Masao Kondô and Takeji Hachisuka
Using high-carbon low-chromium bearing steel, the effects of quenching temperature, martempering and tempering on repeated sabzero-treatments at various treating temperatures were studied. The behavior of retained austenite which transformed to martensite during subzero-cooling was predicated on measuring the change in hardness and dilatation curve. The results obtained are as follows: (1) Changes in hardness and length occured mainly during the first or second subzero-cooling under any treating condition. (2) The higher the quenching temperature and the lower the subzero-temperature, the wider changes in hardness and length resulted with the exception of -183° subzero-cooling. (3) Martempered specimens were subject to more changes in hardness and length than quenched specimens. (4) The specimens tempered at 100° and 150° for 1 hour showed athermal and isothermal expansion during subzero-cooling respectively, but those tempered for 30 minutes at the same temperatures did neither.
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