Effects of friction stir welding on the coefficient of thermal expansion of Invar 36

The purpose of this investigation was to determine if the change in coefficient of thermal expansion observed in the fusion welding of Invar 36 could be avoided by friction stir welding (FSW). Invar 36 steel plates (0.5x3.75x24 inch) were friction stir welded using both polycrystalline cubic boron nitride and W-25% Re pin tools. Coefficient of thermal expansion is critical to Invar applications such as aircraft composite tooling and high precession measuring devices. Since FSW requires no filler material, problems associated with the filler metal and liquid state were avoided. This paper describes the process parameter development, the effect of process parameters, and pin tool materials on friction stir welded Invar's CTE.