Effect of solidification mode and morphology of microstructure on the hydrogen content of duplex stainless steel weld metal

The evolution rate of hydrogen from a duplex weld depends on sample geometry, temperature and microstructure. These factors have important consequences for the determination of hydrogen in duplex stainless steel welds. Because of the low hydrogen diffusibility and high hydrogen solubility in austenite, a standard method (BS 6693: 1988) which existed to determine the hydrogen content of ferritic steel welds as a means of assessing welding consumables, is not suitable for duplex welds. As a result of extensive research, a modified test method has been used involving encapsulation of the weld sample in Pyrex, evolution at 400 °C for 24 h, and followed by hydrogen analysis in an Oerlikon/Yanaco gas chromatograph. In this present work, the effect of solidification mode and microstructure on weld hydrogen content, and the evolution of hydrogen from such welds has been investigated by using experimental electrodes which are designed to give varying ferrite/austenite ratio in the welds. It was found that the measured weld hydrogen contents were almost constant since they arose from the flux/binder combinations which were the same for each type of experimental electrodes. Thus, the potential hydrogen from each type was the same and similar amounts became trapped during the rapid solidification of the weld pool, irrespective of final ferrite content.