CN116377335A - A large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab and its production method - Google Patents

Abstract

A large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab and its production method belong to the field of metallurgy technology, and its chemical composition and mass content are C: 0.07-0.11%, Si: 0.22-0.26%, Mn: 0.65-0.70 %, P≤0.015%, S≤0.003%, Cr: 1.30～1.50%, Mo: 0.17～0.19%, Al: 0.80～1.00%, Ni≤0.10%, Cu≤0.10%, O≤8ppm, N≤50ppm , H≤1.2ppm, the balance is Fe and unavoidable impurities. Its production method includes BOF converter, LF refining, VD vacuum treatment, and continuous casting process; before entering VD, first pour slag, and then add aluminum ingots at 8.0-10.0kg/t to carry out vacuum degassing treatment. The high-aluminum steel continuous casting slab produced by the invention has a maximum diameter of 600mm and good performance.

Description

A large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab and its production method

technical field

The invention belongs to the technical field of metallurgy, and in particular relates to a continuous casting slab of large-scale seawater corrosion-resistant high-alumina steel and a production method thereof.

Background technique

Adding aluminum as an alloying element to steel can refine grains and improve the toughness of steel at low temperatures. In high aluminum steel, the Al element can form a dense Al ₂ O ₃ film between the substrate surface and the air. At the same time, the Al dissolved in the substrate will increase the electrode potential of the substrate and greatly improve the corrosion resistance of the steel. The steel has excellent characteristics such as corrosion resistance, wear resistance, heat resistance, low magnetic permeability, high precision size after treatment, high strength, low quality, and good ductility. It is widely used in ships, military industries, aerospace, and machinery manufacturing. , automobiles, chemicals and other fields.

Studies have shown that microalloying elements such as Cr, Mo, and Al in high-aluminum steel 10CrMoAl can be enriched on the surface of the rust layer to protect the matrix. At the same time, 10CrMoAl contains a variety of Al and Mo compounds, which can also It plays the role of isolating the substrate from the corrosive environment. A layer of firm and dense chromium oxide can be formed on the surface of high-aluminum steel 10CrMoAl, which plays a role in protecting the material. At the same time, most of the Cr in 10CrMoAl steel is well dissolved in the matrix, which can significantly increase the electrode potential of the steel and reduce the electrochemical corrosion caused by different electrode potentials, thereby increasing the seawater corrosion resistance of 10CrMoAl steel.

Due to the high content of Al in 10CrMoAl steel, it is far beyond the scope of conventional deoxidation and grain refinement, resulting in the characteristics of high viscosity and poor fluidity of molten steel, and the chemical properties of Al are active, and it is easy to react with oxygen and nitrogen in the air. reaction. There are several difficulties in the production process: 1. Oxidation reaction is easy to occur, and Al2O3 inclusions and AlN inclusions are generated, which leads to blockage of the nozzle in the continuous casting process. 2. Due to the high Al content, it is easy to denature the mold powder, which affects the surface and internal quality of the continuous casting slab, and has higher requirements on the composition and performance of the mold powder. 3. Al has a low melting point, small specific gravity, easy oxidation, and difficult addition, resulting in unstable yield and difficult component control. If the method of adjusting the Al content is inappropriate, not only will the aluminum loss be large and the production cost will be increased, but also the reaction product will be deposited in the nozzle, causing flocculation in the continuous casting process, and even the interruption of casting.

At present, the patent CN105463299A has been published, and the electric furnace is used as the primary smelting furnace to produce high-quality high-aluminum steel, and aluminum blocks are added in the VD process to adjust the Al content. The use of electric furnaces for production requires high power consumption, large electrode consumption, and tight production rhythms, resulting in a certain waste of resources. In the VD process, the aluminum block is added through the void, and the yield of Al fluctuates greatly. At the same time, the added aluminum block reacts with SiO ₂ in the refining slag to form Al ₂ O ₃ . , the Al ₂ O ₃ generated by the reaction is easy to cause continuous casting flocculation in the continuous casting process, which affects product quality and production smoothness.

Contents of the invention

In order to solve the above technical problems, the present invention provides a large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab and its production method, which can ensure higher purity of molten steel, higher aluminum yield and lower temperature in the VD process loss, the produced high-aluminum steel continuous casting slabs with a diameter of up to 600mm have good performance.

