A large thickness 460mpa grade high toughness steel plate for marine engineering and a production method thereof

Abstract

The application discloses a kind of big thickness 460Mpa level high toughness marine engineering steel plate and production method thereof, alloy component mass percentage of steel plate is C=0.03%~0.06%, Si=0.10%~0.35%, Mn=1.20%~1.50%, P≤0.008%, S≤0.002%, Al=0.02%~0.05%, Nb=0.02%~0.05%, Ti=0.008%~0.02%, Ni=0.30%~0.55%, B≤0.0005%, the rest is Fe and inevitable impurity.Production procedure includes smelting casting, heating rolling and cooling, steel plate thickness ≥800mm, the microstructure of the special thick steel plate produced is acicular ferrite+mainly pearlite;The yield strength of steel plate core is ≥460MPa, tensile strength is ≥560MPa, total elongation is ≥21%, the impact energy of core-40 DEG C is >200J, CTOD value of steel plate base material-30 DEG C is ≥0.70mm, CTOD value of welding joint-30 DEG C is ≥0.38mm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel production, and relates to a 460Mpa-grade green low-carbon-emission high-toughness marine engineering steel plate and a production method thereof. TECHNICAL BACKGROUND

[0002] The marine engineering environment is relatively complex and harsh, and the performance requirements of marine engineering steel are much higher than those of other steel grades. In addition to the conventional strength, plasticity and weldability, the marine engineering steel also needs to have high low-temperature impact toughness and CTOD performance. With the development of the international society's exploitation of polar resources and the large-scale development of marine engineering, the thickness of the marine engineering steel plate gradually increases. The existing super-thick (≥80mm) marine engineering steel plate mainly uses medium and high carbon alloy components, and the CE and Pcm are relatively high, so the welding performance of the steel plate is poor. There is serious segregation in the core of the steel plate, which leads to large fluctuation of the low-temperature impact energy and CTOD performance of the core. In addition, the super-thick marine engineering steel plate is mostly treated offline by quenching and tempering process, the production cycle is long, the carbon emission is relatively large, and the manufacturing process is not environmentally friendly. SUMMARY

[0003] The purpose of the application is to provide a large-thickness 460Mpa-grade high-toughness marine engineering steel plate and a production method thereof, which adopts a green low-carbon-emission production process to meet the demand for good matching of strength and toughness of the marine engineering steel at the present stage.

[0004] The technical scheme of the application is as follows:

[0005] A large-thickness 460Mpa-grade high-toughness marine engineering steel plate, the alloy component mass percentage of the steel plate is C=0.03%~0.06%, Si=0.10%~0.35%, Mn=1.20%~1.50%, P≤0.008%, S≤0.002%, Al=0.02%~0.05%, Nb=0.02%~0.05%, Ti=0.008%~0.02%, Ni=0.30%~0.55%, B≤0.0005%, and the rest is Fe and inevitable impurities; the microstructure of the steel plate is acicular ferrite+pearlite group; the yield strength of the core of the super-thick steel plate is ≥460MPa, the tensile strength is ≥560MPa, the total elongation is ≥21%, the impact energy of the core at-40℃ is >200J, the CTOD value of the steel plate base material at-30℃ is ≥0.70mm, and the CTOD value of the welded joint at-30℃ is ≥0.38mm.

[0006] A production method of a large-thickness 460Mpa-grade high-toughness marine engineering steel plate, the key process steps include:

[0007] 1) Smelting and casting: pure steel smelting combined with low-temperature casting homogenization technology: oxygen converter steelmaking-LF refining-RH refining-continuous casting, steelmaking process H≤1.5ppm, gas N≤60ppm, continuous casting billet cross-section thickness≥300mm, casting superheat≤6℃, dynamic light reduction combined with heavy reduction, reduction≥12mm, slab low-power center segregation Mannesmann 1.0 level within;

[0008] 2) Heating, rolling and cooling: low-temperature burning combined with large-angle grain boundary rolling process, heating furnace temperature≤1150℃, rolling: two-stage rolling process, rough rolling stage opening temperature is 950-1030℃, finishing rolling opening temperature is 800-820℃, finishing temperature is 760-800℃, after rolling, ACC laminar flow accelerated cooling is used, final cooling red temperature is 400-460℃, cold bed air cooling to room temperature.

[0009] The innovation points of the present application are: (1) using ultra-low C, low Mn and Nb micro-alloying composition design, improving the weldability of the steel plate, reducing the influence of C, Mn elements on the toughness and CTOD performance of the center segregation of the thick steel plate; (2) optimizing the heating, rolling and cooling process parameters of the thick≥80mm marine engineering steel plate, controlling the formation of large-angle grain boundaries and acicular ferrite structure, and improving the low-temperature toughness of the steel plate.

