Molybdenum die steel and heat treatment method thereof
Through specific heat treatment methods, including multi-stage heating and cooling control, the structural structure of molybdenum-based thermal work mold steel is optimized, and the problems of insufficient toughness and carbide segregation are solved, and higher impact toughness and high temperature strength are achieved.
Patent Information
- Application Number
- CN202411082511.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-08
- Publication Date
- 2024-12-13
AI Technical Summary
Molybdenum-based hot-working mold steel is not tough enough in some application scenarios, and the existing annealing process cannot effectively improve its impact work and service life, and carbide segregation caused by elements such as Cr and Mo affects the performance of the material.
Specific heat treatment methods are adopted, including vacuum induction furnace casting, multi-stage heating and insulation, cooling rate control, quenching and tempering treatment, to optimize the structural structure of the steel to improve toughness and hardness. The specific steps include heating to different temperatures at a rate of 4-6°C/min, then cooling and annealing, and finally tempering to ensure that the martensite transformation is completed and cracks are prevented.
It significantly improves the impact toughness and high temperature strength of mold steel, refines the grain, improves the carbide distribution, extends the hardness reduction speed, and improves tempering stability and impact performance.
Smart Images
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Abstract
Description
Technical Field
[0001] The invention belongs to the field of heat treatment of metal materials, and in particular relates to a molybdenum-based die steel and a heat treatment method thereof. Background Art
[0002] Molybdenum-based hot working die steel is widely used in industrial production due to its excellent performance in high temperature environment. Molybdenum-based hot working die steel is a high-performance hot working die steel containing alloy elements such as chromium, molybdenum, and vanadium. These alloy elements make molybdenum-based hot working die steel have good resistance to thermal fatigue cracking, thermal shock cracking, thermal wear, plastic deformation and other properties. However, although molybdenum-based hot working die steel has good ductility and high temperature strength, its toughness still needs to be further improved in certain specific application scenarios. Therefore, improving the toughness of molybdenum-based hot working die steel has become an important research direction in the field of materials science.
[0003] Although the existing common annealing process can improve some properties of molybdenum hot working die steel, there is still a gap in the organization of the annealed state compared with the excellent hot working die steel from abroad, resulting in the average impact energy not reaching the ideal level and a low service life. While the elements such as Cr and Mo contained in molybdenum hot working die steel improve the hardenability and thermal strength of the steel, they are also prone to cause carbide segregation, affecting the material's grain size, annealing organization and other properties, and reducing the overall performance. Heat treatment is a key process to improve the toughness of molybdenum hot working die steel. By adjusting parameters such as heating temperature, holding time, cooling rate, etc., the internal organizational structure and properties of the steel can be effectively changed. Summary of the invention
[0004] In order to improve the toughness of molybdenum-based hot working die steel, the present invention provides a molybdenum-based die steel and a heat treatment method thereof, which can improve and optimize the toughness and structure of the material while ensuring the hardness. The specific technical scheme is as follows: A molybdenum-based die steel, characterized in that it includes, by mass percentage: C, 0.25-0.4%, Mn, 0.55-1.00%, Si, ≤0.008%, Gr, ≤0.03%, W, 0.5-1.2%, Ni, 1.0-2.1%, Mo, 3.0-4.0%, Cu, ≤0.07%, and the balance is Fe.
[0005] A heat treatment method for the above-mentioned molybdenum-based die steel, the specific steps are as follows: Step 1: Casting the molybdenum-based die steel into an ingot through a vacuum induction furnace; Step 2: Heat the steel ingot in step 1 to 700°C at a rate of 4-6°C / min, keep it warm for 3 hours, then heat it to 850°C at a rate of 4-6°C / min, keep it warm for 2 hours, then heat it to 1030°C at a rate of 4-6°C / min, keep it warm for 2 hours, then cool it in a cooling medium, cut off the ingot head, and obtain steel ingot 1; after such heat treatment, the obtained mold steel has finer grains and more ideal performance in all aspects.
