Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam Welded Thick S1100 Steel

To take advantage of the excellent mechanical properties of ultra-high-strength steels, welding processes must be properly controlled to maintain the mechanical properties in welded structures. Electron beam welding (EBW) provides high energy density and thus a relatively low heat input compared to arc welding. However, the narrow fusion zone (FZ) and the heat-affected zone (HAZ) can have insufficient toughness values due to the rapid cooling of the joint. In the present study, S1100MC welded by EBW without filler material was investigated with respect of microstructure, toughness properties, strength of the joint, hardness, and residual stresses close to the top surface. The microstructure of the FZ generally consisted of martensite and tempered martensite with inhomogeneous prior austenite grain (PAG) size between root and face FZ. The martensite phase with smaller PAG sizes caused a strong increase in hardness value in finegrained HAZ. Tensile tests fractured only in the base material since welds show higher strength than the base material. Evaluated impact toughness levels are moderate, and fracture path deviations only occurred for a particular notch type. The residual stresses in the transverse and longitudinal direction reached up to 79% of the yield strength.