10. The surface of a 0.1% C steel gear is to be hardened by carburizing. In gas carburizing,the steel gears are placed in an atmosphere that provides 1.2% C at

the surface of the steel at a high temperature. Carbon then diffuses from the surface into the steel. For optimum properties, the steel must contain 0.45% C at a depth of 0.2 cm below the surface. Using the data in Table 5.2, determine the required carburizing time at 900°C and 1100°C that will produce these optimum properties. Assume that the temperature is high enough (>723°C) so that the iron has the FCC structure. (20 points)