抄録
Steam turbine blade steel of 12 Cr-Mo-W-V type has been rupture-tested at 500°-650°C for periods up to 40000hr. The data obtained showed significant differences in the long time properties among various production heats.
Metallurgical examination after exposure at 600°C showed that the microstructures and solute contents of alloying elements, such as tungsten and molybdenum, are similar for all the heats and have no correlation with their rupture strength.
Low aluminum content heats (≤0.007%) showed high strength in the long time tests. It appears that the high aluminum content (≥0.02%) reduces the nitrogen content in solution due to precipitation of AlN during prolonged rupture testing and leads to deterioration in rupture strength.
The rupture ductility variation is suggested to arise from the differences in pre-existed austenite grain, aluminum content, and copper content. A heat with fine grains of pre-existed austenite (G: 5.0), low aluminum content (0.005%), and low copper content (0.03%) showed high ductility over a wide testing range.
