A smelting method for purifying impurities in molten steel and casting produced by the smelting method

Abstract

The present invention discloses a smelting method for purifying impurities in molten steel and a casting produced by the same; the smelting method for purifying impurities in molten steel comprises the following steps: S1, adding steel material into a smelting device for smelting, continuously introducing inert gas from bottom to top in the smelting device, heating the temperature to 1670-1710°C and deoxidizing the molten steel, and then allowing the molten steel to stand for the first time and remove slag; S2, heating the molten steel for smelting and continuously introducing inert gas, heating the temperature to 1715-1730°C, and then allowing the molten steel to stand for the second time and remove slag. The smelting method for purifying impurities in molten steel of the present invention continuously introduces inert gas from bottom to top during the smelting process; when the inert gas passes through the metal liquid, it will take out impurities in the molten steel, thereby improving the performance of the casting; on the basis of the continuous introduction of inert gas treatment process, the present invention is combined with a two-step standing treatment process to achieve the discharge of impurities in the molten steel, thereby achieving the function of simultaneous treatment of smelting and refining molten steel.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting and processing, and more specifically to a smelting method for purifying impurities in molten steel and a casting produced thereby. Background Art

[0002] Investment casting is a precision casting method with the advantages of high precision, high surface quality, the ability to cast various alloys, and flexible production batches. It is widely used in aerospace, aviation, navigation, military and civilian fields. The metal smelting technology in investment casting is particularly important, and is related to the quality indicators of precision casting products such as corrosion resistance, processing performance, and mechanical properties.

[0003] At present, most of the raw materials used in investment casting are scraps left over after stamping, processing and shearing. They are collected, sorted, cleaned and packaged subsequently. Their quality is uneven and they often contain a small amount of impurities such as moisture, oil, plastic, etc., which form various impurities in the molten steel during the subsequent smelting process.

[0004] Ordinary precision castings are adversely affected by molten steel: the probability of black spots and slag spots in precision castings increases. First, during the later use of precision castings, especially when used in the ocean or other corrosive environments, corrosion failure occurs; second, stress concentration occurs around defects such as slag spots during use, resulting in sudden fracture failure; third, slag spots also affect processing accuracy and tool life; the hydrogen inside the precision castings cannot be effectively discharged, resulting in reduced welding performance of the castings, and hydrogen embrittlement fracture is prone to occur during use; finally, the microstructure is also affected by tiny impurities in the molten steel, which greatly reduces the performance and life of the castings; therefore, precision castings that are poorly prepared by molten steel during the smelting process will bring huge risks and losses to people's lives, production, and safety. Improving the process of smelting molten steel in investment casting is particularly important for improving the quality of castings.

[0005] Most of the traditional investment casting steel melting equipment is a medium frequency induction furnace, whose main function is to melt the molten steel, but lacks the function of refining the molten steel. The molten steel is prone to absorption oxidation during the melting process. Generally, the removal of impurities can only rely on deoxidizers, slag removers and other means to deoxidize and remove some impurities, which is time-consuming, labor-intensive, and requires high material consumption, and the effect is not ideal.

[0006] On the one hand, during the smelting process of the medium frequency furnace, the magnetic lines of force generated by electromagnetic induction are along the central axis of the furnace body, forming a closed magnetic field inside and outside the coil. Under the action of the magnetic field, the molten steel rolls continuously from the bottom to the top of the furnace. While rolling, the molten steel contacts the air and inhales to produce an oxidation reaction; at the same time, the closer to the furnace wall, the more violent the molten steel rolls, and the more serious the scouring of the furnace wall. On the other hand, there are limitations in the temperature control of the medium frequency smelting furnace. If the smelting temperature of the molten steel is too high, it is easy to cause secondary oxidation and increase the oxide impurities in the molten steel. Too low a temperature will lead to insufficient deoxidation and impurities cannot float up and be discharged.

