"Microstructural Evolution of Dissimilar Metal Welds involving Grade 91 Steel"
Department: Materials Science and Engineering
Advisor: John DuPont
Abstract:
Fossil fuel and nuclear power plants that involve steam power generation use hundreds of dissimilar metal welds to join metals used in low-temperature regions to the metals used for high-temperature steam vessels. Dissimilar metal welds involving Grade 91 steel are failing prematurely in power plant steam vessel applications. A power plant outage caused by weld failures can cost power plants hundreds of thousands of dollars per day. Failure in these dissimilar metal welds has been shown to occur within a narrow carbide-free region on the ferritic side of the partially mixed zone. Little is understood about the nature of this region, including when and why the carbide-free region forms. The long-term research objective is to determine why the carbide-free region forms so that this failure mechanism can be prevented in the future. In the short term, a fundamental understanding of the microstructural evolution near the interface is being developed to determine when this region forms. Detailed numerical simulations, microscopy, and hardness indentation mapping are being applied to a series of aged weld passes containing various filler metals to examine the evolution of dissimilar metal welds over time with the ultimate objective of preventing premature failure.
