Cooling method during mold steel heat treatment, heat treatment method of mold steel and mold steel

Abstract

The present invention provides a cooling method for mold steel during heat treatment, a heat treatment method for mold steel, and mold steel. The cooling method adopts water-air alternating cooling; the first water cooling time is equal to the maximum effective thickness of the steel ingot*(2.0-2.2)s / mm; the first air cooling time is equal to the maximum effective thickness of the steel ingot*(0.60-0.8)s / mm; the second water cooling time is equal to the maximum effective thickness of the steel ingot*(1.3-1.5)s / mm; the second air cooling time is equal to the maximum effective thickness of the steel ingot*(0.60-0.80)s / mm; the third water cooling time is equal to the maximum effective thickness of the steel ingot*(0.28-0.48)s / mm; and the third air cooling time is 30-40 minutes. The present invention utilizes the characteristics of strong cooling capacity of water and weak cooling capacity of air, and through multiple strong and weak alternating cooling of water and air, accurately optimizes the cooling control time, refines the alloy structure of the steel ingot, and improves the strength and toughness of the steel structure material.

Description

Technical Field

[0001] The present invention relates to the field of steel heat processing, in particular to a cooling method for mold steel during heat treatment. The present invention also relates to a heat treatment method for mold steel and mold steel obtained by adopting the heat treatment method for mold steel. Background Art

[0002] Molds are essential, foundational tooling for the manufacturing industry, often called the "mother of industry." my country is the world's largest mold manufacturer and consumer, accounting for one-third of global output. With the rapid development of new energy vehicles, 5G communications, IT electronics, 3C appliances, and other sectors, the demand for high-quality mold steel is even more pronounced. According to incomplete statistics, my country's total mold steel output is approximately 1.5 million tons, of which plastic mold steel accounts for 60-70%, hot-work mold steel 20-25%, and cold-work mold steel approximately 15%.

[0003] Currently, my country's mold steel production primarily involves smelting and forging, with forged materials accounting for over 60% and the remainder being rolled products. my country's annual net imports total approximately 100,000 tons. Imports primarily come from Japan's Daido, Hitachi Metals, Germany's Grize, Sweden's ASSAB, and the United States' Finkola. Imported mold steel grades include Japanese SKD61, DC53, and SKD11, Swedish 8407 and DIEVAR, German 1.2344 and 1.2379, and American grades H13 and D2. Imported mold steel primarily consists of large-sized forged modules and large-sized flat mold steel. Looking at downstream industries, the automotive industry accounts for approximately 35% of the total mold steel market, while the electronics and communications industries, such as computers, mobile phones, and electronic devices, account for approximately 20%.

[0004] With the continuous expansion of mold application areas and their development towards high-end in the future, facing the current situation of poor quality and performance stability of mold steel in my country and incomplete varieties and specifications, mold steel will inevitably develop towards multiple varieties and specifications, high purity, high isotropy, ultra-fine structure and long life. Summary of the Invention

[0005] In view of this, the present invention proposes a cooling method for mold steel during heat treatment, including: the method adopts water cooling and air cooling of the steel ingot alternately; the first water cooling time is the maximum effective thickness of the steel ingot * (2.0~2.2) s / mm; the first air cooling time is the maximum effective thickness of the steel ingot * (0.60~0.8) s / mm; the second water cooling time is the maximum effective thickness of the steel ingot * (1.3~1.5) s / mm; the second air cooling time is the maximum effective thickness of the steel ingot * (0.60~0.80) s / mm; the third water cooling time is the maximum effective thickness of the steel ingot * (0.28~0.48) s / mm; and the third air cooling time is 30~40 min.

[0006] The cooling method of the mold steel during heat treatment of the present invention adopts water and air as media, utilizes the characteristics of strong cooling capacity of water and weak cooling capacity of air, and uses multiple strong and weak alternating cooling of water and air to accurately optimize the cooling control time, thereby making the alloy structure of the steel ingot finer and improving the strength and toughness of the steel structure material.

[0007] The present invention also proposes a heat treatment method for mold steel, which includes: treating the steel ingot in the following steps in sequence: hot forging, air blowing cooling, heating, water-air alternating cooling, and spheroidizing annealing; wherein, the water-air alternating cooling adopts the cooling method in the above-mentioned mold steel heat treatment process.

