HYDROGEN ABSORPTION AND DIFFUSION in different welded DUPLEX STEELS

摘要

In this study, hydrogen absorption and diffusion were investigated for various high-alloyed ferritic-austenitic duplex steels. On account of the specific transformation and solidification behaviour, respectively, of duplex steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning hydrogen absorption which may ultimately lead to microstructure-dependent hydrogen-assisted weld metal cracking. Hydrogen absorption during welding may occur via the shielding gas, moisture from the surroundings or via the welding filler material. As a contribution to the interpretation and prediction of hydrogen-induced cracking in welded duplex steels, the actual hydrogen absorption via the arc as well as the weld metal hydrogen diffusion was investigated for the first time in a duplex steel DS (1.4462), a super duplex steel SDS (1.4501) and in a lean duplex steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of hydrogen trapped in the respective microstructure areas. The hydrogen diffusion coefficients were determined by analytical and numerical calculation. The total hydrogen concentrations and the diffusion coefficients were found to be nearly identical. Trapped hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of hydrogen on the mechano-technological properties of the weld metal was characterized with the help of tensile tests. In addition, the hydrogen embrittlement effect was detected in scanning electron microscopic analyses.