[0007] Patent CN 216550539 U discloses an argon covering protection device for medium frequency furnace smelting, which uses a protective cover buckled on the top of the medium frequency furnace, forms an exhaust port at the furnace mouth of the medium frequency furnace, and installs an argon injection assembly in the center of the protective cover. By using argon to fully cover the surface of the medium frequency furnace to form a protective layer, the purpose of isolating air and preventing oxidation of molten steel during the medium frequency furnace smelting process is achieved. However, the device cannot remove impurities such as hydrogen and nitrides in molten steel and does not have the function of refining molten steel. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects and shortcomings of the existing smelting process, and to provide a smelting method for purifying impurities in molten steel, which can achieve the refining and impurity removal of molten steel during the smelting process of molten steel.

[0009] Another object of the present invention is to provide a steel casting prepared by the above-mentioned smelting method for purifying impurities in molten steel.

[0010] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0011] The present invention protects a smelting method for purifying impurities in molten steel, comprising the following steps:

[0012] S1, adding steel material into a smelting device for smelting, continuously introducing inert gas from bottom to top in the smelting device, heating the smelting device to 1670-1710° C. and performing deoxidation treatment, then allowing the molten steel to stand for the first time and removing slag;

[0013] S2, heating and melting the molten steel and continuously introducing inert gas, heating the molten steel to a temperature of 1715-1730°C, and then allowing the molten steel to stand for a second time and remove slag.

[0014] In some embodiments, the smelting method for purifying impurities in molten steel comprises the following steps:

[0015] S1, initial melting and first standing and deslagging refining: adding steel materials into a smelting device for melting, and after the molten steel level reaches more than 50% of the volume of the smelting device, continuously introducing inert gas from bottom to top, and continuing to melt the steel materials until the molten steel level is full, and then continuing to introduce inert gas and heating to 1680-1700°C, deoxidizing, and allowing the molten steel to stand for the first time and deslagging;

[0016] S2, secondary heating, static slag removal and refining: After the first static state, the temperature of the molten steel will drop sharply. At this time, the temperature is raised to 1715-1730℃, and the second static slag removal is performed to obtain the refined and impurity-free molten steel.

[0017] It should be noted that:

[0018] In the smelting method of the present invention, when the iron and steel material is melted into a liquid state at the melting point temperature to form molten steel, an inert gas is continuously introduced from bottom to top in the smelting device; on the one hand, when the inert gas passes through the metal liquid, hydrogen and nitrogen elements in the molten steel are taken out, the content of these two elements in the molten steel is greatly reduced, thereby improving the performance of the casting, and the floating of the inert gas will attach to the surface of the impurities in the molten steel to accelerate the floating and discharge of impurities and slag; on the other hand, the inert gas can provide a protective atmosphere for the metal liquid, so that the molten steel can achieve high-temperature (above 1670°C) deoxidation and slag discharge, and prolong the duration of the high-temperature state to facilitate the discharge of impurities and slag. On the basis of the continuous introduction of the inert gas treatment process, the present invention is combined with the two-step static treatment process to achieve the discharge of impurities in the molten steel, thereby achieving the function of simultaneous treatment of smelting and refining molten steel.

[0019] Among them, the deoxidation and slag removal temperature of the present invention reaches above 1670°C. At a higher temperature, the fluidity of the molten steel is enhanced, which is beneficial to the discharge of impurities in the molten steel. At the same time, under the action of inert gas, it can overcome the problem of secondary oxidation caused by excessively high smelting temperature of the molten steel when exposed to the air.

[0020] In addition, conventional smelting devices often require external action to stir the molten steel. Taking the medium frequency smelting furnace as an example, the molten steel rolls continuously from the bottom to the top of the furnace under the action of the magnetic field. While the molten steel rolls, it contacts the air and inhales to produce an oxidation reaction. Especially in the area closer to the furnace wall, the molten steel rolls more violently and the scouring of the furnace wall is more serious. The present invention continuously introduces inert gas from bottom to top in the smelting device. The inert gas floats on the surface of the metal liquid to form a protective atmosphere, which can isolate the air and prevent the inhalation reaction from occurring during tumbling and causing adverse effects; at the same time, the inert gas is filled and floated to form a protective layer on the furnace wall to reduce the scouring of the furnace wall by the rolling metal liquid, which can extend the service life of the furnace lining and reduce the formation of slag.

[0021] In some embodiments, in step S1, the flow rate of the inert gas is 12-18 L / min, and the pressure is 0.3-0.7 MPa.

[0022] In some embodiments, the first standing and deslagging time is 2.5-5 minutes.

