Refractory for secondary steelmaking

There are many operation and process in secondary steelmaking like vacuum degassing, ladle refining etc. Refractories are used in unique combinations of various bricks to meet diversified requirements. Following condition may be noted:

i) High temperature and long holding times of steel in ladle.

ii) Wide variation in slag composition

iii) Many types of vacuum treatment.

iv) Large thermal changes.

v) Molten steel agitation causes attack by motion of liquid steel.

In all ladle refining processes such as ladle furnace, ASE-SKF, VAD process, bricks are used at areas, where slag is in contact with steel. For general wall, high alumina bricks are widely used. For bottom zircon bricks are used to prevent molten steel penetration into brick joint. In certain cases  bricks and castables are used in impact areas.  bricks with addition of a couple of metals provides high hot strength, and are excellent in oxidation resistance.

Refractory for continuous casting

Tundish is a refractory lined vessel in continuous casting. It contains molten steel with minimum heat losses. Selection of refractory is critical due to longer casting sequence, faster tundish turnaround, higher campaign life and cleanliness of steel. Fireclay bricks are used. High alumina bricks are considered to be good for tundish hot rotation. Basic coating material is used over the lining. The coating installation method is gunning. Typically  mixture is used as a coating material.

Tundishes are equipped with dams and weirs. There are made of  boards or alumina bricks.

Molten steel from tundish to mold is fed by nozzle submerged into molten steel in mold. Submerged nozzles must be resistant to corrosion and spalling, nozzle clogging is also important. Isostatic pressed submerged nozzle with alumina- graphite-fused silica are being used.

In recirculation degassing steel is made to flow from the ladle into a separate degassing chamber. In RH process, a refractory lined vessel equipped with two legs (snorkels) is used. These snorkels are immersed into molten steel. The refractory materials must have adequate spalling and abrasion resistance, volume stability and corrosion resistance at high temperature and in vacuum. Direct bonded magnesia- chrome bricks, semi rebonded magnesia chrome bricks are used in the lower vessel and snorkels. Extra high temperature burned magnesia –chrome bricks posses excellent corrosion and abrasion resistance and are preferred lining material.