A process for smelting stainless steel in a VOD furnace

Abstract

This invention discloses a VOD process for smelting stainless steel, which mainly includes the following steps: (1) adding 0.3 to 2 tons of chromium ore powder to a ladle; (2) pouring the stainless steel molten steel that has undergone initial decarburization in the converter into the ladle after slag removal, wherein the temperature of the molten steel in the ladle is 1600℃ to 1650℃; (3) transporting the ladle containing the stainless steel molten steel to the VOD station for vacuum decarburization treatment, wherein the vacuum degree in the VOD furnace reaches below 150Pa, and the top-blown oxygen flow rate is 200 to 300N. 3 / h, bottom blowing argon flow rate is 20-30 Nm 3 The blowing process is carried out at a rate of / h, with a vacuum treatment time of 20–50 min; the VOD oxygen blowing rate is determined by formula 1: Formula 1: V = M1 * (M C *η C +M Si *η Si )-M2*η C Its process is simple, reducing the VOD smelting time for ultrapure ferritic stainless steel to 60 minutes.

Description

TECHNICAL FIELD

[0001] The present application relates to a steel smelting process, in particular to a process for smelting stainless steel by VOD. BACKGROUND

[0002] VOD furnace is often used to produce ultra-low carbon stainless steel products such as ultra-pure ferrite stainless steel, and the main feature of the refining process is that the product of carbon-oxygen reaction is CO gas which can be removed in vacuum treatment, thereby promoting decarburization and achieving the purpose of inhibiting chromium oxidation.

[0003] Chinese patent CN101058837A discloses a smelting method for decarburization and denitrification of ultra-pure ferrite stainless steel, which realizes efficient decarburization by controlling the carbon content, temperature and carbon content and vacuum degree in the VOD smelting process. However, the vacuum treatment time of this method still needs about 70 minutes, which is relatively long and may affect the continuous production of stainless steel and limit the improvement of continuous casting furnace number, resulting in low material yield and high production cost.

[0004] In view of the current situation of VOD smelting process, how to further shorten the vacuum treatment time of VOD smelting process has become an important research topic in the field. SUMMARY

[0005] The purpose of the present application is to provide a process for smelting stainless steel by VOD.

[0006] The technical solution for achieving the purpose of the present application is: a process for smelting stainless steel by VOD, comprising the following steps:

[0007] (1) adding 0.3 tons to 2 tons of chromium ore powder to the ladle, the chromium ore powder containing 30% to 60% of chromium oxide, 20% to 40% of iron oxide, and 10% to 30% of other impurities;

[0008] (2) pouring the stainless steel liquid after initial decarburization in the converter into the ladle after blocking slag tapping, the temperature of the liquid steel in the ladle being 1600°C to 1650°C, and the chemical composition of the stainless steel liquid being controlled as follows: C: 0.05% to 0.2%, Si: 0.05% to 0.2%, Cr: 10% to 25%, Ni: 0% to 30%, and the rest being iron and other residual elements;

[0009] (3) transporting the ladle containing the stainless steel liquid in step (2) to the VOD station for vacuum decarburization treatment, the vacuum degree in the VOD furnace reaching below 150 Pa, the top blowing oxygen flow being 200 to 300 Nm 3 / h, and the bottom blowing argon flow being 20 to 30 Nm 3 / h for blowing, the VOD oxygen blowing amount being determined by formula 1:

[0010] Formula 1: V = M1* (M C *η C +M Si *η Si )-M2*η Cr

[0011] In Formula 1, V-VOD total oxygen blowing amount, Nm 3 ; M1-VOD incoming molten steel amount, t; MC-VOD incoming carbon content, mass fraction; ηC-decarburization oxygen coefficient, Nm 3 / t; M Si -VOD incoming carbon-silicon content, mass fraction; ηSi-desilicon oxygen coefficient, Nm 3 / t; M2-chrome ore addition amount, t; ηCr-chrome ore oxygen coefficient, Nm 3 / t;

[0012] (4) After the vacuum decarburization treatment is finished, reduction operation is performed;

[0013] (5) The mass fraction of the chemical composition of the VOD furnace outgoing molten steel after the treatment in step (4) is as follows: C: 0.00%-0.01%, Si: 0.1%-0.6%, Cr: 10%-30%, Ni: 0%-30%, and the rest is iron and other residual elements.

