浸炭窒化歯車鋼の面圧強度向上に関する研究 ショットピーニング処理とバレル研磨処理の影響

Abstract

When the shot peening process is employed in order to improve the bending fatigue strength of a gear tooth, there is a fear that the surface durability of the shot peened surface may reduce because of degradation of its surface roughness. In this study, the surface durability of the carbo-nitrided steel rollers besides the carburized ones was investigated using a highly loaded two rollers contact fatigue testing machine. It was confirmed that only the shot peening could scantly improve the surface durability because it is very hard to smooth the surface roughness by control of the shot peening conditions. Then, the barreling process was employed to improve the surface roughness, and it was clarified that the surface durability of shot peened rollers was remarkably improved by the barreling process. Also, it was shown using the D-value that the pitting limit increases and amount of wear decreases appreciably when the surface roughness becomes small. Pitting occurred on two kinds of case-hardened steels in the present experiments have always originated at the surface with/without shot peening process. The crack for pitting has rapidly propagated in the inside where a fatigue will be produced by a repeated shear stress, and a large pit (spalling) has immediately occurred all over the face width.