This paper briefly reviews the history of the development of duplex stainless steels and summarises the grades that are currently standardised in JIS and used industrially. The chemical composition, phase equilibrium and phase transformation of duplex stainless steels are described, showing the basic data. The physical and mechanical properties of the duplex stainless steels are touched upon, and in particular the resistance to uniform corrosion and localised corrosion such as pitting corrosion, crevice corrosion and stress corrosion cracking are outlined, citing previously published data. Finally, the main environments in which duplex stainless steels are used and the results of their use are mentioned.

To grasp the long-term liquid ammonia SCC（Stress Corrosion Cracking）-resistance of surface softened clad steel plates applied to liquid ammonia tanks, the results of open inspections of two tanks were analyzed, and it turned out that: （1） Of the two TS610 MPa grade surface softened clad steel plates tanks that have been in use for 29 years, one tank has had no cracks, and the other tank had a cumulative total of six crack incidents. This number of crack incidents is remarkably smaller than the conventional TS610 MPa grade steel plates tank, and the long-term liquid ammonia SCC-resistance of surface softened clad steel plates was confirmed. （2） The cracks that occurred in the surface softened clad steel plates tanks were limited to the welded parts, and this phenomenon was the same as that of TS440 MPa SLA325A （JIS G 3126: Carbon steel plates for pressure vessels for low temperature service）, which has track records of application and operation to liquid ammonia tanks.

The performance of titanium（Ti）fibers with different platinum（Pt）plating thicknesses as the anode side porous transport layer（PTL）for proton exchange membrane water electrolysis（PEMWE）has been evaluated. Their mechanical strength in the thickness direction was about twice better than the carbon paper. Single-cell performance based on i-V measurements showed that Pt plating on Ti fibers contributed to the improvement of cell performance with the best i-V performance at a Pt plating thickness of 0.5μm. This is due not only to the reduction in contact resistance with the effect of the Pt plating, but also to the reduction in charge transfer resistance due to the high oxygen evolution reaction activity of Pt.