Mechanism of Grain Boundary Embrittlement in Fe-Ni-S Alloys

摘要

The hot forming of Fe-Ni alloys such as Invar (Fe-36Ni) is often limited by grain boundary fracture. Grain boundary fracture is generally caused by segregation of S and/or precipitation of nitrides, carbides and sulfides at grain boundaries. It has been shown that very low S concentration (～ a few 10 mass-ppm) is enough to cause hot ductility loss. However, since S segregation at grain boundaries is often observed in Fe-based alloys and steels irrespective of the Ni addition, it is still not clear why hot ductility loss due to grain boundary embrittlement is enhanced in Fe-Ni alloys.