JPS6247417A - Melt refining method for scrap - Google Patents

Abstract

PURPOSE:To produce molten steel at a low cost by using inexpensive steel scrap by using the combustion heat of coke as a heat source in a converter having a top blowing lance and bottom blowing tuyere. CONSTITUTION:The coke is preliminarily charged into the converter having the top blowing lance and bottom blowing tuyere at a 50-200kg/ton ratio prior to charging of steel scrap or stainless steel scrap into the converter. Oxygen is blown into the converter from the bottom blowing tuyere or top blowing lance and the coke is ignited; in succession thereof, steel scrap or stainless steel scrap is charged into the converter and further the coke is added thereto and is burned. The scrap is melted by the combustion heat, by which the melt of >2% C molten iron or high-carbon stainless steel is formed. The molten iron or stainless steel is desulfurized by adjusting the basicity of slag to >=1.2; at the same time, a non-oxidizing gas is blown from the bottom blowing tuyere to stir the molten metal and to reduce the T.Fe in the molten slag to <=3%. The molten metal is decarburized and denitrided by the oxygen blowing from the top blowing lance after removing the slag, by which the molten metal is refined to molten steel or molten stainless steel.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for melting and refining scrap.

More specifically, the present invention relates to a method for melting and refining scraps such as iron scraps and stainless steel scraps using a composite blowing converter equipped with a bottom tuyere and a top blowing lance.

BACKGROUND OF THE INVENTION The blast furnace-converter process has been established in the steel industry for a long time, and steelmaking technology in particular appears to have been fully developed.

The cost of producing mass-produced steel is nearly 1,000 yen per ton, excluding the cost of main raw materials, making it extremely difficult to significantly reduce the cost of mass-produced steel through future improvements in steelmaking technology.

On the other hand, the cost of main raw materials varies by around 5,000 yen per ton depending on the size of the blast furnace equipment and the properties of the scrap. Furthermore, the amount of scrap is on the rise worldwide, and in recent years, the scrap content ratio in converters has been decreasing further due to the development of hot metal pretreatment.

Apart from the predicted increase in industrial waste, steelmaking processes that use large amounts of scrap have the potential to significantly reduce steelmaking costs, and are an extremely important development issue.

However, melting and refining of scrap using an electric furnace is extremely disadvantageous due to the electricity situation in Japan, and there is a difference in steel manufacturing cost of about 10,000 yen per ton compared to the blast furnace-converter method.

Due to these circumstances, steelmaking using scrap as the main raw material requires the use of cheap carbonaceous materials instead of electricity as the heat source for melting, and utilizes converter equipment with high acid delivery capacity that can rapidly supply a large amount of heat. Establishment of technology is required.

Problems to be Solved by the Invention An object of the present invention is to provide a method for melting and refining scrap using an existing composite blowing converter equipped with a top blowing lance and a bottom blowing tuyere.

More specifically, it is an object of the present invention to provide a method for melting and refining high-grade steel and stainless steel from scrap using an existing composite blowing converter equipped with a top-blowing lance and a bottom-blowing tuyere. be.

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have completed the present invention as a result of repeated experiments and studies.

According to the present invention, there is provided a method for melting and refining scrap using a reaction vessel equipped with a gas blowing tuyere at the bottom of the furnace and a lance above the furnace, comprising: (a) prior to scrap charging, 50 kg/t ~
Putting 200 kg/t of coke into the reaction vessel, blowing 02 through the bottom blowing tuyere and/or top blowing lance to ignite the coke and use it as a spark for melting scrap; (b) Next, scrap melt the scrap so that the metal contains 2.0% or more of C by the time melting is completed by charging 0□ from the bottom blowing tuyere and top blowing lance while charging the carbonaceous material. (c) After completing the scrap melting, the slag components are adjusted so that the basicity [:aO/S+02] of the slag is 1.2 or more and desulfurization is performed, and non-oxidizing gas is blown from the bottom blowing tuyere. Stirring the slag ring and metal to reduce the (T-Fe) content in the slag to less than 3%; (d) After completing the desulfurization in step (c) above, remove the slag and residual carbonaceous material. Provided is a method for melting and refining scrap, which is characterized by: decarburizing and denitrifying the obtained metal containing 2.0% or more of C by top-bottom blowing acid.

These scraps may be ordinary steel scraps or stainless steel scraps.

