A multiphase dievar hot work die steel and a method for heat treating the same
By improving the heat treatment process of Dievar steel to form a multiphase structure, the problem of insufficient toughness of Dievar steel under high hardness was solved, achieving a combination of high toughness and high hardness, expanding its application range, and reducing heat treatment time.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FUJIAN UNIV OF TECH
- Filing Date
- 2026-04-20
- Publication Date
- 2026-06-05
AI Technical Summary
While maintaining high hardness, existing Dievar steel has poor toughness, which makes the mold prone to brittle cracking under complex thermomechanical loads.
By improving the heat treatment process, the single martensitic structure is transformed into a multiphase structure, including martensite, bainite and retained austenite. The multiphase Dievar hot work die steel is formed by using salt bath isothermal quenching and rapid heating and holding methods, combined with air cooling or water cooling treatment.
Significantly improves the toughness of Dievar steel while maintaining high hardness, expands its application range under complex loads, and shortens the heat treatment cycle.
Smart Images
Figure CN122147004A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of heat treatment technology for metallic materials, specifically to a multiphase Dievar hot work die steel and its heat treatment method. Background Technology
[0002] Dievar hot work die steel is the preferred die material in the aluminum alloy die casting field due to its excellent thermomechanical fatigue properties. However, Dievar steel's poor toughness limits its application. Improving the overall mechanical properties of Dievar steel can be achieved not only through smelting methods, such as increasing steel purity, but also through heat treatment. Current heat treatment methods for Dievar steel primarily involve quenching and tempering, which requires at least two tempering cycles after quenching. This process is lengthy, and the microstructure consists of lath martensite and dispersed carbides. While the single martensitic structure provides high strength and hardness, it results in poor toughness. Furthermore, existing technologies such as CN114717392A (a Dievar steel and its heat treatment method) improve the hardness of Dievar steel through isothermal quenching, this often sacrifices toughness in pursuit of higher hardness, leading to brittle cracking of the die under complex thermomechanical loads.
[0003] Therefore, how to significantly improve the toughness of Dievar steel while maintaining its high hardness has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention
[0004] In response to the problems existing in the current technology, the purpose of this invention is to provide a multiphase Dievar hot work die steel and its heat treatment method. By improving the heat treatment process, the single martensitic structure is transformed into a multiphase structure, thereby improving the toughness of the material while maintaining high hardness, so as to solve the problem that existing single-phase or multiphase Dievar steels cannot achieve both high toughness and high hardness.
[0005] The first objective of this invention is to provide a heat treatment method for multiphase Dievar hot work die steel, the technical solution of which includes the following steps: Step S1: Perform austenitizing treatment on the Dievar steel to be treated; Step S2: The austenitized Dievar steel is subjected to salt bath isothermal quenching at a first isothermal temperature T1 and held at that temperature for a time t1; the first isothermal temperature T1 is lower than the martensitic transformation initiation temperature of Dievar steel. M s point; Step S3: The Dievar steel treated in Step 2 is rapidly heated to the second isothermal temperature T2 at the second heating rate, and held at that temperature for a time t2; the second isothermal temperature T2 is higher than the stated temperature. M s point; Step S4: Cool the Dievar steel treated in Step 3 to room temperature to obtain multiphase Dievar hot work die steel.
[0006] Further optimization involves heating to 900-960℃ and holding for 5-10 minutes, then heating to 1025-1030℃ and holding for 20-30 minutes.
[0007] Further optimization is achieved by setting the first isothermal temperature T1 to be lower than... M s The temperature range is 10℃-200℃; the first heat preservation time t1 is 10min.
[0008] Further optimization is needed, the second isothermal temperature T2 is: M s The temperature is above 0-50℃, and the second heat preservation time t2 is 30-360min.
[0009] Further optimization resulted in a second heating rate of ≥10℃ / min.
[0010] Further optimization involves using either air cooling or water cooling in step 4.
[0011] Further optimization resulted in the following chemical composition of the Dievar steel by mass percentage: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃.
