Determine the carburizing time necessary to achieve a carbon concentration of 0.45 wt% at a position 2 mm into an iron?carbon alloy that initially contains 0.20 wt% C. The surface concentration is to be maintained at 1.30 wt% C, and the treatment is to be conducted at 1000?C. Use the diffusion data for g-Fe in Table 5.2.

Diffusing Activation Energy Qa Host Calculated Values Species Do(mls) Metal kJ/mol eVlatom D(mls) ) Fe 2.8 x 10-4 a-Fe 251 2.60 500 3.0 x 10-21 18 x 10-15 LI x 10-17 78 x 10-16 (BCC) 900 Fe rFe (FCC) 5.0 x 10- 284 2,94 900 1100 a-Fe 6.2 x 10-7 80 0.83 24 x 10-12 1.7 x 10-10 50 900 2.3 x 10-5 rFe 1.53 148 900 5.9 x 10-12 53 x 10-11 1100 Cu 7.8 x 10-5 2.4 x 10-5 Cu 211 2.19 500 4.2 x 10-19 Zn Cu 189 1.96 500 4.0 x 10-18 Al 2.3 x 104 Al 144 1.49 500 4.2 x 10-14 Cu 6.5 x 10-3 12 x 10-4 2.7 x 10-5 Al 136 141 500 4.1 x 10-14 Mg Al 131 1.35 500 1.9 x 10-3 Cu Ni 256 2.65 500 1.3 x 10-2