Process system and method for reducing smelting cost of 300-series low-phosphorus stainless steel

Abstract

The invention relates to a process system and method for reducing the smelting cost of 300-series low-phosphorus stainless steel, and belongs to the technical field of stainless steel smelting. According to the scheme, the high-phosphorus medium-nickel pig iron is molten through the electric furnace, and the molten liquid is subjected to desilicication, decarburization and dephosphorization treatment; melting alloys such as waste steel, ferronickel and ferrochromium through an intermediate frequency furnace; a pre-melting tank is connected with pre-melting liquid of an intermediate frequency furnace and then connected with dephosphorized molten nickel iron of an electric furnace, and the mixed pre-melting liquid is added into an AOD (Argon Oxygen Decarburization) furnace; and performing stainless steel refining treatment in an AOD furnace, performing desilicication, decarburization, reduction and desulfurization treatment on the pre-molten liquid, and tapping after steel grade components reach the end point. By combining the electric furnace and the intermediate frequency furnace, the smelting cost of the 300-series low-phosphorus stainless steel is reduced. According to the scheme, the high-phosphorus raw material is used to the maximum extent, and the premelting liquid melted by the intermediate frequency furnace is also used as much as possible, so that the target of improving the metal yield in the smelting link is achieved, the use amount of nickel and chromium alloy in the subsequent AOD furnace link is further saved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel smelting, and relates to a process system and method for reducing the smelting cost of 300-series low-phosphorus stainless steel. Background Art

[0002] As a metal material with excellent corrosion resistance and mechanical properties, stainless steel has been widely used in many fields. Among them, 300-series stainless steel has received extensive attention due to its excellent corrosion resistance and processing performance. However, there are some problems in the traditional smelting process of 300-series stainless steel, such as low metal yield and high production cost, which limit the development of the stainless steel industry.

[0003] In the prior art, most stainless steel enterprises use all cold materials to smelt 300-series stainless steel, and the main raw materials include scrap steel, nickel pig iron and ferrochrome and other alloys. For stainless steel enterprises using all cold materials to smelt 300-series, there are three common process flows: electric furnace → AOD furnace, electric furnace + intermediate frequency furnace → AOD furnace, all intermediate frequency furnace → AOD furnace. The electric furnace melting process has the advantages of strong adaptability to raw materials and good charging conditions for the AOD furnace, but its metal yield, especially the yield of chromium, is not high, and the industry level is only 92-94%. In the electric furnace + intermediate frequency furnace melting process, the electric furnace melts all nickel pig iron, and the intermediate frequency furnace only melts ferrochrome. Although the chromium loss in the electric furnace link is reduced, the overall metal yield is still limited. In the all intermediate frequency furnace melting process, all metal raw materials are melted in the intermediate frequency furnace. Since the intermediate frequency furnace does not blow oxygen, the metal yield can reach 99%, which not only improves the yield of chromium, but also improves the yields of nickel and iron. However, one of the disadvantages of this process flow is that the intermediate frequency furnace has no metallurgical function and cannot dephosphorize. When producing low-phosphorus steel grades, it is necessary to control the phosphorus content in the raw materials, which increases a part of the cost. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a process system and method for reducing the smelting cost of 300-series low-phosphorus stainless steel, aiming to reduce the smelting cost of 300-series low-phosphorus stainless steel. This application innovatively combines the electric furnace melting process and the all intermediate frequency furnace melting process. By melting high-phosphorus medium-nickel pig iron in the electric furnace and performing desiliconization, decarburization and dephosphorization treatments, and melting scrap steel, nickel iron and ferrochrome and other alloys in the intermediate frequency furnace to provide a stainless steel pre-melt for the AOD furnace, the goal of reducing the smelting cost is achieved. Compared with the traditional electric furnace + intermediate frequency furnace process, in the present invention, the intermediate frequency furnace not only melts ferrochrome, but also considers melting nickel iron and provides as much pre-melt as possible. The low-phosphorus nickel iron water provided by the electric furnace is used to reduce the phosphorus content of the pre-melt charged into the AOD furnace. The usage amount of the low-phosphorus nickel iron water provided by the electric furnace can be dynamically adjusted according to the phosphorus content requirement of the AOD furnace charge.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A process system for reducing the smelting cost of 300 series low-phosphorus stainless steel, comprising:

