Production method of extra-thick high-quality hot work die steel H13

Abstract

The invention discloses a production method of extra-thick high-quality hot work die steel H13. The thickness of the steel is 100-200 mm, pre-melting refining slag is adopted for slagging to improve the cleanliness of molten steel, H13 composite slag special for a water-cooling die is adopted for pouring the surface of a steel ingot, no defect exists on the surface of the steel ingot, red loading of the steel ingot is adopted for reducing energy consumption, and the manufacturing period of an extra-thick plate is shortened. By combining steel ingot homogenizing heating, controlled rolling and controlled cooling fine grain and nitrogen atmosphere protection annealing processes, the structure uniformity and surface quality of steel are improved, so that the mechanical property and the service life of a product are improved, steel plate metallographic detection shows that ABCD-grade inclusions are all smaller than or equal to 0.5 grade, a steel plate is low in power and free of segregation, an annealed structure contains a small amount of banded structures, the grain size is 7-9 grade, and the steel plate has high strength. And flaw detection meets the GB / T forge piece third-level standard.

Description

Technical Field

[0001] The invention relates to the technical field of metal material manufacturing, and in particular to a production method of extra-thick high-quality hot working die steel H13. Background Art

[0002] H13 die steel is a high-performance hot working die steel, which is widely used in the fields of hot extrusion, die casting and forging die manufacturing in the automotive, home appliance, electronics and other industries. Its products include modules, bars, flat steel, etc. Compared with flat steel, thick plates have the advantages of convenient cutting and high material utilization rate. However, thick plates produced by existing technologies generally have defects such as low purity, non-density, component segregation, many inclusions, and coarse grains, which lead to poor product performance, short service life of the molds, and early cracking and other failures during the use of the molds.

[0003] For example, Chinese patent CN201410224856 discloses a production process for H13 hot working die steel. By optimizing the electroslag remelting process, forging process and heat treatment process, the electroslag ingot obtained after electroslag remelting is subjected to mold cooling, slow cooling and annealing in sequence to improve the purity and density of the steel and reduce segregation, thereby improving the mechanical properties and service life of the product. However, its production cost is high, the production cycle is long, the energy consumption is high, and the product competitiveness is insufficient.

[0004] For example, Chinese patent CN202210420216 discloses a method for producing good low-quality H13 hot working die steel bars. In the molten steel smelting stage, LF refining + VD vacuum treatment is used to effectively reduce harmful elements such as P, S, Cu, Ni, As, Sb, and Sn in the molten steel; by controlling the heating temperature, the formation of oxide scale on the surface of the steel is reduced, and the surface quality of the steel billet is improved. However, the production process using a round billet continuous casting machine is prone to segregation and cracks, the production rhythm is tight, the refining and slag making is insufficient, the purity of the molten steel is poor, and the gas content is high, which ultimately affects the service life of the bar.

[0005] In view of this, it is urgent to develop a production method for thick high-quality hot working die steel H13 with uniform material, high cleanliness, fine grains, uniform structure and good surface quality. Summary of the invention

[0006] In order to achieve the above technical requirements, the purpose of the present invention is to provide a production method of extra-thick high-quality hot working die steel H13, the produced steel plate has uniform material, high cleanliness, fine grains, uniform structure, good surface quality, and meets the technical requirements for H13 die steel.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a production method of extra-thick high-quality hot working die steel H13, the thickness of the steel is 100-200mm, comprising the following production processes: smelting, water-cooled mold pouring, ingot heating, controlled rolling and controlled cooling, and annealing;

[0008] 1) Smelting: After smelting in a converter, 2.5-5 kg / ton of aluminum particles are added to the molten steel for deoxidation in the first heating stage of refining, and then 10-15 kg / ton of active lime is added to make foamy white slag. In the second heating stage, 20-50 kg / ton of pre-melted refined slag is added according to the color of the slag. At the same time, the argon blowing flow rate of the ladle is controlled at 200-300 NL / min, and large argon blowing and stirring are carried out to make slag. The third heating of refining is used to fine-tune the composition. The white slag is kept for more than 30 minutes. Finally, it enters VD vacuum degassing. The VD vacuum degree is less than 65 pa, and the pressure holding time is ≥18 minutes. The gas content in the molten steel is: [H]≤1.2ppm, [O]≤30ppm, [N]≤50ppm;

