STP656: Niobium and Titanium Requirements for Stabilization of Ferritic Stainless Steels

    Dundas, HJ
    Research associate and research supervisor, climax Molybdenum Company of Michigan, Ann Arbor, Mich.

    Bond, AP
    Research associate and research supervisor, climax Molybdenum Company of Michigan, Ann Arbor, Mich.

    Pages: 25    Published: Jan 1978


    Abstract

    The amount of niobium or titanium necessary to prevent intergranular attack of the weld zone of autogenously welded 18Cr-2Mo and 26Cr-1Mo alloys containing 0.02 to 0.05 percent (C + N) was determined using the copper-copper sulfate (Cu-CuS04)-16 percent sulfuric acid (H2SO4) test. The study demonstrated that a niobium or titanium level equal to or greater than 0.20 percent 4 (C + N) would produce immunity of 18Cr-2Mo alloys to intergranular attack. The use of the 10 percent oxalic acid etch test and exposure in the 10 percent nitric acid (HN03)-3 percent hydrofluoric acid (HF) test, and in a Cu-CuSO4-50 percent H2SO4 solution, or an acidified 10 percent ferric chloride (FeCl3) solution confirmed both the effectiveness of the Cu-CuS04-16 percent H2SO4 test and the recommended stabilization formula for alloys containing C + N levels of 0.03 percent. In contrast, the ferric sulfate (Fe2(SO4)3)-50 percent H2SO4 test produced grain dropping of the weld zone on alloys that were stabilized according to the other tests. Exposure of selected alloys demonstrated that intergranular attack of unstabilized ferritic alloys can also occur in boiling seawater and boiling formic acid.

    Keywords:

    stainless steels, intergranular corrosion, corrosion, ferritic stainless, steels, stabilization, pitting, grain boundaries, tests, evaluation


    Paper ID: STP34847S

    Committee/Subcommittee: A01.30

    DOI: 10.1520/STP34847S


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