Improving the structure and properties of thermite weld metal

Abstract

In this study, normalizing thermite welds produced a significant improvement in the tensile ductility of the weld metal. For example, by normalizing weld metal with 0.55 wt.% C and 0.06 wt.% V, ductilities in the range 10%–20% reduction in area were achieved when the cooling rate exceeded 37 K min −1 through the transformation range, whereas the tensile ductility of “as-cast” thermite weld metal was only 2%–6% reduction in area. Tensile strengths comparable with those of the weld metal used in current practice were obtained together with the enhanced tensile ductility. In addition, attempts were made to filter the molten thermite steel by passing it through zirconia-mullite filters. These attempts were only partly successful in that the filters partially dissolved in this application; even so, the filters did reduce the inclusion content of the thermite weld metal. It was concluded that it is possible to produce more ductile thermite welds by judicious control of composition and the application of post-weld normalizing and that, with suitable ceramic filters, filtering could be employed to reduce the amount and sizes of inclusions in thermite weld metal.