Manufacturing method of ultrahigh-strength high-toughness steel

Abstract

The invention relates to a manufacturing method of ultrahigh-strength and high-toughness steel which is used under the condition of high bearing pressure and has ultrahigh strength and high toughness. The ultrahigh-strength and high-toughness steel comprises the following components in percentage by mass: 35%-42% of C, 1.2%-1.9% of Cr, 3.5%-4.5% of Ni, 0.75%-1.2% of Mo, 0.25%-0.45% of V and the balance of iron. Electric arc furnace smelting, vacuum refining and electroslag remelting smelting are carried out; through three-time upsetting and three-time drawing, large and uniform deformation is generated in the steel ingot, the transverse performance of a workpiece is effectively improved, and internal defects of the steel ingot are forged and combined; through normalizing after forging, hydrogen diffusion annealing and tempering, the structure and the grain size are refined; through quenching and graded water cooling, the structure is fully transformed, a fine martensite structure is obtained, uniform and fine tempered sorbite is obtained through tempering, the final mechanical property sigma r0.2 is larger than or equal to 1350 MPa, the impact energy AKV at the temperature of-40 DEG C is larger than or equal to 25 J, and the requirements of products for ultrahigh pressure and light weight are met.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting, forging and heat treatment, and in particular relates to a method for manufacturing ultra-high strength and high toughness steel which is used under high pressure and has ultra-high strength and high toughness. Background Art

[0002] With the increasing pressure requirements for products, as well as the need for lightweight and economical products, the original PCrNi3MoV steel can no longer meet the requirements. It is necessary to develop a new type of steel that has ultra-high strength and high low-temperature toughness, so that the material can obtain better wear resistance; at the same time, due to the high strength of the new steel, the wall thickness of the product is reduced, achieving the purpose of weight reduction, lightweight and economical. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for manufacturing ultra-high strength and high toughness steel that is resistant to high strength and low temperature impact, so as to meet the development needs of products in the direction of ultra-high pressure and lightweight.