[0008] The heat treatment method for mold steel of the present invention performs hot forging and rolling on the steel ingot to roughly shape the steel ingot, then blows air to cool it, accelerates the rapid cooling after the hot forging and rolling process, refines the grains, then heats the steel ingot to austenitize it, continues water-air alternating cooling to further refine the alloy structure of the steel ingot, and then performs spheroidizing annealing to eliminate the stress of the workpiece during the water-air alternating cooling process, and recrystallizes and refines the structure grains.

[0009] Furthermore, the final temperature of the hot forging of the steel ingot is above the secondary carbide precipitation temperature in the CCT curve.

[0010] Furthermore, the temperature of the steel ingot after air cooling is 230-250°C.

[0011] Furthermore, the heating method includes: heating the steel ingot to 600-680°C at a rate of 90-100°C / h and keeping the temperature for 2-3h; then heating the steel ingot to 1030-1050°C at a rate of 90-100°C / h and keeping the temperature for 2-3h.

[0012] Furthermore, the spheroidizing annealing method includes: heating the steel ingot to 600-680°C at a rate of 90-100°C / h, and keeping it warm for 3.5-4.5h; heating the steel ingot to 800-900°C at a rate of 90-100°C / h, and keeping it warm for 8.5-9.5h; cooling the steel ingot to 600-680°C at a rate of ≤30°C / h; heating the steel ingot to 700-720°C at a rate of 90-100°C / h, and keeping it warm for 11-13 hours; cooling the steel ingot to below 400°C at a rate of ≤20°C / h, and taking it out of the furnace.

[0013] The present invention further provides a die steel, which is produced from a steel ingot by the above-mentioned die steel heat treatment method.

[0014] The mold steel of the present invention can refine the steel structure and improve the strength and toughness of the steel structure material by adopting the above-mentioned heat treatment method. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0016] Figure 1 This is a metallographic image magnified 500 times at 1 / 2D of the mold steel prepared by the heat treatment method of the mold steel according to the first embodiment of the present invention;

[0017] Figure 2 This is a metallographic image magnified 500 times at 1 / 2D of the mold steel prepared by the heat treatment method of the mold steel according to the second embodiment of the present invention;

[0018] Figure 3 This is a metallographic image magnified 500 times at 1 / 2D of the mold steel prepared by the heat treatment method of the mold steel in Comparative Example 1. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0020] The experimental methods in the following examples are all conventional methods unless otherwise specified. The experimental materials used in the following examples are all commercially available unless otherwise specified. In addition, unless otherwise specified in this example, the terms and processes involved in this example should be understood in accordance with the general knowledge and conventional methods in the prior art.

[0021] A cooling method for mold steel during heat treatment, the method adopts alternate water cooling and air cooling for steel ingots; the first water cooling time is equal to the maximum effective thickness of the steel ingot*(2.0-2.2)s / mm; the first air cooling time is equal to the maximum effective thickness of the steel ingot*(0.60-0.8)s / mm; the second water cooling time is equal to the maximum effective thickness of the steel ingot*(1.3-1.5)s / mm; the second air cooling time is equal to the maximum effective thickness of the steel ingot*(0.60-0.80)s / mm; the third water cooling time is equal to the maximum effective thickness of the steel ingot*(0.28-0.48)s / mm; and the third air cooling time is 30-40 minutes.

[0022] The cooling method for mold steel during heat treatment of the present invention uses water and air as the cooling medium. Taking advantage of the strong cooling capacity of water and the weak cooling capacity of air, the cooling control time is precisely optimized through multiple alternating cooling cycles of water and air. This ensures that the metallographic structure does not remain in the pearlite and bainite regions of the CCT curve during microstructural transformation, preventing the generation of pearlite and bainite. This refines the microstructure of the steel ingot and improves the strength and toughness of the steel structure. When calculating the cooling time, the maximum effective thickness is determined by the shape of the steel ingot. For round steel ingots, the diameter of the round steel can be used, while for flat steel ingots, the height of the flat steel can be used. The unit of measurement is millimeters.