The reason for limiting the conditions in the scrap melting and refining method of the present invention will be explained below.

(a) Charging and ignition of coke According to the present invention, prior to charging scrap, 50 kg
/t~200kg/t of coke is charged. This is not only to protect the hearth by using coke as a bedding, but also to sufficiently redden the coke by bottom blowing 02 before charging the scrap so that the scrap can be heated from the bottom of the hearth.

By disposing coke at the bottom of the furnace and blowing it from the top, scrap can be melted from above and below. At this time, bottom blowing 02 is preferable, but when the furnace body is sufficiently preheated, coke may be ignited only by top blowing 02. If the amount of crushed coke in the bedding is less than 50 kg/t, it is difficult to use it as a spark for melting scrap, and on the other hand, since coke is an expensive carbon material, it is uneconomical to use more than 200 kg/t of coke in the bedding. . Therefore, the charging amount of bedding coke was set to 50 kg/t to 200 kg/t.

(b) Melting the scrap, then charging the scrap and adding carbon material.02
By top-bottom blowing, a metal with a dissolved mass of 2.0% or more is obtained.

Coke is easy to handle as the carbonaceous material, but coal may also be used. The reason why the carbon content in the metal at the time of completion of melting is set to 2.0% or more is because it is preferable that the post-process desulfurization treatment be surrounded by a reducing cloud as much as possible, and on the other hand, considering the efficiency of carburizing the molten steel. C 2.0
% or more.

(c) Desulfurization Treatment After melting the scrap, it is necessary to mainly remove S from the carbonaceous material, and for this purpose it is preferable to form a slag with a high basicity and stir the metal slag. however,
In the present invention, the C content in the metal is set to 2.0% or more, and if sufficient stirring is performed, the T-Fe content in the slag can be reduced to 3% or less. In such a reducing atmosphere, it was confirmed that sufficient desulfurization could be achieved even when the basicity of the slag, CaO/SiO7, was about 1.2 or more.

Further, the lower the T-Fe content in the slag, the lower the iron content loss, which is preferable from the viewpoint of preventing damage to refractories.

(d) Decarburization and denitrification treatment In the method of the present invention, after desulfurization is completed, slag and residual carbonaceous materials are removed, and 02 is blown in a slag-free state to perform decarburization and denitrification. The higher the C content in the metal, the more desirable it is for denitrification, but in consideration of the carburization efficiency due to the use of a carburizing agent (such as coke), decarburization and denitrification were performed at 2.0% or more. Furthermore, as the heat source becomes excessive, scrap is generally added as a cooling material, but manganese ore can also be used for high manganese steel.

Hereinafter, the present invention will be explained with reference to examples, but these examples are merely illustrative of the present invention, and it goes without saying that they do not limit the technical scope of the present invention in any way.

Example 1 The present invention was carried out using a converter 70 equipped with bottom tuyeres.

6 tons (80 kg/t 2 of scrap) of coke was put into the coke and used as a bedding, and ignited using the heat retained in the furnace and the bottom blower 02. The amount of bottom blowing 02 was 40ONm3/hr, and the bottom blowing of 0□ was continued until the end of scrap charging.

Scrap was charged in four parts: three times of 20 tons and one time of 10 tons. Between each scrap charge, the converter was held vertically and 02 was blown from the top blowing lance and the bottom blowing tuyere. .

After charging scrap, top blowing 02: 1300ONm
3/hr.

Bottom blowing 02: 10100N/hr, bottom blowing N2
: Combined oxygen supply at a blowing flow rate of 30ONm'/hr, while
13 tons (170 kg/t for scrap) of carbonaceous materials are pumped at approximately 300 kg/mi for 40 minutes during the latter half of the composite oxygen supply.
He served as a uniform official at n. In addition, 3 tons of quicklime (40 kg/t for scrap) was added for desulfurization in the converter in the next process.
I put it in.

The desulfurization process was performed with bottom-blown N 2 :40ONm3/hr. The slag composition at this time is as follows.

CaO:5102:A1203=50:25:1
Metal-slag agitation is carried out using double-bottom N2 blowing, and in addition to desulfurization, slag remains due to residual carbonaceous material and [
Achieved an increase of 0.3%.

