Molten steel smelting method of light non-magnetic high-manganese aluminum alloy steel

Abstract

The invention relates to a molten steel smelting method of light non-magnetic high-manganese aluminum alloy steel, and belongs to the technical field of smelting. And the procedures of EAF smelting, LF refining, VD vacuum refining and die casting are sequentially carried out, all the procedures are properly linked, and the production efficiency is high. Dephosphorization is achieved through medium-term rapid slagging of an EAF electric arc furnace, alloying is conducted after carbon-oxygen reaction, the tapping temperature is larger than or equal to 1600 DEG C, and [C] is smaller than or equal to 0.1%; aluminum blocks are adopted for deoxidation in the first middle stage of LF refining, the content of manganese, nickel and aluminum is adjusted, white slag is made for desulfurization, and alloy is finely adjusted in the later stage of refining, so that components reach the standard; and VD vacuum degassing is conducted, gas inclusions in the molten steel are removed, the purity of the molten steel is improved, hydrogen [H] is smaller than or equal to 2.0 ppm after vacuum breaking, the argon soft blowing time is longer than or equal to 15 min, and then the molten steel is hoisted and transferred to die casting.

Description

Technical Field

[0001] The invention belongs to the field of metallurgy, and in particular relates to a method for smelting molten steel. Background Art

[0002] With the development of lightweighting in the automotive industry, the use of new lightweight high-strength steel is one of the important ways to significantly reduce the weight of the entire vehicle while ensuring the required strength and safety and reliability. Currently, Fe-Mn-Al-C system low-density high-strength steel is widely used. The C content of this steel is 0.05%~2.00%, the Mn content is 2.0%~30.0%, and the Al content is 2.0%~12.0%. The smelting process of high alloy content is relatively cumbersome and requires auxiliary heating equipment such as medium frequency furnaces, resulting in a low yield of easily oxidized alloys in the molten steel. At the same time, the introduction of high-temperature molten metal tends to increase the oxygen and sulfur content in the molten steel, resulting in more inclusions. The white slag formation time lags in LF refining, resulting in increased production costs in the smelting process and higher requirements for production coordination and control of the smelting process. Summary of the Invention

[0003] The present invention provides a smelting method for lightweight non-magnetic high-alloy high-strength steel, which can effectively simplify the smelting process, reduce the P and S contents in molten steel, and improve the problem of high inclusions. The smelting process route adopted is: EAF smelting - LF refining - VD refining - die casting.

[0004] The technical solution adopted by the present invention to solve the above problems is: a method for smelting molten steel of lightweight non-magnetic high-manganese aluminum alloy steel, characterized by: a smelting process route: EAF smelting - LF refining - VD refining, specifically as follows: Step 1, EAF electric arc furnace smelting: Use scrap steel + molten iron as raw material for EAF electric arc furnace smelting, where [S]≤0.03% and [Si]≤0.45% in the molten iron, and the molten iron temperature is ≥1300℃. The scrap steel is selected from high-quality scrap steel with low P and S content, and the scrap steel ratio is 45%-65%. In the early stage of EAF electric arc furnace smelting, electrode arc heating and furnace wall burner fluxing are used to accelerate the melting of scrap steel and reduce power consumption. Batch heating is adopted. Dolomite and lime are added as slag-making materials, and the heat energy generated by the electric arc and the furnace wall burners is used to quickly melt the residual scrap steel and slag. At the end of the EAF electric arc furnace smelting, a consumable carbon oxygen lance and a water-cooled oxygen lance are used to spray oxygen and carbon powder to form foam slag in the slag, which covers the arc light and improves the efficiency of electric energy utilization. The EAF electric arc furnace adopts eccentric bottom tapping, the tapping temperature is ≥1600℃, [C] ≤0.1%, alloys and slag-forming agents are added during tapping, and argon gas is blown through the bottom of the ladle.

[0005] Step 2, LF refining: lime is added to the ladle when it enters the station to adjust the slag basicity and deoxidize; metallic manganese and aluminum blocks are added in batches for alloying, and argon is used to softly blow and stir the bottom of the ladle to accelerate alloy melting and uniform composition. During the manganese-aluminum alloying period, the power supply system needs to be adjusted for heating to maintain a stable molten steel temperature. Argon soft blowing from the bottom accelerates alloy homogenization. The recovery rate of aluminum blocks and metallic manganese is calculated based on a weight percentage of 85%-95%, and the recovery rate of nickel plates is calculated based on a weight percentage of more than 95%; in the later stage of LF refining, the alloy composition is fine-tuned to ensure that the molten steel composition meets the design requirements.

