JPH01162714A - Converter - Google Patents

Abstract

PURPOSE:To improve thermal spalling resistance and to enable the refining of a Cr steel and dead soft steel without having carbon pickup into a product by using unburned MgO-C bricks bonded with a pitch-reformed phenolic resin as lining refractory bricks of a converter. CONSTITUTION:A raw material mixture composed of 5-10wt.% carbon such as graphite and the balance MgO clinker is kneaded with the pitch-reformed phenolic resin as a binder and is molded to a brick shape as the lining refractory brick of the converter. Such bricks are lined without being burned over a part or the entire part of the wall or bottom of the converter. These bricks have the excellent thermal spalling resistance as the MgO and the C forming the bricks do not react with each other even at a high temp. of >=1650 deg.C. An increase in the content of the C by the C pickup from the refractory bricks is obviated at the time of refining the dead soft steel. The chemical attack of the bricks by the drop of the m. p. of the Cr2O3-contg. molten slag by reduction of the Cr2O3 in the Cr2O3 contg. slag by the C in the bricks is obviated as well at the time of refining of the Cr-contg. molten iron.

Description

[Detailed description of the invention] [Industrial use! J'F1 The present invention relates to a converter, and includes a converter for high-temperature molten iron metallurgy, a converter for producing Cr-containing molten iron, and a converter for fI'i.

[Prior Art J] In recent converters for steel refining, unfired Mg0-C bricks having a carbon content of 15 to 20% by weight are generally used. This is because MgO is resistant to chemical corrosion caused by highly basic slag and iron oxides, and by combining it with graphite, the heat spalling resistance can be significantly improved compared to other basic refractories.

Various improvements have been made to increase the durability of unfired Mg0-C bricks. For example, optimization of the carbon component content as described above, use of fused MgO, use of metal additives such as AP, and use of high-purity graphite are examples. Furthermore, in terms of manufacturing technology, attempts have been made to make the brick structure more dense, as typified by the use of high-pressure vacuum degassing presses.

However, in the conventional Mg0-C brick, l650°
In high-temperature refining that exceeds C and in heavy equipment of ultra-low carbon steel where FeO content in slag is high, the reduction of MgO by C will significantly increase the embrittlement of bricks, structural deterioration, and chemical corrosion caused by FeO in slag. There was a drawback. Furthermore, there was a problem in that it was difficult to melt and produce ultra-low carbon steel due to the elution of C in the bricks into the molten steel.

Furthermore, conventional Mg0-C bricks have high thermal conductivity and a large amount of heat is transferred to the converter shell through the bricks, which causes the temperature of the steel shell to rise significantly, causing deformation and cracking due to high-temperature creep of the steel shell. It also had the disadvantage of easily inviting

In addition, for stainless steel melting in a converter, Ca
O-CaO-3i02- (Aff203)-Cr20
As a result of the reduction of Cr2O3 in the 3-series slag with C, the melting point of the slag is lowered and the Mg0-C bricks become brittle, causing severe chemical damage.
There is a problem with using Mg0-C bricks due to their thermal characteristics.
Although there are examples of unfired MgO-Ca0-C bricks being used, this type of brick inevitably has drawbacks in terms of manufacturing technology centered on moisture management and usage technology due to the use of CaO-containing raw materials. It was a thing.

On the other hand, in the refining process in converters, the need for refining at higher temperatures has recently increased rapidly, and at the same time, a single steelmaking vessel can consistently perform multiple functions from melting scrap and ore to smelting reduction and refining. There is also a growing need for operations that can be terminated, and in order to meet these needs, there has been a desire to develop refractory materials for converters that can withstand a wide range of changes in usage conditions.

[Problems to be Solved by the Invention] The purpose of the present invention is to eliminate the above-mentioned drawbacks of conventional Mg0-C bricks, and to solve the following problems (1), (2), and (3).
) The object of the present invention is to provide a converter lined with Mg0-C that satisfies the following.

(L) When refining is carried out such that the maximum temperature reached exceeds 1650°C, the reaction between MgO and C that essentially and substantially proceeds at a high reaction rate within the Mg0-C brick, that is, the reduction of MgO by C. The reaction causes embrittlement of the bricks, but in order to prevent this, the graphite content is minimized, and the heat spalling resistance is maintained at the same level as conventional Mg0-C bricks.

(2) Providing refractories that enable the production of Cr-containing molten iron and the melting and/or refining of all types of steel, including ultra-low carbon steel, in the same furnace, thereby reducing the chemical corrosion caused by Cr-containing molten steel and the removal of carbon in the molten steel. Try to prevent pickup.

(3) Reduce the total carbon content of Mg0-C bricks, which have high thermal conductivity, to lower the thermal conductivity and prevent thermal deformation of the steel shell of the converter.

[Means for Solving the Problems] The object of the present invention is to reduce the total carbon component content such as graphite to 5% by weight.
Achieved by applying Mg0-C bricks with a content of 10% by weight or less, the remainder consisting of MgO talin, and these raw materials bonded with pitch-modified phenolic resin as the work lining for part or all of the converter body. be done.

The high-temperature converter of the first aspect of the present invention is a metallurgical blowing, bottom-blowing, or top-bottom blowing high-temperature converter in which the maximum refining temperature is 1650° C. or higher.

The converter according to the second aspect of the present invention is a converter for producing and/or refining Cr-containing molten iron.

[Effect 1 In Mg0-C bricks, when the total carbon component content exceeds 10% by weight, the so-called Mg
The 0-C reaction is significantly accelerated, the brick structure becomes brittle, and its durability is reduced.

