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    STP538

    Passivation Treatments for Resulfurized, Free Machining Stainless Steels

    Published: 01 January 1973


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    Abstract

    The practical aspects of nitric acid passivation are reviewed and new data on the effect of passivation variables on subsequent corrosion resistance are reported. Solution composition and temperature, passivation time, and double acid and alkaline treatments were investigated. Commercial heats of 12Cr (0.5 and 2 percent varieties) and 18Cr-9Ni resulfurized stainless were tested at 95°F (35°C) in either 95 percent humidity or 5 percent salt spray after receiving the various passivation treatments. The variables having the most significant effect were (1) the manganese content of the steel, (2) whether a cross or a long section of a bar was being investigated, and (3) an alkaline post passivation treatment. Without passivation, the low manganese 12Cr alloy has superior corrosion resistance to the high manganese grade. After passivation, the low manganese alloys lost some of their corrosion resistance, whereas the high manganese materials sometimes showed improved resistance. The loss of resistance after passivation is attributed to the retention of acid in partially removed sulfides and it can be minimized with the alkaline treatment. It is also noted that highly oxidizing passivation solutions are required to avoid attack during the passivation treatment itself and that these solutions do not dissolve tool steels, particles of which might be embedded in the stainless surface during machining.

    Keywords:

    stainless steels, cleaning, passivity, corrosion prevention, oxidation


    Author Information:

    Henthorne, Michael
    Manager, Corrosion and Welding, Research and Development, and senior corrosion engineer, Corrosion Research, Carpenter Technology Corp., R & D Center, Reading, Pa.

    Yinger, R. J.
    Manager, Corrosion and Welding, Research and Development, and senior corrosion engineer, Corrosion Research, Carpenter Technology Corp., R & D Center, Reading, Pa.


    Committee/Subcommittee: A01.13

    DOI: 10.1520/STP41377S