CN114875311A - Large-thickness 420 MPa-grade low-yield-ratio steel for ocean engineering and production method thereof - Google Patents
Large-thickness 420 MPa-grade low-yield-ratio steel for ocean engineering and production method thereof Download PDFInfo
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Abstract
The invention relates to a large-thickness 420 MPa-grade low-yield-ratio steel for ocean engineering and a production method thereof, wherein the thickness of a steel plate is 100-120 mm, the chemical components of the steel in percentage by mass are C =0.06% -0.08%, Si =0.18% -0.35%, Mn =1.50% -1.65%, Cr =0.1% -0.2%, Mo =0.1% -0.15%, Ni =0.20% -0.30%, Nb =0.025% -0.035%, Alt =0.02% -0.03%, Zr =0.01% -0.015%, Cu =0.05% -0.20%, P ≦ 0.013%, S ≦ 0.002%, and the balance of Fe and unavoidable impurities. The large-thickness 420 MPa-grade steel plate produced by the method has the advantages of good strength stability, uniform structure in the thickness direction, good low-temperature toughness and corrosion resistance and the like, the yield strength of the steel plate is 450-500 MPa, the tensile strength is 550-600 MPa, the elongation after fracture is more than or equal to 30%, the impact energy at the thickness of 1/4 and at the temperature of-40 ℃ is more than or equal to 400J, and the yield ratio is less than or equal to 0.83.
Description
Technical Field
The invention relates to the technical field of steel smelting, in particular to large-thickness low-yield-ratio ocean engineering steel with yield strength of 420MPa and a production method thereof.
Background
With the development of oceans from offshore to offshore, offshore equipment such as offshore platforms and offshore wind towers is developing in a large-scale direction, and the quality requirements for steel for oceanographic engineering are gradually improved. In addition to the conventional combination properties of high strength, high toughness, lamellar tear resistance, good weldability and corrosion resistance, the steel for ocean engineering needs to be developed toward light weight and large thickness. At present, 355MPa grade steel for ocean engineering accounts for most of steel for ocean engineering, but a large-thickness and high-strength steel plate for key parts still needs to be developed.
Chinese patent CN111041329B discloses a high-strength high-toughness steel plate for ocean engineering and a production method thereof, wherein the alloy comprises 0.09-0.12% of C, less than or equal to 0.10% of Si, 0.80-1.0% of Mn, less than or equal to 0.010% of P, less than or equal to 0.003% of S, 1.5-2.5% of Ni, 0.50-0.70% of Cr, 0.50-0.60% of Mo, 0.20-0.30% of Cu, 0.040-0.050% of V, 0.01-0.02% of Nb, 0.01-0.02% of Ti, 0.02-0.04% of Al and 0.001-0.002% of B. And (3) quenching and tempering by adopting a roller-hearth quenching machine and a roller-hearth tempering furnace to prepare the steel plate with the yield strength not lower than 890 MPa. The steel can be used for components such as pile legs, cantilever beams and the like of an ocean platform, but the welding property of the steel plate is reduced due to the fact that the component design adopts a high C element. In addition, the production of the steel plate also needs heat preservation treatment at 600 ℃, and the production process is complex.
Chinese patent CN108998726B discloses a thick 420 MPa-grade low-yield-ratio low-temperature bridge steel and a production method thereof, wherein the alloy comprises 0.05-0.06% of C, 0.20-0.30% of Si, 1.50-1.60% of Mn, less than or equal to 0.012% of P, less than or equal to 0.005% of S, 0.10-0.20% of Ni, 0.15-0.20% of Cr, 0.025-0.035% of Nb, 0.025-0.050% of Al, 0.030-0.040% of V and 0.01-0.02% of Ti. The steel is designed by adopting low-carbon components, so that the steel plate has good welding performance and low-temperature toughness, but the steel does not contain Cu and Mo elements, and the corrosion resistance of the steel plate is low. In addition, the steel plate after rolling control and cooling control needs to be heated to 480-550 ℃ again for tempering treatment, and the production process is complex.
Chinese patent CN109136752B discloses a 420MPa grade steel for a marine atmospheric corrosion resistant bridge with a low yield ratio and a production method thereof, wherein the alloy comprises 0.04-0.20% of C, 0.15-0.45% of Si, 0.85-1.80% of Mn, 0.015-0.050% of Alt, 2.50-4.75% of Ni, 0.20-0.60% of Cu, 0.020-0.080% of Nb, 0.015-0.036% of Ti, 0.0020-0.0050% of Ca, less than or equal to 0.020% of P, less than or equal to 0.020% of S and less than or equal to 0.004% of N. The steel plate with high strength and excellent marine atmosphere corrosion resistance is obtained by adopting component design, inclusion control, controlled rolling, cooling and heat treatment. However, the steel grade needs to be subjected to two-stage rough rolling and single-stage finish rolling, and the cooled steel plate needs to be heated to 350-500 ℃ for tempering treatment. In addition, the thickness of the steel plate is 10-40 mm, and the thickness of the plate is thin.
