Efficient low-cost ferritic stainless steel smelting method

Abstract

The invention belongs to the technical field of stainless steel smelting, and discloses a high-efficiency low-cost ferritic stainless steel smelting method which comprises the following steps: (1) directly blending high-temperature liquid ferrochrome alloy flowing out of a chromite heat furnace with carbon molten iron subjected to P removal to obtain pre-melted liquid; (2) adding the pre-molten liquid obtained in the step (1) into an AOD furnace for primary decarburization, and cooling by using scrap steel in the primary decarburization process to control the temperature to be less than 1720 DEG C, so as to obtain primary molten steel; (3) the primary smelting molten steel in the step (2) is added into a VOD furnace for fine decarburization, and decarburized molten steel is obtained; and (4) the decarburized molten steel obtained in the step (3) is added into an LF furnace for refining, and refined molten steel is obtained. By means of the method, the smelting efficiency can be improved, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel smelting, and in particular relates to a high-efficiency and low-cost ferritic stainless steel smelting method. Background Art

[0002] my country's crude stainless steel products are mainly 300 series (Cr-Ni steel), accounting for more than 50%. However, with the control of upstream Ni resources, it will become more difficult to obtain raw materials. Ferritic stainless steel, mainly 400 series (Cr steel), will usher in more development opportunities. 400 series stainless steel is called nickel-saving stainless steel because it does not contain nickel. It is characterized by a small thermal expansion coefficient and better resistance to chloride stress corrosion than 300 series stainless steel. At the same time, the chromium element required for 400 series stainless steel is in sufficient supply, the product price is relatively low, and the convenience of scrap steel recycling and the recycling process are better than other types of stainless steel. At present, the production and consumption of 400 series stainless steel products in mature developed countries account for more than 40%. Therefore, the future market space for 400 series stainless steel is broad.

[0003] The medium and low carbon products of 400 series stainless steel belong to ferritic stainless steel with low carbon content, no nickel, high Cr content and difficult decarburization. In addition, due to the high C content of solid high-carbon ferrochrome alloy added in batches during the smelting process, it is difficult to accurately control the carbon content at each stage, which makes the smelting time of ferritic stainless steel in the AOD furnace longer, usually requiring more than 90 minutes, affecting production costs and production efficiency.

[0004] The present invention directly mixes the high-temperature liquid ferrochrome alloy produced in the ferrochrome ore furnace with the carbon molten iron after dephosphorization, adds the pre-melted liquid into the AOD furnace for primary decarburization, then uses the secondary decarburization function of the VOD furnace for fine decarburization, and finally uses the LF furnace to adjust the composition and production rhythm. The goals of shortening the smelting cycle and reducing the production cost are achieved by directly smelting the ore, combining AOD and VOD decarburization and LF refining. Summary of the invention

[0005] The purpose of the present invention is to provide a high-efficiency and low-cost ferritic stainless steel smelting method, which can effectively deal with the drawbacks of large fluctuations in carbon content during the decarburization period, difficulty in carbon reduction, and long smelting time, thereby improving smelting efficiency and reducing production costs. The method has strong practicality and feasibility.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a high-efficiency and low-cost ferritic stainless steel smelting method, comprising the following steps:

[0008] (1) directly mixing the high-temperature liquid ferrochrome alloy flowing out of the ferrochrome ore furnace with the carbon molten iron after dephosphorization to obtain a pre-melted liquid;

[0009] (2) adding the pre-melted liquid of step (1) into an AOD furnace for primary decarburization, wherein the scrap steel is used for cooling during the primary decarburization process to control the temperature to be less than 1720° C., thereby obtaining a primary molten steel;

[0010] (3) adding the primary molten steel in step (2) to a VOD furnace for fine decarburization to obtain decarburized molten steel;

[0011] (4) adding the decarburized molten steel in step (3) into an LF furnace for refining to obtain refined molten steel.

[0012] In some embodiments, in step (1), calculated by mass percentage, the C content of the high-temperature liquid ferrochromium alloy is within 8%, the Cr content is above 50%, and the temperature of the high-temperature liquid ferrochromium alloy is above 1650°C.

