Rapid formation of the sigma phase in 304 stainless steel during friction stir welding

Rapid formation of sigma phase occurred in 304 stainless steel during friction stir welding. A possibility was suggested that the sigma formation can be accelerated by the emergence of delta-ferrite at high temperature and the subsequent decomposition of the ferrite under the high strain and recrystallization induced by friction stirring. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.