[0023] The present invention also proposes a heat treatment method for mold steel, which includes: treating the steel ingot in the following steps in sequence: hot forging, air blowing cooling, heating, water-air alternating cooling, and spheroidizing annealing; wherein, the water-air alternating cooling adopts the cooling method in the above-mentioned mold steel heat treatment process.

[0024] The heat treatment method for mold steel of the present invention performs hot forging and rolling on the steel ingot to roughly shape the steel ingot, then blows air to cool the steel ingot after hot forging and rolling to quickly cool the steel ingot and refine the grains, then heats the steel ingot to austenitize it, continues water-air alternating cooling to further refine the alloy structure of the steel ingot, and then performs spheroidizing annealing to eliminate the stress of the workpiece during the water-air alternating cooling process and recrystallize to refine the structure grains.

[0025] In the present invention, the final temperature of hot forging of the steel ingot can be preferably above the precipitation temperature of secondary carbides in the CCT curve to prevent the generation of secondary carbides. The specific temperature range can be selected according to different steel grades. If it is H11 steel, the final temperature of hot forging is controlled at above 805°C; if it is H12 steel, the final temperature of hot forging is controlled at above 810°C; if it is 5H12 steel, the final temperature of hot forging is controlled at 815°C; if it is H13 steel, the final temperature of hot forging is controlled at above 820°C.

[0026] Then the temperature of the above-mentioned steel ingot after air cooling is 230-250℃. The specific method is to place the steel ingot on a 10-15mm high steel rail, and place an axial flow fan in the east, west, south and north directions around the steel ingot. The air outlet direction of the east-west fan is parallel with the spacing of 10-20mm, and the same is true for the north-south fans. Turn on the fan to make the air flow around the steel ingot form a spiral, so as to force cool the steel ingot to 230-250℃ in a short time. Air cooling can refine the grains and reduce the mixed crystal phenomenon caused by dynamic recrystallization during hot forging and rolling.

[0027] The steel ingot is then heated. The heating method preferably includes: preheating the heating furnace to 300-400°C to prevent the steel ingot from cracking upon entering the furnace; then placing the steel ingot into the heating furnace and holding it at this temperature for 1.5 hours; then heating the steel ingot at a rate of 90-100°C / hour to 600-680°C and holding it at this temperature for 2-3 hours; then heating the steel ingot at a rate of 90-100°C / hour to 1030-1050°C to austenitize the steel ingot and holding it at this temperature for 2-3 hours. After heating, the steel ingot is alternately cooled with water and air to refine the structure of the steel ingot.

[0028] The steel ingot is then subjected to spheroidizing annealing. The spheroidizing annealing method may include: heating the steel ingot at a rate of 90-100°C / h to 600-680°C and holding it for 3.5-4.5 hours; heating the steel ingot at a rate of 90-100°C / h to 800-900°C and holding it for 8.5-9.5 hours; cooling the steel ingot at a rate of ≤30°C / h to 600-680°C; heating the steel ingot at a rate of 90-100°C / h to 700-720°C and holding it for 11-13 hours; and cooling the steel ingot at a rate of ≤20°C / h to below 400°C before removing it from the furnace. Spheroidizing annealing can refine the grain size, adjust the microstructure, and eliminate structural defects.

[0029] The present invention further provides a die steel, which is produced from a steel ingot by the above-mentioned die steel heat treatment method. The die steel of the present invention can refine the steel structure and improve the strength and toughness of the steel structure material by adopting the above-mentioned heat treatment method.

[0030] The specific implementation scheme of the present invention is described in detail below.

[0031] Example 1

[0032] The steel ingot used in this embodiment is a bar with a material of H13, a specification of φ254, and a length of 5000 mm. The following heat treatment method is used for the steel ingot.

[0033] The steel ingot is heated to 1150℃ and then radially forged, and the final forging temperature is controlled at 820℃.

[0034] After hot forging, the steel ingot is placed on a 10-15mm high rail. An axial flow fan is placed around the steel ingot in the east, west, south and north directions. The fans are not opposite to each other and are staggered by 10-20mm to force cool the steel ingot to 250℃.

