Question

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2. An FCC iron-carbon alloy initially containing 0.40 wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1325 K (1052°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 0.25 wt% after a 10-h treatment? The value of D at 1325 K is 3.3 x 10-u mz/s. C(x,t)-C -|-erf * C.-C= l-erf |

Answer 1

solution Ca-Co G-Co 0.25-0.4 o.o.4 2009 = 0-375- 1-eof () - deaf (DF) = 0.623 3 0.6 erfa 0.604 0.625 0.642 0.65 2 -0.6 0.625-0.604 0.642 -0.604 0.65 -0.6 2) z = 0.63 which means that

-0.63 2 ſot = x= 2x0.63 | 3.2x107 m/sec x 3.6X10" See = 1.37x162 m = 1.37 mm Please do like the solution

Answer 2

An iron-carbon alloy initially containing 0.214 wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1070°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 0.0 wt% C. At what position will the carbon concentration be 0.161 wt% after a 8 h treatment? The value of D at 1070°C is 2.0 × 10-10 m2/s.