Exercise 5

The wear resistance of a steel shaft must be strengthened by increasing the hardness of the surface. This should be done by increasing the Nitrogen concentration so that it forms a hard wear layer on the surface as a result of nitrogen diffusion into the steel. The steel shaft is placed in a nitrogen-rich atmosphere at a constant temperature. Initial N - concentration is 0.002 wt%, the N concentration at the surface should be increased to 0.50 wt%. For this treatment to be effective, we must have an N concentration of 0.10 wt%, 0.45 mm below the surface. Find a suitable heat treatment time at a temperature between 475 C and 625 C. D0 = 3x10^-7 m^2 /s and Qd = 76150 J / mol.