Smelting process of ultra-low-phosphorus and ultra-low-sulfur high alloy steel

Abstract

The invention discloses a smelting process of ultra-low-phosphorus and ultra-low-sulfur high alloy steel, which comprises the following steps: molten iron desulfurizer processing, molten iron pre-desulfurization, dephosphorization treatment, alloy melting in an intermediate frequency furnace, and decarburization treatment after adding AOD into molten iron and alloy melt, and the method effectively solves the problems that in the original process, the sulfur content is high when the AOD is added into the molten iron, and the later desulfurization load is heavy. The addition amount of desulfurization materials in the later stage of AOD is reduced, the operation is simple, the molten iron desulfurization function is developed under the condition that existing equipment is not changed, the production period and the production organization are not influenced, the purity of the molten steel is guaranteed under the condition that the aim of successfully smelting the ultra-low-phosphorus and ultra-low-sulfur high alloy steel is achieved, and the production cost is reduced. And the finished product quality is stably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting process for ultra-low phosphorus and sulfur high-alloy steel. Background Art

[0002] Some high-alloy steel grades have extremely high requirements for phosphorus and sulfur, with phosphorus ≤ 0.005% and sulfur ≤ 0.006%. The large amount of alloy added during the AOD smelting process leads to a serious lack of process temperature. The large amount of heated alloy added poses the risk of rephosphorization and is not conducive to subsequent desulfurization, thus failing to meet the phosphorus and sulfur content requirements of high-alloy steel grades. Summary of the Invention

[0003] In response to the problems existing in the prior art, the present invention provides a smelting process for ultra-low phosphorus and high-sulfur alloy steel, which reduces the addition of a large amount of desulfurization materials during the AOD smelting process, reduces the amount of rephosphorization, alleviates the smelting pressure of the AOD furnace, and reduces the AOD smelting cost.

[0004] To this end, the present invention adopts the following technical solutions: A smelting process for ultra-low phosphorus and sulfur high alloy steel comprises the following steps: 1) Refined lime and fluorite powder are mixed in proportion to produce a desulfurizer. The main components of the desulfurizer are as follows by weight: CaO>80%, 3≤CaF≤5, SiO2<3%, and the rest are other uncontrollable elements brought from the raw materials; the desulfurizer is transported to the spray tank in the molten iron pretreatment process; 2) The composition of the molten iron in the molten iron pretreatment process is as follows by weight percentage: C: ≥4.3, Si: 0.5-0.8, P: ≤0.08, S≤0.09, and the rest is Fe and other uncontrollable elements brought from the raw materials; 3) Hot metal pre-desulfurization: Use nitrogen as carrier gas, with a carrier gas flow rate of 2.0-2.3Nm 3 / min, spray the desulfurizer into the molten iron through a spray gun, the desulfurizer spray flow rate is 80-100Kg / min, the spray pressure is 0.40-0.60MPa, the desulfurizer dosage is 15-27Kg / ton of iron, and the carrier gas nitrogen is used to stir the molten pool to provide reaction kinetic conditions. The following reactions occur in the molten iron: CaO+[S] =CaS+[O] 2CaO( s) +[ S] +1 / 2[ Si]=CaS( s) +1 / 2Ca2Si Among them: Si is naturally present in the molten iron, and there is no need to add ferrosilicon separately; 4) Remove desulfurization slag: Stop spraying the desulfurizer when the sulfur content is ≤0.006%, and remove all the slag produced by desulfurization to avoid sulfur back into the dephosphorization process; 5) Hot metal pre-dephosphorization: During the hot metal dephosphorization process, the slag basicity is controlled at 1.4-1.8, and the target phosphorus content is ≤0.005%; 6) Remove dephosphorization slag: After dephosphorization of molten iron, remove high-phosphorus slag to prevent phosphorus return in subsequent smelting; 7) The medium frequency furnace melts the high alloy mother liquor according to the alloy composition requirements of the smelting steel; 8) Low-phosphorus and sulfur molten iron and high-alloy mother liquor are added to the AOD converter respectively. The AOD converter performs decarburization and alloy fine-tuning according to the composition requirements of the smelting steel grade. Steel is tapped after the composition and temperature meet the requirements.

[0005] The beneficial effects of the present invention are: 1. This invention develops the function of molten iron desulfurization under existing equipment conditions, and the molten iron pretreatment process has the ability to desulfurize and dephosphorize simultaneously; 2. The desulfurizer is mixed with cheap fluorite powder, which saves the addition of fluorite blocks, avoids temperature loss, and also reduces smelting costs; 3. During the AOD smelting process, there is no need to add a large amount of alloy for combined reduction desulfurization operation, which effectively solves the problems of insufficient temperature in the AOD process and phosphorus reversion in the reduction stage; 4. The desulfurization and dephosphorization reaction conditions restrict each other. The present invention successfully realizes the operation of desulfurization and dephosphorization of molten iron in the same container, and also responds to the sulfur regeneration and phosphorus regeneration links, achieving good results. DETAILED DESCRIPTION

[0006] Example 1 4J36 steel smelting 1. Refined lime and fluorite powder are mixed in appropriate proportions to produce a desulfurizer. The main components of the desulfurizer, by weight, are as follows: CaO: 86.5%, SiO2: 2.44%, CaF: 5%, with the remainder being uncontrolled elements from the raw materials. The processed desulfurizer is transported to the hot metal pretreatment spray tank using a tank truck.

