Microstrucure of explosively welded 0.1 Pct carbon mild steel tubes to 0.2 Pct carbon mild steel plate

Abstract

The microstructures developed within trial explosive welds between 16 mm diam, 1.2 mm wall thickness tubes of 0.1 pct C 0.4 pct Mn mild steel and a 0.2 pct C 0.8 pct Mn mild steel base plate have been examined. A weld zone typically ∼20 μm wide is formed in which solid-phase bonding is interrupted by pockets of localized melting. The complex microstructure develops as a result of both severe plastic deformation and rapid cooling. Plastic deformation, limited to regions close to the weld interface and the internal surface of the tube, was confirmed by the high density of dislocations in the α phase. Twinning on {112} planes occurs within discrete regions of the tube plate and is discussed in terms of the geometrical arrangement of the tubes in the plate. The morphology of the product in the fusion pockets has been compared with the massive and acicular martensite which is typical of quenched low-carbon steels. The high-pressure shock waves that develop during the collision of the tube and tube plate result in pronounced local deformation adjacent to the weld junction. The closely interwoven microstructure produced has been interpreted as the result of a pressure-induced transformation.