For realizing above-mentioned purpose of the invention, the technical scheme that the present invention adopts is:

A large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab, the chemical composition and mass percentage of which are C: 0.07-0.11%, Si: 0.22-0.26%, Mn: 0.65-0.70%, P≤0.015%, S ≤0.003%, Cr: 1.30～1.50%, Mo: 0.17～0.19%, Al: 0.80～1.00%, Ni≤0.10%, Cu≤0.10%, O≤8ppm, N≤50ppm, H≤1.2ppm, balance It is Fe and unavoidable impurities; the diameter of the continuous casting slab is 500-600mm.

The production method of the above-mentioned large-scale seawater corrosion-resistant high-aluminum steel continuous casting billet includes BOF converter, LF refining, VD vacuum treatment, and continuous casting process;

(1) BOF converter process: steel slag is left in the converter after the previous smelting is completed, nitrogen is blown from the bottom to splash the slag to protect the furnace, the converter is blown for 3 to 5 minutes to pour out the early slag, and the slag is added for secondary slag smelting. Slag is prohibited in the steel process to ensure that the LF refining is in place and the P content is ≤0.012%, and the aluminum wire is fed after tapping to ensure that the LF refining is in place and the Al content is 0.020-0.040%;

(2) LF refining process: CaO/Al ₂ O ₃ in the refining slag system is 1.7-1.9;

(3) VD vacuum treatment process: pour slag before entering VD, control the weight of slag poured to 1/2~1/3 of the total slag weight, then add aluminum ingots at 8.0~10.0kg/t to adjust the Al content in molten steel, add After the aluminum ingot, the cover is buckled immediately for VD vacuum degassing treatment;

(4) Continuous casting process: the continuous casting process is protected by argon sealing throughout the casting process, using special mold slag for low-carbon high-aluminum steel, and the continuous casting slab is slowly cooled off the production line.

Further, in the BOF converter process, the weight ratio of molten iron and scrap steel is: 85-95% of molten iron, 5-15% of scrap steel; 2-5 tons of steel slag is left in the converter furnace after the previous smelting is completed.

Further, in the LF refining process, the refining process uses aluminum particles and silicon carbide for diffusion deoxidation to ensure that the [O] content in molten steel is ≤ 8ppm, the refining time is ≥ 50 minutes, and the white slag retention time is ≥ 20 minutes.

Further, in the LF refining process, the refining slag contains the following components by weight: CaO ≥ 55%, SiO ₂ ≤ 6.3%, Al ₂ O ₃ : 30-32%, TFe+MnO ≤ 0.5%, MgO ≤ 6%, TiO ₂ ≤0.20%; the basicity of refining slag is R≥9.

Further, in the VD vacuum treatment process, the vacuum holding time is controlled at 8-10 minutes, the soft blowing time is ≥15 minutes, and the argon flow rate is ≤10 L/min during soft blowing.

Further, in the continuous casting process, the casting speed is constant at 0.24-0.26m/min, the water flow rate of the mold is 4500-5000L/min·flow, the specific water volume is 0.11-0.13L/kg, and the electromagnetic stirring intensity of the mold is 100-130A. The end electromagnetic stirring strength is 150-180A.

Further, in the continuous casting process, the composition and weight content of mold flux for low-carbon high-aluminum steel are: CaO: 21.5-25%, SiO ₂ : 36-39%, MgO: 4.5-5%, Al ₂ O ₃ : 2.5~3%, Fe ₂ O ₃ : 2.3~3%, Na ₂ O: 8.8~10%, F: 7.5~9%, C: 12~13%; melting point: 950~980°C, viscosity: 0.3 ~0.4Pa.s/1300℃.

The beneficial effects produced by adopting the above-mentioned technical scheme are: the present invention optimizes the design of 10CrMoAl composition, by increasing Cr, Mn, Al content, reducing Mo content, under the situation that guarantees finished material performance, reduces the usage amount of Mo of precious alloy, reasonable Utilize resources and reduce production costs. The present invention uses the converter as the primary furnace to produce low-P and low-S high-alumina steel, which is relatively difficult to produce and requires relatively high technical requirements. Adding aluminum ingots to adjust the Al content before VD vacuum treatment and after deslagging can achieve a higher aluminum yield (≥95%) and lower temperature loss (1.5-1.8°C/min) in the VD process, ensuring VD Vacuum treatment, slag washing and stirring process, the floating of inclusions such as Al ₂ O ₃ ensures the purity of molten steel. Optimize continuous casting process parameters to ensure good product quality.