[0023] In some embodiments, in step S2, the flow rate of the inert gas is 19-22 L / min, and the pressure is 0.4-0.8 MPa.

[0024] In some embodiments, the second standing and slag removal time is 2.5-5 minutes.

[0025] In some embodiments, the inert gas is one or more of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). In the present invention, argon (Ar) is preferably used as the protective gas.

[0026] In some embodiments, the steel material is one or more of 304 stainless steel, 316 stainless steel, 2205 duplex stainless steel and carbon steel.

[0027] In some embodiments, in step S1, a deoxidizing agent is used in the deoxidation treatment, and the amount used is 0.4-0.5% by weight of the molten steel. The deoxidizing agent is preferably a calcium silicon manganese deoxidizer.

[0028] In some embodiments, in steps S1 and S2, the slag removal is performed using a slag removal agent, and the amount of the slag removal agent is 0.8-1% by weight of the molten steel.

[0029] In some embodiments, the smelting device is a medium frequency induction furnace.

[0030] When medium frequency induction furnace smelting is adopted, the smelting method for purifying impurities in molten steel comprises the following steps:

[0031] S1, initial melting and first standing and deslagging refining: add steel materials into the medium frequency melting furnace for melting, the medium frequency furnace melting power is 200-250kW, after the molten steel level reaches more than 50% of the volume of the medium frequency melting furnace, continuously introduce inert gas from bottom to top, continue to melt the steel materials until the molten steel level is full, keep introducing inert gas and continue to raise the temperature to 1680-1700℃, deoxidize, let the molten steel stand for the first time at 0kW power and remove slag;

[0032] S2, secondary heating, static slag removal and refining: After the first static refining, the temperature of the molten steel will drop sharply. At this time, the smelting power is adjusted to 220-270kW, the temperature is raised to 1715-1730℃, and the second static slag removal is performed at 0kW power to obtain the refined and impurity-free molten steel.

[0033] A steel casting is prepared by adopting the smelting method for purifying impurities in molten steel.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides a smelting method for purifying impurities in molten steel. Inert gas is continuously introduced from bottom to top during the smelting process. When the inert gas passes through the metal liquid, it will bring out the impurity elements in the molten steel. Moreover, the inert gas will float and attach to the surface of the impurities in the molten steel to accelerate the floating and discharge of impurities and slag, thereby improving the performance of the casting. The inert gas can provide a protective atmosphere for the molten metal, so that the molten steel can achieve high-temperature deoxidation and slag discharge, and prolong the duration of the high-temperature state to facilitate the discharge of impurities and slag. Based on the continuous introduction of the inert gas treatment process, the present invention is combined with a two-step static treatment process to achieve the discharge of impurities in the molten steel, thereby achieving the function of simultaneous treatment of smelting and refining molten steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a process flow chart of a smelting method for purifying impurities in molten steel according to Example 1.

[0037] Figure 2 This is a physical picture of a defective slag inclusion product prepared by a smelting method for purifying impurities in molten steel in Comparative Example 1.

[0038] Figure 3 This is a physical picture of an electric furnace after operation of a smelting method for purifying impurities in molten steel in Example 1; the one on the left in the figure is a furnace with an operating age of 100, and the one on the right in the figure is a furnace with an operating age of 235.

[0039] Figure 4 This is a physical picture of an electric furnace after operation of a smelting method for purifying impurities in molten steel according to comparative example 1; the one on the left in the picture is a furnace with an operating age of 100, and the one on the right in the picture is a furnace with an operating age of 198.

[0040] Figure 5 Tensile strain curves of tensile tests on samples prepared by argon-purified molten steel and conventionally smelted molten steel. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0042] The raw materials used in the following examples and comparative examples are as follows:

[0043] 304 steel: Implementation standard GB / T20878-2007.

[0044] Calcium silicon manganese deoxidizer: CaSiMn, Pintai Company; (Si≥46%, Ca≥21.65%, Mn≥17.5%).

[0045] Deslagging agent: F02, Ishikawa Co., Ltd., Japan.