[0035] The air-cooled steel ingot is placed in a heating furnace preheated to 350°C, kept warm for 1.5 hours, heated to 650°C at a rate of 90-100°C / h, and kept warm for 2.5 hours; the steel ingot is further heated to 1050°C at a rate of 90-100°C / h, and kept warm for 2.5 hours.

[0036] Then, water-air alternating cooling is carried out. The first time the bar enters the water, it stays in the air for 9 minutes, and then leaves the water and stays in the air for 3 minutes. The second time the bar enters the water, it stays in the air for 6 minutes, then leaves the water and stays in the air for 3 minutes. The third time the bar enters the water, it stays in the air for 1.5 minutes, then leaves the water and stays in the air for 30 minutes. The surface temperature of the bar after the first exit of the water is 320℃, the surface temperature of the bar after the second exit of the water is 230℃, and the surface temperature of the bar after the third exit of the water is 110℃.

[0037] Place the steel ingot in a heating furnace, heat it to 650℃ at a rate of 90-100℃ / h, and keep it warm for 4h; continue to heat it to 900℃ at a rate of 90-100℃ / h, and keep it warm for 9h; then quickly cool the steel ingot to 650℃ at a rate of ≤30℃ / h; heat the steel ingot from 650℃ to 700℃ at a rate of 90-100℃ / h, and keep it warm for 12 hours; slowly cool the steel ingot from 700℃ to 400℃ at a rate of ≤20℃ / h and take it out of the furnace.

[0038] The above steel ingots were straightened and lathe-type. The annealing structure at 1 / 4D and 1 / 2D of the steel ingot was tested. A sample of 10-15mm was taken. The metallographic structure at 1 / 2D was as follows: Figure 1 As shown, according to the SEP1614-1996 standard, the annealed structure of this embodiment is GA2 grade.

[0039] Example 2

[0040] The steel ingot used in this embodiment is a flat steel with a material of H12, a specification of 110X250, and a length of 3000mm. The steel ingot is subjected to the following heat treatment method.

[0041] The steel ingot is heated to 1120℃ and then radially forged, and the final forging temperature is controlled at 810℃.

[0042] After hot forging, the steel ingot is placed on a 10-15mm high steel rail. An axial flow fan is placed around the steel ingot in the east, west, south and north directions. The fans are not opposite to each other and are staggered by 10-20mm to force cool the steel ingot to 230℃.

[0043] The air-cooled steel ingot is placed in a heating furnace preheated to 350°C, kept warm for 1.5 hours, heated to 650°C at a rate of 90-100°C / h, and kept warm for 2.5 hours; the steel ingot is further heated to 1050°C at a rate of 90-100°C / h, and kept warm for 2.5 hours.

[0044] Then, water-air alternating cooling is carried out. The first time it enters the water, it stays in the air for 4 minutes, and then it exits the water and stays in the air for 1 minute. The second time it enters the water, it stays in the air for 2.5 minutes, and then it exits the water and stays in the air for 1 minute. The third time it enters the water, it stays in the air for 1.5 minutes, and then it exits the water and stays in the air for 30 minutes. The surface temperature of the flat steel after the first exit is 270℃, the surface temperature of the bar after the second exit is 210℃, and the surface temperature of the bar after the third exit is 100℃.

[0045] Place the steel ingot in a heating furnace, heat it to 650℃ at a rate of 90-100℃ / h, and keep it warm for 4h; continue to heat it to 900℃ at a rate of 90-100℃ / h, and keep it warm for 9h; then quickly cool the steel ingot to 650℃ at a rate of ≤30℃ / h; heat the steel ingot from 650℃ to 700℃ at a rate of 90-100℃ / h, and keep it warm for 12 hours; slowly cool the steel ingot from 700℃ to 400℃ at a rate of ≤20℃ / h and take it out of the furnace.

[0046] The above steel ingots are straightened and turned. The annealed structures of 1 / 4D and 1 / 2D of the steel ingot are tested. Samples of 10-15mm are taken. The metallographic structure of the structure at 1 / 2D is as follows: Figure 1 As shown, according to the SEP1614-1996 standard, the annealed structure of this embodiment is GA2 grade.