[0006] Step 3, VD refining: The ladle is hoisted into the VD vacuum tank for vacuum degassing. During the vacuum degassing process, argon gas is used to assist stirring at the bottom of the ladle to accelerate the escape of gas in the molten steel and improve the purity of the molten steel. After breaking the air, the hydrogen [H] content is determined to be ≤2.0ppm. After the vacuum is over, argon gas soft blowing is continued. On the premise that the molten steel is not exposed to the air, the argon flow rate at the bottom is adjusted to make the slag layer move slightly, promote the floating of inclusions, and improve the cleanliness of the molten steel.

[0007] Preferably, in step 1, the scrap steel ratio of the raw material is 45%-65%; at the end of the EAF electric arc furnace smelting, the flow rate of the oxygen sprayed by the water-cooled oxygen lance is 2000-4500m 3 / h.

[0008] Preferably, in step 2, the argon soft blowing flow rate at the bottom of the ladle is 20-180 NL / min, and the amount of metallic manganese and aluminum block alloy added in each batch does not exceed 2 t.

[0009] Preferably, in step 3, after the vacuum is completed, the argon soft blowing time is ≥15 minutes.

[0010] Preferably, the molten steel obtained based on this method is cast by mold casting, and the mold casting adopts the bottom casting method to cast the steel ingot, and the steel outlet and the center pouring pipe are connected by a long water nozzle. Argon is used for protection casting throughout the process to prevent secondary oxidation of the molten steel. The steel ingot mold needs to be cleaned and baked in the early stage of pouring, and the baking temperature is controlled within the range of 80-150°C; low-melting-point protective slag is used for the molten steel, and the protective slag needs to be replenished in time during the oxidation pouring process of the molten steel to always keep the liquid level of the molten steel black; after the pouring is completed, a heating block needs to be placed at the cap to compensate for shrinkage and insulation material needs to be placed for insulation; the steel ingot is slowly cooled with the mold.

[0011] Compared with the prior art, the advantages of the present invention are: the process route is simplified in the production process and the production cost is reduced. Dolomite and lime are added in the early stage of EAF smelting to quickly form primary slag, and the large amount of chemical heat of the carbon-oxygen reaction is used in the middle and late stages for alloying and slagging, which shortens the slagging time, reduces the pressure of adding a large amount of alloys in LF refining, and improves production efficiency. The reasonable addition of metallic manganese, aluminum blocks and nickel plates in batches during LF refining, as well as temperature compensation, speeds up the melting rate of the alloy, improves the alloy yield, and increases the purity of the molten steel, while avoiding erosion and oxidation of the furnace lining caused by large temperature gradients. VD vacuum degassing treatment significantly reduces the gas content and the amount of non-metallic inclusions in the molten steel, and improves the purity of the molten steel. DETAILED DESCRIPTION

[0012] The present invention is further described in detail below with reference to the examples. The examples are illustrative and intended to explain the present invention, but are not to be construed as limiting the present invention. Example 1

[0013] A smelting process for lightweight non-magnetic high-alloy high-strength steel, the specific steps are as follows: Step 1: EAF electric arc furnace smelting: EAF electric arc furnace smelting is carried out using scrap steel + molten iron as raw materials, wherein the [S] in the molten iron is 0.029%, [Si] is 0.45%, the molten iron temperature is 1352℃, and the scrap steel is selected high-quality scrap steel with low P and S content, and the scrap steel ratio is 0.48. In the early stage of EAF electric arc furnace smelting, electrode arc heating and furnace wall burner fluxing are used to accelerate the melting of scrap steel and reduce power consumption; slag-making materials such as dolomite and lime are added in batches, and the heat energy generated by the electric arc and furnace wall burner is used to quickly melt the residual scrap steel and slag; at the end of EAF electric arc furnace smelting, a consumable carbon oxygen gun and a water-cooled oxygen gun are used to spray oxygen and carbon powder to form foam slag in the slag, which covers the arc light and improves the efficiency of power utilization. The flow rate of oxygen sprayed by the water-cooled oxygen gun is 2000-4500m 3 / h; EAF electric arc furnace adopts eccentric bottom tapping, the tapping temperature is 1610℃, [C] is 0.09%, alloy and slag-forming agent are added during tapping, and argon gas is soft-blown at the bottom of the ladle.