[0009] 2) Water-cooled mold casting: The mold casting channel adopts mullite-coated flow steel bricks, and H13 special water-cooled mold casting composite slag is used for casting. Argon gas is introduced into the bottom of the ingot mold to exhaust the air before pouring. A water-cooled ingot mold with a thickness greater than 600mm is used for casting. The pouring temperature is controlled at liquidus +20-30℃, the pouring water volume is controlled at 420-560L / min, and the crystallizer cooling water temperature is controlled between 30-35℃. At the same time, the steel output is controlled at 5-6t / min during pouring to achieve a uniform rise in the steel liquid level. The demoulding is completed 7-8 hours after the casting, and the ingot temperature is 500-700℃ during demoulding;

[0010] It should be noted that mullite-coated bricks are cheaper than 90% high-aluminum flow steel bricks, and the mullite coating on the working layer of the flow steel brick can offset the erosion of the molten steel on the soup channel, reduce the inclusions brought into the molten steel by the erosion of the flow steel brick, and ensure the cleanliness of the molten steel. Secondly, during mold casting, control the superheat, maintain a uniform pouring speed, control the cooling water flow and water temperature, increase the formation of dendritic crystals during the solidification of the ingot, reduce the center segregation, and obtain a dense ingot with very little segregation. With the H13 special water-cooled mold casting composite slag, the surface of the ingot has no defects such as cracks, pores, slag inclusions, etc., which is convenient for hot loading after demolding, which not only reduces energy consumption but also shortens the production cycle.

[0011] 3) Ingot heating: the ingot is transferred to the soaking pit within 30 minutes after demoulding, and kept at 600-700℃ for 4-5 hours for hydrogen expansion treatment, and then the heating rate is ≤50℃ / h, the soaking temperature is 1250±20℃, and the holding time is 0.8-1.5min / mm;

[0012] 4) Controlled rolling and controlled cooling: the rolling temperature is greater than 950℃, the pass reduction is ≥50mm, and the steel is dried when it is rolled to 300-350mm. When the temperature drops to 850-890℃, the secondary rolling begins, in which the pass reduction is 60mm, and the final rolling temperature is greater than 820℃. Then the steel plate enters ACC cooling, the cooling rate is controlled at 15-20℃ / min, and the red-return temperature is controlled between 450-550℃. Finally, it enters the cooling bed for air cooling, and the cooling rate is controlled at 2-10℃ / min. When the temperature of the steel plate is lower than 250℃, it is annealed offline. The steel contains about 8% alloy. If it is directly slowly cooled after the final rolling, the secondary carbides precipitated on the grain boundary are easy to form network and chain carbides, which will affect the impact toughness of the steel plate. However, controlling a reasonable cooling rate can effectively inhibit the precipitation of carbides inside the steel plate, refine the grains, and reduce the formation of internal banded structure.

[0013] 5) Annealing: After the surface is shot blasted, the steel plate is transferred to a nitrogen-based atmosphere normalizing furnace for annealing. The annealing furnace is heated for 20 to 30 minutes. 3 / h flow of nitrogen, heating rate 20 ~ 30 ℃ / h, annealing temperature 850 ~ 880 ℃, holding time 4mm / min, then cooling with the furnace, when the temperature of the steel plate drops to 400 ~ 500 ℃, take it out of the furnace and put it into the slow cooling pit for slow cooling. H13 steel has a long holding time during annealing, and the steel contains a high Si element that is easy to oxidize and decarburize. Therefore, the steel plate is loaded into a nitrogen-based atmosphere normalizing furnace for annealing after surface shot blasting, which reduces the oxidation and decarburization of the steel plate during the annealing process, obtains a bright steel plate surface, and further improves the service life of the mold steel.