[0013] In some embodiments, in step (1), calculated by mass percentage, the carbon molten iron after dephosphorization has a C content within 3%, a P content within 0.030%, and a Si content within 0.2%.

[0014] In some embodiments, in step (1), the mass ratio of the carbon molten iron after dephosphorization to the high-temperature liquid ferrochrome is above 2:1.

[0015] In some embodiments, in step (2), the scrap steel used for cooling is carbon scrap steel and / or target stainless steel, and the C content of the scrap steel used for cooling is within 0.2% by mass.

[0016] In some embodiments, in step (2), the initial decarburization includes at least 5 cycles, wherein the mass percentage of C in the pre-melt is reduced to within the range of 1%±0.2% after the first cycle of the initial decarburization.

[0017] In some embodiments, in step (2), the initial decarburization time of the primary steel liquid is 70-80 min, and the C content of the primary steel liquid is 0.15%-0.3% calculated by mass percentage.

[0018] In some embodiments, in step (3), the time of the fine decarburization is 60-70 minutes, the temperature of the decarburized molten steel is 1530-1570°C, and the C content of the decarburized molten steel is 0.03%-0.08% by mass.

[0019] In some embodiments, in step (4), the refining includes adjusting the alloy composition of the decarburized molten steel, and the adjustment of the alloy composition includes adding alloying elements to control the alloy composition in the molten steel to meet the national standard requirements of the target steel grade.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] The beneficial effects of the present invention are:

[0022] The present invention changes the "solid ferrochrome" in the conventional technology into "high-temperature ferrochrome melt", which, on the one hand, avoids the drawbacks of solidification heat dissipation and crushing loss of ferrochrome, improves the utilization rate of ferrochrome alloy, and improves the ferrochrome recovery rate by more than 3%. On the other hand, it avoids the drawbacks of composition fluctuation and endpoint control difficulty caused by multiple additions, realizes one-time direct addition of ferrochrome, and obtains a relatively accurate Cr content in the initial melt, reduces the Cr content in the slag, and improves the Cr recovery rate by more than 2%. In addition, it avoids the drawbacks of low melt temperature and high energy consumption caused by insufficient C content in the initial melt.

[0023] Compared with the existing production of 430 ferritic stainless steel, it does not need to use the VOD process, which leads to a significant extension of the production time in the AOD, thereby causing a significant increase in the consumption of oxygen, nitrogen or argon during the decarburization (blowing) process. The present invention adopts the AOD+VOD+LF process, mainly for 430 ferritic stainless steel, using the AOD furnace for primary decarburization, and then cooperating with the VOD furnace for fine decarburization, thereby reducing the gas consumption of decarburization (blowing) in the AOD furnace. At the same time, the blowing consumption in the VOD furnace itself is lower than that in the AOD furnace, so the overall consumption will be lower than the process of using the AOD furnace alone, and the production cost will be lower.

[0024] It is worth noting that the present invention can effectively shorten the smelting time of molten steel in the AOD furnace by using a VOD furnace to complete part of the decarburization operation, so that the maximum smelting time of a single furnace is controlled within 80 minutes, and the smelting efficiency is effectively improved by controlling the smelting time of the VOD furnace and adjusting the production rhythm of the LF furnace.

[0025] In summary, the present invention can greatly shorten the smelting time in the AOD furnace while simplifying the smelting process, and can improve smelting efficiency and output and reduce the production cost per ton of steel by combining with automated operation. The method has strong practicability and feasibility.

[0026] Other features and beneficial effects of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other beneficial effects of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a process flow chart of the ferritic stainless steel smelting method. DETAILED DESCRIPTION

[0028] The present invention provides a high-efficiency and low-cost ferritic stainless steel smelting method, the process flow of which is as shown in the attached figure. Figure 1 As shown, the following steps are included:

[0029] (1) directly mixing the high-temperature liquid ferrochrome alloy flowing out of the ferrochrome ore furnace with the carbon molten iron after dephosphorization to obtain a pre-melted liquid;

[0030] Specifically, decarbonized molten iron with a C content within 3%, a P content within 0.030% and a Si content within 0.2%, calculated by mass percentage, and a high-temperature liquid ferrochromium alloy with a C content within 8%, a Cr content of more than 50% and a temperature of more than 1650°C are directly mixed in a mass ratio of not less than 2:1 to obtain a pre-melt.

