The surface of a steel gear made of 1022 steel (0.22 wt% C) is to be gas-carburized at 927°C (1700°F). Calculate the time necessary to increase the carbon content to 0.30 wt% at 0.030 in. below the surface of the gear. Assume the carbon content of the surface to be 1.20 wt%. D (C in _ iron) at 927°C = 1.28 × 10_11 m2/s.