A method of manganese alloying of 200 series stainless steels

Abstract

The application provides a manganese alloying method of 200 series stainless steel, which comprises the following steps: in the oxygen blowing decarburization stage of a refining furnace, the blowing gas is selected as oxygen or mixed gas of oxygen and inert gas; when the C in the molten steel in the furnace is reduced to 1.0%-2.0% and the Si is reduced to 0.10% or less, high-carbon ferromanganese is added to increase the Mn content of the molten steel to 3.0%-4.0%; the end C content of the stage is controlled to be 0.04-0.07%, and the end Mn content is controlled to be 1.5%-2.5%; after the oxygen blowing decarburization stage is finished, silicon-manganese alloy and high-silicon silicon-manganese are added for reduction; the adding amount of the silicon-manganese alloy is controlled according to the total C amount of the silicon-manganese alloy = the total C amount required by the finished stainless steel - the total C amount of the molten steel in the furnace; and the adding amount of the high-silicon silicon-manganese is controlled according to the Si content required by the finished stainless steel. The application can reduce the raw material cost of the 200 series stainless steel to the maximum extent.

Description

Technical Field

[0001] This invention relates to the field of stainless steel smelting, and more particularly to a method for manganese alloying of 200 series stainless steel. Background Technology

[0002] The main methods for manganese alloying of 200 series stainless steel are as follows:

[0003] (1) Electrolytic manganese

[0004] During the reduction stage, pure electrolytic manganese is added to the converter to adjust the Mn content of the molten steel in the converter to the Mn content required for the 200 series stainless steel products being smelted.

[0005] (2) Electrolytic manganese + high-silicon silicomanganese

[0006] During the reduction stage, high-silicon manganese is first added to the converter to increase the Mn content of the molten steel to 4.0% to 5.0%, and the silicon content of the molten steel is adjusted to meet the requirements of the steel grade. Then, pure electrolytic manganese is added to further adjust the Mn content of the molten steel to meet the Mn content requirements of the 200 series stainless steel products being smelted.

[0007] (3) Electrolytic manganese + high-silicon ferromanganese + ferromanganese alloy + high-carbon ferromanganese

[0008] First, high-carbon ferromanganese is used to increase the Mn content in the molten steel to 2.0% to 2.8%. CO2+O2+(N2 or Ar) is used to retain manganese and chromium. Then, silicon-manganese alloy is added during reduction. Finally, electrolytic manganese and ferrosilicon are added before tapping to adjust the Mn and Si content of the molten steel to the required Mn and Si content for the 200 series stainless steel product.

[0009] Chinese patent application CN112680565A discloses a method for smelting high-manganese stainless steel in an AOD furnace using CO2 decarburization. This method employs a mixed blowing process of CO2 + O2 + (N2 and / or Ar), where CO2 increases manganese reduction. By adding a large amount of high-carbon ferromanganese during decarburization, the amount of electrolytic manganese and other manganese alloys (including ferrosilicon and high-silicon ferrosilicon) added during alloying is reduced, thereby lowering alloying costs. However, the cost of the manganese alloying method described in this patent is still relatively high. Summary of the Invention

[0010] The purpose of this invention is to provide a manganese alloying method for 200 series stainless steel, which increases the amount of ferrosilicon alloy and high-silicon ferrosilicon manganese by increasing the amount of manganese oxide during the oxidation period and reducing the carbon content at the end point, thereby minimizing the impact of rising electrolytic manganese prices on the production cost of 200 series stainless steel and minimizing the raw material cost of 200 series stainless steel.

[0011] A method for manganese alloying of 200 series stainless steel includes the following steps:

[0012] (1) The stainless steel mother liquor is added to the refining furnace for oxygen blowing decarburization. During the oxygen blowing decarburization stage, the top and bottom lances of the refining furnace are purged with oxygen or a mixture of oxygen and inert gas. When the C content in the molten steel in the furnace is reduced to 1.0%~2.0% and the Si content is reduced to below 0.10%, high-carbon ferromanganese is added to the furnace to increase the Mn content in the molten steel in the furnace to 3.0%~4.0%.

