A process for the production of semi-annular cast alloy steel parts

Abstract

The present application belongs to the technical field of metal material heat treatment, and particularly relates to a process method for preparing a semi-ring type cast alloy steel part. Before smelting, the chemical component value is set, appropriate alloy elements are added in corresponding order, argon is passed through the whole refining process to strengthen stirring and accelerate the homogenization of components and temperature, and the molten steel meeting the requirements and being relatively uniform is obtained. Argon protection pouring is adopted to prevent the molten steel from being oxidized, and sufficient molten steel pouring allowance is left. The one-time high-temperature annealing and one-time high-temperature tempering pretreatment process is adopted to eliminate the non-equilibrium structure in the part, fine carbide particles and ferrite structure are obtained through recrystallization, and the structure inheritance is avoided. The part is heated to above the austenitizing temperature and kept for a sufficient time length, so that the part structure is completely austenitized, then the part is quenched through a faster cooling speed, so that the part temperature is below the Ms point to occur martensite transformation. The part is tempered at a suitable temperature to obtain a part with good comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and specifically relates to a process method for preparing semi-ring-shaped cast alloy steel parts. Background Technology

[0002] In existing technologies, large semi-ring cast alloy steels are highly anticipated as crucial components in hydropower engineering. These components continuously withstand extremely high loads and impacts during operation, requiring not only high strength but also good ductility and toughness. Therefore, high demands are placed on the overall performance of these parts. Furthermore, due to the characteristics of subsequent welding, carbon equivalent control is extremely stringent, making it difficult to optimize the overall performance solely through chemical composition adjustments. In the manufacturing process of large components, uniformity is a key factor affecting their overall performance. Considering the numerous limitations in the production of large components, optimizing their manufacturing process to achieve consistent core and surface properties, while simultaneously achieving uniform and refined microstructure, is a pressing technical problem that needs to be solved. Therefore, optimizing existing heat treatment processes to improve the overall performance of large ring alloy steels is imperative. Summary of the Invention

[0003] The purpose of this invention is to provide a process for preparing semi-ring-shaped cast alloy steel parts, comprising the following steps: Step 1: Accurately calculate the amount to be added based on the measured values ​​of alloy elements to ensure uniform melting. At the same time, argon gas is introduced throughout the refining process to enhance stirring and accelerate the homogenization of composition and temperature. The chemical composition of the parts is as follows by mass fraction: C: 0.14-0.16%, Mn: 0.73-0.80%, Si: 0.43-0.45%, Cr: 0.76-0.81%, Ni: 1.01-1.16%, Mo: 0.23-0.28%, V: 0.01-0.011%, Nb: 0.0004-0.0005%, Cu: ≤0.50%, B: ≤0.004%, with the remainder being Fe and unavoidable impurities, and a carbon equivalent ≤0.60; carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15; Step 2: Argon gas is used for protective pouring to prevent oxidation of molten steel, and sufficient molten steel is left for pouring to complete the casting of the part; Step 3: After solidification, confirm that the part dimensions meet the requirements, load the part into the furnace and perform a high-temperature annealing process, heating it to 900-920℃ in stages, holding it at that temperature, furnace cooling to ≤300℃, and then air cooling it. Check the part temperature when removing it from the furnace, and confirm that the temperature at the maximum effective thickness of the part is ≤300℃. After air cooling to ≤200℃, load the part into the furnace and perform a high-temperature tempering process, heating it to 590-610℃ in stages, holding it at that temperature, furnace cooling to ≤300℃, and then air cooling it. Check the part temperature when removing it from the furnace, and confirm that the temperature at the maximum effective thickness of the part is ≤300℃. Step 4: After processing, the parts undergo heat treatment and are then loaded into the furnace: Place the parts obtained in Step 3 horizontally, support them stably, and attach steel rods at the semi-circular opening. When lifting, ensure that there is a lifting point at the center of the tie rod. Step 5: After the furnace is loaded, the quenching process of the tempering process is carried out: the temperature is raised to 920-940℃ in stages and held at that temperature. After being taken out of the furnace, it is cooled in water. After being taken out of the water, the temperature is checked and found to be ≤150℃. Step 6: After quenching, perform the high-temperature tempering process: heat to 605-615℃ in stages, hold at that temperature, and then air cool after removing from the furnace.

