Method for producing low-phosphorus molten steel through external refining

Abstract

The invention provides a method for producing low-phosphorus molten steel through external refining, and belongs to the technical field of metallurgy. Oxygen is blown into the converter for first decarburization; adding an auxiliary material containing calcium oxide into the converter to perform primary dephosphorization; after converter blowing is finished, the converter blowing endpoint temperature is controlled to be higher than the first set temperature, and the converter blowing endpoint carbon content is controlled to be lower than the first set carbon content; lime with the set weight is added into molten steel in the converter tapping process, no deoxidizing material is added into the molten steel, and converter slag is controlled to enter a steel ladle through slag stopping equipment; after the steel ladle enters the LF refining furnace, the molten steel is heated, the oxygen content of the molten steel is increased to be higher than the set oxygen content, and the molten steel is dephosphorized for the second time under the oxygen enrichment condition of the molten steel; and after the steel ladle enters the RH refining furnace, the molten steel is subjected to secondary decarburization, tertiary dephosphorization and deoxidation under the vacuum condition, and smelting of low-cost, low-phosphorus and low-carbon molten steel is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and more specifically, relates to a method for producing low-phosphorus molten steel by refining outside a furnace. Background Art

[0002] For most types of steel, phosphorus is a harmful element in steel. Phosphorus will greatly reduce the toughness and plasticity of steel, and has a great impact on the performance of steel. Therefore, the lower the phosphorus content in most types of steel, the better. However, due to the constraints of various factors in the converter smelting process, it is difficult to achieve a low level of phosphorus in molten steel. At present, most steel companies carry out dephosphorization in the converter. The converter smelting is difficult, the dephosphorization stability is poor, and the phosphorus content at the converter end fluctuates greatly. The main functions of the refining furnace are heating, desulfurization, fine-tuning of composition, and improving the cleanliness of molten steel. Phosphorus cannot be further removed during the refining process.

[0003] In the prior art, further deep dephosphorization is mainly achieved by adding reducing dephosphorization agents, blowing oxygen into the ladle, or smelting in two converters at the same time. However, the reducing dephosphorization adopted is costly and not easy to operate. Blowing oxygen into the ladle will lead to large equipment modifications and cost increases. Smelting in two converters at the same time will increase equipment costs significantly. Summary of the invention

[0004] The purpose of the present invention is to provide a method for producing low-phosphorus molten steel by off-furnace refining, so as to solve the problems in the prior art that reductive dephosphorization is costly and difficult to operate, blowing oxygen into the ladle will lead to large equipment modifications and cost increases, and simultaneous smelting of two converters will increase equipment costs significantly.

[0005] In order to achieve the above object, the present invention provides a method for producing low-phosphorus molten steel by refining outside a furnace, comprising:

[0006] Add molten iron and scrap steel into the converter for blowing;

[0007] Blowing oxygen into the converter for the first decarburization;

[0008] Adding auxiliary materials containing calcium oxide into the converter to carry out the first dephosphorization;

[0009] After the converter blowing is completed, the converter blowing end temperature is controlled to be above a first set temperature, and the converter blowing end carbon content is controlled to be below a first set carbon content;

[0010] During the converter tapping process, a set weight of lime is added to the molten steel, and no deoxidizing material is added to the molten steel. The converter slag is controlled by the slag blocking device so as not to enter the ladle.

[0011] After the ladle enters the LF refining furnace, the temperature of the molten steel is raised to increase the oxygen content of the molten steel to above the set oxygen content, and the molten steel is dephosphorized for the second time using the oxygen-rich condition of the molten steel;

[0012] After the ladle enters the RH refining furnace, the molten steel is subjected to a second decarburization, a third dephosphorization and deoxidation under vacuum conditions.

[0013] Furthermore, the method for producing low-phosphorus molten steel by refining outside the furnace further comprises:

[0014] When the phosphorus content or carbon content in the molten steel in the RH refining furnace meets the process requirements, deoxidation materials are added to the molten steel for deoxidation.

[0015] Furthermore, the method for producing low-phosphorus molten steel by refining outside the furnace further comprises:

[0016] After RH refining, the ladle slag is removed and the molten steel enters the LF refining furnace again for slag making, and the slag-steel reaction is used to remove inclusions in the molten steel.

[0017] Furthermore, the first set temperature is 1650°C.

[0018] Furthermore, the first set carbon content is 0.04%.

[0019] Furthermore, the set weight is 4-6kg / t.

[0020] Furthermore, the set oxygen content is 700 ppm.

[0021] Furthermore, the auxiliary materials include lime, and / or limestone, and / or dolomite.

[0022] Furthermore, the step of heating the molten steel comprises:

[0023] Apply electricity to heat the molten steel;

[0024] Increasing the oxygen content of molten steel to above the set oxygen content includes:

[0025] Add iron-containing high-oxygen materials to molten steel.

