An efficient homogenization method for improving the impact performance of H13 steel

Abstract

The present invention relates to an efficient homogenization method for improving the impact performance of H13 steel, belonging to the technical field of the metallurgical industry. The method includes electroslag ingot homogenization, blooming forging, forged billet homogenization, and precision forging processes; the blooming forging process is completed in two heats by the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X and Y cross flattening method; the second heat is axial upsetting + commutation drawing, and the upsetting ratio is ≥2.5; the precision forging process adopts the method of one upsetting and one drawing + one commutation, and the upsetting ratio is ≥2.5. The present invention adopts the forging method of two homogenizations + two upsetting and three drawing, which is beneficial to fully break the as-cast dendritic and liquid segregation carbides, can completely eliminate the banded segregation, significantly improve the tissue uniformity and impact toughness, has strong process operability and higher efficiency. The annealing tissue level of the obtained H13 steel product reaches above the AS4 level. When the hardness after heat treatment is 45±1HRC, the average transverse V-notch impact energy ≥17J.

Description

Technical Field

[0001] The present invention belongs to the technical field of the metallurgical industry and relates to an efficient homogenization method for improving the impact performance of H13 steel. Background Art

[0002] H13 steel is a medium-carbon medium-alloy hot work die steel with excellent comprehensive properties and is widely used in hot forging dies, aluminum alloy die-casting dies, and hot extrusion dies. During the service process of H13 steel hot work dies, the die cavity needs to withstand repeated heating and cooling, and is also subject to certain impact effects. Thermal fatigue is the most main failure form of H13 dies. Impact toughness and isotropic properties are the key indicators affecting the fatigue life of H13 dies. To improve the impact performance of H13 steel, homogenization + multi-directional forging means are usually adopted to reduce banded segregation, thereby improving the tissue uniformity and transverse impact toughness. The NADVCA#207-2003 standard requires that the transverse impact energy ≥ 10.84 J, which is a super high-quality steel.

[0003] To obtain a better diffusion effect, it is necessary to increase the homogenization temperature or extend the holding time. Especially when producing large-sized electroslag ingots, due to the serious dendritic segregation in the core of the electroslag ingot, the number and size of massive liquid segregation carbides are large, and the homogenization time is usually higher than 30 h, the production cycle is long, the oxidation loss is very serious, and the economy is poor. At the same time, the transverse impact energy of the vast majority of domestic large-sized H13 forgings does not exceed 15 J. Although it meets the super high-quality steel index in the NADCA standard, there is still a large gap with imported steel during use. Therefore, through reasonable process design, developing an efficient homogenization treatment method to improve the element diffusion efficiency and shorten the process cycle on the basis of ensuring the high isotropy of large-sized forging products has great practical significance for improving the quality and efficiency of H13 steel forging products. Summary of the Invention

[0004] Aiming at the problems of low impact toughness, long homogenization time, and low production efficiency of large-sized H13 forgings, the present invention provides an efficient homogenization treatment method for improving the impact performance of H13 steel to improve the impact performance and economy of H13 steel.

[0005] To achieve the above invention purpose, the technical solution adopted by the present invention is:

[0006] An efficient homogenization method for improving the impact performance of H13 steel, including electroslag ingot homogenization, blooming forging, forging billet homogenization, and precision forging processes;

[0007] (1) Electroslag ingot homogenization process: The H13 electroslag ingot with a temperature ≥ 500 °C is hot charged into the furnace and held at 1260 - 1280 °C for 10 - 14 h;

[0008] (2) Blooming forging process: It is completed in two heats by using the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X and Y cross flattening method. Before forging, it is sprayed with water for cooling to 950 - 1000 °C on the surface of the electroslag ingot; the second heat is axial upsetting + commutation drawing, and the upsetting ratio ≥ 2.5;

[0009] (3) Homogenization process of forging billet: The forging billet is put into the furnace and kept at 1240 - 1260 °C for 10 - 14 h;

[0010] (4) Precision forging process: It adopts the method of one upsetting and one drawing + one commutation, and the upsetting ratio ≥ 2.5.

