Smelting method of 1215MS

Abstract

The invention provides a smelting method of 1215MS, which belongs to the technical field of metallurgy, and comprises the following steps: remaining 2.5-3t of slag during smelting in a converter, and adding 30-40t of scrap steel and 100-110t of molten iron; after oxygen blowing is started, dolomite and magnesium balls are added instead of lime, the lance position is gradually reduced from 2.3 m to 1.6-1.8 m, and then low-lance-position blowing is kept to the end point; when oxygen blowing is carried out for 10-12 min during converter smelting, the temperature of the molten steel is increased to 1650-1670 DEG C, and the carbon content and the oxygen content of the molten steel are controlled to be 0.035-0.045% and 900-1100 ppm respectively; and in the tapping process, 1150-1350kg of silicomanganese, 600-900kg of low manganese and 480-520kg of lime are added instead of aluminum and iron. According to the smelting method of the 1215MS, provided by the invention, the processing quality of the molten steel can be ensured, clients can easily process and cut, and the production cost is relatively low.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metallurgy, and particularly relates to a smelting method of 1215MS. BACKGROUND

[0002] 1215MS is a high-sulfur and high-phosphorus free-cutting steel, and becomes a popular material due to the absence of lead and harmful substances to the environment. The cutting performance of the steel is good, and the steel is suitable for automatic lathe machining, hardware stamping part machining and general part manufacturing. Due to high precision and good surface condition, the product can be directly used, such as spraying, sanding, bending, drilling, and can be directly electroplated, thereby saving a large amount of machining time and machining mechanical cost.

[0003] Currently, the smelting method of 1215MS includes the following steps: 1, after the last converter smelting is completed, the slag is poured, 3.5-4t of slag is left, then 25-30t of scrap steel is added, 110-115t of molten iron is added, and the total amount of 139-141t is controlled. 2, after the oxygen blowing starts, 500kg of lime and 2200-2500kg of light-burned dolomite are added. 3, the gun position control is low-high-low. That is, in 0-5 minutes of blowing, low gun position is used to melt scrap steel and slag, in 5-10 minutes, the gun position is increased to decarburize, in 10-14 minutes, the gun position is reduced to decarburize, and the carbon is decarburized to about 0.04%. 4, when the carbon is decarburized to about 0.04%, the temperature of the molten steel is increased to above 1610℃, and the molten steel can be tapped. 5, during the tapping process, 120kg of aluminum iron, 500kg of silicon manganese, 1600kg of low manganese and 500kg of lime are added. 6, after the molten steel is tapped, the molten steel is transferred to the LF furnace, 500kg of lime is added, the oxygen is controlled to be 0.004-0.006% during the process, and silicon iron is added for deoxidization.

[0004] The molten steel obtained by the above method has a high oxygen content in the cast blank obtained by casting the molten steel, so that the molten steel has a large number of liquid surface fluctuation times during the continuous casting and rolling process, and the billet head is prone to cracking. Therefore, the customer is prone to cracking when the cast blank is machined into small parts. If the oxygen content of the molten steel is reduced in the converter smelting process, although the quality problem in the production process can be improved, the customer will have problems such as difficult cutting and tool consumption when machining the cast blank.

[0005] Therefore, there is an urgent need for a smelting method of 1215MS which can ensure the machining quality of the molten steel, meet the easy machining and cutting of the customer, and has low production cost. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a smelting method of 1215MS which can ensure the machining quality of the molten steel, meet the easy machining and cutting of the customer, and has low production cost.

[0007] To solve the above technical problems, the present application provides a smelting method of 1215MS, comprising the following steps:

[0008] After the completion of the last converter smelting, slag is poured and 2.5-3t of slag is left;

[0009] 30-40t of scrap steel and 100-110t of molten iron are added to the converter, and the total amount of 139-141t is controlled;

[0010] After the converter smelting starts to blow oxygen, dolomite 1800-3200kg and magnesium ball 300-550kg are added without lime, and the total slag amount of slag making is controlled to be 5-6t;

[0011] After starting to blow oxygen, the gun position is gradually reduced from 2.3m to 1.6-1.8m, and then the low gun position is maintained to the end of blowing;

[0012] When the converter smelting blows oxygen to the end, the molten steel temperature is increased to 1650-1670℃, the molten steel carbon content is controlled to be 0.035-0.045%, and the molten steel oxygen content is controlled to be 900-1100ppm;

[0013] During the tapping process, 1150-1350kg of silicon manganese, 600-900kg of low manganese, and 480-520kg of lime are added without adding aluminum iron;

[0014] After the end of tapping, the molten steel is transferred to the LF furnace for treatment;

[0015] When the molten steel leaves the station, the molten steel oxygen content is controlled to be 0.004-0.0055% by using silicon iron deoxidation, and the lower limit of the molten steel sulfur content is increased from 0.26% to 0.30%.

