抄録
It is well known that the martensite processed by ausforming increases in its power of resistance to degeneration due to tempering. In this report, the tempering behaviors of Mn-Cr-B spring steel ausforming at comparatively lower temperatures in the stable phase of austenite were investigated by hardness test, tension test and electron microscopy. Comparing these properties with those of the conventionally quenched specimens, the following results have been obtained.
(1) The tempered hardness of the ausforming steel is higher by one to three Rockwell C units than that of the conventionally treated steel throughout the range of tempering temperatures in consequence of the increase in its power of resistance to degeneration due to tempering. Moreover, the effect of ausforming persists throughout the long holding time in tempering.
(2) The yield strength, the ultimate tensile strength and the yield ratio of the ausforming steel are always higher than those of the conventionally quenched specimens, and the ausforming steel has a slightly higher ductility at higher strength level.
(3) The carbides in the ausforming steel are very fine and dispersed densely in comparison with the conventionally heat-treated specimens, and these carbides grow slowly during the tempering process.
