Dephosphorization process for stainless steel or high alloy steel

Abstract

The invention discloses a dephosphorization process for stainless steel or high alloy steel. The dephosphorization process comprises the following steps: firstly, removing acid slag brought in by a primary smelting furnace; adding a first batch of slagging material into the steel ladle according to the dosage of 20-25kg of barium carbonate per ton of steel and 2-3kg of fluorite per ton of steel; then vacuum oxygen blowing dephosphorization treatment is conducted in a VOD furnace, the oxygen blowing amount per ton of steel is 8-12 m < 3 >, the oxidation burning loss of chromium is smaller than or equal to 0.5%, the amount of Cr2O3 in top slag ranges from 5% to 10%, a BaO-SiO2-FeO-Cr2O3-CaF2 slag system is formed in the oxidation period, and the dephosphorization rate ranges from 20% to 35%; after oxidation is finished, adding a second batch of slag charge and a reducing agent according to 10-15kg of lime per ton of steel, 2-3kg of fluorite per ton of steel and 8-10kg of aluminum ingot per ton of steel; then vacuum reduction is conducted in a VOD furnace, dephosphorization is further conducted, the dephosphorization rate ranges from 20% to 30%, and the comprehensive dephosphorization rate in the oxidation period and the reduction period is larger than or equal to 50%; cr2O3 in slag in the reduction period is reduced and enters molten steel again, and the recovery rate of chromium is larger than or equal to 95%. According to the dephosphorization process, the dephosphorization rate is increased, and the cost is reduced.

Description

Technical Field

[0001] This invention relates to a dephosphorization process for steelmaking, specifically a dephosphorization process for stainless steel or high alloy steel. Background Technology

[0002] Dephosphorization of stainless steel or high-alloy steel is a challenging problem in special steel smelting. The lime oxidation method, where chromium oxidizes before phosphorus, produces a large amount of Cr2O3, making the slag viscous and hindering the dephosphorization reaction, effectively rendering dephosphorization impossible. The calcium reduction method, on the other hand, produces toxic gases such as PH3 and C2H2 in the tailings of the reduction dephosphorization process, which are difficult to handle and cause environmental pollution. Currently, the mainstream methods for controlling phosphorus levels are smelting with low-phosphorus recycled materials or adding low-phosphorus alloys, but these methods are costly. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a dephosphorization process for stainless steel or high alloy steel with good dephosphorization effect and low cost.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a dephosphorization process for stainless steel or high alloy steel, the steps of which include:

[0005] S1: Slag removal, the specific process is: remove the acidic slag brought in by the primary smelting furnace so that the amount of SiO2 in the remaining primary slag does not exceed 15kg per ton of steel.

[0006] S2: Add the first batch of slag-forming material.

[0007] The first batch of slag-forming material is added to the ladle according to the dosage of 20-25 kg of barium carbonate per ton of steel and 2-3 kg of fluorite per ton of steel.

[0008] S3: VOD furnace oxidation

[0009] Under vacuum conditions, at a rate of 8-12m / ton of steel. 3 Introducing oxygen causes phosphorus in the molten steel to be oxidized. Barium carbonate decomposes at high temperature, and the resulting barium oxide reacts with phosphorus pentoxide to form barium phosphate, which enters the slag and is removed. At the same time, some chromium in the molten steel is also oxidized, forming chromium oxide, which enters the slag phase. After oxygen is stopped, the degree of oxidation is controlled by the carbon-oxygen reaction under vacuum, so that the oxidation loss of chromium in the molten steel is ≤0.5%, and the amount of Cr2O3 in the top slag is between 5% and 10%.

[0010] The slag composition of the oxidation process, as determined by slag sample analysis, is as follows: 40-50% BaO, 20-30% SiO2, 5-10% FeO, 5-10% Cr2O3, and 3-5% CaF2.

[0011] The dephosphorization reaction occurring at the steel slag interface is as follows: 9(BaO) + 6[P] + 5(Cr₂O₃) = 3(3BaO·P₂O₅) + 10[Cr], 3(BaO) + 2[P] + 5(FeO) = (3BaO·P₂O₅) + 5[Fe].