After S was reduced to 0.015%, slag and residual carbonaceous material were removed, and 10 scraps were added because there was a surplus of heat source, and then 700 kg of quicklime was added to adjust the composition and top blowing was carried out at 02: 1300 ONm'/ hr, bottom blowing Ar: 2
Slagless decarburization was performed for 10 minutes by combined blowing at 0ONm3/hr.

The components of the metal and slag and their temperature are shown in Table 1 below.

Furthermore, the coke consumption rate up to tapping is 250 kg/t.

02 basic unit was 20ONm3/hr.

Example 2 5IIS 304 was produced by melting Ni-Cr stainless steel scrap using a converter in a steel 70 equipped with a hearth bottom tuyere.

8 tons of coke (105 kg/t 2 based on scrap) was charged as a bedding, and ignited using the heat retained in the furnace and the bottom blower 02. The amount of bottom blowing 02 continued at 40 ONm3/hr until the end of scrap charging.

Scrap was charged in four parts: three times of 20 tons and one time of 10 tons. Between each scrap charge, the converter was held vertically and 02 was blown from the top blowing lance and the bottom blowing tuyere. .

After charging scrap, top blowing 02: 1300ONm3/h
r, bottom blowing 02: 10100N/hr, bottom blowing N2:
Combined oxygen supply was carried out at 30ONm3/hr, while 18t (
Approximately 300 kg/t of carbonaceous material (240 kg/t for scrap) was added over 60 minutes during the latter half of the composite oxygen supply for scrap melting.
kg/min. Furthermore, 2 tons of quicklime (26 tons for scrap) was added for desulfurization in the converter in the next step.
kg/t).

The desulfurization process was performed with bottom-blown N 2 :40ONm3/hr. The slag composition at this time is as follows.

CaO: 5102:81203-32:25
:21 Metal-slag agitation was performed by bottom-blowing N2, and in addition to desulfurization, slag reduction by residual carbonaceous material and an increase of [03% in metal] were achieved.

After reducing S to 0.015%, slag and residual carbonaceous materials were removed, and 10 pieces of SUS 304-based scrap were added for temperature adjustment, and decarburization was started. Injection during the decarbonization period was performed as follows.

First 12 minutes: Top blow 02: 1300ONm3/hr, bottom blow Ar +20
ONm'/hr Next 10 minutes: Top blowing 02: 400ONm'/hr, bottom blowing Ar: 40O
Nm3/hr last 30 minutes: Top blow 02: 10100ON/hr, bottom blow Ar+40O
Nm3/hr Furthermore, raw coal 1 is used for slag adjustment during decarburization.
000 kg was added.

The components of the metal and slag and the temperature of the metal are as shown in Table 2.

After this, the slag a is made using alloys such as FeSi and AI.
Original 1i: After adjusting the composition by adding low carbon ferrochrome and ferromanganese, steel was tapped.

Effects As explained above, the present invention has succeeded in melting and refining high-grade steel and stainless steel from scrap using an existing composite blowing converter, and it is possible to use a large amount of scrap found in the earth. In addition, scrap generated within the steelworks can also be used effectively. Furthermore, the present invention has great industrial value in view of the increasing tendency of car scrap in the future in Japan.

Claims (3)

[Claims] (1) A method of melting and refining scrap using a reaction vessel equipped with a gas blowing tuyere at the bottom of the furnace and a lance above the furnace, comprising:
kg/t of coke is charged into the reaction vessel, and O_2 is blown into the bottom blowing tuyere and/or the top blowing lance to ignite the coke and use it as a spark for melting the scrap; (b) Next, scrap and melt the scrap so that the metal contains 2.0% or more ￥C￥ by the time melting is completed by blowing O_2 from the bottom blowing tuyere and top blowing lance while charging the carbonaceous material. (c) After completing the scrap melting, the basicity C of the slag
Desulfurization is performed by adjusting the slag components so that aO/SiO_2 is 1.2 or more, and non-oxidizing gas is blown from the bottom blowing tuyere to stir the slag and metal.
(d) After completing the desulfurization in step (c) above, remove the slag and residual carbonaceous material to obtain a metal with a carbon content of 2.0% or more. A scrap melting and refining method characterized by performing decarburization and denitrification by top-bottom blowing acid. (2) The method for melting and refining scrap as set forth in claim 1, wherein the scrap is ordinary steel scrap. (3) The method for melting and refining scrap as set forth in claim 1, wherein the scrap is stainless steel scrap.