Properties of 17-4PH Steel
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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Most catastrophic structural failures are preceded by a period during which cracks and other defects grow by combined fatigue and environmental processes from relatively small sizes to a critical size, at which rapid fracture occurs. For applications in an aggressive environment, the factor that determines long-term reliability is the inherent sensitivity of the structural material to environmental crack growth. 17-4PH stainless steel was investigated for its fracture and stress corrosion cracking properties under both open circuit andcathodically coupled conditions. Established fracture mechanics test and interpretation procedures were used to determine the suitability of this material for use in the marine environment. The material was found to be sensitive to environmental cracking processes to such a degree that the characteristic KIscc values for the conditions of cathodic coupling were extremely low for materials in the strength range of interest. Evidence of crack growth was found on the fractured surfaces of test specimens of 17-4PH steel. The conclusions of this investigation were that brittle fracture is not a problem for 17-4PH, but environmental crack growth is expected to cause maintenance problems for structures designed for long life.