[0004] As a preferred embodiment, in step 1, the amount of alloying elements to be added is accurately calculated based on the measured values. A suitable steel plate material is selected for rough refining and melting. During the refining stage, the alloy content is adjusted. First, Cr, Ni, and Mo alloying elements are added, then Mn element is added, and finally V and Nb elements are added. Argon gas is introduced throughout the refining process to enhance stirring and accelerate the homogenization of composition and temperature. During the refining process, steel samples are taken for chemical composition testing. The amount of alloying elements added is adjusted according to the test results to ensure that the alloy content and residual element content of the final molten steel meet the requirements.

[0005] As a preferred embodiment, in step 3, the high-temperature annealing temperature is 900-920℃, the annealing time is 22-26h, where the annealing time includes the total time for temperature uniformization, and the cooling method is furnace cooling to ≤300℃ followed by air cooling.

[0006] As a preferred embodiment, in step 3, the high-temperature tempering temperature is 590-610℃, the tempering time is 18-21h, where the tempering time includes the total time for temperature uniformization, and the cooling method is furnace cooling to ≤300℃ followed by air cooling.

[0007] As a preferred embodiment, in step 5, the temperature is raised to 920-940℃ in stages and held for 6-8 hours.

[0008] As a preferred embodiment, in step 6, the temperature is raised to 605-615℃ in stages and held for 10-12 hours.

[0009] As a preferred embodiment, in the staged heating method, the heating rate is controlled at 40-45℃ / h.

[0010] To achieve the above objectives and solve the problems existing in the prior art, the process method includes the following steps: Before smelting, the chemical composition value is set, and appropriate alloying elements are added in the corresponding order. Simultaneously, argon gas is introduced throughout the refining process to enhance stirring, accelerate the homogenization of composition and temperature, and obtain molten steel that meets the requirements and is relatively uniform. Argon gas is used for protective casting to prevent oxidation of the molten steel, and sufficient casting allowance is left. A pretreatment process of one high-temperature annealing followed by one high-temperature tempering is adopted to eliminate non-equilibrium structures in the parts. Fine carbide particles and ferrite structures are obtained through recrystallization, avoiding the inheritance of structural characteristics. The parts are heated to above the austenitizing temperature and held for a sufficient time to fully austenitize the part structure. Then, quenching is performed at a relatively fast cooling rate to bring the part temperature below the Ms point to induce martensitic transformation. A suitable temperature is selected for high-temperature tempering of the parts to obtain equiaxed ferrite and fine granular carbide structures, eliminate stress during quenching, and obtain parts with good comprehensive properties.

[0011] The semi-ring-shaped high-quality cast alloy steel parts prepared using the raw materials and methods of this invention improve hardenability through the appropriate addition of multi-element alloys, making the core and surface properties of the parts more consistent. Furthermore, the precipitation strengthening and pinning effect of microalloying, combined with the heat treatment tempering process parameters, achieves uniform and refined microstructure at the micro level. The combination of these techniques is the core idea for improving overall performance. Firstly, the ratio and addition of alloying elements directly affect the purity of the molten steel and the effect of subsequent heat treatment. The application of microalloying technology has high control requirements; improper ratios may have adverse effects. Moreover, the selection of the austenitizing temperature in subsequent heat treatment is strictly controlled; excessively high or low austenitizing temperatures will significantly reduce its effectiveness.

[0012] The present invention has the following beneficial effects: This invention proposes a novel process for preparing semi-ring-shaped cast alloy steel parts. It employs alloy element control and micro-alloying technology, followed by a pretreatment process of high-temperature annealing and tempering after solidification. Simultaneously, it utilizes a heat treatment process of low-temperature transformation of supercooled austenite combined with high-temperature tempering and holding. The high-temperature annealing and tempering pretreatment accelerates atomic diffusion efficiency. Furthermore, through microstructural transformation and recrystallization, it ultimately yields equiaxed and fine carbide particles and ferrite, resulting in a homogenized internal structure, eliminating complex stresses, and avoiding the negative impacts of microstructure inheritance, thus preparing the part microstructure for final performance heat treatment. Appropriate austenitizing temperature and holding time can ensure the efficiency of austenitizing transformation. Simultaneously, the improved hardenability of alloying elements and the nanoscale precipitation pinning effect of microalloying technology can control the fineness of the austenite grains after complete austenitization. Rapid cooling to below the Ms point causes the microstructure to transform, resulting in martensite. The addition of Mn, Cr, Ni, and Mo elements can improve hardenability, allowing the core to complete martensitic transformation even at a lower cooling rate than the surface, thus achieving a relatively uniform microstructure in both the surface and core. This provides a good microstructure basis for subsequent high-temperature tempering recovery and recrystallization. The optimal high-temperature tempering temperature, determined through experimentation, precipitates fine carbide particles and promotes their appropriate agglomeration and spheroidization, ultimately yielding equiaxed ferrite and finer granular carbide microstructure. By obtaining an ideal microstructure and finer grains, a product with excellent overall performance is achieved. Attached Figure Description

