JPS6052549A - Method for dissolving solid material in chromium- containing steel bath - Google Patents

Abstract

PURPOSE:To prevent oxidation reaction loss of Cr in the stage of charging chromium contg.- or non-Cr contg. scrap into a Cr-contg. steel bath by using a solid carbon material as a heat source or (C) source and adjusting the (C) level in the steel bath together with temp. at the equilibrium of C-Cr-temp. CONSTITUTION:A solid carbon material (e.g.; coke) is used as a heat source or (C) source and the above-described scrap or alloy iron is dissolved into a Cr- contg. steel bath in the stage of refining a steel in a converter. The scrap and alloy iron are dissolved while the oxidation loss of metallic Cr and the erosion of refractories are decreased by adjusting the (C) or the temp. in the steel bath with respect to the equilibrium of the C-Cr-temp. As a result a large amt. of the inexpensive chromium scrap is melted without decreasing the consumption of the refractories.

Description

DETAILED DESCRIPTION OF THE INVENTION 1) Industrial field of application The present invention provides a method for melting chromium-containing scrap or non-chromium-containing scrap into a chromium-containing steel bath using a solid carbon material as a heat source in a converter. With respect to the [C] temperature in the steel bath, by ensuring conditions for preferential decarburization to occur from the equilibrium relationship of C-Cr temperature, Siscra,
The present invention relates to a method for melting scrap while suppressing oxidation loss of Cr in a steel bath or steel bath.

b) Prior Art Conventionally, when melting solid substances such as chromium-containing scrap or non-chromium-containing scrap or ferroalloy in a chromium-containing steel bath, the equilibrium relationship between C-Cr and temperature has been considered. Since the carbon material was not used as a heat source or a heat source, the only degree of freedom that could be selected in the equilibrium relationship was to adjust the steel bath temperature. Either ferro-alloy such as ferrosilicon or aluminum is used as the heat-raising material to heat the steel bath to a high temperature to melt the scrap or ferro-alloy, or scrap or ferro-alloy is continuously introduced in small amounts while the temperature is lowered. The oxidation reaction of Cr has been controlled only by temperature adjustment, such as by melting the scrap or ferroalloy while reducing the amount of Cr, or by preheating the scrap or ferroalloy and adding it all at once or continuously.

As mentioned above, firstly, the oxidation reaction of Cr was prevented by increasing the steel bath temperature at C-Cr temperature equilibrium, and secondly, the amount of slag was reduced when ferrosilicon was used as the heating material. Due to the increase in the number of refractories, the conventional method caused significant damage to the refractories. In addition, when continuously charging scraps of various shapes generated from the steelmaking and rolling processes, it is necessary to cut them into small pieces in advance to input them from the upper sheet of the converter, which increases the cost. Furthermore, even if preheating was performed, the C-Cr temperature equilibrium was handled only by temperature, so there was a limit to the amount of scrap or alloy iron that could be input at once due to the range of temperature drop.

C) Purpose of the Invention In view of these points, the present invention provides a method for melting chromium-containing scrap or non-chromium-containing scrap by using a solid carbon material as a heat source or [C] source in a chromium-containing steel bath. ! 7 It is possible to prevent oxidation reaction loss of Cr by adjusting the temperature and the [C] level in the steel bath at the same time in the C-Cr-temperature equilibrium. Therefore, [
The amount of refractory loss due to high-temperature refining can be greatly reduced by increasing C] to reduce the amount of steel bath temperature rising, or by making it possible to melt scrap or ferroalloy while keeping the temperature constant. Or, it can be input all at once, making it possible to greatly increase the amount of scrap input.

d) Structure and operation of the invention When stainless steel is melted in a steel plate maker, generally the rotor P serves as the melting furnace and the mill P.

The main raw material is hot metal, and the pCr source is a high carbon ferrochrome alloy. In the converter refining method, thermal constraints are large and 5,0 to 6.
59! Since +C and 2.0 to 5.5% Si are insufficient as a heat source, ferrosilicon or aluminum is further added as a heat source for melting. Therefore, stainless steel scrap could hardly be used, and was only used to a limited extent, mainly as a cold material after being tapped from a converter.

However, recently, in order to reduce melting costs, there has been a strong desire to develop stainless steel melting technology that is flexible for main raw materials or auxiliary raw materials. The use of scrap (stainless steel scraps) is desired. However, as mentioned above, there is a lack of a heat source even for melting ferrochrome alloys with high C and Sl contents. It is economically disadvantageous to dissolve using. t
Even if ferrosilicon and aluminum become inexpensive heat sources, these heat raising materials have a C-Cr temperature equilibrium relationship that must be taken into account when melting chromium-containing scrap, non-chromium-containing scrap, or other ferroalloys. It is a heat source that can only be adjusted with respect to temperature, so the degree of freedom is small.

FIG. 1 shows an equilibrium diagram of C-Cr-temperature-Pco. The line in the figure is P. . = 1 atm In the case of 174 Cr-containing steel, the region below the line is the Cr20H generation region (preferential oxidation region), and the region above the line is the preferential decarburization region. When dealing with C-Cr-temperature equilibrium using ferrosilicon or aluminum, for example, as shown at point A in the figure, C = 0.25%, temperature = 15
Average molten steel [:Cr:I
When refining by adding ferrochrome alloy or stainless steel scrap so that the value becomes 1796, in order to prevent oxidation loss of Cr (5), the temperature must be at least 1750°C as in method (a).
It is necessary to do more than that. However, as shown in Figure 2, the amount of melting loss in converter refractories increases significantly above approximately 1700°C, so methods to prevent oxidation loss of Cr due to temperature rise are disadvantageous. .