可用于生产大规格沿海天然气及石化厂输送水无缝管或大规格阀门法兰盘。The P content and S content of the finished 10CrMoAl product produced by the invention are relatively low, and the mechanical properties of the material can be improved. The seawater corrosion-resistant high-aluminum steel continuous casting slab produced at the same time has a diameter of up to

It can be used to produce large-scale coastal natural gas and petrochemical plant water delivery seamless pipes or large-scale valve flanges.

Detailed ways

The present invention will be described in further detail below in combination with specific embodiments.

The large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab of the present invention has a diameter of 500-600mm, and its chemical composition and mass percentage are C: 0.07-0.11%, Si: 0.22-0.26%, and Mn: 0.65-0.70%. , P≤0.015%, S≤0.003%, Cr: 1.30～1.50%, Mo: 0.17～0.19%, Al: 0.80～1.00%, Ni≤0.10%, Cu≤0.10%, O≤8ppm, N≤50ppm, H≤1.2ppm, the balance is Fe and unavoidable impurities.

The production method of the above-mentioned large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab includes BOF converter, LF refining, VD vacuum treatment, and continuous casting process. The steps of each process are as follows:

(1) BOF converter process: Use high-quality low-P molten iron, requiring P≤0.120%, S≤0.030%, Si 0.30-0.80%, and temperature 1300-1450°C. After the smelting of the previous furnace is completed, 2 to 5 tons of steel slag is left in the converter, and nitrogen is blown from the bottom to protect the furnace by splashing slag for 3 to 5 minutes. The proportion of scrap steel in converter hot metal is: 85-95% of molten iron, 5-15% of scrap steel, and high-quality scrap steel is used. Before smelting, clean up the converter slag near the furnace mouth and furnace cap. If splashing occurs during the blowing process, the residual converter slag in the furnace cap must be cleaned a second time to ensure that the furnace cap is cleaned without residue before tapping. Converter blowing for 3 to 5 minutes needs to pour out the early slag, add slag material for secondary slag smelting, and strictly prohibit slag dropping during the tapping process to ensure that the P content of LF refining is in place ≤0.012%, and the P content of the finished product must be strictly controlled ≤0.015%. Steel core aluminum, alloy, and slag are added in sequence during the tapping process. A small amount of steel is left in the furnace, and slag is strictly prohibited. After tapping, the aluminum wire is fed to ensure that the LF is refined and the Al content is 0.020-0.040%.

(2) LF refining process: After the LF is in place, the ladle is opened with double air-permeable bricks to ensure good fluidity of the refining slag. The LF refining time is ≥ 50 minutes, and the white slag retention time is ≥ 20 minutes. The LF process uses aluminum particles and silicon carbide for diffusion deoxidation, which improves the reducibility of the slag, reduces the oxygen partial pressure in the furnace gas, and reduces the secondary oxidation of the LF process. Because the Al ₂ O ₃ content in the refining slag system reaches about 30%, when the CaO/Al ₂ O ₃ in the slag system is controlled at 1.7-1.9, the melting point of the refining slag is low, and the ability to desulfurize and absorb inclusions is strong, and SiO ₂ causes The reoxidation tendency of molten steel can be effectively suppressed.

Therefore, the control range of the refining slag system in the present invention is: CaO≥55%, SiO ₂ ≤6.3%, Al ₂ O ₃ : 30-32%, TFe+MnO≤0.5%, MgO≤6%, TiO ₂ ≤0.20%, alkali Degree R≥9, CaO/Al ₂ O ₃ is controlled at 1.7~1.9, which can ensure a good deoxidation and desulfurization effect, as well as a good adsorption effect on inclusions, and control a high purity of molten steel.

(3) VD vacuum treatment process: pour slag before entering VD, control the amount of slag poured to 1/2~1/3 of the total slag, then add aluminum ingots at 8.0~10.0kg/t to adjust the Al content in molten steel, add After the aluminum ingot, the cover is buckled immediately for VD vacuum degassing treatment. The VD high-vacuum holding time is controlled at 8-10 minutes, which can ensure a good degassing effect. The high yield of aluminum ingots and the full floating removal of inclusions can also play a role. To achieve energy-saving effect; after VD treatment, the soft blowing time is ≥15min, and the argon flow rate is ≤10L/min during soft blowing, which promotes the floating of inclusions and avoids secondary oxidation caused by excessive fluctuations in the liquid level during soft blowing.

