The wear resistance of a steel shaft is to be improved by nitrogen hardening of its surface. The initial nitrogen content of steel is 0.002 wt%, whereas the surface concentration during heat treatment is maintained at 0.50 wt%. A nitrogen content of 0.1 wt % is desired at a position of 0.40-mm below the surface. (a) Determine the diffusion time required at 600oC. The pre-exponential and activation energy for diffusion of nitrogen in steel is given as 3X10-7m2/s and 76.15 kJ/mol, respectively. (b) What time will be required at 500oC to produce the same result (in terms of concentration at a specific depth) as for 10-hours at 600oC?