Production process of ultra-pure ferritic stainless steel

Abstract

The invention discloses a production process of ultra-pure ferritic stainless steel, which belongs to the technical field of stainless steel smelting, can be used for producing the ultra-pure ferritic stainless steel in one package, and has the characteristics of low electric energy loss, low material loss, low dioxin emission and high chromium recovery rate. Comprising the following steps: S1, preheating and smelting: feeding waste steel into a preheating area of a quantum electric arc furnace for preheating, feeding preheated waste iron and ferrochrome into the quantum electric arc furnace together for smelting, and discharging molten steel by adopting siphoning to obtain primarily-smelted chromium molten steel; s2, oxygen blowing is conducted, specifically, the primarily-smelted chromium steel liquid obtained in the step S1 is fed into a desilicication station to be subjected to oxygen blowing treatment, and silicon-removed chromium steel liquid is obtained; s3, VOD refining is conducted, specifically, the silicon-chromium-removed molten steel obtained in the step S2 is fed into a VOD refining furnace to be refined, and nitrogen-chromium-removed molten steel is obtained; and S4, LF refining, wherein the nitrogen and chromium removed molten steel obtained in the step S3 is fed into an LF refining furnace for refining, and the molten steel is fed onto a casting platform to be cast into steel billets.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel smelting, and more specifically, to a production process of ultra-pure ferritic stainless steel. Background Art

[0002] Stainless steel is divided into martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic (duplex) stainless steel and precipitation hardening stainless steel according to its organizational state. The corrosion resistance, toughness and weldability of ferritic steel increase with the increase of its chromium content. Its resistance to chloride stress corrosion is also better than other types of stainless steel. It is mostly used in acid-resistant structures and as oxidation-resistant steel. This type of steel can resist corrosion from the atmosphere, nitric acid and saline solutions, and has the characteristics of good high-temperature oxidation resistance and small thermal expansion coefficient. It is used in nitric acid and food factory equipment, and can also be used to make parts that work at high temperatures.

[0003] The existing production process of ultra-pure ferritic stainless steel generally directly adds scrap steel or iron ore into an ordinary arc furnace or induction furnace for primary refining, and the obtained molten steel is added to the AOD furnace with alloy and lime to increase the alloy ratio in the molten steel and remove the elements such as magnesium, silicon and aluminum in the molten steel. The ladle is then transported to the ladle refining station, and the ladle refining furnace is used to spray a mixed gas of coke oven gas and argon gas into the ladle, and a hydrogen-containing plasma arc is formed at the lower end of the electrode of the ladle refining furnace to achieve decarbonization and denitrification of the molten steel, and then the continuous casting machine is used for continuous casting to obtain it. The existing production process has the disadvantages of needing to change the ladle, consuming more electricity, using more slag-making agents, being unable to effectively recover metallic chromium, and having high production costs. Therefore, it is urgent to invent a production process of ultra-pure ferritic stainless steel with less slag-making agent and reducing agent and lower production energy consumption to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a production process of ultrapure ferritic stainless steel, by which ultrapure ferritic stainless steel can be produced in one package, and has the characteristics of low power consumption, less material loss and high chromium recovery rate.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A production process of ultrapure ferritic stainless steel, a production process of ultrapure ferritic stainless steel, comprising the following steps:

[0007] S1. Preheating and smelting: sending the scrap steel into the preheating zone of the quantum electric arc furnace for preheating, sending the preheated scrap iron and ferrochrome into the quantum electric arc furnace for smelting, and using siphon to discharge the molten steel to obtain the primary chromium steel liquid;

[0008] S2, oxygen blowing: sending the primary chromium steel liquid obtained in step S1 to a desiliconization station for oxygen blowing treatment to obtain desiliconized chromium steel liquid;

[0009] S3, VOD refining: sending the desiliconized chromium steel liquid obtained in step S2 into a VOD refining furnace for refining to obtain denitrogenated chromium steel liquid;

[0010] S4, LF refining: The denitrified chromium steel liquid obtained in step S3 is sent to a LF refining furnace for refining, and then sent to a casting platform for casting into a steel billet.