Since the LF refining process continues to use aluminum particles and silicon carbide for diffusion deoxidation, at this time the [O] content in molten steel is ≤ 8ppm, and the oxygen content is low. After adding aluminum ingots, it will not react with Al in large quantities, so the Al ₂ produced in molten steel O ₃ is less; at the same time, a large amount of slag is poured before VD to ensure that the total amount of slag is small during VD treatment, and the total oxygen content in the slag is low, which can effectively increase the yield of Al after adding aluminum ingots, and ensure that the added aluminum ingots Al Yield ≥ 95%. At the same time, VD vacuum treatment and slag washing and stirring process can effectively promote the floating of inclusions such as Al ₂ O ₃ in molten steel and ensure the purity of molten steel.

In addition, in the process of melting and uniform composition of aluminum ingots, thermite reaction will occur, and the temperature drop during normal VD vacuum treatment is 2.0-2.5°C/min, and the VD vacuum treatment process is carried out after adding aluminum ingots at 8.0-10.0kg/t The medium temperature is reduced to 1.5-1.8 ℃/min, which can make up for part of the heat loss of VD vacuum treatment, that is, it can reduce the temperature of LF hanging bag by 10-20 ℃, so as to reduce power consumption, reduce electrode consumption, save energy and control costs.

直通式水口，头尾坯切除后整体铸坯收得率≥96％，使用低碳高铝钢专用保护渣，因钢水Al含量较高，易引起保护渣变性，导致铸坯表面出现渣沟、渣圈，连铸坯下线缓冷，出缓冷坑后应加强铸坯表面检查及清理；(4) Continuous casting process: the continuous casting process is protected by argon sealing throughout the pouring process to minimize secondary oxidation during the pouring process. Ensure that the ladle does not burn oxygen by itself, and control the purity of molten steel. The casting speed is constant at 0.24-0.26m/min, the water flow rate of the crystallizer is 4500-5000L/min·flow, the specific water volume is 0.11-0.13L/kg, the electromagnetic stirring intensity of the crystallizer is 100-130A, and the electromagnetic stirring intensity at the end is 150-180A.

Straight-through nozzle, the overall slab yield after the head and tail slabs are cut off is ≥96%, and special mold slag for low-carbon high-alumina steel is used. Due to the high Al content of molten steel, it is easy to cause denaturation of the mold slag, resulting in slag grooves on the surface of the slab. The slag ring, the continuous casting slab is slowly cooled off the production line, and the surface inspection and cleaning of the slab should be strengthened after leaving the slow cooling pit;

The composition and weight content of mold flux for low-carbon high-aluminum steel are: CaO: 21.5-25%, SiO ₂ : 36-39%, MgO: 4.5-5%, Al ₂ O ₃ : 2.5-3%, Fe ₂ O ₃ : 2.3-3%, Na ₂ O: 8.8-10%, F: 7.5-9%, C: 12-13%; melting point: 950-980°C, viscosity: 0.3-0.4Pa.s/1300°C.

Examples 1-8: See Table 1 and Table 2 for the chemical composition and content of the large-scale seawater corrosion-resistant high-aluminum steel continuous casting slabs of each embodiment, and see Tables 3 to 8 for the parameter control of each process in each embodiment. See Table 9 and Table 10 for the observation results of the obtained continuous casting slab under a low-magnification microscope and the detection results of the level of non-metallic inclusions.

Table 1: Chemical composition and content (wt%) of the high-aluminum steel continuous casting slabs of each embodiment

In Table 1, the balance is Fe and unavoidable impurities.

Table 2: Gas content (ppm) of high aluminum steel continuous casting slabs in each embodiment

Example o N h 1 8.0 38.6 0.9 2 7.7 41.9 1.0 3 7.4 40.2 0.9 4 8.0 46.2 1.2 5 7.6 38.1 1.0 6 8.0 35.4 1.1 7 7.8 44.3 0.9 8 7.1 49.8 1.0

Table 3: BOF converter process parameter control in each embodiment

Table 4: Control of LF refining process parameters in each embodiment

Table 5: Composition and content (wt%) of refining slag components in each embodiment

Table 6: Parameter control of each embodiment VD vacuum treatment process

Table 7: Parameter control of continuous casting process in each embodiment

Table 8: Composition and properties of special mold flux for low-carbon high-aluminum steel in each embodiment

Table 9: Observation results of continuous casting slabs under low magnification in each embodiment

Example Central looseness (grade) other defects 1 1.0 none 2 1.0 none 3 1.0 none 4 1.0 none 5 1.0 none 6 1.0 none 7 1.0 none 8 1.0 none

Table 10: Levels of non-metallic inclusions in each example

。

.

