Repeat Prob. 14–90 for a furnace temperature of 500 K at which the diffusion coefficient of carbon in steel is D_AB= 2.1 × 10^-20 m²/s.

Data from problem 90

A steel part whose initial carbon content is 0.12 percent by mass is to be case-hardened in a furnace at 1150 K by exposing it to a carburizing gas. The diffusion coefficient of carbon in steel is strongly temperature dependent, and at the furnace temperature it is given to be D_AB = 7.2 × 10^-12 m²/s. Also, the mass fraction of carbon at the exposed surface of the steel part is maintained at 0.011 by the carbon-rich environment in the furnace. If the hardening process is to continue until the mass fraction of carbon at a depth of 0.7 mm is raised to 0.32 percent, determine how long the part should be held in the furnace.

Transcribed Image Text:

Carbon. : 1150 K ** Steel part