CN117721268B - Dephosphorization slag with excellent phosphorus-rich capability and fluidity for converter steelmaking by double slag method at different temperatures and dephosphorization method - Google Patents

Abstract

The invention discloses dephosphorization slag with excellent dephosphorization capability and mobility in converter steelmaking by a double slag method and a dephosphorization method, wherein through controlling dephosphorization process parameters and various chemical components in dephosphorization slag at a dephosphorization end point, according to different temperatures at the dephosphorization end point, on the basis of introducing R=CaO/SiO ₂ to represent the binary basicity of the dephosphorization slag and reflecting the dephosphorization capability of the dephosphorization slag, the value of M= (FeO+MnO)/(CaO+MgO) is further introduced, the foaming performance and viscosity of the dephosphorization slag are controlled, so that the dephosphorization slag can be smoothly deslagged, and simultaneously, the ratio of N=R/M is controlled, and the balance of the dephosphorization slag between the dephosphorization capability and mobility is comprehensively reflected. According to different dephosphorization period end temperatures, the R value, the M value and the N value are comprehensively controlled, so that the dephosphorization capability of dephosphorization slag at the dephosphorization period end point is excellent, the content of P ₂O₅ in dephosphorization slag components is higher, and the content is more than 3%; the dephosphorization rate in the dephosphorization period is high, and the dephosphorization rate of the molten iron reaches more than 50 percent; meanwhile, the dephosphorization slag has excellent fluidity, and the slag pouring rate reaches more than 50%.

Description

A dephosphorization slag with excellent phosphorus-enriching capacity and fluidity for double-slag converter steelmaking at different temperatures and a dephosphorization method

Technical Field

The invention relates to the technical field of converter steelmaking, and in particular to a dephosphorization slag with excellent phosphorus-enriching capacity and fluidity for double-slag converter steelmaking at different temperatures and a dephosphorization method.

Background technique

The double-slag converter steelmaking process is to first perform desiliconization and dephosphorization operations in the converter, and perform intermediate slag discharge for the dephosphorization slag; then perform decarbonization in the same converter, and retain all the decarbonization slag after steelmaking. After splashing slag to protect the furnace, shake the furnace to confirm that the liquid slag is solidified, and add an appropriate amount of lime to adjust the alkalinity of the dephosphorization slag, then add scrap steel first, and then add molten iron to carry out the next furnace smelting. The double-slag converter steelmaking process uses the thermodynamic condition that the early stage of converter smelting is low, which is conducive to the dephosphorization reaction. The decarbonization final slag of the previous furnace, which has basically no dephosphorization ability due to the high temperature, is used for dephosphorization when the temperature is low in the initial stage of the next furnace blowing. In this way, the lime that has not yet reacted in the previous furnace is fully utilized, so that the amount of lime used can be greatly reduced, and the emission of carbon dioxide is greatly reduced. While reducing the consumption of auxiliary materials such as lime, the amount of converter slag generated is also reduced.

However, the double-slag converter steelmaking process requires a high basicity for a high dephosphorization rate during the dephosphorization period, while a low basicity is required for smooth slag discharge of the dephosphorization slag. Therefore, how to make the dephosphorization slag have both excellent phosphorus-enriching capacity and good fluidity is the key to the smooth and effective implementation of the double-slag converter steelmaking process.

Summary of the invention

The object of the present invention is to provide a dephosphorization slag and a dephosphorization method with excellent phosphorus-enriching capacity and fluidity for double-slag converter steelmaking at different temperatures, wherein the dephosphorization rate during the dephosphorization period is relatively high, and the dephosphorization rate of molten iron reaches more than 50%; the dephosphorization slag at the end of the dephosphorization period has excellent phosphorus-enriching capacity and fluidity, and the slag discharge rate reaches more than 50%; the requirements of high dephosphorization rate during the dephosphorization period of double-slag converter steelmaking and smooth dephosphorization slag discharge can be met at the same time.