[0014] The present application can improve the slag oxidizability by adding chrome ore powder in the ladle in advance, and can serve as one of the decarburization oxygen sources in the VOD smelting process to reduce the amount of oxygen blowing required for VOD decarburization. Since the VOD slag amount needs to be stably controlled at 1 ton-5 tons in the stainless steel smelting process, the addition amount of the chrome ore powder is limited to 0.3 tons-2 tons. The VOD oxygen blowing amount formula is the optimal parameter for VOD smelting of ultra-pure steel prepared according to the composition design of ultra-pure ferrite stainless steel products and the test results of the influence of the addition of chrome ore powder on decarburization. The overall VOD vacuum treatment time can be shortened to 20-50 min, the smelting time is controlled within 60 min, thereby effectively improving the number of continuous casting furnaces, improving the material yield, and reducing the smelting cost. DETAILED DESCRIPTION

[0015] The specific embodiment of the process for VOD smelting of stainless steel of the present application will be described in detail as follows: Example 1

[0016] In this embodiment, VOD smelting of stainless steel is adopted, and the production steel grade is SUH409L, and the smelting steps are as follows:

[0017] (1) Pour 0.32 tons of chrome ore powder into the ladle, the content of chromium oxide in the chrome ore powder is 30% to 60%, and the content of iron oxide is 20% to 40% (the same below);

[0018] (2) Pour the primary decarburization stainless steel liquid smelted by AOD into the ladle containing the chrome ore powder, the temperature of the ladle is 1635°C, and the mass fraction of each element in the liquid steel is:

[0019] C Si Mn Cr Ni 0.0548 0.057 0.15 10.0 0.07

[0020] (3) Transport 125 tons of stainless steel liquid to the VOD station for vacuum decarburization treatment, the top blowing oxygen flow is 200 to 300 Nm 3 / h, the bottom blowing argon flow is 20 to 30 Nm 3 / h (the same below), the top blowing oxygen flow is 151 Nm 3 , the vacuum treatment time is 33 min, and argon is blown throughout the process;

[0021] (4) After the vacuum decarburization treatment, the reducing material is added according to the product composition requirement, specifically, 0.41 tons of ferrosilicon, 0.89 tons of aluminum shot, and 1.3 tons of lime and 0.7 tons of fluorite are added;

[0022] (5) The mass fraction of each element in the outgoing liquid steel is:

[0023] C Si Mn Cr Ni 0.0053 0.33 0.24 11.38 0.06

[0024] The VOD smelting treatment time of Example 1 is 46 min in total.

[0025] Example 2

[0026] In this example, VOD smelting stainless steel is used, and the production steel grade is SUH409L, and the smelting steps are as follows:

[0027] (1) Pour 0.91 tons of chrome ore powder into the ladle;

[0028] (2) Pour the primary decarburization stainless steel liquid smelted by AOD into the ladle containing the chrome ore powder, the temperature of the ladle is 1601°C, and the mass fraction of each element in the liquid steel is:

[0029] C Si Mn Cr Ni 0.105 0.068 0.14 10.68 0.09

[0030] (3) Transport 127 tons of stainless steel liquid to the VOD station for vacuum decarburization treatment, the top blowing oxygen flow is 189 Nm 3 , the vacuum treatment time is 38 min, and argon is blown throughout the process;

[0031] (4) After the vacuum decarburization treatment is completed, reduction materials are added according to the product composition requirements, specifically, 0.51 tons of ferrosilicon, 0.93 tons of aluminum pellets, and 1.6 tons of lime and 0.9 tons of fluorite are added;

[0032] (5) The mass fraction (%) of each element in the outgoing liquid steel is:

[0033] C Si Mn Cr Ni 0.005 0.48 0.23 11.48 0.08

[0034] The VOD smelting treatment time of Example 2 is 58 min in total.

[0035] Example 3

[0036] In this example, VOD smelting is used to smelt stainless steel, and the production steel grade is SUH409L. The smelting steps are as follows:

[0037] (1) 1.2 tons of chromium ore powder is poured into the ladle;

[0038] (2) The primary decarburization stainless steel liquid smelted by AOD is tapped with slag blocking, and poured into the ladle containing chromium ore powder. The temperature of the ladle is 1616°C, and the mass fraction (%) of each element in the liquid steel is:

[0039] C Si Mn Cr Ni 0.12 0.11 0.21 10.96 0.06

[0040] (3) 122 tons of stainless steel liquid is transported to the VOD station for vacuum decarburization treatment, and 193 Nm 3 of oxygen is blown in the top, the vacuum treatment time is 40 min, and argon is blown at the bottom throughout the process;

[0041] (4) After the vacuum decarburization treatment is completed, reduction materials are added according to the product composition requirements, specifically, 0.46 tons of ferrosilicon, 1.01 tons of aluminum pellets, and 1.7 tons of lime and 0.8 tons of fluorite are added;

[0042] (5) The mass fraction (%) of each element in the outgoing liquid steel is:

[0043] C Si Mn Cr Ni 0.0065 0.37 0.31 11.54 0.06

[0044] The VOD smelting treatment time of Example 3 is 59 min in total.