[0013] Figure 1 The image shows a metallographic photograph of the part in sample 1 when the tempering temperature is 615℃.

[0014] Figure 2 The image shows a metallographic photograph of the part in sample 2 when the tempering temperature is 615℃.

[0015] Figure 3 The image shows a metallographic photograph of the part in sample 4 when the tempering temperature was 615℃. Detailed Implementation

[0016] To make the technical means, creative features, objectives, and beneficial effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0017] In addition, to better illustrate the present invention, numerous specific details are given in the following detailed embodiments. Those skilled in the art should understand that the present invention can be implemented even without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the main points of the present invention.

[0018] Example 1

[0019] (1) Accurately calculate the amount of alloying elements to be added based on the measured values ​​of alloying elements, select appropriate steel plate materials for rough refining and melting, adjust the alloy content during the refining stage, add Cr, Ni and Mo alloying elements first, add Mn elements 50 minutes before the end of refining, add V and Nb elements 20 minutes before the end of refining, and purify the mixture with argon gas throughout the refining process to enhance stirring and accelerate the homogenization of composition and temperature. Take steel samples during the refining process for chemical composition testing, and adjust the amount of alloying elements added based on the test results to ensure that the alloy content and residual element content of the final molten steel meet the requirements.

[0020] In step (1) of this embodiment, the final chemical composition of the molten steel is as follows: C: 0.16%, Mn: 0.79%, Si: 0.45%, Cr: 0.81%, Ni: 1.15%, Mo: 0.28%, Nb: 0.0005%, V: 0.011%, Cu: 0.001%, B: 0.00003%, with the remainder being Fe and unavoidable impurities, and a carbon equivalent of 0.588.

[0021] (2) Argon gas is used for protective casting to prevent the molten steel from oxidizing, and sufficient molten steel is left for casting to complete the casting of the parts.

[0022] (3) After solidification, confirm that the dimensions of the parts meet the requirements. The parts must be placed horizontally, with a distance of ≥700mm from the trolley surface and a distance of ≥500mm from the furnace door, rear wall, and side walls. After loading the furnace, perform a high-temperature annealing process, specifically: raise the temperature to 300℃ at a rate of 45℃ / h and hold for 3 hours; raise the temperature to 650℃ at a rate of 45℃ / h and hold for 6 hours; raise the temperature to 910℃ at a rate of 45℃ / h and hold for 8 hours; hold for 18 hours after temperature uniformity; and cool the furnace to ≤3℃. The parts are removed from the furnace at 00℃ and air-cooled. The temperature of the parts is checked upon removal from the furnace to ensure that the temperature at the maximum effective thickness of the parts is ≤300℃. After air-cooling to a temperature ≤200℃, the parts are put back into the furnace for high-temperature tempering. Specifically, the parts are heated to 350℃ at a rate of 45℃ / h and held for 2 hours, then heated to 600℃ at a rate of 45℃ / h and homogenized for 5 hours. After homogenization, the parts are held for 15 hours and then furnace-cooled to ≤300℃ before being removed from the furnace and air-cooled. The temperature of the parts is checked upon removal from the furnace to ensure that the temperature at the maximum effective thickness of the parts is ≤300℃.

[0023] (4) The process of heat treatment and loading the parts into the furnace after processing is as follows: the parts are placed horizontally, with a distance of ≥800mm from the trolley surface and a distance of ≥500mm from the furnace door, the rear wall of the furnace and the two sides of the furnace wall. Steel rods are connected at the semi-circular opening. When lifting, it is necessary to ensure that there is a lifting point in the center of the tie rod.

