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Stainless steels 17-7 PH and PH 15-7 Mo could not be used in their highest strength conditions because they lacked toughness. Overaging was employed to obtain good fracture strengths but with a considerable sacrifice in useful tensile properties. Even in the overaged condition, these steels become embrittled after long-time exposure at temperatures of 600 to 700 F.
This paper described alloy development studies that have resulted in a new precipitation hardening steel, PH 14-8 Mo. This stainless steel has exceptionally high net fracture strengths in excess of 225,000 psi. Long time exposure studies at temperatures of 400 to 750 F show marked resistance to embrittlement.
This breakthrough in toughness and stability is attributed to close control of chemical composition, especially carbon, phosphorus, sulfur, and nitrogen. The merits of air and vacuum melting processes in obtaining the desired results are also discussed.
Perry, D. C.
Senior research engineer, Armco Research Center, Armco Steel Corp., Middletown, Ohio.
Marshall, M. W.
Supervising research metallurgist, Armco Research Center, Armeo Steel Corp., Middletown, Ohio.