Abstract
The method for measuring the internal stress of the ring-type test pieces such as ball bearing was not established firmly, and so the calculating formula for measuring two demensional stresses of it was obtained.
By using this formula, the effect of tempering temperature on the internal stress of the ring-type ball bearing steels was studied and the results were obtained as follows.
(1) In case of oil quenching of the ring-type test pieces, the radial internal stress was very small in comparison with the circlumferential interna1 stress. The latter was tensionstress near the inner face. In quenching, the circumferential stress was about +76.9kg per mm2 (tenson) at about 1.4mm, and then about-28.3kg per mm2 (eompression) at about 5.5 mm from the inner face.
(2) In case of the 130°C×1hr tempering, the internal stress increased about twice by the ε carbide precipitation. The circumferential stress was about +139.5kg per mm2 at about 1.4 mm from the inner face.
(3) When the 180°C tempering ring-type test piece was compared with the 130°C tempering one, the former increased a little in the circumferential stress distribution. If the tempering temperature raised such as the above, the internal stress should be reduced by the stress relief. But the internal stress increased a little in fact. This cause was considered to be the expansion phenomenon that the retained austenite decomposed to martensite at 180°C×1hr tempering. It was necessary for the 180°C tempering to be avoided in the pratical heat-treatment.
(4) In case of the 200°C×1hr tempering, the internal stress decreased in comparison with the 180°C and 150°C tempering.
The circumferential stress was about +25.1kg per mm2 (tension) at about 1.4mm from the inner face.