MgO+C→Mg+CO(g) Also, when producing or refining Cr-containing molten iron, CaO-5i
02-MgO-(AQ20a)-Cr203 in the slag is reduced by the C in the bricks, resulting in chemical erosion of the bricks due to the lower melting point of the slag, deterioration of the structure due to decarburization of the bricks, and a decrease in spall resistance. It becomes noticeable.

Furthermore, it has been found that when the total carbon component content is less than 5% by weight, the infiltration of the low basicity slag into the brick structure is promoted. In addition, even with refractories that do not normally contain carbon components, after use, a phenomenon of carburization is generally observed in 3 to 4% by weight of molten iron. There is no point in restricting it (and, furthermore, in the carbon content range of 5 to 10% by weight, the problem of carbon pickup did not occur in the melting of ultra-low carbon bottom steel.

In ordinary Mg0-C bricks, the most commonly used graphite content is 15 to 20% by weight, but in the present invention, the total carbon content is much lower than in the past. In order to compensate for the accompanying decrease in heat spalling resistance, resins containing pitch, that is, pitch-modified phenolic resins (Japanese Patent Application Laid-Open No. 1983-1989-1), are used as binders for bricks.
221361, Japanese Patent Publication No. 61-5428) was used.

We selected pitch-containing resins because these resins have lower elasticity than ordinary thermosetting phenolic resins.
This is because we focused on the fact that -C bricks are easy to obtain.

This reduces the graphite content and improves heat resistance and poling properties compared to conventional carbon-containing Wxl of 5 to 20% by weight.
It becomes possible to maintain the same level as g0-C bricks.

Addition of metals such as Aff and Aβ-Mg has the effect of densifying the brick structure, and the MgO-〇 brick used in the present invention is also generally used in conventional products with a carbon component content of about 15 to 20% by weight. has the same effect. However, Al1
If the amount of β-Mg added exceeds 5% by weight, the expandability of the bricks will increase, so it is practically desirable that the amount is 5% by weight or less.

As mentioned above, the wear mechanism of Mg0-C bricks caused by Cr-containing molten steel and its slag is thought to be largely related to the reduction reaction of Cr2O3 in the slag with carbon components in the bricks. As a result of the reduction in carbon content, the reaction is significantly alleviated, resulting in a reduction in the wear rate of the bricks.

It is a principle that the low carbon content also reduces the wear and tear of the Mg0-C bricks due to the reaction between CO2 gas and ~gO-C bricks in the secondary combustion operation that has become common in top-bottom blowing converters.

[Example 1 Example 1 Mg0-C bricks of Example 1 according to the present invention shown in Table 1 and conventional Mg0-C bricks in a top-bottom blowing converter for melting general steel
The results of investigating the relationship between wear and maximum temperature of g0-C bricks (Comparative Example 1) are shown in FIG. 1 for comparison.

Compared to the conventional Mg0-C brick of Comparative Example 1, the wear rate of the brick of Example 1 with a total carbon component content of 7% by weight had less temperature dependence, and was significantly lower than that of the Comparative Example when refining at 1650°C or higher. It showed good results.

Example 2 Bricks of Example 2 according to the present invention shown in Table 1 in a top-bottom blowing converter for melting stainless steel and Comparative Example 2.3
The wear rates of conventional Mg0-C bricks and MgO-Ca0-C bricks were compared, and the results shown in Figure 2 were obtained.

1 of Mg0-C brick (comparative example 2) with a total carbon content of 20% by weight for stainless steel ('8)
Although the wear rate is extremely large and unsuitable for practical use, the brick of Example 2 with a total carbon content of 7% is slightly better than the MgO-Ca0-C brick (Comparative Example 3) that has been used so far. Got the results.

In addition, according to the observation results of actual furnaces, both Examples 1 and 2 showed no thermal spalling during use, and showed good wear and tear conditions.

[Effects of the Invention] (1) The present invention has made it possible to melt and refine all types of steel, including Cr-containing steel and ultra-low carbon steel, in the same converter. Therefore, not only the degree of freedom in converter operation is greatly facilitated, but also
The types of refractories used can be reduced, and the storage and management of refractories has also been significantly improved.

■ In addition to making melting at high temperatures of 1,650°C or higher possible while suppressing wear and tear on refractories, it has also become possible to melt at high temperatures of 1,650°C or higher while suppressing wear and tear on refractories. Brick wear was also reduced.

■ The wear and tear of bricks during refining of Cr-containing steels is lower than that of conventional Mg
Significant improvement compared to 0-C brick.

Even compared to MgO-Ca0-C brick, wear resistance equivalent to or higher than that of MgO-Ca0-C brick was exhibited.

■ The carbon content in bricks can be significantly reduced from the conventional 15-20% by weight to 5-10% by weight, reducing M, gO-C.
The thermal conductivity of the bricks was reduced, reducing the occurrence of high-temperature creep deformation and cracking in the steel shell of the converter.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the maximum temperature reached during refining and the wear rate of bricks, and is expressed as an index with the wear of Comparative Example 1 (conventional brick) corresponding to 1650°C as 100. FIG. 2 is a graph showing the wear of the example and the comparative example of the top-bottom blowing converter for stainless steel, and is expressed as an index with the wear of comparative example 3 set as 100.

Claims (1)

[Scope of Claims] 1. Pitch-modified phenolic resin bonded unfired MgO-C bricks having a total carbon component content of 5% by weight or more and 10% by weight or less, with the remainder being MgO clinker, are used as part of the furnace wall and/or bottom of the furnace. A high-temperature converter characterized by being lined in some or all parts. 2. Pitch-modified phenolic resin bonded unfired MgO-C bricks with a total carbon content of 5% by weight or more and 10% by weight or less, the remainder being MgO clinker, are applied to part or all of the furnace wall and/or bottom of the furnace. Lined converter for producing and/or refining Cr-containing molten iron.