5.32 the outer surface of a steel gear is to be hardened by increasing its carbon content; the carbon is to be supplied from an external carbon-rich atmosphere, which is maintained at an elevated temperature. a diffusion heat treatment at 850 (1 123 k) for 10 min increases the carbon concentration to 0.90 wt% at a position 1.0 mm below the surface. estimate the diffusion time required at 650℃ (923 k) to achieve this same concentration also at a 10- mm position. assume that the surface carbon content is the same for both heat treatments, which is maintained constant. use the diffusion data in table 5.2 for c diffusion in a-fe