Effect of thermal cycling on the cold rolled AISI 316L with varying degree of reduction toward their microstructure and hardness

Abstract

Abstract Orthopedic implants had been widely used to treat bone fractures. One of the selected materials for an implant is austenitic stainless steel AISI 316L following the ASTM F138 standard. These implants had been produced locally in Indonesia using investment casting method. Even though the mechanical properties of local implant had met ASTM standards requirements, it was found to be lower in their properties as compared to the imported implant from developed countries. In order to compete with these imported products, local implant 316L was modified by reducing their grain size microstructures of about 83.17 µm on average to become finer grain through recrystallization mechanism. The mechanism can be triggered by thermal cycling treatment after 316L was subjected to cold rolling process. The cold rolling process will induce stored strain energy that affects the dislocation density. Different degrees of cold rolling reduction of 52%, 60%, 69%, 80%, and 90% will give different amounts of dislocation density that will affect the recrystallization stage during thermal cycling. It was found that after thermal cycling treatment at 900 C for 35 seconds with 4 cycles, homogenous full recrystallization was confirmed on 80% and 90% reduction degree samples. The average grain size of 80 and 90% reduction degree samples were decreased from 83.17 µm on average detected in the investment casting product to 3.26 µm and 2.87 µm, respectively. This had resulted also in increased average hardness from 159 HV2 to 257 HV2 and 267 HV2 respectively. Conversely, only partial recrystallization was observed in the other degree of reduction samples. The obtained hardness provides lower value than 80% and 90% reduction degree with larger average grain size being detected on these samples.