Effects of tungsten and molybdenum on high-temperature tensile properties of five heat-resistant austenitic stainless steels

Heat-resistant austenitic stainless steels have been intensively used worldwide for turbo-chargers requiring excellent high-temperature properties to sustain their structures at very high exhaust gas temperatures. Five heat-resistant austenitic stainless steels were fabricated by varying contents of W and Mo, and their high-temperature tensile properties were investigated by analyzing phases (liquid, austenite, ferrite, and carbides) existing at high temperatures. Effects of replacement of expensive alloying element, W, by Mo or reduction in W were also examined. The increase in contents of W and Mo resulted in linearly increased volume fractions of M7C3 and total carbides, while the volume fraction of MC carbide hardly showed any relation, and showed a good correspondence with high-temperature yield and tensile strengths. The steel where 2 wt% of W was replaced by 2 wt% of Mo showed the best 900 °C-tensile properties, thereby confirming the successful achievement of partly replacement of W by Mo. In addition, the low-W-containing steels showed excellent 900 °C-tensile properties, which also indicated that the reduction in 1-2 wt% of W was accepted for saving costs of alloying elements.