Pressure-fired polycrystalline mixed material based on hexagonal boron nitride, oxides and carbides

摘要

Pressure-sintered polycrystalline mixed materials, with a base of boron nitride, oxides and carbides, are provided in which the hexagonal boron nitride fraction is about 30 to about 85% by weight, the oxide fraction (ZrO2, MgO) is about 10 to about 50% by weight, and the carbide fraction (SiC, TiC, ZrC) is about 5 to about 20% by weight. These mixed materials have a density of at least 94% of the theoretical density and can be produced by hot-pressing powder mixtures composed of hexagonal boron nitride, the selected oxides and carbides at temperatures in the range of from 1500 DEG C. to 1800 DEG C. under a die pressure of 7 to 20 MPa or by isostatically hot-pressing, in a vacuum tight closed case, at temperatures in the range from about 1400 DEG C. to about 1700 DEG C. under a pressure of about 100 to about 300 MPa in a high-pressure autoclave using an inert gas as the pressure transfer medium. These mixed materials are resistant to liquid metals, wear resistant and thermal shock resistant and, owing to these properties, are suitable for use as detachment or break rings in the horizontal continuous casting of steel and non-ferrous metals.