A process for smelting 200 series stainless steel using high carbon ferromanganese

Abstract

The application discloses a process for smelting 200 series stainless steel by using high-carbon ferromanganese, which comprises the following steps: (1) pouring molten iron into a GOR furnace; (2) melting 200 series stainless steel scrap and high-carbon ferromanganese by using a medium-frequency furnace, wherein the weight percentage of C, Cr and Mn in the molten steel tapped from the medium-frequency furnace meets the following conditions: C: 1% to 3%, Cr: 8 to 15%, and Mn: 15 to 30%; (3) pouring the molten steel melted by the medium-frequency furnace into the GOR furnace in the middle period of decarburization, wherein the weight percentage of C, Cr and Mn in the molten steel in the GOR furnace meets the following conditions: C: 0.4 to 0.6%, Cr: 10 to 17%, and Mn: 1 to 6%, and 2*[Mn%] < 42*[C%]-[Cr%]; and (4) adding a reducing agent into the GOR furnace for reduction. The application melts 200 series stainless steel scrap and high-carbon ferromanganese by using a medium-frequency furnace to form C-Cr-Mn molten steel, and then the molten steel is poured into the GOR furnace in the middle period of decarburization, so that the yield of manganese elements in the oxidation period is improved, and the smelting cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a steel smelting process, in particular to a process for smelting 200 series stainless steel by using high-carbon ferromanganese. BACKGROUND

[0002] The manganese content of 200 series stainless steel is usually 6-16%, and the existing process usually performs manganese alloying during the reduction period of smelting by adding manganese alloy raw materials such as silicon-manganese alloy, high-silicon silicon-manganese, and electrolytic manganese. As a lower-cost manganese alloy raw material, high-carbon ferromanganese cannot be used as a manganese alloy raw material during the reduction period of stainless steel smelting due to its high carbon content (6-8%).

[0003] There are few researches and reports on the addition of high-carbon ferromanganese during the oxidation period of 200 series stainless steel smelting. Chinese Patent Publication No. CN1928140A discloses a "manganese addition method for high-manganese-content stainless steel during smelting", which proposes a process for adding high-carbon ferromanganese during the oxidation period. This technology takes into account the influence of smelting temperature on manganese oxidation, and reduces the oxidation of manganese after adding high-carbon ferromanganese during the second decarburization period by increasing the temperature during the first decarburization period. However, in actual production, when the temperature of the molten steel is too high and high-manganese-content alloy (high-carbon ferromanganese with a manganese content of more than 60%) is added, high-temperature volatilization of manganese is extremely likely to occur, which will reduce the yield of the manganese alloy added during the oxidation period, resulting in a manganese yield of less than 80% during the manganese alloying of the oxidation period. SUMMARY

[0004] The purpose of the present application is to provide a process for smelting 200 series stainless steel by using high-carbon ferromanganese.

[0005] The technical solution for achieving the purpose of the present application is: a process for smelting 200 series stainless steel by using high-carbon ferromanganese, comprising the following steps:

[0006] (1) pouring the molten iron into a GOR furnace, and performing top and bottom combined blowing of oxygen to remove silicon and carbon, with the carbon content during the middle decarburization period being 0.15-0.65%;

[0007] (2) melting 200 series stainless steel scrap and high-carbon ferromanganese using a medium-frequency furnace, with the weight percentages of C, Cr, and Mn in the molten steel tapped from the medium-frequency furnace satisfying: C: 1%-3%, Cr: 8-15%, and Mn: 15-30%; and the tapping temperature of the medium-frequency furnace being controlled at 1450°C-1550°C;

[0008] (3) pouring the molten steel melted in the medium-frequency furnace into the GOR furnace during the middle decarburization period, controlling the temperature of the molten steel in the GOR furnace at 1650°C-1750°C, and performing bottom blowing of gas to decarburize until the carbon content reaches 0.08-0.2%; the weight percentages of C, Cr, and Mn in the molten steel in the GOR furnace satisfy: C: 0.4-0.6%, Cr: 10-17%, and Mn: 1-6%, and at the same time, 2*[Mn%] < 42*[C%]-[Cr%] is also satisfied.

