Determine the carburizing time necessary to achieve a carbon concentration of 0.30 wt% at a position 4 mm into an iron-carbon alloy that initially contains 0.10 wt% C. The surface concentration is to be maintained at 0.90 wt% C, and the treatment is to be conducted at 1100C. Use the diffusion data for y-Fe in below Table 5.2. Diffusing Activation Energy Od Calculated Value Species Host Metal D.(m/s) kJ/mol eV/atom T(C) D(m/s) Fe a-Fe 2.8 X 10 - 251 2.60 500 3.0 x 10-21 (BCC) 900 1.8 X 10-15 Fe y-Fe 5.0 x 10-5 284 2.94 900 1.1 X 10-17 (FCC) 1100 7.8 X 10-16 a-Fe 6.2 x 10-7 80 0.83 500 2.4 x 10-12 900 1.7 X 10-10 2.3 x 10-5 148 1.53 900 5.9 X 10-12 1100 5.3 X 10-11 Cu Cu 7.8 x 10-5 211 2.19 500 4.2 x 10-19 Zn Cu 2.4 x 10-5 4.0 x 10-18 AI 2.3 x 10-4 144 1.49 4.2 x 10-14 Cu AI 6.5 x 10-5 136 1.41 500 4.1 x 10-14 Mg AI 1.2 x 10-4 131 1.35 500 1.9 X 10-13 Cu Ni 2.7 x 10-5 256 2.65 500 1.3 x 10-22 Source: E. A. Brandes and G. B. Brook (Editors), Smithells Metals Reference Book, 7th edition, Butterworth- Heinemann, Oxford, 1992. y-Fe 189 1.96 uuAAAM 500 500