Current Situation & Development Trend of Light-Burned Magnesia Balls

The current campaign life of converters is nearly 20,000 heats, and the operating rate reaches 97%. This process using light-burned magnesia balls has been adopted in West Germany, South Korea, Japan, Taiwan and other regions. By applying light-burned magnesia balls, the original campaign lives of 500, 700 and 1,100 heats have been raised to 12,000, 1,500, 8,500 and 10,200 heats respectively, delivering remarkable economic benefits.

As a dynamic emerging sector in the modern chemical industry, magnesia-related products constitute an important category of new materials. Globally, the development of magnesia is marked by intensified technological innovation and optimized product mix, with focus placed on high-performance, specialized and eco-friendly products. This has also become the core development direction for the global magnesia industry in the future.

Featuring a wide product range, high added value, extensive applications and strong industrial relevance, magnesia products serve numerous sectors of the national economy and various high-tech industries. Vigorously developing the magnesia industry has become a strategic priority for countries worldwide to restructure the chemical industry, upgrade technical capabilities and boost economic returns. The ratio of magnesia output value to the total chemical industry output value has become a key indicator for evaluating the development level and technical competence of the chemical sector in a country or region.

Light-burned magnesia balls are mainly used for slag formation in converter steelmaking. When added into converter slag, they react rapidly to adjust slag composition effectively. The main mineral phases in the slag are converted into high-melting-point MgO, C₃S and C₂S, which increases the viscosity and melting point of the slag and greatly improves the effect of slag splashing for furnace protection. Therefore, light-burned magnesia balls act as an effective regulator for slag splashing protection in converters.

With the rapid development of the metallurgical industry, open-hearth steelmaking has been phased out, while large-capacity converters have seen tremendous development. In the slag splashing protection process, nitrogen is blown through the oxygen lance after tapping, which evenly coats the converter lining with residual slag containing a certain content of MgO, so as to protect the furnace lining.

Strength and hardness can be enhanced via heat treatment. The effects of different heat treatment processes are listed below for selection according to actual working conditions. Surface quenching is recommended if only higher hardness is required.

Normalizing of ductile iron aims to obtain a pearlite matrix with refined and uniform grains, so as to improve the mechanical properties of castings. It can also serve as a pre-treatment for subsequent surface quenching. Normalizing is divided into high-temperature normalizing and low-temperature normalizing. The temperature for high-temperature normalizing is generally below 950–980℃, while low-temperature normalizing is carried out at 820–860℃. Stress relief treatment is usually conducted after normalizing to eliminate internal stress generated during the process.

To further improve the mechanical properties of ductile iron, castings are generally heated to 30–50℃ above the Ac₁ temperature (Ac₁ refers to the final temperature of austenitization during heating), held at the temperature and then oil-quenched to form martensite. Tempering is normally performed after quenching to reduce residual stress. Low-temperature tempering produces a microstructure consisting of tempered martensite, residual bainite and spheroidal graphite. This structure features excellent wear resistance and is applied to parts requiring high wear resistance and mechanical strength.