[0014] Step 2: LF refining: lime is added to the ladle when it enters the station to adjust the slag basicity and deoxidize; metallic manganese and aluminum blocks are added in batches for alloying, and argon is soft-blown at the bottom of the ladle for stirring with a flow rate of 20-180NL / min to accelerate the melting of the alloy and uniform composition. Since the manganese-aluminum alloying causes the molten steel temperature in the refining furnace to drop significantly, it is necessary to use an appropriate power supply system for heating to keep the molten steel temperature stable. Soft argon blowing at the bottom accelerates the homogenization of the alloy, and the amount added each time does not exceed 2t. The recovery rate of aluminum blocks and metallic manganese is considered to be 85%-95% by weight, and the recovery rate of nickel plates is considered to be more than 95% by weight; in the later stage of LF refining, it is necessary to fine-tune the alloy composition to make the molten steel composition meet the standards.

[0015] Step 3: VD refining: The ladle is hoisted to the VD vacuum tank for vacuum degassing. During the vacuum degassing process, argon gas is used to assist in stirring at the bottom of the ladle to accelerate the escape of gas in the molten steel and improve the purity of the molten steel. The hydrogen [H] content is set to 1.5ppm after breaking the air. After the vacuum is completed, the argon soft blowing time is ≥20min. By properly adjusting the argon flow rate at the bottom, the slag layer is slightly moved to avoid the molten steel being exposed to the air, promote the floating of inclusions, and improve the cleanliness of the molten steel.

[0016] Step 4: Mold Casting: The ingot is cast using the bottom casting method. A 35t ingot mold is used, and the tapping port and center pouring pipe are connected via a long nozzle. Argon is used throughout the casting process to prevent secondary oxidation of the molten steel. The ingot mold needs to be cleaned and baked before casting, with the baking temperature controlled within the range of 80-150°C. Low-melting-point protective slag is used to improve the surface quality of the ingot and prevent oxidation. Protective slag must be replenished promptly during the casting process to ensure that the molten steel surface is always black. After casting, a heating block is placed at the cap to compensate for shrinkage and insulation materials are used for insulation. The ingot is slowly cooled in the mold and then transferred to the rolling mill for the next process. Example 2

[0017] A smelting process for lightweight non-magnetic high-alloy high-strength steel, the specific steps are as follows: Step 1: EAF electric arc furnace smelting: EAF electric arc furnace smelting is carried out using scrap steel + molten iron as raw materials, wherein the [S] in the molten iron is 0.028%, [Si] is 0.44%, the molten iron temperature is 1347℃, and the scrap steel is selected high-quality scrap steel with low P and S content, and the scrap steel ratio is 0.46. In the early stage of EAF electric arc furnace smelting, electrode arc heating and furnace wall burner fluxing are used to accelerate the melting of scrap steel and reduce power consumption; slag-making materials such as dolomite and lime are added in batches, and the heat energy generated by the electric arc and furnace wall burner is used to quickly melt the residual scrap steel and slag; at the end of EAF electric arc furnace smelting, a consumable carbon oxygen gun and a water-cooled oxygen gun are used to spray oxygen and carbon powder to form foam slag in the slag, which covers the arc light and improves the efficiency of power utilization. The flow rate of oxygen sprayed by the water-cooled oxygen gun is 2000-4500m 3 / h; EAF electric arc furnace adopts eccentric bottom tapping, the tapping temperature is 1608℃, [C] is 0.086%, alloy and slag-forming agent are added during tapping, and argon gas is soft-blown at the bottom of the ladle.

[0018] Step 2: LF refining: lime is added to the ladle when it enters the station to adjust the slag basicity and deoxidize; metallic manganese and aluminum blocks are added in batches for alloying, and argon is soft-blown at the bottom of the ladle for stirring with a flow rate of 20-180NL / min to accelerate the melting of the alloy and uniform composition. Since the manganese-aluminum alloying causes the molten steel temperature in the refining furnace to drop significantly, it is necessary to use an appropriate power supply system for heating to keep the molten steel temperature stable. Soft argon blowing at the bottom accelerates the homogenization of the alloy, and the amount added each time does not exceed 2t. The recovery rate of aluminum blocks and metallic manganese is considered to be 85%-95% by weight, and the recovery rate of nickel plates is considered to be more than 95% by weight; in the later stage of LF refining, it is necessary to fine-tune the alloy composition to make the molten steel composition meet the standards.

