Method for smelting pure steel through cooperation of electric furnace bottom hydrogen blowing and RH refining combined hydrogen and argon blowing

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a method for smelting pure steel through cooperation of electric furnace bottom hydrogen blowing and RH refining combined hydrogen and argon blowing. By means of electric furnace bottom hydrogen blowing, strengthening of molten pool stirring, promotion of mass and heat transfer in an electric furnace molten pool, improvement of production efficiency, promotion of carbon-oxygen reaction in a metal molten pool and reaction between molten metal and slag at the same time; dissolved oxygen in molten steel and FeO in slag are controlled, the nitrogen content in the steel is controlled, and the hydrogen content in the molten steel is increased; and then RH blowing hydrogen and argon mixed gas refining is conducted, nitrogen, copper and tin in the steel are removed, RH decarburization is conducted, after nitrogen removal meets the requirement, RH argon blowing is conducted to achieve dehydrogenation, and nitrogen, copper, tin and inclusions in the steel continue to be removed. Through cooperative application of the electric furnace smelting technology and the RH smelting technology, production of the high-purity molten steel is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for smelting pure steel in coordination with electric furnace bottom blowing hydrogen and RH refining combined hydrogen and argon blowing. Background Art

[0002] The steel industry is an important basic industry of my country's national economy. The proportion of electric furnace steelmaking is increasing. However, the molten steel and slag in the electric furnace smelting process are highly oxidizing and have high iron loss. It is difficult to control nitrogen, copper, tin and inclusions in the steel. It is difficult to control the purity of high-grade steel. For example, some automobile manufacturers have required steel companies to use 100% scrap steel to produce automobile steel. The control of oxygen, nitrogen, copper, tin and inclusions in the production of high-quality steel in the electric furnace process will become a difficult technical bottleneck to solve.

[0003] RH refining is an important means of vacuum refining of high-quality steel, which has refining functions such as decarburization, removal of inclusions, degassing (hydrogen, nitrogen), and desulfurization. However, in the production process of electric furnace steel metallurgy, due to the inadequacy of nitrogen and oxygen control in the molten steel of electric furnace steelmaking, it is difficult to deeply remove nitrogen and oxygen in the molten steel during the subsequent RH process refining, especially for some high-grade steel grades, such as automotive plates, high-grade non-oriented silicon steel, etc.

[0004] At the same time, the electric furnace steelmaking process uses a large amount of scrap steel as the main raw material, and the residual copper and tin content in the molten steel is relatively high. When the copper and tin content is high, it will significantly affect the plasticity and high-temperature processing performance of the steel. However, there is currently no good method for removing copper and tin from molten steel. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with combined hydrogen and argon blowing in RH.

[0006] According to one aspect of the present invention, the present invention provides the following technical solution:

[0007] A method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with RH refining and double hydrogen-argon blowing. The bottom hydrogen blowing of the electric furnace realizes oxygen and nitrogen control and hydrogen increase. The subsequent RH refining blowing of hydrogen-argon mixed gas realizes purification refining. Finally, RH argon blowing realizes dehydrogenation to realize pure steel smelting.

[0008] As a preferred embodiment of the method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with double hydrogen-argon blowing for RH refining described in the present invention, hydrogen-argon mixed gas is blown in the riser in the early and middle stages of RH refining to drive the circulation of molten steel to achieve purification refining. After the nitrogen content and carbon content in the molten steel reach the control requirements, the hydrogen-argon mixed gas is switched to argon to achieve dehydrogenation.

[0009] The beneficial effects of the present invention are as follows:

[0010] The present invention proposes a method for smelting pure steel in coordination with bottom blowing hydrogen in an electric furnace and RH refining and double blowing hydrogen and argon. By blowing hydrogen at the bottom of the electric furnace, stirring of the molten pool is enhanced, mass transfer and heat transfer in the molten pool of the electric furnace are promoted, production efficiency is improved, and carbon-oxygen reaction in the molten metal pool and reaction between the molten metal and the slag are promoted, dissolved oxygen in the molten steel and FeO in the slag are controlled, nitrogen content in the steel is controlled, and hydrogen content in the molten steel is increased; then RH blowing of hydrogen and argon mixed gas is used for refining to remove nitrogen, copper and tin in the steel, and RH blowing of argon is used to achieve dehydrogenation after RH decarburization and denitrification meet the requirements, and nitrogen, copper, tin and inclusions in the steel are continuously removed. The production of high-purity molten steel is achieved through the coordinated application of the above-mentioned electric furnace smelting technology and RH smelting technology. DETAILED DESCRIPTION