[0012] A second objective of this invention is to provide a multiphase Dievar hot work die steel prepared by the above-described heat treatment method.
[0013] Further optimization results in the microstructure of the Dievar steel comprising martensite, bainite, and a small amount of retained austenite.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Through multiphase heat treatment technology, a multiphase microstructure of martensite + bainite + retained austenite is obtained, which maintains a high level of hardness while significantly improving impact toughness.
[0015] 2. The multiphase processing technology expands the application range of Dievar steel, enabling its use in molds subjected to more complex stresses.
[0016] 3. Traditional heat treatment of Dievar steel involves quenching and tempering, which requires at least two tempering cycles after quenching to stabilize the microstructure. This process is lengthy. In contrast, this technology only requires holding the steel in the isothermal transformation zone of bainite, eliminating the need for repeated furnace loading and unloading operations and saving heat treatment time. Attached Figure Description
[0017] To more clearly illustrate the technical solutions involved in the embodiments of the present invention or the prior art, the accompanying drawings included in the description of the embodiments or the prior art will be briefly introduced below. It should be noted that these drawings only show some specific embodiments recorded in the present invention and do not cover all possible implementations.
[0018] Figure 1 This is a flowchart of the method of the present invention.
[0019] Figure 2 The process route diagrams are for Examples 1, 2, 3 and 4.
[0020] Figure 3 This is a scanning electron microscope (SEM) image of Example 1.
[0021] Figure 4 This is a scanning electron microscope (SEM) image of Example 2.
[0022] Figure 5 This is a scanning electron microscope (SEM) image of Example 3.
[0023] Figure 6 This is a scanning electron microscope (SEM) image of Example 4. Detailed Implementation
[0024] The technical solution of the present invention will now be described in detail and comprehensively. It should be noted that the embodiments described are only a part of the present invention and do not cover all embodiments. Furthermore, all other embodiments that can be obtained by those skilled in the art based on the embodiments provided by the present invention without creative effort should also fall within the protection scope of the present invention. In the following embodiments, unless otherwise specified, the instruments and materials used are commercially available.
[0025] This invention provides a heat treatment method for multiphase Dievar hot work die steel, comprising the following steps: Step S1: Perform austenitizing treatment on the Dievar steel to be treated, i.e., first heat to 900-960℃ (including 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃) and hold for 5-10 min (including 5 min, 6 min, 7 min, 8 min, 9 min, 10 min), and then heat to 1025-1030℃ (including 1025℃, 1026℃, 1027℃, 1028℃, 1029℃, 1030℃) and hold for 20-30 min (including 20 min, 22 min, 25 min, 27 min, 30 min). The chemical composition of Dievar steel, by mass percentage, is: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃.
[0026] Step S2: The austenitized Dievar steel is subjected to salt bath isothermal quenching at a first isothermal temperature T1 and held at that temperature for a time t1; the first isothermal temperature T1 is lower than the martensitic transformation initiation temperature of Dievar steel. M s Point; the first isothermal temperature T1 is lower than M s The temperature range is 10℃-200℃; the first holding time t1 is 10 minutes. The first isothermal temperature T1 is 305℃, 290℃, 260℃, 275℃, 250℃, 310℃, 120℃, etc.
[0027] Step S3: The Dievar steel treated in Step 2 is rapidly heated to the second isothermal temperature T2 at the second heating rate, and held at that temperature for a time t2; the second isothermal temperature T2 is higher than the stated temperature. M s Point; the second isothermal temperature T2 is M s The temperature is above 0-50℃, and the second holding time t2 is 30-360 min. The second isothermal temperature T2 is 320℃, 330℃, 340℃, 350℃, 360℃, or 370℃. The second heating rate is ≥10℃ / min, and the second heating rate is 10℃ / min, 15℃ / min, 20℃ / min, or 30℃ / min, etc.
[0028] Step S4: Cool the Dievar steel treated in Step 3 to room temperature by air cooling or water cooling to obtain multiphase Dievar hot work die steel.
