Heat treatment process of NiCrMoV low-alloy steel casting material

Abstract

The invention provides a heat treatment process of a NiCrMoV low-alloy steel casting material, and relates to the technical field of metal materials. The heat treatment process comprises the following steps that firstly, a smelted and poured NiCrMoV low alloy steel casting is heated to 620-680 DEG C, heat preservation is conducted for 12-18 h, and then furnace cooling is conducted; the temperature is increased to 880-930 DEG C, heat preservation is carried out for 10-16 h, then the product is discharged out of the furnace and cooled to 300-350 DEG C through strong wind, and then air cooling is carried out to 200 DEG C or below; and finally, the temperature is increased to 630-690 DEG C, heat preservation is conducted for 12-16 h, and then cooling is conducted. According to the heat treatment process, the strength of the NiCrMoV low-alloy steel casting can be guaranteed, the plasticity and toughness of the NiCrMoV low-alloy steel casting can be improved, the mechanical property of the obtained NiCrMoV low-alloy steel casting product is stable, and the heat treatment process is suitable for manufacturing of key castings such as a rack, an anvil block and a base of a large hot die forging press.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to a heat treatment process for NiCrMoV low alloy steel casting materials. Background Art

[0002] Low alloy NiCrMoV steel casting materials are a new type of material, mainly used for manufacturing key components of hot die forging presses. Hot die forging presses operate in high-temperature and high-pressure environments for a long time, and their components need to withstand huge pressures, loads, and high-temperature tests. Therefore, extremely strict requirements are imposed on the performance of the materials. Specifically, these components need to have high strength, high hardness, good wear resistance, and also meet relatively high rigidity and precision requirements.

[0003] The main steel castings of hot die forging presses include anvil blocks, bases, drop hammer frames, etc., and their material is low alloy cast steel. The mechanical property requirements are: yield strength Rp 0.2 ≥245 MPa; tensile strength Rm: 490 MPa - 630 MPa; elongation after fracture A≥18%; reduction of area Z≥35%; impact energy at room temperature KV2≥34 J; Brinell hardness ≤200 HBW. However, in actual manufacturing, it is quite difficult to meet the requirements of strength, hardness, and impact absorption energy simultaneously.

[0004] Currently, there is a lack of relevant performance experimental data for this type of material, and the main technical problem faced in the manufacturing process is how to ensure that the hardness does not exceed 200 HBW while guaranteeing strength and plastic toughness, and at the same time meet the requirement of impact energy at room temperature ≥34 J. Although existing manufacturing technologies can make the strength and hardness of castings close to the upper limit of the standard, it is often difficult to meet the requirement of impact energy at room temperature. In addition, if the strength and hardness are reduced to improve plastic toughness, it will lead to large fluctuations in impact energy at room temperature and be difficult to meet the standard stably. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a heat treatment process for NiCrMoV low alloy steel casting materials.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a heat treatment process for NiCrMoV low alloy steel casting materials, including the following steps:

[0008] (1) Preliminary heat treatment: Heat the smelted and cast NiCrMoV low alloy steel casting to 620°C - 680°C, hold for 12 h - 18 h, and then cool in the furnace;

[0009] (2) Quenching heat treatment: Heat the NiCrMoV low-alloy steel casting material after furnace cooling in step (1) to 880°C - 930°C and hold for 10h - 16h. Then take it out of the furnace and cool it with strong wind to 300°C - 350°C, and then air-cool it to below 200°C;

[0010] (3) Tempering heat treatment: Heat the NiCrMoV low-alloy steel casting after air cooling in step (2) to 630°C - 690°C, hold for 12h - 16h and then cool it;

[0011] The smelted and cast NiCrMoV low-alloy steel casting includes the following components by weight percentage: C: 0.15 - 0.20%, Si: 0.20 - 0.40%, Mn: 0.70 - 0.90%, Cr: 0.15 - 0.30%, Ni: 1.80 - 2.00%, Mo: 0.05 - 0.15%, V: 0.10 - 0.15%, and the balance is Fe and unavoidable impurities.

[0012] The anvil seats, bases, drop hammer frames, etc. of hot die forging presses are all large steel castings. Their casting process has large risers, and there is serious segregation of components under the risers. At the same time, due to their complex structure, if water cooling is used for quenching and cooling, the products are extremely prone to cracking and deformation. Therefore, water cooling cannot be used for quenching and cooling of such products. For this material, the inventor has also conducted air cooling experiments. Due to the slow cooling rate of air cooling, its strength and hardness are barely qualified, but its plasticity and toughness are poor, and the elongation and impact toughness cannot meet the performance requirements.

[0013] In a specific embodiment, Mn: 0.80 - 0.85%.

[0014] In a specific embodiment, C: 0.18%, Si: 0.30%, Mn: 0.80%, Cr: 0.20%, Ni: 1.85%, Mo: 0.08%, V: 0.12%.

