This paper proposes a new mass spectrometry technique to measure hydrogen evolution in the heat affected zone (HAZ) of a welded material while welding. Square block specimens are used, with a small-diameter hole drilled parallel to the surface to be overlaid at such a depth that the hole will be seated in the future HAZ. This hole is connected to a mass spectrometer that will detect hydrogen evolution in the HAZ during welding; also recorded are the evolutions of temperature in the HAZ and bead deposit advance. Parallel to such experiments, hydrogen diffusion and solubility characteristics have been determined versus temperature using mass spectrometry on base metal and HAZ microstructures.
Results show that hydrogen evolves in the HAZ during welding with characteristic humps and maxima, which may be attributed to variations in diffusion coefficients with temperature and phase changes in the HAZ. These observations were confirmed by computer modelling. Thus, this technique, together with the numerical simulation, is powerful in qualitatively and/or quantitatively evaluating various welding parameters such as: nature of the welding material, the welding process, preheating, and postheating.