[0013] (2) The final C content of the oxygen blowing decarbonization stage in step (1) is controlled at 0.04~0.07%, and the final Mn content is controlled at 1.5%~2.5%;

[0014] (3) After the oxygen blowing decarburization stage in step (1) is completed, silicon manganese alloy and high silicon manganese are added to the furnace for reduction. The amount of silicon manganese alloy added is controlled by the total C of silicon manganese alloy = the total C required for stainless steel finished product - the total C of molten steel in the furnace at the end of the oxygen blowing decarburization stage. The amount of high silicon manganese alloy added is controlled by the total Si of high silicon manganese alloy = the total Si required for stainless steel finished product - the total Si of molten steel in the furnace at the end of the oxygen blowing decarburization stage - the total Si of the added silicon manganese alloy.

[0015] (4) After the reduction stage of step (3) is completed, add electrolytic manganese to adjust the Mn content of the molten steel in the furnace to meet the requirements of stainless steel finished products, and then tap the steel.

[0016] This invention addresses the high cost of manganese alloying by using low-cost ferrosilicon and high-silicon ferrosilicon to replace high-cost electrolytic manganese. To achieve this, the inventors controlled the timing of adding high-carbon ferromanganese (i.e., adding it when the carbon content in the molten steel is reduced to 1.0%-2.0% and the silicon content to below 0.10%). Adding high-carbon ferromanganese early allows for carbon removal during the oxygen blowing decarburization stage, preventing it from being encapsulated by slag and causing excessive carbon content during reduction if added too late (e.g., when the carbon content is less than 1.0%). Simultaneously, increasing the amount of high-carbon ferromanganese increases the Mn content in the molten steel to 3.0-4.0%, which, combined with the oxygen blowing process... In the oxygen decarburization stage, the top and bottom lances of the refining furnace are purged with oxygen or a mixture of oxygen and inert gas (without CO2), which will cause more manganese to be oxidized in the molten steel during the oxidation period. The more manganese oxides can increase the amount of silicon required in the reduction stage, thereby increasing the amount of high-silicon manganese used. At the same time, the C content at the end of the oxygen decarburization stage is controlled at 0.04~0.07%, thereby increasing the amount of silicon manganese alloy used. Since silicon manganese alloy and high-carbon ferromanganese are the cheapest, the amount of silicon manganese alloy and high-carbon ferromanganese used is increased to the maximum extent. The amount of high-silicon manganese used is increased to the maximum extent, thereby reducing the amount of high-priced electrolytic manganese used (i.e., the amount of electrolytic manganese added in step (4)) and minimizing the cost of raw materials. Therefore, although the technical solution of this patent will increase the use of silicon-manganese alloy, high-silicon silicon-manganese and high-carbon ferromanganese, and only reduce the use of electrolytic manganese, the overall raw material cost of 200 series stainless steel products is still reduced after comprehensive calculation of raw material costs, and the reduction effect is significant, which can save the company at least 400 million yuan in cost investment every year.

[0017] Furthermore, the converter mentioned in step (1) is either a GOR furnace or an AOD furnace.

[0018] Furthermore, the stainless steel mother liquor in step (1) has a C content of 3.0%~4.0% and a Mn content of 0.5%~1.5%.

[0019] Furthermore, the high-carbon ferromanganese in step (1) has a C content of 6%-8% and a Mn content of 60%-80%. Detailed Implementation

[0020] The preferred embodiment of the manganese alloying method for 200 series stainless steel of the present invention will be described in detail below:

[0021] (a) 200 series stainless steel grade: BN1D4 Example 1

[0022] Example 1 employs the manganese alloying method for 200 series stainless steel of the present invention, which includes the following steps:

[0023] (1) The stainless steel mother liquor is added to the refining furnace (GOR furnace) for oxygen blowing decarburization. During the oxygen blowing decarburization stage, the top and bottom lances of the refining furnace are selected to blow oxygen or a mixture of oxygen and inert gas. When the C in the molten steel in the furnace is reduced to 1.0%~2.0% and the Si is reduced to below 0.10%, high carbon ferromanganese is added to the furnace to increase the Mn content of the molten steel in the furnace to 3.0%~4.0%. The blowing flow rate and blowing intensity of the top and bottom lances of the refining furnace are carried out in accordance with the existing 200 series stainless steel smelting process.