[0026] Furthermore, the iron-containing high-oxygen material includes iron scale oxidized from the continuous casting billet at high temperature.

[0027] The beneficial effects of the present invention are as follows: providing a method for producing low-phosphorus molten steel by off-furnace refining, adding molten iron and scrap steel into a converter for blowing; blowing oxygen into the converter for the first decarburization; adding an auxiliary material containing calcium oxide into the converter for the first dephosphorization; after the converter blowing is completed, controlling the converter blowing end temperature to be above a first set temperature, and controlling the converter blowing end carbon content to be below a first set carbon content; adding a set weight of lime to the molten steel during the converter tapping process, not adding any deoxidizing material to the molten steel, and controlling the converter slag to enter the ladle through a slag blocking device; after the ladle enters the LF refining furnace, heating the molten steel to increase the oxygen content of the molten steel to above the set oxygen content, and performing a second dephosphorization on the molten steel using the oxygen-rich condition of the molten steel; after the ladle enters the RH refining furnace, performing a second decarburization, a third dephosphorization and deoxidation on the molten steel using a vacuum condition, and realizing the smelting of low-cost, low-phosphorus and low-carbon molten steel.

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0030] Figure 1 A flow chart of a method for producing low-phosphorus molten steel through off-furnace refining according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0032] This embodiment provides a method for producing low-phosphorus molten steel by refining outside the furnace, such as Figure 1 As shown, including:

[0033] Add molten iron and scrap steel into the converter for blowing;

[0034] Blowing oxygen into the converter for the first decarburization;

[0035] Specifically, the carbon in the molten iron can react with oxygen to produce carbon monoxide and carbon dioxide, achieving the first decarbonization.

[0036] Adding auxiliary materials containing calcium oxide into the converter to carry out the first dephosphorization;

[0037] Specifically, the auxiliary material containing calcium oxide can control the temperature of molten steel in the converter during the converter blowing process, and at the same time allow the phosphorus element in the steel to react with calcium oxide to generate phosphorus-containing compounds that enter the slag to remove the phosphorus element.

[0038] After the converter blowing is completed, the converter blowing end temperature is controlled to be above the first set temperature;

[0039] Specifically, controlling the end point temperature of the converter blowing can ensure the melting effect of the lime added during the converter steelmaking process, reduce the feeding time of subsequent processes, and help improve the production rhythm.

[0040] Controlling the carbon content at the converter blowing end point to be below a first set carbon content;

[0041] Specifically, controlling the carbon content at the end of converter blowing is beneficial to further dephosphorization of the molten steel in the next process. The carbon content at the end of the converter can be judged by observing the flame conditions at the converter mouth and combining auxiliary equipment.

[0042] Add a set weight of lime to the molten steel during the converter tapping process;

[0043] Specifically, adding lime during the steel-making process can isolate the heat transfer of the molten steel to the air, thereby benefiting the insulation of the molten steel and reducing the feeding time in subsequent processes.

[0044] No deoxidizing material is added to the molten steel;

[0045] No deoxidizing material is added to the ladle during the converter steel-making process, which is conducive to further dephosphorization of molten steel in the LF refining and RH refining processes.

[0046] The converter slag is controlled to prevent it from entering the ladle through the slag blocking equipment;

[0047] Specifically, during the blowing process of the converter, phosphorus-containing compounds generated enter the converter slag, resulting in a high phosphorus content in the converter slag. Once the phosphorus-rich converter slag enters the ladle with the molten steel, the phosphorus content in the ladle slag will increase, seriously affecting the dephosphorization effect of the next process. Therefore, the converter steelmaking process requires slag blocking equipment to control the converter slag from entering the ladle.

[0048] After the ladle enters the LF refining furnace, the temperature of the molten steel is raised to increase the oxygen content of the molten steel to above the set oxygen content, and the molten steel is dephosphorized for the second time using the oxygen-rich condition of the molten steel;

[0049] Specifically, sufficient oxygen in the molten steel is conducive to further dephosphorization of the molten steel in the LF refining process. The dephosphorization formula is:

[0050] 2[P]+5(FeO)+3(CaO)=3CaO·P2O5+5[Fe]

[0051] Or 2[P]+5(FeO)+4(CaO)=4CaO·P2O5+5[Fe].

[0052] After the ladle enters the RH refining furnace, the molten steel is subjected to a second decarburization, a third dephosphorization and deoxidation under vacuum conditions.

[0053] Specifically, after the LF refining furnace finishes treating the molten steel, it enters the RH refining process. The vacuum condition of the RH refining furnace can reduce the partial pressure of carbon monoxide, which is conducive to the further reaction of carbon and oxygen in the steel, and the generated carbon monoxide and other gases are discharged, which can remove the excess oxygen content in the steel and reduce the carbon content in the molten steel. Since the oxygen content in the steel is still conducive to the dephosphorization reaction of the molten steel, the RH vacuum refining process can further reduce the phosphorus content in the molten steel.

