Production method of extra-thick 500MPa-grade high-toughness ocean engineering steel

Abstract

The invention discloses a production method of extra-thick 500MPa-grade high-toughness steel for ocean engineering. The steel comprises the following chemical components in percentage by mass: 0.01%-0.029% of C, 0.15%-0.20% of Si, 1.20%-1.50% of Mn, less than or equal to 0.010% of P, less than or equal to 0.003% of S, 0.02%-0.15% of Mo, 0.02%-0.05% of Nb, 0.01%-0.03% of Ti, 0.01%-0.03% of V, 0.15%-0.2% of Cr, 0.3%-0.5% of Ni, 0.25%-0.55% of Cu and the balance of Fe and inevitable impurities. On the basis of extremely low carbon equivalent, Cu precipitation, NbTi carbide and other microalloying component design are supplemented, and TMCP technological parameters are strictly controlled; the thickness structure of the steel plate mainly comprises equiaxed ferrite, pearlite, acicular ferrite and bainite. At the 1 / 4 thickness position, the yield strength is larger than or equal to 450 MPa, the tensile strength is larger than or equal to 550 MPa, the ductility is larger than or equal to 20%, and the impact energy is gt at And the high-strength and high-toughness welding wire has good obdurability and welding performance, and the requirements of ocean engineering equipment are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-alloy high-strength steel production, and relates to a production method of high-strength, high and low-temperature toughness steel plates applicable to marine environments, with a maximum thickness of up to 120 mm. Background Art

[0002] The key technologies and equipment in the marine field are continuously empowering the construction of the modern marine industrial system, and the marine economy shows a strong development trend. The high-end transformation and upgrading of traditional industries such as marine engineering equipment and offshore wind power are imperative. Existing marine engineering steels such as EH36 / EH40 grades have a relatively low yield strength, generally ≤ 460 MPa, and it is difficult to meet the requirements of large-scale and lightweight structures such as deep-sea platforms and submarine pipelines. There is an urgent need to develop marine engineering steels with higher thickness specifications and more excellent strength and toughness. In addition, for traditional thick plates > 80 mm, the rolling reduction ratio at the center is relatively low, and there are serious center segregations in the rolled steel plates, resulting in low low-temperature toughness at the center and problems such as welding cold cracks, which greatly limit the application of high-strength and tough extra-thick steel plates. Summary of the Invention

[0003] The present invention aims to provide a super-thick high-strength marine engineering steel with high strength, high and low-temperature toughness and its production method, to solve the problem that it is difficult to coordinate strength-toughness-weldability for existing marine steels when the thickness ≥ 80 mm, and to produce marine engineering steels with a thickness of 80 - 120 mm, a yield strength of not less than 450 MPa, a tensile strength of not less than 550 MPa, an elongation of not less than 20%, and an impact energy at -40 °C of not less than 300 J.

[0004] The technical solution of the present invention: A production method of a super-thick 500 MPa grade high-strength and tough marine engineering steel, the mass percentage composition of the chemical components of the steel is C = 0.01% - 0.029%, Si = 0.15% - 0.20%, Mn = 1.20% - 1.50%, P ≤ 0.010%, S ≤ 0.003%, Mo = 0.02% - 0.15%, Nb = 0.02% - 0.05%, Ti = 0.01% - 0.03%, V = 0.01% - 0.03%, Cr = 0.15% - 0.2%, Ni = 0.3% - 0.5%, Cu = 0.25% - 0.55%, and the rest is Fe and inevitable impurities, Ceq ≤ 0.35%, Pcm ≤ 0.15%; the microstructure of the steel plate is mainly equiaxed ferrite, pearlite, acicular ferrite and bainite, the yield strength ≥ 450 MPa, the tensile strength ≥ 550 MPa, the elongation ≥ 20%, the impact energy at -40 °C > 300 J, the CTOD value of the steel plate base metal at -30 °C ≥ 0.70 mm, and the CTOD value of the welded joint at -30 °C ≥ 0.38 mm; the key process steps include: Smelting and casting: Oxygen converter steelmaking - LF refining - RH vacuum degassing - continuous casting. During the steelmaking process, the content of H is controlled ≤ 1.5 ppm, the content of gas N is ≤ 50 ppm, the cross-sectional thickness of the continuous casting billet is ≥ 350 mm, the casting superheat is ≤ 10 °C, and dynamic soft reduction is combined with heavy reduction, with a reduction amount ≥ 12 mm. The center segregation of the slab macrostructure is within the Mannesmann level 1.0. Heating, rolling and cooling: The heating furnace temperature is ≤ 1150 °C. The two-stage rolling process is adopted. The starting rolling temperature in the rough rolling stage is 950 - 1030 °C, the starting rolling temperature in the finish rolling stage is 780 - 820 °C, and the final rolling temperature is 750 - 780 °C. After rolling, ACC laminar accelerated cooling is used, and the final cooling return red temperature is 400 - 440 °C. The hot bed is air-cooled to room temperature.