[0011] Furthermore, in the step S1, the preheating zone of the quantum arc furnace is preheated using the hot exhaust gas generated by the quantum arc furnace during the smelting process, and the scrap iron is preheated to 600-800° C. in the preheating zone of the quantum arc furnace and then fed into the quantum arc furnace.

[0012] Furthermore, in the step S1, the chromium content of the primary chromium steel liquid is 10.5-30.0%, and the carbon content is 1-2.5%.

[0013] Furthermore, in step S2, when oxygen blowing treatment is performed, the oxygen blowing pressure is 12-16 kg, and the oxygen blowing flow rate is 3600 m 3 / h, the total flow rate of bottom argon blowing is 400+400L / min.

[0014] Furthermore, in the step S2, the carbon content of the obtained silicon-chromium-free steel liquid is 0.2-0.5%, and the silicon content is less than or equal to 0.3%.

[0015] Furthermore, in the step S3, when the desiliconized chromium steel liquid is refined, the blowing stop pressure is 15-16 mbr, the steel liquid temperature is controlled at 1620-1660°C when the blowing stops, the height between the top blowing gun and the steel liquid level is 1.5±0.15 m, the argon flow rate is 400+400 L / min, and the processing time is 40-70 min.

[0016] Furthermore, in step S3, the carbon content of the obtained denitrogenated chromium steel liquid is less than 0.015%, and the nitrogen content is less than 0.015%.

[0017] Furthermore, in the step S4, when the denitrified chromium steel liquid is refined, a cold material is added to reduce the temperature of the steel liquid to 1570-1600°C, and then an alloy containing chromium, silicon, aluminum, calcium, manganese and nickel is added, stirred and allowed to stand, and when the steel liquid reaches the target superheat of 20-50°C, it is sent to the casting platform for casting.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The invention discloses a production process of ultrapure ferritic stainless steel. The scrap iron is preheated in the preheating zone of a quantum arc furnace, and then the scrap iron is sent to the quantum arc furnace for smelting together with ferrochrome. The scrap iron is preheated before smelting, so that the power consumption in the smelting process can be reduced and the smelting efficiency can be improved. The quantum arc furnace uses siphon to discharge the molten steel to obtain the primary chromium molten steel. The molten steel obtained by such steelmaking and steel-tapping method does not contain slag, so that its cleanliness is guaranteed. Compared with the traditional electric furnace smelting, a reducing agent needs to be added to the molten steel to reduce the metal in the slag before steel-tapping. However, the production process of the invention does not need to add so much reducing agent, thus saving 60% of the use of reducing agent Si-Fe, and simultaneously reducing the use of slag-making agent by one third, resulting in less material loss.

[0020] The quantum electric arc furnace uses siphon tapping without slag. The metal in the slag will be reduced during the smelting process, the recovery rate of the main metal chromium is improved, and the economic benefits are obvious. The molten steel is siphoned from the quantum electric arc furnace to the ladle. The subsequent oxygen blowing, VOD refining, LF refining, and casting processes do not require changing the ladle or pouring molten steel. Compared with the traditional stainless steel smelting route, a one-bag-to-the-end technology has been formed. Compared with the traditional AOD-VOD refining route, it can reduce temperature drop and temperature drop power transmission, and save more energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below in conjunction with specific implementation methods, but does not constitute any limitation to the present invention.

[0024] Reference Figure 1 As shown, a production process of ultrapure ferritic stainless steel of the present invention comprises the following steps:

[0025] S1. Preheating and smelting: Send the scrap steel into the preheating zone of the quantum arc furnace for preheating, send the preheated scrap iron and ferrochrome into the quantum arc furnace for smelting, and use siphon to discharge the molten steel to obtain the primary chromium steel liquid. The quantum arc furnace uses a motor to heat and melt, and the ferrochrome is added to the furnace through the feeding system. During smelting, it is stirred by bottom blowing to ensure that the alloy iron is completely melted. The quantum arc furnace is heated under atmospheric pressure, and the temperature of the molten steel during heating is 1580-1630℃.

