Heat treatment method for improving structure uniformity of H11 hot work die steel forging material
By using the method of repeated fast cooling and low-temperature spherical annealing in the high-temperature zone during the heat treatment process of H11 hot-working mold steel, the problem of uneven carbide precipitation and coarse crystal mixed crystal defects during the forging and heat treatment of H11 steel is solved, and the uniformity of the annealing structure and impact toughness of the material are significantly improved.
Patent Information
- Application Number
- CN202510250280.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-04
- Publication Date
- 2025-06-13
AI Technical Summary
During the forging and heat treatment process, H11 hot-working mold steel is prone to uneven carbide precipitation, coarse crystal mixed crystal defects and chain carbides, resulting in unstable material quality and risk of heat treatment cracking.
The heat treatment method of repeated rapid cooling and low-temperature spheroidization annealing in the high-temperature zone is adopted. Through two austenitization and three high-temperature rapid cooling, the carbide precipitation process is controlled, the forging tissue is refined, and the secondary carbide agglomeration is avoided, and the granular pearlite tissue with fine dispersion is obtained.
It significantly improves the uniformity of the structure of H11 steel forged materials, reduces the formation of carbide chains, improves the annealing structure quality and impact toughness of the material, and reduces the risk of heat treatment cracking.
Smart Images
Figure CN120138280A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of hot work die steel, and relates to a heat treatment method for improving the tissue uniformity of H11 hot work die steel forgings. Background Art
[0002] H11 steel is a typical Cr-based hot work die steel, with high strength and toughness and good thermal fatigue resistance, and is widely used in the fields of large die-casting dies and high-polish plastic molds. Compared with H13 steel, the contents of Mo and V in H11 steel are relatively low, and the band segregation is alleviated. At the same time, during forging and heat treatment cooling processes, due to the weakening of the strong carbide pinning effect, coarse grain and mixed grain defects are more likely to occur. For example, the probability of chain carbides appearing due to improper cooling also increases significantly.
[0003] H11 steel is usually used for non-ferrous alloy die-casting dies and high-polish and high-wear plastic molds, and the mold specifications are relatively large. If there are uneven carbide precipitation and coarse grain and mixed grain defects in the mold material, there is a greater risk of cracking during the heat treatment process. How to control the carbide precipitation process through heat treatment means, avoid carbide precipitation along the grain boundaries and carbide agglomeration, and obtain an annealing structure with dispersed carbide distribution and high particle roundness is particularly important for improving the quality level of H11 steel, especially H11 steel with a large cross-section thickness.
[0004] The conventional isothermal annealing process after forging of H11 steel is: austenitizing at 840 - 880°C, furnace cooling to 700 - 740°C for isothermal spheroidization, and then furnace cooling to ≤500°C and discharging for air cooling. After annealing treatment according to this process, the carbide precipitation process of H11 steel is the coexistence of martensite spheroidization and pearlite spheroidization. The non-uniformity of carbide particle size increases, the carbide aggregation tendency is serious, and the risk of forming chain carbides increases. Summary of the Invention
[0005] To solve the above technical problems, the present invention provides a heat treatment method for improving the tissue uniformity of H11 hot work die steel forgings. By repeatedly fast cooling in the high-temperature zone, carbide precipitation along the grain boundaries is inhibited, the forging structure is refined, and low-temperature spheroidizing annealing is used to control and avoid secondary carbide agglomeration, obtaining a fine and dispersed granular pearlite structure, significantly improving the uniformity of the material annealing structure.
[0006] To achieve the above invention object, the technical solution adopted by the present invention is: a heat treatment method for improving the tissue uniformity of H11 hot work die steel forgings, including the following steps: (1) Cooling the forged H11 steel to 300 - 400°C, loading it into a heating furnace, heating to 980 - 1020°C for heat preservation, and then discharging for water cooling; (2) After water-cooling the H11 steel processed in step (1) to 500 - 600 °C, it is hot-charged into the furnace. After preheating and holding at 800 - 850 °C, it is further heated to 1030 - 1070 °C for holding, and then taken out of the furnace for alternate water-air cooling; (3) After the H11 steel processed in step (2) is alternately water-air cooled to 300 - 400 °C, it is hot-charged into the furnace. After heating to 780 - 820 °C for holding, it is cooled at a cooling rate of ≤ 30 °C / h to ≤ 500 °C, and then taken out of the furnace for air cooling; The medium for water-cooling and water-air alternate cooling is a saline solution with a mass fraction of 5 - 10%.