Claims (9)

1. A large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab, characterized in that the chemical composition and mass percentage of the high-aluminum steel are C: 0.07-0.11%, Si: 0.22-0.26%, Mn: 0.65～0.70%, P≤0.015%, S≤0.003%, Cr: 1.30～1.50%, Mo: 0.17～0.19%, Al: 0.80～1.00%, Ni≤0.10%, Cu≤0.10%, O≤8ppm, N≤50ppm, H≤1.2ppm, the balance is Fe and unavoidable impurities. 2. The large-scale continuous casting slab of seawater corrosion-resistant high-aluminum steel according to claim 1, characterized in that the diameter of the continuous casting slab is 500-600 mm. 3. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab according to claim 1 or 2, characterized in that it comprises BOF converter, LF refining, VD vacuum treatment, and continuous casting process; (1) BOF converter process: steel slag is left in the converter after the previous smelting is completed, nitrogen is blown from the bottom to splash the slag to protect the furnace, the converter is blown for 3 to 5 minutes to pour out the early slag, and the slag is added for secondary slag smelting. Slag is prohibited in the steel process to ensure that the LF refining is in place and the P content is ≤0.012%, and the aluminum wire is fed after tapping to ensure that the LF refining is in place and the Al content is 0.020-0.040%; (2) LF refining process: CaO/Al ₂ O ₃ in the refining slag system is 1.7-1.9; (3) VD vacuum treatment process: pour slag before entering VD, control the weight of slag poured to 1/2~1/3 of the total slag weight, then add aluminum ingots at 8.0~10.0kg/t to adjust the Al content in molten steel, add After the aluminum ingot, the cover is buckled immediately for VD vacuum degassing treatment; (4) Continuous casting process: the continuous casting process is protected by argon sealing throughout the casting process, using special mold slag for low-carbon high-aluminum steel, and the continuous casting slab is slowly cooled off the assembly line. 4. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab according to claim 3, characterized in that, in the BOF converter process, the weight ratio of molten iron and steel scrap is: 85% to 95% of molten iron, 5% to 5% of steel scrap 15%; 2-5 tons of steel slag is left in the converter after the previous furnace smelting. 5. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab according to claim 4, characterized in that, in the LF refining process, the refining process uses aluminum particles and silicon carbide to carry out diffusion deoxidation to ensure that [ O] content ≤ 8ppm, refining time ≥ 50min, white slag retention time ≥ 20min. 6. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slabs according to claim 5, characterized in that, in the LF refining process, the refining slag contains the following components by weight: CaO≥55%, SiO ₂ ≤6.3%, Al ₂ O ₃ : 30-32%, TFe+MnO ≤0.5%, MgO ≤6%, TiO ₂ ≤0.20%; the basicity of refining slag is R≥9. 7. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slabs according to claim 6, characterized in that, in the VD vacuum treatment process, the vacuum holding time is controlled at 8-10 minutes, and the soft blowing time is ≥ 15 minutes. The flow rate of argon gas during soft blowing is ≤10L/min. 8. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slab according to claim 7, characterized in that, in the continuous casting process, the casting speed is constant at 0.24-0.26m/min, and the mold water flow rate is 4500 ～5000L/min·flow, specific water volume 0.11～0.13L/kg, electromagnetic stirring intensity of crystallizer 100～130A, terminal electromagnetic stirring intensity 150～180A. 9. The production method of large-scale seawater corrosion-resistant high-aluminum steel continuous casting slabs according to any one of claims 3-8, characterized in that, in the continuous casting process, the composition of the special mold flux for low-carbon high-aluminum steel And the weight content is: CaO: 21.5-25%, SiO ₂ : 36-39%, MgO: 4.5-5%, Al ₂ O ₃ : 2.5-3%, Fe ₂ O ₃ : 2.3-3%, Na ₂ O : 8.8~10%, F: 7.5~9%, C: 12~13%; melting point: 950~980℃, viscosity: 0.3~0.4Pa.s/1300℃.