Abstract
Improvement of thermal efficiency of new power plants by increasing temperature and pressure of boilers has led us to the development of high creep strength steels in the last 10 years. HCMA is the new steel with base composition of 1.25Cr-0.4Mo-Nb-V-Nd, which has been developed by examining the effects of alloying elements on microstructures, creep strength, weldability, and ductility. The microstructure of the HCMA is controlled to tempered bainite with low carbon content and the Vickers hardness value in HAZ is less than 350Hv to allow the application without preheating and post weld heat treatment. The HCMA tube materials were prepared in commercial tube mills. It has been demonstrated that the allowable stress of the HCMA steel tube is 1.3 times higher than those of conventional 1%Cr boiler tubing steels in the temperatures range of 430 to 530°C. It is noted that creep ductility has been drastically improved by the suitable amount of Nd (Neodymium)-bearing. The steam oxidation resistance and hot corrosion resistance of the HCMA have been proved to be the same level of the conventional 1%Cr and 2%Cr steels. It is concluded that the HCMA has a practical capability to be used for steam generator tubing from the aspect of good fabricability and very high strength. This paper deals with the concept of material design and results on industrial products.
