Production method of high-strength, high-toughness and corrosion-resistant ship anchor chain steel

Abstract

The invention relates to a production method of high-strength, high-toughness and corrosion-resistant ship anchor chain steel. The steel comprises the following chemical components in percentage by mass: 0.25-0.30% of C; si is equal to 0.10% to 0.30%; mn is equal to 0.80%-1.20%; less than or equal to 0.015% of P; less than or equal to 0.015% of S; the content of Cr is 0.80%-1.20%; ni < = 0.40%; al is equal to 0.030% to 0.050%; b is equal to 0.0006 percent to 0.0020 percent; ti is equal to 0.015 to 0.025 percent; v is equal to 0.010 percent to 0.050 percent; n is less than or equal to 0.0040%, and the balance is Fe and inevitable impurities. Mn is replaced by Cr, so that the hardenability, strength and toughness are guaranteed, and meanwhile, the corrosion resistance of the steel is improved; the hardenability is improved by adding B, the nitrogen is fixed by adding Ti, the effect of B is ensured, grains are refined by adding Nb, and the toughness of the anchor chain steel is improved. Through coordination and optimization of a refining process, the purity of molten steel is improved, a continuous casting process is reasonably designed, segregation of a continuous casting billet is controlled, and performance fluctuation caused by segregation is eliminated; and the toughness of the steel is improved through two quenching processes.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material manufacturing and relates to a method for producing low-cost, high-strength, toughness, and corrosion-resistant ship anchor chain steel. Background Art

[0002] Anchor chain steel is the core material of a ship's anchor chain system and must withstand extreme conditions in the marine environment, including complex alternating loads, seawater corrosion, and biofouling. Traditional anchor chain steels, such as M3 grade steel, have the following problems: Their high carbon content of 0.2% to 0.3% results in insufficient weldability and low-temperature toughness. Especially in larger sizes, the core is difficult to harden through, resulting in insufficient core toughness. Their corrosion resistance relies on the surface coating, which can easily peel off over long-term use, leading to localized corrosion. The alloy design is not optimized for the high-pressure environment of the deep sea, resulting in a short fatigue life. Existing technologies improve strength by adding high amounts of manganese and trace amounts of niobium and vanadium, but this does not address the core toughness and corrosion resistance issues. Chinese patent CN2014104516156 proposes alloying with copper and nickel, but this significantly increases costs.

[0003] Therefore, there is an urgent need to develop a new type of anchor chain steel that has toughness, corrosion resistance and economy. Summary of the Invention

[0004] The present invention aims to provide a low-cost, high-strength, toughness, and corrosion-resistant ship anchor chain steel production method. The performance requirements of the produced steel are as follows: after overall heat treatment, the 1 / 6D and 1 / 2D positions are tested, the tensile strength is ≥720MPa, the elongation is ≥20%, the cross-sectional shrinkage is ≥50%, the impact energy at -20°C is ≥80J; the banded structure is ≤level 2.0, the structure is uniform, and the performance is stable.

