On the variation of grain size and fractal dimension in an austenitic stainless steel

Samples of an AISI type 316L stainless steel were subjected to different treatments to promote changes in their microstructure. The specimens were heated in a box furnace set at four different temperatures for 30 min and cooled in air to room temperature by placing them in water after the cycle was completed. The samples were prepared following standard metallographic procedures, the microstructure was revealed with an electrolytic etchant, and the average grain size in each sample was determined by the mean line intercept technique. Images from the microstructures were digitized and fed into a personal computer for their fractal analysis by box counting. Two different approaches were used to obtain the fractal dimension of the structure, yielding to similar values in both cases. It was found that the fractal dimension of the microstructure increased with the reduction in grain size.