[0007] An electric furnace for melting high-phosphorus medium-nickel pig iron and performing desiliconization, decarburization, and dephosphorization on the molten liquid;

[0008] An intermediate frequency furnace for melting scrap steel, ferrochrome alloy, and ferronickel alloy to produce a stainless steel pre-molten liquid;

[0009] A pre-melting tank connected to the electric furnace and the intermediate frequency furnace for receiving and mixing the dephosphorized ferronickel water provided by the electric furnace and the stainless steel pre-molten liquid provided by the intermediate frequency furnace;

[0010] An AOD furnace connected to the pre-melting tank for refining the mixed pre-molten liquid, including desiliconization, decarburization, reduction, and desulfurization operations;

[0011] Wherein, the dephosphorized ferronickel water provided by the electric furnace accounts for 1 / 3 of the total amount of the pre-molten liquid charged into the AOD furnace, and the stainless steel pre-molten liquid provided by the intermediate frequency furnace accounts for 2 / 3 of the total amount of the pre-molten liquid charged into the AOD furnace; the pre-molten liquid ratio of the electric furnace to the intermediate frequency furnace is dynamically adjusted according to the phosphorus content requirement of the AOD furnace charge.

[0012] Optionally, the electric furnace is a scrap preheating continuous feeding electric furnace, with a smelting power consumption ≤ 380 kWh / t of steel, a smelting cycle of 50 - 60 minutes, and a metal recovery rate > 93%.

[0013] Optionally, the medium-nickel pig iron melted by the electric furnace has the following composition: C = 2.0 - 4.0%, Si = 0.01 - 1.0%, Mn = 0.9 - 1.0%, P ≤ 0.035%, S ≤ 0.3%, Ni = 10 - 12%, Cr = 2.0 - 5.0%, and the balance is iron; and the phosphorus content of the ferronickel water at the smelting end point ≤ 0.03%, and the temperature > 1630 °C.

[0014] Optionally, the temperature of the stainless steel pre-molten liquid melted by the intermediate frequency furnace ≥ 1570 °C, and the raw materials of the intermediate frequency furnace include scrap steel, ferrochrome alloy, and ferronickel alloy.

[0015] Optionally, the composition of the pre-molten liquid charged into the AOD furnace includes: C = 2.0 - 3.6%, Si ≤ 1.3%, Mn = 0.01 - 0.02%, P ≤ 0.035%, S ≤ 0.12%, Ni = 6 - 10%, Cr = 16 - 20%, and the balance is iron; the charging temperature range is 1400 - 1500 °C, and the consumption of the pre-molten liquid is 700 - 850 kg / t of steel.

[0016] A process method for reducing the smelting cost of 300 series low-phosphorus stainless steel, comprising the following steps:

[0017] S1. The electric furnace melts high-phosphorus medium-nickel pig iron, and performs desiliconization, decarburization, and dephosphorization treatments to produce dephosphorized nickel molten iron;

[0018] S2. The intermediate-frequency furnace melts scrap steel, ferrochrome alloy, and nickel-iron alloy to produce a stainless steel pre-melted liquid;

[0019] S3. Mix the dephosphorized nickel molten iron provided by the electric furnace and the stainless steel pre-melted liquid provided by the intermediate-frequency furnace in proportion in a pre-melting tank, where the dephosphorized nickel molten iron accounts for 1 / 3 of the total amount of the pre-melted liquid charged into the AOD furnace, and the stainless steel pre-melted liquid accounts for 2 / 3;

[0020] S4. Pour the mixed pre-melted liquid into the AOD furnace for refining treatment, including desiliconization, decarburization, reduction, and desulfurization operations, and tap the steel until the steel grade components meet the standards;

[0021] Among them, the proportion of the pre-melted liquid provided by the electric furnace and the intermediate-frequency furnace in step S3 is dynamically adjusted according to the phosphorus content requirement of the AOD furnace charge.