[0009] (4) When the carbon content of step (3) meets the requirements, a reducing agent is added to the GOR furnace for reduction.

[0010] Further, in step (3), the bottom blowing oxygen-nitrogen mixed gas is used for decarburization, the volume ratio of oxygen to nitrogen in the bottom gun is 0.67-1, until the carbon content reaches 0.2-0.3%; then, the volume ratio of oxygen to nitrogen in the bottom gun is 0.25-0.43, until the carbon content reaches 0.08-0.2%. The adjustment of the oxygen blowing system can control the manganese content within 1-6%.

[0011] Manganese alloy is a high-temperature volatile element. If pure metal manganese or high-manganese-content alloy is used in the GOR furnace for high-temperature smelting, the volatilization of manganese alloy will occur, and the manganese yield will be reduced. The inventors have found through experiments that, by melting 200 series stainless steel scrap and high-carbon ferromanganese in a medium-frequency furnace to form a C-Cr-Mn steel liquid, controlling a low manganese content, and then pouring into the GOR in the decarburization middle stage, the manganese activity in the steel liquid can be reduced, and the volatilization of manganese during the pouring into the GOR can be reduced or even avoided, thereby improving the yield of manganese elements in the oxidation stage, and the scheme enables the low-cost high-carbon ferromanganese to replace the high-cost manganese alloy raw material in the smelting process, thereby reducing the smelting cost of 200 series stainless steel. Embodiment

[0012] The specific embodiments of the process for smelting 200 series stainless steel by using high-carbon ferromanganese according to the present application will be described in detail as follows: Example 1

[0013] In this embodiment, the IF+GOR process is used to smelt stainless steel, and the production steel grade is 09Cr14Mn10Ni2CuN. The smelting steps are as follows:

[0014] (1) The molten iron is poured into the GOR furnace, and the top and bottom blowing oxygen is used for desiliconization and decarburization. The carbon content in the decarburization middle stage is 0.18%. The top and bottom blowing oxygen for desiliconization and decarburization is a conventional operation, which is not described herein.

[0015] (2) The 15t 200 series scrap steel + 5t high-carbon ferromanganese is melted in a medium-frequency furnace, and the temperature of the molten steel liquid discharged from the medium-frequency furnace is controlled at 1450-1550°C. The mass fraction (%) of each element in the molten steel liquid is as follows:

[0016] C Si Mn P S Cr Ni Cu N 1.92 0.35 25.41 0.056 0.03 8.63 0.92 0.43 0.16

[0017] (3) The molten steel liquid is poured into the GOR in the decarburization middle stage, and the mass fraction (%) of each element in the molten steel liquid after mixing is as follows:

[0018] C Si Mn P S Cr Ni Cu N 0.57 0.03 5.34 0.037 0.032 12.65 1.22 0.09 0.12

[0019] The calculated manganese yield of the manganese alloying during the oxidation period was 95%, and then the molten steel was further deep decarburized, the GOR furnace molten steel temperature was controlled at 1650-1750°C, the bottom blowing oxygen flow rate was 45m 3 / min, the nitrogen flow rate was 55m 3 / min, so that the carbon content was reduced to 0.28%; then, the bottom blowing oxygen flow rate was 25m 3 / min, the nitrogen flow rate was 75m 3 / min, so that the final carbon content was 0.081%.

