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Recent unexpected occurrences of stress-corrosion cracking (SCC) with 17-4 PH structural components indicated a need for improved characterization of the alloy and application of more advanced analytical procedures for reliably predicting structural performance. Accordingly, the purpose of the present studies was to establish systematically the SCC properties of 17-4 PH steel over a wide range of yield strengths and applied cathodic potentials. Six different heat treatments were selected for the SCC studies. The data, when analyzed in terms of ratio analysis procedures, are immediately useful for predictions of service reliability of the steel in marine structures.
The results show that 17-4 PH steel is moderately sensitive to SCC at high-strength levels, less sensitive to SCC at intermediate strength levels, and relatively insensitive to SCC in the metallurgically overaged, low yield strength condition. Increased applied cathodic potentials increase the SCC susceptibility of the alloy significantly which strongly suggests the involvement of hydrogen in the SCC mechanism. The minimum specimen thickness required for determining a thickness-independent KIscc for steels by the cantilever method appears to be considerably less than for a standard KIc test.
stress corrosion, galvanic corrosion, hydrogen, precipitation hardening steels, heat treatment, mechanical properties
Head, Strength of Metals Branch, Engineering Materials Division, Naval Research Laboratory, Washington, D. C.