[0011] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0012] The present invention provides a method for smelting pure steel by combining hydrogen blowing at the bottom of an electric furnace with hydrogen and argon blowing for RH refining. First, hydrogen is blown at the bottom of the electric furnace to strengthen stirring at the bottom of the electric furnace, promote carbon-oxygen reaction in molten steel in the electric furnace molten pool, reaction between molten steel and slag, shorten metallurgical time, control overoxidation of molten steel and slag, and reduce iron loss. At the same time, bubbles generated by gas blowing react with oxygen in molten steel and iron oxide in slag to further control overoxidation of molten steel and slag, generate hydrogen in bubbles to control oxygen on the surface of bubbles, promote nitrogen in molten steel to precipitate on the surface of bubbles to generate nitrogen gas that enters bubbles, and on the other hand, hydrogen in gas blowing dissolves in molten steel to increase the hydrogen content of molten steel, thus providing preparation for subsequent RH purification refining. In subsequent RH purification refining, hydrogen and argon blowing are blown into the riser to drive molten steel circulation, and at the same time, a vacuum tank near the bottom is selected to be used for the molten steel. The blown hydrogen and argon are blown from the sides of the part, the bottom of the vacuum tank and the downcomer. The blown hydrogen or hydrogen-argon mixed gas generates a large number of bubbles, which increases the gas-liquid reaction interface. Part of the hydrogen is dissolved in the molten steel and dispersed tiny hydrogen bubbles are precipitated in the molten steel in the vacuum tank, which significantly increases the gas-liquid reaction interface. The hydrogen in the bubbles and the hydrogen in the molten steel control the oxygen at the gas-liquid interface, which promotes the precipitation of nitrogen, copper and tin in the molten steel to the gas phase. At the same time, RH blowing can also increase the mass transfer of carbon, nitrogen, copper and tin in the molten steel and the surface area of ​​the molten steel in the vacuum tank. Through these mechanisms, the removal of carbon, nitrogen, copper and tin in the molten steel during the RH refining process is enhanced. After the decarburization and denitrification of the molten steel meet the requirements during the RH refining process, RH argon is blown for dehydrogenation, and nitrogen, copper and tin can be continuously removed at the same time, and a large number of tiny hydrogen bubbles generated in the molten steel are used to promote the removal of inclusions in the molten steel.

[0013] Specifically, the present invention provides a method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with RH refining and double hydrogen-argon blowing. Bottom hydrogen blowing of the electric furnace is used to control oxygen, nitrogen and hydrogen. Subsequent RH refining blowing of hydrogen-argon mixed gas is used to achieve purification refining. Finally, RH argon blowing is used to achieve dehydrogenation and pure steel smelting.

[0014] In one embodiment of the present invention, hydrogen blowing at the bottom of the electric furnace is blowing hydrogen or hydrogen-rich gas, including methane, natural gas, coke oven gas, etc., into the molten steel from the bottom of the electric furnace through nozzle-type and air-permeable plug-type bottom blowing elements. In order to strengthen the interaction between bubbles and molten steel and slag and the effect of controlling oxygen and nitrogen, air-permeable plug-type bottom blowing elements are preferred to generate more and more diffuse bubbles; the number of bottom blowing elements is 3-20, which can be preferentially arranged at the center of the furnace bottom, between electrodes and outside, and in the slow flow area of ​​molten steel, avoiding the position of electrodes and oxygen flow blown by oxygen lances, so as to promote the melting of scrap steel, strengthen the heat and mass transfer of the molten pool, and strengthen the reaction of bubbles with molten steel and slag.

[0015] In one embodiment of the present invention, the blowing volume of the bottom blowing of the electric furnace is 200-4000NL / min. The bottom blowing gas flow rate is generally based on the liquid surface turning over and not blowing the slag surface. It is also possible to use a small flow of nitrogen or argon in the early stage of smelting and before melting and clearing; after melting and clearing, blow in a large flow of hydrogen or hydrogen-rich gas. At the end of oxidation, the bottom blowing flow rate is appropriately increased to balance the molten pool, stabilize the carbon-oxygen balance, reduce the total iron content of the final slag, and improve the metal recovery rate.

