STP679: Effect of Small Additions of Niobium on the Welding Behavior of an Austenitic Stainless Steel

    Moorhead, AJ
    Metallurgist, Welding and Brazing Group, metallurgist, Mechanical Properties Group, and senior engineering technician, Welding and Brazing Group, Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Sikka, VK
    Metallurgist, Welding and Brazing Group, metallurgist, Mechanical Properties Group, and senior engineering technician, Welding and Brazing Group, Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Reed, RW
    Metallurgist, Welding and Brazing Group, metallurgist, Mechanical Properties Group, and senior engineering technician, Welding and Brazing Group, Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Pages: 21    Published: Jan 1979


    Abstract

    The mechanical property data for Type 304 stainless steel show large variations in tensile, creep, and creep-fatigue properties. Previous researchers have attributed these differences to variations either in carbon and nitrogen content or in grain size, but we have found some heats which are stronger than can be explained by these factors and attribute this apparent anomaly to the strengthening effect of niobum. To systematically study the effect of niobium on the behavior of Type 304 stainless steel, a low-niobium commercial heat was remelted with varying niobium additions—up to 1000 ppm. A standardized weldability test, the Spot Varestraint, was used to compare the propensity of various heats for hot-cracking. We found that the fusion and heat-affected zone cracking behavior of the experimental heats was similar to that of a heat of commercial Type 304, and much superior to that of a commercial heat of Type 347 stainless steel. The superior resistance to fusion zone cracking was attributed to the presence of a small amount of delta ferrite in the microstructure of the weld nugget in the experimental materials. The outstanding heat-affected zone cracking behavior was at least partly attributable to backfilling of grain boundary separations in the experimental heats, as well as in the commercial Type 304. We hypothesize that a relatively wide partially melted zone prevents backfilling of heat-affected zone cracks in the Type 347 steels.

    Keywords:

    stainless steel, weldability, hot-cracking, residual element, Spot Varestraint


    Paper ID: STP38355S

    Committee/Subcommittee: A01.13

    DOI: 10.1520/STP38355S


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