Forging method for improving carbon segregation of hot work die steel H13

Abstract

A forging method for improving carbon segregation in hot work die steel H13 belongs to the field of metallurgical technology. It includes a pre-forging high-temperature diffusion process and a forging process. In the pre-forging high-temperature diffusion process, the steel ingot is heated to 1320±10℃ after being hot-sent to a heating furnace, and held for 1.5~2h / 100mm. In the forging process, a four-upsetting and four-drawing process is adopted. The upsetting ratio for the first two upsetting operations is 1.5~1.8, the drawing ratio is 1.8~2.0, and the drawing reduction is 10~15%. The upsetting ratio for the latter two upsetting operations is 2.2~2.4, the drawing ratio is 2~2.2, and the drawing reduction is 10%~15%. This invention uses a high-temperature, short-time pre-forging high-temperature diffusion process combined with a four-upsetting and four-drawing forging process. The resulting hot work die steel H13 has a uniform banded structure, significantly reduced segregation, and meets the GB / T6402-2008 Level 4 requirement for flaw detection. Furthermore, it exhibits fine and uniform grain size and good low-temperature impact toughness.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a forging method for hot work die steel, especially a forging method for improving carbon segregation in H13 hot work die steel. Background Technology

[0002] H13 is a hot work die steel, grade 4Cr5MoSiV1; chemical composition: C: 0.32-0.45%; Si: 0.8-1.2%; Mn: 0.2-0.5%; Cr: 4.75-5.5%; Mo: 1.1-1.75%; V: 0.8-1.2%; it belongs to the medium alloy chromium series of hot work die steels. Due to its good hot strength, red hardness, high toughness and resistance to thermal fatigue, it is widely used in hot extrusion dies and die casting dies for aluminum alloys; it can also be used to make hot forging dies and plastic molds.

[0003] In H13 steel, some carbon elements enter the matrix, causing solid solution strengthening, while others combine with alloying elements to form carbides. During hot working and heat treatment processes, the type, distribution, and size of these carbides significantly impact the steel's final service performance, including its thermal strength, thermal stability, impact toughness, and thermal fatigue properties. Since molds operate without directionality, they require excellent isotropic mechanical properties, and the uniformity of carbide distribution greatly influences their performance.

[0004] In the large forging industry, high-temperature diffusion before forging of steel ingots is generally used to improve dendrite segregation and carbon segregation. The heating temperature is generally 1240℃±10℃, and the holding time is 4h / 100mm. Due to the relatively low temperature, carbon atom diffusion is relatively slow, often resulting in uneven banded structure, large fluctuation range of impact value, and failure to meet the level 4 requirements of GB / T6402-2008 for flaw detection. Furthermore, this method greatly prolongs the time that steel ingots are in the furnace, affecting production efficiency and hindering production organization and cost optimization. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a forging method for improving carbon segregation in hot work die steel H13. The technical solution adopted by the present invention is as follows:

[0006] A forging method for improving carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes.

[0007] The high-temperature diffusion process before forging involves hot-feeding the steel ingot to a heating furnace at a temperature of ≥550℃, raising the temperature to 1320±10℃ at a rate of 100~120℃ / min, holding the temperature for 1.5~2h / 100mm, and then air-cooling it after holding the temperature.

[0008] The steel ingot is air-cooled to a surface temperature of 1160-1180℃ before forging.

[0009] The forging process adopts a four-upsetting and four-drawing process. The upsetting ratio of the first two upsetting operations is 1.5 to 1.8, the drawing ratio is 1.8 to 2.0, and the drawing reduction is 10 to 15%. The upsetting ratio of the last two upsetting operations is 2.2 to 2.4, the drawing ratio is 2 to 2.2, and the drawing reduction is 10% to 15%. The total forging ratio is 10 to 12.

[0010] The specifications for H13 hot work die steel after forging are φ700~φ800mm.

