THERMAL COMPATIBILITY OF CHROMIUM STEEL AS METALLIC INTERCONNECTS FOR SOLID OXIDE FUEL CELLS

Among high temperature alloys, stainless steels in general and ferritic stainless steel in particular, offer the lowest cost and reasonable manufacturability. A disadvantage of the ferritic stainless steels however is their lower mechanical strength, especially at high temperatures required for operation of solid oxide fuel cells, SOFCs. Research and development has made it is possible to use ferritic stainless steels after improving its strength and corrosion resistance properties by addition of more chromium and other alloying elements. But this addition could also cause the secondary phases formation at the SOFCs operating temperature, resulting in a possible coefficient of thermal expansion, CTE, mismatch. The effect of additions of alloying elements, such as aluminum, manganese, molybdenum, titanium, and / or niobium on the CTE of high chromium steels (22-28%Cr) has been studied. With this respect various developed steels were melted in induction furnace, and then subjected to hot deformation to sheets. The chemical composition of the developed grades was determined using spectroscopic analysis. The microstructure and phases of the produced steel were determined by scanning electron microscope, SEM, and X-ray phase analysis. It was found that the CTE of most developed steels are in 100% matching with the CTE of the ceramic components of the SOFCs despite the difference in their chemical composition. Steels alloyed with silicon showed different behavior where their CTE are in mismatch to that of the ceramic components of the SOFCs. The bad effect of silicon on CTE can be improved by addition of another element like Mo.