The wear resistance of a steel shaft is to be improved by hardening its surface. This is to be accomplished by increasing the nitrogen content within an outer surface layer as a result of nitrogen diffusion into the steel. The nitrogen is to be supplied from an external nitrogen-rich gas at an elevated and constant temperature. The initial nitrogen content of the steel is 0.002 wt%,whereas the surface concentration is to be maintained at 0.50 wt%. For this treatment to be effective, a nitrogen content of 0.10 wt% must be established at a position 0.40 mm below the surface. Specify appropriate heat treatments in terms of temperature and time for temperatures-between 475°C and 625°C. Calculate values for 500°C, 550°C, 600°C temperatures that lie-within the range stipulated in the problem. The pre-exponential and activation energy for the-diffusion of itrogen in iron are 3 × 107 m/s and 76150 J/mol, respectively, over this temperature range. (8 marks including 2 marks for each final answer in the table and 3marks for the solution)

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The wear resistance of a steel shaft is to be improved by hardening its surface. This is to be accomplished by increasing the nitrogen content within an outer surface layer as a result of nitrogen diffusion into the steel. The nitrogen is to be supplied from an external nitrogen-rich gas at an elevated and constant te