A silicon nitride sintered body and its manufacturing method

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The silicon nitride sintered material of the present invention contains a silicon nitride component in an amount of 100 mass% and silicon carbide having an average particle size of 1 mu m or less in an amount of at least 1 mass% and less than 4 mass%, the carbide being dispersed in the silicon nitride component, and has a thermal expansion coefficient of at least 3.7 ppm/ DEG C between room temperature and 1, 000 DEG C. The silicon nitride component contains a rare earth element in an amount of 15-25 mass% as reduced to a certain oxide thereof and Cr in an amount of 5-10 mass% as reduced to a certain oxide thereof, and a crystalline phase is present in intergrain regions of the sintered material. Therefore, aciculation of particles of silicon nitride, which is an insulating substance, is prevented, to thereby increase the specific surface area of the silicon nitride particles; formation of paths for conduction of electricity by a high thermal expansion coefficient compound is prevented; the thermal expansion coefficient of the resultant sintered material is increased; and deterioration of the insulating property of the sintered material is prevented. Thus, the silicon nitride sintered material is suitable for use as, for example, a base material for ceramic glow plugs.