[0020] (4) After the GOR molten steel carbon content was qualified, the reducing agent high-silicon silicon-manganese alloy 8.9t was added, and then the slag was blocked and the molten steel was tapped, the mass fraction (%) of each element in the molten steel composition was:

[0021] C Si Mn P S Cr Ni Cu N 0.083 0.41 10.39 0.036 0.003 13.82 1.35 0.88 0.149 Example 2

[0022] In this example, the IF+GOR process was used to smelt stainless steel, and the production steel grade was 12Cr14Mn10NiN, and the smelting steps were as follows:

[0023] (1) The molten iron was poured into the GOR furnace, and the top and bottom combined blowing oxygen was used to remove silicon and decarburize, and the carbon content during the decarburization period was 0.26%;

[0024] (2) The 17t 200 series scrap steel + 3t high-carbon ferromanganese was melted in the intermediate frequency furnace, and the intermediate frequency furnace steel tapping temperature was controlled at 1450-1550°C, and the mass fraction (%) of each element in the molten clean steel was:

[0025] C Si Mn P S Cr Ni Cu N 1.35 0.32 18.39 0.049 0.024 8.79 1.02 0.51 0.17

[0026] (3) The molten clean steel was poured into the GOR during the decarburization period, and after mixing, the mass fraction (%) of each element in the molten steel was:

[0027] C Si Mn P S Cr Ni Cu N 0.53 0.06 3.97 0.035 0.029 11.93 1.24 0.11 0.11

[0028] The calculated manganese yield of the manganese alloying during the oxidation period was 97%, and then the molten steel was further deep decarburized, the GOR furnace molten steel temperature was controlled at 1650-1750°C, the bottom blowing oxygen flow rate was 45m 3 / min, the nitrogen flow rate was 55m 3 / min, so that the carbon content was reduced to 0.28%; then, the bottom blowing oxygen flow rate was 25m 3 / min, the nitrogen flow rate was 75m 3 / min, so that the final carbon content was 0.081%.

[0029] (4) After the GOR molten steel carbon content was qualified, the reducing agent high-silicon silicon-manganese alloy 8.9t was added, and then the slag was blocked and the molten steel was tapped, the mass fraction (%) of each element in the molten steel composition was:

[0030] C Si Mn P S Cr Ni Cu N 0.124 0.47 9.54 0.034 0.003 13.53 1.21 0.31 0.157 Example 3

[0031] This example adopts IF+GOR process to smelt stainless steel, and the production steel grade is 12Cr14Mn10NiCuN, and the smelting steps are as follows:

[0032] (1) The molten iron is mixed into the GOR furnace, and the top and bottom combined blowing oxygen is used to remove silicon and carbon, and the carbon content in the middle of decarburization is 0.24%;

[0033] (2) The 13 t 200 series scrap steel + 6 t high-carbon ferromanganese is melted in the intermediate frequency furnace, and the molten steel temperature is controlled at 1450-1550°C, and the mass fraction of each element in the molten steel is (%):

[0034] C Si Mn P S Cr Ni Cu N 1.75 0.35 29.43 0.061 0.032 9.13 0.83 0.34 0.15

[0035] (3) The molten steel is mixed into the GOR furnace in the middle of decarburization, and the mass fraction of each element in the molten steel after mixing is (%):

[0036] C Si Mn P S Cr Ni Cu N 0.54 0.02 5.64 0.039 0.031 11.33 1.21 0.07 0.13

[0037] After calculation, the manganese yield of manganese alloying in the oxidation period is 96%, and then the molten steel is further deep decarburized, the GOR furnace molten steel temperature is controlled at 1650-1750°C, the bottom blowing oxygen flow is 40 m 3 / min, the nitrogen flow is 60 m 3 / min, so that the carbon content is reduced to 0.33%; then the bottom blowing oxygen flow is 25 m 3 / min, the nitrogen flow is 75 m 3 / min, so that the final carbon content is 0.12%.