The above patents all relate to low-alloy high-strength corrosion-resistant steel for ocean engineering, the main alloy components are alloy elements such as Mn, Cr, Ni + V + Ti, etc., part of the steel types relate to Cu elements, although the strength of the steel plate can be improved by increasing the content of C elements, and the addition of Cu elements ensures that the steel plate has good ocean atmosphere corrosion resistance, but has adverse effect on the weldability of the steel plate. In the aspect of production process, the low-temperature impact toughness of the steel plate is improved through tempering treatment after rolling, and the production process is relatively complex. In addition, the thickness of the steel plate of the invention is less than 100mm, and the uniformity of the structure and performance of the steel plate is difficult to realize after the thickness exceeds 100 mm.
Disclosure of Invention
The invention aims to solve the problems that the existing steel grade is low in strength grade and the thickness specification cannot meet the current ocean engineering development requirements, and provides ocean engineering steel with large thickness of 420MPa and low yield ratio and a production method thereof, so that ocean engineering steel with the thickness of 100-120 mm, the strength of more than 420MPa and good low-temperature toughness can be obtained.
The technical scheme of the invention is as follows:
the steel plate is 100-120 mm thick, the chemical components of the steel in percentage by mass are C =0.06% -0.08%, Si =0.18% -0.35%, Mn =1.50% -1.65%, Cr =0.1% -0.2%, Mo =0.1% -0.15%, Ni =0.20% -0.30%, Nb =0.025% -0.035%, Alt =0.02% -0.03%, Zr =0.01% -0.015%, Cu =0.05% -0.20%, P is less than or equal to 0.013%, S is less than or equal to 0.002%, and the balance is Fe and inevitable impurities; the process comprises the following steps:
1) smelting and continuous casting: after desulfurization treatment, molten iron is subjected to converter smelting, LF refining and RH vacuum treatment and then is continuously cast into a blank, the sulfur content after desulfurization treatment of the molten iron is controlled to be less than or equal to 0.002%, P is controlled to be less than or equal to 0.013% by adopting a double-slag method in a converter, desulfurization and deoxidation are carried out by adopting white slag in LF refining, the vacuum degree of RH vacuum treatment is less than or equal to 3.0mbar, the vacuum holding time is more than or equal to 15min, calcium treatment is carried out after vacuum treatment is finished, then the static stirring time is more than or equal to 12min, and the superheat degree of a tundish is controlled to be 10-15 ℃ in continuous casting.
2) Heating: the heating temperature 1180-1200 ℃ is realized when the plate blank is heated.
3) Rolling: the slab rolling is divided into two stages of rough rolling and finish rolling, the initial rolling temperature of the rough rolling is more than or equal to 1100 ℃, the rolling is carried out for 4-5 times, and the final reduction rate of the two times is more than or equal to 20%. The initial rolling temperature of the finish rolling stage is 800-850 ℃, the pass reduction rate is 4% -7% after 5-7 passes of rolling, and the final rolling temperature is more than or equal to 730 ℃.
4) And (3) controlling cooling: and cooling by adopting a laminar cooling mode after rolling, wherein the cooling speed is 10-15 ℃/s, the water inlet temperature is 550-700 ℃, and the red returning temperature is 300-500 ℃.
5) Quenching and tempering: and (3) after rolling, quenching and tempering the steel plate, wherein the quenching temperature is 900-950 ℃, the tempering temperature is 550-650 ℃, and cooling is carried out in a laminar flow mode after heat preservation.
The steel plate produced by the method has a dual-phase structure consisting of bainite and a small amount of ferrite, and the thickness of the steel plate is 100-120 mm. The yield strength is 450-500 MPa, the tensile strength is 550-600 MPa, the elongation is more than 30%, the impact energy at the thickness of 1/4 and the temperature of-40 ℃ is 400-430J, and the yield ratio is less than or equal to 0.83.
Compared with the prior art, the invention has the following advantages:
(1) in the aspect of component design, the yield ratio of the steel plate is reduced by reducing the content of C element, and meanwhile, a small amount of Nb + Zr element is added for micro-alloying, so that the microstructure of the steel plate is refined, and the steel plate is ensured to have good strength, low-temperature toughness and weldability. By adding Cr and Cu elements, the marine atmosphere corrosion resistance of the steel plate is improved.
