Consider the gas carburizing of a gear of 1018 steel (0.18%) at 927C (1700F). Calculate the time necessary to increase the carbon content to 0.35% at 0.40 mm below the surface of the gear. Assume the carbon content at the surface is 1.55 % and that the nominal carbon content of the steel gear before carburizing is 0.18%. D (C in iron) at 927C = 1.28 10-11 m2/s. (Round the final answer to two decimal places.)

The time necessary to increase the carbon content is ____ min.?