Electrically fused from alumina, white colour, its hardness is a little higher， but toughness slighily lower than tliat of A. It is used for fabrication of bonded and coated abrasive products for the grinding of the steels with grelat hardness， such as high carbon steel,alloy steel， and high speed steel． Its non-abrasive uses are precision casting moulding sand, spray coating materia1,catd'lyst cai11er, high temperature ceramic，and super refractorv materiaL, etc.