Dissimilar metal overlays and welds are commonly used in the Power Generation, Oil and Gas, and Petrochemical industries. The most common joints consist of low alloy steel and/or stainless steel components joined or overlaid with Ni-base or stainless steel filler metal. These weldments require a post-weld heat treatment (PWHT) to temper the martensite that forms in the steel heat-affected zone (HAZ), so that the hardness is reduced and the impact toughness is improved.
Several phenomena occur during PWHT that can potentially lead to failures in service: 1) carbon migration from HAZ to fusion boundary region during PWHT results in a formation of a hard and brittle band along the fusion boundary. 2) loss of mechanical properties in HAZ due to over-tempering. 3) hydrogen embrittlement in fusion boundary region, due to high hardness created by carbon migration. In addition to these potential failure issues, PWHT in the field is time consuming and often impractical.
Temper bead welding could be a viable alternative to traditional PWHT, which is difficult to perform in the field. Ultimately, the temper bead procedure will be optimized to meet specified hardness and impact toughness requirements.
Industry Sponsor: EPRI, AZZ
Faculty: Boian Alexandrov
Graduate Student: Jeff Stewart, Eun Jang
Industry Contact: Steve McCracken & Darren Barborak