[0004] To achieve the above object, the present invention adopts the following technical solutions: A method for manufacturing ultra-high strength and high toughness steel, characterized in that: the material comprises the following components in mass percentage: C%: 35-42, Cr%: 1.2-1.9, Ni%: 3.5-4.5, Mo%: 0.75-1.2%, V%: 0.25-0.45, and the balance is iron; and the manufacturing method adopts electric arc furnace smelting, vacuum refining, electroslag remelting, forging three-upsetting and three-drawing, double normalizing + tempering after forging, rough machining, and performance heat treatment, and the manufacturing process steps are as follows: Step 1), raw material selection includes: first-grade scrap steel or high-quality steel scrap or return steel 100-110kg / t, high-purity pig iron 600-900kg / t, ferromolybdenum 15-20kg / t, added to the electric furnace; Step 2), electric furnace: add 2.0-3.5Kg / t of aluminum cake and 3-5Kg / t of high calcium lime into the electric furnace respectively to ensure that [C]≥0.05% and [P]≤0.003% of the steel produced by the electric furnace; Step 3), refining furnace: strengthen the deoxidation operation of the refining furnace, use 1.0-2.0Kg / t of calcium carbide and 2.0-4.0Kg / t of carbon powder and aluminum powder for deoxidation during slagging; use one of carbon powder, aluminum powder and calcium silicon powder during refining, the dosage is 1-2kg / t, deoxidation is carried out in small batches and multiple batches and the reducing atmosphere is maintained, and the white slag is maintained for ≥20 minutes; Step 4), VD vacuum degassing: maintain the temperature at ≤0.7mbar for ≥20 minutes, add rare earth alloy deoxidizer under vacuum at a rate of 0.1-0.4kg / t for further deoxidation, and perform online hydrogen and oxygen determination after VD to control [H]≤0.8ppm and [O]≤4.0ppm; take glass tube samples to analyze nitrogen content to control [N]≤40ppm; and control residual [Al]≤0.025%; Step 5), ingot casting: the calming time before pouring is ≥5 minutes, and the preheating temperature of the electrode blank mold is ≥30℃ when swinging the mold; the argon filling in the mold and the argon protection pouring at the center injection nozzle are adopted, and each mold is filled with argon for 3-5 minutes, and the pouring temperature is 1525-1535℃; Step 6), electroslag remelting: When electroslag is used, a rare earth deoxidizer is selected according to the mass ratio: MgO:CaO:CaF2:Al2O3=20:16:10:44:10 special pre-melted slag, the average melting rate is controlled at 550-800kg / h, and the shrinkage feeding time is 100-150 minutes; Step 7), heating: the blank is loaded into a trolley type heating furnace, preheated at 800-900°C, and then quickly heated to 1230-1250°C for high temperature diffusion, kept warm for 20-25 hours, cooled to 1200°C and kept warm for 3-5 hours before being taken out of the furnace, so that the blank has uniform composition and structure and good plastic deformation ability; Step 8), forging: forging is carried out by hydraulic press three-upsetting and three-drawing and fine forging machine. During the forging process, the initial forging temperature of the hydraulic press is 900℃~1200℃, and the final forging temperature is 750~950℃; the initial forging temperature of the fine forging machine is 950℃~700℃, and the final forging temperature is ≥700℃; Step 9), preparatory heat treatment after forging: normalizing + hydrogen annealing + tempering, the pretreatment process is as follows: air cooling to 500-600℃ after forging, the purpose is to make the inner and outer surface temperatures of the workpiece tend to be consistent and the surface temperature is higher than the bainite transformation temperature; after air cooling, put into the furnace at 600-650℃ to keep the inner and outer surface temperatures of the workpiece uniform and achieve the purpose of stress relief; heat up to the normalizing temperature of 850-900℃ at 50-80℃ / h, the average temperature is ≥1.5h / 100mm, and the heat preservation is 1.5h / 100mm, the purpose is to fully austenitize the organization and make the organization uniform, air cooling or mist cooling to 280 ~350℃ to form a preparatory structure for hydrogen expansion treatment, in preparation for full hydrogen expansion; heat to 630~690℃ for hydrogen expansion and stress relief tempering, cool to 280~350℃ at ≤50℃ / h and heat to 630~690℃ for average temperature ≥1.5h / 100mm, heat for 2h / 100mm, to achieve the purpose of full transformation of retained austenite; air cool to below 150℃ at ≤40℃ / h to prevent thermal stress caused by fast surface cooling and slow internal cooling of workpiece, which will cause cracking of workpiece, and at the same time obtain a prepared uniform structure, to achieve the purpose of structure refinement and homogenization; Step 10), rough machining: adopt marking + drilling center hole + rough turning outer circle + drilling and boring inner hole + rough turning outer circle forming, the process is as follows: align the workpiece on the marking platform, find the center on both end faces of the workpiece and mark the center circle φ40mm; drill a 20-40mm center hole according to the marking position on the horizontal boring machine; leave 12mm machining allowance to rough turn the outer circle on the semi-finishing lathe, drill and bore the inner hole on the deep hole drilling and boring machine to form, the outlet deviation is ≤3mm; rough turn the outer circle on the semi-finishing lathe to form; Step 11), performance heat treatment adopts quenching + high temperature tempering, and the heat treatment system is as follows: quenching temperature 850 ~ 900 ℃, average temperature ≥ 1.5h / 100mm, insulation 1.5h / 100mm, water cooling, the initial water temperature ≤ 35℃, to enhance the quenching cooling effect; the workpiece water outlet temperature ≤ 80℃, to promote complete transformation of the organization; tempering in time after quenching, tempering temperature 530 ~ 600℃, average temperature ≥ 3h / 100mm, insulation 3h / 100mm, air cooling, to ensure that the material has high strength and good toughness.

[0005] Compared with the prior art, the present invention has the following advantages: the ultra-high strength and high toughness steel produced by the present invention is smelted by electric arc furnace + vacuum refining + electroslag remelting; the inner part of the steel ingot is deformed larger and uniformly by three upsetting and three drawing, which effectively improves the lateral performance of the workpiece and forges the internal defects of the steel ingot; the structure and grain size are further refined by normalizing + hydrogen annealing + tempering after forging; the structure is fully transformed by quenching and graded water cooling to obtain a fine martensite structure, and then a uniform and fine tempered troostite is obtained by tempering, and the final mechanical properties reach σ r0.2 ≥1350MPa, -40℃ impact energy AKV≥25J, meeting the needs of product development towards ultra-high pressure, lightweight and economical. DETAILED DESCRIPTION

[0006] The following examples are detailed descriptions of the present invention. The examples are merely descriptions of the best mode for carrying out the present invention and do not limit the scope of the present invention in any way.

