SURFACE-COVERED THERMET MADE CUTTING TOOL HARD COVERED LAYER OF WHICH HAS EXCELLENT THERMAL SHOCK RESISTANCE

摘要

PROBLEM TO BE SOLVED: To provide a surface-covered thermet made cutting tool a hard covered layer of which has excellent thermal shock resistance. SOLUTION: The surface-covered thermet made cutting tool is constituted by forming the hard covered layer constituted of (a) a Ti compound layer constituted of lamination layers of one layer or more than two layers of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer and a TiCNO layer evaporated and formed as a lower side layer and having average layer thickness of 3-20μm as a lower side layer and (b) a composite double a type Al2O3 layer a lower part layer of which isαtype crystal structured by applying heating transforming treatment on an Al2O3 layer of aκtype crystal structure in an evaporated and formed state, having a structure where a transformed crack made by the heating transforming treatment is uniformly dispersed and distributed and constituted of a transformedαtype Al2O3 layer having average layer thickness of 3-15μm and an evaporatedαtype Al2O3 layer of anαtype crystal structure evaporated and formed having average layer thickness of 0.5-2μm on its upper layer.