Development of heat-resistant Fe-based alloys for A-USC steam boiler using ultra-high purity (UHP) technology

The design of ultra-high purity (UHP) Fe-based alloys for advanced ultra-supercritical (A-USC) technology is suggested in this work. The creep testing at 700 °C and a stress level of 150 MPa have been performed in air. The addition of small amount of reactive-elements, W, Nb, Zr and Sc, has been undertaken into model alloys with the intention to promote the precipitation strengthening. Optimizing the chemical composition coupled by pre-straining enabled improving the creep resistance; hence a creep-rupture life of 750 h was reached. The oxidation resistance in supercritical water is remarkably enhanced by small addition of Sc.