250 maraging steel after treatment in Example 1 of the present application. DETAILED DESCRIPTION

[0028] The present application provides a heat treatment process for refining the grains of C250 maraging steel, comprising the following steps:

[0029] (1) The C250 maraging steel is heated to 945-955°C and kept at this temperature for 1-1.5 hours, and then water-cooled to room temperature to achieve the first cycle treatment, thereby obtaining the heat-treated C250 maraging steel;

[0030] (2) The material after the first cycle treatment is heated to 925-935℃ and kept warm for 1-1.5h, and then water-cooled to room temperature to achieve the second cycle treatment;

[0031] (3) The material after the second cycle treatment is heated to 895-905℃ and kept at this temperature for 1-1.5h, and then water-cooled to room temperature to achieve the third cycle treatment;

[0032] (4) The material after the third cycle treatment is heated to 815-825 ° C and kept at this temperature for 1-1.5 hours, and then air-cooled to room temperature to achieve the fourth cycle treatment;

[0033] (5) The C250 maraging steel treated in step (4) is aged at 475-485°C for 5-8h and air-cooled to room temperature.

[0034] Furthermore, step (5) is to keep the C250 maraging steel treated in step (4) at 475-485°C for 2-3 hours, and air-cool it to room temperature; then continue to keep it at 475-485°C for 2-3 hours, and air-cool it to room temperature.

[0035] The C250 maraging steel used in the embodiments of the present application has a specification of Φ150×500 mm; its chemical composition, in terms of mass percentage, includes: C content 0.0039%, Ni content 17.93%, Co content 7.87%, Mo content 4.89%, Ti content 0.40%, Al content 0.11%, P content 0.0023%, S content 0.0004%, and the balance is Fe.

[0036] The raw materials, solvents, etc. of this application can be obtained commercially.

[0037] The present application is further described in detail below with reference to the embodiments, performance testing and accompanying drawings. Example 1

[0038] Example 1 provides a heat treatment process for refining the grains of C250 maraging steel, comprising the following steps:

[0039] (1) C250 maraging steel was heated to 950 °C and kept at this temperature for 1 h, and then water-cooled to room temperature to achieve the first cycle treatment;

[0040] (2) The material after the first cycle treatment is heated to 930 °C and kept at this temperature for 1 h, and then water-cooled to room temperature to achieve the second cycle treatment;

[0041] (3) The material after the second cycle treatment is heated to 900 °C and kept at this temperature for 1 hour, and then water-cooled to room temperature to achieve the third cycle treatment;

[0042] (4) The material after the third cycle treatment is heated to 820 °C and kept at this temperature for 1 h, and then air-cooled to room temperature to achieve the fourth cycle treatment, thereby obtaining the heat-treated C250 maraging steel;

[0043] (5) The C250 maraging steel treated in step (4) was kept at 480°C for 6 h and then air-cooled to room temperature.

[0044] The metallographic structure of C250 maraging steel after heat treatment in Example 1 is shown in FIG. Figure 2 shown.

[0045] Examples 2-4

[0046] Examples 2-4 respectively provide a heat treatment process for refining the grains of C250 maraging steel.

[0047] The difference between the above embodiment and embodiment 1 is that the temperature and time of the four-cycle treatment are shown in Table 1 below.

[0048] Comparative Examples 1-7

[0049] Comparative Examples 1-7 respectively provide a heat treatment process for refining the grains of C250 maraging steel.

[0050] The difference between the comparative example and Example 1 is that the temperature and time of the four-cycle treatment are shown in Table 1 below.

[0051] Table 1 Temperatures of the four cycles of treatment in Examples 1-4 and Comparative Examples 1-7

[0052] Example 5

[0053] Example 5 provides a heat treatment process for refining the grains of C250 maraging steel.

[0054] The difference between the above embodiment and embodiment 1 is that the aging treatment process in step (5) is as follows:

[0055] (5) The C250 maraging steel treated in step (4) was kept at 480°C for 3 hours and air-cooled to room temperature; then, the temperature was continued to be kept at 480°C for 3 hours and air-cooled to room temperature. Comparative Example 8

[0056] Comparative Example 8 provides a heat treatment process for refining the grains of C250 maraging steel, comprising the following steps: heating the C250 maraging steel to 750° C., holding the temperature for 5 minutes, and then water-quenching the steel to room temperature, thereby achieving a first cycle of treatment; heating the steel that has undergone the first cycle of treatment to 930° C., holding the temperature for 5 minutes, and then water-quenching the steel to room temperature, thereby achieving a second cycle of treatment, thereby obtaining heat-treated C250 maraging steel. Comparative Example 9

[0057] Comparative Example 9 provides a heat treatment process for refining the grains of C250 maraging steel, comprising the following steps: heating the C250 maraging steel to 750° C., holding the temperature for 1 hour, and then water-quenching the steel to room temperature, thereby achieving a first cycle of treatment; heating the steel that has undergone the first cycle of treatment to 930° C., holding the temperature for 1 hour, and then water-quenching the steel to room temperature, thereby achieving a second cycle of treatment, thereby obtaining heat-treated C250 maraging steel.

[0058] Detection test

[0059] The microstructure and performance of the C250 maraging steel obtained in Examples 1-5 and Comparative Examples 1-9 were tested, and the results are shown in Table 2 below.

[0060] 1. Microstructure Observation: The microstructure of the heat-treated C250 maraging steels of Examples 1-5 and Comparative Examples 1-9 was observed using a scanning electron microscope to determine the grain size. The grain grade was then determined according to the Grain Size Comparison Table (Grade 12).

