Method for deeply desulfurizing stainless steel

Abstract

The invention belongs to the field of steelmaking, and relates to a method for deeply desulfurizing molten stainless steel in a stainless steel refining process, which comprises the following steps: after AOD tapping to a steel ladle, carrying out first slagging-off on the molten steel in a furnace rear argon blowing station, after the first slagging-off, adding lime and aluminum shots in the furnace rear argon blowing station, carrying out strong stirring by utilizing bottom blowing argon of the steel ladle, and carrying out second slagging-off after strong stirring, and after the second time of slagging-off, the molten steel is hoisted to the LF furnace, power is supplied for heating, lime and aluminum shots are added after power is supplied, steel ladle bottom blowing argon blowing is utilized for strong stirring again, and the purpose of deep desulfurization is achieved. The residue thickness of a slag layer of steel slag in a steel ladle after slagging-off, the stirring strength of argon blowing at the bottom of the steel ladle, the stirring time of argon blowing at the bottom of the steel ladle, the temperature of molten steel after power transmission and heating, and the adding amount and adding time of lime aluminum shots are determined through practices, and a set of technological parameters for deep desulfurization of stainless steel are designed. After the high-nickel stainless steel is refined in the LF furnace, the sulfur content of the molten steel can be reduced by 5 ppm or below, and the purpose of deep desulfurization of the high-nickel stainless steel is achieved.

Description

Technical Field

[0001] The invention belongs to the field of steelmaking, and in particular relates to a method for deep desulfurization of stainless steel. Background Art

[0002] Sulfur mainly comes from steel-making raw materials and is difficult to remove during steelmaking. Sulfur exists in the form of sulfide inclusions in steel, which has an adverse effect on the plasticity, toughness, welding performance, thickness direction performance, fatigue performance and corrosion resistance of steel. Since the affinity of S with elements such as Ni, Mn, Ti, and Zr is much greater than that of Fe, sulfides such as MnS, TiS (titanium-containing steel), and NiS (high-nickel steel) are commonly found in steel. In high-nickel stainless steel (the lower limit of nickel content is greater than or equal to 10%), sulfur exists in the steel in the form of nickel sulfide (NiS) and iron sulfide (FeS), and FeS and Fe form low-melting point (985°C) compounds. The hot working temperature of steel is generally above 1150-1200°C, so when the steel is hot-worked, the workpiece cracks due to the premature melting of FeS compounds. This phenomenon is called "hot brittleness". The melting point of nickel sulfide is even lower (797°C). During the hot processing of steel, NiS is more likely to melt and cause cracking of the workpiece. Therefore, during the steelmaking process, the sulfur content of high-nickel stainless steel (the lower limit of nickel content is greater than or equal to 10%) needs to be controlled as low as possible.

[0003] Under conventional technology, when smelting high-nickel stainless steel (nickel content lower limit standard is greater than or equal to 10%), the AOD refining furnace can reduce the sulfur content in the steel to less than 100ppm. After the AOD is tapped into the ladle, the molten steel passes through the LF furnace or the argon blowing station after the furnace, lime and fluorite are added, and argon is blown and stirred at the bottom of the ladle to achieve the purpose of secondary refining and desulfurization. After secondary refining and desulfurization, the sulfur content in the steel can only be reduced to about 10-50ppm. Therefore, it is necessary to invent a method for deep desulfurization of stainless steel, especially high-nickel stainless steel.

[0004] In the stainless steel refining process, a method for deep desulfurization of stainless steel molten steel is designed, that is, after AOD is tapped into the ladle, the molten steel is first deslagging at the argon blowing station behind the furnace. After the first deslagging, lime and aluminum balls are added at the argon blowing station behind the furnace, and argon is blown from the bottom of the ladle for strong stirring. After strong stirring, the second deslagging is carried out. After the second deslagging, the molten steel is hoisted to the LF furnace, and the power is supplied for heating. After the power is supplied, lime and aluminum balls are added, and argon is blown from the bottom of the ladle for strong stirring again to achieve the purpose of deep desulfurization. Through the practice of the invention, the residual thickness of the slag layer of the slag in the ladle after deslagging, the stirring intensity of argon blowing at the bottom of the ladle, the stirring time of argon blowing at the bottom of the ladle, the temperature of the molten steel after power supply and heating, the amount of lime and aluminum balls added and the timing of adding are determined, and a set of process parameters for deep desulfurization of stainless steel are designed. After the implementation of the invention, the sulfur content of the molten steel of high-nickel stainless steel (the lower limit of nickel content is greater than or equal to 10%) can be reduced to less than 5ppm after the LF furnace refining is completed, achieving the purpose of deep desulfurization of high-nickel stainless steel molten steel. Summary of the invention

[0005] The purpose of the present invention is to provide a method for deep desulfurization of stainless steel water in view of the above problems.

