A method for smelting cast steel in rotary furnace

Abstract

The present invention discloses a method for returning cast steel water to a rotary furnace for smelting, which mainly solves the technical problems of slag overflow, splashing and low dephosphorization rate in the existing process of returning cast steel water to a rotary furnace for smelting. The technical scheme is a method for returning cast steel water to a rotary furnace for smelting, comprising: 1) turning over the bottom molten iron; 2) transporting the molten iron ladle containing the bottom molten iron to the ladle slag turning area below the ladle turntable of the continuous casting machine; 3) pouring out the cast steel water in the ladle; 4) adding metal material to the converter; 5) performing slag blowing in the converter; 6) tapping the converter after the blowing is completed; 7) performing slag splashing to protect the converter after the tapping is completed, and the slag is not dumped after the slag splashing to protect the converter is completed. The method of the present invention is simple to operate, safe and reliable, reduces the cost of slag treatment, steel material consumption and heat loss, and reduces the steel material consumption by 41kg / t on average.

Description

Technical Field

[0001] The invention relates to a production and utilization technology of excess molten steel, in particular to a method for smelting excess molten steel in a rotary furnace, and belongs to the technical field of iron and steel metallurgy. Background Art

[0002] During the continuous casting process, when the slag detector detects a large amount of slag in the ladle, the slide is closed and the casting of the molten steel in the ladle is completed. At this time, there is still 3 to 7 tons of molten steel in the casting residue in the ladle. In order to utilize this part of molten steel, the original process is to pour the casting residue into a slag basin with a grid, crush and magnetically separate the casting residue after cooling, screen out the steel slag with high metal content, and then add it to the converter for recycling in the form of scrap steel. This process completely loses the heat of the casting residue, increases the cost of slag treatment, and reduces the metal recovery rate in the casting residue, which is not conducive to the converter's high scrap steel ratio smelting and cost reduction. For this reason, a process of directly returning the casting residue slag to the converter for hot recycling has been developed. However, due to the strong oxidizing property of the steel slag and the large amount of slag, there is slag overflow during the casting process and splashing during the converter blowing process, which is easy to damage the equipment and increase the consumption of steel materials. At the same time, since Al2O3 is an amphoteric oxide, its mass percentage in the casting residue is relatively high, above 20%, and as high as 40%, which will greatly reduce the dephosphorization capacity of CaO.

[0003] The Chinese patent application document with application publication number CN102399916A discloses a method for recycling and reusing the waste hot slag in a continuous casting ladle, wherein the molten waste hot slag in the ladle is poured into a heavy iron tank with a clearance height greater than 15%, and then the waste hot slag is added into a converter together with the molten iron for steelmaking; this technology can only recycle the waste of one furnace at a time, the heavy iron tank is very prone to slag overflow, the converter is also prone to splashing and dephosphorization is difficult, and the production rhythm is slow.

[0004] The Chinese patent application document with application publication number CN103333980A discloses a method for recycling casting slag, which uses a heavy iron tank with a clearance height greater than 500mm to collect continuous casting slag. The waiting time of the heavy iron tank does not exceed 2 hours. After the collection, the molten iron in the iron tank is added to the converter, and then single slag smelting is carried out. This technology recycles one furnace of casting slag each time, with low efficiency, and is prone to slag overflow during the collection of casting slag and splashing during the smelting process, and the converter dephosphorization is adversely affected by Al2O3.

[0005] The Chinese patent application document with application publication number CN102994689A discloses a method for hot application of low-basicity casting slag in steelmaking. The converter adopts a slag smelting process, 15-18 kg / t of lime is added before the semi-steel is put into the furnace, and then 5-7 kg / t of hot low-basicity casting slag from the ladle is added to the converter along with the semi-steel for smelting, lime is added in small batches for a total of 12-16 kg / t, and the smelting is continued for 8-10 minutes, and then lime is added in batches for a total of 20-25 kg / t. When the smelting temperature reaches 1600-1630°C, the furnace is turned over once, and 1.5-2.3 kg / t of lime is added. The smelting temperature is continued to reach 1650-1680°C and steel is tapped. This technology only recovers one furnace of casting slag each time and does not specifically describe the recovery method. At the same time, the lime consumption is high, the slag volume is large, and the converter blowing process is prone to splashing and dephosphorization is difficult.