To achieve the above purpose, the technical solution of the present invention is as follows:

A dephosphorization slag with excellent phosphorus-enriching capacity and fluidity for double-slag converter steelmaking at different temperatures, wherein the dephosphorization slag has the following components by weight percentage: CaO: 30-40%, SiO ₂ : 15-30%, FeO: 10-32%, MnO: 3-12%, MgO: 5-10%, and the rest are inevitable impurities; wherein the FeO content includes iron oxide FeO and Fe ₂ O ₃ , and the Fe ₂ O ₃ content therein is converted into the corresponding FeO content;

(1) The end temperature T of the dephosphorization period is between 1300 and 1350 °C, and the dephosphorization final slag composition must also satisfy the following relationship:

1.3≤R≤2.1, 0.7≤M≤1.0, 1.5≤N≤2.1;

(2) Dephosphorization end temperature: 1350℃＜T≤1400℃. The dephosphorization final slag composition must also satisfy the following relationship:

1.5≤R≤2.3, 0.6≤M≤0.9, 2.0≤N≤2.8;

(3) Dephosphorization end temperature: 1400℃＜T≤1450℃. The dephosphorization final slag composition must also satisfy the following relationship:

1.7≤R≤2.5, 0.5≤M≤0.8, 2.5≤N≤3.5;

Wherein, R=CaO/SiO ₂ ; M=(FeO+MnO)/(CaO+MgO); N=R/M.

In the composition design of dephosphorization slag in the double slag converter steelmaking process at different temperatures of the present invention:

CaO is the main dephosphorization component in converter slag, and can combine _{with P2O5} in the slag to form tricalcium phosphate or tetracalcium phosphate. For the double slag converter steelmaking process, in order to ensure a stable dephosphorization effect, the present invention controls the lower limit of the CaO content to 30%. However, excessive addition of CaO will easily form high-melting calcium silicate, the slag components will enter the heterogeneous region, and the slag viscosity will increase. In the intermediate slag discharge process, the high viscosity of the dephosphorization slag will affect the smooth discharge of the dephosphorization slag. Therefore, the present invention controls the upper limit of the CaO content to 40%.

_SiO2 is mainly used to stabilize the physical properties of slag and adjust the slag basicity. When the _SiO2 content in the dephosphorization slag is less than 15%, the dephosphorization slag basicity is too high, the fluidity of the dephosphorization slag is reduced, and the intermediate slag discharge is difficult; when the _SiO2 content in the dephosphorization slag is greater than 30%, the dephosphorization slag basicity is too low, and the dephosphorization rate during the dephosphorization period is reduced. Therefore, according to the different Si content in the molten iron, the _SiO2 content in the dephosphorization slag should be controlled at 15~30%.

FeO, including iron oxides FeO and Fe ₂ O ₃ , and the Fe ₂ O ₃ content therein is converted into the corresponding FeO content. Under the action of top-blown oxygen, a part of the molten iron is oxidized into FeO or Fe ₂ O ₃ and enters the slag, and the addition of iron oxide auxiliary materials can more directly increase the FeO content in the slag. The FeO content in the slag can be used to reflect the oxidizability of the slag. The higher the FeO content, the stronger the oxidizability of the dephosphorization slag, which can promote the combination of P elements in the molten iron with oxygen to generate P ₂ O ₅ , thereby promoting the dephosphorization reaction. At the same time, the lime added to the converter will generate high-melting-point calcium silicate on its surface during the slagging process, preventing the further melting of the lime. When the FeO content in the dephosphorization slag is high, the iron oxide will react with calcium silicate to generate low-melting-point slag phases such as calcium ferrite, promote lime slag, and improve the dephosphorization efficiency. In addition, a higher FeO content can also reduce the viscosity of the dephosphorization slag, so that the dephosphorization slag can be discharged smoothly during the intermediate slag discharge process. Therefore, in order to achieve a higher iron dephosphorization rate and smooth slag discharge, the lower limit of FeO content in the dephosphorization slag is controlled to be 10%. However, when the FeO content in the dephosphorization slag is too high, it shows that the iron is over-oxidized, or the iron oxide auxiliary material added is too much, and the metal Fe is consumed in a large amount in iron oxide as a valuable metal, which can cause the yield of iron to decrease, increasing production costs. In addition, a higher FeO content promotes the oxidation of C in the iron molten iron, thereby easily making the slag contain a large amount of CO bubbles, the dephosphorization slag foams seriously, and the dephosphorization slag overflows the converter. Therefore, the FeO content in the dephosphorization slag should not be too high, and its upper limit is controlled to be 32%.

