AUSTENITE AND FERRITE GRAIN SIZES IN INTERSTITIAL-FREE STEEL

An oxidation method has been employed to reveal prior austenite grain boundaries in C-Mn and interstitial free (IF) steels. The ability of t his technique to reveal prior austenite gain boundaries is assessed by comparing its results with those of an etching method applied on the C-Mn steel. Optimum conditions were established by trial and error. Th e conditions varied with different steels and with heat treatment temp erature. In the IF steel vapid grain growth at high temperatures in th e ferrite range made a significant contribution to the prevention of g rain refinement through transformation. Attempts to obtain the smalles t prior austenite gain size in the IF steel to assess the ability of t he oxidation technique to reveal fine austenite grains led to an avera ge austenite grain size of 80 mu m in warm rolled samples after the sh ortest holding time at 950 degrees C.