[0038] (4) After the GOR molten steel carbon content is qualified, the reducing agent high-silicon ferromanganese alloy 8.2 t is added, and then the slag is blocked and tapped, and the mass fraction of each element in the molten steel composition is (%):

[0039] C Si Mn P S Cr Ni Cu N 0.124 0.43 10.41 0.041 0.003 13.56 1.19 0.33 0.165 Example 4

[0040] This example adopts IF+GOR process to smelt stainless steel, and the production steel grade is 10Cr14Mn10NiN, and the smelting steps are as follows:

[0041] (1) The molten iron is mixed into the GOR furnace, and the top and bottom combined blowing oxygen is used to remove silicon and carbon, and the carbon content in the middle of decarburization is 0.31%;

[0042] (2) The 15 tons of 200 series scrap steel and 3 tons of high-carbon ferromanganese are melted in the intermediate frequency furnace, the tapping temperature of the intermediate frequency furnace is controlled at 1450-1550°C, and the mass fraction of each element in the molten steel is (%):

[0043] C Si Mn P S Cr Ni Cu N 1.05 0.35 17.96 0.043 0.027 11.34 1.17 0.43 0.14

[0044] (3) The molten steel is mixed into the GOR in the decarburization middle stage, and the mass fraction of each element in the molten steel after mixing is (%):

[0045] C Si Mn P S Cr Ni Cu N 0.45 0.08 3.34 0.04 0.031 12.03 1.19 0.08 0.13

[0046] It is calculated that the manganese alloying manganese yield in the oxidation stage is 96%. Then, the molten steel is further deep decarburized, the GOR furnace molten steel temperature is controlled at 1650-1750°C, the bottom blowing oxygen flow is 40m 3 / min, the nitrogen flow is 60m 3 / min, so that the carbon content is reduced to 0.27%; then, the bottom blowing oxygen flow is 20m 3 / min, the nitrogen flow is 80m 3 / min, so that the final carbon content is 0.10%.

[0047] (4) After the GOR molten steel carbon content is qualified, 9.5 tons of reducing agent high-silicon ferromanganese alloy is added, and then the slag is blocked and tapped, and the mass fraction of each element in the molten steel composition is (%):

[0048] C Si Mn P S Cr Ni Cu N 0.103 0.36 9.32 0.031 0.003 14.01 1.16 0.41 0.146

[0049] Comparative Example 1

[0050] This comparative example uses GOR process to smelt stainless steel, and the production steel grade is 10Cr14Mn10Ni2CuN, and the smelting steps are as follows:

[0051] (1) The molten iron is mixed into the GOR furnace, and the silicon and carbon are removed by top and bottom combined blowing of oxygen, and the mass fraction of each element in the molten steel in the GOR decarburization middle stage is (%):

[0052] C Si Mn P S Cr Ni Cu N 0.35 0.03 0.05 0.031 0.029 11.89 1.21 0.04 0.13

[0053] (2) 3 tons of high-carbon ferromanganese is added, and the mass fraction of each element in the molten steel after mixing is (%):

[0054] C Si Mn P S Cr Ni Cu N 0.51 0.06 1.57 0.035 0.032 11.59 1.2 0.04 0.13

[0055] It is calculated that the manganese alloying manganese yield in the oxidation stage is 63%. Then the molten steel is deep decarburized.

[0056] (3) After the GOR molten steel carbon content is qualified, 8.7 tons of reducing agent high-silicon ferromanganese alloy and 2.5 tons of electrolytic manganese are added, and then the slag is blocked and tapped, and the mass fraction of each element in the molten steel composition is (%):

[0057] C Si Mn P S Cr Ni Cu N 0.098 0.32 9.55 0.033 0.003 13.88 1.21 0.40 0.149

[0058] Comparative Example 2

[0059] The present comparative example smelts stainless steel by GOR process, and the production steel grade is 12Cr14Mn10NiCuN, and the smelting steps are as follows:

[0060] (1) The molten iron is mixed into the GOR furnace, and the top and bottom are blown with oxygen to remove silicon and carbon, and in the middle of GOR decarburization, the mass fraction of each element in the molten steel is (%):

[0061] C Si Mn P S Cr Ni Cu N 0.41 0.04 0.08 0.032 0.027 11.95 1.22 0.07 0.12

[0062] (2) 2t high-carbon ferromanganese is added, and after mixing, the mass fraction of each element in the molten steel is:

[0063] C Si Mn P S Cr Ni Cu N 0.50 0.05 1.11 0.034 0.030 11.72 1.21 0.04 0.13

[0064] It is calculated that the manganese yield of manganese alloying in the oxidation period is 67%, and then the molten steel is deeply decarburized.