[0007] Further, in step (1), it is heated to 980 - 1020 °C at a heating rate of 50 - 120 °C / h for holding for 0.6 min / mm + 2 h.
[0008] Further, in step (2), it is heated to 800 - 850 °C at a heating rate of 50 - 120 °C / h for preheating and holding for 2 - 4 h; it is heated to 1030 - 1070 °C at a heating rate of 50 - 120 °C / h for holding for 0.6 min / mm + 2 h.
[0009] Further, in step (3), it is heated to 780 - 820 °C at a heating rate of 50 - 120 °C / h for holding for 1.2 min / mm + 28 h.
[0010] Further, the temperature after water-cooling and water-air alternate cooling is the surface temperature of the H11 steel 10 minutes after air cooling out of water.
[0011] Further, the cross-sectional thickness of the forged H11 steel is 100 - 400 mm.
[0012] The beneficial effects of adopting the above technical solutions are as follows: 1. The forged H11 steel of the present invention is cooled to 300 - 400 °C, then heated to 980 - 1020 °C for holding, water-cooled to 500 - 600 °C, and heated to 1030 - 1070 °C again for holding, and then alternately water-air cooled. Through two austenitizations and three high-temperature rapid coolings, solute redistribution is achieved, the carbide precipitation process is controlled, the precipitation of secondary carbides containing Cr and Mo along the grain boundaries is avoided, and the forged structure can be refined at the same time. 2. After the forged H11 steel of the present invention is first heated to 980 - 1020 °C for austenitization and then water-cooled to 500 - 600 °C and immediately hot-charged into the furnace for the second heating, on the one hand, rapid cooling avoids the M 23 C 6 type and M 7 C 3 type Cr-rich carbides and M 6The temperature range for the precipitation of Mo-rich carbide of type C, i.e., 600 - 900 °C, inhibits the precipitation of carbide along the grain boundaries; on the other hand, it avoids the formation of excessive bainite structure due to too slow cooling and too low temperature in the core of the forging, thus improving the production efficiency. 3. The heat treatment medium for water cooling and water-air alternating cooling of the H11 steel of the present invention is an aqueous solution of sodium chloride with a mass fraction of 5 - 10%, which can quickly break the steam film formed at high temperature, improve the cooling capacity in the high-temperature zone, and also increase the water temperature control by about 15 °C compared with pure water, showing stronger compatibility between the cooling capacity of the quenching equipment and the production efficiency. 4. After the water-air ultra-refinement treatment of the H11 steel of the present invention, after holding at 780 - 820 °C, it is cooled to ≤500 °C at a cooling rate of ≤30 °C / h and then air-cooled out of the furnace. The traditional isothermal spheroidizing annealing is replaced by low-temperature long-time spheroidizing annealing, appropriately increasing the number of undissolved carbides, avoiding the agglomeration of secondary carbides caused by high annealing heating temperature, controlling the precipitation size and number of carbides, and improving the uniformity of carbide distribution. 5. Compared with the traditional isothermal spheroidizing annealing, in the present invention, after sampling from the core of the H11 forging billet and quenching and tempering the specimen according to the heat treatment process of oil quenching at 1030 °C × 30 min + air cooling secondary tempering at 605 °C × 2 h, it is processed into a standard Charpy impact specimen of 10 mm × 10 mm × 55 mm. The transverse impact energy ≥15 J, and the ratio of transverse to longitudinal impact energy is ≥0.8. The transverse impact toughness and isotropic properties are increased by more than 20% and more than 14% respectively. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 It is the metallographic structure diagram of the H11 steel after heat treatment in Example 1 of the present invention; Figure 2 It is the metallographic structure diagram of the H11 steel after conventional spheroidizing annealing treatment; Figure 3 It is the SEM diagram of the H11 steel after heat treatment in Example 1 of the present invention; Figure 4 It is the SEM diagram of the H11 steel after conventional spheroidizing annealing treatment. DETAILED DESCRIPTION OF THE INVENTION Example 1
[0014] The cross-sectional thickness of the H11 steel forging material in this example is 100 mm and the width is 710 mm. The heat treatment method for improving the microstructure uniformity of the H11 hot work die steel forging material is as follows: (1) Cool the forged H11 steel to 380 °C, load it into the heating furnace, heat it to 1000 °C at a heating rate of 100 °C / h, hold for 3 h, and then water-cool it out of the furnace; (2) After water-cooling the H11 steel treated in step (1) to 600 °C, hot load it into the furnace, heat it to 850 °C for preheating and holding at a heating rate of 100 °C / h for 2 h; then heat it to 1050 °C at a heating rate of 120 °C / h and hold for 3 h; water-air alternating cooling out of the furnace; (3) The H11 molten steel processed in step (2) is alternately cooled by water and air until it reaches 388 °C, then hot charged into the furnace, heated to 800 °C at a heating rate of 120 °C / h, held for 30 h, cooled to 480 °C at a cooling rate of 30 °C / h, and then air cooled after discharging from the furnace.