[0016] Further, the 1215MS comprises C: 0.04-0.07, Si≤0.06, Mn: 1.25-1.38, P: 0.05-0.09, S: 0.26-0.38, and O: 0.004-0.006 in mass percentage.

[0017] Further, the silicon content of the molten iron added to the converter is 0.45-0.70%, and the temperature of the molten iron is 1370-1400℃.

[0018] Further, the phosphorus content of the molten iron is 0.095-0.115%, and the phosphorus content of the scrap steel is 0.02-0.04%.

[0019] Further, the molten steel temperature is 1610-1630℃ and the molten steel carbon content is 0.08-0.12% when the molten steel is measured for carbon and temperature when the converter smelting blows oxygen for 10-12min.

[0020] Further, when the molten steel is transferred to the LF furnace for treatment, the molten steel is sent first for 60-100 seconds, and then 480-520 kg of lime is added into the molten steel.

[0021] Further, when the molten steel is transferred to the LF furnace for treatment, after the lime is added into the molten steel, the argon blowing speed is controlled to be 150-180 cubic meters per hour, so that the manganese oxide in the slag is reduced to 10-11%, the iron oxide in the slag is reduced to within 5%, and the slag basicity is controlled to be 2.1-2.5.

[0022] The present application provides a smelting method of 1215MS, after the last furnace is smelted in the converter, a small amount of slag is left in the converter during the slag pouring process. The smelting of the converter with a small amount of slag can not only reduce the consumption of slag, but also reduce the basicity of the slag, so as to realize the phosphorus preservation in the smelting process of 1215MS, and save the addition amount of phosphorus and iron. In addition, when the converter is smelted, the addition amount of scrap steel is appropriately increased and the addition amount of molten iron is reduced, so as to dilute the phosphorus content in the molten iron, so that the phosphorus content in the molten steel can be ensured to be within the qualified range in the case of reducing the dephosphorization.

[0023] Table 1

[0024] Tons of hot metal Hot metal phosphorus % Tons of scrap Scrap phosphorus % Total phosphorus after 100 0.115 40 0.03 0.0907 105 0.115 35 0.03 0.0938 110 0.115 30 0.03 0.0968 115 0.115 25 0.03 0.0998 120 0.115 20 0.03 0.1029

[0025] However, in the actual smelting process, even if the dephosphorization is not needed, the amount of scrap steel cannot be infinitely increased, because when the amount of scrap steel is increased, the physical heat and chemical heat of the molten iron are insufficient, which will lead to a low final smelting temperature, and the molten steel will be over-oxidized in the process of continuous temperature rising, so that the phosphorus in the molten steel is oxidized into the slag, and the effect of dephosphorization is achieved. Therefore, at the end of smelting, the over-oxidation of the molten steel due to low temperature should be avoided, and therefore, when the total addition amount of scrap steel and molten iron is 139-141 t and the temperature of the molten iron is 1370-1400℃, the amount of scrap steel is 30-40 t, which is more appropriate.

[0026] In addition, the present application provides a smelting method of 1215MS, in the process of tapping, 1150-1350 kg of silicon manganese, 600-900 kg of low manganese, and 480-520 kg of lime are added instead of aluminum iron. By optimizing the addition ratio of the tapping alloy, the generation of aluminum oxide inclusions in the molten steel can be reduced, and the alloy cost can be reduced by replacing part of the low manganese with silicon manganese, so as to reduce the smelting cost of the molten steel and improve the economic effect.

[0027] In addition, the application provides a smelting method of the 1215MS, wherein the oxygen content of the outgoing molten steel is controlled at 0.004-0.0055% by using ferrosilicon to deoxidize when the oxygen of the molten steel is determined, and the lower limit of the sulfur content range of the molten steel is increased from 0.26% to 0.30%. By reducing the oxygen content of the molten steel and increasing the sulfur content of the molten steel, the quality of the molten steel can be ensured, the smooth production and use of the 1215MS can be ensured, the cracking problem in processing can be avoided, and the use demand of the customer on the cutting performance of the 1215MS can be met. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A flow chart of the smelting method of the 1215MS provided by the application is shown. DETAILED DESCRIPTION

[0029] Reference Figure 1 The smelting method of the 1215MS provided by the application includes the following steps. The 1215MS includes C: 0.04-0.07, Si≤0.06, Mn: 1.25-1.38, P: 0.05-0.09, S: 0.26-0.38, and O: 0.004-0.006 in percentage by mass.