[0011] The beneficial effects of adopting the above technical solution are as follows:

[0012] 1. This invention's pre-forging high-temperature diffusion process breaks with conventional heating concepts. The steel ingot heating temperature of 1320±10℃ is approximately 800℃ higher than conventional processes, which is more conducive to the dissolution and uniform distribution of carbides, improving C segregation. Higher heating temperatures increase the energy gained by C atoms and alloy components, facilitating migration from areas of high concentration to areas of low concentration, resulting in full atomic diffusion and a material with uniform composition. The holding time is halved compared to conventional methods, improving production efficiency, saving energy consumption, reducing production costs, decreasing carbon emissions, and enhancing product profits and competitiveness.

[0013] 2. The heating temperature of this invention is increased to 1320±10℃, which easily leads to coarse grains, seriously affecting flaw detection and microstructure. The subsequent four-upsetting and four-drawing forging process increases the upsetting ratio and drawing ratio to ensure that the carbides are fully broken, thus breaking the coarse grains. This helps to solve the problem of uniform carbide distribution and grain refinement, which is beneficial to improving the flaw detection level.

[0014] 3. This invention adopts a four-upsetting and four-drawing process, and the upsetting ratio and drawing ratio of the first two and the last two are different, which distinguishes the different welding capabilities of the cast state and the forging state, solves the welding of internal micropores, is conducive to improving impact resistance, effectively solves the problems of residual cast structure and grain refinement, and plays a significant role in improving banded structure and improving the level of flaw detection.

[0015] This invention effectively solves the problems of composition and carbon segregation in H13 hot work die steel, avoiding premature fatigue cracks or substandard product quality caused by uneven hardness or microstructure during die use, thus ensuring that the die steel product quality meets usage requirements. After forging, the banded microstructure of the H13 hot work die steel is significantly improved, the degree of carbon segregation is significantly reduced, the flaw detection level reaches the highest level 4 of GB / T6402-2008, the room temperature impact value reaches over 280J, and the austenite grain size reaches fine grain level 5 or above. Detailed Implementation

[0016] Example 1

[0017] In this embodiment, the cross-sectional dimensions of the forged H13 steel are φ700mm, the cross-sectional dimensions of the steel ingot are 900*930mm, and the height is 1500mm.

[0018] A forging method to improve carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes. The specific process steps are as follows:

[0019] (1) High-temperature diffusion process before forging: the steel ingot is hot-sent to the heating furnace at 600°C and heated to 1320°C at a rate of 100°C / min. The holding time is 17h. After holding, the ingot is taken out of the furnace and air-cooled.

[0020] (2) The steel ingot is air-cooled to a surface temperature of 1160℃ and then forged;

[0021] (3) Forging process, four upsetting and four drawing process is adopted. The ratio of upsetting in the first two upsetting processes is 1.5, the ratio of drawing and forging is 1.8, and the drawing and reduction amount is 10%. The ratio of upsetting in the last two upsetting processes is 2.2, the ratio of drawing and forging is 2.0, the drawing and reduction amount is 12%, and the total forging ratio is 10. After forging, ultra-fine heat treatment is carried out according to conventional process.

[0022] The H13 round steel obtained in this embodiment, when inspected under high magnification, showed a banded microstructure reaching SA1 level, with significantly reduced segregation. Its flaw detection level reached GB / T6402-2008 Level 4, the austenite grain size reached Level 9, and the impact energy at 20℃ was 320J.

[0023] Example 2

[0024] In this embodiment, the cross-sectional dimensions of the forged H13 steel are φ750mm, the cross-sectional dimensions of the steel ingot are 1000*1030mm, and the height is 1650mm.

[0025] A forging method to improve carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes. The specific process steps are as follows:

[0026] (1) High-temperature diffusion process before forging: the steel ingot is hot-sent to the heating furnace at 580°C and heated to 1330°C at a rate of 120°C / min. The holding time is 20.6h. After holding, the ingot is taken out of the furnace and air-cooled.