[0006] The object of the present invention is achieved as follows: A method for deep desulfurization of stainless steel liquid, comprising the following steps: Step 1: After AOD taps steel into a ladle, the molten steel is subjected to the first slag removal at the AOD rear argon blowing station, and the residual thickness of the slag layer of the slag in the ladle after slag removal is ≤50mm. After the first slag removal, 3-5kg / t of lime and 1.0-2.0kg / t of aluminum shot are added at the rear argon blowing station, and argon is blown from the bottom of the ladle for strong stirring, the ladle bottom blowing intensity is 8-12Nl / min / t, and the stirring time is 8- 12min; Step 2: After strong stirring, carry out the second slag removal. After the slag removal, the residual thickness of the slag layer in the ladle is ≤50mm. After the second slag removal, the molten steel is hoisted to the LF furnace; Step 3: After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. After the temperature of the molten steel rises to 1600-1640℃, 2-3kg / t of lime and 0.5-1.0kg / t of aluminum shot are added, and strong stirring is carried out by blowing argon from the bottom of the ladle. The bottom blowing intensity of the ladle is 5-8Nl / min / t, and the stirring time is 5-8min.

[0007] The method relates to a high-nickel stainless steel of SUS316L, whose steel composition is C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.030%, Cr: 16.00-18.00%, Ni: 12.00-15.00%, and Mo: 2.00-3.00%; and another high-nickel stainless steel of 0Cr25Ni20, whose steel composition is C≤0.08%, Si≤1.50%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr: 24.00-26.00%, Ni: 19.00-22.00%, and the rest is Fe and unavoidable impurities.

[0008] The beneficial effect of the present invention is that after the implementation of the present invention, the sulfur content of molten steel of high-nickel stainless steel (nickel content lower limit standard is greater than or equal to 10%) can be reduced to less than 5ppm after LF furnace refining. DETAILED DESCRIPTION

[0009] Under conventional technology, when smelting high-nickel stainless steel (nickel content lower limit standard is greater than or equal to 10%), the AOD refining furnace can reduce the sulfur content in the steel to less than 100ppm. After the AOD is tapped into the ladle, the molten steel passes through the LF furnace or the argon blowing station after the furnace, lime and fluorite are added, and argon is blown and stirred at the bottom of the ladle to achieve the purpose of secondary refining and desulfurization. After secondary refining and desulfurization, the sulfur content in the steel can only be reduced to about 10-50ppm. Therefore, it is necessary to invent a method for deep desulfurization of stainless steel, especially high-nickel stainless steel.

[0010] The purpose of the present invention is to design a method for deep desulfurization of stainless steel molten steel, that is, after AOD is tapped into the ladle, the molten steel is first deslagging in the argon blowing station behind the furnace. After the first deslagging, the residual thickness of the slag layer of the slag in the ladle is ≤50mm. In the argon blowing station behind the furnace, 3-5kg / t of lime and 1.0-2.0kg / t of aluminum shot are added, and the ladle bottom is blown with argon for strong stirring. The ladle bottom blowing intensity is 8-12Nl / min / t and the stirring time is 8-12min. After strong stirring, the second deslagging is carried out. After the deslagging, the residual thickness of the slag layer in the ladle is ≤50mm. After the second deslagging, the molten steel is hoisted to the LF furnace, and the power is supplied for heating. After the temperature of the molten steel is raised to 1600-1640℃, 2-3kg / t of lime and 0.5-1.0kg / t of aluminum shot are added, and the ladle bottom is blown with argon for strong stirring. The ladle bottom blowing intensity is 5-8Nl / min / t and the stirring time is 5-8min, so as to achieve the purpose of deep desulfurization. Through the practice of the invention, the residual thickness of the slag layer in the ladle after slagging, the stirring intensity of argon blowing at the bottom of the ladle, the stirring time of argon blowing at the bottom of the ladle, the temperature of the molten steel after power supply and heating, the amount and timing of adding lime aluminum shots were determined, and a set of process parameters for deep desulfurization of stainless steel was designed. After the implementation of the invention, the sulfur content of molten steel of high-nickel stainless steel (the lower limit of nickel content is greater than or equal to 10%) can be reduced to less than 5ppm after the LF furnace refining is completed, achieving the purpose of deep desulfurization of high-nickel stainless steel molten steel.