[0005] The technical solution of the present invention: A method for producing high-strength, toughness, and corrosion-resistant ship anchor chain steel, wherein the chemical composition of the steel is as follows by weight: C=0.25%-0.30%; Si=0.10%-0.30%; Mn=0.80%-1.20%; P≤0.015%; S≤0.015%; Cr=0.80%-1.20%; Ni≤0.40%; Al=0.030%-0.050%; B=0.0006%-0.0020%; Ti=0.015%-0.025%; V=0.010%-0.050%; N≤0.0040%, with the remainder being Fe and unavoidable impurities. The method comprises the following key process steps: 1) Converter smelting: converter end point C = 0.05% ~ 0.10%, P ≤ 0.015%, tapping temperature 1600 ~ 1630 ℃, Mn alloy, Cr alloy, Al block and top slag are added along the steel flow during tapping, and argon is blown throughout the furnace; 2) LF refining: The total argon blowing time of molten steel in LF is not less than 45 minutes; rapid white slag deoxidation is carried out, with a total slag volume of ≥12kg / t and a white slag holding time of ≥20 minutes; after slagging, aluminum particles are used for diffusion deoxidation, with the amount of aluminum particles used as a diffusion deoxidizer being ≥0.90kg / t; aluminum wire is fed once in the middle of refining to adjust the aluminum content; ferrotitanium, ferroniobium, and ferroboron are added in the later stages of refining; calcium wire is fed for 70-120m for calcification treatment before leaving the station; the soft blowing time after calcium treatment is ≥10min; 3) Continuous casting: Protective pouring is performed throughout the casting process. Slag discharge from large ladles is strictly prohibited. Special protective slag for low-carbon steel is used. Fluctuation of the molten steel in the crystallizer is controlled to be no more than ±6mm, and any excess is removed. The superheat of the molten steel in the tundish is 30-40°C. The electric stirring current of the crystallizer is 200A and the frequency is 3Hz, while the electric stirring current at the end is 400A and the frequency is 3Hz. The casting speed is 0.55m / min, and the secondary cooling water volume is 0.16L / kg. The billet is pressed down from the position where the solidification rate is 97%-99%. The reduction of the five consecutive pressing devices is 4mm / 5mm / 5mm / 4mm / 2mm, respectively, with a total reduction of 20mm. The cross-sectional dimensions of the billet are 350mm×430mm. 4) Rolling: The billet heating time is not less than 200 minutes; the preheating section temperature is ≤700℃, and the time is not less than 60 minutes; the heating section temperature is 1200-1220℃; the soaking section temperature is 1220-1240℃, and the time is not less than 100 minutes; no water cooling is performed during the rolling process to avoid local low temperature of the red steel; the steel is densely arranged on the cooling bed, covered with an insulation cover for slow cooling, and quickly collected and bundled after the cooling bed is off the line, and placed in a slow cooling pit for insulation. The temperature entering the pit is not less than 200℃; 5) Heat treatment: Heat the anchor chain to 850±℃, keep warm for the diameter D (mm)*1min / mm, then cool to room temperature with water; heat again to 760±5℃, keep warm for the anchor chain diameter (mm)×1min / mm, then cool to room temperature with water; heat again to 630±5℃, keep warm for the anchor chain diameter (mm)×1.5min / mm, then cool to room temperature with water.

[0006] The innovative features and beneficial effects of the present invention are as follows: by replacing Mn with Cr, the corrosion resistance of the steel is improved while ensuring hardenability and strength and toughness; by adding B to increase hardenability, adding Ti to fix nitrogen and ensure that B can function, and adding Nb to refine the grains, the toughness of the anchor chain steel is improved. By coordinating and optimizing the refining process, the purity of the molten steel is improved, the continuous casting process is rationally designed, the segregation of the continuous casting billet is controlled, and the performance fluctuations caused by segregation are eliminated; the toughness of the steel is improved through two quenching processes. After the overall heat treatment, the 1 / 6D and 1 / 2D positions are tested, the tensile strength is ≥720MPa, the elongation is ≥20%, the cross-sectional shrinkage is ≥50%, the impact energy at -20℃ is ≥80J; the banded structure is ≤2.0 level, the structure is uniform, and the performance is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is the hot-rolled metallographic structure diagram of the anchor chain steel in Example 1.

[0008] Figure 2 This is the metallographic structure diagram of the anchor chain steel in heat-treated state in Example 1. DETAILED DESCRIPTION Example 1

[0009] A method for producing high-strength, toughness, and corrosion-resistant ship anchor chain steel, wherein the composition by mass percentage is C = 0.27%; Si = 0.20%; Mn = 1.17%; P = 0.010%; S = 0.008%; Cr = 1.12%; Ni = 0.21%; Al = 0.042%; B = 0.0022%; Ti = 0.021%; V = 0.043%; N = 0.0036%, with the balance being Fe and unavoidable impurities. The method comprises the following key process steps: 1) Converter smelting: converter end point C=0.08%, P=0.010%, tapping temperature 1612℃, alloy and top slag are added during tapping, and argon is blown throughout the furnace.

