軸受鋼のころがり疲れにおける板状炭化物の生成に及ぼす接触応力と基地炭素量の影響

抄録

Platelike carbides form immediately under flakings during rolling fatigue tests in the ball/washer thrust type fatigue testing rig.
Carbon content in the matrix and shear stress in the thrust type test specimens were studied in this report which influence the formation of the platelike carbides closely related to bearing life.
It has been revealed for the formation of the platelike carbides that carbon content of approx. 0.25% and a hertzian stress of approx. 60 kgf/mm² are necessary and also a minimum required stress cycle varies depending on the product of these two factors (carbon content × shear stress). It has also been confirmed that the same critical conditions can apply to industrial bearings to produce the platelike carbides.
Another investigation made in relation to diffusion frequency of carbon and nitrogen at 120-deg. has shown that it is difficult for the platelike carbides to form when the diffusion frequency of these elements gets too large.
We have made an overall conclusion from the above mentioned results together with those obtained in the previous experiments that oxide inclusions as sources of stress concentration must be reduced down to as small an amount as possible and carbon content had better be lowered in the matrix to extend bearing life as long as a proper hardness is maintained.