Variations in weld metal microstructure after impact at different strain rates for three weld metals, SAF 2507 DSS, SAF 2205 DSS and 254 SMO steel, are addressed. The twin grain forms that appear inside the gamma grain of duplex stainless steel at low impact strain rates may be caused by adiabatic heat. The needle-like or thick streak-like twins occur in the gamma grain of duplex stainless steel, caused by shear stress at a high strain rate. The impact induces dislocation loop formation in the gamma phase of 254 SMO steel at low strain rate, but martensite is produced at a high strain rate. The chemical composition affects the stacking fault energy coupled with adiabatic heat to determine the final structure of the impact. (c) 2008 Elsevier B.V. All rights reserved.