Question

Q#9) The wear resistance of a steel shaft is to be improved by hardening its surface 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 0.0020wt%, whereas the surface concentration is to be maintained at 0.50wt%. For this application, a nitrogen content of 0.10wt% at a position 0.40 mm below the surface is desired. I. Will this process be a steady state or non-steady state process? Why? II. Would you expect nitrogen to diffuse by a vacancy mechanism or an interstitial mechanism? Why?

Answer 1

Q = 0.0620wt% N G=0.5owth ,༠ནས་ Ood wt% N a non) steady Nitrogen diffused by interstitial mechanism 0.4 mm state process. It is ac aYc D at 2009 Which follows of flux J Nitrogen atomic radius Small Which can be fit into interstitial voids C is very Second law diffusion. dependent on time and Where flux is distance. f Coc, t х Cx-to :( 27 =l-erf 2 ſot esco x of unit all. of Steele che D = Do exp RT interstitial activation enersy