Influence of temperature and grain size on the tensile ductility of AISI 316 stainless steel

Abstract

The influence of temperature and grain size on the tensile ductility of AISI 316 stainless steel has been examined in the temperature range 300–1223 K for specimens with grain sizes varying from 0.025 to 0.650 mm at a nominal strain rate of 3 × 10 −4s −1. The percentage total elongation and reduction in area at fracture show minimum ductility at an intermediate temperature, and the temperature corresponding to this ductility minimum has been found to increase with increase in grain size. The total elongation is found to decrease with increase in grain size at high temperatures where failures are essentially intergranular in nature. At 300 K, both uniform and total elongation increase with increase in grain size and then show a small decrease for a very coarse grain size. The high ductility observed at low temperatures (300 K) is consistent with the observation of characteristic dimples associated with transgranular ductile fracture. The ductility minimum with respect to temperature is associated with the occurrence of intergranular fracture, as evidenced by optical and scanning electron microscopy. The present results support the suggestion that the ductility minimum coincides with the maximum amount of grain boundary sliding; at temperatures beyond the ductility minimum, grain boundary separation by cavitation is retarded by the occurrence of grain boundary migration, as evidenced by the grain boundary cusps. In tests conducted at various strain rates in the range 10 −3–10 −6 s −1 at 873 K the ductility was found to decrease with decreasing strain rate, emphasizing the increased importance of grain boundary sliding at lower strain rates.