[0026] Furthermore, in the step S1, the preheating zone of the quantum arc furnace is preheated by using the hot exhaust gas generated by the quantum arc furnace during the smelting process, and the scrap iron is preheated to 600-800°C in the preheating zone of the quantum arc furnace and then fed into the quantum arc furnace. The preheating zone is located directly above the quantum arc furnace and is composed of multiple vertical furnace systems. The hot exhaust gas generated by the quantum arc furnace during the smelting process is discharged from the preheating zone after exhaust gas treatment to achieve preheating of the scrap iron placed in the preheating zone, so that the energy can be reused for a second time, and the energy utilization rate is higher. The preheating zone can also block the flue gas of the quantum arc furnace, reduce dust collection by 40-60%, and reduce the metal loss caused by the flue gas by 0.5-2%. Furthermore, the feeding system of the quantum arc furnace directly adds alloy iron to the molten steel, reducing the oxidation of the metal by the arc.

[0027] Furthermore, in the step S1, the chromium content of the primary chromium steel liquid is 10.5-30.0%, and the carbon content is 1-2.5%.

[0028] S2, oxygen blowing: sending the primary chromium steel liquid obtained in step S1 to a desiliconization station for oxygen blowing treatment to obtain desiliconized chromium steel liquid.

[0029] Furthermore, in step S2, when oxygen blowing treatment is performed, the oxygen blowing pressure is 12-16 kg, and the oxygen blowing flow rate is 3600 m 3 / h, the total flow rate of bottom argon blowing is 400+400L / min, the general oxygen blowing time is 12-20min, and the treatment is completed when the oxygen blowing process reaches the temperature of the molten steel at 1680-1720℃.

[0030] Furthermore, in the step S2, the carbon content of the obtained silicon-chromium-free steel liquid is 0.2-0.5%, and the silicon content is less than or equal to 0.3%.

[0031] S3, VOD refining: sending the desiliconized chromium steel liquid obtained in step S2 into a VOD refining furnace for refining to obtain denitrogenated chromium steel liquid;

[0032] Furthermore, in the step S3, when the desiliconized chromium steel liquid is refined, the blowing stop pressure is 15-16 mbr, the steel liquid temperature is controlled at 1620-1660°C when the blowing stops, the height between the top blowing gun and the steel liquid level is 1.5±0.15 m, the argon flow rate is 400+400 L / min, and the processing time is 40-70 min.

[0033] Furthermore, in step S3, the carbon content of the obtained denitrogenated chromium steel liquid is less than 0.015%, and the nitrogen content is less than 0.015%.

[0034] S4, LF refining: The denitrified chromium steel liquid obtained in step S3 is sent to a LF refining furnace for refining, and then sent to a casting platform for casting into a steel billet.

[0035] Furthermore, in the step S4, when the denitrified chromium steel liquid is refined, a cold material is added to reduce the temperature of the steel liquid to 1570-1600°C, and then an alloy containing chromium, silicon, aluminum, calcium, manganese and nickel is added, stirred for 15 minutes and then allowed to stand, and when the steel liquid reaches the target superheat of 20-50°C, it is sent to the casting platform for casting.