[0022] Optionally, the electric furnace uses lime with a lime activity of not less than 320 and a CaO content of not less than 85% for dephosphorization treatment.

[0023] Optionally, when it is necessary to reduce the phosphorus content of the AOD furnace charge, increase the proportion of the dephosphorized nickel molten iron provided by the electric furnace to higher than 1 / 3, and at the same time reduce the proportion of the pre-melted liquid provided by the intermediate-frequency furnace; conversely, reduce the proportion of the dephosphorized nickel molten iron provided by the electric furnace.

[0024] Optionally, the phosphorus content at the end point of the refining treatment of the AOD furnace is ≤0.035%.

[0025] The beneficial effects of the present invention are as follows:

[0026] Reduce production costs: By using relatively inexpensive high-phosphorus medium-nickel pig iron and combining the processes of electric furnace smelting and all-intermediate-frequency furnace smelting, this solution can effectively reduce the smelting cost of 300-series low-phosphorus stainless steel. The electric furnace melts high-phosphorus medium-nickel pig iron and performs desiliconization, decarburization, and dephosphorization treatments, while the intermediate-frequency furnace is used to melt alloys such as scrap steel, nickel iron, and ferrochrome to provide a stainless steel pre-melted liquid for the AOD furnace. This combined process not only improves the metal recovery rate but also saves the usage of nickel and chromium alloys in the subsequent AOD furnace process, thereby reducing production costs.

[0027] Improve the metal recovery rate: This solution optimizes the process flow, uses as much pre-melted liquid provided by the intermediate-frequency furnace as possible, improves the metal recovery rate in the smelting process, saves the usage of nickel and chromium alloys in the subsequent AOD furnace process, and reduces the production cost of the entire process.

[0028] Flexible control of phosphorus content: In this solution, by dynamically adjusting the proportion of pre-melted liquid provided by the electric furnace and the intermediate frequency furnace, the phosphorus content of the molten steel entering the AOD furnace can be flexibly controlled to meet the requirements of different steel grades. This flexibility enables this solution to produce stainless steel products that meet various phosphorus content requirements.

[0029] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0031] Figure 1 is a schematic process flow diagram of the present invention.

[0032] Reference numerals in the drawings: 1 - electric furnace; 2 - intermediate frequency furnace; 3 - pre-melting tank; 4 - AOD furnace. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention schematically. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0034] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and cannot be construed as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0035] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be construed as a limitation of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0036] Please refer to Figure 1 , the present invention provides a process method for reducing the smelting cost of 300-series low-phosphorus stainless steel, including the following steps:

[0037] S1. Melting high-phosphorus medium-nickel pig iron in electric furnace 1: Use electric furnace 1 to melt relatively inexpensive high-phosphorus medium-nickel pig iron, and perform desiliconization, decarburization, and dephosphorization treatments on the molten liquid. The electric furnace 1 can use a scrap preheating continuous feeding electric furnace, and the melting raw material is high-phosphorus medium-nickel pig iron. The electric furnace 1 produces one furnace and supplies it to the subsequent AOD furnace 4 in multiple times. Each time, the pre-molten liquid provided to the AOD furnace 4 accounts for about 1 / 3 of the total amount of the pre-molten liquid entering the AOD furnace 4. The phosphorus content at the end of tapping from the electric furnace 1 is controlled below 0.03%.

[0038] S2. Melting alloys such as scrap steel, nickel iron, and ferrochrome in intermediate frequency furnace 2: Use intermediate frequency furnace 2 to melt alloys such as scrap steel, nickel iron, and ferrochrome to provide a stainless steel pre-molten liquid for the AOD furnace 4. The melting raw materials of the intermediate frequency furnace 2 include scrap steel, ferrochrome alloy, and nickel iron alloy, etc. Each time, the pre-molten liquid provided by the intermediate frequency furnace 2 to the AOD furnace 4 accounts for about 2 / 3 of the total amount of the pre-molten liquid entering the AOD furnace 4. The temperature of the stainless steel pre-molten liquid melted by the intermediate frequency furnace 2 is ≥1570 °C.

