Since 2008, Japanese boiler, turbine and valve manufacturers, research institutes and utility companies have been working together to develop 700V A·USC technology, with support from the Japanese government. The key areas of discussion are technology development of high temperature materials such as nickel-based alloys and advanced 9Cr steels, and their application to actual power plants. At the EPRI conference in 2013, our report mainly focused on the development of fundamental material and manufacturing technology during the first five years of the project, and the preparation status of the boiler component test and turbine rotor test for the latter four years of the project. The boiler component test, using a commercially-operating boiler, began in May 2015 and is scheduled to be finished by the end of 2016. The turbine rotor test at 700°C with actual speed will be carried out from September 2016 to March 2017. At this year’s conference, we will: l) briefly summarize the development of fundamental material and manufacturing technology and 2) provide an update on the progress of the boiler component test and the turbine rotor test.

This paper describes microstructure control aimed for wear-resistance improvement of Co-based (Co-Cr-W-B-Si) self-fluxing alloy coating by diffusion treatment. The diffusion treatments of thermally sprayed Co-based self-fluxing alloy coating on steel substrate were carried out at 1370K to 1450K for 600s to 6000s under an Ar gas atmosphere. Microstructural variations of the coating and the interface between the substrate and the coating were investigated in detail. A proper diffusion treatment precipitates two kinds of fine compounds in Co-based matrix. XRD and EPMA analysis revealed these precipitates to be a chromium boride dissolving cobalt and a wolfram boride containing cobalt and chromium. The size of each precipitate became larger with increasing treatment temperature and time. A coating with the proper size borides showed a superior wear-resistance.

Nickel based self-fluxing alloy coating extends the service life of furnace wall tubes at waste incineration plants due to its excellent corrosion resistance and heat resistance. With our system, fusing of such coatings is performed by induction heating, which offers improved efficiency and reliability of products. Compared with conventional plasma, flame, and HVOF thermal-sprayed coatings, induction-fused coatings provide a far stronger metallurgical bond at the interface, while minimizing the inclusion of pores. In addition, the tubes are less costly than those with welded coatings, and the process reduces the distortion of the products, facilitating easier final assembly. A successful experimental application of 11 units (four, six-meter pipes per unit) revealed virtually no corrosion on the exposed surfaces, and showed an improved water heating efficiency over that of the original mortar-coated tubes. Over 200 such units are now being employed in four incinerators in Taiwan, and further installations are in progress.

This study focuses on two major advantages of induction heating over flame heating in the treatment of coated boiler tubes. In both cases the induction heating process is simple, fast and effective. Firstly, we will show how the use of induction heating results in exceptionally thick and hard coatings with low porosity. Having high corrosion and wear resistant properties, the products can satisfy industry's needs for reliable coatings with a long service life. Next, the study will detail how a pipe with the coating already applied can be simultaneously bent by induction heating while the coating is melted and fused to the pipe. The result is a thicker, more even and reliable coating than that accomplished by the flame sprayed method on a bent pipe. The process is not only less cumbersome, but again provides a superior product for the market.

The aim of this study was to improve the properties of atmospheric plasma sprayed WC-Co-Ni coatings by post treatment with induction heating. The spray powders used were WC-Co-Ni composite powders, produced by adding Ni-P alloy to WC-Co powder. Induction heating applied to the coating caused fusion of the Ni-P alloy with the WC-Co-Ni coating and a strong metallurgical bond with the steel substrate. An innovation in recent experiments was the use of an antioxidant paste applied to the outer surface of the coating under treatment. This eliminated the need for working under the restrictions of a hydrogen gas environment. The properties of the treated coating were investigated regarding microstructure, hardness, adhesive strength, abrasion resistance and porosity.