A Comparison of Creep Rupture Strength of Ferritic/Austenitic Dissimilar Weld Joints of Different Grades of Cr-Mo Ferritic Steels

Abstract

Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.

Hydrogen pre-charging effects on the notch tensile properties and fracture behaviour of heat-affected zones of thermally aged welds between T24 and T92 creep-resistant steels

“…The situation becomes even more complex in the case of dissimilar welds, i.e. the welded joints between chemically different steels which are very frequent in power engineering [5][6][7][8]. For instance, the dissimilar welds combined of lower and higher chromium ferritic steels, such as T24/T92 welded joints can be used in a number of steam generator circuits.…”

Creep behavior of dissimilar metal weld joints between P91 and AISI 304

“…The only possible reason which would help increasing the life of three layer welds is gradient in coefficient of thermal expansion. It has been reported that the presence of inhomogeneous microstructure across the interface develop stress concentration and stress triaxiality which also promotes the failure of dissimilar weld joints [7]. Similarly, in the three and single layer welds apart from inhomogeneous microstructure across the weld interface, another factor which contributes to stress concentration is the mismatch in CTE value.…”

“…Though dissimilar welding has been practiced for many high temperature tubular applications, failures have been reported in these welds [6,7]. Laha et al [7] reported inferior stress rupture properties of dissimilar welds of Cr-Mo steels with austenitic stainless steels compared to the base metal counterparts [7].…”

“…Though dissimilar welding has been practiced for many high temperature tubular applications, failures have been reported in these welds [6,7]. Laha et al [7] reported inferior stress rupture properties of dissimilar welds of Cr-Mo steels with austenitic stainless steels compared to the base metal counterparts [7]. The main reasons cited for these failures are the mismatch between the coefficients of thermal expansion (CTE) between ferritic and austenitic stainless steel [6][7][8][9] and carbon migration from ferritic to austenitic steel [6,[8][9][10][11][12].…”

“…Laha et al [7] reported inferior stress rupture properties of dissimilar welds of Cr-Mo steels with austenitic stainless steels compared to the base metal counterparts [7]. The main reasons cited for these failures are the mismatch between the coefficients of thermal expansion (CTE) between ferritic and austenitic stainless steel [6][7][8][9] and carbon migration from ferritic to austenitic steel [6,[8][9][10][11][12]. To help reduce the carbon diffusion from ferritic to austenitic side, nickel based fillers are used instead of austenitic filler [8,10,13].…”