[0024] In the oxygen blowing decarburization stage described in this step, high-carbon ferrochrome, scrap steel (200 series or 400 series scrap steel) and lime are also added. The addition of high-carbon ferrochrome, scrap steel and lime are all carried out in accordance with the existing 200 series stainless steel smelting process. Among them, high-carbon ferrochrome is used to supplement the chromium content in the molten steel, scrap steel is mainly used to adjust the process temperature, and lime is a slagging agent.

[0025] (2) The final C content of the oxygen blowing decarbonization stage in step (1) is controlled at 0.04~0.07%, and the final Mn content is controlled at 1.5%~2.5%;

[0026] (3) After the oxygen blowing decarburization stage in step (1) is completed, silicon manganese alloy and high silicon manganese are added to the furnace for reduction. The amount of silicon manganese alloy added is controlled by the total C content of silicon manganese alloy = the total C content required for the finished stainless steel product - the total C content of the molten steel in the furnace at the end of the oxygen blowing decarburization stage. The amount of high silicon manganese is controlled according to the Si content required for the finished stainless steel product (i.e., the amount of high silicon manganese is controlled by the total Si content of high silicon manganese = the total Si content required for the finished stainless steel product - the total Si content of the molten steel in the furnace at the end of the oxygen blowing decarburization stage - the total Si content of the added silicon manganese alloy).

[0027] Fluorite balls are also added during the reduction stage described in this step; the fluorite balls are a slag-reducing agent.

[0028] (4) After the reduction stage of step (3) is completed, electrolytic manganese is added to adjust the Mn content of the molten steel in the furnace to meet the requirements of stainless steel finished products. In addition, electrolytic copper is added to adjust the Cu content in the molten steel to meet the requirements of stainless steel finished products, and then the steel is tapped.

[0029] The composition and temperature of the stainless steel mother liquor in Example 1 are shown in Table 1-1 below:

[0030] Table 1-1

[0031]

[0032] The amounts of each material used in Example 1 are shown in Tables 1-2 below:

[0033] Table 1-2

[0034] Stainless steel mother liquor 79.6t High carbon ferrochrome 0.69t High-carbon ferromanganese 3.416t 400 series scrap steel 7.806t lime 8.912t Fluorite sphere 1.488t silicon-manganese alloy 3.02t High silicon manganese 6.068t Electrolytic manganese 0 Electrolytic copper 0.128t

[0035] The steel composition of Example 1 is shown in Tables 1-3 below:

[0036] Table 1-3

[0037] C Si Mn Cr Ni Cu 0.116 0.35 9.44 14.16 1.06 0.21

[0038] The tapping temperature in Example 1 was 1580℃.

[0039] The applicant also provided Comparative Example 1 and Comparative Example 2 for producing the steel grade of Example 1.

[0040] Comparative Example 1

[0041] The difference between Comparative Example 1 and Example 1 is that:

[0042] (1) No high-carbon ferromanganese was added to the furnace during the entire oxygen blowing decarburization stage;

[0043] (2) The C content at the end of the oxygen blowing decarburization stage is controlled at 0.09~0.12%, at which point the Mn content of the molten steel in the furnace is reduced to 0.4%~0.8%.