[0047] Comparative Example 1

[0048] The steel ingot used in this comparative example is a bar with a material of H13, a specification of φ254, and a length of 5000 mm. The following heat treatment method is applied to the steel ingot.

[0049] The steel ingot is heated to 1150°C and radially forged, and the final forging temperature is controlled at 820°C.

[0050] After hot forging, the steel ingot is placed on a 10-15mm high rail. An axial flow fan is placed around the steel ingot in the east, west, south and north directions. The fans are not opposite to each other and are staggered by 10-20mm to force cool the steel ingot to 250℃.

[0051] The air-cooled steel ingot is placed in a heating furnace preheated to 350°C, kept warm for 1.5 hours, heated to 650°C at a rate of 90-100°C / h, and kept warm for 2.5 hours; the steel ingot is further heated to 1050°C at a rate of 90-100°C / h, and kept warm for 2.5 hours.

[0052] Then, water-air alternating cooling is performed, with the first water entry staying for 4 minutes, the second water entry staying for 1.5 minutes, the third water entry staying for 1 minute, and the third water entry staying for 1 minute, and the third water entry staying for 30 minutes. The surface temperature of the rods after the first water exit is 480°C, the second water exit is 360°C, and the third water exit is 230°C.

[0053] Place the steel ingot in a heating furnace, heat it to 650℃ at a rate of 90-100℃ / h, and keep it warm for 4h; continue to heat it to 900℃ at a rate of 90-100℃ / h, and keep it warm for 9h; then quickly cool the steel ingot to 650℃ at a rate of ≤30℃ / h; heat the steel ingot from 650℃ to 700℃ at a rate of 90-100℃ / h, and keep it warm for 12 hours; slowly cool the steel ingot from 700℃ to 400℃ at a rate of ≤20℃ / h and take it out of the furnace.

[0054] The above steel ingots were straightened and lathe-type. The annealed structures at 1 / 4D and 1 / 2D were tested. Samples of 10-15mm were taken. The metallographic structure at 1 / 2D was as follows: Figure 3 This comparative example is essentially the same heat treatment method as Example 1, differing in the duration of the alternating water-air cooling process. Changing the alternating water-air cooling time resulted in the presence of a significant amount of bainite, which does not comply with the SEP1614-1996 standard and significantly reduces the service life of the ingot.

[0055] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A heat treatment method for mold steel, characterized in that: include: The steel ingot is processed in the following steps: hot forging, air cooling, heating, water-air alternating cooling, and spheroidizing annealing; Among them, water-air alternating cooling adopts the method of alternately cooling the steel ingot with water and air; The first water cooling time is the maximum effective thickness of the ingot*(2.0~2.2)s / mm; The first air cooling time is the maximum effective thickness of the ingot*(0.60~0.8)s / mm; The second water cooling time is the maximum effective thickness of the ingot*(1.3~1.5)s / mm; The second air cooling time is the maximum effective thickness of the ingot*(0.60~0.80)s / mm; The third water cooling time is the maximum effective thickness of the ingot*(0.28~0.48)s / mm; The third air cooling time is 30 to 40 minutes; The final temperature of the hot forging of the steel ingot is above the secondary carbide precipitation temperature in the CCT curve; The temperature of the steel ingot after air cooling is 230-250°C; The heating method comprises: The steel ingot is heated to 600-680°C at a rate of 90-100°C / h and kept at this temperature for 2-3h; Then, the steel ingot is heated to 1030-1050° C. at a rate of 90-100° C. / h and kept at this temperature for 2-3 hours; The spheroidizing annealing method comprises: The steel ingot is heated to 600-680°C at a rate of 90-100°C / h and kept at this temperature for 3.5-4.5h; The steel ingot is heated to 800-900°C at a rate of 90-100°C / h and kept at this temperature for 8.5-9.5h; Cooling the steel ingot to 600-680°C at a rate of ≤30°C / h; Heating the steel ingot to 700-720°C at a rate of 90-100°C / h and keeping the temperature for 11-13 hours; The steel ingot is cooled to below 400° C. at a rate of ≤20° C. / h and taken out of the furnace.

2. A mold steel, characterized by: The mold steel is produced by heat treating the mold steel according to claim 1.

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