抄録
Smaller specimen rings were examined under the same testing condition as mentioned in the previousr eport No. 1 (Tetsu-to-Hagane Vol. 42, No. 7, p.556-561) and effects of cooling rate due to variation of specimen size have been studied primarily. Then specimens quenched from 830°C and 850°C have been scrutinized from various standpoints employing subzero treatment in order to clarify its effects, and at the same time crushing loads for these test rings were recorded.
The results were as follows:
1) Dimensional changes by aging for these specimens were smaller compared with larger rings previously tested. This decrease of dimensional changes is due to decomposing of retained austenite that takes place promptly in between quenching and tempering operations as a result of rapid cooling of smaller rings.
2) Effects of subzero treatment were as follows: At 830°C oil quenching, dimensional changes were contractive due to increase of martensite, moreover crushing values dropped and its standard deviation decreased. At 850°C oil quenching, crushing values dropped further and could not be increased very much by raising oil temperature. Very little effect was recognized even by applying marquenching and subzero treatment jointly.