[0006] The Chinese patent application document with application publication number CN1789431A discloses a method for recovering excess steel and slag from a steelmaking ladle, in which all the excess steel and slag are poured into a ladle filled with molten iron, and after the excess steel, slag and molten iron are fully mixed by stirring, they are added into a steelmaking electric arc furnace or a converter to achieve direct recycling of the casting waste; however, when the casting slag is highly oxidizing, it will undergo a violent carbon-oxygen reaction with the molten iron under stirring, resulting in explosion, posing a safety hazard.

[0007] The Chinese patent application document with application publication number CN109609721A discloses a method for recycling hot ladle casting slag in a converter, wherein the hot casting slag is collected in a heavy iron tank after molten iron desulfurization and slag removal, and the basicity of the casting slag is required to be 6-8. The molten iron is then added to the converter with slag from the upper furnace for smelting. The converter adopts a single slag or double slag process, and 5-10 kg / t of lime is added after one pouring of the furnace. This technology is only applicable to steel grades that have been deeply desulfurized by a LF refining furnace, and has a narrow application range. Only one furnace of casting slag is recovered each time, and the production efficiency is low. In addition, there is an adverse effect of Al2O3 on dephosphorization. Summary of the invention

[0008] The purpose of the present invention is to provide a method for smelting excess steel in a rotary furnace, which mainly solves the technical problems of slag overflow, splashing and low dephosphorization rate in the existing process of smelting excess steel in a rotary furnace; the method of the present invention realizes the safe recycling of excess steel and reduces the cost of returning excess steel to production.

[0009] The technical solution adopted by the present invention is a method for smelting cast steel in a rotary furnace, comprising the following steps:

[0010] 1) Turn over the bottom molten iron. When the steel type in the ladle is non-copper steel, non-nickel steel or non-molybdenum steel, pour the bottom molten iron into the ladle at the molten iron pouring station. The mass of the bottom molten iron is m1, in t. The minimum value of m1 is calculated according to formulas (1) to (7).

[0011] T0=1536-(w[C]*100+w[Si]*8.5+w[Mn]*5+w[P]*30)-7(1)

[0012]

[0013] T≥T0+ΔT1(3)

[0014]

[0015]

[0016]

[0017]

[0018] In formulas (1) to (7), T is the temperature of the molten iron in the ladle after the excess steel is poured out, in °C; T0 is the melting point of the molten iron in the ladle after the excess steel is poured out, in °C; T1 is the temperature of the molten iron in the ladle before pouring the excess steel, in °C; T2 is the temperature of the excess steel, in °C; ΔT1 is the superheat of the molten iron, in °C; k is the number of furnaces in which the excess steel in a ladle is returned for use, 1≤k≤3; ΔT 2 is the temperature drop of the molten iron in the ladle from the end of pouring the excess molten steel in the k-1 furnace to the beginning of pouring the excess molten steel in the k furnace, in °C; m2 is the mass of the excess molten steel poured into the ladle per furnace, in t; w[C], w[Si], w[Mn], w[P] are the mass percentage of carbon, silicon, manganese, and phosphorus in the molten iron in the ladle after pouring the excess molten steel, in %, respectively; w[C] 铁 、w[Si] 铁 、w[Mn] 铁 , w[P] 铁 They are the carbon mass percentage, silicon mass percentage, manganese mass percentage and phosphorus mass percentage in the bottom iron of the ladle, in %; w[C] 钢 、w[Si] 钢 、w[Mn] 钢 , w[P] 钢 They are the mass percentage of carbon, silicon, manganese and phosphorus in the molten steel in the ladle, in %;

