Effects of Rare Earth Lanthanum on the Solidification Structure and Hot Ductility of Fe-43Ni Expansion Alloy

Abstract

AbstractEffects of lanthanum content on the solidification structure and the hot ductility of Fe-43Ni expansion alloy were investigated, the corresponding mechanisms were also discussed. The results showed that the macrostructures of the alloys were first significantly refined with increasing lanthanum content in the range of 0~0.025 % and then became coarse again with lanthanum content up to 0.04 %. La2O2S inclusions can serve as the effective inclusions sites promoting the refinement of the macrostructures. The changes of the macrostructures were influenced by the quantity density and the size distribution of La2O2S inclusions. The addition of 0.01–0.025 % lanthanum can improve the hot ductility over the whole testing temperature range, especially at 1000–1050 °C. The improvement of the hot ductility was mainly associated with the grain boundary strengthening and the acceleration of dynamic recrystallization by adding lanthanum. With addition of 0.04 % lanthanum, the hot ductility of the alloy became deteriorated, which was owed to the presence of brittle Fe-Ni-La intermetallic compounds.