[0014] Furthermore, in the refining process, the pre-melted refining slag is a CaO-SiO2-Al2O3-CaF2 slag system, with a particle size of 2-5 mm, a melting point of <1400°C, and components of SiO2≤5%, CaO: 55-65%, Fe2O3≤3%, Al2O3: 33-43%, CaF2: 8-12%, and H2O<0.08%. It should be noted that the pre-melted slag has uniform chemical composition, low melting point, and fast melting speed. When used with active lime, it can quickly form foamy white slag to absorb inclusions. The refining slag has strong fluidity, improves the kinetic conditions of the desulfurization reaction, can achieve deep desulfurization, and is beneficial to improving the quality of molten steel.

[0015] The H13 special water-cooled mold casting composite slag adopts a CaO-SiO2-Al2O3 ternary slag system, with a basicity of 0.3-0.45, a melting point of 1050-1100°C, a viscosity of 1.0-2.0pa.S, a melting speed of 35-45s, an expansion multiple of 3-5, and a composition of SiO2: 30-40%, Al2O3: 3-9%, CaO: 11-21%, MgO≤6.0%, C: 13-19%, S≤0.15%, and H2O≤1.0%.

[0016] The mullite coating flow steel brick has a mullite coating on the surface in contact with molten steel, the coating thickness is 2-3mm, and the aluminum content in the coating is greater than 95%.

[0017] The present invention adopts pre-melting refined slag to improve the cleanliness of molten steel, adopts H13 composite slag specially used for water-cooling mold to cast steel ingot with no surface defects, adopts red filling of steel ingot to reduce energy consumption, shortens the manufacturing cycle of extra-thick plates, combines the steel ingot homogenization heating, controlled rolling and controlled cooling fine grain, and nitrogen atmosphere protection annealing process to improve the uniformity of steel structure and surface quality, thereby improving the mechanical properties and service life of the product. According to the metallographic detection of the steel plate, the ABCD-level inclusions are all ≤0.5 level, the steel plate has no segregation at low magnification, a small amount of banded structure is contained in the annealing structure, the grain size is 7-9 level, and the flaw detection meets the GB / T forging level 3 standard. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear, they will be described in detail below with reference to specific embodiments.

[0019] Embodiment 1:

[0020] The production of a 100 mm thick high-quality H13 hot working die steel plate contains the following chemical components by mass fraction (unit, %): C: 0.38, Si: 1.1, Mn: 0.45, P: 0.14, S: 0.002, V: 1.0, Cr: 4.8, Mo: 1.2, Ni: 0.95, Ti: 0.035, and includes the following processes: smelting, water-cooled mold pouring, ingot heating, controlled rolling and controlled cooling, and annealing.

[0021] 1) Smelting: After KR pre-desulfurization and converter smelting, LF refining begins. During the refining process, 3kg / ton of steel aluminum particles are added for deoxidation in the first heating stage, and then 10kg / ton of steel active lime is added to make gray slag. In the second heating stage, 50kg / ton of steel pre-melting refined slag is added according to the color of the slag. At the same time, the ladle argon blowing flow rate is controlled at 250-300NL / min, and large argon blowing and stirring are carried out to make slag. The third heating of refining is used to fine-tune the composition. The ladle argon blowing flow rate is controlled at 50-100NL / min to meet the H13 composition requirements. The white slag is kept for 35min, and finally enters VD vacuum degassing. The VD vacuum degree is less than 65pa and the pressure is maintained for 20min. The gas content in the steel plate is finally detected: [H] = 0.9ppm, [O] = 25ppm, [N] = 30ppm.

[0022] Among them, the particle size of the pre-melted refined slag is 2-5mm, the melting point is 1380°C, and the composition is SiO2: 4.5%, CaO: 61.3%, Fe2O3: 2.6%, Al2O3: 40.2%, CaF2: 10.6%, H2O: 0.05%.

[0023] 2) Water-cooled mold pouring: The mold casting channel adopts mullite coated flow steel bricks, and H13 special water-cooled mold casting composite slag is used for pouring. Argon gas is introduced into the bottom of the ingot mold to exclude air for 10 minutes before pouring. A 35.2-ton water-cooled ingot mold is used to cast an ingot with a thickness of 640mm. The pouring temperature is controlled at liquidus +25℃, the pouring water volume is controlled at 500L / min, the water temperature of the crystallizer is between 31 and 34℃, the steel output during pouring is controlled at 5 to 6t / min, and the mold is demolded 8 hours after the pouring is completed. The ingot temperature is 690℃ when demolding.