[0019] 2) The ladle containing the bottom molten iron is transported to the ladle slag turning area below the ladle turntable of the continuous casting machine;

[0020] 3) pouring out the excess molten steel in the ladle. After the ladle is finished pouring steel, the ladle is hoisted to the ladle above the ladle containing the bottom molten iron in the ladle slag turning area, and the ladle is changed from a vertical state to a horizontal state. The excess molten steel in the ladle is poured into the ladle containing the bottom molten iron. The mass of the poured excess molten steel is 40% to 60% of the total mass of the excess molten steel and hot slag in the ladle after the steel pouring is completed. One ladle receives the excess molten steel of k furnaces.

[0021] 4) Adding metal materials to the converter, adding scrap steel, molten iron after desulphurization and slag removal, and bottom molten iron containing residual molten steel from furnace K in sequence into the converter with slag from the upper furnace, wherein the mass of scrap steel is 18% to 22% of the nominal capacity of the converter, and the mass of molten iron before desulphurization is 80% to 84% of the nominal capacity of the converter;

[0022] 5) The converter is used for slag blowing and dephosphorization smelting. The oxygen lance position is 170-190 cm and the oxygen supply intensity is 3.2-3.4 Nm 3 / (t·min), when the oxygen blowing amount is 200~300Nm 3 When the amount of oxygen blowing reaches 22% to 26% of the total oxygen blowing amount, the blowing is stopped;

[0023] The dephosphorization slag is discharged during the converter dephosphorization period, and the slag surface is purged with nitrogen. The nitrogen supply intensity is 3.6~4.0Nm 3 / (t·min), oxygen lance position is 400~550cm, after purging time 50~90s, sufficient amount of dephosphorization slag is discharged;

[0024] During the converter decarburization period, the oxygen lance position is 190-240 cm, and the oxygen supply intensity is 3.4-3.75 Nm 3 / (t·min), lime is added in three batches, light-burned dolomite is added at one time, light-burned dolomite and the first batch of lime are added after blowing is started, the value of w(CaO) / w(SiO2) in the converter terminal slag is controlled to be 3.5-4.5, the mass percentage of MgO in the converter terminal slag is 7.0%-8.0%, the temperature of molten steel at the converter blowing terminal is controlled to be 1610-1660°C, and the mass percentage of carbon in the molten steel is 0.035%-0.065%;

[0025] 6) Steel is tapped after converter blowing is completed;

[0026] 7) After the steel is tapped from the converter, slag splashing is carried out to protect the furnace. After the slag splashing is completed, the slag is not dumped.

[0027] In step 1) of the present invention, the bottom molten iron is poured into the ladle at the molten iron pouring station, and the time when the ladle starts to receive iron should be controlled to be s~(s+10)min before the completion of pouring of the molten steel to be recovered, s=s0+m1 / v, wherein s0 is the time for the ladle to be transported from the molten iron pouring station to the slag turning area of ​​the ladle, in min, m1 is the mass of the bottom molten iron in the ladle, in t, and v is the iron receiving speed of the ladle at the pouring station, in t / min.

[0028] In step 1) of the present invention, the mass m1 of the bottom molten iron is 8% to 12% of the nominal capacity of the molten iron ladle, which has a good effect.

[0029] Furthermore, the method of the present invention also includes, when the steel type in the casting ladle is ultra-low carbon steel, before pouring the cast molten steel into the ladle containing the bottom molten iron, first adding 0.12-0.20 kg / t of high-aluminum slag deoxidizer into the ladle, so as to remove oxygen in the ladle slag brought into the ladle, thereby preventing splashing or large-scale slag overflow.

[0030] The mass percentage of the chemical components of the high-aluminum slag deoxidizer of the present invention is: CaO 20%-30%, Al2O3 5%-10%, SiO2 0%-5%, Al≥41%, and CaF2 2%-6%.