In addition, with heat raising materials such as ferrosilicon, after the oxidation reaction shown in equation (1) below, reaction products remain in the furnace, and the amount of slag increases due to the addition of CaO for basicity adjustment. This is disadvantageous for corrosion of refractories.

(remains in the furnace as slag) However, as in the present invention, solid carbon material is used as a heat source or [C
] By using it as a source, there are two degrees of freedom regarding PC-Cr-temperature equilibrium: C and temperature, and the range of adjustment is greatly expanded. In method (b) in Figure 1, the [C] content in the steel bath is increased while the temperature is maintained at a constant level to ensure a preferential decarburization region. A specific method is to add a solid carbon material to the carbonaceous paste metal to once maintain the [C] content in the steel bath in the preferential decarburization region, and then add solid carbon material and scrap or At the same time as the ferroalloy is added, acid is blown to melt the scrap so that the [C] and temperature levels in the steel bath are always maintained in the preferential decarburization region.

In addition, as shown in method (c) in Figure 1, chromium-containing pace metal is blown with acid while adding a solid carbon substance to the steel bath temperature [C]
It is also possible to secure a preferential decarburization region by increasing the content at the same time.

As mentioned above, using a solid carbon material, C-
By adjusting the equilibrium relationship between Cr and temperature, the amount of erosion of the refractory can be greatly reduced.

This is because, if we take the low-rise area as an example, C=0.1.
% increase contributes to a temperature drop of 40°C.
This is because scrap or ferroalloy melting can be easily performed while maintaining the temperature at 0° C. or lower while preventing oxidation loss of Cr. Second, in solid carbon materials, CO, which is a reaction product after the oxidation reaction shown in equation (2) below, becomes a gas and escapes from the furnace, so unlike ferrosilicon, the amount of slag does not increase, but in large amounts. Even if it is added, there is no risk that refractory corrosion will increase.

9+9→Co(g)...Equation (2) (Escapes from inside the furnace as a gas) e) Example As a preliminary treatment for hot metal, desiliconization, desiliconization and desulfurization were carried out.71. Ot's low P1 low S1 pace metal was charged into the converter. The hot metal components are C=3.8%, 5l=t, Mn=0.
35%, P=0.014%, S=0.004%, Tem
p, = 1.335°C. 7. Top blows immediately after charging. V) 02 = 18,000 Nrn3/h
Decarburization heating was carried out for about 8 minutes at a feed rate of r, and C = 1.1
% and a temperature of 1.588°C was obtained. Here preheated C=6.0%, 5i=5.2%, 5=O101
0, Cr = 52.1% high carbon ferrochrome 1
A 5t'i ferroalloy cooker was used to charge the 02, and oxygen was supplied from a top blowing lance at a supply rate of 18,000 Nm/hr for 5 minutes to perform melting and refining. The result is C=1.5q6
A chromium-containing pace metal with Cr = 9.67 and a temperature of 1411°C was obtained. Next, 5.5 tons of lump coke (solid carbon source) with a size of 15 to 30 ma+ and a composition of C=88 and S=0.50% were added to the upper auxiliary raw materials, and at the same time, C=0.05 %, 5I=0.40%, Cr=16
．． 3191 stainless steel scrap (chromium-containing scrap) 1
5. Ot was added using a scrap pack. Estimated calculations after charging indicate that the molten steel temperature is 1486°C and the C content is 2.4%, which is the preferential decarburization region. Then from top blowing lance 1
Acid blowing was carried out at a supply rate of 4,000 Nm/hr8.
The refining was completed after melting and decarburizing for several minutes. When stopped, C=0.52t, 51=0.05t, Cr=16.
61 To, stainless crude molten steel 111 at a temperature of 1748°C
．． Obtained 6t.

After that, decarburization refining was performed under vacuum using RH, and further deoxidation and component adjustment were performed, resulting in C = 0.07% and S content = 0.
．． 35%, Mn = 0.5 1%, Cr =
1 6.5'Ir, 8=0.007ch 5US43
0 steel was obtained.

f) Detailed Description of the Invention As described above, the present invention utilizes a solid carbon material as a heat source or [C] source to melt scrap or ferroalloy in a chromium-containing steel bath. By adjusting the [:C:l or temperature in the steel bath regarding equilibrium, the oxidation loss of metal Cr and the amount of corrosion of refractories can be reduced while melting scrap and ferroalloy. It is possible to melt a large amount of inexpensive chromium-containing scrap without reducing the unit consumption of large items.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the equilibrium relationship between C-Cr temperature, and FIG. 2 is a diagram showing the relationship between steel bath temperature and refractory unit consumption. Patent Applicant: Nippon Steel Corporation 7th Hana 2nd Annual Melting Warm Skin ('c) −

Claims (1)

[Claims] When refining steel in a converter furnace, in a method of dissolving solid substances in a chromium-containing steel bath, by adding solid carbon substances to the chromium-containing steel bath, it is possible to improve the priority in the C-Cr-temperature equilibrium relationship of the chromium-containing steel bath. A method for dissolving solid substances in a chromium-containing steel bath, characterized in that the solid substances are dissolved by creating decarburization conditions.