Showing papers by "John C. Lippold published in 2007"

Single Sensor Differential Thermal Analysis of Phase Transformations and Structural Changes During Welding and Postweld Heat Treatment

Abstract: The technique of Single Sensor Differential Thermal Analysis (SS DTA) has been subjected to series of verification experiments. Its accuracy and sensitivity to various phase transformations and structural changes has been evaluated by comparison to the classic differential thermal analysis (DTA) and to dilatometric analysis (DA). The reliability of thermocouple and SS DTA measurements in the typical ranges of heat treatment and weld heating rates has been estimated utilizing the endothermic effect of the ferromagnetic to paramagnetic transition and the Curie temperature as a reference point. The sensitivity of SS DTA to various phase transformations and structural changes has been demonstrated by in-situ applications during fusion and solid-state welding, casting, heat treatment and post weld heat treatment (PWHT). Its application range includes construction of continuous cooling transformation (CCT) diagrams, development and testing of processing procedures, weldability studies, development of welding consumables and new alloys.

Further Investigations of Ductility-Dip Cracking in High Chromium, Ni-Base Filler Metals

Abstract: The ductility-dip cracking (DDC) susceptibility of high-chromium, nickel-base filler metals was evaluated using the strain-to-fracture (STF) test technique These filler metals were of the Ni-30Cr type and included INCONEL® Filler Metals 52 and 52M supplied by Special Metals Welding Products Company, and Sanicro 68HP® and Sanicro 69HP® supplied by Sandvik AB In addition, two experimental Ni-30Cr filler metals were evaluated which contained variations in other alloy additions including Nb above 1 wt % and Mo up to 4 wt % A wide range in DDC susceptibility was observed with these filler metals, including large heat-to-heat variations in filler metals with similar compositions The experimental filler metals were found to be remarkably resistant to DDC Cracking susceptibility is primarily associated with the type and form of precipitate that forms along the weld metal migrated grain boundaries The formation of Nb-rich, M(C, N) at the end of solidification has the most profound effect on DDC, since these precipitates are most effective in pinning the boundaries The formation of M23C6 carbides during weld cooling or subsequent reheating can also affect DDC susceptibility in these filler metals

Investigation of grain refinement during a rejuvenation heat treatment of wrought Alloy 718

Abstract: The grain refinement resulting from a rejuvenation heat treatment (RHT) of Alloy 718 was investigated by using both metallographic analysis and orientation imaging microscopy (OIM). A step heat treatment was used to show that a phase transformation induced recrystallization process did not occur and supported static recrystallization as the method by which grain refinement occurred. Prior deformed grains in the wrought Alloy 718 microstructure were subject to recrystallization during RHT once the intragranular δ-phase pinning grain boundaries was dissolved. The coexistence of fully recrystallized, substructured and deformed grains in the rejuvenated microstructure revealed by OIM showed that an inhomogeneous recrystallization process occurred during RHT. Both the orientation relationship of grains and the behavior of grain boundaries involved in the recrystallization process were differentiated based on OIM characterization.