[0031] It should be noted that controlling C within 3% in the pre-melt of the present invention can reduce the difficulty of subsequent decarburization; since it is difficult to remove P and Si in the subsequent smelting process, it is necessary to control the content of both to reach the target as soon as possible; controlling the Cr content can avoid continuous addition of Cr in the subsequent smelting process.

[0032] (2) adding the pre-melted liquid of step (1) into an AOD furnace for primary decarburization, wherein the scrap steel is used for cooling during the primary decarburization process to control the temperature to be less than 1720° C., thereby obtaining primary molten steel;

[0033] Specifically, the pre-melted liquid iron is poured directly from the AOD furnace mouth, and after the front door of the furnace is closed, the oxygen reduction gun is used for blowing, and the side blowing is turned on at the same time. The side blowing is to start blowing one of N2 or Ar at the same time. Carbon reduction is carried out in 5 cycles. At the end of each cycle, the temperature is controlled to be less than 1720°C. If overheated, scrap steel with a mass percentage of C within 0.2% is preferably added from a high-level silo for cooling. The scrap steel is carbon scrap steel and / or target stainless steel. Within 60-70 minutes of smelting, Mn and Si elements are added to the requirements of GB / T1222-2007, thereby realizing the primary smelting function; the time for primary decarburization of the AOD furnace is controlled at 70-80 minutes, and the mass percentage of C in the primary smelting steel liquid is controlled at 0.15%-0.3%.

[0034] It should be noted that the five cycles in the initial decarburization process of the present invention are defined according to the requirements of the mass percentage of C in the primary molten steel and the control of the temperature rise process, wherein the first decarburization period requires the C to be removed to the range of 1%±0.2%. During the initial decarburization stage, the volume ratio of oxygen and N2 or oxygen and Ar is gradually adjusted from 6:1 to 1:3, and the partial pressure of carbon monoxide is adjusted by controlling the amount of N2 or Ar, and the oxidation of Cr is avoided while controlling the decarburization, thereby achieving decarburization and chromium preservation.

[0035] (3) sending the primary molten steel in step (2) into a VOD furnace for fine decarburization to obtain decarburized molten steel;

[0036] Specifically, the primary molten steel is sent to a VOD furnace for vacuum oxygen blowing and decarburization, the ladle after steelmaking from the AOD furnace is hoisted into a vacuum tank by a crane, and after vacuuming, oxygen blowing is started through an oxygen reduction gun, the smelting cycle is controlled at 60-70 minutes, the steelmaking temperature is at 1530-1570°C, and the C content is at 0.03%-0.08%.

[0037] It should be noted that the VOD furnace used in the present invention does not need to go through the deep decarburization process of VOD, but directly utilizes the secondary decarburization function of VOD together with the primary decarburization function of AOD to achieve the goal of shortening the smelting time.

[0038] (4) sending the decarburized molten steel in step (3) into an LF furnace for refining to obtain refined molten steel.

[0039] Specifically, the decarburized molten steel is sent to the LF furnace for refining, and the ladle after the VOD furnace is hoisted into the ladle car of the LF process by a crane, and driven to the processing position, and the electrode is lowered to heat up and control the alloy composition to meet the national standard requirements to obtain refined molten steel. The tapping temperature is controlled to be 1530-1550℃, and the processing cycle is 60-70min. At the same time, the LF furnace coordinates the production of the steelmaking furnace and the subsequent continuous casting machine to keep the continuous casting and pouring capacity at more than 15 furnaces.

[0040] The present invention is further described in detail in conjunction with specific embodiments. The following embodiments can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0041] Embodiment 1:

[0042] The steel grade smelted in this embodiment is 430 stainless steel.

