Abstract: The vitrified bonded grinding stone includes a vitrified bond in which super abrasives such as cubic crystal boron nitride grains or diamond grains and an aggregate are contained. The aggregate is formed by porous ceramics and a substance which closes pores of the porous ceramics and the substance is weaker in strength than the porous ceramics and has a physical property that the substance does not dissolve under a burning temperature of the vitrified bond.

Abstract: In a grinding wheel comprising a disc-like core member and a ring-shape grinding wheel layer wherein superabrasive grains selected from cubic boron nitride particles and diamond particles are contained together with aggregates in a bonding material, the aggregates are made of porous ceramics particles and have an average particle size which is in a range of 70% to 150% relative to the average particle size of the superabrasive grains, and bridges made of the bonding material are formed between the aggregates adjoining to one another or between the aggregates and the superabrasive grains adjoining to the aggregates.

Abstract: In a vitrified bonded grinding wheel having superabrasive grains 11 such as CBN, diamond or the like bonded with a vitrified bond 12, pores 16 of the vitrified bonded grinding wheel has impregnated thereinto a resin 17 consisting of any resin selected from, e.g., unsaturated polyester, vinyl ester and allyl ester which are in a liquid state at the normal temperature and which have a thermosetting property, and being capable of radical polymerization. Thus, any separation gas or the like is not generated when the impregnated resin is hardened, whereby the strength of the grinding wheel can be enhanced.