[0027] (2) The steel ingot is air-cooled to a surface temperature of 1170℃ and then forged;

[0028] (3) Forging process, four upsetting and four drawing process is adopted. The ratio of upsetting in the first two upsetting processes is 1.6, the ratio of drawing and forging is 1.9, and the drawing and reduction amount is 13.2%; the ratio of upsetting in the last two upsetting processes is 2.3, the ratio of drawing and forging is 2.2, the drawing and reduction amount is 15%, and the total forging ratio is 12. After forging, ultra-fine heat treatment is carried out according to conventional process.

[0029] The H13 round steel obtained in this embodiment, when inspected under high magnification, showed a banded microstructure reaching SA1 level, with significantly reduced segregation. Its flaw detection level reached GB / T6402-2008 Level 4, austenite grain size reached Level 8, and its impact energy at 20℃ was 325J.

[0030] Example 3

[0031] In this embodiment, the cross-sectional dimensions of the forged H13 steel are φ800mm, the cross-sectional dimensions of the steel ingot are 1180*1200mm, and the height is 1700mm.

[0032] A forging method to improve carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes. The specific process steps are as follows:

[0033] (1) High-temperature diffusion process before forging: the steel ingot is hot-sent to the heating furnace at 570°C and heated to 1310°C at a rate of 115°C / min. The holding time is 23.5h. After holding, the ingot is taken out of the furnace and air-cooled.

[0034] (2) The steel ingot is air-cooled to a surface temperature of 1180℃ and then forged;

[0035] (3) Forging process, four upsetting and four drawing process is adopted. The ratio of upsetting in the first two upsetting processes is 1.8, the ratio of drawing and forging is 2.0, and the drawing and reduction amount is 15%; the ratio of upsetting in the last two upsetting processes is 2.2, the ratio of drawing and forging is 2.1, and the drawing and reduction amount is 15%, with a total forging ratio of 11.5; after forging, ultra-fine heat treatment is carried out according to conventional process.

[0036] The H13 round steel obtained in this embodiment, when inspected under high magnification, showed a banded microstructure reaching SA1 level, with significantly reduced segregation. Its flaw detection level reached GB / T6402-2008 Level 4, the austenite grain size reached Level 8, and the impact energy at 20℃ was 315J.

[0037] Example 4

[0038] In this embodiment, the cross-sectional dimensions of the forged H13 steel are φ780mm, the cross-sectional dimensions of the steel ingot are 1050*1120mm, and the height is 1600mm.

[0039] A forging method to improve carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes. The specific process steps are as follows:

[0040] (1) High-temperature diffusion process before forging: the steel ingot is hot-sent to the heating furnace at 560°C and heated to 1315°C at a rate of 105°C / min. The holding time is 17h. After holding, the ingot is taken out of the furnace and air-cooled.

[0041] (2) The steel ingot is air-cooled to a surface temperature of 1175℃ and then forged;

[0042] (3) Forging process, four upsetting and four drawing process is adopted. The ratio of upsetting in the first two upsettings is 1.7, the ratio of drawing to forging is 1.85, and the drawing reduction is 14%; the ratio of upsetting in the last two upsettings is 2.4, the ratio of drawing to forging is 2.15, the drawing reduction is 14%, and the total forging ratio is 10.5. After forging, ultra-fine heat treatment is carried out according to conventional process.

[0043] The H13 round steel obtained in this embodiment, when inspected under high magnification, showed a banded microstructure reaching SA2 level, with significantly reduced segregation. Its flaw detection level reached GB / T6402-2008 Level 4, the austenite grain size reached 8.5 level, and its impact energy at 20℃ was 315J.

[0044] Example 5

[0045] In this embodiment, the cross-sectional dimensions of the forged H13 steel are φ740mm, the cross-sectional dimensions of the steel ingot are 1100*1150mm, and the height is 1650mm.

[0046] A forging method to improve carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes. The specific process steps are as follows:

[0047] (1) High-temperature diffusion process before forging: the steel ingot is hot-sent to the heating furnace at 590°C and heated to 1312°C at a rate of 120°C / min. The holding time is 18.7h. After holding, the ingot is taken out of the furnace and air-cooled.