[0015] In a specific embodiment, in step (1), the heating is: heating to 620°C - 680°C at a rate of 30°C / h - 60°C / h.

[0016] In a specific embodiment, in step (1), after holding, furnace cool to the temperature range of 400°C - 450°C at a rate of ≤50°C / h and hold for 4h, and then take it out of the furnace and air-cool it.

[0017] In a specific embodiment, in step (2), the heating is: heating to 880°C - 930°C at a rate of 30°C / h - 60°C / h.

[0018] In a specific embodiment, in step (3), the heating is as follows: heating at a rate of 30°C / h to 60°C / h to 630°C to 690°C.

[0019] In a specific embodiment, in step (3), the cooling is at a rate of ≤40°C / h to below 200°C, and then taken out of the furnace and air-cooled to room temperature.

[0020] In a specific embodiment, in step (3), the cooling is furnace cooling.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention can eliminate the composition segregation that may occur in the casting during solidification due to the different solidification sequences of different elements, can reduce the internal stress after casting, prevent the casting from deforming or cracking, and lay a foundation for the quality of subsequent performance heat treatment products.

[0023] (2) The method of the present invention is beneficial to reducing the dislocation density of the material, improving the toughness of the material, and solving the problem of the strength-toughness matching of cast steel materials.

[0024] (3) The mechanical properties of the NiCrMoV low-alloy steel casting material of the present invention meet the following requirements: yield strength Rp0.2≥245MPa; tensile strength Rm: 490MPa to 630MPa; elongation after fracture A≥18%; reduction of area Z≥35%; impact energy at room temperature KV2≥34J; Brinell hardness ≤200HBW. It is suitable for the manufacture of key castings of large hot die forging presses, such as frames, anvil blocks, bases, etc. Specific embodiments

[0025] The following specific examples are used to further illustrate the present invention, but the implementation manners of the invention are not limited thereto.

[0026] Example 1

[0027] In this example, the element proportions of the NiCrMoV low-alloy steel casting material are: C = 0.18%, Si = 0.30%, Mn = 0.80%, Cr = 0.20%, Ni = 1.85%, Mo = 0.08%, V = 0.12%, and Fe is the balance.

[0028] The heat treatment process is as follows: Place the NiCrMoV low alloy steel casting material in a high-temperature furnace, heat it up to 650°C at a rate of 30°C / h to 60°C / h and hold for 16 h. After the holding is completed, cool it in the furnace at a rate of ≤50°C / h to the temperature range of 400°C to 450°C and hold for 4 h, then take it out of the furnace and air-cool it. Then, heat the cast steel material up to 890°C at a rate of 30°C / h to 60°C / h and hold for 12 h, then take it out of the furnace and cool it strongly with air until it reaches 330°C, and then air-cool it to below 180°C and immediately put it into the furnace. Then, heat it up to 670°C at a rate of 30°C / h to 60°C / h and hold for 14 h. After the holding is completed, cool it at a rate of ≤40°C / h to below 200°C, and then take it out of the furnace and air-cool it to room temperature.

[0029] Perform mechanical property tests on the attached test blocks that have completed the entire heat treatment. The mechanical property test results are shown in Table 1 and all meet the requirements.

[0030] Table 1

[0031]

[0032] Example 2

[0033] In this example, the element proportions of the NiCrMoV low alloy steel casting are: C = 0.19%, Si = 0.28%, Mn = 0.85%, Cr = 0.18%, Ni = 1.82%, Mo = 0.10%, V = 0.12%, and the balance is Fe.

[0034] The heat treatment process is as follows: Place the NiCrMoV low alloy steel casting in a high-temperature furnace, heat it up to 650°C at a rate of 30°C / h to 60°C / h and hold for 16 h. After the holding is completed, cool it in the furnace at a rate of ≤50°C / h to the temperature range of 400°C to 450°C and hold for 4 h, then take it out of the furnace and air-cool it. Then, heat the cast steel material up to 920°C at a rate of 30°C / h to 60°C / h and hold for 12 h, then take it out of the furnace and cool it with air until it reaches 340°C, and then air-cool it to below 180°C and immediately put it into the furnace. Then, heat it up to 640°C at a rate of 30°C / h to 60°C / h and hold for 14 h. After the holding is completed, cool it at a rate of ≤40°C / h to below 200°C, and then take it out of the furnace and air-cool it to room temperature.

[0035] Perform mechanical property tests on the attached test blocks that have completed the entire heat treatment. The mechanical property test results are shown in Table 2 and all meet the requirements.

[0036] Table 2

[0037]

[0038]

[0039] Example 3

[0040] In this embodiment, the elemental proportions of the NiCrMoV low-alloy steel casting are: C = 0.18%, Si = 0.30%, Mn = 0.83%, Cr = 0.20%, Ni = 1.86%, Mo = 0.08%, V = 0.12%, and Fe is the balance.

