Abstract
Selected commercial and experimental nickel/chromium and 37% nickel/chromium/iron alloys have been exposed, in industrial heat-treatment furnaces, to controlledatmospheres of various types, and the nature and degree of the corrosion attack has been assessed by measurement of weight-change and by metallographic examination.
Specimens of the same materials, and of a more extended range of alloys, were exposed, in laboratory tests, to an atmosphere of carbon monoxide, and additional tests were made in atmospheres of the water gas type contaminated by lead.
Except in lead-contaminated atmospheres, high-chromium content conferred protection against severe attack by carburisation and oxidation. In alloys of insufficient chromiumcontent, beneficial effects were produced by additions of niobium and silicon, and sometimes by tungsten and titanium. In 37% nickelf chromium/iron alloys, vanadium proved detrimental.
In a lead-contaminated atmosphere chromium was detrimental, but, as in the other atmospheres, niobium was found to be the most effective addition.
Separation of the oxide-containing and carbon-containing zones on specimens attacked by ‘green rot’ corrosion indicates that the mechanism of attack is not necessarily by direct oxidation of carbide particles, but by internal precipitation of oxides from a solid–solution band behind the carbide.
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