[0010] The beneficial effects of the present application are: using a green low-carbon emission production process to produce≥80mm thick marine engineering steel plate, the microstructure of the steel plate is mainly acicular ferrite and pearlite. The Ceq of the steel plate is≤0.34%, and the Pcm is≤0.15%. The yield strength of the thick steel plate at the center is≥460MPa, the tensile strength is≥560MPa, the total elongation is≥21%, the impact energy at the center-40℃ is>200J, the CTOD value of the steel plate base material at-30℃ is≥0.70mm, and the CTOD value of the welded joint at-30℃ is≥0.38mm. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 The microstructure morphology of the 80mm thick 460Mpa grade steel plate of Example 1 at the 1 / 2 position of the plate thickness;

[0012] Figure 2 The microstructure morphology of the 100mm thick 460Mpa grade steel plate of Example 2 at the 1 / 2 position of the plate thickness. DETAILED DESCRIPTION

[0013] The present application will be further described in detail below in combination with the drawings and specific examples.

[0014] Example 1

[0015] The production of a 460Mpa grade green low-carbon emission high-toughness steel plate for marine engineering, the thickness of the steel plate is 80mm, the chemical composition in weight percentage and the carbon equivalent percentage can be seen in Table 1. The production process includes smelting and casting, heating, rolling and controlled cooling processes, the key process steps and parameters are as follows:

[0016] (1) Smelting and casting: oxygen converter steelmaking-LF refining-VD refining-continuous casting, H content 1.0ppm, gas N content 43ppm, continuous casting billet section thickness 350mm, slab low center segregation Mannesmann 1.0 level;

[0017] (2) Heating, rolling and cooling: two-stage rolling is adopted, the rough rolling opening temperature is 980℃, the finish rolling opening temperature is 810℃, water cooling after rolling, the red temperature is 430℃;

[0018] The microstructure of the steel plate produced in this embodiment at 1 / 2 thickness can be seen in Figure 1 , it can be known from Figure 1 that the structure is acicular ferrite and pearlite structure, and the mechanical property indexes can be seen in Table 2.

[0019] Example 2

[0020] The production of a 460Mpa grade green low-carbon emission high-toughness steel plate for marine engineering, the thickness of the steel plate is 100mm, the chemical composition in weight percentage and the carbon equivalent percentage can be seen in Table 1. The production process includes smelting and casting, heating, rolling and controlled cooling processes, the key process steps and parameters are as follows:

[0021] (1) Smelting and casting: oxygen converter steelmaking-LF refining-VD refining-continuous casting, H content 0.9ppm, gas N content 40ppm, continuous casting billet section thickness 350mm, slab low center segregation Mannesmann 1.0 level;

[0022] (2) Heating, rolling and cooling: two-stage rolling is adopted, the rough rolling opening temperature is 980℃, the finish rolling opening temperature is 822℃, water cooling after rolling, the red temperature is 418℃;

[0023] The microstructure of the steel plate produced in this embodiment at 1 / 2 thickness can be seen in Figure 2 , it can be known from Figure 2 that the structure is acicular ferrite and pearlite structure, and the mechanical property indexes can be seen in Table 2.

[0024] Table 1 Chemical composition of 460MPa grade steel plate for marine engineering produced in the example (%)

[0025]

[0026] Table 2 Mechanical property test results of the steel plate after heat treatment in the example

[0027]

Claims

1. A method for producing a thick 460MPa grade high-toughness marine engineering steel plate, characterized in that: The alloy composition of the steel plate, by mass percentage, is C = 0.03%~0.06%, Si = 0.10%~0.35%, Mn = 1.20%~1.50%, P ≤ 0.008%, S ≤ 0.002%, Al = 0.02%~0.05%, Nb = 0.02%~0.05%, Ti = 0.008%~0.02%, Ni = 0.30%~0.55%, B ≤ 0.0005%, with the remainder being Fe and unavoidable impurities. The steel plate thickness is 100mm, and the microstructure consists of acicular ferrite + pearlite. The yield strength of the core of the extra-thick steel plate is ≥ 460MPa, the tensile strength is ≥ 560MPa, the total elongation is ≥ 21%, the impact energy of the core at -40℃ is > 200J, and the CTOD value of the base material at -30℃ is ≥ 0.70mm, CTOD value of welded joint at -30℃ ≥ 0.38mm; Key process steps include: 1) Smelting and casting: Pure steel smelting combined with low-temperature casting homogenization technology is adopted: oxygen converter steelmaking - LF refining - RH refining - continuous casting. During the steelmaking process, H ≤ 1.5ppm, gas N ≤ 60ppm, continuous casting billet cross-sectional thickness ≥ 300mm, casting superheat ≤ 6℃, dynamic light reduction combined with heavy reduction, reduction ≥ 12mm, slab low magnification center segregation Mannesmann grade within 1.0; 2) Heating, rolling and cooling: Low-temperature steel burning combined with large-angle grain boundary rolling process, heating furnace temperature ≤ 1150℃, rolling: adopting a two-stage rolling process, roughing stage initial rolling temperature is 950~1030℃, finishing stage initial rolling temperature is 800~820℃, finishing stage final rolling temperature is 760~800℃, after rolling, ACC laminar flow accelerated cooling is adopted, the reddening temperature is 400~460℃, and the cooling bed is air-cooled to room temperature.

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