高硬度鋼の疲労強度に及ぼす研削加工の影響 : 第2報, 疲労き裂生成との関連

抄録

Tool steel (SK5) was ground with WA or CBN abrasive grains to determine the effect of grinding on the initiation of fatigue cracks. The grinding direction was parallel or perpendicular to the loading axis. The main results are as follows. (1) About 66% of fatigue cracks originated at grinding streaks or inclusions. In all cases, fatigue cracks originating at inclusions were observed. The major origin, however, of the specimens ground perpendicular to the loading axis, with WA abrasive grains was grinding streaks. (2) In every case, a large percent of fatigue life was spent to form fatigue cracks. (3) When ground with WA abrasive grains, spark-out does not raise the fatigue limit of the specimens ground parallel to the loading axis but raises that of specimens ground perpendicular to it. When ground with CBN abrasive grains, the fatigue limit does not depend upon the grinding direction. Spark-out raises the fatigue limit to a higher value than in the case of WA abrasive grains. Although there were some exceptions, the minimum hardness of the ground surfaces was proportional to the fatigue limit.