Title

INFLUENCE OF ANTIOXIDANT CONTENT ON THE THERMOMECHANICAL PROPERTIES OF MGO–C REFRACTORY BRICKS USED IN BOF LINING

INFLUENCE OF ANTIOXIDANT CONTENT ON THE THERMOMECHANICAL PROPERTIES OF MGO–C REFRACTORY BRICKS USED IN BOF LINING

Authorship

FONSECA, GUILHERME DIAS DA; COUTO, RICARDO ISRAEL DO

FONSECA, GUILHERME DIAS DA

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COUTO, RICARDO ISRAEL DO

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DOI

10.5151/2594-5300-42606

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Abstract

The service life of refractory linings in basic oxygen furnace (BOFs), is strongly influenced by operational, thermal, and chemical factors intrinsic to the steelmaking process. Among the most widely used materials, magnesia-carbon (MgO–C) bricks are notable for their high refractoriness, excellent thermal shock resistance, and stability in contact with basic slags. The presence of free carbon in the refractory matrix reduces wettability by slags and molten metals, thereby limiting chemical attack. However, it also increases the material’s susceptibility to oxidation at elevated temperatures, which compromises long-term durability. To counter this effect, the addition of antioxidants to the refractory formulation has been widely adopted, as it promotes the formation of protective phases that inhibit carbon oxidation. Still, the dosage of such additives must be carefully optimized, since they directly affect the material’s structural integrity, physicochemical stability, and thermomechanical performance. In this study, three commercial MgO–C brick formulations containing different antioxidant levels were investigated. The analysis was carried out through laboratory testing, in-service laser wear measurements over the campaign duration, and a literature review. The primary objective was to correlate refractory performance with material composition, with particular emphasis on the role of antioxidants in thermomechanical behavior and oxidation resistance. The results showed that increasing the antioxidant content enhances surface oxidation resistance, improves compressive strength after heat treatment at 1400 °C, and reduces the apparent porosity of the materials. In contrast, the formulation with the lowest antioxidant content exhibited inferior performance, with a high oxidation rate and significant loss of mechanical strength. The number of heats recorded at the end of the campaign corroborated the laboratory results, as the formulation with the lowest antioxidant content exhibited a campaign life approximately 53.85% shorter than the others, highlighting the importance of proper antioxidant control to maximize the performance of MgO–C refractories in highly aggressive thermal environments.

THE SERVICE LIFE OF REFRACTORY LININGS IN BASIC OXYGEN FURNACE (BOFS), IS STRONGLY INFLUENCED BY OPERATIONAL, THERMAL, AND CHEMICAL FACTORS INTRINSIC TO THE STEELMAKING PROCESS. AMONG THE MOST WIDELY USED MATERIALS, MAGNESIA-CARBON (MGO–C) BRICKS ARE NOTABLE FOR THEIR HIGH REFRACTORINESS, EXCELLENT THERMAL SHOCK RESISTANCE, AND STABILITY IN CONTACT WITH BASIC SLAGS. THE PRESENCE OF FREE CARBON IN THE REFRACTORY MATRIX REDUCES WETTABILITY BY SLAGS AND MOLTEN METALS, THEREBY LIMITING CHEMICAL ATTACK. HOWEVER, IT ALSO INCREASES THE MATERIAL’S SUSCEPTIBILITY TO OXIDATION AT ELEVATED TEMPERATURES, WHICH COMPROMISES LONG-TERM DURABILITY. TO COUNTER THIS EFFECT, THE ADDITION OF ANTIOXIDANTS TO THE REFRACTORY FORMULATION HAS BEEN WIDELY ADOPTED, AS IT PROMOTES THE FORMATION OF PROTECTIVE PHASES THAT INHIBIT CARBON OXIDATION. STILL, THE DOSAGE OF SUCH ADDITIVES MUST BE CAREFULLY OPTIMIZED, SINCE THEY DIRECTLY AFFECT THE MATERIAL’S STRUCTURAL INTEGRITY, PHYSICOCHEMICAL STABILITY, AND THERMOMECHANICAL PERFORMANCE. IN THIS STUDY, THREE COMMERCIAL MGO–C BRICK FORMULATIONS CONTAINING DIFFERENT ANTIOXIDANT LEVELS WERE INVESTIGATED. THE ANALYSIS WAS CARRIED OUT THROUGH LABORATORY TESTING, IN-SERVICE LASER WEAR MEASUREMENTS OVER THE CAMPAIGN DURATION, AND A LITERATURE REVIEW. THE PRIMARY OBJECTIVE WAS TO CORRELATE REFRACTORY PERFORMANCE WITH MATERIAL COMPOSITION, WITH PARTICULAR EMPHASIS ON THE ROLE OF ANTIOXIDANTS IN THERMOMECHANICAL BEHAVIOR AND OXIDATION RESISTANCE. THE RESULTS SHOWED THAT INCREASING THE ANTIOXIDANT CONTENT ENHANCES SURFACE OXIDATION RESISTANCE, IMPROVES COMPRESSIVE STRENGTH AFTER HEAT TREATMENT AT 1400 °C, AND REDUCES THE APPARENT POROSITY OF THE MATERIALS. IN CONTRAST, THE FORMULATION WITH THE LOWEST ANTIOXIDANT CONTENT EXHIBITED INFERIOR PERFORMANCE, WITH A HIGH OXIDATION RATE AND SIGNIFICANT LOSS OF MECHANICAL STRENGTH. THE NUMBER OF HEATS RECORDED AT THE END OF THE CAMPAIGN CORROBORATED THE LABORATORY RESULTS, AS THE FORMULATION WITH THE LOWEST ANTIOXIDANT CONTENT EXHIBITED A CAMPAIGN LIFE APPROXIMATELY 53.85% SHORTER THAN THE OTHERS, HIGHLIGHTING THE IMPORTANCE OF PROPER ANTIOXIDANT CONTROL TO MAXIMIZE THE PERFORMANCE OF MGO–C REFRACTORIES IN HIGHLY AGGRESSIVE THERMAL ENVIRONMENTS.

Keywords

MgO–C Refractories, Antioxidant, Oxidation Resistance, BOF Lining

MgO–C Refractories, Antioxidant, Oxidation Resistance, BOF Lining