Abstract
Understanding of the mechanisms of annealing twin formation is fundamental for grain boundary engineering. In this work, the formation of annealing twins in a 304L austenitic stainless steel is examined in relation to the thermo-mechanical history. The behaviour of annealing twins of various morphologies is analysed using an in-situ annealing device and EBSD. The results confirm that there is a synergistic effect of prior strain level on annealing twin density generated during recrystallization. The higher the prior strain level, the higher the velocity of grain boundary migration and the higher the annealing twin density in the recrystallized grains. This effect decreases as the recrystallization fraction increases. The existing mathematical models (Pande's model and Gleiter's model), which were established to predict annealing twin density in the grain growth regime, can not predict this phenomenon.
Highlights
In 1926, Carpenter and Tamura [1] were the first to observe the formation of annealing twins
In both samples the twin density increases as the recrystallization fraction increases at the beginning of the recrystallization regime and the maximum value of annealing twin density corresponds to the maximum value of grain boundary migration velocity
The higher stored energy level of sample 2 has a synergistic influence on annealing twin density via its accelerating effect on grain boundary migration
Summary
In 1926, Carpenter and Tamura [1] were the first to observe the formation of annealing twins. The growth accident theory, which suggests that a coherent twin boundary forms at a migrating grain boundary due to a stacking error, is supported by a majority of recent experimental results [3,4,5]. In the growth accident theory, the migration distance and migration velocity of grain boundary are two key positive factors to annealing twin generation. The only two mathematical models based on this theory [6,7], which were established to predict annealing twin density in the grain growth regime, are not capable of predicting annealing twin density in the recrystallization regime. The aim of the present work is to extract some regular patterns of annealing twin formation during recrystallization especially the relationship between the stored energy level and the annealing twin density by analysing the experimental results from a 304L austenitic stainless steel
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