[0015] The medium for water cooling and water-air alternate cooling is a saline solution with a mass fraction of 6%.
[0016] The metallographic diagram of the annealing structure of H11 steel in this example is shown in Figure 1 , and the SEM diagram of the annealing structure is shown in Figure 3 (The metallographic diagrams and SEM diagrams of the annealing structures of H11 steel in Examples 2-5 are similar to those in Example 1, so they are omitted.), compared with Figure 2 and Figure 4 , the H11 steel of the present invention has more carbides, smaller sizes, more uniform distribution, higher roundness, no carbide chains in the annealing structure, and can be rated as AS2 level according to the NADCA #207 standard, significantly improving the uniformity of the annealing structure.
[0017] In this example, samples are taken from the core of the H11 forging billet, and the specimens are quenched and tempered according to the heat treatment process of oil quenching at 1030 °C for 30 min + air cooling for 2 h at 605 °C for secondary tempering, and processed into standard Charpy impact specimens of 10 mm × 10 mm × 55 mm. The transverse impact energy of H11 steel is 16.8 J, and the ratio of transverse to longitudinal impact energy is 0.87. Compared with Comparative Example 1, the transverse impact toughness and isotropic properties are increased by 29.2% and 24.3% respectively. Example 2
[0018] The cross-sectional thickness of the H11 steel forging in this example is 200 mm and the width is 810 mm. The heat treatment method for improving the microstructure uniformity of H11 hot work die steel forgings is as follows: (1) Cool the forged H11 steel to 400 °C, load it into the heating furnace, heat it to 1020 °C at a heating rate of 90 °C / h, hold for 4 h, and then water cool after discharging from the furnace; (2) Water cool the H11 steel processed in step (1) to 565 °C, then hot charge it into the furnace, heat it to 830 °C at a heating rate of 90 °C / h for preheating and holding for 3 h; then heat it to 1040 °C at a heating rate of 100 °C / h and hold for 4 h; discharge it and cool it alternately by water and air; (3) Alternately cool the H11 steel processed in step (2) by water and air until it reaches 388 °C, then hot charge it into the furnace, heat it to 810 °C at a heating rate of 100 °C / h, hold for 32 h, cool it to 490 °C at a cooling rate of 25 °C / h, and then air cool after discharging from the furnace.
[0019] The medium for water cooling and water-air alternate cooling is a saline solution with a mass fraction of 9.2%.
[0020] In this example, samples were taken from the core of the H11 forged billet. The specimens were quenched in oil at 1030 °C for 30 min and then tempered twice by air cooling at 605 °C for 2 h. The specimens were processed into standard Charpy impact specimens with dimensions of 10 mm × 10 mm × 55 mm. The transverse impact energy of the H11 steel was 16.3 J, and the ratio of transverse to longitudinal impact energy was 0.86. Compared with Comparative Example 1, the transverse impact toughness and isotropic properties increased by 25.4% and 22.9% respectively. Example 3
[0021] In this example, the cross-sectional thickness of the H11 steel forging is 300 mm and the width is 910 mm. The heat treatment method for improving the microstructure uniformity of the H11 hot work die steel forging is as follows: (1) Cool the forged H11 steel to 375 °C, load it into a heating furnace, heat it to 980 °C at a heating rate of 60 °C / h, hold for 5 h, and then cool it in water after removing from the furnace; (2) After water-cooling the H11 steel treated in step (1) to 550 °C, hot charge it into the furnace, heat it to 850 °C for preheating and holding at a heating rate of 60 °C / h for 3 h; then heat it to 1070 °C at a heating rate of 90 °C / h and hold for 5 h; cool it by alternating water cooling and air cooling after removing from the furnace; (3) After alternately cooling the H11 steel treated in step (2) by water and air to 376 °C, hot charge it into the furnace, heat it to 820 °C at a heating rate of 80 °C / h, hold for 34 h, cool it to 490 °C at a cooling rate of 20 °C / h, and then cool it in air after removing from the furnace.
[0022] The medium for water cooling and alternating water and air cooling is a 10% by mass sodium chloride aqueous solution.
