| Abstract Scope |
PTAW (Plasma Transferred Arc Welding) hardfacing has been in practice since 60’s . It has several advantages over other welding methods like GTAW because of precise control of both welding parameters and metallic powder which reduces amount of machining. However, except from being a complex process with so many parameters to control, hardfacing is challenging when the base material is martensitic stainless steel and the hardfacing layer is Cobalt-6 alloy (Stellite 6, Stellite is a registered trademark of Deloro Stellite Company, part of the Kennametal group) and the part has to be manufactured based on the ASME Code requirements. Different ways to overcome this challenge are through optimization of the welding process and also pre and post heat treatments. One of the biggest challenges is cracking in the hardfacing layer of sealing surface, sometimes it propagates to the base metal, where no indication is permitted. Cracking is initiated because of difference in coefficient of thermal expansion of steel and cobalt alloy. The sensitivity to cracking is increased as the size and complexity of the part is increased. One of the important parameters to lower sensitivity to cracking is dilution control because dilution with the base metal will usually increase the hardness of hardfacing layer; Stellite 6 powder hardness is 38-45HRC, but the hardness of the overlay is more than 48HRC usually. In this presentation the best way to overcome this challenge is discussed. |