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    Effect of Composition and Section Size on Mechanical Properties of Some Precipitation Hardening Stainless Steels

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    Applications have developed in which the high-strength properties associated with precipitation hardening stainless steel alloys are of considerable interest in large and medium section sizes. In a number of instances, transverse loading is involved. In common with other high strength materials, ductility in the transverse direction is lower than in the longitudinal direction. This paper presents transverse tension data obtained on a number of these alloys which serve to define this characteristic in a variety of shapes and sizes. The alloys discussed are 17-7 PH, PH 15-7 Mo, PH 13-8 Mo, 17-4 PH, and 15-5 PH. It is demonstrated that structural characteristics, particularly delta ferrite and certain precipitates, markedly influence transverse ductility and, in large section of 17-7 PH and PH 15-7 Mo, longitudinal ductility. Vacuum remelting does not help the directional ductility characteristics in compositions in which delta ferrite is a major controlling factor. Alloys in which composition changes have been incorporated to vary these structural factors have been developed. One of these is PH 13-8 Mo which is a composition employing aluminum as a hardening agent in which the analysis is adjusted to eliminate delta ferrite. This steel has excellent transverse ductility, especially in products made from double vacuum melted ingots. Another new material which has been called 15-5 PH contains copper as a hardening agent and is free of delta ferrite. In this modified composition the transverse ductility across the dead center of large sections is somewhat inferior to the transverse ductility obtainable at intermediate and surface locations in products made from air-melted ingots. Consumable electrode vacuum remelting eliminates the lower dead center transverse ductility in delta ferrite free products, such as 15-5 PH, by minimizing gross segregation, and excellent transverse ductility is obtained in any location.

    Some discussion is presented on the effects of varying heat treatments on transverse ductility of several of these steels.

    Author Information:

    Clarke, W. C.
    Senior research engineer, Research and Technology, Armco Steel Corp., Baltimore, Md

    Garvin, H. W.
    Research engineer, Research and Technology, Armco Steel Corp., Baltimore, Md.

    Committee/Subcommittee: A01.13

    DOI: 10.1520/STP43741S