JPH04183811A - Method for refining stainless steel or the like - Google Patents

Abstract

PURPOSE:To prevent the erosion of the refractories in a bottom blown converter and to improve the hit rate of heat sizes by using CaCO3, MgCO3, etc., as a slag making agent in the method for reducing and recovering the oxides of the valuable metals in molten slag after subjecting carbon steels and alloy steels to decarburization refining in the converter. CONSTITUTION:The carbon steels, stainless steels, high-alloy steels, etc., are subjected to the oxidation decarburization refining in the converter provided with tuyeres for blowing refining gases under a molten steel surface, such as bottom blowing tuyeres, and thereafter, the Fe and a part of the alloy elements entering as the oxides the inside of the molten slag are reduced to metals by reducing agents, such as Fe-Si. The reduced metals are recovered. An extremely high temp. is generated by the oxidation decarburization and the exothermic reaction by the oxidation of the Fe, Mn, Ni and others during this refining stage and the refractory materials in the converter are eroded and, therefore, carbonates, such as CaCO3 and MgCO3, are used as the slag making agent and the inside of the converter is cooled by the endothermic reaction effected by the pyrolysis thereof, by which the erosion of the refractories is prevented. Since there is no need for using scrap, etc., as the coolant of the superheat converter like heretofore, the hit rate of the heat sizes and the yield of the valuable metals are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing high alloy steel, stainless steel, high carbon special steel, etc.

<Prior art> High alloy steel, stainless steel, and high carbon special media are used under the bath surface such as AOD and top-bottom blowing converter (K-OBM/NI-BOf)). Steel is often decarburized and refined using a converter equipped with gas injection tuyeres, then subjected to reduction refining and tapped steel. When reduction refining is carried out, F oxidized during decarburization refining
E, Mn, Cr, etc. are reduced and recovered to almost 100%. Therefore, the heat size is expressed as the weight of the charged metal.

On the other hand, in the case of ordinary ordinary steel, after decarburization and dephosphorization refining, it is extracted as is without reduction refining, so oxides such as Fe, Mn, and Cr produced during decarburization refining are reduced and recovered. The sludge remains in the slag without being washed away. Therefore, the heat size is not uniquely determined by the amount of metal charged, but is greatly influenced by the degree of oxidation of the metal during decarburization, and has wide variations.

By the way, during decarburization refining, C, Si, Fe,
Since oxidation of Cr etc. occurs, the temperature of the molten steel increases due to the heat of oxidation. Since an increase in the temperature of the molten steel more than necessary promotes wear and tear on the refractories, cooling is generally performed during the blowing process to lower the degree of melt IIgIa.

Specific methods for cooling molten steel include temporarily suspending blowing, tilting the furnace, and adding scrap using a crane;
For example, as disclosed in Japanese Patent Publication No. 60-22045, a method is adopted in which ferroalloys or metal oxides are added from the top of the furnace without interrupting the blowing process.

<Problems to be Solved by the Invention> However, although the conventional cooling method using scrap or ferroalloy is effective in lowering the temperature of molten steel, it has the following decisive drawbacks. That is,
The fundamental principle of production is to make the necessary products in the required quantities, but the method of controlling the rise in molten steel temperature by using scrap or ferroalloy leads to an increase in the amount of molten steel, which leads to the production of excess molten steel. You will be making a product.

In order to achieve the production target, it is possible to control the amount of coolant added at the start of blowing in anticipation of the weight of coolant added during preliminary blowing, but in reality, the amount of coolant added at the start of blowing may be controlled. The degree of rise in molten steel temperature is controlled by various factors such as the concentration of C and Si in the hot metal at the start of blowing, the amount of slag material added, and the heat content of the converter refractory, and there is a large variation in this temperature. It is impossible to synchronize production volume by method.

In other words, the conventional refining method using a scrap or a ferroalloy as a coolant cannot take advantage of the characteristic of the process including reduction refining that the heat size is easily reduced.

An object of the present invention is to propose a refining method that can easily produce heat-sized steel in a process involving reduction refining of stainless steel and the like.

