STP1042

    The Effect of Boron, Copper, and Molybdenum Residuals on the Corrosion Resistance of Type 304 Stainless Steel

    Published: Jan 1989


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    Abstract

    Systematic variations in the chromium, nickel, copper, molybdenum, and boron and B contents of American Iron and Steel Institute (AISI) Type 304 stainless steel (UNS S30400) were evaluated by electrochemical and immersion corrosion tests in oxidizing, reducing, and chloride solutions. In one series of tests, the chromium and nickel alloy contents were maintained within the flat rolled product tolerance range (17.8 to 18.0 wt% chromium, 7.8 to 8.0 wt% nickel) while the copper and molybdenum alloy contents were increased from a residual level (< 0.5 wt%) to a range from 0.6 to 0.7 wt%. Strip specimens with such compositions performed as well as others that had chromium and nickel contents within the specified analytical limits for tubular products (18.0–20.0 wt% chromium; 8.0–11.0 wt% nickel) and copper and molybdenum contents below 0.5 wt%. The results of an ASTM A01.17 committee interlaboratory program (twelve industrial labs testing per ASTM Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels (A 262-85a), Practice C, did not reveal any significant difference in the intergranular corrosion resistance of the said compositions. None of the compositional modifications resulted in increased susceptibility to sensitization as caused by welding or heat treating.

    The effect of residual boron on the carbide precipitation kinetics and intergranular corrosion resistance of mill and laboratory produced Type 304 stainless was also evaluated. The corrosion rates for fully annealed samples in boiling nitric, phosphoric, acetic, oxalic, and lactic acids were not related to alloy boron contents in the range 0.0003 to 0.0056 wt%. The rate of corrosion for sensitized (815°C for 24 h) samples in boiling 65 wt% nitric acid declined rapidly with increasing boron contents in the range from 0.0004 to 0.0011 wt%. The corrosion rates for sensitized samples containing 0.0011 to 0.0056 wt% boron were constant and, on average, 0.6 mm/y (0.002 ipm) higher than those for samples in a fully annealed condition.

    Keywords:

    stainless steel, residual elements, corrosion resistance, sensitization, carbides, AISI Type 304, copper, molybdenum, boron


    Author Information:

    Kearns, JR
    Senior corrosion engineer, research specialist, and manager, Allegheny Ludlum Corporation, Technical Center, Brackenridge, PA

    Johnson, MJ
    Senior corrosion engineer, research specialist, and manager, Allegheny Ludlum Corporation, Technical Center, Brackenridge, PA

    Aggen, G
    Senior corrosion engineer, research specialist, and manager, Allegheny Ludlum Corporation, Technical Center, Brackenridge, PA

    Edsall, WD
    Director of Quality Assurance and Services, Allegheny Ludlum Corporation, Brackenridge, PA


    Paper ID: STP24577S

    Committee/Subcommittee: A01.14

    DOI: 10.1520/STP24577S


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