[0043] 1) Dephosphorization of molten iron: Dephosphorization of 80t carbon molten iron. The molten iron after dephosphorization has the following mass percentages: C content is 3%, P content is 0.020%, and Si content is 0.1%;

[0044] 2) Ferrochrome smelting: smelting high carbon ferrochrome alloy in ferrochrome ore furnace at a temperature of 1650°C. Calculated by mass percentage: the C content in the high carbon ferrochrome alloy is 7.5% and the Cr content is 50%;

[0045] 3) Pre-melt mixing: The carbon molten iron after P removal is transported to the tapping span of the ferrochrome ore furnace workshop by a molten iron tank car. The high-carbon ferrochrome molten iron is collected by the tapping trough, and 40t of high-carbon ferrochrome is added.

[0046] 4) AOD primary decarburization: the pre-melt is added into the AOD furnace and blown by an oxygen reduction gun. The blowing is divided into 5 stages. The temperature of each stage is controlled at less than 1720°C. The coolant used is 430 return stainless steel. 430 return stainless steel is the target steel grade and meets the requirements of GB / T1222-2007. The mass percentage of C is controlled to be 0.15%-0.2% during the reduction period. Then, the alloy is fine-tuned to control the Mn and Si components to meet the requirements of GB / T1222-2007 to obtain the primary molten steel.

[0047] The smelting time sequence is shown in Table 1:

[0048] Table 1

[0049] Serial number content Time Stage time / minute 1 Pre-melt 0 4 2 Decarbonization Phase 1 4 8 3 Decarbonization Phase 2 12 10 4 Decarbonization Phase 3 22 9 5 Decarbonization Phase 4 31 8 6 Decarbonization Phase 5 39 8 7 Recovery period 47 12 8 Alloy fine-tuning 59 5 9 Equal components, slag 64 5 10 Steel tapping 69 3 total 72

[0050] 5) VOD fine decarburization: the primary molten steel is sent to a VOD furnace for vacuum oxygen blowing decarburization, the ladle after the AOD furnace is hoisted into a vacuum tank by a crane, and after evacuation, oxygen blowing is started by an oxygen reduction gun, and the decarburization time is controlled to be 65 minutes. The temperature of the decarburized molten steel is 1550° C., and the C content of the primary molten steel is 0.05% by mass percentage.

[0051] 6) LF refining: The decarburized molten steel is sent to the LF furnace for refining, and the ladle after the VOD furnace is hoisted by a crane onto the ladle car of the LF process, driven to the processing position, and the electrode is lowered for heating and alloy fine-tuning, and the composition is controlled to meet the national standard requirements to obtain refined molten steel. The tapping temperature is controlled to be 1550°C, and the processing cycle is 60min.

[0052] Embodiment 2:

[0053] The steel grade smelted in this embodiment is 410L stainless steel.

[0054] 1) Dephosphorization of molten iron: Dephosphorization of 80t carbon molten iron. The molten iron after dephosphorization has the following mass percentages: C content is 3%, P content is 0.020%, and Si content is 0.1%;

[0055] 2) Ferrochrome smelting: smelting high carbon ferrochrome alloy in ferrochrome ore furnace at a temperature of 1650°C. Calculated by mass percentage: the C content in the high carbon ferrochrome alloy is 7.5% and the Cr content is 50%;

[0056] 3) Pre-melt mixing: The carbon molten iron after P removal is transported to the tapping span of the ferrochrome ore furnace workshop by a molten iron tank car. The high-carbon ferrochrome molten iron is collected by the tapping trough, and 35t of high-carbon ferrochrome is added.

[0057] 4) AOD primary decarburization: the pre-melt is added into the AOD furnace and blown by an oxygen reduction gun. The blowing is divided into 5 stages. The temperature of each stage is controlled at less than 1720°C. The coolant used is 410L return stainless steel. 410L return stainless steel is the target steel grade and meets the requirements of GB / T1222-2007. The mass percentage of C is controlled to be 0.15%-0.2% during the reduction period. Then, the alloy is fine-tuned to control the Mn and Si components to meet the requirements of GB / T1222-2007 to obtain the primary molten steel.