[0045] Example 4

[0046] In this example, VOD smelting is used to smelt stainless steel, and the production steel grade is SUH409L. The smelting steps are as follows:

[0047] (1) 1.4 tons of chromium ore powder is poured into the ladle;

[0048] (2) The AOD smelted primary decarburization stainless steel liquid is blocked slag tapping and poured into a ladle containing chromium ore powder, the temperature of the ladle is 1624°C, the mass fraction of each element in the steel liquid is:

[0049] C Si Mn Cr Ni 0.13 0.06 0.31 11.01 0.06

[0050] (3) The 129 tons of stainless steel liquid is transported to a VOD station for vacuum decarburization treatment, 131 Nm 3 of oxygen is blown into the top, the vacuum treatment time is 31 min, and argon is blown at the bottom throughout the process;

[0051] (4) After the vacuum decarburization treatment, the reducing material is added according to the product composition requirement in the reduction stage, specifically, 0.36 tons of ferrosilicon, 1.08 tons of aluminum shot, and 2.2 tons of lime and 0.5 tons of fluorite are added;

[0052] (5) The mass fraction of each element in the outgoing steel liquid is (%):

[0053] C Si Mn Cr Ni 0.0063 0.36 0.37 11.37 0.06

[0054] The VOD smelting treatment time of Example 4 is 45 min.

[0055] Comparative Example 1

[0056] The stainless steel of this comparative example 1 is smelted by VOD, and the production steel grade is SUH409L, and the smelting steps are as follows:

[0057] (1) The AOD smelted primary decarburization stainless steel liquid is blocked slag tapping and poured into a ladle, the temperature of the ladle is 1632°C, the mass fraction of each element in the steel liquid is (%):

[0058] C Si Mn Cr Ni 0.223 0.098 0.14 11.55 0.05

[0059] (2) The 126 tons of stainless steel liquid is transported to a VOD station for vacuum decarburization treatment, 862 Nm 3 of oxygen is blown into the top, the vacuum treatment time is 86 min, and argon is blown at the bottom throughout the process;

[0060] (3) 0.55 tons of ferrosilicon, 0.83 tons of aluminum shot, and 1.8 tons of lime and 0.5 tons of fluorite are added for reduction;

[0061] (4) The mass fraction of each element in the outgoing steel liquid is (%):

[0062] C Si Mn Cr Ni 0.0059 0.37 0.23 11.52 0.04

[0063] The VOD smelting treatment time of Comparative Example 1 is 98 min.

[0064] Comparative Example 2

[0065] The example adopts VOD smelting of stainless steel, and the production steel grade is SUH409L, and smelting steps are as follows:

[0066] (1) The primary decarburization stainless steel liquid of AOD smelting is blocked slag tapping, and is poured into a ladle, the ladle temperature is 1605°C, and the mass fraction of each element in the liquid steel is (%):

[0067] C Si Mn Cr Ni 0.185 0.153 0.16 11.6 0.06

[0068] (2) 123 tons of stainless steel liquid is transported to a VOD station, vacuum decarburization treatment is carried out, 805 Nm 3 of oxygen is blown into the top, the vacuum treatment time is 82 min, and argon is blown at the bottom throughout the process;

[0069] (3) 0.59 tons of silicon iron, 0.76 tons of aluminum pellets, 1.7 tons of lime and 0.53 tons of fluorite are added;

[0070] (4) The mass fraction of each element in the liquid steel at the outlet is (%):

[0071] C Si Mn Cr Ni 0.0061 0.41 0.23 11.38 0.06

[0072] The VOD smelting treatment time of Comparative Example 2 is 96 min.

[0073] Comparative Example 3

[0074] The example adopts VOD smelting of stainless steel, and the production steel grade is SUH409L, and smelting steps are as follows:

[0075] (1) The primary decarburization stainless steel liquid of AOD smelting is blocked slag tapping, and is poured into a ladle, the ladle temperature is 1634°C, and the mass fraction of each element in the liquid steel is (%):

[0076] C Si Mn Cr Ni 0.213 0.064 0.21 11.7 0.05

[0077] (2) 128 tons of stainless steel liquid is transported to a VOD station, vacuum decarburization treatment is carried out, 782 Nm 3 of oxygen is blown into the top, the vacuum treatment time is 93 min, and argon is blown at the bottom throughout the process;

[0078] (3) 0.57 tons of silicon iron, 0.67 tons of aluminum pellets, 2.7 tons of lime and 0.82 tons of fluorite are added;

[0079] (4) The mass fraction of each element in the liquid steel at the outlet is (%):

[0080] C Si Mn Cr Ni 0.0045 0.36 0.21 11.59 0.05

[0081] The VOD smelting treatment time of Comparative Example 3 is 113 min.