[0024] Among them, the composite slag adopts CaO-SiO2-Al2O3 ternary slag system, with basicity of 0.41, melting point of 1081℃, viscosity of 1.62Pa.S, melting speed of 41s, expansion multiple of 3.86, and composition of Si02: 38.02%, Al203: 6.35%, CaO: 15.61%, MgO: 4.58%, C: 16.32%, S: 0.12%, H2O: 0.85%; mullite coated flow steel brick, the contact surface with molten steel is mullite coating, the coating thickness is 2-3mm, and the aluminum content in the coating is 95.83%.

[0025] 3) Ingot heating: within 30 minutes after demoulding, the ingot is transferred to the soaking pit and the temperature is raised. The temperature is kept between 600 and 700 °C for 4-5 hours. Then the heating rate is 50 °C / h. The soaking temperature in the soaking section is 1250±20 °C and the holding time is 13 hours.

[0026] 4) Controlled rolling and controlled cooling: the starting rolling temperature is 1050℃. After the taper is flattened, the single-pass reduction is 50mm. When the steel is rolled to 300mm, it is dried. When the temperature drops to 890℃, the secondary rolling begins. The reductions of the first three passes are 60mm, 50mm, and 40mm respectively. The final rolling temperature is 840℃. After rolling, the steel plate enters ACC cooling, the cooling rate is controlled at 15-18℃ / min, and the red-return temperature is controlled at 500-550℃. Then it enters the cooling bed for air cooling. During the air cooling stage, the cooling rate of the steel plate is controlled at 2.5-5℃ / min. When the temperature of the steel plate is lower than 250℃, it is annealed off the line.

[0027] 5) Nitrogen-based atmosphere annealing: After the surface of the steel plate is shot blasted and qualified, it is transferred to the nitrogen-based atmosphere normalizing furnace for annealing. 3 / h flow of nitrogen, heating rate of 20 ℃ / h, annealing temperature of 880 ℃, holding time of 400min, then cooling with the furnace, when the temperature of the steel plate drops to 500 ℃, it is taken out of the furnace and hoisted by a crane into a slow cooling pit for slow cooling.

[0028] The steel plate inclusion detection is carried out according to GB / T10561-2005, the banded structure detection is carried out according to GB / T34474.1-2017, the steel plate decarburization layer depth detection is carried out according to GB / T224-2019, and the steel plate is tested according to GB / T6402-2008. The specific physical quality is as follows:

[0029]

[0030] Embodiment 2:

[0031] The production of a 200mm thick high-quality H13 hot working die steel plate contains the following chemical composition by mass fraction (unit, %), C: 0.39, Si: 1.15, Mn: 0.48, P: 0.14, S: 0.001, V: 1.05, Cr: 4.9, Mo: 1.15, Ni: 0.95, Ti: 0.038, including the following processes: smelting, water-cooled mold pouring, ingot heating, controlled rolling and controlled cooling, annealing

[0032] 1) Smelting:

[0033] After KR pre-desulfurization and converter smelting, LF refining begins. During the refining process, 3kg / ton of steel and aluminum particles are added for deoxidation in the first heating stage, and then 10kg / ton of steel active lime is added to make gray slag. In the second heating stage, 50kg / ton of steel pre-melted refined slag is added according to the color of the slag. At the same time, the argon blowing flow rate of the ladle is controlled at 300NL / min, and large argon blowing and stirring are carried out to make slag. The third refining heating is used to fine-tune the composition. The argon blowing flow rate of the steel plate ladle is controlled at 50-100NL / min, and the white slag is kept for 40min. Finally, it enters VD vacuum degassing. After the VD vacuum degree is less than 65pa, the pressure is maintained for 20min. Finally, the gas content in the steel plate is detected: [H]=0.7ppm, [O]=25ppm, [N]=30ppm.

