Abstract
Super 304H austenitic stainless steel tubes containing 2.3 to 3 (wt.%) of Cu are mainly used in superheaters and reheaters of ultra super critical boilers due their excellent corrosion and oxidation resistance. Cu addition causes precipitation strengthening effect by fine Cu-rich precipitates which evolve during creep conditions and results in increased creep strength. The microstructural evolution of stainless steels during welding significantly affects the material properties. In this work, solidification mode microstructure and hot tensile properties of autogenous and filler-added Super 304H gas tungsten arc (GTA) welded tube joints were correlated. Autogenous welds of Super 304H solidified as austenite with 1.57 % delta ferrite and intercellular (Fe,Cr)23(C,B)6 borocarbides. In filler-added welds, the higher Ni equivalent and addition of carbide stabilizing elements (Nb,Mo) eliminated δ ferrite and segregation of B as borocarbides. The filler-added welds exhibited superior tensile strength than autogenous welds at both room and high temperature.
Highlights
Super 304H austenitic stainless steel tubes containing 2.3 to 3 of Cu are mainly used in superheaters and reheaters of ultra super critical boilers due their excellent corrosion and oxidation resistance
Super 304H austenitic stainless steel is used in recently installed ultra super critical (USC) power units of Japan operating at steam temperature of about 613 °C (Thomas 2013)
Super 304H is listed as a candidate material for superheaters and reheaters in the US program for development of materials for USC with steam temperatures of 760 °C (Viswanathan et al 2005)
Summary
Super 304H austenitic stainless steel tubes containing 2.3 to 3 (wt.%) of Cu are mainly used in superheaters and reheaters of ultra super critical boilers due their excellent corrosion and oxidation resistance. Austenitic stainless steels are selected for use in sections of superheaters and reheaters, which require good oxidation and fire side corrosion resistance, in addition to the creep strength. Future plans of increasing the efficiency of the power plants up to 49 % require creep-resistant steels operating at steam temperatures of 760 °C and pressures of 35 MPa (Viswanathan et al 2005). Super 304H austenitic stainless steel is used in recently installed ultra super critical (USC) power units of Japan operating at steam temperature of about 613 °C (Thomas 2013). Super 304H with nominal composition of 0.1C-18Cr-9Ni-3Cu-Nb-N derives excellent creep strength from the distinct Cu addition which precipitates as fine Cu-rich particle under creep conditions, in addition to NbCrN, Nb(C,N) and M23C6 particles (Li et al 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
