Research outline of Stack Materials Group

R & D of metallic separator with high corrosion resistance
♦ Although graphite separator is generally used for mobile fuel cell at present, there are several problems for mass-production such as not-easily forming, heavy weight, high cost performance etc. Therefore, metallic separator with high-reliability, long life, high cost performances are strongly required to be developed.
♦ The goal of the research is to propose a new design concept for low environmentally friendly and reusable metallic separator for PEFC by using low Ni and high nitrogen austenitic stainless steel (HNS), which was developed in NIMS. HNS is fabricated by the addition of nitrogen to Fe-Cr series alloys under high pressure condition. HNS has fully austenitic phase after solution treatment with two times in tensile strength compared to those of conventional stainless steels. The corrosion resistant property is equivalent to that of Ti. Ni-free HNS is also available by the addition of N. In order to develop good metallic separator several key technologies should be taken into account such as ultra-fine grained process, structure control process and so on.

Research topics

♦As research topics in the Stack Materials Group
1)Base material (HNS)
HNS was developed as one of the new materials as one of the targets of the Ultra-Steel Projects, in NIMS since 1997. HNS is usually fabricated by using a pressurized-ESR furnace developed in NIMS. Both types of HNS, low Ni HNS and Ni-free HNS are available by using this facility.

2)Strength
In spite the fact that HNS has relatively higher tensile strength than 1000-1200 MPa after solution treatment, elongation of HNS is almost equivalent to that of conventional austenitic stainless steel. High strength of material is one of the important properties for light-weighting of metallic separator.

3)Corrosion properties
HNS has an excellent corrosion resistant property especially in seawater because this material was originally developed for the use of marine environment. As for one of the problems related to fuel cell, corrosion resistant property under strong acid condition is required. It was already found that HNS could be endured the corrosion conditions down to pH=0.3 by choosing appropriate alloying elements.

4)Formability
Hardness of HNS increases with increasing nitrogen content as an interstitial element due to solution strengthening by nitrogen. Apart from carbon content, which is also an interstitial element, HNS is not brittle and the formability to be processed to wires or thin plates are maintained to some extent.

Members in Stack Materials Group

List of recent publications