Confirmation of tensile residual stress reduction in electron beam welding using low transformation temperature materials (LTT) as localized metallurgical injection – Part 1: Metallographic analysis

Abstract For the reduction of the distortion and the residual tensile stresses in welded seams on carbon manganese steels, low transformation temperature materials (LTT) were developed. These materials use the volume expansion effect during martensitic transformation. The volume expansion counteracts volume shrinkage during cooling. The positive effects of the low transformation temperature alloys on the residual tensile stresses were demonstrated in various investigations. The low transformation temperature materials were, so far, used as filler material in arc welding processes in large volumes. The use of modular thermal fields of the electron beam welding processes offers the potential of a temporally activated use of compressive stress induction by phase transformation of the low transformation temperature alloys. The aim is to exert influence in situ on the welding residual stress state and thus on the distortion of complex parts. The metallographic analysis of an electron beam welded seam in unalloyed steel with low transformation temperature filler material is demonstrated. The evaluation is made via electron backscatter diffraction (EBSD) and is shown in the first part. The second part will show the effect on near surface residual stresses examined by hole-drilling method in combination with an optical evaluation by electronic speckle pattern interferometry.