[0011] The invention relates to a high-nickel stainless steel of SUS316L, whose steel components include C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.030%, Cr: 16.00-18.00%, Ni: 12.00-15.00%, and Mo: 2.00-3.00%; and another high-nickel stainless steel of 0Cr25Ni20, whose steel components include C≤0.08%, Si≤1.50%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr: 24.00-26.00%, and Ni: 19.00-22.00%.

[0012] The steps of the embodiment are as follows: the present invention designs high-nickel stainless steel, after AOD taps steel into the ladle, the molten steel is first deslagging at the argon blowing station behind the furnace, and the residual thickness of the slag layer of the slag in the ladle after deslagging is ≤50mm. After the first deslagging, 3-5kg / t of lime and 1.0-2.0kg / t of aluminum shot are added at the argon blowing station behind the furnace, and strong stirring is performed by blowing argon at the bottom of the ladle, the bottom blowing intensity of the ladle is 8-12Nl / min / t, and the stirring time is 8-12min. After strong stirring, the second deslagging is performed, and the residual thickness of the slag layer of the slag in the ladle after deslagging is ≤50mm. After the second deslagging, the molten steel is hoisted to the LF furnace. After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. When the temperature of the molten steel rises to 1600-1640℃, 2-3kg / t of lime and 0.5-1.0kg / t of aluminum shot are added. The molten steel is stirred by blowing argon from the bottom of the ladle. The intensity of the bottom blowing is 5-8Nl / min / t, and the stirring time is 5-8min.

[0013] Example

[0014] The steel grade of this example is high nickel stainless steel SUS316L, and its steel grade composition is C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.030%, Cr:16.00-18.00%, Ni:12.00-15.00%, Mo:2.00-3.00%. The steps of the embodiment are as follows: (1) After AOD tapping into the ladle, the molten steel is first deslagging at the argon blowing station behind the furnace. After deslagging, the slag layer of the slag in the ladle is 40mm thick. After the first deslagging, 4.2kg / t of lime and 1.6kg / t of aluminum shot are added at the argon blowing station behind the furnace. The ladle is blown with argon for strong stirring. The ladle bottom blowing intensity is 10.2Nl / min / t, and the stirring time is 10.1min.

[0015] (2) After strong stirring, the second slag removal is carried out. After the slag removal, the slag layer in the ladle has a residual thickness of 35 mm. After the second slag removal, the molten steel is hoisted to the LF furnace.

[0016] (3) After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. When the temperature of the molten steel rises to 1622°C, 2.4kg / t of lime and 0.6kg / t of aluminum shot are added. Strong stirring is carried out by blowing argon from the bottom of the ladle. The blowing intensity of the ladle bottom is 6.5Nl / min / t, and the stirring time is 7.1min.

[0017] After LF furnace refining, the sulfur content of molten steel is 4ppm.

[0018] Another example steel grade is SUS316L high nickel stainless steel, and its steel grade composition is C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.030%, Cr:16.00-18.00%, Ni:12.00-15.00%, Mo:2.00-3.00%. The steps of the embodiment are as follows: (1) After the AOD is tapped into the ladle, the molten steel is first deslagging at the argon blowing station behind the furnace. After deslagging, the slag layer of the slag in the ladle is 35mm thick. After the first deslagging, 4.8kg / t of lime and 1.9kg / t of aluminum shot are added at the argon blowing station behind the furnace. The ladle is blown with argon for strong stirring. The ladle bottom blowing intensity is 11.5Nl / min / t, and the stirring time is 11.6min.

[0019] (2) After strong stirring, the second slag removal is carried out. After the slag removal, the slag layer in the ladle has a residual thickness of 25 mm. After the second slag removal, the molten steel is hoisted to the LF furnace.

[0020] (3) After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. When the temperature of the molten steel rises to 1631°C, 2.8kg / t of lime and 0.8kg / t of aluminum shot are added. Strong stirring is carried out by blowing argon from the bottom of the ladle. The bottom blowing intensity of the ladle is 7.8Nl / min / t, and the stirring time is 7.6min.