[0054] Optionally, the method for producing low-phosphorus molten steel by refining outside the furnace further comprises:

[0055] When the phosphorus content or carbon content in the molten steel in the RH refining furnace meets the process requirements, deoxidation materials are added to the molten steel for deoxidation.

[0056] Optionally, when the phosphorus content or carbon content in the molten steel meets the process requirements, deoxidation materials can be added to the molten steel to further reduce the oxygen content in the molten steel to the process requirements.

[0057] Optionally, the method for producing low-phosphorus molten steel by refining outside the furnace further comprises:

[0058] After RH refining, the ladle slag is removed and the molten steel enters the LF refining furnace again for slag making, and the slag-steel reaction is used to remove inclusions in the molten steel.

[0059] Specifically, for steel types with strict requirements on inclusions, the ladle slag can be scraped off after RH refining to avoid phosphorus-rich ladle slag from transferring phosphorus to the molten steel, and then returned to the LF refining furnace for re-slaging, and the slag-steel reaction can be used to remove inclusions in the molten steel. After the LF treatment is completed, the molten steel can be transported to the continuous casting process for pouring.

[0060] Preferably, the first set temperature is 1650°C.

[0061] Specifically, practice has shown that a converter final temperature above 1650°C is beneficial to the melting effect of lime added during the converter steelmaking process.

[0062] Preferably, the first set carbon content is 0.04%.

[0063] Specifically, according to the converter carbon-oxygen product formula, it can be known that by making the converter final carbon content less than 0.04%, high-oxygen steel tapping can be achieved.

[0064] Preferably, the weight is set at 4-6 kg / t.

[0065] Specifically, practice has shown that adding 4-6kg / t of lime during the steel-making process is beneficial to isolating the heat transfer from molten steel to the air.

[0066] Preferably, the oxygen content is set to 700 ppm.

[0067] Specifically, practice has shown that controlling the oxygen content in molten steel to greater than 700 ppm is conducive to the dephosphorization reaction.

[0068] Preferably, the auxiliary material comprises lime, and / or limestone, and / or dolomite.

[0069] Preferably, the heating treatment of the molten steel comprises:

[0070] Apply electricity to heat the molten steel;

[0071] Increasing the oxygen content of molten steel to above the set oxygen content includes:

[0072] Add iron-containing high-oxygen materials to molten steel.

[0073] Preferably, the iron-containing high-oxygen material comprises iron scale oxidized from a continuous casting ingot at high temperature.

[0074] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for producing low-phosphorus molten steel by refining outside a furnace, characterized in that: include: Add molten iron and scrap steel into the converter for blowing; Blowing oxygen into the converter for the first decarburization; Adding auxiliary materials containing calcium oxide into the converter to carry out the first dephosphorization; After the converter blowing is completed, the converter blowing end temperature is controlled to be above a first set temperature, and the converter blowing end carbon content is controlled to be below a first set carbon content; During the converter tapping process, a set weight of lime is added to the molten steel, and no deoxidizing material is added to the molten steel. The converter slag is controlled by the slag blocking device so as not to enter the ladle. After the ladle enters the LF refining furnace, the temperature of the molten steel is raised to increase the oxygen content of the molten steel to above the set oxygen content, and the molten steel is dephosphorized for the second time using the oxygen-rich condition of the molten steel; After the ladle enters the RH refining furnace, the molten steel is subjected to a second decarburization, a third dephosphorization and deoxidation under vacuum conditions.

2. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: Also includes: When the phosphorus content or carbon content in the molten steel in the RH refining furnace meets the process requirements, deoxidation materials are added to the molten steel for deoxidation.

3. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 2, characterized in that: Also includes: After RH refining, the ladle slag is removed and the molten steel enters the LF refining furnace again for slag making, and the slag-steel reaction is used to remove inclusions in the molten steel.

4. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: The first set temperature is 1650°C.

5. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: The first set carbon content is 0.04%.

6. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: The set weight is 4-6 kg / t.

7. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: The set oxygen content is 700 ppm.

8. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: The auxiliary materials include lime, and / or limestone, and / or dolomite.

9. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 1, characterized in that: The heating treatment of molten steel comprises: Apply electricity to heat the molten steel; Increasing the oxygen content of molten steel to above the set oxygen content includes: Add iron-containing high-oxygen materials to molten steel.

10. The method for producing low-phosphorus molten steel by refining outside a furnace according to claim 9, characterized in that: The iron-containing high-oxygen material includes iron scale oxidized from the continuous casting billet at high temperature.

Images