A silicon nitride sintered body

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PROBLEM TO BE SOLVED : To provide a silicon nitride sintered compact capable of being produced at a low cost, stably having high strength and excellent in fatigue life characteristics, and to provide a method for producing the same. SOLUTION : This silicon nitride sintered compact is composed of a β-silicon nitride crystal phase 1, a grain-boundary crystal phase 2 consisting of rare earth element, silicon, aluminum, oxygen and nitrogen, and a grain-boundary amorphous phase. Rare earth element is contained in an amount of 2-10 wt.% in terms of oxides, aluminum is contained in an amount of 2-5 wt.% in terms of aluminum oxide, excess oxygen is contained in an amount of 0.5-5 wt.% in terms of silicon oxide, the ratio of the amount reduced to oxide of rare earth element to the amount reduced to aluminum oxide of aluminum is 0.2-0.7 and the ratio of the amount reduced to oxide of rare earth element to the amount reduced to silicon oxide of excess oxygen is 0.2-0.7. The average thickness of the grain-boundary amorphous phase 3 existing between silicon nitride particles themselves in the silicon nitride sintered compact is <=2 nm and the average thickness of the grain-boundary amorphous phase 4 existing between silicon nitride particles and the grain-boundary crystal phase is <=5 nm.