THE EFFECT OF DECARBURIZATION ON THE MICROSTRUCTURE OF QUENCHED HIGH SPEED STEELS

Abstract

In microstructure of the high speed steel quenched from a high temperature such as 1, 300°C, the troostitic structure is often observable in its decarburized portion. In order to elucidate theformation of the structure, a sectional diagram of constant 18% W and 4% Cr with varying carbon content was constructed by means of thermal analysis, differential dilatometric measurement and microscopic investigation. From the diagram obtained the change of microstructure of the high speed steels with different carbon content cooled from the melt was made clear. The troostitic structure also appears in the low carbon high speed steel cooled from the melt owing to the occurrence of a eutectoid reaction, γ→α+η, in a range of temperature below 1340° (aperitecto-eutectic point). The formation of the similar troostitic structure observable in decarburized portion of quenched high speed steel is, therefore, attributed to the same reaction taking place during rapid cooling.