[0006] Step 3: The steel ingot 1 obtained in step 2 is repeatedly heated to 850°C at a rate of 4-6°C / min, kept warm for 3 hours, then cooled to 735°C in a heat treatment furnace, kept warm for 4 hours, and finally cooled to 500°C, and then air-cooled, and the steel ingot 1 is homogenized annealed to obtain the steel ingot 2; cooling under this condition can effectively ensure the completion of the martensitic transformation in the mold steel, and controlling the cooling temperature can effectively prevent the occurrence of cracks.
[0007] Step 4: Heat the steel ingot 2 in step 3 to 1010°C at a rate of 4-6°C / min, and then forge it, keeping it warm for 30 minutes; Step 5: placing the steel ingot forged in step 4 into a quenching medium and cooling it to room temperature to obtain steel ingot 3; Step 6: Temper the steel ingot 3 in step 5 at 100-660°C for 4-5 hours.
[0008] A further improvement is that the heating rate in step 2 is 5°C / min.
[0009] A further improvement is that the temperature of the heat preservation and tempering treatment is 200-660°C.
[0010] A further improvement is that the insulation time of the insulation and tempering treatment is 4 hours.
[0011] A further improvement is that in step 5, the steel ingot forged in step 4 is taken out and then oil-quenched and oil-cooled to room temperature.
[0012] By adopting the heat treatment method of molybdenum die steel proposed in the present invention, the austenitization time of hot working die steel is short during quenching, the austenite grains are extremely fine, and the size of the generated martensite grains will not be coarsened. Finally, the product structure obtained has fine grains and high toughness.
[0013] By adopting the method provided by the present invention, the grains of the obtained hot working die steel after refinement and annealing will not be distributed in a chain shape, and the carbides will be more dispersedly distributed, achieving the following effects: compared with the traditional quenching and tempering process, the tempering stability of the die steel is better, and at the same tempering temperature, the hardness of the die steel decreases slowly; the high-temperature strength of the die steel is greatly improved when treated to the same hardness, and after heat treatment to the same hardness, the impact toughness of the die steel treated by the new process is higher than that of the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 It is the metallographic structure diagram in Example 1; Figure 2 This is a high-magnification metallographic image in Example 1; Figure 3 It is the metallographic structure diagram in Example 2; Figure 4 This is a high-magnification metallographic image in Example 2; Figure 5 This is the annealing process diagram in Example 3; Figure 6 It is the impact energy and hardness curve diagram in Example 3; Figure 7 This is a diagram of the thinning and annealing process in Example 4; Figure 8 It is the impact energy and hardness curve diagram in Example 4; DETAILED DESCRIPTION
[0015] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and do not limit the scope of protection. Example
[0016] This embodiment uses a molybdenum die steel with a specification of 10*10*5. The heat treatment method is as follows: the temperature is raised to 760°C at a rate of 5°C / min, kept at this temperature for 2h, then cooled to 600°C at a rate of 10°C / h in a heat treatment furnace, and air-cooled; the metallographic structure after annealing is as follows: Figure 1 As shown, the metallographic structure after annealing treatment at 500 times; the high-magnification metallographic picture after annealing is as follows Figure 2 As shown, the metallographic structure after 500 times refinement and annealing treatment. Example
[0017] This embodiment uses molybdenum die steel with a specification of 10*10*5, and the heat treatment method is as follows: First, the mold steel was heated to 700°C, 850°C, and 1030°C at a rate of 5°C / min, and kept warm for 3h, 2h, and 2h, respectively, and finally cooled in the medium; The temperature was raised to 850°C at a rate of 5°C / min and kept at that temperature for 3h. Then, the sample was cooled to 735°C in a heat treatment furnace and kept at that temperature for 4h. Finally, the sample was cooled to 500°C and air-cooled.
[0018] The metallographic structure after annealing is Figure 3 As shown, the metallographic structure after 1000 times annealing treatment, the high-magnification metallographic picture after annealing is as follows Figure 4As shown, the metallographic structure after 1000 times refinement and annealing treatment. Example
[0019] This embodiment uses molybdenum die steel with a specification of 10*10*5, and the heat treatment method is as follows: The temperature was raised to 760°C at a rate of 5°C / min, kept at that temperature for 2h, and then cooled to 600°C at a rate of 10°C / h in a heat treatment furnace, and then air-cooled; Figure 5 Annealing process diagram; Heat the die steel to 1010°C at a rate of 5°C / min and keep it at that temperature for 30 minutes; The die steel is taken out from the induction coil and then oil-quenched to room temperature; After quenching, tempering is carried out immediately, and the temperature is kept at 200℃-660℃ for 4-5h.