[0044] The composition and temperature of the stainless steel mother liquor in Comparative Example 1 are shown in Tables 1-4 below:

[0045] Table 1-4

[0046] temperature C Si Mn Cr Ni 1453℃ 3.23% 0.25% 1.13% 14.32% 1.28%

[0047] The amounts of each material used in Comparative Example 1 are shown in Tables 1-5 below:

[0048] Table 1-5

[0049]

[0050] The steel composition of Comparative Example 1 is shown in Tables 1-6 below:

[0051] Table 1-6

[0052] C Si Mn Cr Ni Cu 0.117 0.4 9.12 14.19 1.19 0.22

[0053] The tapping temperature of Comparative Example 1 was 1572℃.

[0054] Comparative Example 2

[0055] In Comparative Example 2, high-carbon ferromanganese was added during the oxygen decarburization stage when the carbon content was reduced to below 1.0%. However, because the high-carbon ferromanganese was added too late, some of it was encapsulated by the slag, resulting in a carbon content exceeding 0.14% during reduction, which exceeds the carbon content requirements for stainless steel products. Therefore, adding high-carbon ferromanganese during the oxygen decarburization stage when the carbon content is reduced to below 1.0% cannot produce 200-series stainless steel that meets the carbon content requirements.

[0056] Therefore, the key process parameters of Example 1 and Comparative Example 1 (including the timing of adding high-carbon silicon manganese, the Mn content in the molten steel in the furnace after adding high-carbon silicon manganese, the final C content, and the final Mn content) are summarized in Tables 1-7 below:

[0057] Table 1-7

[0058]

[0059] The manganese alloying costs of Example 1 and Comparative Example 1 are compared, as shown in Tables 1-8 below. The unit prices of high-carbon ferromanganese, ferrosilicon, high-silicon ferrosilicon, and electrolytic manganese are based on the market prices in 2021.

[0060] Table 1-8

[0061]

[0062] The applicant produces 1.5 million tons of 200 series stainless steel annually. Based on a reduction of 260 yuan per ton, this would save at least 400 million yuan in costs annually.

[0063] (ii) 200 series stainless steel grade: BN1G Example 2

[0064] Example 2 uses the manganese alloying method of the 200 series stainless steel of the present invention. The only difference between Example 1 and Example 2 is that the steel grade has a lower requirement for C content. Therefore, the amount of silicon-manganese alloy added is 0. That is, after the oxygen blowing decarburization stage, only high silicon-manganese alloy is added to the furnace for reduction.

[0065] The composition and temperature of the stainless steel mother liquor in Example 2 are shown in Table 2-1 below:

[0066] Table 2-1

[0067] temperature C Si Mn Cr Ni 1445℃ 3.24% 0.31% 1.16% 14.21% 1.24%

[0068] The amounts of each material used in Example 2 are shown in Table 2-2 below:

[0069] Table 2-2

[0070] Stainless steel mother liquor 83.6t High carbon ferrochrome 1.023t High-carbon ferromanganese 3.385t 200 series scrap steel 6.859t lime 9.128t Fluorite sphere 1.533t High silicon manganese 8.763t Electrolytic manganese 0.5t Electrolytic copper 0.75t

[0071] The steel composition of Example 2 is shown in Table 2-3 below:

[0072] Table 2-3

[0073] C Si Mn Cr Ni Cu 0.086 0.32 10.27 13.6 1.1 0.81

[0074] The tapping temperature in Example 2 was 1590℃.

[0075] Comparative Example 3

[0076] Comparative Example 3 is a manganese alloying method for producing 200 series stainless steel of the steel grade of Example 2, which differs from Example 2 in that:

[0077] (1) No high-carbon ferromanganese was added during the entire oxygen blowing decarburization stage;

[0078] (2) The C content at the end of the oxygen blowing decarburization stage is controlled at 0.04~0.07%, and the Mn content of the molten steel in the furnace is reduced to 0.4%~0.8%.