[0030] Step 1) After the completion of the converter smelting of the previous furnace, the slag is poured out and 2.5-3t of slag is retained.

[0031] When the slag is poured out, a small amount of slag is retained in the converter, which can reduce the amount of slag used for the next furnace steel, and at the same time, the low basicity of the slag used in the smelting of the previous furnace can also reduce the dephosphorization effect during the smelting of the next furnace steel. For example, when the smelting of the previous furnace steel reaches the end point, the slag basicity is 1.5, and if the slag basicity of 1.5 is to be ensured during the smelting of the next furnace steel, the amount of slag containing calcium oxide will increase with the increase of the amount of retained slag, because part of the slag containing calcium oxide will be neutralized by the oxygen in the slag of the previous furnace. However, if no slag is retained at the end point of the smelting of the previous furnace, the amount of slag used for the slag splashing and the amount of slag used for the converter slag layer will increase, i.e. the amount of other slag will increase, so the slag retention control of the application is to pour out most of the slag of the previous furnace and continue to retain 2.5-3t of slag for the smelting of the next furnace. After the smelting of the next furnace is completed, most of the slag of the next furnace steel is poured out, and 2.5-3t of slag is cyclically retained for the smelting of the next furnace.

[0032] Based on the above slag retention control method, taking 3t of retained slag, 120t of molten steel, 6t of slag, 1.5 of basicity, and 0.4% of silicon content of the molten iron as an example, the calculation of the amount of slag used during smelting is as follows: dolomite addition amount = molten steel amount × [molten iron silicon Si] × basicity target value × 1000 / CaO content, dolomite addition amount

[0033] =120*0.4%*1.5*1000 / 30%=2400kg. Magnesium ball added amount = [(slag + dolomite weight * magnesium content in slag - dolomite dosage * 10%)] / magnesium content of magnesium ball. The magnesium content in the slag is configured to 10-13%, taking 10% as an example, the magnesium ball added amount = [(3000+2400)*10%-2400*10%] / 60%=500kg. The total amount added = 2400+500=2900kg, after smelting this furnace of steel, the amount of slag = total slag amount + slag iron oxide content (14%-22%), for example, 15% of iron oxide, that is, the amount of slag = 2900+2900*15%=3335kg. Through slag control, 2.5-3t of circulating slag is reserved for the next furnace smelting, and the basicity is controlled at 1.5-1.8.

[0034] Because the slag basicity is low, only 1.5-1.8, this low basicity is beneficial to phosphorus preservation, but it will cause greater erosion of the furnace lining, so through the method of reserving 2.5-3t of slag (10%-13% of the amount of converter slag) for the converter, the magnesium content of the furnace lining brick (magnesite carbon brick) is supplemented, and the erosion of the converter smelting to the furnace lining is reduced.

[0035] The reason why the basicity range of the present application is controlled at 1.5-1.8 is that the present application adds molten iron with a phosphorus content of 0.095-0.115% to the converter, and the scrap steel amount is large, 30-40t, and the scrap steel used is ordinary scrap steel, with a phosphorus content of only 0.02-0.04%, so after mixing the molten iron and scrap steel, the phosphorus content of the steelmaking raw material is only 0.09-0.1%, even if the maximum molten iron addition amount is 110t, the maximum molten iron phosphorus content is 0.115%, the minimum scrap steel addition amount is 30t, and the maximum scrap steel phosphorus content is 0.04%, the obtained phosphorus content is (0.115%*110+0.04%*30) / (110+30)=0.099%, so in the process of converter smelting, the molten steel only needs to be dephosphorized by 0.01% to make the phosphorus content of the molten steel qualified.

[0036] And the upper limit of the phosphorus content of 1215MS steel is 0.09%, so according to the actual needs, only the basicity needs to be controlled at 1.5-1.8, and in the decarburization process at the end point, part of the phosphorus can be oxidized to the slag through oxidation of the molten steel, to achieve the purpose of dephosphorization.

[0037] Therefore, the present application provides a 1215MS smelting method, which reserves a small amount of slag in the converter after smelting the last furnace, which not only reduces the consumption of slag, but also reduces the basicity of the slag, realizes the phosphorus preservation in the smelting process of 1215MS, saves the addition amount of phosphorus iron, reduces the production cost, and improves the economic benefit.