[0010] 2) LF refining: The total argon blowing time of molten steel in LF is 52 minutes; aluminum particles are used for diffusion deoxidation, and the amount of diffusion deoxidizer is ≥0.90kg / t; rapid white slag deoxidation, the total slag volume is ≥12kg / t, and the white slag holding time is ≥20 minutes; after deoxidation, aluminum wire is used to adjust the aluminum content; 100m of calcium wire is fed for calcification treatment before leaving the station; the soft blowing time after calcium treatment is 12 minutes.

[0011] 3) Continuous casting: Protective pouring throughout the entire process, slag discharge from large ladles is strictly prohibited, and special protective slag for low-carbon steel is used; the fluctuation of molten steel in the crystallizer is controlled to be no more than ±6mm, and the excess part is removed; the superheat of molten steel in the tundish is 31-35℃; the electric stirring current of the crystallizer is 200A, the frequency is 3Hz, and the electric stirring current at the end is 400A, the frequency is 3Hz; the casting speed is 0.55m / min, and the secondary cooling water volume is 0.16L / kg; the billet is pressed down from the position where the solidification rate is 98%, and the reduction of 5 consecutive pressing devices is 4mm / 5mm / 5mm / 4mm / 2mm respectively, and the total reduction is controlled to be 20mm; the cross-sectional size of the billet is 350mm×430mm.

[0012] 4) Rolling: Billet heating time: 230 minutes; preheating temperature: 680°C, time: 70 minutes; heating temperature: 1200-1220°C; soaking temperature: 1220-1240°C, time: 120 minutes. No water cooling is used during rolling to avoid localized low temperatures in the red steel. Steel is densely arranged on the cooling bed, covered with an insulation cover for slow cooling. After the cooling bed is removed from the line, the steel is quickly collected and bundled and placed in a slow cooling pit for insulation. The pit temperature is 320°C. The rolling specification is Φ170mm. Example 2

[0013] A method for producing high-strength, toughness, and corrosion-resistant ship anchor chain steel, comprising the following components by mass: C = 0.27%; Si = 0.21%; Mn = 0.94%; P = 0.009%; S = 0.009%; Cr = 1.05%; Ni = 0.02%; Al = 0.044%; B = 0.0015%; Ti = 0.021%; V = 0.046%; N = 0.0032%, with the remainder being Fe and unavoidable impurities. The method includes the following key process steps: 1) Converter smelting: converter end point C=0.09%, P=0.010%, tapping temperature 1622℃, alloy and top slag are added during tapping, and argon is blown throughout the furnace.

[0014] 2) LF refining: The total argon blowing time of molten steel in LF is 52 minutes; aluminum particles are used for diffusion deoxidation, and the amount of diffusion deoxidizer is ≥0.90kg / t; rapid white slag deoxidation, the total slag volume is ≥12kg / t, and the white slag holding time is ≥20 minutes; after deoxidation, aluminum wire is used to adjust the aluminum content; 100m of calcium wire is fed for calcification treatment before leaving the station; the soft blowing time after calcium treatment is 12 minutes.

[0015] 3) Continuous casting: Protective pouring is carried out throughout the entire process. Slag discharge from large ladles is strictly prohibited. Special protective slag for low-carbon steel is used. The fluctuation of the molten steel in the crystallizer is controlled to be no more than ±6mm, and the excess part is removed. The superheat of the molten steel in the middle ladle is 35-36℃. The electric stirring current of the crystallizer is 200A and the frequency is 3Hz. The electric stirring current at the end is 400A and the frequency is 3Hz. The casting speed is 0.55m / min and the secondary cooling water volume is 0.16L / kg. The billet is pressed down from the position where the solidification rate is 98.2%. The reduction of the five consecutive pressing devices is 4mm / 5mm / 5mm / 4mm / 2mm respectively, and the total reduction is controlled to be 20mm. The cross-sectional dimensions of the billet are 350mm×430mm.

