Production method of large-thickness high-Ni steel plate formed by continuous casting billets

Abstract

The invention discloses a method for producing a large-thickness high-Ni steel plate from a continuous casting billet. The thickness of the continuous casting billet is 350-450 mm, and the thickness of the steel plate is 100-150 m; in the VD vacuum treatment process, large and small argon treatment is adopted in sequence; after vacuum breaking, soft blowing is conducted for 8-12 min, and the argon flow is 20-50 NL / min; the pulling speed in the continuous casting process is 0.55-0.75 m / min, and the water inlet and outlet temperature difference of a crystallizer is controlled to be 5-7 DEG C; the blank is subjected to mechanical grinding treatment; rough rolling with large rolling reduction is adopted for rolling, and the rolling reduction of the last three passes is 35-45 mm; the quenching temperature is 830-890 DEG C, and the tempering temperature is 590-630 DEG C. According to the steel plate produced through the technology, the flaw detection SA578 C-grade qualification rate of the steel plate reaches 98% or above, the delivery state and die welding state yield strength is 360-420 MPa, the tensile strength is 490-530 MPa, the impact absorption energy at the temperature of-100 DEG C is larger than or equal to 120 J, the surface quality of the steel plate is good, and the surface grinding rate is smaller than or equal to 5%.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a method for producing a thick high-Ni steel plate formed by continuous casting. Background Art

[0002] As a strong austenite-forming element, Ni can significantly expand the austenite phase of steel, stabilize the austenite structure, inhibit the transformation of austenite to brittle phase, and reduce the segregation of harmful elements such as P and S at the grain boundary, refine the grains, and significantly improve the low-temperature impact toughness of the steel plate. When the Ni content reaches about 3.5%, it still has good low-temperature impact toughness and high strength at -100℃. It is a key material for manufacturing ultra-low temperature equipment and is widely used in low-temperature washing towers, concentration towers and other equipment.

[0003] Traditionally, the production of thick high-Ni steel plates mostly adopts die casting process, which has problems such as low yield rate, high energy consumption and high production cost. In addition, when producing thick 3.5Ni steel plates with existing technology, defects such as surface cracks and excessive iron oxide scale are prone to occur, which affects the surface quality and delivery of the steel plates.

[0004] The continuous casting process has the advantages of high yield rate, low energy consumption and high production efficiency, and has gradually become the mainstream technology for the production of thick high-Ni steel plates. However, when producing thick 3.5Ni steel plates, the continuous casting process faces technical difficulties such as surface cracks and center segregation of the ingot, which need to be solved by optimizing continuous casting parameters, improving heating and rolling processes, etc. With the rapid development of the petrochemical, chemical and energy industries, the demand for ultra-low temperature equipment continues to increase, and the market demand for thick high-Ni steel plates is growing. However, the low-temperature toughness and strength requirements of thick steel plates are higher. The chemical composition, rolling temperature and heat treatment process need to be strictly controlled during the production process to ensure the mechanical properties and surface quality of the steel plates. Summary of the invention

[0005] The present invention aims to provide a method for producing a thick high-Ni steel plate made of continuous casting billet, wherein the thickness of the continuous casting billet is 350-450 mm, and the thickness of the steel plate is 100-150 mm; the qualified rate of SA578 C grade of the steel plate flaw detection reaches more than 98%, the yield strength in the delivery state and the mold welding state is 360-420 MPa, the tensile strength is 490-530 MPa, the impact absorption energy at -100°C is ≥120 J, the surface quality of the steel plate is good, and the surface grinding rate is ≤5%.