[0020] The tempered sample was processed into a 10.5×10.5×55.2mm V-mouth impact energy sample. The V-mouth impact energy sample was subjected to impact and hardness test experiments to obtain the impact energy and hardness curves as shown in the figure. Figure 6 shown. Example
[0021] This embodiment uses molybdenum die steel with a specification of 10*10*5, and the heat treatment method is as follows: First, the mold steel was heated to 700°C, 850°C, and 1030°C at a rate of 5°C / min, and kept warm for 3h, 2h, and 2h, respectively, and finally cooled in the medium; The temperature was raised to 850°C at a rate of 5°C / min, kept at that temperature for 3h, then cooled to 735°C in a heat treatment furnace, kept at that temperature for 4h, and finally cooled to 500°C for air cooling. The above two steps are refinement and annealing processes, refer to Figure 7 ; Heat the die steel to 1010°C at a rate of 5°C / min and keep it at that temperature for 30 minutes; The die steel is taken out from the induction coil and then oil-quenched to room temperature; After quenching, tempering is carried out immediately, and the temperature is kept at 200℃-660℃ for 4h.
[0022] The tempered sample was processed into a 10.5×10.5×55.2mm V-mouth impact energy sample. The V-mouth impact energy sample was subjected to impact and hardness test experiments to obtain the impact energy and hardness curves as shown in the figure. Figure 8 shown.
[0023] It can be seen from the impact energy and hardness curve that after heat treatment to the same hardness, the impact toughness of the mold steel treated with the new process is higher than that of the traditional process.
Claims
1. A molybdenum-based die steel, characterized in that: In terms of mass percentage, it includes: C, 0.25-0.4%, Mn, 0.55-1.00%, Si, ≤0.008%, Cr, ≤0.03%, W, 0.5-1.2%, Ni, 1.0-2.1%, Mo, 3.0-4.0%, Cu, ≤0.07%, and the balance is Fe.
2. A heat treatment method for the molybdenum-based die steel according to claim 1, comprising the following steps: Step 1: Casting the molybdenum-based die steel into an ingot through a vacuum induction furnace; Step 2: heating the steel ingot in step 1 to 700°C at a rate of 4-6°C / min, keeping the temperature for 3h, then heating it to 850°C at a rate of 4-6°C / min, keeping the temperature for 2h, then heating it to 1030°C at a rate of 4-6°C / min, keeping the temperature for 2h, then cooling it in a cooling medium, cutting off the ingot head, and obtaining steel ingot 1; Step 3: The steel ingot 1 obtained in step 2 is heated to 850°C at a rate of 4-6°C / min, kept at this temperature for 3 hours, then cooled to 735°C in a heat treatment furnace, kept at this temperature for 4 hours, and finally cooled to 500°C, and then air-cooled, and the steel ingot 1 is homogenized and annealed to obtain steel ingot 2; Step 4: Heat the steel ingot 2 in step 3 to 1010°C at a rate of 4-6°C / min, and then forge it, keeping it warm for 30 minutes; Step 5: placing the steel ingot forged in step 4 into a quenching medium and cooling it to room temperature to obtain steel ingot 3; Step 6: Temper the steel ingot 3 in step 5 at 100-660°C for 4-5 hours.
3. The heat treatment method of a molybdenum-based die steel according to claim 2, characterized in that: The heating rate in step 2 is 5°C / min.
4. The heat treatment method of a molybdenum-based die steel according to claim 2, characterized in that: The temperature of the heat preservation and tempering treatment is 200-660°C.
5. The heat treatment method of a molybdenum-based die steel according to claim 2, characterized in that: The holding time of the heat preservation and tempering treatment is 4 hours.
6. The heat treatment method of a molybdenum-based die steel according to claim 2, characterized in that: In the step 5, the steel ingot forged in the step 4 is taken out and then oil-quenched and oil-cooled to room temperature.