[0024] (5) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 930℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0025] (6) After quenching, the high-temperature tempering process of the tempering process is carried out. The parts must be placed horizontally, with a distance of ≥800mm from the trolley surface and a distance of ≥500mm from the furnace door, the rear wall of the furnace and the two sides of the furnace wall. After loading the furnace, the process is executed. Specifically, the process is as follows: the temperature is raised to 350℃ at a heating rate of 40℃ / h and held for 3h, then raised to 615℃ at a heating rate of 40℃ / h and held for 12h, and then air-cooled after being taken out of the furnace.

[0026] Example 2

[0027] The preparation conditions and processes are the same as in Example 1, except that in step (1), different chemical compositions are set to form a comparison, and the following comparative steel chemical composition is finally obtained: C: 0.16%, Mn: 0.80%, Si: 0.44%, Cr: 0.79%, Ni: 1.16%, Mo: 0.26%, Nb: 0.0004%, V: 0.010%, Cu: 0.001%, B: 0.00003%, the remainder being Fe and unavoidable impurities, and carbon equivalent: 0.583.

[0028] Example 3

[0029] The remaining preparation conditions and processes are the same as in Example 1, except that: In step (1), different chemical compositions are set up for comparison, and the following chemical composition of molten steel is finally obtained: C: 0.15%, Mn: 0.76%, Si: 0.43%, Cr: 0.77%, Ni: 1.01%, Mo: 0.25%, Nb: 0.0005%, V: 0.011%, Cu: 0.001%, B: 0.00003%, the remainder being Fe and unavoidable impurities, and carbon equivalent: 0.550.

[0030] Comparative Example 1 The remaining preparation conditions and processes are the same as in Example 1, except that: In step (1), different chemical compositions are set up for comparison, and the following chemical composition of molten steel is finally obtained: C: 0.15%, Mn: 0.77%, Si: 0.46%, Cr: 0.80%, Ni: 1.13%, Mo: 0.28%, Cu: 0.0015%, B: 0.00004%, the remainder being Fe and unavoidable impurities, and carbon equivalent: 0.569.

[0031] After the above heat treatment process, samples of the parts were taken for mechanical property testing. The measured values ​​of T / 4 (1 / 4 thickness) and T / 2 (1 / 2 thickness) of the sample areas of Examples 1-2 and Comparative Example 1 are shown in the table below: Table 1. Test data of Examples 1, 2, and Comparative Example 1 In the table, the reduction in area Z refers to the cross-sectional area reduction rate Z.

[0032] Comparative Example 2 The remaining preparation conditions and processes are the same as in Example 1, except that: In step (1), different chemical compositions are set up for comparison, and the following chemical composition of molten steel is finally obtained: C: 0.14%, Mn: 0.74%, Si: 0.42%, Cr: 0.75%, Ni: 1.16%, Mo: 0.24%, V: 0.011%, Cu: 0.001%, B: 0.00004%, the remainder being Fe and unavoidable impurities, and carbon equivalent: 0.541.

[0033] Comparative Example 3 In step (1), different chemical compositions are set up for comparison, and the following chemical composition of molten steel is finally obtained: C: 0.15%, Mn: 0.75%, Si: 0.45%, Cr: 0.75%, Ni: 1.13%, Mo: 0.26%, Nb: 0.0006%, Cu: 0.001%, B: 0.00004%, the remainder being Fe and unavoidable impurities, and carbon equivalent: 0.552.

[0034] In this article, samples 1 to 6 were made by one-time casting molding in step (2) of Examples 1 to 3 and Comparative Examples 1 to 3; the mechanical property parameters of Examples 1, 2 and Comparative Example 1 were obtained by sampling and testing the corresponding cast parts after a complete set of heat treatment; the other examples and comparative examples were all made by cutting samples from the parts made by step (2) of the above casting molding, and then carrying out different heat treatment process tests and testing the performance.

[0035] Example 4

[0036] The remaining preparation conditions and processes are the same as in Example 1, except that: (1) The sample 1 cut from the part made in step (2) of Example 1 is subjected to a heat treatment process; (2) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 920℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0037] Example 5

[0038] The remaining preparation conditions and processes are the same as in Example 2, except that: (1) The sample 2 cut from the part made in step (2) of Example 2 is subjected to heat treatment process; (2) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 920℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0039] Comparative Example 4 The preparation conditions and processes were the same as in Comparative Example 1, except that: (1) The sample 3 cut from the part made in step (2) of Comparative Example 1 is subjected to heat treatment process; (2) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 920℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0040] After the above heat treatment process was performed on the samples of Examples 4, 5 and Comparative Example 4, the parts were sampled for mechanical property testing. The measured values ​​of sample areas T / 4 and T / 2 are shown in Table 2 below.

