The Temperature Dependence of Abnormal Grain Growth and Grain Boundary Faceting in 316L Stainless Steel

Abstract

When commercial 316L stainless steel specimens are heat-treated in a single phase state at 1 100 degreesC, abnormal grain growth (AGG) occurs and some grain boundaries are observed to be faceted with hill-and-valley structures in transmission electron microscopy. Some segments of these faceted grain boundaries are expected to be singular. When heat-treated at 1 300 degreesC normal grain growth occurs with all grain boundaries smoothly curved. These grain boundaries are expected to be atomically rough. At 1 200 degreesC AGG still occurs but there is no excessively large grain as in the specimen heat-treated at 1 100 degreesC. This correlation between the grain boundary structure and grain growth is consistent with those observed previously in pure metals, oxides, and a single phase model alloy. The occurrence of AGG with faceted grain boundaries is attributed to grain boundary movement with boundary steps either produced by two-dimensional nucleation or existing at the junctions with dislocations. As the grain boundaries become rough at 1 300 degreesC normal growth oc curs because the grain boundaries migrate continuously with their rate expected to increase linearly with the driving force arising from the size difference. If a specimen heat-treated at 1 100 degreesC is further heat-treated at 1 300 degreesC, the AGG mode appears to switch to normal growth.