[0034] Among them, the particle size of the pre-melted refined slag is 2-5mm, the melting point is 1380°C, and the composition is SiO2: 4.5%, CaO: 61.3%, Fe2O3: 2.6%, Al2O3: 40.2%, CaF2: 10.6%, H2O: 0.05%.

[0035] 2) Water-cooled mold casting:

[0036] The mold casting channel uses mullite coated flow steel bricks, and H13 special water-cooled mold casting composite slag is used for pouring. Argon gas is introduced into the bottom of the ingot mold to exclude air for 10 minutes before pouring. A 45.2-ton water-cooled ingot mold is used to cast ingots with a thickness of 840mm. The pouring temperature is controlled at liquidus +25℃, the pouring water volume is controlled at 560L / min, the water temperature of the crystallizer is between 31 and 34℃, the steel output during pouring is controlled at 5 to 6t / min, and the mold is demolded 8 hours after the pouring is completed. The ingot temperature is 680℃ when demolding.

[0037] Among them, the composite slag adopts CaO-SiO2-Al2O3 ternary slag system, with basicity of 0.41, melting point of 1081℃, viscosity of 1.62Pa.S, melting speed of 41s, expansion multiple of 3.86, and components of Si02: 38.02%, Al203: 6.35%, CaO: 15.61%, MgO: 4.58%, C: 16.32%, S: 0.12%, H2O: 0.85%; mullite coated flow steel brick, the contact surface with molten steel is mullite coating, the coating thickness is 2 to 3mm, and the aluminum content in the coating is 95.83%.

[0038] 3) Ingot heating:

[0039] The steel ingot is transferred to the soaking pit within 30 minutes after demoulding and starts to heat up. It is kept at 600-700℃ for 4-5 hours, and then the heating rate is 50℃ / h. The soaking temperature in the soaking section is 1250±20℃ and the holding time is 21h.

[0040] 4) Controlled rolling and controlled cooling:

[0041] The starting rolling temperature is 1050℃. After the taper is flattened, the single-pass reduction is 50mm. When the steel is rolled to 350mm, it is dried. When the temperature drops to 890℃, the secondary rolling begins. The first two passes have reductions of 60mm and 50mm, and the final rolling temperature is 840℃. After rolling, the steel plate enters ACC cooling, the cooling rate is controlled at 17-19℃ / min, the red-return temperature is controlled at 500-550℃, and then enters the cooling bed for air cooling. During the air cooling stage, the cooling rate of the steel plate is controlled at 3-6℃ / min, and it is annealed offline when the temperature is lower than 250℃.

[0042] 5) Nitrogen-based atmosphere annealing:

[0043] After the surface of the steel plate is shot blasted and qualified, it is transferred to the nitrogen-based atmosphere normalizing furnace for annealing. 3 / h flow of nitrogen, heating rate of 20℃ / h, annealing temperature of 880℃, holding time of 800min, then cooling with the furnace, when the temperature drops to 500℃, take it out of the furnace and hoist it into the slow cooling pit for slow cooling.

[0044] The steel plate inclusion detection is carried out according to GB / T10561-2005, the banded structure detection is carried out according to GB / T34474.1-2017, the steel plate decarburization layer depth detection is carried out according to GB / T224-2019, and the steel plate is tested according to GB / T6402-2008. The specific physical quality is as follows:

[0045]

[0046] In summary, the extra-thick H13 hot working die steel obtained by this scheme has high molten steel cleanliness, and the ABCD inclusions in metallographic detection are all ≤0.5 level. The ingot red loading technology uses low energy consumption and short production cycle. A reasonable rolling and heat treatment process is adopted, the steel plate has low-magnification and no segregation, the annealing structure contains a small amount of banded structure, the grain size is 7-9, and the flaw detection meets the GB / T forging level 3 standard.

