Modifications of grain-boundary structure by friction stir welding in the joint of nano-structured oxide dispersion strengthened ferritic steel and reduced activation martensitic steel

The joint of oxide dispersion strengthened (ODS) ferritic steel and martensitic steel was produced by friction stir welding. The thermo-mechanical process during welding causes recrystallization in the ODS steel and phase transformation in the martensitic steel. In stir zones of both steels, low-angle boundaries significantly convert to high-angle boundaries. The recrystallization in ODS steel is characterized by the increase in the Sigma 3 twin boundary with an almost constant fraction of Sigma 5-Sigma 29 boundaries, while the martensitic steel shows an opposite trend. 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.