[0041] Table 2 Test data of Examples 4, 5 and Comparative Example 4 Example 6

[0042] The remaining preparation conditions and processes are the same as in Example 1, except that: (1) The sample 1 cut from the part made in step (2) of Example 1 is subjected to heat treatment process; (2) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 940℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0043] Example 7

[0044] The remaining preparation conditions and processes are the same as in Example 2, except that: (1) The sample 2 cut from the part made in step (2) of Example 2 is subjected to heat treatment process; (2) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 940℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0045] Comparative Example 5 The preparation conditions and processes were the same as in Comparative Example 1, except that: (1) The sample 3 cut from the part made in step (2) of Comparative Example 1 is subjected to heat treatment process; (2) After the furnace is loaded according to the relevant requirements of step (4), the quenching process of the tempering process is carried out. Specifically, the temperature is raised to 650℃ at a heating rate of 40℃ / h and held for 3 hours, then raised to 940℃ at a heating rate of 40℃ / h and held for 8 hours. After being taken out of the furnace, the furnace is cooled in water for 40 minutes. After being taken out of the water, the temperature is tested to be ≤150℃.

[0046] After the above heat treatment process was performed on the samples of Examples 6, 7 and Comparative Example 5, the parts were sampled for mechanical property testing. The measured values ​​of T / 4 and T / 2 of the sample area are shown in Table 3 below.

[0047] Table 3 Test data of Examples 6, 7 and Comparative Example 5 Examples 8-10

[0048] The remaining preparation conditions and processes are the same as in Example 1, except that: (1) The heat treatment process of the part made in step (2) of Example 1 is changed to the heat treatment process of sample 1. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0049] The process was changed sequentially as follows: heating at a rate of 40℃ / h to 605℃, 610℃, and 615℃, holding at these temperatures for 12 hours, and then air-cooling the furnace.

[0050] Comparative Examples 6 and 7 The remaining preparation conditions and processes are the same as in Example 8, except that: (1) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled. This is changed to: the temperature is raised to 600℃ and 625℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0051] Examples 11-13

[0052] The remaining preparation conditions and processes are the same as in Example 2, except that: (1) The heat treatment process of the part made in step (2) of Example 2 is changed to the heat treatment process of sample 2; (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0053] The process was changed sequentially as follows: heating at a rate of 40℃ / h to 605℃, 610℃, and 615℃, holding at these temperatures for 12 hours, and then air-cooling the furnace.

[0054] Comparative Examples 8 and 9 The remaining preparation conditions and processes are the same as in Example 11, except that: (1) The heat treatment process of the part made in step (2) of Example 11 is changed to the heat treatment process of sample 2. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0055] The process was changed to: heating at a rate of 40℃ / h to 600℃, holding at 625℃ for 12 hours, and then air-cooling after removal from the furnace.

[0056] Examples 14-16

[0057] The remaining preparation conditions and processes are the same as in Example 3, except that: (1) The heat treatment process of the part made in step (2) of Example 3 is changed to the heat treatment process of sample 3. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0058] The process was changed sequentially as follows: heating at a rate of 40℃ / h to 605℃, 610℃, and 615℃, holding at these temperatures for 12 hours, and then air-cooling the furnace.

[0059] Comparative Examples 10 and 11 The remaining preparation conditions and processes are the same as in Example 14, except that: (1) The heat treatment process of the part made in step (2) of Example 14 is changed to the heat treatment process of sample 3. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0060] The process was changed to: heating at a rate of 40℃ / h to 600℃, holding at 625℃ for 12 hours, and then air-cooling after removal from the furnace.