[0016] 4) Rolling: Billet heating time: 260 minutes; preheating temperature: 676°C, time: 76 minutes; heating temperature: 1200-1220°C; soaking temperature: 1220-1240°C, time: 142 minutes. No water cooling is used during rolling to avoid localized low temperatures in the red steel. Steel is densely packed on the cooling bed, covered with an insulation cover for slow cooling. After the cooling bed is removed from the line, the steel is quickly collected and bundled, and then placed in a slow cooling pit for insulation. The pit temperature is 250°C. The rolling specification is Φ80mm.

[0017] The hot rolling performance test results of the wire rod produced in the embodiment are shown in Table 1.

[0018] Table 1 Test results of hot rolling properties of wire rods and bolt properties produced in the embodiment .

Claims

1. A method for producing high-strength, toughness, and corrosion-resistant ship anchor chain steel, characterized by: The chemical composition of the steel is as follows: C = 0.25% to 0.30%; Si = 0.10% to 0.30%; Mn = 0.80% to 1.20%; P ≤ 0.015%; S ≤ 0.015%; Cr = 0.80% to 1.20%; Ni ≤ 0.40%; Al = 0.030% to 0.050%; B = 0.0006% to 0.0020%; Ti = 0.015% to 0.025%; V = 0.010% to 0.050%; N ≤ 0.0040%, with the remainder being Fe and unavoidable impurities. The key process steps are as follows: 1) Converter smelting: converter end point C = 0.05% ~ 0.10%, P ≤ 0.015%, tapping temperature 1600 ~ 1630 ℃, Mn alloy, Cr alloy, Al block and top slag are added along the steel flow during tapping, and argon is blown throughout the furnace; 2) LF refining: The total argon blowing time of molten steel in LF is not less than 45 minutes; rapid white slag deoxidation is carried out, with a total slag volume of ≥12kg / t and a white slag holding time of ≥20 minutes; after slagging, aluminum particles are used for diffusion deoxidation, with the amount of aluminum particles used as a diffusion deoxidizer being ≥0.90kg / t; aluminum wire is fed once in the middle of refining to adjust the aluminum content; ferrotitanium, ferroniobium, and ferroboron are added in the later stages of refining; calcium wire is fed for 70-120m for calcification treatment before leaving the station; the soft blowing time after calcium treatment is ≥10min; 3) Continuous casting: Protect the pouring throughout the whole process, and do not allow large slag to be dropped. Use special protective slag for low-carbon steel. The fluctuation of the molten steel in the crystallizer should not exceed ±6mm, and the excess part should be cut off. The superheat of the tundish steel was 30-40°C; the electric stirring current of the crystallizer was 200A and the frequency was 3Hz; the electric stirring current of the end was 400A and the frequency was 3Hz; the casting speed was 0.55m / min, and the secondary cooling water volume was 0.16L / kg; the slab was pressed down from the position where the solidification rate was 97%-99%, and the reduction of the five consecutive pressing devices was 4mm / 5mm / 5mm / 4mm / 2mm respectively, with a total reduction of 20mm; the cross-sectional dimensions of the slab were 350mm×430mm. 4) Rolling: The billet heating time is not less than 200 minutes; the preheating section temperature is ≤700℃, the time is not less than 60 minutes; the heating section temperature is 1200-1220℃; the soaking section temperature is 1220-1240℃, the time is not less than 100 minutes; no water cooling is performed during the rolling process; the steel is densely arranged on the cooling bed, covered with an insulation cover for slow cooling, and quickly collected and bundled after the cooling bed is off the line, and placed in a slow cooling pit for insulation. The temperature entering the pit is not less than 200℃; 5) Heat treatment: Heat the anchor chain to 850±℃, keep warm for the diameter D (mm)*1min / mm, then cool to room temperature with water; heat again to 760±5℃, keep warm for the anchor chain diameter (mm)×1min / mm, then cool to room temperature with water; heat again to 630±5℃, keep warm for the anchor chain diameter (mm)×1.5min / mm, then cool to room temperature with water.

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