[0031] The selection basis of the process parameters of the method of the present invention is:

[0032] 1, step 1) in the one hand, increase the molten iron quality of the bottoming iron ladle can reduce the melting point of liquid metal after molten iron is mixed with cast surplus molten steel, thereby ensure that the temperature of liquid metal after molten iron is mixed with cast surplus molten steel is greater than its melting point and has a certain superheat, prevent solidification, improve the number of recovery furnaces of cast surplus molten steel; But on the other hand, the molten iron quality of the bottoming iron cannot be too much, is unfavorable for increasing the number of recovery furnaces of cast surplus molten steel of single molten iron ladle, increases the molten iron heat loss of waiting process, is unfavorable for improving converter scrap steel ratio; The number of recovery furnaces of cast surplus molten steel of single molten iron ladle cannot be too much, should be controlled at below 3 furnaces, because when the total charge of converter is constant, the amount of turning over of another molten iron ladle must be reduced, it can cause the molten iron liquid level height in the molten iron ladle to be insufficient and cannot be temperature measurement sampling and molten iron desulfurization after slagging, thereby cannot meet converter smelting, if the total charge of converter changes, then it will cause the converter terminal molten steel quality to increase significantly, there will be a risk of wearing, affecting equipment operation safety.

[0033] 2. In step 3), according to the characteristics that the density of molten steel is significantly greater than that of ladle slag and the viscosity of molten steel is significantly less than that of ladle slag, the molten steel is always located below the ladle slag. When the ladle changes from a vertical state to a horizontal state, the molten steel flows out before the ladle slag and enters the iron ladle, thereby achieving separation of steel and slag, thereby greatly reducing the amount of ladle slag entering the iron ladle, avoiding slag overflow and splashing problems caused by the more intense carbon-oxygen reaction during the pouring of excess molten steel, and reducing the influence of Al2O3 on converter dephosphorization; the change in the mass of the ladle during the pouring of excess molten steel is used to judge the amount of slag poured out. Through a large number of studies, it is found that when the reduction in the mass of the ladle is controlled at 40% to 60% of the total mass of the excess molten steel and hot slag in the ladle after the steel pouring is completed, the amount of molten steel poured out can be maximized and the amount of ladle slag poured out can be reduced. When it is greater than 60%, the amount of ladle slag poured out increases significantly.

[0034] 3. In step 4), the converter loading system should meet the heat requirements for converter smelting, reduce or avoid the mass of exothermic agent added, and at the same time increase the converter scrap ratio as much as possible. When the scrap steel mass is 18% to 22% of the nominal capacity of the converter and the molten iron mass before desulfurization is 80% to 84% of the nominal capacity of the converter, the converter heat just meets the requirements of the smelting end point.

[0035] 4. In step 5), a "slag retention + double slag" smelting process is adopted. During the dephosphorization period, a low lance position of 170 to 190 cm is used for smelting to strengthen the stirring of the molten pool, promote the reaction in the furnace, avoid FeO aggregation in the converter slag and splashing, and at the same time control the value of w(CaO) / (w(SiO2)+w(Al2O3)) in the slag to 1.6 to 2.1, without adding magnesium auxiliary materials, to achieve higher w(CaO) / w(SiO2) and w(CaO) / w(Al2O3) and lower w(MgO), so as to increase the activity of 2CaO·SiO2, improve the enrichment capacity of phosphorus, prevent the formation of magnesium-aluminum spinel, and improve the fluidity of the slag, thereby improving the dephosphorization rate during the dephosphorization period. ; During the intermediate slag discharge period, high-flow nitrogen is used to purge the slag surface to improve the slag foaming, quickly promote the sedimentation of iron beads in the slag, and reduce the iron loss during intermediate slag discharge. However, the gun position should be controlled reasonably so that the nitrogen gas flow only stirs the liquid slag. If the gun position is too low, the impact will be too deep, and a large amount of metallic iron will be wrapped in the slag. If the gun position is too high, the stirring effect on the liquid slag layer will be weakened, and the iron bead sedimentation effect will be poor; During the decarbonization period, high-alkalinity, low-MgO slag is used to control the alkalinity w(CaO) / w(SiO2) in the converter terminal slag to 3.5-4.5 and the MgO mass percentage to 7.0%-8.0%, which can further eliminate the adverse effects of Al2O3 and MgO on dephosphorization.