[0038] Step 2) adding scrap steel 30-40t and molten iron 100-110t into the converter, and controlling the total addition amount to be 139-141t.

[0039] The silicon content of the molten iron added into the converter is 0.45-0.70%, and the temperature of the molten iron is 1370-1400℃.

[0040] The phosphorus content of the molten iron is 0.095-0.115%, and the phosphorus content of the scrap steel is 0.02-0.04%.

[0041] When the materials are added into the converter, the addition of the scrap steel is appropriately increased and the addition of the molten iron is reduced, so that the phosphorus content in the molten iron is diluted, and the phosphorus content in the molten steel can be ensured in the qualified range in the smelting process under the condition of reducing dephosphorization.

[0042] Step 3) After the converter smelting starts to blow oxygen, 1800-3200 kg of light-burned dolomite is added for slagging without adding lime, 300-550 kg of magnesium balls are added for protecting the lining, and the total slag amount for slagging is controlled to be 5-6 t.

[0043] Step 4) During the converter smelting, the low gun position is adopted throughout the gun position control, the gun position is gradually reduced from 2.3 m to 1.6-1.8 m in 0-3 minutes after starting to blow oxygen, in 3-5 minutes, according to the oxidation of the molten iron silicon, after the molten iron silicon is oxidized, the carbon monoxide in the furnace gas will rapidly rise, when it exceeds 35%, the oxygen lance is raised to 1.8-2 m, the appropriate amount of iron oxide in the slag is supplemented for 1-2 minutes, then the gun is lowered to 1.6-1.8 m and the oxygen blowing is continued to 10-11 minutes, and the molten steel is measured and sampled at this time, then the gun is lowered to the low gun position of 1.4-1.5 m and the blowing is continued to the end. In this way, the dissolution of the scrap steel and the temperature rise of the molten steel can be accelerated, and the content of iron oxide in the slag is reduced, so that the slag is dried to reduce the dephosphorization.

[0044] Under normal circumstances, the gun is gradually lowered after starting to blow oxygen, then the gun is raised when the carbon monoxide content increases, and the gun is lowered after 8 minutes to keep a high content of iron oxide in the slag. Since the application needs to retain phosphorus, the high gun position time is shortened compared with the conventional process. However, if the smelting is always at a low gun position, the slag will be seriously dried, and metal spitting will easily occur. Therefore, when observing the slag at the furnace mouth, if metal spitting is found, the gun needs to be raised to supplement the iron oxide in the slag. And since silicon dioxide and manganese oxide are generated preferentially in the early stage of oxygen blowing, and the content of iron oxide in the slag is very low, the iron oxide in the slag is supplemented after the silicon oxidation is completed.

[0045] Because no lime is added during the smelting process, although the low temperature of the molten steel is conducive to dephosphorization in the early stage of smelting, the steel's basicity is insufficient to remove phosphorus. Although the added lightly calcined dolomite can decompose calcium carbonate into calcium oxide during the steelmaking process, which can remove phosphorus, the temperature of the molten steel has already risen above 1300℃ during the melting of scrap steel and slag. Therefore, although the calcium oxide decomposed at this time increases the basicity of the slag, it is not conducive to dephosphorization due to the high temperature of the molten steel.

[0046] Step 5) When the oxygen blowing in the converter reaches 10-12 minutes, the molten steel is sampled for temperature and carbon determination. Based on the requirements for molten iron, scrap steel matching, and lance position control, the molten steel temperature is usually between 1610-1630℃, and the carbon content is usually between 0.1-0.2%. The actual temperature and carbon content should be determined according to the actual situation on site. Based on the actual values, calculated at 1℃ increase and 0.008% decarburization every 2 seconds, the molten steel temperature needs to be raised to 1650-1670℃ when the oxygen blowing in the converter reaches the end point, the carbon content of the molten steel should be controlled at 0.035-0.045%, and the oxygen content should be controlled at 900-1100ppm.

[0047] Step 6) During the tapping process, no aluminum iron is added, only silicon manganese alloy is added. Silicon is used to replace aluminum for deoxidation. Add 1150-1350 kg of silicon manganese, 600-900 kg of low manganese, and 480-520 kg of lime.

[0048] Based on the chemical formula of silicon dioxide, 875 ppm of silicon is required to remove 1000 ppm of oxygen. Calculated with 130t of molten steel, and silicon manganese (containing 18% silicon, with a yield of 85%), the amount of silicon added by 1 kg of silicon manganese is 1*0.18*0.85 / 130000*1000000=1.176 ppm. Therefore, the amount of silicon manganese needed to add 875 ppm of silicon is 875 / 1.176=743 kg.