[0016] During the electric furnace smelting process, hydrogen is blown into the molten steel to form hydrogen bubbles; part of the hydrogen dissolves in the molten steel, increasing the hydrogen content of the molten steel; when the hydrogen bubbles rise in the molten steel, they react with the dissolved oxygen in the molten steel, especially when the oxygen content in the molten steel is high, the hydrogen-oxygen reaction is easier to proceed, and the peroxidation of the molten steel can be controlled; the oxygen content in the molten steel on the surface of the hydrogen bubbles is low, and the nitrogen partial pressure in the bubbles is low, and the nitrogen in the molten steel will undergo a denitrification reaction on the surface of the bubbles; the low CO content in the hydrogen bubbles can promote the reaction of carbon and oxygen in the molten steel on the surface of the bubbles to generate CO that enters the bubbles, promoting the decarburization reaction of the molten steel; when the hydrogen bubbles float up and pass through the slag, they will react with FeO in the slag to control the peroxidation of the slag. When hydrogen-rich gases such as natural gas and coke oven gas are blown in, although there is a process in which the hydrogen-rich gas in the gas decomposes to generate carbon and hydrogen, the bubbles generated will also play the metallurgical role of the above-mentioned blowing of hydrogen bubbles.

[0017] In one embodiment of the present invention, the dissolved hydrogen content in the molten steel at the end of electric furnace smelting is controlled at (4-15)×10 -6 It can not only ensure the oxygen and nitrogen control effect of the electric furnace, but also ensure that the molten steel has a higher initial hydrogen content during the subsequent RH refining, and ensure that RH has better decarburization, denitrification and inclusion removal effects.

[0018] In one embodiment of the present invention, after the electric furnace blows hydrogen, it can also undergo LF refining and then RH refining. During LF refining, bottom blowing of hydrogen or hydrogen-rich gas or argon can be used for stirring. For example, the use of hydrogen or hydrogen-rich gas bottom blowing and stirring in LF refining can enhance the hydrogen enrichment effect of the molten steel and control the nitrogen enrichment during the LF refining process; LF bottom blowing of hydrogen or hydrogen-rich gas can generate hydrogen bubbles in the molten steel, and the nitrogen in the molten steel will react on the surface of the bubbles to generate nitrogen and enter the bubbles; at the same time, bottom blowing of hydrogen will reduce the nitrogen partial pressure generated in the LF arc zone, inhibit the production of nitrogen plasma in the arc zone during the LF refining process, and inhibit the absorption of nitrogen by the molten steel. The LF endpoint controls the hydrogen content in the molten steel to be (6-25)×10 -6 , enhance the subsequent RH purification and refining effect.

[0019] In one embodiment of the present invention, hydrogen-argon mixed gas is blown through the riser in the early and middle stages of RH refining to drive the circulation of molten steel to achieve purification refining. After the nitrogen content and carbon content in the molten steel reach the control requirements, the hydrogen-argon mixed gas is switched to argon to achieve dehydrogenation.

[0020] In one embodiment of the present invention, hydrogen-argon mixed gas is blown in the riser in the early and middle stages of RH refining to drive the circulation of molten steel, and hydrogen-argon mixed gas can also be blown on the side of the vacuum tank near the bottom, hydrogen is blown at the bottom of the vacuum tank, and hydrogen is blown in the downcomer. The flow rate of hydrogen-argon mixed gas blown in the riser is controlled to be 1000-4000NL / min, and the hydrogen in the hydrogen-argon mixed gas accounts for 50-100vol%; the flow rate of hydrogen-argon mixed gas blown on the side of the vacuum tank near the bottom is controlled to be 400-2000NL / min, and the hydrogen in the hydrogen-argon mixed gas accounts for 50-100vol%; the flow rate of hydrogen blown at the bottom of the vacuum tank is controlled to be 200-2000NL / min; the flow rate of hydrogen blown in the downcomer is controlled to be 200-800NL / min.

[0021] During the RH vacuum refining process, nitrogen, copper and tin in the molten steel will precipitate nitrogen, gaseous copper and gaseous tin at the gas-liquid reaction interface and enter the gas phase to be removed from the molten steel. The hydrogen and hydrogen-argon mixed gas blown in will form hydrogen or hydrogen-argon bubbles in the molten steel, increasing the gas-liquid reaction interface; at the same time, the dissolved hydrogen in the molten steel will precipitate small dispersed hydrogen bubbles in the molten steel in the vacuum tank, further increasing the gas-liquid reaction interface; RH multi-position re-blowing blows in more gas, strengthens the stirring and mass transfer of the molten steel pool in the vacuum tank, and promotes the mass transfer of carbon, nitrogen, copper, tin and hydrogen in the molten steel; RH re-blowing causes the surface of the molten steel in the vacuum tank to fluctuate, and the molten steel splashes violently due to the outflow of bubbles, and the surface area of ​​the molten steel is significantly increased; hydrogen in the bubbles and hydrogen in the molten steel controls the enrichment of oxygen at the gas-liquid interface; through the strengthening effect of these mechanisms, RH high-efficiency decarburization, nitrogen, copper and tin are achieved.