[0029] The multiphase Dievar hot work die steel prepared by the above-described heat treatment method has a microstructure comprising martensite, bainite, and a small amount of retained austenite. This multiphase microstructure treatment technology expands the application range of Dievar steel, allowing it to be used in dies subjected to more complex stresses.
[0030] The following is a further explanation with reference to specific embodiments: Example 1
[0031] This embodiment provides a heat treatment method for multiphase Dievar hot work die steel, including the following steps: Step S1: The Dievar steel to be treated is subjected to austenitizing treatment. The chemical composition of the Dievar steel, by mass percentage, is: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃; the austenitic treatment is as follows: heat Dievar steel to 960℃ and hold for 5 minutes, then continue to heat to 1030℃ and hold for 30 minutes. Step S2: Then the Dievar steel obtained in step S1 is quickly placed into a 305℃ salt bath furnace for isothermal quenching for 10 minutes; Step S3: Rapidly heat the Dievar steel treated in Step 2 by rapidly raising the temperature of the salt bath furnace to 330°C at a rate of 10°C / min, and holding it at the same temperature for 4 hours. Step S4: Place the Dievar steel treated in step 3 into room temperature water and cool it to room temperature to obtain multiphase Dievar hot work die steel. Example 2
[0032] This embodiment provides a heat treatment method for multiphase Dievar hot work die steel, including the following steps: Step S1: The Dievar steel to be treated is subjected to austenitizing treatment. The chemical composition of the Dievar steel, by mass percentage, is: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃; the austenitic treatment is as follows: heat Dievar steel to 960℃ and hold for 5 minutes, then continue to heat to 1030℃ and hold for 30 minutes. Step S2: Then the Dievar steel obtained in step S1 is quickly placed into a 290℃ salt bath furnace for isothermal quenching for 10 minutes; Step S3: Rapidly heat the Dievar steel treated in Step 2 by rapidly raising the temperature of the salt bath furnace to 330°C at a rate of 10°C / min, and holding it at the same temperature for 4 hours. Step S4: Place the Dievar steel treated in step 3 into room temperature water and cool it to room temperature to obtain multiphase Dievar hot work die steel. Example 3
[0033] This embodiment provides a heat treatment method for multiphase Dievar hot work die steel, including the following steps: Step S1: The Dievar steel to be treated is subjected to austenitizing treatment. The chemical composition of the Dievar steel, by mass percentage, is: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃; the austenitic treatment is as follows: heat Dievar steel to 960℃ and hold for 5 minutes, then continue to heat to 1030℃ and hold for 30 minutes. Step S2: Then the Dievar steel obtained in step S1 is quickly placed into a 275°C salt bath furnace for isothermal quenching for 10 minutes; Step S3: Rapidly heat the Dievar steel treated in Step 2 by rapidly raising the temperature of the salt bath furnace to 330°C at a rate of 10°C / min, and holding it at the same temperature for 4 hours. Step S4: Place the Dievar steel treated in step 3 into room temperature water and cool it to room temperature to obtain multiphase Dievar hot work die steel. Example 4
[0034] This embodiment provides a heat treatment method for multiphase Dievar hot work die steel, including the following steps: Step S1: The Dievar steel to be treated is subjected to austenitizing treatment. The chemical composition of the Dievar steel, by mass percentage, is: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃; the austenitic treatment is as follows: heat Dievar steel to 960℃ and hold for 5 minutes, then continue to heat to 1030℃ and hold for 30 minutes. Step S2: Then the Dievar steel obtained in step S1 is quickly placed into a 260℃ salt bath furnace for isothermal quenching for 10 minutes; Step S3: Rapidly heat the Dievar steel treated in Step 2 by rapidly raising the temperature of the salt bath furnace to 330°C at a rate of 10°C / min, and holding it at the same temperature for 4 hours. Step S4: Place the Dievar steel treated in step 3 into room temperature water and cool it to room temperature to obtain multiphase Dievar hot work die steel.
