An FCC iron–carbon alloy initially containing 0.35 wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1450 K (1177 degree C). Under these circumstances the carbon diffuses from the alloy and reacts at the surface with the oxygen in the atmosphere; that is, the carbon concentration at the surface position is maintained essentially at 0 wt% C. (This process of carbon depletion is termed decarburization.) At what position will the carbon concentration be 0.15 wt% after a 15-h treatment? The value of D at 1400 K is 6.9 x 10^(-11) m^2/s.

An FCC iron–carbon alloy initially containing 0.35
wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1450
K (1177 degree C). Under
these circumstances the carbon diffuses from the alloy and reacts at the
surface with the oxygen in the atmosphere; that is, the carbon concentration at
the surface position is maintained essentially at 0 wt% C. (This process of
carbon depletion is termed decarburization.) At what position will the
carbon concentration be 0.15 wt% after a 15-h treatment? The value of D at
1400 K is 6.9 x 10^(-11)
m^2/s.