[0019] Step 3: VD refining: The ladle is hoisted into the VD vacuum tank for vacuum degassing. During the vacuum degassing process, argon gas is used to assist in stirring at the bottom of the ladle to accelerate the escape of gas in the molten steel and improve the purity of the molten steel. The hydrogen [H] content is set to 1.3ppm after breaking the air. After the vacuum is completed, the argon soft blowing time is 23min. By properly adjusting the argon flow rate at the bottom, the slag layer is slightly moved to avoid the molten steel being exposed to the air, promote the floating of inclusions, and improve the cleanliness of the molten steel.

[0020] Step 4: Mold Casting: The ingot is cast using the bottom casting method. A 45t ingot mold is used, with the tapping port and center pouring pipe connected via a long nozzle. Argon is used throughout the casting process to prevent secondary oxidation of the molten steel. The ingot mold needs to be cleaned and baked before casting, with the baking temperature controlled within the range of 80-150°C. Low-melting-point mold slag is used to improve the surface quality of the ingot and prevent oxidation. During the casting process, mold slag must be replenished to ensure the molten steel surface is always black. After casting, a heating block is placed at the cap to compensate for shrinkage and insulation materials are used for insulation. The ingot is slowly cooled in the mold and then transferred to the rolling mill for the next process. Example 3

[0021] Step 1: EAF electric arc furnace smelting: EAF electric arc furnace smelting is carried out using scrap steel + molten iron as raw materials, wherein the [S] in the molten iron is 0.03%, [Si] is 0.45%, the molten iron temperature is 1359℃, and the scrap steel is selected high-quality scrap steel with low P and S content, and the scrap steel ratio is 0.49. In the early stage of EAF electric arc furnace smelting, electrode arc heating and furnace wall burner fluxing are used to accelerate the melting of scrap steel and reduce power consumption; slag-making materials such as dolomite and lime are added in batches, and the heat energy generated by the electric arc and furnace wall burner is used to quickly melt the residual scrap steel and slag; at the end of EAF electric arc furnace smelting, a consumable carbon oxygen gun and a water-cooled oxygen gun are used to spray oxygen and carbon powder to form foam slag in the slag, which covers the arc light and improves the efficiency of power utilization. The flow rate of oxygen sprayed by the water-cooled oxygen gun is 2000-4500m 3 / h; EAF electric arc furnace adopts eccentric bottom tapping, the tapping temperature is 1603℃, [C] is 0.095%, alloy and slag-forming agent are added during tapping, and argon gas is soft-blown at the bottom of the ladle.

[0022] Step 2: LF refining: lime is added to the ladle when it enters the station to adjust the slag basicity and deoxidize; metallic manganese and aluminum blocks are added in batches for alloying, and argon is soft-blown at the bottom of the ladle for stirring with a flow rate of 20-180NL / min to accelerate the melting of the alloy and uniform composition. Since the manganese-aluminum alloying causes the molten steel temperature in the refining furnace to drop significantly, it is necessary to use an appropriate power supply system for heating to keep the molten steel temperature stable. Soft argon blowing at the bottom accelerates the homogenization of the alloy, and the amount added each time does not exceed 2t. The recovery rate of aluminum blocks and metallic manganese is considered to be 85%-95% by weight, and the recovery rate of nickel plates is considered to be more than 95% by weight; in the later stage of LF refining, it is necessary to fine-tune the alloy composition to make the molten steel composition meet the standards.

[0023] Step 3: VD refining: The ladle is hoisted to the VD vacuum tank for vacuum degassing. During the vacuum degassing process, argon gas is used to assist in stirring at the bottom of the ladle to accelerate the escape of gas in the molten steel and improve the purity of the molten steel. The hydrogen [H] content is set to 1.6ppm after breaking the air. After the vacuum is completed, the argon soft blowing time is 25min. By properly adjusting the argon flow rate at the bottom, the slag layer is slightly moved to avoid the molten steel being exposed to the air, promote the floating of inclusions, and improve the cleanliness of the molten steel.

[0024] Step 4: Mold Casting: The ingot is cast using the bottom casting method. A 35t ingot mold is used, and the tapping port and center pouring pipe are connected via a long nozzle. Argon is used throughout the casting process to prevent secondary oxidation of the molten steel. The ingot mold needs to be cleaned and baked before casting, with the baking temperature controlled within the range of 80-150°C. Low-melting-point protective slag is used to improve the surface quality of the ingot and prevent oxidation. Protective slag must be replenished promptly during the casting process to ensure that the molten steel surface is always black. After casting, a heating block is placed at the cap to compensate for shrinkage and insulation materials are used for insulation. The ingot is slowly cooled in the mold and then transferred to the rolling mill for the next process.