[0023] In this example, samples were taken from the core of the H11 forged billet. The specimens were quenched in oil at 1030 °C for 30 min and then tempered twice by air cooling at 605 °C for 2 h. The specimens were processed into standard Charpy impact specimens with dimensions of 10 mm × 10 mm × 55 mm. The transverse impact energy of the H11 steel was 15.8 J, and the ratio of transverse to longitudinal impact energy was 0.82. Compared with Comparative Example 1, the transverse impact toughness and isotropic properties increased by 21.5% and 17.1% respectively. Example 4
[0024] In this example, the cross-sectional thickness of the H11 steel forging is 400 mm and the width is 910 mm. The heat treatment method for improving the microstructure uniformity of the H11 hot work die steel forging is as follows: (1) Cool the forged H11 steel to 356 °C, load it into a heating furnace, heat it to 1010 °C at a heating rate of 50 °C / h, hold for 6 h, and then cool it in water after removing from the furnace; (2) After water-cooling the H11 steel processed in step (1) to 570 °C, it is hot charged into the furnace, heated to 800 °C at a heating rate of 50 °C / h for preheating and holding for 4 h; then heated to 1050 °C at a heating rate of 80 °C / h and held for 6 h; then taken out of the furnace and cooled alternately in water and air. (3) After water-air alternately cooling the H11 steel processed in step (2) to 355 °C, it is hot charged into the furnace, heated to 790 °C at a heating rate of 50 °C / h, held for 36 h, cooled to 475 °C at a cooling rate of 30 °C / h, and then taken out of the furnace and air-cooled.
[0025] The medium for the water-cooling and water-air alternate cooling is a saline solution with a mass fraction of 7.5%.
[0026] In this example, samples were taken from the core of the H11 forging billet, and the samples were quenched and tempered according to the heat treatment process of oil quenching at 1030 °C for 30 min + air cooling at 605 °C for 2 h. Standard Charpy impact specimens with dimensions of 10 mm × 10 mm × 55 mm were machined. The transverse impact energy of the H11 steel was 15.6 J, and the ratio of transverse to longitudinal impact energy was 0.80. Compared with Comparative Example 1, the transverse impact toughness and isotropic properties were increased by 20.0% and 14.3% respectively. Example 5
[0027] In this example, the cross-sectional thickness of the H11 steel forging is 300 mm and the width is 910 mm. The heat treatment method for improving the tissue uniformity of the H11 hot work die steel forging is as follows: (1) After forging, the H11 steel is cooled to 300 °C, charged into the heating furnace, heated to 1000 °C at a heating rate of 120 °C / h, held for 5 h, and then taken out of the furnace and water-cooled. (2) After water-cooling the H11 steel processed in step (1) to 520 °C, it is hot charged into the furnace, heated to 830 °C at a heating rate of 80 °C / h for preheating and holding for 3.5 h; then heated to 1030 °C at a heating rate of 50 °C / h and held for 5 h; then taken out of the furnace and cooled alternately in water and air. (3) After water-air alternately cooling the H11 steel processed in step (2) to 400 °C, it is hot charged into the furnace, heated to 780 °C at a heating rate of 80 °C / h, held for 34 h, cooled to 470 °C at a cooling rate of 25 °C / h, and then taken out of the furnace and air-cooled.
[0028] The medium for the water-cooling and water-air alternate cooling is a saline solution with a mass fraction of 5%.
[0029] In this example, samples were taken from the core of the H11 forging billet. The samples were quenched in oil at 1030 °C for 30 min and then tempered twice by air cooling at 605 °C for 2 h according to the heat treatment process. Standard Charpy impact specimens with dimensions of 10 mm × 10 mm × 55 mm were machined. The transverse impact energy of the H11 steel was 16.5 J, and the ratio of transverse to longitudinal impact energy was 0.83. Compared with Comparative Example 1, the transverse impact toughness and isotropic properties increased by 26.9% and 18.6% respectively. Example 6
[0030] In this example, the cross-sectional thickness of the H11 steel forging was 200 mm and the width was 810 mm. A heat treatment method for improving the microstructural uniformity of the H11 hot work die steel forging is as follows: (1) Cool the forged H11 steel to 330 °C, load it into a heating furnace, heat it to 990 °C at a heating rate of 70 °C / h, hold for 4 h, and then cool it in water after taking it out of the furnace. (2) After water cooling the H11 steel treated in step (1) to 500 °C, hot charge it into the furnace, heat it to 850 °C for preheating and holding at a heating rate of 120 °C / h for 2 h; then heat it to 1050 °C at a heating rate of 90 °C / h and hold for 4 h; cool it alternately in water and air after taking it out of the furnace. (3) After alternately cooling the H11 steel treated in step (2) in water and air to 300 °C, hot charge it into the furnace, heat it to 800 °C at a heating rate of 120 °C / h, hold for 32 h, cool it at a cooling rate of 25 °C / h to 480 °C, and then cool it in air after taking it out of the furnace.
