Effect of grain size on machining strength in an austenitic stainless steel

Abstract

This paper explores the effect of grain size on machining strength in an Fe-Cr-Ni alloy, namely AISI 316L. Ideal grain growth law, proposed by Burke,[1] was used to obtain the activation energy for this steel based on data published by Stanley and Perrota,[2] which was 185 kJ.mol-1. The initial grain size was measured - 12 0m - And by considering these values, both temperature and time values needed to achieve a final grain size ten times larger than the initial one could be calculated, which were 1200°C and 2 hours. Ternary phase diagram analysis showed that austenite was stable at this temperature. Following, samples of 200-mm length were annealed and quenched in water to prevent any formation of sigma (0) phase. Annealed and as-received bars were then used to compare their machining strength. Results showed that the machining strength is higher in the as received condition than the one after annealing (127 0m). It may be concluded that the bigger the grain size, the lower its machining strength. It is believed that this is caused by the pile-up of dislocations on grain boundaries, since this material exhibits large plastic deformation before fracture.