The Dependence of Abnormal Grain Growth on Initial Grain Size in 316L Stainless Steel

Abstract

When 316 L stainless steel specimens are compressed to 30% and annealed at 1300 degrees C, primary recrystallization rapidly occurs and grains grow normally during further annealing treatment. Thus by annealing for various periods at 1300 degrees C, specimens with varying average sizes with identical normalized grain size distributions are obtained. When these specimens are heat-treated again at temperatures below 1150 degrees C, abnormal grain growth (AGG) occurs depending critically on the initial grain size.With decreasing initial grain size, AGG begins earlier during the heat-treatment, and if the initial grain size is large, only slow grain growth occurs without any distinct AGG for periods up to 48 and 96 h. It is observed that AGG occurs by faster growth of large grains with their velocities expected to increase nonlinearly with the driving force arising from the size difference. Because the AGG structure develops gradually, there is not really a well defined incubation time. With the same initial grain size the initiation ofAGGis slower at lower temperatures. A step heat-treatment experiment shows that if there are large grains embedded in the matrix of fine grains, they can grow abnormally under the condition where no AGG occurs with a narrow grain size distribution. The extremely slow grain growth with initially large average grain sizes is attributed to the low grain boundary velocity limited by the boundary step nucleation or growth. It is proposed that the same boundary step mechanism is qualitatively consistent with abnormal growth of the large grains with singular grain boundaries at low temperatures.