Electron beam welding process for joining thick gage section of martensitic stainless steels

Abstract

Sustainable manufacturing for assembly of turbines used in hydro power generation systems is driving the development of advanced technologies targeted to reduce life-cycle costs whilst assuring high performance over the prolonged product life-span. The turbine runner, a critical component in hydro power generation systems, requires weld assembly between the crown, band and blade sub-components. With due consideration of the thick-gauge sections involved, design and fabrication of a turbine runner that integrates a high energy density technology for assembly, such as vacuum electron beam welding (EBW), has marked potential to achieve deep penetration with a low heat input, thereby rendering a weldment with narrow heat-affected zones (HAZ) and low distortion. In this study, the weldability of thick-gauge section of cast and wrought grades of 13%Cr- 4%Ni low carbon martensitic stainless steels that are widely utilized in hydro turbine manufacturing was investigated by EBW. Particularly, a single pass bead-on-plate (BOP) and/or butt joint in 60 mm to 90 mm thick CA6NM and UNS S41500 plates were carried out using a 42 kW high vacuum EBW system without using filler addition. Preheating before welding and post-weld heat treatment of the welds was also studied. The characteristics of the weldments, including the size of the fusion zone (FZ) and HAZ, their phase constituents, microstructures and hardness evolution, were evaluated. The mechanical response of the welds, locally and globally determined through uniaxial tensile testing at room temperature with an automated non-contact three-dimensional (3D) digital image correlation (DIC) deformation measurement system, indicated that the tensile properties in both the as-welded and PWHTed conditions met the acceptance criteria in the ASME Section VIII & IX standard. A non-contact photometry system was also used to measure the distortion after EBW. In addition the distribution in the longitudinal residual stresses was mapped by the contour method for both CA6NM and UNS S41500 in the aswelded and PWHTed conditions.

Date	28 Jan 2016
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Henri Champliaud (Supervisor) & Priti Wanjara (Co-supervisor)