[0036] Compared with the prior art, the present invention has the following positive effects: 1. The method of the present invention is simple to operate, safe and reliable. By determining a reasonable amount of molten iron as the bottom, reducing the amount of hot slag entering the ladle, controlling the appropriate converter slag composition at different smelting stages of the converter, and implementing nitrogen purge on the slag surface, the problems of molten iron solidification, molten iron splashing, large amounts of slag overflow from the ladle, and converter splashing during the return of cast molten steel to the converter are solved, and the adverse effects of Al2O3 on converter dephosphorization are solved, and multiple cast molten steel can be recovered in each converter smelting, with high production efficiency. 2. The method of the present invention reduces the cost of slag treatment, steel material consumption, and heat loss, and reduces steel material consumption by an average of 41kg / t. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments 1 to 5, as shown in Tables 1 to 5.

[0038] In Examples 1 to 5, the iron receiving speed of the ladle is 6 t / min, the time for transporting the ladle from the pouring station to the slag turning area is 16 min, the converter has a nominal capacity of 250 t, and the continuous casting cycle is 40 min.

[0039] A method for smelting cast steel in a rotary furnace, comprising the following steps:

[0040] 1) Turn over the bottom molten iron. When the steel in the ladle is non-copper steel, non-nickel steel or non-molybdenum steel, pour the bottom molten iron into the ladle at the molten iron pouring station 21 to 32.7 minutes before the end of steel pouring. The mass of the bottom molten iron is 8% to 12% of the nominal capacity of the ladle;

[0041] 2) The ladle containing the bottom molten iron is transported to the ladle slag turning area below the ladle turntable of the continuous casting machine; when the steel type in the ladle is ultra-low carbon steel, 0.12-0.20 kg / t of high-aluminum slag deoxidizer is added to the ladle containing the bottom molten iron;

[0042] 3) pouring out the excess molten steel in the ladle. After the ladle is finished pouring steel, the ladle is hoisted to the ladle above the ladle containing the bottom molten iron in the ladle slag turning area, and the ladle is changed from a vertical state to a horizontal state. The excess molten steel in the ladle is poured into the ladle containing the bottom molten iron. The mass of the poured excess molten steel is 40% to 60% of the total mass of the excess molten steel and hot slag in the ladle after the casting is completed. One ladle can handle 1 to 3 furnaces of excess molten steel.

[0043] 4) Adding metal materials to the converter, adding scrap steel, molten iron after desulfurization and slag removal, and bottom molten iron mixed with residual molten steel into the converter with slag from the upper furnace in sequence, wherein the mass of scrap steel is 45t~55t, and the mass of molten iron before desulfurization is 200t~210t;

[0044] 5) The converter is used for slag blowing and dephosphorization smelting. The oxygen lance position is 170-190 cm and the oxygen supply intensity is 3.2-3.4 Nm 3 / (t·min), when the oxygen blowing amount is 200~300Nm 3 When the amount of oxygen blowing reaches 22% to 26% of the total oxygen blowing amount, the blowing is stopped;

[0045] The dephosphorization slag is discharged during the converter dephosphorization period, and the slag surface is purged with nitrogen. The nitrogen supply intensity is 3.6~4.0Nm 3 / (t·min), oxygen lance position is 400~550cm, after purging time 50~90s, sufficient amount of dephosphorization slag is discharged;

