Grain size and particle dispersion effects on the tensile behavior of friction stir welded MA956 oxide dispersion strengthened steel from low to elevated temperatures

This paper shows the dependence of tensile behavior of friction stir welded oxide dispersion strengthened steel (MA956) on testing temperature and welding parameters. Eight welding conditions were utilized and three produced consolidated defect-free welds in MA956 plate material. Tensile samples were prepared from the welded plate and were subjected to tensile testing with a strain rate of 10−3 s−1 over temperatures from ambient to 600 °C. The base plate material possessed a fine-grained microstructure that exhibited limited ductility, high yield strength, and moderate strain hardening at low temperatures. At elevated temperatures the base plate was more ductile and possessed limited strain hardening. Friction stir welding caused a significant (42%) reduction in yield strength at low temperatures and a corresponding increase in ductility compared to the base plate material. These changes became more pronounced as the heat input increased. The change in tensile behavior was the result of ferrite grain and oxide particle coarsening. The effect of grain coarsening was well-described by the Hall-Petch relationship and oxide particle coarsening resulted in the loss of particle strengthening.