[0049] At the same time, the silicon in the molten steel is adjusted to 0.06% using silicon from the ferrosilicon manganese. The amount of ferrosilicon manganese needed is 0.06% * 130000 / 0.85 / 0.18 = 509 kg. Thus, the total amount of ferrosilicon manganese needed is 743 + 509 = 1253 kg.

[0050] Therefore, the present invention provides a smelting method for 1215MS, in which 1150-1350 kg of silicon manganese, 600-900 kg of low-manganese, and 480-520 kg of lime are added during the tapping process instead of aluminum ferroalloys. By optimizing the alloy addition ratio during tapping, not only can the formation of aluminum oxide inclusions in the molten steel be reduced, but the replacement of some low-manganese with silicon manganese can also reduce alloy costs, thereby reducing the smelting cost of molten steel and improving economic efficiency.

[0051] Step 7) After tapping, the molten steel is transferred to the LF furnace for processing.

[0052] Wherein, when the molten steel is transferred to the LF furnace for treatment, the molten steel is sent to the station first for 60-100 seconds, and then 480-520 kg of lime is added into the molten steel.

[0053] Furthermore, when the molten steel is transferred to the LF furnace for treatment, the speed of the argon blowing after the lime is added into the molten steel is controlled to be 150-180 cubic meters per hour, so that the oxidized manganese in the slag is separated and reduced, the oxidized manganese in the slag is reduced from 16-19% to 10-11%, the oxidized iron in the slag is reduced to within 5%, and the slag basicity is controlled to be 2.1-2.5.

[0054] In step 8), when the oxygen content of the molten steel is determined, the oxygen content of the molten steel is controlled to be 0.004-0.0055% by using ferrosilicon to deoxidize the molten steel when the molten steel is sent out of the station, and the lower limit of the sulfur content of the molten steel is increased from 0.26% to 0.30% in order to guarantee the cutting performance of the molten steel.

[0055] The present application provides a smelting method of 1215MS, when the oxygen content of the molten steel is determined, the oxygen content of the molten steel is controlled to be 0.004-0.0055% by using ferrosilicon to deoxidize the molten steel, and the lower limit of the sulfur content of the molten steel is increased from 0.26% to 0.30%. By reducing the oxygen content of the molten steel and increasing the sulfur content of the molten steel, not only the quality of the molten steel can be guaranteed, the smooth production of 1215MS in use can be guaranteed, and the cracking problem in processing can be avoided, but also the use demand of the customers for the cutting performance of 1215MS can be met.

[0056] The smelting method of 1215MS provided by the present application is specifically described below through examples.

[0057] Example 1

[0058] Firstly, according to the silicon content of the molten steel of the next furnace, the adding amount of dolomite and magnesium ball is calculated to be 2400 kg and 500 kg respectively, after the smelting of the last furnace is completed, the furnace is shaken and the slag is poured, after the slag added in the last furnace is poured out, 2.5-3 t of slag is left, then 500 kg of magnesium ball is added for magnesium matching of the slag, so that the magnesium oxide reaches 10%-13%, then nitrogen is blown by the oxygen lance, the slag left is splashed on the furnace wall, during the nitrogen blowing process, the oxygen lance is lowered from 2.3 meters to 1 meter, and then raised to 2.3 meters, the up and down is repeated for three times, and the splashing of the slag is completed.

[0059] Add scrap 40 tons, add hot metal 100 tons. Start oxygen blowing, gun position from 2.3 meters gradually to 1.6 meters, oxygen pressure 0.90-0.92 MPa, gradually melt the floating scrap into hot metal, at the same time, open the argon bottom blowing flow to 120 cubic meters / hour, after 100-120 seconds of oxygen blowing, add dolomite 2400 kg. When the carbon monoxide content reaches 35% at 300 seconds of oxygen blowing, lower the oxygen pressure of the oxygen lance to 0.86-0.88 MPa, raise the gun position to 1.8 meters, let the slag supplement some iron oxide to avoid dry return, after 420 seconds of oxygen blowing, lower the gun position to 1.6 meters to accelerate the temperature rise and decarburization, at the same time, reduce the dephosphorization reaction, after 700 seconds of oxygen blowing, take a sample to measure the temperature and determine the carbon content of the molten steel, then lower the gun to 1.4 meters, oxygen pressure 0.90-0.92 MPa, until the end of oxygen blowing. After taking a sample to measure the temperature and determine the carbon content of the molten steel, calculate according to the actual value, until the carbon is reduced to below 0.05%, the temperature of the molten steel is raised to above 1650°C, and the oxygen blowing is ended. After using the automatic temperature measuring system, open the argon bottom blowing flow to 240 cubic meters / hour, to promote the carbon-oxygen reaction, at the same time, promote the deoxidation in the slag, and reduce the iron oxide content to 14% or below.