[0011] Further, in the homogenization process of the electroslag ingot, after the electroslag ingot is hot charged into the furnace, it is first heated to 800 - 850 °C for preheating and holding for 2 - 4 h, and then heated to 1260 - 1280 °C, with a heating rate of 50 - 120 °C / h.

[0012] Further, in the blooming forging process, the electroslag ingot is cooled to 1200 - 1220 °C and held for 1.5 - 2 h before blooming forging.

[0013] Further, in the precision forging process, the forging billet is cooled to 1200 - 1220 °C and held for 1.5 - 2 h before precision forging; after forging, it is air-cooled to 250 - 350 °C, and then sand-cooled to room temperature.

[0014] Further, the H13 steel product obtained by precision forging is a round steel with a diameter of φ240 - 450 mm or a module with a cross-sectional size of 240 - 450 mm × 610 - 810 mm.

[0015] Further, when the H13 steel product obtained is sampled from the core and the hardness of the specimen after heat treatment is 45 ± 1 HRC, the average transverse V-notch impact energy ≥ 17 J, and the ratio of transverse and longitudinal impact energies ≥ 0.85.

[0016] The beneficial effects of adopting the above technical solutions are as follows: 1. In the present invention, the H13 electroslag ingot is hot-transported to the forging workshop for hot charging into the furnace, and the homogenization is carried out by means of stepped temperature rise; the internal stress of the electroslag ingot is effectively eliminated, avoiding the cracking of the electroslag ingot caused by excessive tissue stress due to improper cooling or long-term storage at room temperature. At the same time, the cooling time is shortened and the production efficiency is improved. 2. In the present invention, the blooming process of the electroslag ingot adopts the deformation mode of drawing + upsetting + drawing (reversing), and the first drawing operation is carried out in the X and Y cross-flattening mode. Before forging, the water mist device is used for spraying water cooling until the surface of the electroslag ingot is quickly cooled to 950-1000 °C; the JTS forging method is used to enhance the compaction effect of the core of the electroslag ingot, effectively breaking the coarse dendrites in the core and the large blocky liquid segregation carbides between dendrites, shortening the element diffusion distance, reducing the number of upsetting times, and improving the forging efficiency. 3. In the preparation process of the H13 steel forgings of the present invention, two homogenizations + two upsetting and three drawing are adopted. Among them, the total duration of the two homogenizations is within 28 h. Compared with the conventional homogenization treatment time of more than 30 h, it has certain economy; the two upsetting + two reversing drawing operations are simple. Compared with the forging method of three upsetting and three drawing + cross forging of conventional die steel, the process is more operable, the forging efficiency is higher, and the process advantages are obvious. 4. For the H13 steel product of the present invention, when sampling from the core, the annealing structure level reaches above the AS4 level in the NADCA #207-2003 standard. When the hardness of the heat-treated sample is 45 ± 1 HRC, the average transverse V-notch impact energy ≥ 17 J, and the ratio of transverse and longitudinal impact energies ≥ 0.85. Description of the Drawings

[0017] Figure 1 It is the metallographic structure diagram of the H13 steel after annealing treatment in Example 1 of the present invention;

[0018] Figure 2 It is the SEM diagram of the H13 steel after annealing treatment in Example 1 of the present invention;

[0019] Figure 3 It is the banded structure diagram of the H13 steel after annealing treatment in Example 1 of the present invention;

[0020] Figure 4 It is the metallographic structure diagram of the H13 steel after quenching and tempering treatment in Example 1 of the present invention. Detailed Description of the Invention

[0021] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0022] The specific steps of the high-efficiency homogenization method for improving the impact performance of H13 steel in this example are as follows:

[0023] (1) Heat the H13 electroslag ingot at a temperature ≥500°C to the forging workshop for hot charging into the furnace. Heat it up to 800°C at a heating rate of 80°C / h for preheating and insulation, with an insulation time of 4 h; then heat it up to 1260°C at a heating rate of 120°C / h, with an insulation time of 14 h for electroslag ingot homogenization.