[0012] Based on the phosphorus content of the molten steel samples before and after oxidation, the dephosphorization rate during the oxidation process is between 20% and 35%.

[0013] S4: The VOD furnace is ventilated, and lime, fluorite (second batch of slag-forming material), and aluminum ingots as a deoxidizer are added.

[0014] The second batch of slag-forming material and deoxidizer is added according to the following amounts: 10-15 kg of lime per ton of steel, 2-3 kg of fluorite per ton of steel, and 8-10 kg of aluminum ingot per ton of steel. The lime is used to absorb aluminum oxide and silicon dioxide to avoid the slag having too low alkalinity in the subsequent process, which is not conducive to the dephosphorization reaction.

[0015] S5: VOD oven restoration

[0016] During reduction, aluminum oxidizes to form aluminum oxide, which, along with the added lime, melts into the slag system described in step S3, ultimately forming the BaO-CaO-SiO2-Al2O3-CaF2 slag system, i.e., the final slag. The dephosphorization reaction continues at the steel-slag interface, further reducing the phosphorus content in the molten steel. Calculations based on the phosphorus content of the molten steel samples before and after the dephosphorization process show a dephosphorization rate between 20% and 30%. Slag sample testing revealed that the final slag contains: 25%–35% BaO, 15%–25% CaO, 15%–20% SiO2, 15%–20% Al2O3, and 3%–5% CaF2.

[0017] During the reduction process, the dephosphorization reaction at the steel slag interface is as follows:

[0018] 3(BaO)+2[Al]=3[Ba]+(Al2O3),

[0019] 3[Ba]+[Cr3P2]=(Ba3P2)+3[Cr],

[0020] (Ba3P2)+8(FeO)=(3BaO·P2O5)+8[Fe],

[0021] During the reduction process, Cr2O3 in the slag is reduced and reintroduced into the molten steel. Based on the chromium content of the molten steel sample, the chromium recovery rate is ≥95%.

[0022] S6: Add alloy to adjust composition

[0023] The chemical composition is finely adjusted by adding alloys based on the composition of the reduced molten steel.

[0024] S7: VD furnace vacuum degassing

[0025] Under high vacuum conditions, bottom blowing argon gas is used for degassing to reduce the hydrogen content in molten steel to the target range.

[0026] As a preferred embodiment, in the dephosphorization process of stainless steel or high alloy steel, the oxygen flow rate in step S3 is controlled at 800–1000 m³ / h. 3 Between / h.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] The beneficial effects of this invention are:

[0029] 1. This invention employs a barium-based slag weak oxidation method, which can dephosphorize during both the oxidation and reduction phases, achieving a dephosphorization rate of over 50%, thus achieving ideal results. This provides a pathway for the production of low-phosphorus stainless steel and high-alloy steel, expands the applicable range of steelmaking raw materials, and reduces production costs. Furthermore, no toxic gases are generated at the production site, and the environment is not polluted.

[0030] 2. In this invention, the Cr2O3 generated during the oxidation period re-enters the molten steel during the reduction stage, resulting in a chromium recovery rate of ≥95% with virtually no burn-off, thus reducing production costs.

[0031] 3. The barium-based materials generated during the dephosphorization process of this invention exist only in the slag phase. No barium-containing particles were found in the energy dispersive spectroscopy analysis of the finished steel, which shows that this invention does not have any other impact on the material properties of the steel and ensures the quality of the steel.

[0032] 4. This invention performs desulfurization simultaneously with dephosphorization during the oxidation and reduction periods, and the resulting residue enters the corresponding slag system. The combined desulfurization rate of the two stages is ≥90%. Detailed Implementation

[0033] The following describes in detail the implementation plan of the dephosphorization process for stainless steel or high alloy steel described in this invention, taking the dephosphorization of 50 tons of 304 stainless steel as an example.

