高強度鋼の海水環境各種条件下における疲労強度

抄録

The fatigue life was investigated in synthetic sea water at a constant flow rate (condition 1) and in the environment of repetition of the sea water and air for every 1 min (condition 2) using a 80kgf/mm² grade high strength steel at the frequency of 0.5Hz and 20Hz and at the stress ratio of 0.10. The following results are mainly obtained.
At the frequency of 0.5Hz and at the stress amplitude of about 35 kgf/mm² the fatigue life in condition 2 was only a half of that in condition 1. In condition 2, many cracks initiated at the root of the pits with spike-like shape which were about 50-60μm deep, and some of these cracks propagated and linked each other to failure. But in condition 1, many pits with cup-like shape which were less than 10μm deep hardly influenced the crack initiation.
The difference in fatigue life between condition 1 and condition 2 decreased with decrease of stress amplitude. At the stress amplitude of about 10 kgf/mm², pits with cup-like shape existed in conditions 1 and 2 which were about 10μm and 50-60μm deep respectively. They hardly influenced the crack initiation.
The same trend was observed at the frequency of 20Hz as at that of 0.5Hz.