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EP-4737426-A1 - METHOD FOR MANUFACTURING UNBURNED MAGNESIA-CHROME BRICK

EP4737426A1EP 4737426 A1EP4737426 A1EP 4737426A1EP-4737426-A1

Abstract

The present invention addresses a technical problem of suppressing structural spalling in an unfired magnesia-chrome brick. In order to solve this technical problem, the present invention comprises: kneading a refractory raw material mixture containing a magnesia-chrome based raw material in an amount of 73% by mass to 98% by mass in total, an alumina-based raw material in an amount of 1% by mass to 25% by mass in total, and a binder; press-molding the kneaded mixture; and then subjecting the resulting molded body to heat treatment at a temperature of 60°C to 1000°C.

Inventors

  • KAWANO, Hayate

Assignees

  • Krosakiharima Corporation

Dates

Publication Date
20260506
Application Date
20240814

Claims (4)

  1. A method for manufacturing an unfired magnesia-chrome brick, comprising: kneading a refractory raw material mixture containing a magnesia-chrome based raw material in an amount of 73% by mass to 98% by mass in total, an alumina-based raw material in an amount of 1% by mass to 25% by mass in total, and a binder; press-molding the kneaded mixture; and then subjecting the resulting molded body to heat treatment at a temperature of 60°C to 1000°C.
  2. The method as claimed in claim 1, wherein the alumina-based raw material has a particle size of less than 0.1 mm.
  3. The method as claimed in claim 1 or 2, wherein the binder is silica having a particle size of less than 75 µm.
  4. The method as claimed in claim 3, wherein the refractory raw material mixture contains, as the magnesia-chrome based raw material, at least one of magnesia having a particle size of less than 75 µm and magnesia-chrome having a particle size of less than 75 µm, in an amount of 0.2% by mass to 30% by mass in total, and contains, as the binder, silica having a particle size of less than 75 µm in an amount of 0.3% by mass to 2.5% by mass.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an unburned or unfired magnesia-chrome brick used in a steelmaking process, particularly in secondary refining. BACKGROUND ART In a secondary refining process, basic bricks including magnesia-chrome bricks are generally used. When magnesia-chrome bricks are fired at a temperature of 1700°C or more, a chrome-containing spinel develops and forms strong bonds, thereby provides high corrosion resistance. On the other hand, manufacturing of magnesia-chrome bricks requires ultra-high temperature firing at 1700 °C or more, which entails disadvantages such as CO2 emission and cost increase. Therefore, there has been studied a method for manufacturing an unfired magnesia-chrome brick that does not require firing at high temperatures. For example, Patent Document 1 discloses a method for manufacturing an unfired refractory material, characterized in that condensed lithium phosphate, in which the ratio by weight of Li2O/P2O5 is in the range of 2.5/7.5 to 1.5/8.5, is used as a binder in an amount of 0.5 to 5 parts by weight with respect to 100 parts by weight of aggregates whose MgO component is adjusted to a range exceeding 50% by mass. Further, Patent Document 2 discloses a method for manufacturing an unfired magnesia-chrome brick, the method comprising: adding 0.5 to 3.5 parts by weight of sodium aluminate to 100 parts by weight of a refractory composition comprising a magnesia-based raw material and a chromia-based raw material; kneading the resulting mixture; and then subjecting the resulting kneaded mixture to pressure-forming, and drying at a temperature of 100 to 500°C. PRIOR ART DOCUMENTS [Patent Document] Patent Document 1: JP S63-24944 B2Patent Document 2: JP H11-157917 APatent Document 3: JP H4-6150 A SUMMARY OF INVENTION [Technical Problem] As a result of tests on unfired magnesia-chrome bricks, the present inventor has found that the unfired magnesia-chrome bricks have a problem of being significantly more prone to structural spalling as compared with fired magnesia-chrome bricks. That is, since magnesia-chrome bricks are inherently more prone to slag penetration than graphite-containing bricks such as magnesia-carbon bricks, structural spalling becomes a factor causing wear damage of the magnesia-chrome bricks during use. In this situation, it has been found that, particularly in unfired magnesia-chrome bricks, a significant increase in the severity of structural spalling becomes the biggest factor causing wear damage thereof during use. The term "structural spalling" herein means a phenomenon that an altered portion, which is formed due to slag penetration to have a microstructure significantly different from an original portion, peels off due to cracks developed at the boundary between the original and altered portions by rapid temperature rise and fall during use of a molten metal container. On the other hand, in Examples of Patent Document 3, there is disclosed a magnesia-chrome based refractory material obtained by: adding an alumina-based raw material having a particle size of 0.35 to 1.0 mm in an amount of 1 to 5 % by weight with respect to and in addition to a total amount of the magnesia-chrome based refractory material to an aggregate that is a blend of sintered magnesia clinker (particle size: 5 mm or less), natural chrome ore (particle size: 5 mm or less), and chrome oxide (fine powder); then molding the resulting mixture under a pressure of 760 kgf/cm2; and further firing the resulting molded body at 1800°C or more. That is, in Patent Document 3, as described in the section [Functions] in the upper right column on page 2, during firing, the alumina-based raw material reacts with magnesia in the aggregate, and undergoes spinelization (spinel formation), whereby volume expansion occurs, which in turn causes microcracks to be formed in the microstructure of the refractory material. In this way, microcracks introduced in the refractory serve to prevent or suppress the development of cracks that occur in the refractory material during use, thereby improving spalling resistance. However, Patent Document 3 is merely a technique for improving spalling resistance in fired magnesia-chrome bricks, and is not a technique for suppressing structural spalling, which is a problem particularly faced by unfired magnesia-chrome bricks. The technical problem to be solved by the present invention is to suppress structural spalling in unfired magnesia-chrome bricks. [Solution to Technical Problem] The summary of the present invention is as follows. 1. A method for manufacturing an unfired magnesia-chrome brick, comprising: kneading a refractory raw material mixture containing a magnesia-chrome based raw material in an amount of 73% by mass to 98% by mass in total, an alumina-based raw material in an amount of 1% by mass to 25% by mass in total, and a binder; press-molding the kneaded mixture; and then subjecting the resulting molded body