[0082] Comparative Example 4

[0083] The present embodiment adopts VOD smelting of stainless steel, and the production steel grade is SUH409L, and the smelting steps are as follows:

[0084] (1) The primary decarburization stainless steel liquid of AOD smelting is blocked slag tapping and poured into a ladle, and the ladle temperature is 1627°C, and the mass fraction (%) of each element of the liquid steel is:

[0085] C Si Mn Cr Ni 0.18 0.063 0.20 11.5 0.05

[0086] (2) The 123 tons of stainless steel liquid is transported to the VOD station for vacuum decarburization treatment, and 753 Nm 3 of oxygen is blown in, the vacuum treatment time is 91 min, and argon is blown throughout the process.

[0087] (3) 0.52 tons of silicon iron, 0.70 tons of aluminum shot, and 2.8 tons of lime and 0.9 tons of fluorite are added;

[0088] (4) The mass fraction (%) of each element of the outgoing liquid steel is:

[0089] C Si Mn Cr Ni 0.0051 0.35 0.20 11.36 0.05

[0090] The VOD smelting treatment time of Comparative Example 4 is 109 min.

[0091] Compared with Comparative Examples 1-4, the present embodiments 1-4 add chromium ore powder to the ladle in advance, and then smelt the ultra-low carbon steel grade in the VOD furnace, the chromium ore powder can improve the oxidizability of the slag, and the chromium ore powder as one of the decarburization oxygen sources in the VOD smelting process can reduce the amount of oxygen blown in for VOD decarburization, effectively shorten the VOD oxygen blowing time, and thus shorten the VOD smelting time and improve the VOD smelting efficiency. Since the VOD slag amount needs to be stably controlled at 1 ton to 5 tons during the smelting of stainless steel, the addition amount of the chromium ore powder is limited to 0.3 tons to 2 tons. The process is simple, realizes VOD smelting of ultra-pure ferrite stainless steel, the time is shortened to 60 min, the two-furnace continuous casting is improved to five-furnace continuous casting, the product yield is improved, and the production cost is reduced.

[0092] The above only describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent process transformation or direct or indirect application in other related technical fields by using the content of the present application is also included in the patent protection scope of the present application.

Claims

1. A process for VOD smelting stainless steel, characterized in that, It includes the following steps: (1) Add 0.3 to 2 tons of chromium ore powder to the ladle, wherein the chromium ore powder contains 30% to 60% chromium oxide, 20% to 40% iron oxide, and 10% to 30% other impurities; (2) After the stainless steel molten steel is decarburized in the converter, it is poured into the ladle. The temperature range of the molten steel in the ladle is 1600°C to 1650°C. The mass fraction of the chemical composition of the stainless steel molten steel is controlled as follows: C: 0.05% to 0.2%, Si: 0.05% to 0.2%, Cr: 10% to 25%, Ni: 0% to 30%, and the remainder is iron and other residual elements. (3) Transport the ladle containing the stainless steel molten steel from step (2) to the VOD station for vacuum decarburization treatment. The vacuum degree inside the VOD furnace reaches below 150 Pa, and the top-blown oxygen flow rate is 200-300 Nm³. 3 / h, bottom blowing argon flow rate is 20-30 Nm 3 The oxygen blowing rate (VOD) is determined by formula 1 for the blowing process at / h. Formula 1: V = M1 * (M C * η C + M Si * η Si ) - M2 * η Cr In Formula 1: V - Total oxygen blowing volume (Nm³) 3 ; M1-VOD molten steel inflow, t; M C -VOD carbon content at the inlet, mass fraction; η C - Decarbonization oxygen coefficient, Nm 3 / t;M Si -VOD inlet silicon content, mass fraction; η Si -Desilication oxygen coefficient, Nm 3 / t; M2-chromite addition amount, t; η Cr - Oxygen coefficient of chromite, Nm 3 / t; (4) After the vacuum decarburization process is completed, a reduction operation is performed; (5) The chemical composition of the molten steel from the VOD furnace after step (4) is as follows: C: 0.00% to 0.01%, Si: 0.1% to 0.6%, Cr: 10% to 30%, Ni: 0% to 30%, and the remainder is iron and other residual elements.