[0061] 2. Tensile strength test: Refer to GB / T 228.1 to test the tensile strength of C250 maraging steel;

[0062] 3. Fatigue performance test: Kt=1.0, strain ratio 0, maximum strain 0.006mm / mm, frequency 0.5Hz, triangular waveform.

[0063] Table 2 Performance test results of C250 maraging steel obtained in Examples 1-5 and Comparative Examples 1-9

[0064]

[0065] The test results in Table 2 indicate that the C250 maraging steel obtained in Examples 1-5 of the present application has a grain grade of 8-9, a compressive strength greater than 1900 MPa, and a fatigue life greater than 200,000 cycles. This demonstrates that the four-stage, step-by-step cooling heat treatment process provided in Examples 1-5 of the present application can achieve sufficient grain refinement and microstructure homogenization in the C250 maraging steel, thereby achieving excellent mechanical properties in the C250 maraging steel after aging treatment.

[0066] The C250 maraging steel obtained in Comparative Examples 1-4 had a grain grade of only 7-8, a compressive strength of only 1812-1883 MPa, and a fatigue life of only 98,246-217,787 cycles. This indicates that a three-stage, step-by-step cooling heat treatment process is insufficient to achieve optimal grain and microstructure in C250 maraging steel.

[0067] The C250 maraging steel obtained in Comparative Examples 5-6 had a grain grade of only 6-7.5, a compressive strength of only 1776-1790 MPa, and a fatigue life of only 33,492-54,222 cycles. This indicates that the four-stage, stepwise heating process is insufficient to achieve optimal grain and microstructure in the C250 maraging steel, especially since the final high-temperature heating step can lead to grain growth.

[0068] The C250 maraging steel obtained in Comparative Example 7 had a grain grade of 4.0-7.5, a compressive strength of only 1294 MPa, and a fatigue life of only 9493 cycles. Therefore, the four-stage, step-by-step cooling heat treatment process provided in Comparative Example 7 is insufficient to achieve excellent grain and microstructure properties in the C250 maraging steel.

[0069] The C250 maraging steel obtained in Comparative Examples 8-9 had a grain grade of 5.5-6, a compressive strength of only 1799-1831 MPa, and a fatigue life of only 18,971-19,564 cycles. This indicates that heat treatment of the C250 maraging steel using the two-stage heating process in the related art results in poor grain refinement and microstructure uniformity, leading to inferior mechanical properties of the C250 maraging steel.

[0070] The test results of Example 1 and Example 5 show that Example 5 can further optimize the comprehensive performance of C250 maraging steel and further improve the fatigue life by adopting a two-stage aging treatment process.

[0071] In summary, the present application provides a heat treatment process for grain refinement of C250 maraging steel. The heat treatment process adopts a four-stage gradient cooling treatment method. The present application controls the temperature and holding time of the four stages within the following ranges: S1: holding at 945-955°C for 1-1.5 hours, water cooling to room temperature; S2: holding at 925-935°C for 1-1.5 hours, water cooling to room temperature; S3: holding at 895-905°C for 1-1.5 hours, water cooling to room temperature; S4: holding at 815-825°C for 1-1.5 hours, air cooling to room temperature. This process achieves sufficient grain refinement and microstructure homogenization of the C250 maraging steel, thereby achieving excellent mechanical properties for the C250 maraging steel. Furthermore, by performing a two-stage aging treatment on the heat-treated C250 maraging steel, the comprehensive performance of the C250 maraging steel is further optimized, and the fatigue life of the C250 maraging steel is increased to more than 215,000 times.

[0072] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A heat treatment process for refining the grains of C250 maraging steel, characterized in that: The method comprises the following steps: heat treating C250 maraging steel according to the following process: S1: Keep at 945-955℃ for 1-1.5h, then cool to room temperature with water; S2: Keep at 925-935℃ for 1-1.5h, then cool to room temperature with water; S3: Keep at 895-905℃ for 1-1.5h, then cool to room temperature with water; S4: Keep at 815-825℃ for 1-1.5h, then air cool to room temperature; The chemical composition of the C250 maraging steel, in percentage by mass, comprises: 0.0039% C, 17.93% Ni, 7.87% Co, 4.89% Mo, 0.40% Ti, 0.11% Al, 0.0023% P, 0.0004% S, and the balance being Fe.

2. The heat treatment process for refining the grains of C250 maraging steel according to claim 1, characterized in that: The temperature of the S1 process is 950° C. and the holding time is 1 hour.

3. The heat treatment process for refining the grains of C250 maraging steel according to claim 1, characterized in that: The temperature of the S2 process is 930° C. and the holding time is 1 hour.

4. The heat treatment process for refining the grains of C250 maraging steel according to claim 1, characterized in that: The temperature of the S3 process is 900° C. and the holding time is 1 hour.

5. The heat treatment process for refining the grains of C250 maraging steel according to claim 1, characterized in that: The temperature of the S4 process is 820° C. and the holding time is 1 hour.

6. The heat treatment process for refining C250 maraging steel grains according to any one of claims 1 to 5, characterized in that: The heat treatment process of the C250 maraging steel also includes aging treatment, which specifically comprises the following steps: keeping the C250 maraging steel after the S4 process at 475-485° C. for 2-3 hours, air-cooling to room temperature; then keeping the temperature at 475-485° C. for another 2-3 hours, and air-cooling to room temperature.

7. C250 maraging steel obtained by the heat treatment process for refining the grains of C250 maraging steel according to any one of claims 1 to 6.

8. The C250 maraging steel according to claim 7, characterized in that The grain size of the C250 maraging steel is 8-9.

Images