[0024] (2) Cool the H13 steel electroslag ingot processed in step (1) to 1200°C, with an insulation time of 2 h, and perform cogging forging. The cogging is completed in two heats using the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out in the X and Y cross-flattening manner. Before forging, use a water spray device to cool it by spraying water until the surface temperature of the electroslag ingot reaches 980°C; the second heat is axial upsetting + commutation drawing, with an upsetting ratio of 2.7.

[0025] (3) Return the forged billet to the furnace, heat it up to 1250°C, with an insulation time of 11 h, for forged billet homogenization.

[0026] (4) Cool the H13 steel forged billet processed in step (3) to 1218°C, with an insulation time of 1.5 h, and perform finish forging. The finish forging method is one upsetting and one drawing + one commutation, with an upsetting ratio of 2.5. After forging, air-cool it to 280°C and then cool it with sand.

[0027] The H13 steel product obtained after finish forging in this example is a φ240 mm round steel. Sampling is taken from its core. When the hardness of the test specimen after heat treatment is 44.8 HRC, the average transverse V-notch impact energy is 19.6 J, and the ratio of transverse to longitudinal impact energy is 0.92. Example 2

[0028] The specific steps of the high-efficiency homogenization method for improving the impact performance of H13 steel in this example are as follows:

[0029] (1) Heat the H13 electroslag ingot at a temperature ≥500°C to the forging workshop for hot charging into the furnace. Heat it up to 830°C at a heating rate of 50°C / h for preheating and insulation, with an insulation time of 3 h; then heat it up to 1270°C at a heating rate of 100°C / h, with an insulation time of 12 h for electroslag ingot homogenization.

[0030] (2) Cool the H13 steel electroslag ingot processed in step (1) to 1210°C, with an insulation time of 2 h, and perform cogging forging. The cogging is completed in two heats using the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out in the X and Y cross-flattening manner. Before forging, use a water spray device to cool it by spraying water until the surface temperature of the electroslag ingot reaches 980°C; the second heat is axial upsetting + commutation drawing, with an upsetting ratio of 3.0.

[0031] (3) Return the forged billet to the furnace, heat it up to 1240°C, with an insulation time of 12 h, for forged billet homogenization.

[0032] (4)The H13 steel forging billet processed in step (3) is cooled to 1215 °C and held for 1.5 h, followed by precision forging. The precision forging method is one upsetting and one drawing + one commutation, with an upsetting ratio of 2.8. After forging, it is air-cooled to 320 °C and then sand-cooled.

[0033] The H13 steel product obtained after precision forging in this example is a round steel with a diameter of φ350 mm. Samples are taken from its core. When the hardness of the sample after heat treatment is 45.2 HRC, the average transverse V-notch impact energy is 18.7 J, and the ratio of transverse to longitudinal impact energy is 0.90. Example 3

[0034] The specific steps of the high-efficiency homogenization method for improving the impact performance of H13 steel in this example are as follows:

[0035] (1) The H13 electroslag ingot with a temperature ≥500 °C is hot-transported to the forging workshop and hot-charged into the furnace. It is heated to 850 °C for preheating and holding at a heating rate of 70 °C / h for 2 h; then it is heated to 1280 °C at a heating rate of 120 °C / h and held for 10 h for electroslag ingot homogenization.

[0036] (2) The H13 steel electroslag ingot processed in step (1) is cooled to 1220 °C and held for 2 h, followed by cogging forging. The cogging is completed in two heats by the method of one upsetting and two drawings + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X and Y cross-flattening method. Before forging, it is sprayed and cooled to 990 °C on the surface of the electroslag ingot by a water mist device; the second heat is axial upsetting + commutation drawing, with an upsetting ratio of 2.8.

[0037] (3) The forging billet is returned to the furnace, heated to 1260 °C, and held for 10 h for forging billet homogenization.

[0038] (4) The H13 steel forging billet processed in step (3) is cooled to 1210 °C and held for 2 h, followed by precision forging. The precision forging method is one upsetting and one drawing + one commutation, with an upsetting ratio of 2.6. After forging, it is air-cooled to 305 °C and then sand-cooled.