[0006] The technical solution adopted by the present invention is:

[0007] A production method of large-thickness high-Ni steel plates from continuous casting billets. The chemical composition of the steel plates by mass percentage is C = 0.05% - 0.09%, Si = 0.15% - 0.40%, Mn = 0.50% - 0.70%, Ni = 3.4 - 3.6%, Cr + Mo + Cu ≤ 0.5%, and the rest is Fe and unavoidable impurities; the thickness of the continuous casting billet is 350 - 450 mm, and the thickness of the steel plate is 100 - 150 mm; the qualification rate of the steel plate flaw detection by SA578 Class C reaches over 98%, the yield strength in the delivered state and the die-welded state is 360 - 420 MPa, the tensile strength is 490 - 530 MPa, and the impact energy absorption at -100 °C is ≥ 120 J; the key process steps include:

[0008] 1) Smelting and casting: VD vacuum treatment, the high-vacuum holding time is 15 - 18 min. For the first 10 - 13 min, large argon gas is used with a flow rate of 400 - 500 NL / min, and then small argon gas is used with a flow rate of 100 - 150 NL / min; after breaking the vacuum, soft blowing is carried out for 8 - 12 min with an argon gas flow rate of 20 - 50 NL / min; during the continuous casting process, the drawing speed is 0.55 - 0.75 m / min, and the temperature difference between the inlet and outlet water of the mold is controlled at 5 - 7 °C;

[0009] 2) Rolling: Before rolling, the billet is mechanically ground; the rolling adopts rough rolling with large reduction, and the reduction in the last 3 passes is 35 - 45 mm;

[0010] 3) Heat treatment: The quenching temperature is 830 - 890 °C, the holding time is 100 - 200 min, the roller speed of the quenching machine is 0.01 - 0.05 m / s, the tempering temperature is 590 - 630 °C, and the holding time is 120 - 230 min.

[0011] Beneficial effects of the present invention: The present invention successfully solves the technical difficulties in the production of thick high-Ni steel plates from continuous casting billets by optimizing the continuous casting process and improving the heating and rolling parameters. During the vacuum treatment process, the argon flow rate and blowing time are strictly controlled, and the soft blowing time is strictly controlled after breaking the air, which can ensure that the inclusions fully float up during the vacuum process and improve the purity of the molten steel; during the continuous casting process, a low pulling speed is adopted and the temperature difference between the inlet and outlet water of the crystallizer is controlled, which can reduce the internal segregation of the ingot and the surface cracks of the billet; during the rolling process, a large reduction rolling process is adopted to refine the grains and provide a tissue reserve for the low-temperature impact toughness of the steel plate; the heat treatment adopts a quenching + return process to ensure the expected microstructure and the mechanical properties of the steel plate. The thickness of the steel plate continuous casting billet obtained is 350-450mm, and the thickness of the steel plate is 100-150mm; the SA578 C grade qualified rate of the steel plate is more than 98%, the yield strength of the delivery state and the mold welding state is 360-420MPa, the tensile strength is 490-530MPa, the impact absorption energy at -100℃ is ≥120J, the surface quality of the steel plate is good, and the surface grinding rate is ≤5%. The method of the present invention not only improves the yield rate and surface quality of the steel plate, but also significantly reduces the production cost, providing high-quality material support for the manufacture of ultra-low temperature equipment. DETAILED DESCRIPTION

[0012] The present invention will be further described below in conjunction with specific embodiments.

[0013] Embodiment 1:

[0014] The method for producing a thick high-Ni steel plate made of continuous casting billet has a thickness of 100 mm and is rolled from a 350 mm thick continuous casting billet. The chemical composition of the steel plate is C=0.05%, Si=0.15%, Mn=0.50%, Ni=3.4%, Cr+Mo+Cu=0.1%. The key process steps include:

[0015] 1) Smelting and pouring: During the VD vacuum treatment process, the high vacuum insulation time is 15 minutes, and a large amount of argon gas with a flow rate of 400NL / min is used for the first 10 minutes, and a small amount of argon gas with a flow rate of 100NL / min is used afterwards; after breaking the vacuum, soft blowing is performed for 8 minutes, and the argon gas flow rate is 20NL / min. The slag interface fluctuates, but no molten steel is exposed; during the continuous casting process, the pulling speed is 0.55m / min, and the temperature difference between the inlet and outlet water of the crystallizer is controlled to be 5°C;

[0016] 2) Rolling: The billet is mechanically ground before rolling; the rolling adopts rough rolling with large reduction, and the reduction of the last three passes is 35mm;

[0017] 3) Heat treatment: quenching temperature 830℃, holding time 100min, quenching machine roller speed 0.05m / s, tempering temperature 630℃, holding time 120min.