(2) In the process, the reduction rate of the last two passes in the rough rolling stage is more than or equal to 20 percent so as to ensure that the rolling force can permeate the core of the blank, refine the core structure and realize the homogenization of the structure in the thickness direction of the steel plate. And (3) quenching and tempering the steel plate after controlled rolling and cooling to obtain a bainite and ferrite dual-phase structure, and regulating the proportion of soft-phase ferrite and hard-phase bainite by controlling the technological parameters of rolling, cooling and quenching and tempering so as to control the strength and plasticity of the steel plate.
Drawings
FIG. 1 shows the texture of tempered samples 1/4 of 100mm thick 420MPa grade steel plate of example 1.
FIG. 2 shows the texture of the tempered test piece 1/4 of the 120mm thick 420MPa grade steel plate of example 2.
Detailed Description
The technical solution of the present invention is further described below with reference to specific examples.
Example 1:
the steel plate for 420MPa grade ocean engineering is produced, the thickness of the steel plate is 100mm, the chemical components and the mass percentage content are shown in the table 1, and the balance is Fe and inevitable impurities. The method comprises the working procedures of smelting, continuous casting, heating, rolling, quenching and tempering, and comprises the following specific process steps:
(1) smelting and continuous casting: the sulfur content of the molten iron after desulfurization treatment is 0.0015%, the phosphorus content of the converter is controlled to be 0.010% by adopting a double-slag method, the LF refining is desulfurized and deoxidized by adopting white slag operation, the vacuum degree of RH vacuum treatment is 3.0mbar, the vacuum holding time is 30min, calcium treatment is carried out after the vacuum is finished, static stirring is carried out after the calcium treatment is finished, the static stirring is carried out for 15min, and the superheat degree of a tundish in continuous casting is controlled to be 10 ℃.
(2) Heating: after continuous casting into a blank, heating a continuous casting billet with the thickness of 300mm for soaking time of 130min, wherein the in-furnace time is 520min, and the tapping temperature is 1200 ℃.
(3) Rolling: the method adopts two stages of rolling of rough rolling and finish rolling, wherein the initial rolling temperature of the rough rolling is 1100 ℃, the final rolling temperature is 1010 ℃, and the reduction ratios of the last two passes of the rough rolling stage are 20% and 21%. The initial rolling temperature in the finish rolling stage is 840 ℃, the final rolling temperature is 740 ℃, and the pass reduction rates are 7%, 6%, 5% and 5% in sequence.
(4) Controlling: and cooling by adopting a laminar cooling mode after rolling is finished. The temperature of the entering water is 650 ℃, and the temperature of the red returning is 400 ℃.
(5) Quenching and tempering: the quenching temperature is 900 ℃, the heat preservation time is 24min, the cooling is carried out in a laminar flow mode after the heat preservation is finished, the cooling speed is 13 ℃/s, and the cooling is carried out to the room temperature; tempering temperature is 550 ℃, heating rate is 2.5min/mm, heat preservation time is 28min, and air cooling is carried out to room temperature.
In the embodiment, the metallographic structure of the steel plate 1/4 for ocean engineering with the thickness of 100mm and the thickness of 420MPa is shown in FIG. 1, and the structure is bainite and a small amount of quasi-polygonal ferrite as shown in FIG. 1; the tensile properties are shown in Table 2, and the impact energy at-40 ℃ is shown in Table 3.
Example 2:
the steel plate for 420MPa grade ocean engineering is produced, the thickness of the steel plate is 120mm, the chemical components and the mass percentage content are shown in table 1, and the balance is Fe and inevitable impurities. The method comprises the working procedures of smelting, continuous casting, heating, rolling, quenching and tempering, and comprises the following specific process steps:
(1) smelting and continuous casting: the sulfur content of the molten iron after desulfurization treatment is 0.001%, the phosphorus content of the converter is controlled to be 0.012% by adopting a double-slag method, the LF refining is desulfurized and deoxidized by adopting white slag operation, the vacuum degree of RH vacuum treatment is 3.5mbar, the vacuum holding time is 50min, calcium treatment is carried out after the vacuum is finished, static stirring is carried out for 20min after the calcium treatment is finished, and the superheat degree of a tundish in continuous casting is controlled to be 15 ℃.
(2) Heating: after continuous casting into a blank, heating a continuous casting billet with the thickness of 300mm, soaking for 150min, the in-furnace time for 550min, and the tapping temperature for 1190 ℃.