[0060] During tapping, start adding silicon-manganese alloy at 1 / 4 of the tapping, the amount of silicon-manganese alloy added is calculated according to the final oxygen content of the molten steel, the amount of silicon in the silicon-manganese alloy required for deoxidization and the amount of silicon-manganese alloy required to add silicon to 0.09% in the molten steel, and then add 500 kg of silicon-manganese alloy.

[0061] After the end of tapping, pour the slag, pour out the slag added in this furnace, continue to retain 2.5-3 tons of slag, and continue to circulate smelting in the next furnace.

[0062] After the end of tapping, transfer the molten steel to the LF furnace for treatment. After the molten steel arrives at the station, directly use 4th gear power supply, open the argon bottom blowing to 20-30 cubic meters / hour, supply power for 60-100 seconds, use the carbon in the electrode to react with the oxygen in the slag to reduce some iron oxide and manganese oxide into the molten steel, then add lime 500 kg, after adding lime, open the argon bottom blowing to 150-180 cubic meters / hour, blow argon for 40-60 seconds, use the lime to increase the basicity of the slag while separating the manganese oxide in the slag, then the separated manganese oxide reacts with silicon in the molten steel to replace the metal manganese back into the molten steel. Reduce the argon blowing flow to 20-30 cubic meters / hour to continue to raise the temperature to 1540-1550°C, take a sample to determine the oxygen content, according to the oxygen value, add ferrosilicon to the molten steel, the specific amount of addition is shown in Table 2.

[0063] Table 2

[0064] Oxygen value range ppm 10-30 30-50 50-70 More than 70 Silicon iron addition (kg) None 30 40 50

[0065] If the oxygen value of the molten steel is greater than 70 ppm, then after adding 50 kg of ferrosilicon and stirring for 2 minutes, the oxygen is determined again, and the sample 1 is taken until the oxygen in the molten steel is reduced to less than 70 ppm. After adding ferrosilicon according to the oxygen value, argon is blown for 40-60 seconds at a rate of 150-180 cubic meters / hour to reduce the manganese oxide in the slag to 10-11%, and the argon blowing rate is reduced to 20-30 cubic meters / hour to continue to increase the temperature to 1600-1610°C. During the power transmission process, the manganese, sulfur and other elements are adjusted according to the composition of sample 1 to be within the range. After the power transmission is completed, the oxygen is determined, and the oxygen value is within the range of 40-55 ppm. If the oxygen value is less than 40 ppm, add iron oxide to supplement oxygen, and calculate the oxygen increase of 3 ppm per 10 kg of iron oxide to increase the oxygen to 45 ppm. If the oxygen value is greater than 55 ppm, continue to add ferrosilicon to deoxidize, and calculate the deoxidization of 1.5 kg of ferrosilicon per 1 ppm to deoxidize the oxygen to 50 ppm. After the oxygen is controlled well before soft blowing, soft blowing is carried out for 10-20 minutes to exit the station.

[0066] Comparative Example 1

[0067] If the slag is too much, it will affect the exhaust of the slag during the smelting process. If the exhaust is not smooth, overflow of the slag will occur. If the slag is too little or no slag is left, the oxygen blown into the smelting process is limited by the slag absorption, which will waste oxygen and reduce the heating speed of the molten steel.

[0068] Comparative Example 2

[0069] Adding magnesium ball to splash magnesium slag is to protect the furnace lining. If the amount of magnesium ball is too little, the furnace lining will be eroded quickly, and if the amount of magnesium ball is too much, the cost will be wasted. The technical personnel can obtain a suitable value through on-site tracking test.

[0070] Comparative Example 3

[0071] During the oxygen blowing process, the gun position mode is gradually reduced-high-low-lower. If it is changed to gradually reduced-high-low, the high gun position time is extended, which will increase the steel-slag dephosphorization reaction, resulting in excessive dephosphorization and the need for phosphorus iron supplement in the later period. If the gun is changed to gradually reduced-low, there is no high gun position in the process, and the slag will be dry due to lack of oxygen, which will hinder the exhaust of carbon monoxide, and the slag will be like a lid covering the rice and will overflow from the furnace after a period of time.