[0018] Embodiment 2:

[0019] Production method of large-thickness high-Ni steel plate from continuous casting billet. The thickness of the steel plate is 150 mm, and it is rolled from a 450-mm-thick continuous casting billet. The chemical composition of the steel plate is by mass percentage: C = 0.09%, Si = 0.40%, Mn = 0.70%, Ni = 3.6%, Cr + Mo + Cu = 0.5%. The key process steps include:

[0020] 1) Smelting and casting: During the VD vacuum treatment process, the high-vacuum holding time is 18 min. For the first 13 min, large argon gas is used with a flow rate of 500 NL / min, and then small argon gas is used with a flow rate of 150 NL / min. After breaking the vacuum, soft blowing is carried out for 12 min with an argon gas flow rate of 50 NL / min. The steel slag interface fluctuates, but there is no exposure of the molten steel. During the continuous casting process, the drawing speed is 0.75 m / min, and the temperature difference between the inlet and outlet water of the mold is controlled at 7 °C;

[0021] 2) Rolling: Before rolling, the billet is mechanically ground. The rolling adopts large reduction rolling in rough rolling, and the reduction in the last 3 passes is 45 mm;

[0022] 3) Heat treatment: The quenching temperature is 890 °C, the holding time is 200 min, the roller speed of the quenching machine is 0.01 m / s, the tempering temperature is 590 °C, and the holding time is 230 min.

[0023] Example 3:

[0024] Production method of large-thickness high-Ni steel plate from continuous casting billet. The thickness of the steel plate is 120 mm, and it is rolled from a 450-mm-thick continuous casting billet. The chemical composition of the steel plate is by mass percentage: C = 0.06%, Si = 0.31%, Mn = 0.62%, Ni = 3.51%, Cr + Mo + Cu = 0.2%. The key process steps include:

[0025] 1) Smelting and casting: During the VD vacuum treatment process, the high-vacuum holding time is 16 min. For the first 12 min, large argon gas is used with a flow rate of 450 NL / min, and then small argon gas is used with a flow rate of 120 NL / min. After breaking the vacuum, soft blowing is carried out for 10 min with an argon gas flow rate of 43 NL / min. The steel slag interface fluctuates, but there is no exposure of the molten steel. During the continuous casting process, the drawing speed is 0.60 m / min, and the temperature difference between the inlet and outlet water of the mold is controlled at 6 °C;

[0026] 2) Rolling: Before rolling, the billet is mechanically ground. The rolling adopts large reduction rolling in rough rolling, and the reduction in the last 3 passes is 41 mm;

[0027] 3) Heat treatment: The quenching temperature is 860 °C, the holding time is 150 min, the roller speed of the quenching machine is 0.04 m / s, the tempering temperature is 610 °C, and the holding time is 210 min.

[0028] Example 4:

[0029] Production method of large-thickness high-Ni steel plate from continuous casting billet. The thickness of the steel plate is 110 mm, and it is rolled from a 350-mm-thick continuous casting billet. The chemical composition of the steel plate is, by mass percentage, C = 0.07%, Si = 0.35%, Mn = 0.67%, Ni = 3.49%, and Cr + Mo + Cu = 0.4%. The key process steps include:

[0030] 1) Smelting and casting: During the VD vacuum treatment, the high-vacuum holding time is 17 min. For the first 10 min, large-flow argon is used with a flow rate of 410 NL / min, and then small-flow argon is used with a flow rate of 130 NL / min. After breaking the vacuum, soft blowing is carried out for 11 min with an argon flow rate of 27 NL / min. The steel slag interface fluctuates, but there is no exposure of the molten steel. During the continuous casting process, the drawing speed is 0.74 m / min, and the temperature difference between the inlet and outlet water of the mold is controlled at 5°C.

[0031] 2) Rolling: Before rolling, the billet is mechanically ground. The rolling adopts large reduction in rough rolling, and the reduction in the last 3 passes is 37 mm.

[0032] 3) Heat treatment: The quenching temperature is 840°C, the holding time is 130 min, the roller speed of the quenching machine is 0.03 m / s, the tempering temperature is 620°C, and the holding time is 200 min.