<Means for Solving the Problem> That is, the present invention uses a converter having a tuyere for blowing refining gas under the bath surface, decarburizes molten steel, and then performs reduction refining to produce high alloy steel and stainless steel. Alternatively, a method for refining stainless steel or the like is characterized in that a slag material containing at least one of CaCO3, MgCO, and their compounds is added as a coolant in the process of melting high carbon special steel and the like.

<Function> CaC01, MgCCh and their compounds are materials that do not change the amount of molten steel as a coolant and are not wasted. Incidentally, as auxiliary raw materials added into the furnace during blowing, Can for adjusting the basicity of slag and MgO for protecting refractories are used in boat fishing.

Therefore, CaCO3, MgC01, and their compounds are extremely rational materials that have cooling ability and are useful for adjusting the basicity of slag and protecting refractories, and do not change the amount of molten steel.

When minerals containing CaC0z, MgC0, and their compounds, such as carbonate minerals such as limestone, magnezite, and dolomite, are placed in a furnace, they are converted to "ζ" according to the following formula in a high-temperature atmosphere.
It decomposes endothermically and removes the heat necessary for heating CaOlMgO, Co2 from the molten steel and slag, so it fully fulfills its role as a coolant.

CaCO3->CaO+CO2 ΔH' 298 =42.8kcal/moleMgC
O, → MBo+ co□ 8H629B = 24.3 kcal/mole CaO, MgO, and other gangue components produced by decomposition enter the slag, and co□ is discharged outside the furnace as a gas, so it remains inside the converter. amount of molten steel and F in slag to be recovered in the reduction period.
Since there is no change in the absolute amounts of e, Mn, Cr, etc., variations in the amount of molten steel tapped after reduction refining, that is, the heat size, can be reduced.

That is, according to the present method, the heat size can be easily controlled by using a coolant as a substance that migrates after being added to the slag, instead of scrap or ferroalloy that has been mainly used in the past.

Furthermore, in the case of carbonate compounds such as CaCO5 and MgCO3, when added to the furnace, the products CaO and MRO become useful as slag-making materials, and the generated CO□ reacts with C in the molten steel, resulting in the following formula: It also contributes to the decarburization reaction.

Furthermore, since the generated CO□ gas and CO gas promote the agitation between slag and metal during decarburization, reduction of oxidized Cr, Mn oxide, and oxidized Pe, etc., which were once oxidized and floated during decarburization, by molten steel C is also carried out. You also get the additional benefit of progression.

CO□＋C→2CO↑ Next, the present invention will be explained in more detail based on examples.

<Example> Table 1 shows an example of the steel refining method according to the present invention method performed in an 85-ton top-bottom blowing converter (K-BOP) in comparison with a conventional method. The conventional method is a method in which ferroalloy and iron scraps are added during blowing using an auxiliary material feeding device on the furnace. As shown in Table 1, in the heat in which limestone was added, there was almost no ferroalloy for cooling, and only the ferroalloy needed for component adjustment was left.

FIG. 1 and FIG. 2 compare the conditions of heat size, which is the object of the present invention. Number of heats is 50 each
It's a heat. In the conventional method, there was a large variation in the temperature rise of molten steel during blowing due to differences in furnace conditions and blowing conditions. 3.21) There were large variations in the number/ch and the heat size itself. On the other hand, in the case of the method of the present invention, σ
= 1.64) n/ch, the variation decreased, and the heat size success rate increased significantly.

Table 1〈Effects of the invention〉 Steels such as high-alloy steel, stainless steel, and high-carbon special steel can be produced through the process of decarburizing, refining, and tapping in a converter with tuyere for blowing refining gas under the bath surface. In the present invention, molten steel is cooled from a metal coolant to CaCO3 and/or Mg.
By changing to a slag-based coolant containing C01, heat-sized products can now be made into containers, and the generation of surplus products can be greatly reduced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the variation in heat size according to the method of the present invention, and FIG. 2 is a graph showing the variation in heat size according to the conventional method. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] In the process of decarburizing molten steel and then reductively refining it to produce high-alloy steel, stainless steel, high-carbon special steel, etc. using a converter with a tuyere for blowing refining gas under the bath surface.
A method for refining stainless steel, etc., characterized in that a slag material containing at least one of CaCO_3, MgCO_3 and their compounds is added as a coolant.