MnO is obtained partly by oxidation of manganese contained in molten iron and partly from recycled decarburization slag. It mainly plays the role of regulating the oxidizability of slag. According to the Mn content in molten iron, the MnO in dephosphorization slag fluctuates less and is generally controlled at 3~12%.

MgO, part of it comes from the light-burned dolomite added to the converter, which plays a role in solidifying the decarburization slag and avoiding the splashing of molten iron during the process of adding molten iron. The other part comes from the magnesium-containing refractory material on the inner wall of the converter. The production environment of the converter with strong oxygen blowing causes the molten iron and slag to roll violently, corroding the converter wall, and some magnesium-containing refractory materials fall off and enter the slag. The MgO content in the dephosphorization slag is too low, indicating that the amount of light-burned dolomite added to solidify the decarburization slag during the slag splashing furnace protection is insufficient. If the decarburization slag of the previous furnace is fully retained, the decarburization slag may not be fully solidified, which may easily cause the molten iron to splash when adding molten iron, causing safety hazards. Therefore, the lower limit of the MgO content is controlled to be 5%. However, excessive MgO will cause the slag viscosity to be too high. In order to ensure the smooth discharge of the dephosphorization slag during the intermediate slag discharge process, the upper limit of the MgO content is controlled to be 10%.

At the same time, three relations are defined:

R=CaO/SiO ₂ , M=(FeO+MnO)/(CaO+MgO), N=R/M=(CaO/SiO ₂ )/((FeO+MnO)/(CaO+MgO)).

R is defined as the ratio of CaO/ _SiO2 , which is the binary basicity of the dephosphorization slag and mainly reflects the dephosphorization ability of the dephosphorization slag. When the R value is too small, the phosphorus-rich capacity of the dephosphorization slag drops sharply, and there is not enough CaO to combine with _P2O5 to play a dephosphorization role. When the R value is too large, although the _{dephosphorization} slag has a strong dephosphorization ability, the dephosphorization slag has a large viscosity and poor fluidity. It is difficult to pour out the dephosphorization slag during the intermediate slag discharge process, or it takes a long time to pour out, affecting production efficiency.

M is defined as the ratio of (FeO+MnO)/(CaO+MgO). The sum of the FeO and MnO contents in the dephosphorization slag reflects the oxidizability of the dephosphorization slag and is directly related to the foaming performance of the dephosphorization slag, while CaO and MgO are important components that increase the viscosity of the dephosphorization slag. When the M value is too small, the contents of FeO and MnO in the slag are low, and the contents of CaO and MgO are high. The dephosphorization slag is viscous and cannot be discharged smoothly, and calcining the slag is difficult. When the M value is too large, the contents of FeO and MnO in the slag are high, and the contents of CaO and MgO are low. The viscosity of the dephosphorization slag is low and the slag can be discharged smoothly, but it is easy to cause excessive foaming of the dephosphorization slag and overflow of the converter.

Define N as the ratio of R/M = (CaO/SiO ₂ )/((FeO+MnO)/(CaO+MgO)), where CaO/SiO ₂ is the binary basicity, reflecting the phosphorus-rich capacity of the dephosphorization slag, and (FeO+MnO)/(CaO+MgO) reflects the fluidity of the dephosphorization slag. The ratio of the two (CaO/SiO ₂ )/((FeO+MnO)/(CaO+MgO)) can more comprehensively reflect the balance between the phosphorus-rich capacity and fluidity of the dephosphorization slag. When the N value is too large, the dephosphorization slag has excellent phosphorus-rich capacity, but poor fluidity and cannot be discharged smoothly. When the N value is too small, the dephosphorization slag has excellent fluidity and can be discharged smoothly, but the phosphorus-rich capacity of the dephosphorization slag is reduced, and the molten iron dephosphorization rate at the end of the dephosphorization period is low.

