A heat treatment process for improving the strength and toughness of H13 steel for hot-rolled shear blades

Abstract

The present invention relates to a heat treatment process for improving the toughness of H13 steel for hot-rolled shear blades, and belongs to the technical field of heat treatment of mold steel. The thickness of the H13 steel for hot-rolled shear blades is 35 to 70 mm, and the specific process is: heating the H13 steel to 1080 to 1100°C, keeping it warm for 25 to 35 minutes, and cooling it out of the furnace; then heating it to 780 to 820°C, keeping it warm for 2 to 2.5 hours, and cooling it out of the furnace to room temperature; then entering a vacuum heating furnace, heating it to 1040 to 1060°C, keeping it warm for 30 to 40 minutes, and cooling it out of the furnace; finally keeping it warm at 300 to 350°C for 2 to 2.5 hours, cooling it to room temperature, and performing three temperings to complete the heat treatment process. The H13 steel produced by the above heat treatment process is sampled at the core and made into a V-notch Charpy impact specimen. After testing, its impact energy is ≥9.0J and the hardness is 52 to 56HRC.

Description

Technical Field

[0001] The invention belongs to the technical field of die steel heat treatment, and in particular relates to a heat treatment process for improving the strength and toughness of H13 steel for hot-rolled shear blades. Background Art

[0002] Shearing tools are important mechanical spare parts in the steel rolling industry. The quality of hot-rolled shear blades directly affects the quality of rolled products, yield rate and production efficiency. H13 steel has high thermal strength, high toughness, excellent thermal fatigue resistance and comprehensive mechanical properties, and is widely used in the hot and cold shear blade manufacturing industry. With the continuous advancement of steel rolling technologies such as controlled rolling and controlled cooling, the requirements for shear blade quality are getting higher and higher. During the use of H13 steel hot shear blades, they often fail prematurely due to poor matching of strength and toughness, resulting in chipping, stacking and other early failures, reducing the service life of the shear blades. Therefore, improving the strength and toughness of H13 steel through heat treatment is an important way to increase the life of shear blade products, which is of great significance to improving the quality of rolled products and reducing production costs.

[0003] The conventional heat treatment process of H13 steel hot-rolled shear blades is annealing + quenching + secondary high-temperature tempering to obtain tempered martensite structure with a hardness range of 48-52HRC. At the same time, high-temperature tempering is prone to cause coarsening of martensite laths and carbides, which often causes early failures such as blade stacking due to low strength during use. The present invention provides a heat treatment process suitable for H13 shear blade steel: high quenching and high tempering + quenching + three low-temperature tempering. Through the coordinated design of shear blade pretreatment and quenching and tempering process, tempered martensite structure is obtained with a hardness range of 52-56HRC, the uniformity of grains and structure is improved, and the strength and toughness are matched to meet the product use requirements. Summary of the invention

[0004] The invention provides a heat treatment process for improving the toughness of H13 steel for hot-rolled shear blades, which can obtain H13 steel structure with dispersed distribution of carbides and fine tempered martensite, avoid coarsening of carbides and martensite laths, and significantly improve the uniformity and toughness of material structure.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0006] A heat treatment process for improving the strength and toughness of H13 steel for hot rolling shear blades, wherein the thickness of the H13 steel for hot rolling shear blades is 35 to 70 mm, and the heat treatment process includes four steps: high temperature quenching, high temperature tempering, vacuum quenching, and low temperature tempering. The specific process is as follows:

[0007] (1) High temperature quenching: Load H13 steel into the heating furnace, heat it to 1080-1100℃, keep it warm for 25-35min, and then cool it with air or oil.

[0008] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 780-820°C, kept at this temperature for 2-2.5 hours, and then air-cooled to room temperature.

[0009] (3) Vacuum quenching: After rough machining of the H13 steel treated in step (2), the steel is placed in a vacuum heating furnace and heated to 1040-1060°C. The furnace is kept warm for 30-40 minutes and then cooled by air or oil. Rough machining here refers to machining such as milling and drilling of the tool to meet the tool size and shape requirements.