[0061] Comparative Examples 12-16 The preparation conditions and processes were the same as in Comparative Example 1, except that: (1) The heat treatment process of the part made in step (2) of Comparative Example 1 was changed to that of the sample 4. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled. This is changed to: the temperature is raised to 600℃, 605℃, 610℃, 615℃, and 625℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0062] Comparative Examples 17-21 (1) The heat treatment process of the part made in step (2) of Comparative Example 2 was changed to that of the sample 5. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled. This is changed to: the temperature is raised to 600℃, 605℃, 610℃, 615℃, and 625℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0063] Comparative Examples 22-26 (1) The heat treatment process of the part made in step (2) of Comparative Example 3 was changed to that of Sample 6. (2) In step (6), the temperature is raised to 615℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled. This is changed to: the temperature is raised to 600℃, 605℃, 610℃, 615℃, and 625℃ at a rate of 40℃ / h and held for 12h, then removed from the furnace and air-cooled.

[0064] Table 4 Test results of samples 1 and 2 (Examples 8-13 and some comparative examples) Table 5 Test results of samples 3 and 4 (Examples 14-16 and some comparative examples) Table 6 Test results of samples 5 and 6 (Comparative Examples 17-26) The test data of samples 1-6 were analyzed based on the results in Table 4-6.

[0065] Samples 1-6 were tempered within the temperature range of 600-625℃. Analysis of the measured values ​​shows that the strength of the samples at 600℃ is relatively high, with higher measured values ​​for yield strength and tensile strength, but lower elongation, with most elongations failing to meet the requirements. The impact value is also relatively low. However, when tempered at 625℃, the strength of the samples decreases significantly, with most yield strength and tensile strength failing to meet the performance requirements in the procurement specifications. This is because as the tempering temperature increases, carbides aggregate and grow, while the degree of ferrite recovery and recrystallization increases, weakening dislocation strengthening, reducing strength, and increasing ductility and toughness.

[0066] It should be noted that under tempering conditions of 605℃, the elongation at the T / 2 portion of sample 1 was 16.5%, slightly lower than the standard requirement of 17%, while the remaining samples all met the performance requirements at this temperature. When the tempering temperature was increased to 610~615℃, the elongation of all samples consistently met the standard, and the impact toughness was further improved. Therefore, the feasible high-temperature tempering temperature for this invention is 605-615℃, and a more preferred high-temperature tempering temperature is 610~615℃.

[0067] The impact value of sample 4 is significantly lower than that of the other comparative samples. At the same time, the tensile impact value is generally lower than that of the other two groups. This is because it did not use micro-alloying technology, but only alloy control and heat treatment process parameter adjustment to increase hardenability. However, its fine grain strengthening and precipitation strengthening mechanisms are not as good as those of the other two comparative samples. In addition, when its tempering temperature is high, the strength margin is small, close to the lower limit of the required value. As the tempering temperature decreases, the strength increases, but the impact value also shows a synchronous downward trend. If the impact value fluctuates, it is easy to fail the impact test.

[0068] The Ni content of sample 3 was lower than that of the other comparative samples, which affected its hardenability. The overall performance of the core T / 2 was worse than that of the near-surface T / 4 because Ni can reduce the critical cooling rate, thus allowing the core to obtain martensitic structure even at a slower cooling rate.

[0069] Analysis of samples 5 and 6 shows that sample 5 had Nb removed and only V added. The mechanism of V is precipitation strengthening, which can improve the yield strength of the part, but its effect on grain refinement is weak. Therefore, the impact value is lower than that of sample 6. Sample 6 had V removed and only Nb added. The mechanism of Nb is grain refinement strengthening, which can inhibit austenite recrystallization, expand the non-recrystallization zone, refine the initial austenite grains before cooling, refine the grain size, improve the toughness of the part, and increase the impact value.

[0070] The chemical compositions of samples 1 and 2 are relatively similar, and the proportions of microalloyed V and Nb are also similar. Comparing their performance results at different tempering temperatures, the microalloyed addition ratio is superior, with a certain margin in all tensile and impact values, especially the impact value is more stable. This is because the microalloyed elements form high-melting-point, diffusely distributed nanoscale carbides in the steel, which pin the grain boundaries during high-temperature recrystallization, preventing grain growth and preparing for the subsequent acquisition of fine and uniform grain structure. The finer the grains, the greater the amount of plastic deformation that can be accommodated per unit area, thereby improving strength and crack resistance, and increasing the impact value.