[0021] After LF furnace refining, the sulfur content of molten steel is 3ppm.

[0022] Another example steel grade is 0Cr25Ni20 high nickel stainless steel, and its steel grade composition is C≤0.08%, Si≤1.50%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr: 24.00-26.00%, Ni: 19.00-22.00%. The steps of the embodiment are as follows: (1) After the AOD is tapped into the ladle, the molten steel is first deslagging at the argon blowing station behind the furnace. After deslagging, the slag layer of the slag in the ladle is 30mm thick. After the first deslagging, 4.6kg / t of lime and 1.5kg / t of aluminum shot are added at the argon blowing station behind the furnace, and the ladle is blown with argon for strong stirring. The ladle bottom blowing intensity is 10.5Nl / min / t, and the stirring time is 11.2min.

[0023] (2) After strong stirring, the second slag removal is carried out. After the slag removal, the slag layer in the ladle has a residual thickness of 25 mm. After the second slag removal, the molten steel is hoisted to the LF furnace.

[0024] (3) After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. After the temperature of the molten steel rises to 1635°C, 2.6 kg / t of lime and 0.9 kg / t of aluminum shot are added. The molten steel is stirred by blowing argon from the bottom of the ladle. The bottom blowing intensity of the ladle is 7.6 Nl / min / t, and the stirring time is 7.4 min.

[0025] After LF furnace refining, the sulfur content of molten steel is 3ppm.

[0026] Another example steel grade is 0Cr25Ni20 high nickel stainless steel, and its steel grade composition is C≤0.08%, Si≤1.50%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr: 24.00-26.00%, Ni: 19.00-22.00%. The steps of the embodiment are as follows: (1) After the AOD is tapped into the ladle, the molten steel is first deslagging at the argon blowing station behind the furnace. After deslagging, the slag layer of the slag in the ladle is 45mm thick. After the first deslagging, 4.2kg / t of lime and 1.2kg / t of aluminum shot are added at the argon blowing station behind the furnace. The ladle is blown with argon for strong stirring. The ladle bottom blowing intensity is 9.8Nl / min / t, and the stirring time is 8.5min.

[0027] (2) After strong stirring, the second slag removal is carried out. After the slag removal, the slag layer in the ladle has a residual thickness of 35 mm. After the second slag removal, the molten steel is hoisted to the LF furnace.

[0028] (3) After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. When the temperature of the molten steel rises to 1615°C, 2.1kg / t of lime and 0.6kg / t of aluminum shot are added. Strong stirring is carried out by blowing argon from the bottom of the ladle. The bottom blowing intensity of the ladle is 6.8Nl / min / t, and the stirring time is 7.2min.

[0029] After LF furnace refining, the sulfur content of molten steel is 4ppm.

[0030] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for deep desulfurization of stainless steel, characterized in that: The following steps are involved: Step 1: After AOD is tapped into the ladle, the molten steel is deslagging for the first time at the AOD rear argon blowing station. After deslagging, the residual thickness of the slag layer in the ladle is ≤50mm. After the first deslagging, 3-5kg / t of lime and 1.0-2.0kg / t of aluminum shot are added at the rear argon blowing station. The ladle bottom is blown with argon for strong stirring. The ladle bottom blowing intensity is 8-12Nl / min / t, and the stirring time is 8-12min. Step 2: After strong stirring, the second slag removal is carried out. After the slag removal, the residual thickness of the slag layer in the ladle is ≤50mm. After the second slag removal, the molten steel is hoisted to the LF furnace; Step 3: After the molten steel is hoisted to the LF furnace, power is supplied to increase the temperature. When the temperature of the molten steel rises to 1600-1640℃, 2-3kg / t of lime and 0.5-1.0 kg / t of aluminum shot are added. The argon is blown from the bottom of the ladle for strong stirring. The intensity of the bottom blowing is 5-8Nl / min / t, and the stirring time is 5-8min.

2. A method for deep desulfurization of stainless steel according to claim 1, characterized in that: The method relates to a high-nickel stainless steel of SUS316L, whose steel composition is C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.030%, Cr: 16.00-18.00%, Ni: 12.00-15.00%, Mo: 2.00-3.00%; Another type of high-nickel stainless steel involved is 0Cr25Ni20, whose steel components are C≤0.08%, Si≤1.50%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr: 24.00-26.00%, Ni: 19.00-22.00%, and the rest are Fe and unavoidable impurities.