Abstract: A silicon nitride sintered body having improved wear resistance and a wear-resistant member using the silicon nitride sintered body are provided. A silicon nitride sintered body according to an embodiment includes silicon nitride crystal grains and a grain boundary phase. An average value of solid solution oxygen amounts of the silicon nitride crystal grains in a 20 ?m×20 ?m region at any cross section is not less than 0.2 wt %. In a 50 ?m×50 ?m region at any cross section, an average value of major diameters of the silicon nitride crystal grains is not less than 0.1 ?m and not more than 10 ?m, and an average value of aspect ratios of the silicon nitride crystal grains is not less than 1.5 and not more than 10.

Abstract: In a silicon nitride substrate including a silicon nitride sintered body including silicon nitride crystal grains and a grain boundary phase, a plate thickness of the silicon nitride substrate is 0.4 mm or les, and a percentage of a number of the silicon nitride crystal grains including dislocation defect portions inside the silicon nitride crystal grains in a 50 ?m×50 ?m observation region of any cross section or surface of the silicon nitride sintered body is not less than 0% and not more than 20%. Etching resistance can be increased when forming the circuit board.

Abstract: In a silicon nitride substrate including a silicon nitride sintered body including silicon nitride crystal grains and a grain boundary phase, a plate thickness of the silicon nitride substrate is 0.4 mm or les, and a percentage of a number of the silicon nitride crystal grains including dislocation defect portions inside the silicon nitride crystal grains in a 50 ?m×50 ?m observation region of any cross section or surface of the silicon nitride sintered body is not less than 0% and not more than 20%. Etching resistance can be increased when forming the circuit board.

Abstract: In a silicon nitride sintered body including silicon nitride crystal grains and a grain boundary phase, dislocation defect portions exists inside at least some of the silicon nitride crystal grains. A percentage of a number of the at least some of the silicon nitride crystal grains among any 50 of the silicon nitride crystal grains having completely visible contours in any cross section or surface of the silicon nitride sintered body is not less than 50% and not more than 100%. It is favorable that a plate thickness of the silicon nitride substrate, in which the silicon nitride sintered body is used, is within the range not less than 0.1 mm and not more than 0.4 mm. The TCT characteristics can be improved by using the silicon nitride substrate in the silicon nitride circuit board.