2006 Volume 55 Issue 8 Pages 732-737
The internal friction behavior by hydrogen in the 329J4L super duplex stainless weld metal was examined. Two internal friction peaks at low temperature in the weld metal were observed after hydrogen charging. These peaks appear to be caused by stress-induced diffusion of hydrogen in sigma and austenite. These peaks gradually increased with hydrogen charging time and were unique to duplex stainless steel.
A sharp peak of significant strength occurred at 245K for a frequency of 1.5Hz in as-welded condition. The activation energy of this peak after 7.2ks charging is approximately 38.7kJ/mol which compares favorably with the hydrogen diffusion energy for austenitic stainless steel. This peak is associated with the stress-induced motion of hydrogen in an interstitial-substitutional pair.
On the other hand, the sigma (s) phase precipitation suppressed this peak and showed slightly broader peak, providing a strong indication of hydrogen trapping into the sigma phase. After peak separating calculation using theoretical internal friction curve, two peaks were observed after hydrogen charging. One of the peaks observed at 245K exhibited an activation energy of 38.7kJ/mol. A broad peak at 225K is interpreted as a stress-induced motion of hydrogen in tetragonal sigma phase. The activation energy of peak by hydrogen in sigma phase was estimated to 36.7kJ/mol. Consequently, a broad peak by hydrogen in sigma phase was observed at 225K in the hydrogenated weld metal precipitating sigma phase. It is apparent from these results that hydrogen can easily diffuse in the sigma phase as compared to austenite.