Recent boilers have been designed for higher temperatures and pressures than those in the past and require steels with high temperature strength that is greater than that of conventional 18-8 austenitic stainless steels. The effects of various alloying elements on the creep rupture strength of 18-8 austenitic steels were examined. As a result, a new heat resisting steel (0.1C-18Cr-10Ni-3Cu-Ti-Nb) was developed. The new steel has a creep rupture strength at 600 - 700°C that is 30% higher than that of TP347H. This steel tube, called TEMPALOY AA-1, is expected to be a candidate material for ultra supercritical boilers.

creep rupture strength, boiler tube, precipitation strengthening, Cu-rich phase, austenitic stainless steel, steam oxidation, high temperature corrosion, ultra super critical boiler.