[0058] The smelting time sequence is shown in Table 2:

[0059] Table 2

[0060] Serial number content Time Stage time / minute 1 Pre-melt 0 4 2 Decarbonization Phase 1 4 6 3 Decarbonization Phase 2 10 8 4 Decarbonization Phase 3 18 8 5 Decarbonization Phase 4 26 8 6 Decarbonization Phase 5 34 8 7 Recovery period 42 12 8 Alloy fine-tuning 54 5 9 Equal components, slag 59 5 10 Steel tapping 64 3 total 67

[0061] 5) VOD fine decarburization: the primary molten steel is sent to a VOD furnace for vacuum oxygen blowing decarburization, the ladle after the AOD furnace is hoisted into a vacuum tank by a crane, and after evacuation, oxygen blowing is started by an oxygen reduction gun, and the decarburization time is controlled to be 70 minutes. The temperature of the decarburized molten steel is 1560°C, and the C content of the primary molten steel is 0.02% by mass percentage.

[0062] 6) LF refining: The decarburized molten steel is sent to the LF furnace for refining, and the ladle after the VOD furnace is hoisted by a crane onto the ladle car of the LF process, driven to the processing position, and the electrode is lowered for heating and alloy fine-tuning, and the composition is controlled to meet the national standard requirements to obtain refined molten steel. The tapping temperature is controlled to be 1550°C, and the processing cycle is 60min.

[0063] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A high-efficiency and low-cost ferritic stainless steel smelting method, characterized in that: The following steps are involved: (1) directly mixing the high-temperature liquid ferrochrome alloy flowing out of the ferrochrome ore furnace with the carbon molten iron after dephosphorization to obtain a pre-melted liquid; (2) adding the pre-melted liquid of step (1) into an AOD furnace for primary decarburization, wherein the scrap steel is used for cooling during the primary decarburization process to control the temperature to be less than 1720° C., thereby obtaining a primary molten steel; (3) adding the primary molten steel in step (2) to a VOD furnace for fine decarburization to obtain decarburized molten steel; (4) adding the decarburized molten steel in step (3) into an LF furnace for refining to obtain refined molten steel.

2. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1 is characterized in that: In step (1), calculated by mass percentage, the C content of the high-temperature liquid ferrochromium alloy is within 8% and the Cr content is above 50%.

3. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1 is characterized in that: In step (1), the temperature of the high-temperature liquid ferrochromium alloy is above 1650°C.

4. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1 is characterized in that: In step (1), calculated by mass percentage, the carbon content of the carbon iron water after dephosphorization is within 3%, the P content is within 0.030%, and the Si content is within 0.2%.

5. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1, characterized in that: In step (1), the mass ratio of the carbon molten iron after dephosphorization to the high-temperature liquid ferrochrome is greater than 2:

1.

6. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1 is characterized in that: In step (2), the scrap steel used for cooling is carbon scrap steel and / or target stainless steel, and the C content of the scrap steel used for cooling is within 0.2% by mass.

7. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1 is characterized in that: In step (2), the primary decarburization includes at least 5 cycles, wherein the mass percentage of C in the pre-melt is reduced to within the range of 1%±0.2% after the first cycle of the primary decarburization.

8. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1 is characterized in that: In step (2), the initial decarburization time of the primary steel liquid is 70-80 minutes, and the C content of the primary steel liquid is 0.15%-0.3% calculated by mass percentage.

9. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1, characterized in that: In step (3), the time of the fine decarburization is 60-70 minutes, the temperature of the decarburized molten steel is 1530-1570° C., and the C content of the decarburized molten steel is 0.03%-0.08% by mass percentage.

10. The high-efficiency and low-cost ferritic stainless steel smelting method according to claim 1, characterized in that: In step (4), the refining includes adjusting the alloy composition of the decarburized molten steel; The adjustment of the alloy composition includes adding alloy elements to control the alloy composition in the molten steel to meet the national standard requirements of the target steel grade.

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