[0047] The present invention described above is a preferred embodiment. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A production method for extra-thick high-quality hot working die steel H13, characterized in that: The thickness of the steel is 100 to 200 mm, and the production process includes the following: smelting, water-cooled mold pouring, ingot heating, controlled rolling and controlled cooling, and annealing; 1) Smelting: After smelting in a converter, 2.5-5 kg / ton of aluminum particles are added to the molten steel for deoxidation in the first heating stage of refining, and then 10-15 kg / ton of active lime is added to make foamy white slag. In the second heating stage, 20-50 kg / ton of pre-melted refined slag is added according to the color of the slag. At the same time, the argon blowing flow rate of the ladle is controlled at 200-300 NL / min, and large argon blowing and stirring are carried out to make slag. The third heating of refining is used to fine-tune the composition. The white slag is kept for more than 30 minutes. Finally, it enters VD vacuum degassing. The VD vacuum degree is less than 65 pa, and the pressure holding time is ≥18 minutes. The gas content in the molten steel is: [H]≤1.2ppm, [O]≤30ppm, [N]≤50ppm; 2) Water-cooled mold casting: The mold casting channel adopts mullite-coated flow steel bricks, and H13 special water-cooled mold casting composite slag is used for casting. Argon gas is introduced into the bottom of the ingot mold to exhaust the air before pouring. A water-cooled ingot mold with a thickness greater than 600mm is used for casting. The pouring temperature is controlled at liquidus +20-30℃, the pouring water volume is controlled at 420-560L / min, and the crystallizer cooling water temperature is controlled between 30-35℃. At the same time, the steel output is controlled at 5-6t / min during pouring to achieve a uniform rise in the steel liquid level. The demoulding is completed 7-8 hours after the casting, and the ingot temperature is 500-700℃ during demoulding; 3) Ingot heating: the ingot is transferred to the soaking pit within 30 minutes after demoulding, and kept at 600-700℃ for 4-5 hours for hydrogen expansion treatment, and then the heating rate is ≤50℃ / h, the soaking temperature is 1250±20℃, and the holding time is 0.8-1.5min / mm; 4) Controlled rolling and controlled cooling: the starting rolling temperature is greater than 950℃, the pass reduction is ≥50mm, and the steel is dried when it is rolled to 300-350mm. When the temperature drops to 850-890℃, the secondary rolling begins, in which the first pass reduction is 60mm, and the final rolling temperature is greater than 820℃. Then the steel plate enters ACC cooling, the cooling rate is controlled at 15-20℃ / min, and the red-return temperature is controlled between 450-550℃. Finally, it enters the cooling bed for air cooling, and the cooling rate is controlled at 2-10℃ / min. When the temperature of the steel plate is lower than 250℃, it is annealed offline; 5) Annealing: After the surface is shot blasted, the steel plate is transferred to a nitrogen-based atmosphere normalizing furnace for annealing. The annealing furnace is heated for 20 to 30 minutes. 3 / h flow of nitrogen, heating rate of 20 ~ 30 ℃ / h, annealing temperature of 850 ~ 880 ℃, holding time of 4mm / min, then cooling with the furnace, when the temperature of the steel plate drops to 400 ~ 500 ℃, take it out of the furnace and put it into the slow cooling pit for slow cooling.

2. The production method of extra thick high quality hot working die steel H13 as claimed in claim 1, characterized in that: In the refining process, the pre-melted refined slag is a CaO-SiO2-Al2O3-CaF2 slag system with a particle size of 2-5 mm, a melting point of <1400°C, and a composition of SiO2≤5%, CaO: 55-65%, Fe2O3≤3%, Al2O3: 33-43%, CaF2: 8-12%, and H2O<0.08%.

3. The production method of extra thick high quality hot working die steel H13 as claimed in claim 1, characterized in that: The H13 special water-cooled mold casting composite slag adopts a CaO-SiO2-Al2O3 ternary slag system, with a basicity of 0.3-0.45, a melting point of 1050-1100°C, a viscosity of 1.0-2.0pa.S, a melting speed of 35-45s, an expansion multiple of 3-5, and a composition of SiO2: 30-40%, Al2O3: 3-9%, CaO: 11-21%, MgO≤6.0%, C: 13-19%, S≤0.15%, and H2O≤1.0%.

4. The method for producing the extra thick high quality hot working die steel H13 as claimed in claim 1, characterized in that: The mullite coating flow steel brick has a mullite coating on the surface in contact with molten steel, the coating thickness is 2-3mm, and the aluminum content in the coating is greater than 95%.

Images