Comparative investigation of some austenitic chromium-nickel steels in hot air

Abstract The hot air behaviour of “economically” alloyed stainless steel containing approximately 20% Cr, 19% Ni and 4% Al as well as of a modified type 314 steel was compared with the behaviour of common type 314 steel and of “expensively” alloyed steel containing approximately 24% Cr, 26% Ni, 3% Mo, 3% Cu and 2% Si. The specimens were exposed to air at 1100°C in 5 cycles of 120 h each with intermittent cooling to room temperature. Corrosion processes and other phenomena were investigated using visual inspection, gravimetric techniques, mechanical tests, optical and electronic micrography and electronic microanalysis. The modification of type 314 steel with vanadium and boron affects favourably the oxidation resistance in hot air. The economically alloyed steel, containing aluminium but less chromium, is still better, and expensively alloyed steel with molybdenum, copper, silicon and more nickel is slightly inferior to the modified type 314 steel. Mechanical properties, obtained by tensile, impact and hardness tests, vary during the exposure which also depends on the type of steel. The oxidation of economically alloyed steel is almost uniform, and on other steels intercrystalline attack has been detected.