[0046] Example 1

[0047] A smelting method for purifying impurities in molten steel, referring to Figure 1 , including the following steps:

[0048] 1) Preparation before the furnace: Industrial argon gas (purity ≥ 99.96%) supply device, connect the pressure reducing valve and flow meter, and connect to the bottom air brick of the medium frequency induction furnace through the gas pipe;

[0049] 2) Add the cold-forged 304 steel tailings into a 150KG medium-frequency induction furnace for smelting. The power of the medium-frequency induction furnace is 250kW. When the molten steel rises to 50% of the furnace body height, argon gas (pressure 0.5MPa, flow rate 15L / min) is continuously introduced from bottom to top in the medium-frequency induction furnace.

[0050] 3) Continue to add steel until the molten steel is fully melted, adjust the argon gas to (pressure 0.6MPa, flow rate 18L / min), continue to heat up to 1680°C, and start using calcium silicon manganese deoxidizer for deoxidation, the amount of which accounts for 0.5% of the weight of the molten steel, and sprinkle it evenly on the surface of the molten steel twice to complete the deoxidation operation;

[0051] 4) After heating for 1 minute, the temperature of the molten steel rises to 1700°C, and the molten steel is allowed to stand at 0kW power while using a slag remover to remove slag. The slag remover is evenly covered on the surface of the molten steel, and is removed after sufficient slag is formed. This is repeated three times. The amount of slag remover is 0.9% of the weight of the molten steel. After 0kW power, the molten steel is allowed to stand for a total of 3 minutes, including the slag removal time;

[0052] 5) After 3 times of slag removal, the temperature of the molten steel will drop sharply; at this time, the molten steel melting power is increased to 260kW and the argon gas flow rate is adjusted to 20L / min, and the pressure is 0.7MPa. When the molten steel temperature rises to 1720℃, it is once again left at 0kW power and slag removal is performed using a slag remover. The slag remover is evenly covered on the surface of the molten steel and removed after sufficient slag formation. This is repeated three times. The amount of slag remover is 0.9% of the weight of the molten steel. After zero power, the molten steel is left to stand for 3 minutes, including the slag removal time. After slag removal is completed, impurities in the molten steel are purified;

[0053] 6) When the temperature drops to 1660°C, take samples for analysis;

[0054] 7) Use a temperature measuring gun to detect the temperature. When the temperature drops to 1640°C, adjust the medium frequency induction furnace to the insulation power and start pouring.

[0055] Example 2

[0056] A smelting method for purifying impurities in molten steel comprises the following steps:

[0057] 1) Preparation before the furnace: Industrial argon gas (purity ≥ 99.96%) supply device, connect the pressure reducing valve and flow meter, and connect to the bottom air brick of the medium frequency induction furnace through the gas pipe;

[0058] 2) Add the cold-forged 304 steel tailings into a 150KG medium-frequency induction furnace for smelting. The power of the medium-frequency induction furnace is 250kW. When the molten steel rises to 50% of the furnace body height, argon gas (pressure 0.4MPa, flow rate 13L / min) is continuously introduced from bottom to top in the medium-frequency induction furnace.

[0059] 3) Continue to add steel until the molten steel is fully melted, adjust the argon gas to (pressure 0.5MPa, flow rate 16L / min), continue to heat up to 1680℃, add silicon calcium deoxidizer for deoxidation treatment, the addition amount is 1% of the furnace capacity;

[0060] 4) After heating to 1680°C and maintaining for 1 minute, adjust the power of the medium frequency induction furnace to 0kW, start the first standing for 3 minutes, and add 1.7KG of slag remover to remove the surface slag 3 times;

[0061] 5) After three slag removals, the temperature of the molten steel drops sharply; at this time, the power is adjusted to 255kW to raise the temperature of the molten steel to 1700°C, and the argon gas flow rate is adjusted to 18L / min and the pressure is 0.6MPa;

[0062] 6) Keep the argon gas flowing continuously, adjust the power of the medium frequency induction furnace to 0kW, start the second standing for 3 minutes, and add 1.7KG of slag remover to remove the surface slag twice; after the slag removal is completed, the impurities in the molten steel are purified;

[0063] 7) When the temperature drops to 1660°C, take samples for analysis;

[0064] 8) Use a temperature measuring gun to detect the temperature. When the temperature drops to 1640°C, adjust the medium frequency induction furnace to the insulation power and start pouring.

