Oxidation of Iron-Chromium Alloys at 750-1025C

The rates of oxidation of iron alloys containing 0.2 to 10 percent chromium were measured at 750 to 1025 C. The nature of the corrosion products was investigated by metallography, x-ray diffraction and chemical analysis. At very low chromium concentrations there was a small increase in the oxidation rate compared with pure iron for short times, but for longer times the rate diminished. The oxidation rate at a given temperature diminished with increasing chromium concentration. The rates were not given by any simple rate law, presumably because the products contained many pores and cracks. The accelerations in rate during an isothermal measurement did not occur at reproducible times or average thicknesses, which suggested that scale fracture played an important role. A mechanism for scale embrittlement by chromium was proposed. The ways in which chromium might contribute to a reduced rate of oxidation of iron were discussed. 6.2.2, 3.5.9, 3.7.2