[0007] 2. Hot metal pretreatment process: Pre-desulfurization. The hot metal composition by weight is as follows: C: 4.32%, Si: 0.488%, Mn: 0.53%, P: 0.092%, S: 0.085%, and the remainder is Fe and other uncontrolled elements brought in from the raw materials.

[0008] 3. During the pre-desulfurization process of molten iron, the desulfurizer flow rate is 95Kg / min, the pressure is 0.5MPa, the desulfurizer usage is 27Kg / ton of iron, and the final sulfur content is 0.006%.

[0009] 4. After removing the desulfurization slag, continue with pre-dephosphorization, the dephosphorization alkalinity is 1.8, and the end point phosphorus content is 0.005%.

[0010] 5. The high alloy mother liquor and low phosphorus and sulfur molten iron melted in the medium frequency furnace are added to AOD for decarburization and composition fine-tuning operations, and the sulfur content of the steel is 0.006%.

[0011] Through molten iron pretreatment, the molten iron is desulfurized and dephosphorized successively. The phosphorus and sulfur contents after AOD steelmaking meet the requirements, and the composition of the finished product is within the range of steel grade development requirements.

[0012] Example 2 SUS436L ultra-pure ferritic stainless steel smelting 1. Refined lime and fluorite powder are mixed in appropriate proportions to produce a desulfurizer. The main components of the desulfurizer, by weight, are as follows: CaO: 86.5%, SiO2: 2.44%, CaF: 5%, with the remainder being uncontrolled elements from the raw materials. The processed desulfurizer is transported to the hot metal pretreatment spray tank using a tank truck.

[0013] 2. Hot metal pretreatment process: Pre-desulfurization. The hot metal composition by weight is as follows: C: 4.92%, Si: 0.308%, Mn: 0.90%, P: 0.078%, S: 0.080%, and the remainder is Fe and other uncontrolled elements brought in from the raw materials.

[0014] 3. During the pre-desulfurization process of molten iron, the desulfurizer flow rate is 90Kg / min, the pressure is 0.48MPa, the desulfurizer usage is 19.5Kg / ton of iron, and the final sulfur content is 0.006%.

[0015] 4. After removing the desulfurization slag, continue with pre-dephosphorization, the dephosphorization alkalinity is 1.7, and the end point phosphorus content is 0.009%.

[0016] 5. The high alloy mother liquor and low phosphorus and sulfur molten iron melted in the medium frequency furnace are added to AOD for decarburization and composition fine-tuning operations. The sulfur content of AOD steel is 0.0095%. Compared with the conventional process for smelting ultra-pure steel, the amount of ferrosilicon and lime used in AOD desulfurization is halved.

[0017] Through molten iron pretreatment, the molten iron is desulfurized and dephosphorized successively. After AOD steelmaking, the phosphorus and sulfur contents meet the requirements and the composition of the finished product is within the required range.

[0018] Example 3 Conventional process for smelting 4J36 steel 1. The hot metal pretreatment process only involves pre-dephosphorization of the hot metal. The hot metal composition by weight is as follows: C: 4.64%, Si: 0.771%, Mn: 0.73%, P: 0.074%, S: 0.045%. The remainder is Fe and other uncontrolled elements introduced from the raw materials.

[0019] 2. The dephosphorization alkalinity is 1.6, the dephosphorization lime powder dosage is 1511 kg, the final phosphorus content is 0.003%, no desulfurization operation is performed in the pretreatment, the outgoing sulfur content is 0.027%, and after dephosphorization, the dephosphorization slag is completely removed and sent to AOD.

[0020] 3. The high alloy mother liquor and low phosphorus molten iron melted in the medium frequency furnace are added to AOD for smelting respectively. AOD is first used for decarburization, and then reduction desulfurization is carried out after decarburization. During the desulfurization process, 300 kg of ferrosilicon and 400 kg of lime are added.

[0021] Example 4 Conventional process for smelting Z2CN19-10 steel 1. The hot metal pretreatment process only involves pre-dephosphorization of the hot metal. The hot metal composition by weight is as follows: C: 4.39%, Si: 0.729%, Mn: 0.64%, P: 0.090%, S: 0.052%. The remainder is Fe and other uncontrolled elements introduced from the raw materials.