[0065] Comparative Example 1

[0066] A smelting method, in which argon gas is not introduced during the smelting process, specifically comprises the following steps:

[0067] 1) Add 304 steel material into a 150KG medium frequency induction furnace for smelting. The power of the medium frequency induction furnace is 250kW. Continuously add steel material to melt the molten steel.

[0068] 2) After the molten steel is fully melted, the surface of the molten steel is preferably covered with a slag remover that completely covers the surface of the molten steel. When the temperature continues to rise to 1660°C, calcium silicon manganese deoxidizer is used for deoxidation. It is evenly sprinkled on the surface of the molten steel twice, and the amount is 1.5% of the weight of the molten steel; then 0kW power is started to stand still while using a slag remover to remove slag. The slag remover is evenly covered on the surface of the molten steel, and is removed after sufficient slag is formed. This is repeated 5 times, and the amount of the slag remover is 1.5% of the weight of the molten steel. After 0kW, the slag removal time is included in the total standing time of 1.5 minutes; since the molten steel is continuously exposed to the air during the melting process and is continuously oxidized by air absorption, the temperature should not be too high and the standing time should not be too long;

[0069] 3) Use a temperature measuring gun to detect the temperature. When the temperature drops to 1640°C, adjust the medium frequency induction furnace to the insulation power and start pouring.

[0070] Performance Testing

[0071] 1. Surface quality evaluation of precision casting blanks and polished parts

[0072] Example 1, Example 2 and Comparative Example 1 were cast into workpieces, including 72 pre-filters (6 inches), 90 octagonal handles (5 inches), and 360 1" external thread inserts (12 inches). The following items were tested respectively, and the results are shown in Table 1:

[0073] (1) Quality evaluation of precision casting blanks: observe under a light intensity of 1000 lux, with a visual distance of 45 cm; observe the surface morphology, and record the precision castings with slag holes or pores as defective products. The defective products are repaired by means of grinding, argon arc welding, etc., and the repair rate is calculated. If the defective phenomenon cannot be eliminated after 10 repairs, it is recorded as scrap and the average repair rate is calculated. Among them, the precision casting blank slag inclusion defective products such as Figure 2 shown.

[0074] (2) Quality evaluation of polished parts: Observe under an illumination of 1000 lux and a visual distance of 45 cm;

[0075] Observe the surface morphology. The polished surface is divided into A surface, B surface and C surface according to the importance. Among them, A surface is the main decorative surface, which is directly visible to customers after installation.

[0076] Side B: A secondary decorative surface. After installation, customers need to be able to see the surface directly at uncommon angles.

[0077] C surface: invisible surface, which cannot be observed by customers after installation.

[0078] When the polished parts meet the following requirements at the same time, they are recorded as qualified products, otherwise they are recorded as defective products and are repaired. If the defective phenomenon cannot be eliminated after 10 repairs, they are recorded as scraps;

[0079] Black spots: The phenomenon is that inclusions and pores appear as black spots; the requirements are: A surface is not allowed, the number of black spots on the B surface is ≤3, the maximum diameter is ≤0.2mm, and the area of ​​the triangle formed by the three points is ≥3cm 2 , the number of black spots on surface C is ≤6, and the maximum diameter is ≤0.2mm.

[0080] Shrinkage: The phenomenon is that there are many small, scattered, irregularly shaped holes with rough hole walls inside the casting; the requirements are: not allowed on the A side, not allowed on the B side, and the C side can be repaired with stainless steel metal repair agent if it is relatively minor.

[0081] Crack: The phenomenon is the formation of cracks on the surface or inside due to internal stress or external impact; the requirements are: not allowed on the A side, not allowed on the B side, and not allowed on the C side.

[0082] Table 1

[0083]

[0084] The results show that the smelting method of the present invention can achieve the refining effect, reducing the average rework rate of the blank from 5.10% to below 1.28%, and the scrap rate from 2.81% to below 0.50%; the rework rate of the polished parts is reduced from 44.67% to below 10.8%, and the scrap rate is reduced from 4.33% to below 1.19%.

[0085] 2. Furnace lining service life test

[0086] Furnace A: The method of Example 1 was used to pass argon twice and then stand at high temperature. The furnace age of the argon passing operation was 235 furnaces. The results were as follows: Figure 2 As shown, the furnace wall is smooth and even without any holes.

