A faulty thermocouple in a carburizing heat-treatment furnace leads to unreliable temperature measurement during the process. Microstructure analysis from the carburized steel that initially contained 0.2% carbon revealed that the surface had 93% pearlite and 7% primary Fe3C, while at a depth of 0.5 cm, the micro constituents were 99% pearlite and 1% primary Fe3C. Estimate the temperature at which the heat treatment was carried out if the carburizing heat treatment was carried out for four hours. For interstitial carbon diffusion in FCC iron, the diffusion coefficient D0 = 2.3 × 10-5 m2/s and the activation energy Q = 1.38 × 105 J/mol. It may be helpful to refer to
Sections 5-6 and 5-8.