The present invention has found through a large number of experimental studies that in the double-slag converter steelmaking process, at different temperatures at the end of the dephosphorization period, the ratios R, M, and N need to meet different conditions.

When the terminal temperature T of the dephosphorization period is low, 1300~1350℃, it is thermodynamically favorable for the dephosphorization reaction, and adding less lime can achieve a better dephosphorization effect. At this time, the CaO content in the dephosphorization slag can be at a lower content, but the low temperature will lead to poor fluidity of the dephosphorization slag. At this time, it is necessary to increase the FeO content in the dephosphorization slag to reduce the viscosity of the dephosphorization slag to ensure the smooth progress of the intermediate slag discharge. Therefore, the R value is lower, the M value is higher, and the N value is lower.

As the end temperature of the dephosphorization period increases, high temperature is not conducive to the dephosphorization reaction. At this time, it is necessary to increase the CaO content in the dephosphorization slag. At the same time, the viscosity of the dephosphorization slag decreases with the increase of temperature. Therefore, the dephosphorization slag with a low FeO content also has excellent fluidity. Therefore, different end temperature ranges of the dephosphorization period are set. As the temperature rises, the R value increases, the M value decreases, and the N value increases.

After a large number of industrial experiments on double-slag converter steelmaking, the following conclusions are drawn:

(1) The end temperature T of the dephosphorization period is between 1300 and 1350 °C, and the dephosphorization final slag composition must also satisfy the following relationship:

1.3≤R≤2.1, 0.7≤M≤1.0, 1.5≤N≤2.1;

(2) Dephosphorization end temperature: 1350℃＜T≤1400℃. The dephosphorization final slag composition must also satisfy the following relationship:

1.5≤R≤2.3, 0.6≤M≤0.9, 2.0≤N≤2.8;

(3) Dephosphorization end temperature: 1400℃＜T≤1450℃. The dephosphorization final slag composition must also satisfy the following relationship:

1.7≤R≤2.5, 0.5≤M≤0.8, 2.5≤N≤3.5;

The present invention also provides a dephosphorization method for double-slag converter steelmaking at different temperatures, wherein after the decarburization of the previous converter is completed, all 100% of the decarburization slag is retained for the next dephosphorization, lightly burned dolomite is added as a liquid slag solidifying agent, slag splashing is performed to protect the furnace, lime is added to adjust the alkalinity of the dephosphorization slag, and then scrap steel is added first, and then molten iron is added; desiliconization and dephosphorization operations are performed during the dephosphorization period, and after the dephosphorization slag is poured out, decarburization operations are performed in the same converter during the decarburization period, and then 100% of the decarburization slag is retained and used for the next dephosphorization, thereby cyclically performing desiliconization, dephosphorization and decarburization operations;

The weight percentage of the dephosphorization slag components at the end of the dephosphorization period is: CaO: 30-40%, SiO ₂ : 15-30%, FeO: 10-32%, MnO: 3-12%, MgO: 5-10%, and the rest are inevitable impurities; the FeO content includes iron oxide FeO and Fe ₂ O ₃ , and the Fe ₂ O ₃ content is converted into the corresponding FeO content;

(1) The end temperature T of the dephosphorization period is between 1300 and 1350 °C, and the dephosphorization final slag composition must also satisfy the following relationship:

1.3≤R≤2.1, 0.7≤M≤1.0, 1.5≤N≤2.1;

(2) Dephosphorization end temperature: 1350℃＜T≤1400℃. The dephosphorization final slag composition must also satisfy the following relationship:

1.5≤R≤2.3, 0.6≤M≤0.9, 2.0≤N≤2.8;

(3) Dephosphorization end temperature: 1400℃＜T≤1450℃. The dephosphorization final slag composition must also satisfy the following relationship:

1.7≤R≤2.5, 0.5≤M≤0.8, 2.5≤N≤3.5;

Wherein, R=CaO/SiO ₂ ; M=(FeO+MnO)/(CaO+MgO); N=R/M.

Preferably, the amount of light-burned dolomite added is 5-10 kg/ton of steel.