(3) Rolling: the method adopts two stages of rolling of rough rolling and finish rolling, wherein the initial rolling temperature of the rough rolling is 1150 ℃, the final rolling temperature is 1050 ℃, and the reduction ratios of the last two passes of the rough rolling stage are 22% and 20%. The initial rolling temperature in the finish rolling stage is 850 ℃, the final rolling temperature is 730 ℃, and the pass reduction rates are 7%, 5% and 4% in sequence.
(4) And (3) controlling cooling: and cooling by adopting a laminar cooling mode after rolling is finished. The temperature of the entering water is 680 ℃, and the temperature of the red returning is 450 ℃.
(5) Quenching and tempering: the quenching temperature is 950 ℃, and the heat preservation time is 29 min; the tempering temperature is 600 ℃, the heating rate is 2.8min/mm, the heat preservation time is 23min, and the laminar flow mode is adopted for cooling after the heat preservation is finished, wherein the cooling speed is 14 ℃/s.
In the embodiment, the metallographic structure of the steel plate 1/4 for ocean engineering with the thickness of 120mm and the thickness of 420MPa is shown in FIG. 2, and the structure is bainite and a small amount of quasi-polygonal ferrite as shown in FIG. 2; the tensile properties are shown in Table 2, and the impact energy at-40 ℃ is shown in Table 3.
Table 1 main chemical composition (wt.%) of the example steels
TABLE 2 tensile properties of samples after thermal refining in examples
TABLE 3 Low temperature impact properties of samples after thermal refining in examples
Claims (1)
1. The large-thickness low-yield-ratio ocean engineering steel with the yield strength of 420MPa and the production method thereof are provided, the thickness of the steel plate is 100-120 mm, and the steel plate is characterized in that: the steel comprises the following chemical components, by mass, 0.06-0.08% of C, 0.18-0.35% of Si, 1.50-1.65% of Mn, 0.1-0.2% of Cr, 0.1-0.15% of Mo, 0.20-0.30% of Ni, 0.025-0.035% of Nb, 0.02-0.03% of Alt, 0.01-0.015% of Zr, 0.05-0.20% of Cu, less than or equal to 0.013% of P, less than or equal to 0.002% of S, and the balance of Fe and inevitable impurities; the process comprises the following steps:
1) smelting and continuous casting: after desulfurization treatment, molten iron is subjected to converter smelting, LF refining and RH vacuum treatment and then is continuously cast into a blank, the sulfur content after desulfurization treatment of the molten iron is controlled to be less than or equal to 0.002%, P is controlled to be less than or equal to 0.013% by adopting a double-slag method in a converter, desulfurization and deoxidation are carried out by adopting white slag in LF refining, the vacuum degree of RH vacuum treatment is less than or equal to 3.0mbar, the vacuum holding time is more than or equal to 15min, calcium treatment is carried out after vacuum treatment is finished, then the static stirring time is more than or equal to 12min, and the superheat degree of a tundish in continuous casting is controlled to be 10-15 ℃;
2) heating: heating the plate blank at 1180-1200 ℃;
3) rolling: the slab rolling is divided into two stages of rough rolling and finish rolling, wherein the initial rolling temperature of the rough rolling is more than or equal to 1100 ℃, the rolling is carried out for 4-5 times, and the final reduction rate of the two times is more than or equal to 20%;
the initial rolling temperature of the finish rolling stage is 800-850 ℃, the pass reduction rate is 4% -7% after 5-7 passes of rolling, and the final rolling temperature is more than or equal to 730 ℃;
4) and (3) controlling cooling: cooling by adopting a laminar cooling mode after rolling, wherein the cooling speed is 10-15 ℃/s, the water inlet temperature is 550-700 ℃, and the red returning temperature is 300-500 ℃;
5) quenching and tempering: and (3) after rolling, quenching and tempering the steel plate, wherein the quenching temperature is 900-950 ℃, the tempering temperature is 550-650 ℃, and cooling is carried out in a laminar flow mode after heat preservation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210445643.1A CN114875311B (en) | 2022-04-26 | 2022-04-26 | Large-thickness 420 MPa-level low-yield-ratio steel for ocean engineering and production method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210445643.1A CN114875311B (en) | 2022-04-26 | 2022-04-26 | Large-thickness 420 MPa-level low-yield-ratio steel for ocean engineering and production method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN114875311A true CN114875311A (en) | 2022-08-09 |
| CN114875311B CN114875311B (en) | 2023-05-26 |
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| CN117701999A (en) * | 2024-02-06 | 2024-03-15 | 北京科技大学 | Thick high-toughness ocean engineering structural steel and preparation method thereof |
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| CN117701999B (en) * | 2024-02-06 | 2024-04-30 | 北京科技大学 | Thick high-toughness ocean engineering structural steel and preparation method thereof |
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