[0079] The composition and temperature of the stainless steel mother liquor in Comparative Example 3 are shown in Table 2-4 below:

[0080] Table 2-4

[0081] temperature C Si Mn Cr Ni 1452℃ 3.41% 0.27% 1.11% 14.02% 1.27%

[0082] The amounts of each material used in Comparative Example 3 are shown in Table 2-5 below:

[0083] Table 2-5

[0084] Stainless steel mother liquor 88.3t High carbon ferrochrome 0.548t High-carbon ferromanganese 0t 200 series scrap steel 5.83t lime 9.036t Fluorite sphere 1.504t High silicon manganese 6.357t Electrolytic manganese 0.428t Electrolytic copper 0.78t

[0085] The steel composition of Comparative Example 3 is shown in Table 2-6 below:

[0086] Table 2-6

[0087] C Si Mn Cr Ni Cu 0.078 0.35 10.26 13.68 1.18 0.82

[0088] The tapping temperature of Comparative Example 3 was 1576℃.

[0089] The key process parameters of Example 2 and Comparative Example 3 (including the timing of adding high-carbon silicon manganese, the Mn content in the molten steel in the furnace after adding high-carbon silicon manganese, the final C content, and the final Mn content) are summarized in Table 2-7 below:

[0090] Table 2-7

[0091]

[0092] The manganese alloying costs of Example 2 and Comparative Example 3 were compared, as shown in Tables 2-8 below. The unit prices of high-carbon ferromanganese, high-silicon ferromanganese, and electrolytic manganese were based on the market prices in 2021.

[0093] Table 2-8

[0094]

[0095] The applicant produces 1.5 million tons of 200 series stainless steel annually. Based on a reduction of RMB 413 per ton, this would save at least RMB 600 million in costs annually.

[0096] The converter in step (1) of this application can be a GOR furnace or an AOD furnace, depending on the specific steel grade and actual situation.

[0097] For those skilled in the art, without departing from the concept of this invention, several simple deductions or substitutions can be made, and all such deductions or substitutions should be considered to fall within the scope of protection of this invention.

Claims

1. A method for manganese alloying of 200 series stainless steel, characterized in that, Includes the following steps: (1) The stainless steel mother liquor is added to the refining furnace for oxygen blowing decarburization. During the oxygen blowing decarburization stage, the top and bottom lances of the refining furnace are purged with oxygen or a mixture of oxygen and inert gas. When the [C] in the molten steel in the furnace is reduced to 1.0%~2.0% and the [Si] is reduced to below 0.10%, high-carbon ferromanganese is added to the furnace to increase the Mn content of the molten steel in the furnace to 3.0%~4.0%. (2) The final C content of the oxygen blowing decarbonization stage in step (1) is controlled at 0.04~0.07%, and the final Mn content is controlled at 1.5%~2.5%; (3) After the oxygen blowing decarburization stage in step (1) is completed, silicon manganese alloy and high silicon manganese are added to the furnace for reduction. The amount of silicon manganese alloy added is controlled by the total C of silicon manganese alloy = the total C required for stainless steel finished product - the total C of molten steel in the furnace at the end of the oxygen blowing decarburization stage. The amount of high silicon manganese is controlled by the total Si of high silicon manganese = the total Si required for stainless steel finished product - the total Si of molten steel in the furnace at the end of the oxygen blowing decarburization stage - the total Si of the added silicon manganese alloy. (4) After the reduction stage of step (3) is completed, add electrolytic manganese to adjust the Mn content of the molten steel in the furnace to meet the requirements of stainless steel finished products, and then tap the steel.

2. The manganese alloying method for 200 series stainless steel according to claim 1, characterized in that: The refining furnace mentioned in step (1) is either a GOR furnace or an AOD furnace.

3. The manganese alloying method for 200 series stainless steel according to claim 1, characterized in that: The stainless steel mother liquor in step (1) has a C content of 3.0%~4.0% and a Mn content of 0.5%~1.5%.

4. The manganese alloying method for 200 series stainless steel according to claim 1, characterized in that: The high-carbon ferromanganese in step (1) has a C content of 6%-8% and a Mn content of 60%-80%.

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