Abstract
The length changes in hot-bath quenching both above and below the Ms temperature and aging at room temperature as well as in tempering of a 0.8%C steel were measured. The experiment has revealed the following: The expansion in hot-bath quenching at the martensitic range, of 200°C-1 hr or 180°C-5 hr, in which a mixed structure of lower-bainite and tempered martensite containing a lot of retained austenite is formed, is much smaller than that in ordinary quenching or martempering, and then, during the subsequent aging at room temperature a comparatively large expansion occurs with time in these hot-bath quenched specimens as a part of the retained austenite decomposes into martensite. The retained austenite is more stabilized in consequence of the proceeding of the lower-bainite reaction, but does not decompose at room temperature, causing little change in length.
