Abstract

Fired dolomite is the preferred refractory for stainless converters worldwide. It is typically produced from sintered doloma and is often blended with magnesia to enhance its prosperities.

Lining wear is usually caused by three mechanisms: (a) chemical attack i.e. the infiltration of slag which are unsaturated in CaO, (b) mechanical erosion , abrasion and (c) thermal attack i.e.  softening at elevated operating temperatures, spalling via thermal cycling. The tuyere zone represents the highest wear rates due to a combination of high localized temperatures, severe thermal cycling, The slagline / trunnion above the tuyeres is a high wear area due to abrasion from solid decarburisation slags, alloy impact & high velocity flow currents. Ultimately therefore the wear rate of these two areas determines the refractory lifetime of the converter and consequently demands the use of refractories with enhanced properties.

The addition of sintered magnesia to doloma refractory is typically used to increase the volume stability and the corrosion resistance. Replacing sintered components with fused increase the crystal size which improves the corrosion resistance.

Adding fused doloma rather than magnesia reinforces the brick matrix, which is critical in terms of corrosion resistance.This is reflected in the final product whose physical properties are similar to those of traditional magnesia doloma bricks – however the wear resistance is significantly improved.

A tuyere grade based on fused doloma and sintered magnesia was developed. The high concentration of fused component increases the corrosion resistance and reduces the shrinkage at high temperatures and therefore joint opening. Furthermore it lowers the glassy phase content of the brick which increases the thermal shock resistance.

The slagline / trunnion covers a much larger area than the tuyere zone and suffers from less localized high temperatures and thermal cycling. The fused doloma containing brick developed for this application was therefore optimised in terms of performance versus cost. It is a blend of fused and sintered doloma and sintered magnesia.

To date the fused doloma containing tuyere grade has been tested in over 35 linings at 10 different customers with AODs ranging from 12 - 180Mt, realizing a reduction in wear of upto14%. The fused doloma containing slagline grade has been trialled in over 15 linings in units ranging from 50 - 180Mt at 6 customers. The wear rates were typically reduced by 4 - 30% compared to conventional magnesia doloma.

Based on the field trial results it can be concluded that the fused doloma containing tuyere and slagline grades allow increasing the performance in the critical areas of stainless converters and reduce the overall specific refractory cost.