[0046] During the converter decarburization period, the oxygen lance position is 190-240 cm, and the oxygen supply intensity is 3.4-3.75 Nm 3 / (t·min), lime is added in three batches, light-burned dolomite is added at one time, light-burned dolomite and the first batch of lime are added after blowing is started, the value of w(CaO) / w(SiO2) in the converter terminal slag is controlled to be 3.5-4.5, the mass percentage of MgO in the converter terminal slag is 7.0%-8.0%, the temperature of molten steel at the converter blowing terminal is controlled to be 1610-1660°C, and the mass percentage of carbon in the molten steel is 0.035%-0.065%;

[0047] 6) Steel is tapped after converter blowing is completed;

[0048] 7) After the converter is finished tapping, slag splashing is carried out to protect the furnace. After the converter is finished splashing, the slag is not dumped.

[0049] Table 1 Parameters of main raw materials for converter in the embodiment of the present invention

[0050]

[0051] Table 2 Casting waste recovery parameters of the embodiment of the present invention

[0052]

[0053] Table 3 Control parameters of converter dephosphorization smelting and dephosphorization slag discharge in the embodiment of the present invention

[0054]

[0055] Table 4 Control parameters of converter decarburization period in the embodiment of the present invention

[0056]

[0057]

[0058] Table 5 Converter endpoint composition and steel material consumption parameters of the embodiment of the present invention

[0059]

[0060] Tables 1 to 5 show the parameters of the main raw materials of the converter, the parameters of the recovery of the casting residue, the control parameters of the smelting and dephosphorization slag discharge during the dephosphorization period of the converter, the control parameters of the smelting during the decarburization period of the converter, the final composition of the converter and the consumption of steel material. The calculation formula of the consumption of steel material is: The average dephosphorization rate of Examples 1-5 is 89.97%, and the average steel consumption is 1043.79 kg / t, which is 41 kg / t lower than the average steel consumption of 1085 kg / t in the conventional process, thereby greatly reducing the steelmaking production cost and having broad application prospects.