[0039] The H13 steel product obtained after precision forging in this example is a round steel with a diameter of φ450 mm. Samples are taken from its core. When the hardness of the sample after heat treatment is 45.2 HRC, the average transverse V-notch impact energy is 18.1 J, and the ratio of transverse to longitudinal impact energy is 0.88. Example 4

[0040] The specific steps of the high-efficiency homogenization method for improving the impact performance of H13 steel in this example are as follows:

[0041] (1) Heat the H13 electroslag ingot at a temperature ≥ 500 °C to the forging workshop for hot charging into the furnace. Heat it up to 830 °C at a heating rate of 90 °C / h for preheating and holding, with a holding time of 3 h; then heat it up to 1270 °C at a heating rate of 110 °C / h and hold for 11 h for homogenization of the electroslag ingot.

[0042] (2) Cool the H13 steel electroslag ingot processed in step (1) to 1200 °C and hold for 1.5 h for cogging forging. The cogging is completed in two heats by the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X, Y cross flattening method. Before forging, use a water spray device to spray and cool to 960 °C on the surface of the electroslag ingot; the second heat is axial upsetting + commutation drawing, with an upsetting ratio of 3.1.

[0043] (3) Return the forged billet to the furnace, heat it up to 1245 °C and hold for 13 h for homogenization of the forged billet.

[0044] (4) Cool the H13 steel forged billet processed in step (3) to 1220 °C and hold for 2 h for finish forging. The finish forging method is one upsetting and one drawing + one commutation, with an upsetting ratio of 2.8. After forging, air cool to 250 °C and then sand cool.

[0045] The H13 steel product obtained after finish forging in this example is a module with a cross-sectional size of 240 mm × 610 mm. When sampling from its core and the hardness of the specimen after heat treatment is 44.3 HRC, the average transverse V-notch impact energy is 18.9 J, and the ratio of transverse to longitudinal impact energy is 0.93. Example 5

[0046] The specific steps of the high-efficiency homogenization method for improving the impact performance of H13 steel in this example are as follows:

[0047] (1) Heat the H13 electroslag ingot at a temperature ≥ 500 °C to the forging workshop for hot charging into the furnace. Heat it up to 840 °C at a heating rate of 100 °C / h for preheating and holding, with a holding time of 3.5 h; then heat it up to 1275 °C at a heating rate of 100 °C / h and hold for 13 h for homogenization of the electroslag ingot.

[0048] (2) Cool the H13 steel electroslag ingot processed in step (1) to 1200 °C and hold for 2 h for cogging forging. The cogging is completed in two heats by the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X, Y cross flattening method. Before forging, use a water spray device to spray and cool to 950 °C on the surface of the electroslag ingot; the second heat is axial upsetting + commutation drawing, with an upsetting ratio of 2.7.

[0049] (3) Return the forged billet to the furnace, heat it up to 1255 °C and hold for 14 h for homogenization of the forged billet.

[0050] (4)The H13 steel forging blank processed in step (3) is cooled to 1200 °C and held for 2 h, followed by precision forging. The precision forging method is one upsetting and one drawing + one commutation, with an upsetting ratio of 2.5. After forging, it is air-cooled to 275 °C and then sand-cooled.

[0051] The H13 steel product obtained after precision forging in this example is a module with a cross-sectional size of 350 mm × 710 mm. Samples are taken from its core. When the hardness of the sample after heat treatment is 44.9 HRC, the average transverse V-notch impact energy is 17.7 J, and the ratio of transverse to longitudinal impact energy is 0.87. Example 6

[0052] The specific steps of the high-efficiency homogenization method for improving the impact performance of H13 steel in this example are as follows:

[0053] (1)The H13 electroslag ingot with a temperature ≥ 500 °C is hot-transported to the forging workshop and hot-charged into the furnace. It is heated to 850 °C for preheating and holding at a heating rate of 70 °C / h for 3 h; then it is heated to 1280 °C at a heating rate of 90 °C / h and held for 12 h for electroslag ingot homogenization.

[0054] (2)The H13 steel electroslag ingot processed in step (1) is cooled to 1220 °C and held for 2 h, followed by cogging forging. The cogging is completed in two heats by the method of one upsetting and two drawings + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X and Y cross-flattening method. Before forging, it is sprayed and cooled to 1000 °C on the surface of the electroslag ingot by a water mist device; the second heat is axial upsetting + commutation drawing, with an upsetting ratio of 2.5.