[0034] The dephosphorization process for stainless steel or high alloy steel described in this invention includes the following steps:

[0035] S1: Slag Removal. The specific process is as follows: Remove the acidic slag brought in from the primary smelting furnace, ensuring that the amount of SiO2 in the remaining primary slag does not exceed 750 kg.

[0036] S2: Add 1000-1250 kg of barium carbonate and 100-150 kg of fluorite to the ladle as the first batch of slag-forming materials;

[0037] S3: VOD furnace oxidation

[0038] Under vacuum conditions, at 800–1000 m 3A flow rate of / h is blown into 500m 3 The oxygen in the molten steel oxidizes the phosphorus. The barium carbonate decomposes at high temperature, and the resulting barium oxide reacts with phosphorus pentoxide to form barium phosphate, which enters the slag phase and is removed. At the same time, some chromium in the molten steel is also oxidized and forms chromium oxide, which enters the slag phase. After the oxygen is stopped, the degree of oxidation is controlled by a carbon-oxygen reaction under vacuum for 20 minutes, so that the oxidation loss of chromium in the molten steel is ≤0.5%, and the amount of Cr2O3 in the top slag is between 5% and 10%.

[0039] The slag composition of the oxidation process, as determined by slag sample analysis, is as follows: 40-50% BaO, 20-30% SiO2, 5-10% FeO, 5-10% Cr2O3, and 3-5% CaF2.

[0040] The dephosphorization reaction occurring at the steel slag interface is as follows: 9(BaO) + 6[P] + 5(Cr₂O₃) = 3(3BaO·P₂O₅) + 10[Cr], 3(BaO) + 2[P] + 5(FeO) = (3BaO·P₂O₅) + 5[Fe].

[0041] Based on the phosphorus content of the molten steel samples before and after oxidation, the dephosphorization rate during the oxidation process is between 20% and 35%.

[0042] S4: The VOD furnace is ventilated (meaning after the vacuum is completed, the lid is opened and it enters a normal pressure state). 500-750 kg of lime and 100-150 kg of fluorite are added as the second batch of slag-forming materials, and 400-500 kg of aluminum ingots are added as deoxidizers or reducing agents to the VOD furnace. The lime is used to absorb aluminum oxide and silicon dioxide to avoid the slag having too low alkalinity in the subsequent process, which is not conducive to the dephosphorization reaction.

[0043] S5: VOD oven restoration

[0044] During reduction, aluminum oxidizes to form aluminum oxide, which, along with the added lime, melts into the slag system described in step S3, ultimately forming the BaO-CaO-SiO2-Al2O3-CaF2 slag system, i.e., the final slag. The dephosphorization reaction continues at the steel-slag interface, further reducing the phosphorus content in the molten steel. Calculations based on the phosphorus content of the molten steel samples before and after the dephosphorization process show a dephosphorization rate between 20% and 30%. Slag sample testing revealed that the final slag contains: 25%–35% BaO, 15%–25% CaO, 15%–20% SiO2, 15%–20% Al2O3, and 3%–5% CaF2.

[0045] During the reduction process, the dephosphorization reaction at the steel slag interface is as follows:

[0046] 3(BaO)+2[Al]=3[Ba]+(Al2O3),

[0047] 3[Ba]+[Cr3P2]=(Ba3P2)+3[Cr],

[0048] (Ba3P2)+8(FeO)=(3BaO·P2O5)+8[Fe],

[0049] During the reduction process, Cr2O3 in the slag is reduced and reintroduced into the molten steel. Based on the chromium content of the molten steel sample, the chromium recovery rate is ≥95%.

[0050] S6: Add alloy to adjust composition

[0051] The chemical composition is fine-tuned by adding alloys according to the composition of the reduced molten steel (this is a common technique in the field and will not be described in detail here);

[0052] S7: VD furnace vacuum degassing

[0053] Under high vacuum conditions, bottom blowing argon gas is used for degassing to reduce the hydrogen content in the molten steel brought in by raw materials and auxiliary materials to the target range.

