Role of welding process energy on the microstructural variations in a cobalt base superalloy hardfacing

Cobalt base superalloy hardfacings have been deposited by manual arc welding. Such deposits of total thickness 15 to 17 turn are realised in four successive layers on a steel substrate. The aim of this study is to analyse the role of the welding energy on hardfacings microstructural. variations. Microstructure of these hardfacings is formed of a mixture of eutectic precipitates between primary dendrites of a cobalt-ricb fee phase. The high resulting dilution with the substrate induced by such manual arc welding process generates a chemical gradient in the deposit thickness able to involve various carbides volume fraction: the eutectic precipitates volume fraction varies in the reverse order of dilution with no significant difference versus welding energy. On the other hand, the fact of producing hardfacing in successive layers causes a secondary precipitation. In other terms, this kind of deposit involving high temperatures for a sufficient long time makes the dendritic Cr and Co-rich zones precipitate. Thus, fine cuboids particles of Cr23C6 carbides are formed in the dendrites. In accordance with higher welding energy used, the higher temperatures reached generate the Cr23C6 carbides size increasing. (c) 2007 Elsevier B.V. All rights reserved.