[0072] Comparative Example 4

[0073] Adding silicon manganese too early during tapping will easily form a clinker, which will be more difficult to melt, and adding silicon manganese too late will result in less silicon loss in silicon manganese, which will lead to the addition of low-manganese to supplement manganese in the later period, increasing the cost of alloy.

[0074] Comparative Example 5

[0075] If the slag is added first and then the power is sent after the molten steel is sent to the LF furnace, the slag will mix with the manganese oxide and iron oxide in the slag, making it more difficult to reduce these oxides; but if the power is sent all the time without adding slag, after the partial reduction of the oxides, the slag will become thin, the arc will be poor, and the temperature of the molten steel will slow down, so after the partial reduction of the oxides, lime is added to slag the arc.

[0076] Comparative Example 6

[0077] After sending power for 60-100 seconds, lime is added, and after the addition is completed, the large argon gas is not opened for stirring, and the separated manganese oxide is difficult to react with silicon and be reduced, but if the large argon gas is continuously stirred, the effect is also not much better, that is, the reduced manganese oxide is not much, but the electrode will increase a lot of carbon, which will cause the carbon content of the molten steel to exceed the standard.

[0078] Comparative Example 7

[0079] If the oxygen content of the LF furnace is controlled too low, the steel will be difficult to cut off when it is processed by a lathe at the customer's place, which is not conducive to the processing of finished parts, but if the oxygen content is high, liquid surface fluctuation will occur during continuous casting and pouring, or cracking will occur during rolling.

[0080] Comparative Example 8

[0081] In the paper "Metallurgical Effect of Decarburization and Phosphorus Preservation in 120t Converter with Less Slag", a deep desulfurization molten iron less slag decarburization and phosphorus preservation process is adopted to realize w(S)≤0.006% and w(P)≥0.050% at the end of the converter. To this end, the following phosphorus preservation measures are adopted: 1) reducing the amount of lime added, controlling the basicity at about 2.0, using only magnesium balls and lime as slagging materials, and the total slag amount is 33.7kg / t, that is, 4044kg for 120t of molten steel; 2) rapid decarburization and temperature rise, due to the small amount of added slag, only the furnace body maintenance is considered, the converter can be rapidly heated before blowing oxygen to promote the carbon-oxygen reaction and further increase the heating speed, which can effectively inhibit the dephosphorization reaction.

[0082] The difference between the present application and the technical solution is that: first, the problem of desulfurization, the paper needs desulfurization, while the present application not only does not need it, but also increases the sulfur content to increase the cutting performance of the steel, and the lower limit of the sulfur content of the finished product is increased from 0.26% to 0.30%. Second, the total slag amount in the paper is 4044kg, the basicity is about 2, and the slagging material only uses magnesium balls and lime. The present application does not use lime, but uses dolomite instead of lime. From a technical point of view, both lime and dolomite can increase the basicity of the slag, but their functions are different. The paper directly uses lime to adjust the basicity of the slag, while the present application mainly uses the setting property of dolomite to delay the timing of dephosphorization after the lime is produced, rather than being mainly used to adjust the basicity.

[0083] Comparative Example 9

[0084] The paper "80 t converter smelting high phosphorus steel production practice", determine the scrap mode, slag system, oxygen lance control are the key factors affecting the converter dephosphorization.

[0085] Scrap mode: with the increase of heavy scrap ratio, the temperature rises faster in the early stage, when the temperature is higher than the selective oxidation of carbon and phosphorus turning point temperature, the dephosphorization reaction is inhibited. Therefore, when smelting high phosphorus steel, in order to achieve the purpose of decarburization and phosphorus preservation, 100% heavy scrap mode should be used.

[0086] Slag system: the key factor of carbon phosphorus preservation effect. The production application results show that when the final slag basicity is lower than 2.0, the erosion of the splashing layer of the lining is obviously increased, so when smelting high phosphorus steel, the final slag basicity is controlled at 2.0-2.5, and the average w(P) of tapping can reach 0.04%.

[0087] Oxygen lance control: low lance position increases the oxygen lance penetration depth, speeds up the early stage of the furnace reaction, rises the temperature rapidly, shortens the low temperature interval with good dephosphorization effect, makes the decarburization reaction in advance, and inhibits the dephosphorization reaction. At the same time, low lance position is beneficial to reduce the oxidation of the slag. Therefore, the process fixed low lance position and the working oxygen pressure of 0.85 MPa oxygen lance control mode is beneficial to decarburization and phosphorus preservation.

