Microstructure Development and Control in Steel Welds

Abstract

In welded structures, welds are required to have performances equivalent to base metals in wrought and annealed conditions. To achieve the performance required, various microstructure controls have been developed and applied for steel weld metals and heat-affected zone to minimize the coarse, heterogeneous and brittle structures. In this article, these microstructure controls are reviewed with a particular emphasis on the toughness of carbon-manganese and low-alloy steel welds. The control of inclusions and the optimization of steel compositions for the improved microstructure refinement are discussed, since the refinement of weld microstructure has been achieved by the inclusion-assisted grain refinement of prior austenite and the enhancement of intra-granular ferrite formation. The discussions are extended to the role of inclusions as pinning particles and as preferential nucleation sites of ferrite, which is important for further improvement of the technology. Toughness degradation due to martensite-austenite constituent in welds is also referred. Current understandings of the microstructure controls in carbon-manganese and low-alloy steels welds and issues to be solved are summarized.