[0031] The medium for water cooling and water-air alternate cooling is an aqueous solution of sodium chloride with a mass fraction of 8%.
[0032] In this example, samples were taken from the core of the H11 forging billet. The samples were quenched in oil at 1030 °C for 30 min and then tempered twice by air cooling at 605 °C for 2 h according to the heat treatment process. Standard Charpy impact specimens with dimensions of 10 mm × 10 mm × 55 mm were machined. The transverse impact energy of the H11 steel was 16.9 J, and the ratio of transverse to longitudinal impact energy was 0.84. Compared with Comparative Example 1, the transverse impact toughness and isotropic properties increased by 30.0% and 20.0% respectively.
[0033] Comparative Example 1 In this comparative example, the cross-sectional thickness of the H11 steel forging was 100 mm and the width was 710 mm. The specific heat treatment steps are as follows: (1) Cool the forged H11 steel to room temperature. (2) Heat the H11 steel treated in step (1) to 860 °C at a heating rate of 120 °C / h, hold for 4 h, cool it in the furnace to 720 °C, hold for 6 h, and then cool it in the furnace to 480 °C and take it out of the furnace for air cooling.
[0034] Samples were taken from the core of the H11 steel forging billet in this comparative example. The metallographic and SEM images of the annealed microstructure are shown in Figure 2 and Figure 4 . According to the NADCA #207 standard, it can be rated as grade AS7. The specimens were quenched in oil at 1030 °C for 30 min and then tempered at 605 °C for 2 h in air according to the heat treatment process. Standard Charpy impact specimens with dimensions of 10 mm × 10 mm × 55 mm were machined. The transverse impact energy of the H11 steel was 13.0 J, and the ratio of transverse to longitudinal impact energy was 0.70.
Claims
1. A heat treatment method for improving the uniformity of the microstructure of H11 hot working die steel forgings, characterized in that: It includes the following steps: (1) Cool the forged H11 steel to 300-400°C, put it into a heating furnace, heat it to 980-1020°C, keep it warm, and then cool it in water; (2) Cooling the H11 molten steel treated in step (1) to 500-600°C and then hot charging the furnace, heating it to 800-850°C for preheating and insulation, and then heating it to 1030-1070°C for insulation, and then cooling it alternately with water and air after it is taken out of the furnace; (3) Cooling the H11 molten steel treated in step (2) to 300-400°C by alternating air cooling, then hot charging the furnace, heating it to 780-820°C and keeping it warm, cooling it to ≤500°C at a cooling rate of ≤30°C / h, and air cooling it out of the furnace; The medium for water cooling and water-air alternating cooling is a salt water solution with a mass fraction of 5 to 10%.
2. The heat treatment method for improving the uniformity of the microstructure of H11 hot working die steel forgings according to claim 1, characterized in that: In the step (1), the temperature is raised to 980-1020°C at a heating rate of 50-120°C / h and kept at this temperature for 0.6 min / mm+2h.
3. The heat treatment method for improving the uniformity of the microstructure of H11 hot working die steel forgings according to claim 2, characterized in that: In the step (2), the temperature is raised to 800-850°C at a heating rate of 50-120°C / h and preheated for 2-4 hours.
4. The heat treatment method for improving the uniformity of the microstructure of H11 hot working die steel forgings according to claim 3, characterized in that: In the step (2), the temperature is raised to 1030-1070°C at a heating rate of 50-120°C / h and kept at this temperature for 0.6 min / mm+2h.
5. The heat treatment method for improving the uniformity of the microstructure of H11 hot working die steel forgings according to claim 4, characterized in that: In the step (3), the temperature is raised to 780-820°C at a heating rate of 50-120°C / h and kept at this temperature for 1.2 min / mm+28h.
6. The heat treatment method for improving the uniformity of the structure of H11 hot working die steel forgings according to any one of claims 1 to 5, characterized in that: The temperature after the water cooling and water-air alternating cooling is the surface temperature of H11 steel after 10 minutes of water-air cooling.
7. The heat treatment method for improving the uniformity of the microstructure of H11 hot working die steel forgings according to claim 6, characterized in that: The cross-sectional thickness of the forged H11 steel is 100-400 mm.