[0022] In one embodiment of the present invention, after the nitrogen content and carbon content in the RH refined steel liquid reach the control requirements, the gases blown into the riser, the side of the vacuum tank near the bottom, the bottom of the vacuum tank and the downcomer are all switched to argon gas, and the blowing flow rate remains unchanged or is adjusted within a smaller range (0-20% of the blowing flow rate) to perform rapid dehydrogenation and further denitrification, decoppering, detinning and removal of inclusions, and the refining is terminated after the hydrogen content in the steel reaches the requirements.

[0023] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0024] Example 1

[0025] A steel plant uses a 250-ton electric furnace to produce IF steel for automobiles. When the electric furnace starts to smelt steel, the amount of steel left in the previous furnace is 40 tons, and 230 tons of scrap steel are added in batches. During the smelting process, hydrogen is blown into the molten steel through 5 air-permeable bricks installed at the bottom. The total blowing flow rate is 1500NL / min, and the smelting time is shortened to 46 minutes, which is 7 minutes shorter than the furnace without bottom hydrogen blowing. The carbon oxygen content of the molten steel at the end of smelting is controlled to 0.0026, and the FeO in the end slag is controlled to 27wt%, which is significantly lower than 0.0035 and 34wt% without bottom hydrogen blowing. After the smelting is completed, the steel is tapped, the amount of steel tapped is 200 tons, the amount of steel left is 40 tons, and the carbon content in the steel is 350×10 -6 , hydrogen is 6×10 -6 , the copper and tin contents are 400×10 -6 and 500×10 -6 , nitrogen is 60×10 -6 The nitrogen content is less than 65×10 -6 .

[0026] RH refining was used for subsequent refining. The RH refining riser used 90vol%H2+10vol%Ar as the lifting gas, and the blowing flow rate was 1500NL / min in the first 4 minutes of vacuum and 3000NL / min in the later period. Five vent plugs were installed at the bottom of the vacuum tank to blow in hydrogen, and the blowing flow rate was 750NL / min in the first 4 minutes of vacuum and 1500NL / min in the later period. At the same time, 8 blowing pipes with a diameter of 1.0mm were arranged in the downcomer to blow hydrogen into the molten steel at a blowing flow rate of 450NL / min. After 9 minutes of vacuum refining, the carbon content in the molten steel dropped to 20×10 -6 , reaching the control requirements, after smelting for 16 minutes, the nitrogen content in the steel dropped to 32×10 -6Aluminum was added to the molten steel for deoxidation, and RH blowing refining was switched to combined blowing Ar refining. The argon blowing flow rate of the riser was 3500NL / min, the argon blowing flow rate of the vacuum tank bottom was 1750NL / min, and the argon blowing flow rate of the downcomer was controlled at 450NL / min. After 5 minutes of refining, the hydrogen in the steel dropped to 1×10 -6 , the nitrogen content dropped to 30×10 -6 , oxygen dropped to 8×10 -6 , the copper and tin contents are 300×10 -6 and 400×10 -6 .

[0027] Example 2

[0028] A steel plant uses a 250-ton electric furnace to produce IF steel for automobiles. When the electric furnace starts to smelt steel, the amount of steel left in the previous furnace is 40 tons, and 230 tons of scrap steel are added in batches. During the smelting process, hydrogen is blown into the molten steel through 7 air-permeable bricks installed at the bottom. The total blowing flow rate is 2100NL / min, and the smelting time is shortened to 45 minutes, which is 8 minutes shorter than the furnace without bottom hydrogen blowing. The carbon oxygen content of the molten steel at the end of smelting is controlled to 0.0023, and the FeO in the end slag is controlled to 24wt%, which is significantly lower than 0.0035 and 34wt% without bottom hydrogen blowing. After the smelting is completed, the steel is tapped, with a steel tapping amount of 204 tons, a steel retention amount of 40 tons, and a carbon content of 350×10 -6 , hydrogen is 8×10 -6 , copper and tin contents are 500×10 -6 and 600×10 -6 , nitrogen is 58×10 -6 The nitrogen content is less than 65×10 -6 .

[0029] Subsequently, LF refining was used to increase the temperature and slag was modified. Bottom hydrogen was blown during LF refining with a flow rate of 700 NL / min. LF refining lasted for 30 minutes. The hydrogen content in the molten steel at the time of leaving the station was 10×10 -6 , nitrogen is 65×10 -6 .