[0055] (3)The forging blank is returned to the furnace, heated to 1260 °C, and held for 13 h for forging blank homogenization.

[0056] (4)The H13 steel forging blank processed in step (3) is cooled to 1220 °C and held for 2 h, followed by precision forging. The precision forging method is one upsetting and one drawing + one commutation, with an upsetting ratio of 2.5. After forging, it is air-cooled to 350 °C and then sand-cooled.

[0057] The H13 steel product obtained after precision forging in this example is a module with a cross-sectional size of 450 mm × 810 mm. Samples are taken from its core. When the hardness of the sample after heat treatment is 45.4 HRC, the average transverse V-notch impact energy is 17.2 J, and the ratio of transverse to longitudinal impact energy is 0.85.

[0058] Take the H13 steel product obtained after precision forging in Example 1 of the present invention, and perform isothermal spheroidizing annealing at 880 °C for 2 h, slow cooling to 720 °C for 4 h, and slow cooling to below 500 °C and then air-cooling out of the furnace; perform quenching and tempering treatment at 1030 °C for 30 min, oil-cooling, 595 °C for 2 h, and air-cooling for secondary tempering. It can be Figure 1 seen that the metallographic structure after annealing treatment is a uniform granular pearlite structure, and the structure grade is AS2; it can beFigure 2 It can be seen that the carbide particles have high roundness, uniform size, and are dispersed; from Figure 3 it can be seen that the band segregation after annealing treatment is relatively light, and the banded structure grade is SA1; from Figure 4 it can be seen that the metallographic structure after quenching and tempering treatment is tempered sorbite structure, and the structure grade is HS5.

Claims

1. An efficient homogenization method for improving the impact performance of H13 steel, characterized in that, The method includes electroslag ingot homogenization, cogging forging, forged billet homogenization, and precision forging processes; (1) Electroslag ingot homogenization process: Heat charge the H13 electroslag ingot with a temperature ≥500°C into the furnace, and keep it at 1260 - 1280°C for 10 - 14 h; the heating rate after heat charging the electroslag ingot is 50 - 120°C / h; after heat charging the electroslag ingot, first heat it up to 800 - 850°C for preheating and heat preservation for 2 - 4 h, and then heat it up to 1260 - 1280°C; (2) Cogging forging process: It is completed in two heats by the method of one upsetting and two drawing + one commutation. The first heat is unidirectional drawing, and the deformation is carried out by the X, Y cross flattening method. Spray water for cooling before forging until the surface temperature of the electroslag ingot reaches 950 - 1000°C; the second heat is axial upsetting + commutation drawing, and the upsetting ratio ≥2.5; after the electroslag ingot cools down to 1200 - 1220°C and is kept warm for 1.5 - 2 h, cogging forging is carried out; (3) Forged billet homogenization process: The forged billet is returned to the furnace and kept at 1240 - 1260°C for 10 - 14 h; (4) Precision forging process: Adopt the method of one upsetting and one drawing + one commutation, with an upsetting ratio ≥2.

5. After the forged billet cools down to 1200 - 1220°C and is kept warm for 1.5 - 2 h, precision forging is carried out.

2. The efficient homogenization method for improving the impact performance of H13 steel according to claim 1, characterized in that, In the said precision forging process, after forging, it is air-cooled to 250 - 350°C, and then sand-cooled to room temperature.

3. The efficient homogenization method for improving the impact performance of H13 steel according to claim 1 or 2, characterized in that The H13 steel product obtained by precision forging is a round steel with a diameter of φ240 - 450 mm or a module with a cross-sectional size of 240 - 450 mm × 610 - 810 mm.

4. The efficient homogenization method for improving the impact performance of H13 steel according to claim 3, characterized in that Samples are taken from the core of the obtained H13 steel product. When the hardness of the sample after heat treatment is 45 ± 1 HRC, the average transverse V-notch impact energy ≥17 J, and the ratio of transverse and longitudinal impact energies ≥0.85.

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