[0005] The present invention uses extremely low carbon copper microalloying to produce extra-thick high-strength offshore engineering steel with a thickness of 80 - 120 mm, high strength, and high and low temperature toughness. Its beneficial effects are as follows: Based on an extremely low carbon equivalent, supplemented by the design of microalloying components such as Cu precipitation and NbTi carbides, the TMCP process parameters are strictly controlled. The thickness structure of the steel plate is mainly composed of equiaxed ferrite, pearlite, acicular ferrite, and bainite. At the 1 / 4 thickness position, the yield strength ≥ 450 MPa, the tensile strength ≥ 550 MPa, the elongation ≥ 20%, the impact energy at -40 °C > 300 J, and it has good strength and toughness and welding performance to meet the requirements of offshore engineering equipment. Description of the drawings

[0006] Figure 1 、 Figure 2 、 Figure 3 They are respectively the optical micrographs of the surface, 1 / 4 position, and core of the extra-thick plate obtained in Example 1.

[0007] Figure 4 、 Figure 5 、 Figure 6 They are respectively the distribution maps and sizes of the precipitation phases on the surface, 1 / 4 position, and core of the extra-thick plate obtained in Example 1. Detailed implementation manners

[0008] The technical solutions of the present invention are further described below in combination with examples and comparative steels. The data of yield strength, tensile strength, uniform elongation, yield ratio, and elongation after fracture are obtained by room temperature tensile testing according to the national standard "GB / T 228.1-2021 Metallic materials - Tensile testing", and the Charpy impact energy at -40 °C is obtained by testing under low temperature conditions according to the national standard "GB / T 229-2020 Metallic materials - Charpy pendulum impact test method".

[0009] Example 1 Production of high-strength and tough steel for ocean engineering. The chemical composition of the steel in mass percentage is: C = 0.02%, Si = 0.2%, Mn = 1.5%, Mo = 0.02%, Cu = 0.35%, Nb = 0.026%, V = 0.015%, Ti = 0.015%, Cr = 0.17%, Ni = 0.30%. Key process steps: heating temperature 1140°C, holding time 200 min, slab thickness 420 mm, rough rolling temperature 1120°C, intermediate slab thickness 180 mm, finish rolling final rolling temperature 810°C, water cooling to 500°C, recrystallization temperature 420°C, finished product thickness 90 mm. Finally, at 1 / 4 thickness, a microstructure of 76% ferrite, 10% pearlite and 14% bainite is obtained, and the width of ferrite grains is 5.9 μm.

[0010] Results: Using the above preparation method, the finished product has a thickness of 90 mm, a yield strength of 451 MPa, a tensile strength of 566 MPa, an elongation of 28%, and an impact energy of 333 J at -40°C at 1 / 4 thickness.

[0011] Example 2 Production of high-strength and tough steel for ocean engineering. The chemical composition of the steel in mass percentage is: C = 0.02%, Si = 0.17%, Mn = 1.4%, Mo = 0.10%, Cu = 0.25%, Nb = 0.03%, V = 0.015%, Ti = 0.015%, Cr = 0.2%, Ni = 0.40%. Key process steps: heating temperature 1200°C, holding time 300 min, slab thickness 400 mm, rough rolling temperature 1110°C, intermediate slab thickness 150 mm, finish rolling final rolling temperature 780°C, water cooling to 550°C, recrystallization temperature 480°C, finished product thickness 100 mm. Finally, at 1 / 4 thickness, a microstructure of 71% ferrite, 5% pearlite and 24% bainite is obtained, and the width of ferrite grains is 8.4 μm.

[0012] Results: Using the above preparation method, the finished product has a thickness of 100 mm, a yield strength of 468 MPa, a tensile strength of 601 MPa, an elongation of 21%, and an impact energy of 302 J at -40°C at 1 / 4 thickness.

Claims

1. A method for producing extra-thick 500MPa grade high-strength and tough marine engineering steel, characterized in that: The chemical composition of steel is C= 0.01%~0.029%, Si= 0.15%~0.20%, Mn=1.20%~1.50%, P ≤0.010%, S ≤0.003%, Mo=0.02%~0.15%, Nb=0.02%~0.05%, Ti= 0.01%~0.03%, V=0.01%~0.03%, Cr= 0.15%~0.2%, Ni=0.3%~0.5%, Cu=0.25%~0.55%, the rest is Fe and unavoidable impurities, Ceq≤ 0.35%, Pcm≤0.15%; produce 80~120mm steel plates, the steel structure is mainly equiaxed ferrite, pearlite, acicular ferrite and bainite, yield strength ≥450MPa, tensile strength ≥550MPa, elongation ≥20%, -40℃ impact energy>300J, -30℃ steel plate parent material CTOD value ≥ 0.70mm, -30℃ welded joint CTOD value ≥ 0.38mm; The key process steps include: Smelting and casting: oxygen converter steelmaking - LF refining - RH vacuum degassing - continuous casting, steelmaking process control H ≤ 1.5ppm, gas N ≤ 50ppm, continuous casting billet section thickness ≥ 350mm, casting superheat ≤ 10℃, dynamic light pressure combined with heavy pressure, pressure reduction ≥ 12mm, slab low multiple center segregation Mannesmann 1.0 level or less; Heating, rolling and cooling: The heating furnace temperature is ≤ 1150℃, and a two-stage rolling process is adopted. The starting rolling temperature of the rough rolling stage is 950~1030℃, the starting rolling temperature of the finishing rolling is 780~820℃, and the final rolling temperature is 750~780℃; after rolling, ACC laminar flow accelerated cooling is adopted, the final cooling temperature is 400~440℃, and the cooling bed is air-cooled to room temperature.

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