[0025] In addition to the above embodiments, the present invention also includes other implementation methods. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for smelting molten steel of lightweight non-magnetic high manganese aluminum alloy steel, characterized by: Smelting process route: EAF smelting - LF refining - VD refining, specifically as follows: Step 1, EAF electric arc furnace smelting: EAF electric arc furnace smelting is carried out using scrap steel + molten iron as raw materials, wherein the molten iron has [S]≤0.03%, [Si]≤0.45%, and the molten iron temperature is ≥1300℃. The scrap steel is selected to have a low P and S content, and the scrap steel ratio is 45%-65%. In the early stage of EAF electric arc furnace smelting, electrode arc heating and furnace wall burner fluxing are used to accelerate the melting of scrap steel. Slag-making materials such as dolomite and lime are added in batches, and the heat energy generated by the arc and furnace wall burners is used to quickly melt the residual scrap steel and slag. At the end of EAF electric arc furnace smelting, a consumable carbon oxygen gun and a water-cooled oxygen gun are used to spray oxygen and carbon powder to form foam slag in the slag to cover the arc light. The EAF arc furnace adopts eccentric bottom tapping, the tapping temperature is ≥1600℃, and [C]≤0.1%. Alloy and slag-making agent are added during tapping, and argon gas is soft-blown through the bottom of the ladle. Step 2, LF refining: lime is added to the ladle when it enters the station to adjust the slag basicity and deoxidize; metallic manganese and aluminum blocks are added in batches for alloying, and argon gas is used to softly blow and stir the bottom of the ladle. During the manganese-aluminum alloying period, the power supply system needs to be adjusted to keep the molten steel temperature stable. Argon gas soft blowing at the bottom accelerates the homogenization of the alloy. The recovery rate of aluminum blocks and metallic manganese is calculated as 85%-95% by weight, and the recovery rate of nickel plates is calculated as more than 95% by weight; in the later stage of LF refining, the alloy composition is fine-tuned to ensure that the molten steel composition meets the design requirements; Step 3, VD refining: The molten steel ladle is hoisted into the VD vacuum tank for vacuum degassing. During the vacuum degassing process, argon gas is used to assist stirring at the bottom of the ladle to accelerate the escape of gas in the molten steel; after breaking the air, the hydrogen [H] content is determined to be ≤2.0ppm. After the vacuum is over, argon gas soft blowing is continued. On the premise that the molten steel is not exposed to the air, the argon flow rate at the bottom is adjusted to make the slag layer move slightly to promote the floating of inclusions.

2. The method for smelting molten steel of lightweight non-magnetic high manganese aluminum alloy steel according to claim 1, characterized in that: Step 1: The scrap steel ratio of the raw material is 45%-65%; at the end of the EAF electric arc furnace smelting, the flow rate of the oxygen sprayed by the water-cooled oxygen lance is 2000-4500m 3 / h.

3. The method for smelting molten steel of lightweight non-magnetic high manganese aluminum alloy steel according to claim 1, characterized in that: Step 2: The argon soft blowing flow rate at the bottom of the ladle is 20-180NL / min, and the amount of metal manganese and aluminum block alloy added in each batch does not exceed 2t.

4. The method for smelting molten steel of lightweight non-magnetic high manganese aluminum alloy steel according to claim 1, characterized in that: Step 3: After the vacuum is completed, the argon soft blowing time is ≥15min.

5. The method for smelting molten steel of lightweight non-magnetic high manganese aluminum alloy steel according to claim 1, characterized in that: The molten steel obtained based on this method is cast by mold casting. The mold casting adopts the bottom casting method to cast the steel ingot. The steel outlet and the center pouring pipe are connected by a long water nozzle. Argon is used for protection casting throughout the process to prevent the secondary oxidation of the molten steel. The steel ingot mold needs to be cleaned and baked in the early stage of pouring, and the baking temperature is controlled within the range of 80-150°C. The molten steel adopts low-melting-point protective slag. The protective slag needs to be replenished in time during the oxidation pouring process of the molten steel to always keep the liquid surface of the molten steel black. After the pouring is completed, a heating block needs to be placed at the cap to compensate for shrinkage and insulation material needs to be placed for insulation. The steel ingot is slowly cooled with the mold.

6. The method for smelting molten steel of lightweight non-magnetic high manganese aluminum alloy steel according to claim 1, characterized in that: This method is applicable to Fe-Mn-Al-C system steel, in which the C content is 0.05%~2.00%, the Mn content is 2.0%~30.0%, and the Al content is 2.0%~12.0%.