The present research may be summarized as follows : (1) Heat treatments, in one case austempering and in other case quenching and tempering, had been done on 0.9 per cent carbon steel, so that a troostitic structure with the same hardness might result. (2) With these specimens, tensile tests and impact tests were carried out at room temperature. (3) Load-elongation diagrams of test-pieces subjected to quenching and tempering clearly show the phenomenon of yielding while those for austempered one were all smooth. (4) The interpretation for the phenomenon of yielding already proposed by one of the authors was ascertained. (5) Austempered specimens show superior mechanical properties as generally known. In conclusion the authors express their cordial thanks to Mr. S. Oba, the ex-Director of Yonezawa Technical College, for his enthusiastic encouragement and to Dr. K. Honda, the ex-President of the Tohoku University, for his kind guidance