[0088] The paper and the invention are different in the following aspects: first, the type of scrap steel. The paper requires heavy scrap steel and does not like to use light scrap steel and other scrap steel. The invention does not have requirements for the type of scrap steel, and ordinary scrap steel is used. Second, the paper states that the larger the amount of scrap steel, the faster the temperature rises, which is beneficial to phosphorus conservation. However, in the actual smelting process, the heat balance is mainly considered, so it is impossible to infinitely increase the amount of scrap steel for phosphorus conservation. There is an upper limit range, so the invention has a scrap steel usage requirement of 30-40 tons, while the paper does not. Third, the paper states that the slag should be controlled between 2.0-2.5 to protect the furnace lining and achieve 0.04% phosphorus conservation. In terms of slag making and alkalinity control, the production practice of 80t converter smelting high phosphorus steel is better than the metallurgical effect of 120t converter less slag smelting decarburization and phosphorus conservation. The latter only considers phosphorus conservation and controls the slag alkalinity to about 2, without considering the protection of the furnace lining. The invention uses white dolomite + magnesium ball slagging method, which is based on the protection of the furnace lining to optimize the process of phosphorus conservation in molten steel. When using a lower alkalinity slagging method, magnesium balls are used to supplement magnesium to the furnace brick (magnesium carbon brick), which makes up for the lack of low alkalinity. In this way, even when the slag alkalinity is low, the goal of phosphorus conservation can be achieved without serious erosion of the furnace brick. Fourth, the paper uses the method of high to low without lifting the gun. As everyone who has worked in a converter knows, this operation can easily lead to a lack of iron oxide in the slag and dryness, causing metal spatter. However, the paper is only a test, so it is necessary to observe the slag during the converter smelting process and supplement the slag with iron oxide when metal spatter is found. In the invention, the gun position control method is a scientific method of gradually reducing-high-low-lower.

[0089] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, which should be covered by the claims of the present application.

Claims

1. A method of smelting 1215MS, characterized by, The method comprises the following steps: After the previous converter smelting is completed, slag is poured and retained for 2.5-3t; 30-40t of scrap steel and 100-110t of molten iron are added into the converter, and the total amount is controlled to be 139-141t; After the oxygen blowing of the converter smelting is started, white cloud stone 1800-3200kg and magnesium ball 300-550kg are added without lime, and the total slag amount is controlled to be 5-6t; After the oxygen blowing is started, the lance position is gradually reduced from 2.3m to 1.6-1.8m, and then the low lance position is kept to blow until the end point; When the oxygen blowing of the converter smelting is 10-12min, the molten steel temperature is increased to 1650-1670℃, the molten steel carbon content is controlled to be 0.035-0.045%, and the molten steel oxygen content is controlled to be 900-1100ppm; During the tapping process, 1150-1350kg of silicon manganese, 600-900kg of low manganese, and 480-520kg of lime are added without adding aluminum iron; After the tapping is completed, the molten steel is transferred to the LF furnace for treatment; When the molten steel is discharged, the molten steel oxygen content is controlled to be 0.004-0.0055% by using silicon iron deoxidation, and the lower limit of the molten steel sulfur content is increased from 0.26% to 0.30%.

2. The method of smelting 1215MS as claimed in claim 1 wherein: The 1215MS comprises C: 0.04-0.07, Si≤0.06, Mn: 1.25-1.38, P: 0.05-0.09, S: 0.26-0.38, and O: 0.004-0.006 in mass percentage.

3. The method of smelting 1215MS as claimed in claim 1, wherein: The silicon content of the molten iron added into the converter is 0.45-0.70%, and the temperature of the molten iron is 1370-1400℃.

4. The method of smelting 1215MS as claimed in claim 3 wherein: The phosphorus content of the molten iron is 0.095-0.115%, and the phosphorus content of the scrap steel is 0.02-0.04%.

5. The method of smelting 1215MS as claimed in claim 1, wherein: When the oxygen blowing of the converter smelting is 10-12min, the molten steel is measured for carbon and temperature, the molten steel temperature is 1610-1630℃, and the molten steel carbon content is 0.08-0.12%.

6. The method of smelting 1215MS as claimed in claim 1, wherein: When the molten steel is transferred to the LF furnace for treatment, the molten steel is first powered for 60-100S, and then 480-520kg of lime is added into the molten steel.

7. The method of smelting 1215MS as claimed in claim 6 wherein: When the molten steel is transferred to the LF furnace for treatment, after the lime is completely added into the molten steel, the argon blowing speed is controlled to be 150-180 cubic meters / hour, so that the manganese oxide in the slag is reduced to 10-11%, the iron oxide in the slag is reduced to within 5%, and the slag basicity is controlled to be 2.1-2.5.

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