Consider the gas carburizing of a gear of 1020 steel at 927C°. Calculate the time in minutes needed necessary to increase

the carbon content to 0.40% at 0.5 mm below the surface. Assume the carbon content at the surface is 0.90% and that the

steel has a nominal carbon content of 0.20%. The diffusion coefficient of C in 1020 steel at this temperature is

1.28 x 10-11 m²/s.