[0033] Example 5:

[0034] Production method of large-thickness high-Ni steel plate from continuous casting billet. The thickness of the steel plate is 105 mm, and it is rolled from a 350-mm-thick continuous casting billet. The chemical composition of the steel plate is, by mass percentage, C = 0.07%, Si = 0.39%, Mn = 0.59%, Ni = 3.53%, and Cr + Mo + Cu = 0.3%. The key process steps include:

[0035] 1) Smelting and casting: During the VD vacuum treatment, the high-vacuum holding time is 17 min. For the first 11 min, large-flow argon is used with a flow rate of 490 NL / min, and then small-flow argon is used with a flow rate of 140 NL / min. After breaking the vacuum, soft blowing is carried out for 11 min with an argon flow rate of 32 NL / min. The steel slag interface fluctuates, but there is no exposure of the molten steel. During the continuous casting process, the drawing speed is 0.57 m / min, and the temperature difference between the inlet and outlet water of the mold is controlled at 7°C.

[0036] 2) Rolling: Before rolling, the billet is mechanically ground. The rolling adopts large reduction in rough rolling, and the reduction in the last 3 passes is 43 mm.

[0037] 3) Heat treatment: The quenching temperature is 870°C, the holding time is 180 min, the roller speed of the quenching machine is 0.05 m / s, the tempering temperature is 620°C, and the holding time is 200 min.

[0038] The detection results of the qualified rate of flaw detection, mechanical properties and surface quality of the steel plate in the embodiment are shown in Table 1, where the die welding process is 610±10°C and the heat preservation time is 450-480 min.

[0039] Table 1 Detection Results of Surface Quality and Mechanical Properties of the Steel Plate in the Embodiment

[0040]

[0041] The execution standard for the steel plate produced in the above embodiments is ASME SA203 / SA203M-2023. The internal quality of the steel plate is good. The qualified rate of flaw detection of the steel plate at SA578 Class C reaches more than 98%. The yield strength in the as-delivered state and the die welding state is 360-420 MPa, the tensile strength is 490-530 MPa, the impact energy absorption at -100°C is ≥120 J, the surface quality of the steel plate is good, and the surface grinding rate is ≤5%.

Claims

1. A production method for large-thickness high-Ni steel plates made from continuous casting billets, characterized in that: The mass percentages of the chemical composition of the steel plate are as follows: C = 0.05% - 0.09%, Si = 0.15% - 0.40%, Mn = 0.50% - 0.70%, Ni = 3.4 - 3.6%, Cr + Mo + Cu ≤ 0.5%, and the rest are Fe and inevitable impurities; the thickness of the continuous casting billet is 350 - 450 mm, and the thickness of the steel plate is 100 - 150 mm; the qualified rate of TI level in the steel plate flaw detection according to NB / T 47013.3 - 2023 reaches more than 98%. The yield strength in the delivered state and the die-welded state is 360 - 420 MPa, the tensile strength is 490 - 530 MPa, and the impact absorption energy at -100 °C is ≥ 120 J; The key process steps include: 1) Smelting and pouring: VD vacuum treatment, the high-vacuum holding time is 15 - 18 min. In the first 10 - 13 min, large argon gas is used with a flow rate of 400 - 500 NL / min, and then small argon gas is used with a flow rate of 100 - 150 NL / min; after breaking the vacuum, soft blowing is carried out for 8 - 12 min with an argon gas flow rate of 20 - 50 NL / min; during the continuous casting process, the drawing speed is 0.55 - 0.75 m / min, and the temperature difference between the inlet and outlet water of the mold is controlled at 5 - 7 °C; 2) Rolling: Before rolling, the billet is mechanically ground; rolling is carried out with large reduction in rough rolling, and the reduction in the last 3 passes is 35 - 45 mm; 3) Heat treatment: The quenching temperature is 830 - 890 °C, the holding time is 100 - 200 min, the roller speed of the quenching machine is 0.01 - 0.05 m / s, the tempering temperature is 590 - 630 °C, and the holding time is 120 - 230 min.

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