Abstract
Influences of various factors of heat-treatments on hardness and compressive breaking strength of SUJ-2 bearing steels for races were investigated physico-metallurgically.
These mechanical properties, which were referred to Japanese Industrial Standard, showed the contrary changes each other: The higher the austenitizing temperature, the longer the austenitizing period as well as the lower the tempering temperature, the more hardness would be raised while compressive breaking strength would be the less. Therefore, the conditions under which both of these designated values were satisfied were proved to be limited to a very narrow range. It was concluded that the tetragonality i. e. the soluble carbon content of the quenched martensite chiefly determined both these mechanical properties.
Besides, it was found that hardness and compressive breaking strength of the quenchedand-tempered steels were both raised as their spheroidized cementite particles prior to quenching had been diminished in size, and the causes were speculated.
Furthermore, effects of subzero treatment as well as martempering on the properties of the steels were investigated. These results showed evidently that the compressive breaking strength depended mainly upon the conditions of their martensite, while their retained austenite would scarecely display a cushiony action in the compressive breaking test.