[0071] Metallographic analysis was performed on some samples after tempering at 615℃. Metallographic photographs are shown below. Figure 1-3 The samples were prepared and observed in accordance with GB / T 13298-2015 "Methods for Examination of Microstructure of Metals". The grain size was evaluated by referring to the comparison rating chart of GB / T 6394-2017 "Methods for Determination of Average Grain Size of Metals". The grain size of samples 1 and 2 reached grade 6 to 6.5, with uniform and fine grains, while the grain size of sample 4 was grade 5.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A process for preparing semi-ring-shaped cast alloy steel parts, characterized in that: Includes the following steps: Step 1: Accurately calculate the amount to be added based on the measured values ​​of alloy elements to ensure uniform melting. At the same time, argon gas is introduced throughout the refining process to enhance stirring and accelerate the homogenization of composition and temperature. The chemical composition of the parts is as follows by mass fraction: C: 0.14-0.16%, Mn: 0.73-0.80%, Si: 0.43-0.45%, Cr: 0.76-0.81%, Ni: 1.01-1.16%, Mo: 0.23-0.28%, V: 0.01-0.011%, Nb: 0.0004-0.0005%, Cu: ≤0.50%, B: ≤0.004%, with the remainder being Fe and unavoidable impurities, and a carbon equivalent ≤0.

60. Step 2: Argon gas is used for protective pouring to prevent oxidation of molten steel, and sufficient molten steel is left for pouring to complete the casting of the part; Step 3: After solidification, confirm that the part dimensions meet the requirements, load the part into the furnace and perform a high-temperature annealing process, heating it to 900-920℃ in stages, holding it at that temperature, furnace cooling to ≤300℃, and then air cooling it. Check the part temperature when removing it from the furnace, and confirm that the temperature at the maximum effective thickness of the part is ≤300℃. After air cooling to ≤200℃, load the part into the furnace and perform a high-temperature tempering process, heating it to 590-610℃ in stages, holding it at that temperature, furnace cooling to ≤300℃, and then air cooling it. Check the part temperature when removing it from the furnace, and confirm that the temperature at the maximum effective thickness of the part is ≤300℃. Step 4: After processing, the parts undergo heat treatment and are then loaded into the furnace: Place the parts obtained in Step 3 horizontally, support them stably, and attach steel rods at the semi-circular opening. When lifting, ensure that there is a lifting point at the center of the tie rod. Step 5: After the furnace is loaded, the quenching process of the tempering process is carried out: the temperature is raised to 920-940℃ in stages and held at that temperature. After being taken out of the furnace, it is cooled in water. After being taken out of the water, the temperature is checked and found to be ≤150℃. Step 6: After quenching, perform the high-temperature tempering process: heat to 605-615℃ in stages, hold at that temperature, and then air cool after removing from the furnace.

2. The process for preparing a semi-ring-shaped cast alloy steel part according to claim 1, characterized in that: In step 1, the amount of alloying elements to be added is accurately calculated based on the measured values. A suitable steel plate material is selected for rough refining and melting. During the refining stage, the alloy content is adjusted. First, Cr, Ni, and Mo alloying elements are added, then Mn element is added, and finally V and Nb elements are added. Argon gas is introduced throughout the refining process to enhance stirring and accelerate the homogenization of composition and temperature. During the refining process, steel samples are taken for chemical composition testing. The amount of alloying elements added is adjusted according to the test results to ensure that the alloy content and residual element content of the final molten steel meet the requirements.

3. The process for preparing a semi-ring-shaped cast alloy steel part according to claim 1, characterized in that: In step 3, the high-temperature annealing temperature is 900-920℃, the annealing time is 22-26h, and the cooling method is furnace cooling to ≤300℃ followed by air cooling.

4. The process for preparing a semi-ring-shaped cast alloy steel part according to claim 1, characterized in that: In step 3, the high-temperature tempering temperature is 590-610℃, the tempering time is 18-21h, and the cooling method is furnace cooling to ≤300℃ followed by air cooling.

5. The process for preparing a semi-ring-shaped cast alloy steel part according to claim 1, characterized in that: In step 5, the temperature is raised to 920-940℃ in stages and held for 6-8 hours.

6. The process for preparing a semi-ring-shaped cast alloy steel part according to claim 1, characterized in that: In step 6, the temperature is raised to 605-615℃ in stages and held for 10-12 hours.

7. A process for preparing a semi-ring-shaped cast alloy steel part according to any one of claims 1-6, characterized in that: In the aforementioned staged heating method, the heating rate is controlled at 40-45℃ / h.

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