[0010] (4) Low-temperature tempering: The H13 steel treated in step (3) is loaded into a heating furnace and heated to 300-350°C. The temperature is kept for 2-2.5 hours and air-cooled to room temperature. This completes the first tempering. Repeat this step twice. A total of three temperings are performed to complete the heat treatment process.

[0011] The high temperature quenching step also includes heating the H13 steel to 800-850°C with the furnace after loading it into the heating furnace, keeping it warm for 40-60 minutes, and then heating it to 1080-1100°C and keeping it warm.

[0012] In the high temperature quenching step, the furnace is air-cooled or oil-cooled to ≤100°C.

[0013] In the vacuum quenching step, the furnace is cooled by air or oil to ≤100°C.

[0014] The H13 steel produced by the above heat treatment process was sampled at the core and processed into a 10mm×10mm×55mm V-notch Charpy impact specimen. The impact energy was tested to be ≥9.0J and the hardness was 52-56HRC.

[0015] The present invention keeps H13 steel at 1080-1100° C. for 25-35 minutes. On the one hand, high-temperature diffusion is used to further uniformize the composition and reduce and eliminate band segregation. On the other hand, carbides are fully dissolved and reprecipitated to improve the uniformity of carbide distribution, obtain a uniform and fine single cryptocrystalline martensite structure, and avoid the influence of different pearlite types and carbide morphology differences on subsequent heat treatment.

[0016] The present invention heats the H13 steel after high-temperature quenching and cooling to 780-820°C, keeps the temperature for 2-2.5 hours, and air-cools to room temperature to obtain a tempered bainite structure with a hardness lower than 235 HBW. On the one hand, it is required in the production link to use high-temperature tempering instead of annealing to facilitate mechanical processing; on the other hand, before vacuum quenching, high-temperature tempering is added to change the organizational state, avoid direct heating of martensite to transform into austenite, avoid organizational inheritance of austenite coarse grains and mixed grains caused by uneven forging or improper heat treatment heating, and affect material properties.

[0017] According to the present invention, after rough processing, the pretreated H13 steel is loaded into a vacuum heating furnace for quenching at 1040-1060° C. and tempering at 300-350° C. three times to obtain tempered martensite, effectively avoiding the coarsening of martensite laths and carbides caused by high-temperature tempering. Under the premise of ensuring high hardness, the toughness of the material is taken into consideration. The three temperings can basically eliminate the residual austenite, thereby ensuring the stability of the shear blade during use.

[0018] After the treatment of the present invention, a sample is taken from the core of H13 steel and processed into a 10mm×10mm×55mm V-notch Charpy impact specimen, with a quenched and tempered impact energy of ≥9.0J, a hardness of 52-56HRC, a fine tempered martensite structure, and better strength and toughness matching. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the metallographic structure diagram of the H13 steel after pretreatment in Example 1;

[0020] Figure 2 This is the SEM image of the H13 steel after pretreatment in Example 1;

[0021] Figure 3 This is the metallographic structure diagram of the H13 steel product of Example 1;

[0022] Figure 4 This is the SEM image of the H13 steel product of Example 1. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0024] 50mm thick H13 steel plate is selected, and the specific heat treatment process is as follows:

[0025] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 830℃, keep it warm for 50min, continue to heat it to 1090℃, keep it warm for 30min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0026] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 800°C, kept at this temperature for 2 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0027] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1050°C, kept at this temperature for 40 minutes, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0028] (4) Low-temperature tempering: The H13 steel pretreated in step (3) is placed in a heating furnace, heated to 320°C, kept at this temperature for 2.5 h, and air-cooled to room temperature. This completes one tempering step. Repeat this step twice, for a total of three tempering steps.