[0022] 2. The dephosphorization alkalinity is 1.7, the dephosphorization lime powder dosage is 1703 kg, the final phosphorus content is 0.006%, no desulfurization operation is performed in the pretreatment, the outgoing sulfur content is 0.038%, and after dephosphorization, the dephosphorization slag is completely removed and sent to AOD.

[0023] 3. The high alloy mother liquor and low phosphorus molten iron melted in the medium frequency furnace are added to AOD for smelting respectively. AOD is first used for decarburization, and then reduction desulfurization is carried out after decarburization. During the desulfurization process, 300 kg of ferrosilicon and 400 kg of lime are added.

[0024] According to the normal process flow: molten iron → three dephosphorization → AOD iron addition → AOD decarburization → AOD alloying → AOD reduction desulfurization → AOD tapping. Under the process conditions, the sulfur content of AOD entering the furnace is in the range of 0.020%-0.090%, and the sulfur content of the molten steel entering the AOD reduction stage is 0.010%-0.020%. In the reduction desulfurization stage, 300-500Kg of desulfurized ferrosilicon and 800-1500Kg of desulfurized lime need to be added for desulfurization. The sulfur content of AOD tapping can meet the tapping requirements. In Example 3, 4J36 steel grade is smelted according to the conventional process, 300Kg of desulfurized ferrosilicon and 400Kg of desulfurized lime are added in the reduction desulfurization stage, and Z2CN19-10 steel grade is smelted according to the conventional process in Example 4. 482Kg of desulfurized ferrosilicon and 1500Kg of desulfurized lime are added in the reduction desulfurization stage.

[0025] According to the patented process flow: molten iron → three-desulfurization → three-dephosphorization → AOD iron addition → AOD decarburization → AOD alloying → (AOD reduction desulfurization) → AOD tapping. Under the process conditions, the sulfur content of AOD entering the furnace is less than 0.010%, and the sulfur content of the molten steel entering the AOD reduction stage is less than 0.005%. AOD only needs to add a small amount of desulfurized ferrosilicon and desulfurized lime to achieve the purpose of desulfurization, and can even directly tap the steel without desulfurization. In Example 1, 4J36 steel is smelted according to the process provided by the patent. After the decarburization and alloying stages are completed, the sulfur content meets the tapping requirements, and the steel is directly tapped without reduction desulfurization. In Example 2, only 153 kg of desulfurized ferrosilicon and 400 kg of desulfurized lime are added for desulfurization, and the desulfurization materials are halved. The AOD smelting load and smelting cost of Examples 1 and 2 are greatly reduced, and the reduction in the amount of materials in the reduction desulfurization stage is beneficial to improving the purity of the molten steel.

Claims

1. A smelting process for ultra-low phosphorus and sulfur high alloy steel, characterized in that: The following steps are involved: 1) Refined lime and fluorite powder are mixed in proportion to produce a desulfurizer. The main components of the desulfurizer are as follows by weight: CaO>80%, 3≤CaF≤5, SiO2<3%, and the rest are other uncontrollable elements brought from the raw materials; the desulfurizer is transported to the spray tank in the molten iron pretreatment process; 2) The composition of the molten iron in the molten iron pretreatment process is as follows by weight percentage: C: ≥4.3, Si: 0.5-0.8, P: ≤0.08, S≤0.09, and the rest is Fe and other uncontrollable elements brought from the raw materials; 3) Hot metal pre-desulfurization: Use nitrogen as carrier gas, with a carrier gas flow rate of 2.0-2.3Nm 3 / min, spray the desulfurizer into the molten iron through a spray gun, the desulfurizer spray flow rate is 80-100Kg / min, the spray pressure is 0.40-0.60MPa, the desulfurizer dosage is 15-27Kg / ton of iron, and the carrier gas nitrogen is used to stir the molten pool to provide reaction kinetic conditions. The following reactions occur in the molten iron: CaO+[S] =CaS+[O] 2CaO( s) +[ S] +1 / 2[ Si] =CaS( s) +1 / 2Ca2Si Among them: Si is naturally present in the molten iron, and there is no need to add ferrosilicon separately; 4) Remove desulfurization slag: Stop spraying the desulfurizer when the sulfur content is ≤0.006%, and remove all the slag produced by desulfurization to avoid sulfur back into the dephosphorization process; 5) Hot metal pre-dephosphorization: During the hot metal dephosphorization process, the slag basicity is controlled at 1.4-1.8, and the target phosphorus content is ≤0.005%; 6) Remove dephosphorization slag: After dephosphorization of molten iron, remove high-phosphorus slag to prevent phosphorus return in subsequent smelting; 7) The medium frequency furnace melts the high alloy mother liquor according to the alloy composition requirements of the smelting steel; 8) Low-phosphorus and sulfur molten iron and high-alloy mother liquor are added to the AOD converter respectively. The AOD converter performs decarburization and alloy fine-tuning according to the composition requirements of the smelting steel grade. Steel is tapped after the composition and temperature meet the requirements.

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