[0030] RH refining was used for subsequent refining. The RH refining riser used 85vol%H2+15vol%Ar as the lifting gas, and the blowing flow rate was 1500NL / min in the first 4 minutes of vacuum, and 3000NL / min in the later period; and 5 breathable plugs were installed at the bottom of the vacuum tank to blow in hydrogen, and the blowing flow rate was 750NL / min in the first 4 minutes of vacuum, and 1500NL / min in the later period; 1 gas nozzle was installed on both sides of the central common vertical section of the two immersion tubes of the vacuum tank and 5mm above the bottom of the vacuum tank, and hydrogen was sprayed into the molten steel through the nozzle, and the blowing flow rate was 500NL / min in the first 5 minutes of vacuum, and 1600NL / min in the later period; at the same time, 8 blowing pipes with a diameter of 1.0mm were arranged in the downcomer to blow hydrogen into the molten steel, and the blowing flow rate was 450NL / min; after 8 minutes of vacuum refining, the carbon content in the molten steel dropped to 19×10 -6 , reaching the control requirements, after smelting for 17 minutes, the nitrogen content in the steel dropped to 33×10 -6 The control requirements were met; aluminum was added to the molten steel for deoxidation, and the RH blowing refining was switched to double blowing Ar refining. The argon blowing flow rate of the riser was 3500NL / min, the argon blowing flow rate of the vacuum tank bottom was 1750NL / min, the argon blowing flow rate of the vacuum tank side was 1800NL / min, and the argon blowing flow rate of the downcomer was controlled at 450NL / min. After refining for 5 minutes, the hydrogen content in the steel dropped to 0.8×10 -6 , the nitrogen content dropped to 30×10 -6 , oxygen dropped to 7×10 -6 , the copper and tin contents are 300×10 -6 and 400×10 -6 .

[0031] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with RH refining and combined hydrogen and argon blowing, characterized in that: Hydrogen blowing at the bottom of the electric furnace is used to control oxygen, nitrogen and hydrogen. Subsequent RH refining uses hydrogen-argon mixed gas to achieve purified refining. Finally, RH argon blowing is used to dehydrogenate and achieve pure steel smelting.

2. The method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 1, characterized in that: Bottom blowing of hydrogen in an electric furnace is the blowing of hydrogen or hydrogen-rich gas, including methane, natural gas, and coke oven gas, into the molten steel from the bottom of the electric furnace through nozzle-type and breathable plug-type bottom blowing elements.

3. The method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 1, characterized in that: The air blowing volume of the bottom blowing of the electric furnace is 200-4000NL / min.

4. The method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 1, characterized in that: The dissolved hydrogen content in the steel liquid at the end of electric furnace smelting is controlled at (4-15)×10 -6 .

5. The method for smelting pure steel by combining bottom hydrogen blowing of an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 1, characterized in that: In the early and middle stages of RH refining, hydrogen and argon mixed gas is blown through the riser to drive the circulation of molten steel to achieve pure refining. After the nitrogen and carbon contents in the molten steel meet the control requirements, the hydrogen and argon mixed gas is switched to argon to achieve dehydrogenation.

6. The method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 5, characterized in that: In the early and middle stages of RH refining, hydrogen-argon mixed gas is blown on the side of the vacuum tank near the bottom, hydrogen is blown at the bottom of the vacuum tank, and hydrogen is blown in the downcomer.

7. The method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 5, characterized in that: The flow rate of the hydrogen-argon mixed gas blown by the riser is controlled to be 1000-4000NL / min, and the hydrogen content in the hydrogen-argon mixed gas is 50-100 vol%.

8. The method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 6, characterized in that: The flow rate of hydrogen-argon mixed gas blown on the side of the vacuum tank near the bottom is controlled to be 400-2000NL / min, and the hydrogen content in the hydrogen-argon mixed gas is 50-100 vol%.

9. The method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 6, characterized in that: The flow rate of hydrogen blowing at the bottom of the vacuum tank is controlled to be 200-2000NL / min; the flow rate of hydrogen blowing at the downcomer is controlled to be 200-800NL / min.

10. The method for smelting pure steel by combining bottom hydrogen blowing in an electric furnace with RH refining and combined hydrogen and argon blowing according to claim 6, characterized in that: When the nitrogen and carbon contents in the RH refined steel liquid reach the control requirements, the gases blown into the riser, the side of the vacuum tank near the bottom, the bottom of the vacuum tank and the downcomer are all switched to argon. The refining is terminated when the hydrogen content in the steel reaches the requirements.