[0087] B furnace: the method of comparative example 1 was used for ordinary smelting, with operating furnace ages of 100 furnaces and 198 furnaces. The results are as follows Figure 3 As shown in the figure, the inner wall is adhered with a lot of slag, uneven, and has obvious pits. As the number of uses increases, the furnace wall gradually becomes uneven, the service life is reduced, and the casting quality cannot be guaranteed.

[0088] The results show that when the method of Example 1 is used, the inner wall of the furnace is always kept smooth and clean, and all free slag is completely taken out of the molten steel surface by the floating argon flow. The slag in the molten steel is reduced during the casting process, and the slag porosity of the casting is reduced. When the method of Comparative Example 1 is used, the inner wall of the furnace becomes rougher and rougher as the furnace age increases, and the impurities covered with slag on the inner wall cannot float up and be discharged. During the casting process, the slag in the molten steel flows into the mold shell with the molten steel, causing slag inclusion. Compared with the method of Comparative Example 1, the furnace life of the present invention with argon high-temperature static operation is increased by 18.7%, and the slag porosity is reduced by 19.3%.

[0089] 3. Mechanical properties test

[0090] The mechanical properties test bars cast in Example 1 and Comparative Example 1 were tested for mechanical properties according to the test standard GB / T228.1-2021. The obtained stress-strain curves are shown in Figure 5 The results are summarized in Table 2.

[0091] Among them, samples 2# and 3# are test bars cast from molten steel of comparative example 1 and embodiment 1 at 1640°C, respectively; samples 4# and 5# are test bars cast from molten steel of comparative example 1 and embodiment 1 at 1620°C, respectively.

[0092] Table 2

[0093]

[0094] The results show that the test rod prepared by the method of the present invention has higher strength and plastic deformation capacity. Compared with comparative example 1, the tensile strength of the present invention is increased by more than 7%, the elongation of the cross section is increased by more than 40%, and the mechanical properties are excellent.

[0095] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A smelting method for purifying impurities in molten steel, characterized in that: The following steps are involved: S1, adding steel material into a smelting device for smelting, continuously introducing inert gas from bottom to top in the smelting device, heating the smelting device to 1670-1710° C. and performing deoxidation treatment, then allowing the molten steel to stand for the first time and removing slag; S2, heating and melting the molten steel and continuously introducing inert gas, heating the molten steel to a temperature of 1715-1730°C, and then allowing the molten steel to stand for a second time and remove slag.

2. The smelting method for purifying impurities in molten steel according to claim 1, characterized in that: In step S1, the flow rate of the inert gas is 12-18 L / min.

3. The smelting method for purifying impurities in molten steel according to claim 1, characterized in that: In step S2, the flow rate of the inert gas is 19-22 L / min.

4. The smelting method for purifying impurities in molten steel according to claim 1, characterized in that: In step S1, the specific operation is as follows: adding steel materials into a smelting device for smelting, and after the molten steel level reaches more than 50% of the volume of the smelting device, continuously introducing inert gas from bottom to top, and continuing to smelt the steel materials until the molten steel level is full, and then continuing to introduce inert gas and continue to heat up to 1680-1700°C, deoxidize, and let the molten steel stand for the first time and remove slag.

5. The smelting method for purifying impurities in molten steel according to claim 1 or 4, characterized in that: The first standing and slag removal time is 2.5-5 minutes.

6. The smelting method for purifying impurities in molten steel according to claim 14, characterized in that: The second standing and slag removal time is 2.5-5 minutes.

7. The smelting method for purifying impurities in molten steel according to claim 1, characterized in that: The inert gas is one or more of argon, helium, neon, krypton or xenon.

8. The smelting method for purifying impurities in molten steel according to claim 1, characterized in that: The smelting device is a medium frequency induction furnace.

9. The smelting method for purifying impurities in molten steel according to claim 1, characterized in that: The steel material is one or more of 304 stainless steel, 316 stainless steel, 2205 duplex stainless steel and carbon steel.

10. A steel casting, characterized in that: The steel molten steel is prepared by the smelting method for purifying impurities in molten steel as described in any one of claims 1 to 9.

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