[0007] Example 1: A method for manufacturing ultra-high strength and high toughness steel, the forging specification is Φ390*Φ270*8300, and the manufacturing method is as follows: The chemical composition of the ultra-high strength and high toughness steel is based on PCrNi3MoV, with increased C and Mo, reduced Ni and V, especially controlling relatively low P, S, Si and five harmful elements, improving strength and refining grains to improve low temperature toughness, that is, the material is ѡC%: 35-42, ѡCr%: 1.2-1.9, ѡNi%: 3.5-4.5, ѡMo%: 0.75-1.2%, ѡV%: 0.25-0.45, and the balance is iron; at the same time, a manufacturing method of electric arc furnace smelting, vacuum refining, electroslag remelting, forging three-upsetting and three-drawing, double normalizing + tempering after forging, rough machining, and performance heat treatment is adopted, and the manufacturing process steps are as follows: Step 1), raw material selection includes: first-grade scrap steel or high-quality steel scrap or return steel 100-110kg / t, high-purity pig iron 600-900kg / t, ferromolybdenum 15-20kg / t, added to the electric furnace; Step 2), electric furnace: add 2.0-3.5Kg / t of aluminum cake and 3-5Kg / t of high calcium lime into the electric furnace respectively to ensure that [C]≥0.05% and [P]≤0.003% of the steel produced by the electric furnace; Step 3), refining furnace: strengthen the deoxidation operation of the refining furnace, use 1.0-2.0Kg / t of calcium carbide and 2.0-4.0Kg / t of carbon powder and aluminum powder for deoxidation during slagging; use one of carbon powder, aluminum powder and calcium silicon powder during refining, the dosage is 1-2kg / t, deoxidation is carried out in small batches and multiple batches and the reducing atmosphere is maintained, and the white slag is maintained for ≥20 minutes; the foamy white slag is maintained until steel is tapped; Step 4), VD vacuum degassing: maintain the temperature at ≤0.7mbar for ≥20 minutes, add rare earth alloy deoxidizer under vacuum at a rate of 0.1-0.4kg / t for further deoxidation, and perform online hydrogen and oxygen determination after VD to control [H]≤0.8ppm and [O]≤4.0ppm; take glass tube samples to analyze nitrogen content to control [N]≤40ppm; and control residual [Al]≤0.025%; Step 5), the calming time before pouring is ≥5 minutes, and the preheating temperature of the electrode blank mold is ≥30℃ when swinging the mold. Use argon filling in the mold and argon protection pouring at the center injection nozzle. Each mold is filled with argon for 3 to 5 minutes, and the pouring temperature is 1525-1535℃; Step 6), electroslag remelting: When electroslag is used, a rare earth deoxidizer is selected according to the mass ratio: MgO:CaO:CaF2:Al2O3=20:16:10:44:10 special pre-melted slag, the average melting rate is controlled at 550-800kg / h, and the shrinkage feeding time is 100-150 minutes; Step 7), heating: the blank is loaded into a trolley type heating furnace, preheated at 800-900°C, and then quickly heated to 1230-1250°C for high temperature diffusion, kept warm for 20-25 hours, cooled to 1200°C and kept warm for 3-5 hours before being taken out of the furnace, so that the blank has uniform composition and structure and good plastic deformation ability; Step 8), forging: 5.0T steel ingot is used for forging, and three-upsetting and three-drawing of hydraulic press and forging of fine forging machine are used for forging. The initial forging temperature of hydraulic press is 1200℃~900℃, and the final forging temperature is 750~950℃; the initial forging temperature of fine forging machine is 950℃~700℃, and the final forging temperature is ≥700℃; Step 9), preparatory heat treatment after forging: normalizing + hydrogen annealing + tempering, the pretreatment system process is as follows: air cooling to 550-600℃ after forging, the purpose is to make the inner and outer surface temperatures of the workpiece tend