[0036] The production process of ultrapure ferritic stainless steel of the present invention first uses the preheating zone of the quantum arc furnace to preheat the scrap iron, and then sends it into the quantum arc furnace together with ferrochrome for smelting. By preheating the scrap iron first and then smelting it, the preheated scrap iron has a certain temperature when entering the quantum arc furnace, which can shorten its heating time in the quantum arc furnace, and also reduce the power consumption of the smelting process, and can save about 75 degrees of electricity per ton of steel, thereby improving the smelting efficiency. The quantum arc furnace uses siphoning to discharge the molten steel to obtain the primary chromium molten steel. The molten steel obtained by such steelmaking and steel-tapping methods is the molten steel in the upper part of the furnace, and the molten steel at this position will not be accompanied by slag, which ensures its cleanliness. Compared with traditional electric furnace smelting, a reducing agent needs to be added to the molten steel before steel-tapping to reduce the metal in the slag, while the production process of the present invention does not need to add so much reducing agent, saving 60% of the use of reducing agent Si-Fe, and simultaneously reducing the use of slag-making agent by one-third, with less material loss. The quantum electric arc furnace uses siphon tapping without slag. The metal in the slag will be reduced during the smelting process, and the recovery rate of the main metal chromium has increased by 2-3%, with obvious economic benefits. The molten steel is siphoned from the quantum electric arc furnace to the ladle. The subsequent oxygen blowing, VOD refining, LF refining, and casting processes do not require changing the ladle or pouring the molten steel. Compared with the traditional stainless steel smelting route, a one-bag-to-the-end technology has been formed. Compared with the traditional AOD-VOD refining route, the temperature drop can be reduced by about 150℃ / ton of steel, and the temperature drop power transmission is also reduced, saving about 4.5 yuan / ton of steel in electricity consumption.

[0037] The above description is only a preferred embodiment of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A production process for ultrapure ferritic stainless steel, characterized in that: The following steps are involved: S1. Preheating and smelting: sending the scrap steel into the preheating zone of the quantum electric arc furnace for preheating, sending the preheated scrap iron and ferrochrome into the quantum electric arc furnace for smelting, and using siphon to discharge the molten steel to obtain the primary chromium steel liquid; S2, oxygen blowing: sending the primary chromium steel liquid obtained in step S1 to a desiliconization station for oxygen blowing treatment to obtain desiliconized chromium steel liquid; S3, VOD refining: sending the desiliconized chromium steel liquid obtained in step S2 into a VOD refining furnace for refining to obtain denitrogenated chromium steel liquid; S4, LF refining: The denitrified chromium steel liquid obtained in step S3 is sent to a LF refining furnace for refining, and then sent to a casting platform for casting into a steel billet.

2. The production process of ultrapure ferritic stainless steel according to claim 1, characterized in that: In the step S1, the preheating zone of the quantum arc furnace is preheated by utilizing the hot exhaust gas generated by the quantum arc furnace during the smelting process. The scrap iron is preheated to 600-800° C. in the preheating zone of the quantum arc furnace and then fed into the quantum arc furnace.

3. The production process of ultrapure ferritic stainless steel according to claim 2, characterized in that: In the step S1, the chromium content of the primary chromium steel liquid is 10.5-30.0%, and the carbon content is 1-2.5%.

4. The production process of ultrapure ferritic stainless steel according to claim 1, characterized in that: In step S2, when oxygen blowing treatment is performed, the oxygen blowing pressure is 12-16 kg and the oxygen blowing flow rate is 3600 m 3 / h, the total flow rate of bottom argon blowing is 400+400L / min.

5. The production process of ultrapure ferritic stainless steel according to claim 4, characterized in that: In the step S2, the carbon content of the obtained silicon-chromium-free steel liquid is 0.2-0.5%, and the silicon content is less than or equal to 0.3%.

6. The production process of ultrapure ferritic stainless steel according to claim 1, characterized in that: In the step S3, when the desiliconized chromium steel liquid is refined, the blowing stop pressure is 15-16 mbr, the steel liquid temperature is controlled at 1620-1660°C when the blowing stops, the height between the top blowing gun and the steel liquid level is 1.5±0.15 m, the argon flow rate is 400+400 L / min, and the processing time is 40-70 min.

7. The production process of ultrapure ferritic stainless steel according to claim 6, characterized in that: In the step S3, the carbon content of the obtained denitrogenated chromium steel liquid is less than 0.015%, and the nitrogen content is less than 0.015%.

8. The production process of ultrapure ferritic stainless steel according to claim 1, characterized in that: In the step S4, when the denitrified chromium steel liquid is refined, a cold material is added to reduce the temperature of the steel liquid to 1570-1600°C, and then an alloy containing chromium, silicon, aluminum, calcium, manganese and nickel is added, stirred and allowed to stand, and the steel liquid is sent to a casting platform for casting after reaching a target superheat of 20-50°C.

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