Preferably, the amount of lime added is 5-20 kg/ton of steel.

Preferably, during the dephosphorization period, the oxygen lance is lowered and oxygen blowing starts at a high lance position. The blowing time in the dephosphorization stage is 3 to 10 min, and the top blowing oxygen supply intensity is 1.5 to 3.5 m ³ /(t·min); iron oxide auxiliary material is added during blowing, and the added amount is 6 to 12 kg/ton of steel; before the end of blowing in the dephosphorization period, the oxygen lance is adjusted to a low lance position, and the top blowing oxygen supply intensity is increased to 2.0 to 4.0 m ³ /(t·min); after the blowing is completed, the oxygen lance is lifted, the converter is tilted, and the dephosphorization slag is poured into the slag pot.

Preferably, the iron oxide auxiliary material is sintered ore, return ore, OG pellets or an auxiliary material whose main component is iron oxide.

Preferably, the content of P ₂ O ₅ in the dephosphorization slag is relatively high, greater than 3%.

The dephosphorization rate of molten iron in the dephosphorization period of the present invention is increased to more than 50%, and the slag discharge rate at the end of the dephosphorization period reaches more than 50%.

In the dephosphorization method of the present invention:

Leave all 100% of the liquid decarbonization slag from the previous furnace in the furnace as the dephosphorization agent for the next batch, add 5-10 kg/ton of light-burned dolomite, and perform slag splashing and furnace protection operations to ensure that the decarbonization slag is fully solidified. When the amount of light-burned dolomite added is less than 5 kg/ton of steel, the decarbonization slag may not be fully solidified, which may easily cause molten iron to splash when adding molten iron, causing safety hazards. At the same time, the MgO content in the dephosphorization slag is far from the saturation concentration, which corrodes the furnace lining. When the amount of light-burned dolomite added is greater than 10 kg/ton of steel, the viscosity of the dephosphorization slag will be too high, making it difficult to discharge the slag in the middle. Then add lime, the amount of lime added is 5-20 kg/ton of steel, and then add scrap steel and molten iron.

During the dephosphorization period, the oxygen lance is lowered and oxygen blowing starts at a high lance position. The blowing time of the dephosphorization stage is 3 to 10 minutes. The high lance position is to achieve the desiliconization of the molten iron in the early stage to avoid causing a violent decarburization reaction that causes the converter molten pool to heat up too quickly. When the blowing time of the dephosphorization stage is less than 3 minutes, the lime slag is not sufficient, and the competition reaction between silicon and phosphorus in the molten iron prioritizes the desiliconization reaction, and the dephosphorization reaction has not yet begun. When the blowing time of the dephosphorization stage is more than 10 minutes, the molten iron temperature is too high, which is not conducive to the dephosphorization reaction. At the same time, excessive oxygen blowing will increase the FeO content in the dephosphorization slag, resulting in higher iron loss.

The top blowing oxygen supply intensity during the high-lance oxygen blowing dephosphorization stage is 1.5~3.5 ^m3 /(t·min); iron oxide auxiliary materials are added during blowing, and the addition amount is 6~12 kg/ton of steel. The iron oxide auxiliary materials can be sintered ore, return ore, OG briquette and other auxiliary materials whose main components are iron oxides; before the end of blowing in the dephosphorization period, the oxygen lance is adjusted to a low lance position, and the top blowing oxygen supply intensity is increased to 2.0~ ^4.0m3 /(t·min). At this time, the low lance position and the increase in the top blowing oxygen supply intensity are to improve the mass transfer in the molten pool and promote the dephosphorization reaction; after the blowing is completed, the oxygen lance is lifted, the converter is tilted, and the dephosphorization slag is poured into the slag pot as much as possible.

Compared with the prior art, the present invention has the following beneficial effects:

Traditional dephosphorization slag only considers the control of binary basicity, and it is difficult to meet both high dephosphorization rate and slag discharge rate.