to be consistent and the surface temperature is higher than the bainite transformation temperature; after air cooling, put into the furnace at 600-650℃ to keep the inner and outer surface temperatures of the workpiece uniform and achieve the purpose of stress relief; heat up to the normalizing temperature of 850-900℃ at 50-80℃ / h, the average temperature is ≥1.5h / 100mm, and the heat preservation is 1.5h / 100mm, the purpose is to fully austenitize the organization and make the organization uniform, air cooling or mist cooling to 280 ~350℃ to form a preparatory structure for hydrogen expansion treatment, in preparation for full hydrogen expansion; heat to 630~690℃ for hydrogen expansion and stress relief tempering, cool to 280~350℃ at ≤50℃ / h and heat to 630~690℃ for average temperature ≥1.5h / 100mm, heat for 2h / 100mm, to achieve the purpose of full transformation of retained austenite; air cool to below 150℃ at ≤40℃ / h to prevent thermal stress caused by fast surface cooling and slow internal cooling of workpiece, which will cause cracking of workpiece, and at the same time obtain a prepared uniform structure, to achieve the purpose of structure refinement and homogenization; Step 10), rough machining: adopt marking + drilling center hole + rough turning outer circle + drilling and boring inner hole + rough turning outer circle forming, the process is as follows: align the workpiece on the marking platform, find the center on both end faces of the workpiece and mark the center circle φ40mm; drill a 20-40mm center hole according to the marking position on the horizontal boring machine; leave 12mm machining allowance to rough turn the outer circle on the semi-finishing lathe, drill and bore the inner hole on the deep hole drilling and boring machine, and the outlet deviation is ≤3mm; rough turn the outer circle on the semi-finishing lathe to control the curvature and wall thickness difference of the inner hole; Step 11), performance heat treatment adopts quenching + high temperature tempering, and the heat treatment system is as follows: quenching temperature 850 ~ 900 ℃, average temperature ≥ 1.5h / 100mm, insulation 1.5h / 100mm, water cooling, the initial water temperature ≤ 35℃, strengthen the quenching cooling effect; the workpiece water temperature ≤ 80℃, promote the complete transformation of the organization; tempering in time after quenching, tempering temperature 530 ~ 600℃, average temperature ≥ 3h / 100mm, insulation 3h / 100mm, air cooling, to ensure that the material has high strength and good toughness. After leaving the furnace, tensile and impact specimens are cut at the riser and ingot tail respectively, and the mechanical properties test results are shown in Table 1: Table 1 Mechanical properties test results Ingot No. <![CDATA[σ r0.2 (MPa)]]> σb(MPa) δ5(%) ψ(%) AKV (-40℃) (J) 1 1386 1565 12.0 51 27 2 1360 1564 11 50 31 3 1407 1577 15.0 54 29 4 1427 1577 16.5 56 31 5 1420 1582 13.0 52 29 6 1410 1585 13.0 49 25 7 1371 1545 12.0 53 32 8 1371 1550 14.5 54 33 The mechanical property test results show that the ultra-high strength and high toughness steel produced by the present invention is smelted by electric arc furnace + vacuum refining + electroslag remelting; the inner part of the steel ingot is deformed larger and uniformly by three upsetting and three drawing, which effectively improves the lateral performance of the workpiece and forges the internal defects of the steel ingot; the structure and grain size are further refined by normalizing + hydrogen annealing + tempering after forging; the structure is fully transformed by quenching and graded water cooling to obtain a fine martensite structure, and then a uniform and fine tempered troostite is obtained by tempering, and the final mechanical properties reach σ r0.2 ≥1350MPa, -40℃ impact energy AKV≥25J, meeting the needs of product development towards ultra-high pressure, lightweight and economical.