[0041] The heat treatment process is as follows: Place the NiCrMoV low-alloy steel casting in a high-temperature furnace and heat it up to 650°C at a rate of 30°C / h to 60°C / h and hold for 16 h. After holding, cool it in the furnace at a rate of ≤50°C / h to a temperature range of 400°C to 450°C and hold for 4 h, then take it out of the furnace and air-cool. Then heat the cast steel material to 920°C at a rate of 30°C / h to 60°C / h and hold for 12 h, then take it out of the furnace and air-cool to below 180°C and promptly put it into the furnace; then heat it to 685°C at a rate of 30°C / h to 60°C / h and hold for 14 h. After holding, cool it to below 200°C at a rate of ≤40°C / h, then take it out of the furnace and air-cool to room temperature.

[0042] Perform mechanical property tests on the attached test blocks that have completed the entire heat treatment. The mechanical property test results are shown in Table 3 and all meet the requirements.

[0043] Table 3

[0044]

[0045] The results of the above embodiments show that the products processed by the preliminary heat treatment and performance heat treatment processes formulated by the present invention can meet the mechanical property requirements of the products.

[0046] Comparative Example

[0047] In this embodiment, the elemental proportions of the NiCrMoV low-alloy steel casting are: C = 0.18%, Si = 0.30%, Mn = 0.83%, Cr = 0.20%, Ni = 1.86%, Mo = 0.08%, V = 0.12%, and Fe is the balance.

[0048] The heat treatment process is as follows: Place the NiCrMoV low-alloy steel casting in a high-temperature furnace and heat it up to 650°C at a rate of 30°C / h to 60°C / h and hold for 16 h. After holding, cool it in the furnace at a rate of ≤50°C / h to a temperature range of 400°C to 450°C and hold for 4 h, then take it out of the furnace and air-cool. Then heat the cast steel material to 920°C at a rate of 30°C / h to 60°C / h and hold for 12 h, then take it out of the furnace and air-cool to below 180°C and promptly put it into the furnace; then heat it to 685°C at a rate of 30°C / h to 60°C / h and hold for 14 h. After holding, cool it to below 200°C at a rate of ≤40°C / h, then take it out of the furnace and air-cool to room temperature.

[0049] The mechanical properties of the attached cast test blocks that have completed the entire heat treatment are detected, and the test results of the mechanical properties are shown in Table 4. The plastic toughness does not meet the requirements.

[0050] Table 4

[0051]

[0052]

[0053] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A heat treatment process for NiCrMoV low alloy steel casting materials, characterized in that, It includes the following steps: (1) Preliminary heat treatment: Heat the smelted and cast NiCrMoV low-alloy steel casting to 620°C - 680°C, hold for 12h - 18h, and then cool in the furnace. (2) Quenching heat treatment: Heat the NiCrMoV low-alloy steel casting material after furnace cooling in step (1) to 880°C - 930°C, hold for 10h - 16h, then take it out of the furnace and cool it with strong wind to 300°C - 350°C, and then air-cool it to below 200°C. (3) Tempering heat treatment: Heat the NiCrMoV low-alloy steel casting after air cooling in step (2) to 630°C - 690°C, hold for 12h - 16h, and then cool. The smelted and cast NiCrMoV low-alloy steel casting includes the following components by weight percentage: C: 0.15 - 0.20%, Si: 0.20 - 0.40%, Mn: 0.70 - 0.90%, Cr: 0.15 - 0.30%, Ni: 1.80 - 2.00%, Mo: 0.05 - 0.15%, V: 0.10 - 0.15%, and the balance is Fe and unavoidable impurities.

2. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, Mn: 0.80 - 0.85%.

3. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, C: 0.18%, Si: 0.30%, Mn: 0.80%, Cr: 0.20%, Ni: 1.85%, Mo: 0.08%, V: 0.12%.

4. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, In step (1), the heating is carried out at a rate of 30°C / h - 60°C / h to 620°C - 680°C.

5. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, In step (1), after holding, cool in the furnace at a rate of ≤50°C / h to a temperature range of 400°C - 450°C, hold for 4h, and then take it out of the furnace and air-cool.

6. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, In step (2), the heating is carried out at a rate of 30°C / h - 60°C / h to 880°C - 930°C.

7. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that In step (3), the heating is carried out at a rate of 30°C / h - 60°C / h to 630°C - 690°C.

8. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, In step (3), the cooling is carried out at a rate of ≤40°C / h to below 200°C, and then take it out of the furnace and air-cool to room temperature.

9. The heat treatment process of a NiCrMoV low alloy steel casting material according to claim 1, characterized in that, In step (3), the cooling is furnace cooling.

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