[0054] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any equivalent changes and modifications made based on the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A dephosphorization process for stainless steel or high-alloy steel, comprising the following steps: S1: Slag removal, the specific process is: remove the acidic slag brought in by the primary smelting furnace so that the amount of SiO2 in the remaining primary slag does not exceed 15kg per ton of steel. S2: Add the first batch of slag-forming material. The first batch of slag-forming material is added to the ladle according to the dosage of 20-25 kg of barium carbonate per ton of steel and 2-3 kg of fluorite per ton of steel. S3: VOD furnace oxidation Under vacuum conditions, at a rate of 8-12m / ton of steel. 3 Introducing oxygen causes phosphorus in the molten steel to be oxidized. Barium carbonate decomposes at high temperature, and the resulting barium oxide reacts with phosphorus pentoxide to form barium phosphate, which enters the slag and is removed. At the same time, some chromium in the molten steel is also oxidized, forming chromium oxide, which enters the slag phase. After oxygen is stopped, the degree of oxidation is controlled by the carbon-oxygen reaction under vacuum, so that the oxidation loss of chromium in the molten steel is ≤0.5%, and the amount of Cr2O3 in the top slag is between 5% and 10%. The slag composition of the oxidation process, as determined by slag sample analysis, is as follows: 40-50% BaO, 20-30% SiO2, 5-10% FeO, 5-10% Cr2O3, and 3-5% CaF2. The dephosphorization reaction occurring at the steel slag interface is as follows: 9(BaO) + 6[P] + 5(Cr₂O₃) = 3(3BaO·P₂O₅) + 10[Cr] 3(BaO) + 2[P] + 5(FeO) = (3BaO·P₂O₅) + 5[Fe] Based on the phosphorus content of the molten steel samples before and after oxidation, the dephosphorization rate during the oxidation process is between 20% and 35%. S4: The VOD furnace is ventilated, and lime, fluorite (second batch of slag-forming material), and aluminum ingots as a deoxidizer are added. The second batch of slag-forming material and deoxidizer is added according to the following amounts: 10-15 kg of lime per ton of steel, 2-3 kg of fluorite per ton of steel, and 8-10 kg of aluminum ingot per ton of steel. The lime is used to absorb aluminum oxide and silicon dioxide to avoid the slag having too low alkalinity in the subsequent process, which is not conducive to the dephosphorization reaction. S5: VOD oven restoration During reduction, aluminum oxidizes to form aluminum oxide, which, along with the added lime, melts into the slag system described in step S3, ultimately forming the BaO-CaO-SiO2-Al2O3-CaF2 slag system, i.e., the final slag. The dephosphorization reaction continues at the steel-slag interface, further reducing the phosphorus content in the molten steel. Calculations based on the phosphorus content of the molten steel samples before and after the dephosphorization process show a dephosphorization rate between 20% and 30%. Slag sample testing revealed that the final slag contains: 25%–35% BaO, 15%–25% CaO, 15%–20% SiO2, 15%–20% Al2O3, and 3%–5% CaF2. During the reduction process, the dephosphorization reaction at the steel slag interface is as follows: 3(BaO)+2[Al]=3[Ba]+(Al2O3), 3[Ba]+[Cr3P2]=(Ba3P2)+3[Cr], (Ba3P2)+8(FeO)=(3BaO·P2O5)+8[Fe], During the reduction process, Cr2O3 in the slag is reduced and reintroduced into the molten steel. Based on the chromium content of the molten steel sample, the chromium recovery rate is ≥95%. S6: Add alloy to adjust composition The chemical composition is finely adjusted by adding alloys based on the composition of the reduced molten steel. S7: VD furnace vacuum degassing Under high vacuum conditions, bottom blowing argon gas is used for degassing to reduce the hydrogen content in molten steel to the target range.

2. The dephosphorization process for stainless steel or high-alloy steel according to claim 1, characterized in that, In step S3, the oxygen flow rate is controlled at 800–1000 m³ / h. 3 Between / h.