The dephosphorization slag composition design adopted by the present invention controls various chemical components in the dephosphorization slag, and further introduces the M=(FeO+MnO)/(CaO+MgO) value based on the introduction of R=CaO/ _SiO2 to represent the binary basicity of the dephosphorization slag and reflect the dephosphorization ability of the dephosphorization slag according to different temperatures at the end of the dephosphorization period, controls the foaming performance and viscosity of the dephosphorization slag, enables the dephosphorization slag to be discharged smoothly, and controls the ratio of N=R/M at the same time, and more comprehensively reflects the balance between the phosphorus-rich ability and fluidity of the dephosphorization slag. The present invention comprehensively controls the R value, M value and N value according to different temperatures at the end of the dephosphorization period, so that _the phosphorus-rich ability of the dephosphorization slag at the end of the dephosphorization period is excellent, the content of _P2O5 in the dephosphorization slag is high, and the content is greater than 3%; the dephosphorization rate during the dephosphorization period is high, and the molten iron dephosphorization rate reaches more than 50%; at the same time, the dephosphorization slag has excellent fluidity, and the slag pouring rate reaches more than 50%.

In the dephosphorization method of the present invention, by controlling the addition amount of light-burned dolomite, lime and iron oxide auxiliary materials in the dephosphorization process, as well as the blowing time and the top blowing oxygen supply intensity, the dephosphorization slag components at the end of the dephosphorization period are controlled according to different temperature ranges at the end of the dephosphorization period to meet different control requirements, thereby achieving the requirements of high dephosphorization rate and smooth dephosphorization slag discharge during the double-slag converter steelmaking dephosphorization period at different temperatures.

Detailed ways

The present invention will be further described below in conjunction with the embodiments.

The process control parameters of the embodiments of the present invention and the comparative examples are shown in Table 1. Table 2 shows the dephosphorization slag composition and slag dumping rate of the embodiments of the present invention and the comparative examples.

The operation steps of the embodiment of the present invention are as follows:

100% of the liquid decarbonization slag from the previous furnace is left in the furnace as the dephosphorization agent for the next furnace. 5-10 kg/ton of light-burned dolomite is added to splash the slag to protect the furnace to ensure that the decarbonization slag is fully solidified. Then lime is added to adjust the alkalinity. The amount of lime added is 5-20 kg/ton of steel. Then scrap steel and molten iron are added. During the dephosphorization period, the oxygen lance is lowered to start blowing oxygen at a high lance position. The blowing time of the dephosphorization stage is 3-10 min, and the top blowing oxygen supply intensity is 1.5-3.5 ^m3 /(t·min). During the blowing period, iron oxide auxiliary materials are added in an amount of 6-12 kg/ton of steel. The iron oxide auxiliary materials can be auxiliary materials whose main components are iron oxides, such as sintered ore, return ore, OG briquette, etc. Before the end of the blowing of the dephosphorization period, the oxygen lance is adjusted to a low lance position and the top blowing oxygen supply intensity is increased to 2.0-4.0 ^m3 /(t·min); After blowing is completed, lift the oxygen lance, tilt the converter, and pour as much dephosphorization slag as possible into the slag pot.

As shown in Table 2, the dephosphorization slag at the end _of the dephosphorization period of the present invention has excellent phosphorus enrichment ability, the content of _P2O5 in the dephosphorization slag is relatively high, and its content is greater than 3%; the dephosphorization rate during the dephosphorization period is relatively high, and the molten iron dephosphorization rate reaches more than 50%; at the same time, the dephosphorization slag has excellent fluidity, and the slag discharge rate reaches more than 50%. The dephosphorization slag can simultaneously meet the requirements of high dephosphorization rate during the dephosphorization period of double-slag converter steelmaking and smooth dephosphorization slag discharge.

In Comparative Example 1, the terminal temperature of the dephosphorization period is 1376°C, and the corresponding N value is greater than the upper limit of 2.8, resulting in excessive viscosity of the dephosphorization slag, general fluidity of the dephosphorization slag, 29% slag pouring rate, and difficulty in intermediate slag discharge. The reasons are shown in Table 1. The amount of iron oxide added is lower than the lower limit of 6kg/ton of steel, resulting in insufficient foaming and high viscosity in the dephosphorization slag.