[0035] Comparative Example The Dievar steel to be treated was heated to 1030℃ and held for 30 minutes to austenitize it, then oil quenched, and then the hardness was adjusted to 51HRC by two tempering processes.
[0036] 1. Performance Testing The samples obtained in this implementation case were subjected to hardness and impact energy tests. Hardness was tested using an HR-150A hardness tester (150kg load, diamond indenter). Each sample underwent at least five valid measurements. The average value after removing the highest and lowest values was taken as the sample hardness. The impact samples were V-notch specimens, tested according to the national standard GB / T229-2007. Each set of conditions was repeated five times. The average value after removing the highest and lowest values was taken as the sample impact energy. The results are shown in Table 1. Under similar hardness conditions, the impact energy of the samples treated with QB increased by a maximum of 35.4%. Scanning electron microscopy (SEM) analysis was performed on the samples obtained in this implementation case. Figure 3 and Figure 4 As shown.
[0037] Table 1 Hardness and impact energy of Dievar steel after QB treatment
[0038] 2. Quantitative analysis of microstructure was performed using EBSD, as shown in Table 2. EBSD was used to detect multiphase microstructures. Martensite and bainite were distinguished based on the band contrast (BC) index. The BC data were analyzed using multi-peak Gaussian fitting. A threshold was set in the Gaussian curve as the intersection point of martensite and bainite. Two main peaks appeared on the band contrast graph. The side with the lower peak value was martensite, and the side with the higher peak value was bainite.
[0039] Table 2 shows the quantitative analysis of the microstructure of Dievar steel.
[0040] The technical solutions of this invention are not limited to the specific embodiments described above. Any technical modifications, alterations, substitutions, and variations made to the technical solutions of this invention without departing from the spirit and scope of the claims are within the protection scope of this invention.
Claims
1. A heat treatment method for multiphase Dievar hot work die steel, characterized in that, Includes the following steps: Step S1: Perform austenitizing treatment on the Dievar steel to be treated; Step S2: The austenitized Dievar steel is subjected to salt bath isothermal quenching at a first isothermal temperature T1 and held at that temperature for a time t1; the first isothermal temperature T1 is lower than the martensitic transformation initiation temperature of Dievar steel. M s point; Step S3: The Dievar steel treated in Step 2 is rapidly heated to the second isothermal temperature T2 at the second heating rate and held at that temperature for t2 time; The second isothermal temperature T2 is higher than the stated M s point; Step S4: Cool the Dievar steel treated in Step 3 to room temperature to obtain multiphase Dievar hot work die steel.
2. The heat treatment method according to claim 1, characterized in that, The austenitizing treatment includes first heating to 900-960℃ and holding for 5-10 minutes, and then heating to 1025-1030℃ and holding for 20-30 minutes.
3. The heat treatment method according to claim 1, characterized in that, The first isothermal temperature T1 is lower than M s The temperature range is 10℃-200℃; the first heat preservation time t1 is 10min.
4. The heat treatment method according to claim 1, characterized in that, The second isothermal temperature T2 is M s The temperature is above 0-50℃, and the second heat preservation time t2 is 30-360min.
5. The heat treatment method according to claim 1, characterized in that, The second heating rate is ≥10℃ / min.
6. The heat treatment method according to claim 1, characterized in that, The cooling method in step 4 is air cooling or water cooling.
7. The heat treatment method according to claim 1, characterized in that, The chemical composition of the Dievar steel, by mass percentage, is: C 0.38%, Si 0.25%, Mn 0.46%, Cr 5.15%, Mo 2.46%, V 0.53%, P 0.005%, S 0.003%, with the balance being Fe and unavoidable impurities. M s The temperature is 320℃.
8. A multiphase Dievar hot work die steel prepared by the heat treatment method according to any one of claims 1 to 7.
9. The multiphase Dievar hot work die steel according to claim 8, characterized in that, The microstructure of the Dievar steel comprises martensite and bainite, as well as a small amount of retained austenite.