1989 Volume 75 Issue 4 Pages 673-680
Environmental embrittlement of 17-4PH martensitic stainless steel castings for sea water use is studied. Failure analysis, stress corrosion cracking test, and crevice corrosion test yield the following results.
1) It is suggested that failure of the 17-4PH steel sliding contact components may be due to the hydrogen embrittlement cracking initiated at pits. Furthermore it seems that a rather high frequency of failure occurrence in an initial few year period may be caused by the initial presence of some factors responsible for the failure.
2) The cracking susceptibility persists at an applied stress lower than 15kgf/mm2 when the hardness of the steel exceeds HV = 310. On the other hand when the hardness is lower than 310, the steel remains uncracked even at an applied stress higher than 60 kgf/mm2. The cracking susceptibility is slightly affected by chemical composition and microstructure of the steel.
Based on these findings, following countermeasures are taken. The steel should be aged so as to be the hardness below 310 HV and the compressive stress is induced at the component surface by shrink fitting. Moreover the injection of fresh water into a shaft casing during the shut-off period is recommended.
No failure has been reported for over ten years since the countermeasures had been adapted.