Claims

1. A method for manufacturing ultra-high strength and high toughness steel, characterized in that: The material includes the following components in mass percentage: C%: 35-42, Cr%: 1.2-1.9, Ni%: 3.5-4.5, Mo%: 0.75-1.2%, V%: 0.25-0.45, and the balance is iron; at the same time, the manufacturing method adopts electric arc furnace smelting, vacuum refining, electroslag remelting, forging three-upsetting and three-drawing, double normalizing + tempering after forging, rough machining, and performance heat treatment, and the manufacturing process steps are as follows: Step 1), raw material selection includes: first-grade scrap steel or high-quality steel scrap or return steel 100-110kg / t, high-purity pig iron 600-900kg / t, ferromolybdenum 15-20kg / t, added to the electric furnace; Step 2), electric furnace: add 2.0-3.5Kg / t of aluminum cake and 3-5Kg / t of high calcium lime into the electric furnace respectively to ensure that [C]≥0.05% and [P]≤0.003% of the steel produced by the electric furnace; Step 3), refining furnace: strengthen the deoxidation operation of the refining furnace, use 1.0-2.0Kg / t of calcium carbide and 2.0-4.0Kg / t of carbon powder and aluminum powder for deoxidation during slagging; use one of carbon powder, aluminum powder and calcium silicon powder during refining, the dosage is 1-2kg / t, deoxidation is carried out in small batches and multiple batches and the reducing atmosphere is maintained, and the white slag is maintained for ≥20 minutes; Step 4), VD vacuum degassing: maintain the temperature at ≤0.7mbar for ≥20 minutes, add rare earth alloy deoxidizer under vacuum at a rate of 0.1-0.4kg / t for further deoxidation, and perform online hydrogen and oxygen determination after VD to control [H]≤0.8ppm and [O]≤4.0ppm; take glass tube samples to analyze nitrogen content to control [N]≤40ppm; and control residual [Al]≤0.025%; Step 5), ingot casting: the calming time before pouring is ≥5 minutes, and the preheating temperature of the electrode blank mold is ≥30℃ when swinging the mold; the argon filling in the mold and the argon protection pouring at the center injection nozzle are adopted, and each mold is filled with argon for 3-5 minutes, and the pouring temperature is 1525-1535℃; Step 6), electroslag remelting: When electroslag is used, a rare earth deoxidizer is selected according to the mass ratio: MgO:CaO:CaF2:Al2O3=20:16:10:44:10 special pre-melted slag, the average melting rate is controlled at 550-800kg / h, and the shrinkage feeding time is 100-150 minutes; Step 7), heating: the blank is loaded into a trolley type heating furnace, preheated at 800-900°C, and then quickly heated to 1230-1250°C for high temperature diffusion, kept warm for 20-25 hours, cooled to 1200°C and kept warm for 3-5 hours before being taken out of the furnace, so that the blank has uniform composition and structure and good plastic deformation ability; Step 8), forging: forging is carried out by hydraulic press three-upsetting and three-drawing and fine forging machine. During the forging process, the initial forging temperature of the hydraulic press is 900℃~1200℃, and the final forging temperature is 750~950℃; the initial forging temperature of the fine forging machine is 950℃~700℃, and the final forging temperature is ≥700℃; Step 9), preparatory heat treatment after forging: normalizing + hydrogen annealing + tempering, the pretreatment process is as follows: air cooling to 500-600℃ after forging, the purpose is to make the inner and outer surface temperatures of the workpiece tend to be consistent and the surface temperature is higher than the bainite transformation temperature; after air cooling, put into the furnace at 600-650℃ to keep the inner and outer surface temperatures of the workpiece uniform and achieve the purpose of stress relief; heat up to the normalizing temperature of 850-900℃ at 50-80℃ / h, the average temperature is ≥1.5h / 100mm, and the heat preservation is 1.5h / 100mm, the purpose is to fully austenitize the organization and make the organization uniform, air cooling or mist cooling to 280 ~350℃ to form a preparatory structure for hydrogen expansion treatment, in preparation for full hydrogen expansion; heat to 630~690℃ for hydrogen expansion and stress relief tempering, cool to 280~350℃ at ≤50℃ / h and heat to 630~690℃ for average temperature ≥1.5h / 100mm, heat for 2h / 100mm, to achieve the purpose of full transformation of retained austenite; air cool to below 150℃ at ≤40℃ / h to prevent thermal stress caused by fast surface cooling and slow internal cooling of workpiece, which will cause cracking of workpiece, and at the same time obtain a prepared uniform structure, to achieve the purpose of structure refinement and homogenization; Step 10), rough machining: adopt marking + drilling center hole + rough turning outer circle + drilling and boring inner hole + rough turning outer circle forming, the process is as follows: align the workpiece on the marking platform, find the center on both end faces of the workpiece and mark the center circle φ40mm; drill a 20-40mm center hole according to the marking position on the horizontal boring machine; leave 12mm machining allowance to rough turn the outer circle on the semi-finishing lathe, drill and bore the inner hole on the deep hole drilling and boring machine to form, the outlet deviation is ≤3mm; rough turn the outer circle on the semi-finishing lathe to form; Step 11), performance heat treatment adopts quenching + high temperature tempering, and the heat treatment system is as follows: quenching temperature 850 ~ 900 ℃, average temperature ≥ 1.5h / 100mm, insulation 1.5h / 100mm, water cooling, the initial water temperature ≤ 35℃, to enhance the quenching cooling effect; the workpiece water outlet temperature ≤ 80℃, to promote complete transformation of the organization; tempering in time after quenching, tempering temperature 530 ~ 600℃, average temperature ≥ 3h / 100mm, insulation 3h / 100mm, air cooling, to ensure that the material has high strength and good toughness.