[0039] S3. Mixing pre-molten liquids in pre-melting tank 3: Mix the pre-molten liquids provided by the electric furnace 1 and the intermediate frequency furnace 2 and then pour them into the AOD furnace 4 to ensure that the phosphorus content of the molten steel entering the AOD furnace 4 meets the standard. The pre-molten liquid provided by the electric furnace 1 and the pre-molten liquid melted by the intermediate frequency furnace 2 are poured into the same pre-melting tank and then into the AOD furnace 4. The P content of the stainless steel pre-molten liquid entering the AOD furnace 4 is ≤0.035%.

[0040] S4. Stainless steel refining treatment in AOD furnace 4: Perform stainless steel refining treatment in AOD furnace 4, and perform desiliconization, decarburization, reduction, and desulfurization treatments on the pre-molten liquid. After the steel grade components reach the end point, tap the steel.

[0041] During the smelting process, the amount of stainless steel pre-melt provided by the electric furnace 1 and the medium-frequency furnace 2 can be flexibly adjusted according to the phosphorus content of the raw materials and the end-point phosphorus content of the steel grade. If the steel grade requires a lower phosphorus content of the pre-melt entering the AOD furnace 4, the amount of low-phosphorus ferronickel water provided by the electric furnace 1 can be increased, and the amount of stainless steel pre-melt provided by the medium-frequency furnace 2 can be reduced. Conversely, the amount of low-phosphorus ferronickel water provided by the electric furnace 1 can be reduced.

[0042] In a further refined embodiment, the medium nickel pig iron used in the electric furnace 1 has a composition of C = 2.0 - 4.0%, Si = 0.01 - 1.0%, Mn = 0.9 - 1.0%, P ≤ 0.035%, S ≤ 0.3%, Ni = 10 - 12%, Cr = 2.0 - 5.0%, and the balance is iron. The lime used in the electric furnace 1 has an activity of not less than 320, and the CaO content in the lime is not less than 85%. The smelting cycle of the electric furnace 1 is 50 - 60 min. The metal recovery rate of the electric furnace 1 is > 93%. The phosphorus content of the ferronickel water at the end of smelting in the electric furnace 1 is ≤ 0.03%, and the temperature of the ferronickel water is > 1630 °C.

[0043] The electric furnace 1 only melts ferronickel alloy, and a scrap steel preheating type continuous feeding electric furnace 1 can be used, and the smelting power consumption is ≤ 380 kWh / t of steel. The raw materials melted by the medium-frequency furnace 2 include scrap steel, ferrochrome alloy, ferronickel alloy, etc. The temperature of the stainless steel pre-melt melted by the medium-frequency furnace 2 is ≥ 1570 °C. Each time the medium-frequency furnace 2 provides the pre-melt for the AOD furnace 4, it accounts for 2 / 3 of the total amount of the pre-melt entering the AOD furnace 4. The composition of the stainless steel pre-melt entering the AOD furnace 4 is C = 2.0 - 3.6%, Si ≤ 1.3%, Mn = 0.01 - 0.02%, P ≤ 0.035%, S ≤ 0.12%, Ni = 6 - 10%, Cr = 16 - 20%, and the balance is iron. The temperature of the stainless steel pre-melt entering the AOD furnace 4 is 1400 - 1500 °C. The consumption of the stainless steel pre-melt in the AOD furnace 4 is about 700 - 850 kg / t of steel.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A process system for reducing the smelting cost of 300 series low-phosphorus stainless steel, characterized in that: include: The electric furnace (1) is used to melt high-phosphorus medium-nickel pig iron and perform desiliconization, decarburization and dephosphorization treatment on the melt; A medium frequency furnace (2) for melting scrap steel, ferrochrome and ferronickel to produce a stainless steel premelt; A premelting tank (3), connected to the electric furnace (1) and the medium frequency furnace (2), for receiving and mixing the dephosphorized nickel iron water provided by the electric furnace (1) and the stainless steel premelting liquid provided by the medium frequency furnace (2); An AOD furnace (4) connected to the premelting tank (3) is used to perform a refining process on the mixed premelting liquid, including desiliconization, decarburization, reduction and desulfurization operations; The dephosphorized nickel iron water provided by the electric furnace (1) accounts for 1 / 3 of the total amount of pre-melted liquid entering the AOD furnace (4), and the stainless steel pre-melted liquid provided by the medium frequency furnace (2) accounts for 2 / 3 of the total amount of pre-melted liquid entering the AOD furnace (4); the ratio of the pre-melted liquids of the electric furnace (1) and the medium frequency furnace (2) is dynamically adjusted according to the phosphorus content requirement of the AOD furnace (4).