[0029] After pretreatment and three low-temperature tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch and observe the transverse structure. The metallographic structure and SEM structure of the H13 steel after pretreatment are as follows: Figure 1 , Figure 2 As shown in the figure, the tempered troostite structure is fine and uniform, and the carbide spheroidization effect is obvious, which can provide good organizational preparation for tool quenching and tempering. The metallographic structure and SEM structure of the finished H13 steel after three low-temperature tempering are shown in Figure 1. Figure 3 , Figure 4 As shown in the figure, the tempered martensite lath bundles are small and still retain the morphological characteristics of cryptocrystalline martensite, while ensuring high hardness and taking into account the toughness of the material. The average heat treatment hardness is 54.2HRC, and the average V-mouth Charpy impact energy is 9.6J. Example 2

[0030] 45mm thick H13 steel plate is selected, and the specific heat treatment process is as follows:

[0031] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 820℃, keep it warm for 45min, continue to heat it to 1090℃, keep it warm for 30min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0032] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 800°C, kept at this temperature for 2.5 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0033] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1050°C, kept at this temperature for 35 minutes, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0034] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 320°C, kept at this temperature for 2 h, and air-cooled to room temperature. This completes one tempering step. Repeat this step twice, for a total of three tempering steps.

[0035] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 54.6HRC, and the average V-mouth Charpy impact energy was 9.6J. Example 3

[0036] 40mm thick H13 steel plate is selected, and the specific heat treatment process is as follows:

[0037] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 810℃, keep it warm for 45min, continue to heat it to 1080℃, keep it warm for 25min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0038] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 780°C, kept at this temperature for 2.5 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0039] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1040°C, kept at this temperature for 30 min, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0040] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 310°C, kept at this temperature for 2.5 h, and air-cooled to room temperature. This completes one tempering. Repeat this step twice, for a total of three temperings.

[0041] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 55.2HRC, and the average V-mouth Charpy impact energy was 9.3J. Example 4

[0042] 35mm thick H13 steel plate is selected, and the specific heat treatment process is as follows:

[0043] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 800℃, keep it warm for 40min, continue to heat it to 1080℃, keep it warm for 25min, and then take it out of the furnace and air-cool or oil-cool it to ≤100℃;

[0044] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 780°C, kept at this temperature for 2 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0045] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1040°C, kept at this temperature for 30 minutes, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0046] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 300°C, kept at this temperature for 2.5 h, and air-cooled to room temperature. This completes one tempering step. Repeat this step twice, for a total of three tempering steps.

[0047] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 55.8HRC, and the average V-mouth Charpy impact energy was 9.2J. Example 5

[0048] 55mm thick H13 steel plate is selected, and the specific heat treatment process is as follows:

[0049] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 830℃, keep it warm for 50min, continue to heat it to 1095℃, keep it warm for 30min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0050] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 800°C, kept at this temperature for 2.5 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0051] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1050°C, kept at this temperature for 35 minutes, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0052] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 320°C, kept at this temperature for 2 h, and air-cooled to room temperature. This completes one tempering step. Repeat this step twice, for a total of three tempering steps.

[0053] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 53.8HRC, and the average V-mouth Charpy impact energy was 10.2J. Example 6

[0054] Select 60mm thick H13 steel plate, the specific heat treatment process is as follows:

[0055] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 840℃, keep it warm for 50min, continue to heat it to 1095℃, keep it warm for 30min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0056] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 800°C, kept at this temperature for 2 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0057] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1050°C, kept at this temperature for 40 minutes, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0058] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 330°C, kept at this temperature for 2.5 h, and air-cooled to room temperature. This completes one tempering. Repeat this step twice, for a total of three temperings.

[0059] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch and observe the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 53.5HRC, and the average V-mouth Charpy impact energy was 10.5J. Example 7

[0060] Select 65mm thick H13 steel plate, the specific heat treatment process is as follows:

[0061] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 840℃, keep it warm for 1h, continue to heat it to 1100℃, keep it warm for 35min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0062] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 820°C, kept at this temperature for 2.5 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0063] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1060°C, kept at this temperature for 35 minutes, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0064] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 340°C, kept at this temperature for 2 h, and air-cooled to room temperature. This completes one tempering step. Repeat this step twice, for a total of three tempering steps.

