Sadao Koshiba, Kazuo Tanaka and Asao Inada
For isothermal transformation of high speed steel, we investigated the effect of hot bath temperature and holding time on the Ar'' transformation by tempering after quenching, and then the change of intensity of magnetization and dilatometric curve in the hot bath. Results of this experiment are as follows: (1) When the holding was done in hot bath of 250∼300°, the Ar'' transformation was difficult to occur on cooling because lower bainite came to be present, and then this stabilized austenite more. Therefore, more austenite was retained at room temperature and secondary Ar'' transformation on tempering was increased more than by oil quenching. (2) When the sample it was held for a long time in hot bath of 600°, two steps of dilatation were presented on cooling and the retained austenite was decreased at room temperature, and secondary Ar'' transformation on tempering was lowered.
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