[0048] (2) The steel ingot is air-cooled to a surface temperature of 1165℃ and then forged;

[0049] (3) Forging process, four upsetting and four drawing processes are adopted. The ratio of upsetting in the first two upsetting processes is 1.65, the ratio of drawing and forging is 2.0, and the drawing and reduction amount is 12.5%; the ratio of upsetting in the last two upsetting processes is 2.25, the ratio of drawing and forging is 2.15, the drawing and reduction amount is 12.5%, and the total forging ratio is 11.2. After forging, ultra-fine heat treatment is carried out according to conventional processes.

[0050] The H13 round steel obtained in this embodiment, when inspected under high magnification, showed a banded microstructure reaching SA 1 level, with significantly reduced segregation. Its flaw detection level reached GB / T6402-2008 level 4, the austenite grain size reached level 9, and the impact energy at 20℃ was 330J.

[0051] Example 6

[0052] In this embodiment, the cross-sectional dimensions of the forged H13 steel are φ710mm, the cross-sectional dimensions of the steel ingot are 1120*1200mm, and the height is 1700mm.

[0053] A forging method to improve carbon segregation in hot work die steel H13 includes pre-forging high-temperature diffusion and forging processes. The specific process steps are as follows:

[0054] (1) High-temperature diffusion process before forging: the steel ingot is hot-sent to the heating furnace at 600°C and heated to 1325°C at a rate of 120°C / min. The holding time is 20.2h. After holding, the ingot is taken out of the furnace and air-cooled.

[0055] (2) The steel ingot is air-cooled to a surface temperature of 1168℃ and then forged;

[0056] (3) Forging process, four upsetting and four drawing processes are adopted. The ratio of upsetting in the first two upsetting processes is 1.72, the ratio of drawing and forging is 1.95, and the drawing and reduction amount is 11.5%; the ratio of upsetting in the last two upsetting processes is 2.25, the ratio of drawing and forging is 2.05, the drawing and reduction amount is 11.5%, and the total forging ratio is 11.8. After forging, ultra-fine heat treatment is carried out according to conventional processes.

[0057] The H13 round steel obtained in this embodiment, when inspected under high magnification, showed a banded microstructure reaching SA1 level, with significantly reduced segregation. Its flaw detection level reached GB / T6402-2008 Level 4, austenite grain size reached Level 7, and its impact energy at 20℃ was 315J.

Claims

1. A forging method for improving carbon segregation in hot work die steel H13, characterized in that, It includes pre-forging high-temperature diffusion and forging processes; In the pre-forging high-temperature diffusion process, the steel ingot is heated to 1320±10℃ after being sent to the heating furnace, and the holding time is 1.5~2h / 100mm; after the steel ingot is held at the temperature, it is taken out of the furnace and air-cooled until the surface temperature is 1160~1180℃ before forging. The forging process adopts a four-upsetting and four-drawing process. The upsetting ratio of the first two upsettings is 1.5 to 1.8, the drawing ratio is 1.8 to 2.0, and the drawing reduction is 10 to 15%. The upsetting ratio of the last two upsettings is 2.2 to 2.4, the drawing ratio is 2 to 2.2, and the drawing reduction is 10% to 15%.

2. The forging method for improving carbon segregation in hot work die steel H13 according to claim 1, characterized in that, In the pre-forging high-temperature diffusion process, the hot delivery temperature of the steel ingot is ≥550℃.

3. The forging method for improving carbon segregation in hot work die steel H13 according to claim 2, characterized in that, The high-temperature diffusion process before forging has a heating rate of 100-120℃ / min.

4. The forging method for improving carbon segregation in hot work die steel H13 according to claim 3, characterized in that, The forging process has a total forging ratio of 10 to 12.

5. The forging method for improving carbon segregation in hot work die steel H13 according to any one of claims 1-4, characterized in that, The specifications for H13 hot work die steel after forging are φ700~φ800mm.