CHARACTERISTICS OF ELECTRON BEAM WELDED CA6NM S. Sarafan 1, 2 , P. Wanjara 2 , H. Champliaud 1 , L. Mathieu 3 and J. Lanteigne 4 1 École de technologie supérieure, Montréal, Québec, Canada, H3C 1K3 2 National Research Council Canada, Aerospace, Montréal, Québec, Canada, H3T 2B2 3 ALSTOM Canada Inc., Sorel-Tracy, Québec, Canada, J3R 5P9 4 Institut de recherche d’Hydro-Québec (IREQ), Varennes, Québec, Canada, J3X 1S1 Keywords: Electron beam welding, Cast CA6NM martensitic stainless steel, Microstructure. Abstract In this study, the viability of thick-gauge section assembly for hydroelectric turbine manufacture was considered by electron beam welding (EBW) of CA6NM martensitic stainless steel, a widely utilized hydro-turbine cast material. Particularly, bead-on-plate (BOP) trials on 60 mm- thick CA6NM plates were carried out using a 42 kW high vacuum EBW system. The influence of the heat input, beam focus (BF) position, beam defocusing, and in-situ pre-heating conditions on the characteristics of the weldments, such as the bead geometry, weld integrity, fusion zone (FZ) and heat affected zone (HAZ) microstructures and hardness were evaluate. A relationship between the welding parameters and the resulting depth of penetration was first established. A methodology for in-situ heating of the thick gauge section prior to welding was then developed and evaluated for reducing welding defects in CA6NM. Introduction With due consideration of the geometry and size of hydroelectric turbine elements, exigent challenges exist in manufacturing for the assembly of thick gauge section runner components. Presently, conventional fusion welding technologies are employed for assembly and repair of the turbine elements by a series of welding passes with filler metal addition. This multiple-pass arc welding/repair process is high in heat input and distortion of the assembly involves costly re-working/shaping. In addition, repeated heating to the fusion temperature during multiple-pass arc welding may also be problematic for generating a homogeneous microstructure in the weldment. That is, repeated melting during each pass results in microstructural variation within the FZ and HAZ of the previous passes that may then render inconsistencies in the performance of the assembly. Thus, the application of a high energy density technology, such as EBW, for joining thick gauge sections with a single pass has the overall advantages of low heat input over arc welding without the need for filler metal addition and the capability of minimizing microstructural changes in the weldment [1-6]. However, as the energy of the EBW process is focused and highly localized at the weld interface, large temperature gradients can occur within the weldment [7, 8]. Hence, the temperature distribution in the weld must be understood and related to the resulting microstructural constituents in the assembly. In this regard, the parametric conditions of the EBW process thus need to be studied and optimized to achieve the required penetration in thick gauge section components whilst ensuring the weld integrity and performance. The relatively good weldability of the martensitic stainless steels, and in particular CA6NM, applied for the manufacture of turbine elements provides a reasonable premise for the development of a EBW process for the assembly of thick gauge sections. However, the cracking tendency of thick Materials Science and Technology (MS&T) 2013 October 27-31, 2013, Montreal, Quebec, Canada Copyright © 2013 MS&T'13® Advances in Hydroelectric Turbine Manufacturing and Repair 720