2. The process system according to claim 1, characterized in that: The electric furnace (1) is a scrap steel preheating continuous charging electric furnace, its smelting power consumption is ≤380kWh / t steel, the smelting cycle is 50-60 minutes, and the metal recovery rate is >93%.

3. The process system according to claim 1, characterized in that: The components of the medium nickel pig iron melted in the electric furnace (1) include: C=2.0-4.0%, Si=0.01-1.0%, Mn=0.9-1.0%, P≤0.035%, S≤0.3%, Ni=10-12%, Cr=2.0-5.0%, and the balance is iron; and the phosphorus content of the nickel iron water at the smelting end point is ≤0.03%, and the temperature is greater than 1630°C.

4. The process system according to claim 1, characterized in that: The temperature of the stainless steel pre-melted liquid melted by the medium frequency furnace (2) is ≥1570°C, and the raw materials of the medium frequency furnace (2) include scrap steel, ferrochrome alloy and ferronickel alloy.

5. The process system according to claim 1, characterized in that: The composition of the pre-melt entering the AOD furnace (4) comprises: C=2.0-3.6%, Si≤1.3%, Mn=0.01-0.02%, P≤0.035%, S≤0.12%, Ni=6-10%, Cr=16-20%, and the balance is iron; the temperature entering the furnace ranges from 1400 to 1500° C., and the consumption of the pre-melt is 700-850 kg / t steel.

6. A process for reducing the smelting cost of 300 series low-phosphorus stainless steel, characterized in that: The following steps are involved: S1. An electric furnace (1) melts high-phosphorus nickel pig iron, and performs desiliconization, decarburization and dephosphorization treatment to generate dephosphorized nickel iron water; S2. The medium frequency furnace (2) melts the scrap steel, ferrochrome and ferronickel to generate a stainless steel pre-melt; S3. The dephosphorized nickel iron water provided by the electric furnace (1) and the stainless steel pre-melted liquid provided by the medium frequency furnace (2) are mixed in proportion in the pre-melting tank (3), wherein the dephosphorized nickel iron water accounts for 1 / 3 of the total amount of pre-melted liquid entering the AOD furnace (4), and the stainless steel pre-melted liquid accounts for 2 / 3; S4. The mixed pre-melt is added to the AOD furnace (4) for stainless steel refining, including desiliconization, decarburization, reduction and desulfurization operations, until the steel composition reaches the standard and the steel is tapped; In step S3, the ratio of the pre-melted liquid provided by the electric furnace (1) and the medium frequency furnace (2) is dynamically adjusted according to the phosphorus content requirement of the AOD furnace (4).

7. The process according to claim 6, characterized in that: The electric furnace (1) uses lime with an activity of not less than 320 and a CaO content of not less than 85% for dephosphorization.

8. The process according to claim 6, characterized in that: When it is necessary to reduce the phosphorus content entering the AOD furnace (4), the proportion of dephosphorized nickel iron water provided by the electric furnace (1) is increased to more than 1 / 3, and the proportion of pre-melted liquid provided by the medium frequency furnace (2) is reduced; otherwise, the proportion of dephosphorized nickel iron water provided by the electric furnace (1) is reduced.

9. The process according to claim 6, characterized in that: The phosphorus content at the end point of the refining treatment in the AOD furnace (4) is ≤0.035%.

Images