[0065] (3) After the carbon content of the GOR molten steel is qualified, 9.3t of high-silicon ferromanganese alloy and 3.4t of electrolytic manganese are added, and then the slag is blocked and tapped, and the mass fraction of each element in the molten steel is (%):

[0066] C Si Mn P S Cr Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si Mn Ni Cu Si N 0.121 0.35 10.37 0.033 0.003 13.49 1.2 0.35 0.161

[0067] The embodiments of the present application obtain the molten steel containing manganese by adopting the intermediate frequency furnace melting, and are mixed into the GOR in the middle of decarburization smelting, effectively inhibit the volatilization of manganese alloy, so that the manganese yield of manganese alloying in the oxidation period is increased from below 80% to above 95%; at the same time, by reasonably controlling the composition of the molten steel in the middle of oxidation and the oxygen blowing system, the oxidation of manganese is reduced, the comprehensive yield of manganese is improved, and it is stabilized at above 95%, thereby effectively reducing the manganese alloying cost of 200 series stainless steel.

[0068] The present application controls the tapping temperature of the intermediate frequency furnace to be 1450-1550℃, so that after being mixed into the GOR furnace in the middle of decarburization, the temperature of the mixed molten steel is controlled at 1650-1750℃, if the temperature is too high, the volatilization of manganese element will be increased, and if the temperature is too low, it will be not conducive to decarburization and manganese preservation, resulting in the oxidation of manganese.

[0069] The above is only an embodiment of the present application, and does not limit the patent range of the present application, and any equivalent process transformation by using the content of the present application specification, or direct or indirect application in other related technical fields, are also included in the patent protection range of the present application.

Claims

1. A process for smelting 200 series stainless steel using high carbon ferromanganese characterized in that: It comprises the following steps: (1) The molten iron is mixed into the GOR furnace, and top and bottom combined blowing oxygen is used to remove silicon and carbon, and the carbon content in the middle period of decarburization is 0.15-0.65%; (2) The 200 series stainless steel scrap and high-carbon ferromanganese are melted by using the intermediate frequency furnace, the weight percentages of C, Cr and Mn in the tapping of the intermediate frequency furnace meet C: 1%-3%, Cr: 8-15%, and Mn: 15-30%; the tapping temperature of the intermediate frequency furnace is controlled at 1450-1550℃; (3) The molten steel melted by the intermediate frequency furnace is mixed into the GOR furnace in the middle period of decarburization, the temperature of the molten steel in the GOR furnace is controlled at 1650-1750℃, bottom blowing gas is used for decarburization, and the carbon content reaches 0.08-0.2%; the weight percentages of C, Cr and Mn in the molten steel in the GOR furnace meet C: 0.4-0.6%, Cr: 10-17%, and Mn: 1-6%, and also meet 2*[Mn%]<42*[C%]-[Cr%]; (4) When the carbon content in step (3) meets the requirement, the reducing agent is added into the GOR furnace for reduction.

2. The process for smelting 200 series stainless steel using high carbon ferromanganese as claimed in claim 1, wherein: In step (3), bottom blowing oxygen-nitrogen mixed gas is used for decarburization, the volume ratio of oxygen to nitrogen of the bottom lance is 0.67-1, and the carbon content reaches 0.2-0.3%; then, the volume ratio of oxygen to nitrogen of the bottom lance is 0.25-0.43, and the carbon content reaches 0.08-0.2%.