[0061] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for smelting cast steel in a rotary furnace, characterized in that: The method comprises the following steps: 1) Turn over the bottom molten iron. When the steel type in the ladle is non-copper steel, non-nickel steel or non-molybdenum steel, pour the bottom molten iron into the ladle at the molten iron pouring station. The mass of the bottom molten iron is m1, in t. The minimum value of m1 is calculated according to formulas (1) to (7). T0=1536-(w[C]*100+w[Si]*8.5+w[Mn]*5+w[P]*30)-7 (1) T≥T0+ΔT1 (3) In formulas (1) to (7), T is the temperature of the molten iron in the ladle after the excess steel is poured out, in °C; T0 is the melting point of the molten iron in the ladle after the excess steel is poured out, in °C; T1 is the temperature of the molten iron in the ladle before pouring the excess steel, in °C; T2 is the temperature of the excess steel, in °C; ΔT1 is the superheat of the molten iron, in °C; k is the number of furnaces in which the excess steel in a ladle is returned for use, 1≤k≤3; ΔT 2 is the temperature drop of the molten iron in the ladle from the end of pouring the excess molten steel in the k-1 furnace to the beginning of pouring the excess molten steel in the k furnace, in °C; m2 is the mass of the excess molten steel poured into the ladle per furnace, in t; w[C], w[Si], w[Mn], w[P] are the mass percentage of carbon, silicon, manganese, and phosphorus in the molten iron in the ladle after pouring the excess molten steel, in %, respectively; w[C] 铁 、w[Si] 铁 、w[Mn] 铁 , w[P] 铁 They are the carbon mass percentage, silicon mass percentage, manganese mass percentage and phosphorus mass percentage in the bottom iron of the ladle, in %; w[C] 钢 、w[Si] 钢 、w[Mn] 钢 , w[P] 钢 They are the mass percentage of carbon, silicon, manganese and phosphorus in the molten steel in the ladle, in %; 2) The ladle containing the bottom molten iron is transported to the ladle slag turning area below the ladle turntable of the continuous casting machine; 3) pouring out the excess molten steel in the ladle. After the ladle is finished pouring steel, the ladle is hoisted to the ladle above the ladle containing the bottom molten iron in the ladle slag turning area, and the ladle is changed from a vertical state to a horizontal state. The excess molten steel in the ladle is poured into the ladle containing the bottom molten iron. The mass of the poured excess molten steel is 40% to 60% of the total mass of the excess molten steel and hot slag in the ladle after the steel pouring is completed. One ladle receives the excess molten steel of k furnaces. 4) Adding metal materials to the converter, adding scrap steel, molten iron after desulphurization and slag removal, and bottom molten iron containing residual molten steel from furnace K in sequence into the converter with slag from the upper furnace, wherein the mass of scrap steel is 18% to 22% of the nominal capacity of the converter, and the mass of molten iron before desulphurization is 80% to 84% of the nominal capacity of the converter; 5) The converter is used for slag blowing and dephosphorization smelting. The oxygen lance position is 170-190 cm and the oxygen supply intensity is 3.2-3.4 Nm 3 / (t·min), when the oxygen blowing amount is 200~300Nm 3 When adding lime at one time, control the w(CaO) / (w(SiO2)+w(Al2O3)) in the slag to be 1.6-2.1, and stop blowing when the oxygen blowing amount is 22%-26% of the total oxygen blowing amount; In the early stage of smelting, the dephosphorized slag is discharged and the slag surface is purged with nitrogen. The nitrogen supply intensity is 3.6~4.0Nm 3 / (t·min), oxygen lance position is 400~550cm, after purging time 50~90s, sufficient amount of dephosphorization slag is discharged; During the converter decarburization period, the oxygen lance position is 190-240 cm, and the oxygen supply intensity is 3.4-3.75 Nm 3 / (t·min), lime is added in three batches, light-burned dolomite is added at one time, light-burned dolomite and the first batch of lime are added after blowing is started, the value of w(CaO) / w(SiO2) in the converter terminal slag is controlled to be 3.5-4.5, the mass percentage of MgO in the converter terminal slag is 7.0%-8.0%, the temperature of molten steel at the converter blowing terminal is controlled to be 1610-1660°C, and the mass percentage of carbon in the molten steel is 0.035%-0.065%; 6) Steel is tapped after converter blowing is completed; 7) After the converter is finished tapping, slag splashing is carried out to protect the furnace. After the converter is finished splashing, the slag is not dumped.

2. The method for smelting cast steel in a rotary furnace as claimed in claim 1, characterized in that: In step 1), the bottom molten iron is poured into the ladle at the molten iron pouring station, and the time when the ladle starts to receive iron should be controlled to be s~(s+10)min before the completion of pouring of the molten steel to be recovered, s=s0+m1 / v, wherein s0 is the time for the ladle to be transported from the molten iron pouring station to the slag turning area of ​​the ladle, in min; m1 is the mass of the bottom molten iron in the ladle, in t; v is the iron receiving speed of the ladle at the pouring station, in t / min.

3. The method for smelting cast steel in a rotary furnace as claimed in claim 1, characterized in that: In step 1), the mass m1 of the bottom molten iron is 8% to 12% of the nominal capacity of the molten iron ladle.

4. The method for smelting cast steel in a rotary furnace as claimed in claim 1, characterized in that: When the steel type in the casting ladle is ultra-low carbon steel, before pouring the remaining molten steel into the ladle containing the bottom molten iron, add 0.12-0.20 kg / t of high-aluminum slag deoxidizer into the ladle.

5. The method for smelting cast steel in a rotary furnace as claimed in claim 4, characterized in that: The mass percentage of the chemical components of the high-alumina slag deoxidizer is: CaO 20%-30%, Al2O3 5%-10%, SiO2 0%-5%, Al≥41%, and CaF2 2%-6%.

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