STP948: Fractographic Studies of the Ductile-to-Brittle Transition in Austenitic Stainless Steels

    Place, TA
    Professor, University of Idaho, Moscow, Idaho

    Sudarshan, TS
    Former graduate student, Virginia Polytechnic Institute, Blacksburg, VA

    Waters, CK
    Former graduate student, Virginia Polytechnic Institute, Blacksburg, VA

    Louthan, MR
    Professor, Virginia Polytechnic Institute, Blacksburg, VA

    Pages: 16    Published: Jan 1987


    Abstract

    Austenitic stainless steels are not generally thought to undergo ductile-to-brittle transitions as the temperature is lowered to 77 K or to be susceptible to hydrogen embrittlement. However, some austenitic steels do undergo a classic ductile-to-brittle transition, and are susceptible to hydrogen embrittlement even at the high strain rates used in an impact test. In this study the fracture behavior of Tenelon, 21-6-9, and 304L was investigated by testing hydrogen charged and uncharged Charpy specimens at temperatures ranging from 77 to 298 K. The fracture mode was determined with the aid of optical and scanning electron microscopy and X-ray analysis. Fracture initiation in the 21-6-9 and 304L was generally by ordinary dimple zone formation, though the Tenelon developed a brittle initiation mode at low temperatures. All of the steels showed a change from single to multiple crack initiation as the temperature was reduced. Propagation was by microvoid coalescence at higher temperatures, with a strong orientation effect in evidence where inclusions provided weak interfaces. A ductile-to-brittle transition was observed in both the Tenelon and the 21-6-9 steels. In the case of Tenelon, this transition resulted from {111} plane separation, and the reduction in toughness in 304L and 21-6-9 was associated with strain localization and formation of large microvoids. The presence of hydrogen did not introduce any new fracture modes but did enhance the embrittlement mechanisms which were promoted by low temperatures.

    Keywords:

    stainless steel, mechanical properties, fracture (metals), impact testing, fractography


    Paper ID: STP25628S

    Committee/Subcommittee: D30.02

    DOI: 10.1520/STP25628S


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