In Comparative Example 2, the terminal temperature of the dephosphorization period is 1432°C, at which the corresponding R value is less than the specified lower limit of 1.7, and the N value is less than the specified lower limit of 2.5, resulting in insufficient CaO in the dephosphorization slag for dephosphorization, and a low dephosphorization rate of only 35%. This is because at high temperatures above 1400°C, a higher basicity is required to ensure a higher molten iron dephosphorization rate.

The present invention is further illustrated above through the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent replacement methods. As long as they meet the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the protection scope of the present invention.

Claims (6)

1. A dephosphorization method for converter steelmaking by a double slag method at different temperatures is characterized in that after tapping at the decarburization end point of a previous converter, 100% of decarburization slag is completely left for next dephosphorization, light-burned dolomite is added as a liquid slag curing agent, slag splashing furnace protection is carried out, lime is added to adjust the alkalinity of dephosphorization slag, then waste steel is added first, and molten iron is added; desilication dephosphorization operation is carried out in the dephosphorization period, after the dephosphorization slag is poured out, decarburization operation is carried out in the decarburization period in the same converter, and 100% of the decarburization slag is left for the dephosphorization of the next converter, so that desilication dephosphorization and decarburization operation are circularly carried out;

The dephosphorization slag at the end of the dephosphorization period comprises the following components in percentage by weight: caO: 30-40%, wherein the content of SiO ₂：15~30%,FeO：10~32%,MnO：3~12%,MgO：5~10%,P₂O₅ is more than 3%, and the balance is unavoidable impurities; wherein the FeO content comprises iron oxides FeO and Fe ₂O₃, and converting the Fe ₂O₃ content therein into a corresponding FeO content;

(1) The dephosphorization end point temperature T is 1300-1350 ℃, and dephosphorization slag components at the dephosphorization end point also need to satisfy the following relations:

1.3≤R≤2.1，0.7≤M≤1.0，1.5≤N≤2.1；

(2) Dephosphorization period end point temperature: the dephosphorization slag components at 1350 ℃ and less than or equal to 1400 ℃ at the end of the dephosphorization period also need to satisfy the following relations:

1.5≤R≤2.3，0.6≤M≤0.9，2.0≤N≤2.8；

(3) Dephosphorization period end point temperature: the dephosphorization slag components at the end of the dephosphorization period also need to satisfy the following relations:

1.7≤R≤2.5，0.5≤M≤0.8，2.5≤N≤3.5；

Wherein, R=CaO/SiO ₂; m= (feo+mno)/(cao+mgo); n=r/M.

2. The dephosphorization method for double slag converter steelmaking at different temperatures according to claim 1, wherein the addition amount of the light burned dolomite is 5-10 kg/ton of steel.

3. The dephosphorization method for double slag converter steelmaking at different temperatures according to claim 1, wherein the lime is added in an amount of 5-20 kg/ton of steel.

4. The dephosphorization method of double slag method converter steelmaking at different temperatures according to claim 1, wherein in the dephosphorization period, oxygen lance is lowered to start high lance position oxygen blowing, the blowing time in the dephosphorization period is 3-10 min, and the top blowing oxygen supply strength is 1.5-3.5 m ³/(t.min); adding iron oxide auxiliary materials in the blowing period, wherein the addition amount is 6-12 kg/ton of steel; before converting in the dephosphorization period is finished, adjusting an oxygen lance to a low lance position, and improving the top-blown oxygen intensity to 2.0-4.0 m ³/(t.min); and lifting the oxygen lance after converting, tilting the converter, and pouring dephosphorization slag into the slag pot.

5. The dephosphorization method for converter steelmaking by a double slag method at different temperatures according to claim 4, wherein the iron oxide auxiliary materials are sinter, return ore, OG pressed balls or auxiliary materials with iron oxide as main components.

6. The dephosphorization method for converter steelmaking by a double slag method at different temperatures according to any one of claims 1 to 5, wherein the dephosphorization rate of molten iron in the dephosphorization period is increased to more than 50%, and the slag pouring rate at the end of the dephosphorization period is increased to more than 50%.