[0065] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 52.6HRC, and the average V-mouth Charpy impact energy was 11.0J. Example 8

[0066] 70mm thick H13 steel plate is selected, and the specific heat treatment process is as follows:

[0067] (1) High temperature quenching: Load the H13 steel shear blade blank into the heating furnace, heat it to 850℃, keep it warm for 50min, continue to heat it to 1100℃, keep it warm for 35min, and then cool it to ≤100℃ by air or oil after it is taken out of the furnace;

[0068] (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 820°C, kept at this temperature for 2 hours, and then air-cooled to room temperature to complete the pretreatment process;

[0069] (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace, heated to 1060°C, kept at this temperature for 40 min, and then air-cooled or oil-cooled to ≤100°C after being taken out of the furnace;

[0070] (4) Low-temperature tempering: The H13 steel treated in step (3) is placed in a heating furnace, heated to 350°C, kept at this temperature for 2 h, and air-cooled to room temperature. This completes one tempering step. Repeat this step twice, for a total of three tempering steps.

[0071] After pretreatment and three tempering treatments, samples were taken from the core of the H13 steel plate, and after mechanical grinding and polishing, 4% nitric acid alcohol was used to etch the transverse structure. The structure was uniform and fine, and the carbides were dispersed. The average heat treatment hardness was 52.1HRC, and the average V-mouth Charpy impact energy was 11.7J.

Claims

1. A heat treatment process for improving the toughness of H13 steel for hot rolling shear blades, characterized in that: The thickness of the H13 steel for hot-rolled shear blades is 35 to 70 mm, and the heat treatment process includes four steps: high temperature quenching, high temperature tempering, vacuum quenching, and low temperature tempering. The specific process is as follows: (1) High temperature quenching: Load H13 steel into the heating furnace, heat it to 1080-1100℃, keep it warm for 25-35min, and then cool it with air or oil. (2) High temperature tempering: The H13 steel treated in step (1) is placed in a heating furnace, heated to 780-820°C, kept at this temperature for 2-2.5 hours, and then air-cooled to room temperature. (3) Vacuum quenching: After rough processing, the H13 steel treated in step (2) is placed in a vacuum heating furnace and heated to 1040-1060°C, kept at this temperature for 30-40 minutes, and then air-cooled or oil-cooled after being taken out of the furnace; (4) Low-temperature tempering: The H13 steel treated in step (3) is loaded into a heating furnace and heated to 300-350°C. The temperature is kept for 2-2.5 hours and air-cooled to room temperature. This completes the first tempering. Repeat this step twice. A total of three temperings are performed to complete the heat treatment process.

2. The heat treatment process for improving the toughness of H13 steel for hot rolling shear blades according to claim 1 is characterized in that: The high temperature quenching step also includes heating the H13 steel to 800-850°C with the furnace after loading it into the heating furnace, keeping it warm for 40-60 minutes, and then heating it to 1080-1100°C and keeping it warm.

3. The heat treatment process for improving the toughness of H13 steel for hot rolling shear blades according to claim 2 is characterized in that: In the high temperature quenching step, the furnace is air-cooled or oil-cooled to ≤100°C.

4. The heat treatment process for improving the toughness of H13 steel for hot rolling shear blades according to claim 3 is characterized in that: In the vacuum quenching step, the furnace is cooled by air or oil to ≤100°C.

5. The heat treatment process for improving the toughness of H13 steel for hot rolling shear blades according to any one of claims 1 to 4, characterized in that: The H13 steel produced by the heat treatment process is sampled at the core and processed into a 10mm×10mm×55mm V-notch Charpy impact specimen. The impact energy is ≥9.0J and the hardness is 52-56HRC after testing.

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