Abstract
High-pressure valves and fittings used in coal-fired 600/625 °C power plants are hardfaced for protection against wear and corrosion and to provide optimum sealing of the guides and seats. Stellite 6 and Stellite 21 are often used for hardfacing, which is carried out by build-up welding, usually in several layers. The valve materials are generally heat-resistant steels such as 10CrMo9-10 (1.7380), X20CrMoV1 (1.4922), or Grade 91 / Grade 92 (1.4903 / 1.4901). In recent years, cracks or delaminations have frequently occurred within the hardfaced layer. The influence of cycling operation is not well understood. Other essential factors are the chemical composition of the base material and of the filler metal; especially in terms of the resulting iron dilution during the deposition of the welding overlays. The research project was initiated to investigate the crack and delamination behavior and to understand the involved damage mechanisms. Thermostatic and cyclic exposure tests have shown that cracking is favored by the formation of brittle phases due to iron dilution from the substrate material during the manufacturing process. Recommendations for the welding process of hardfaced sealing surfaces of fittings were derived from the investigation results.