Abstract: Effects of Zr on the solidification structure and hot ductility of Fe-36Ni invar alloy were investigated,and the corresponding mechanisms were also discussed. Results showed that a great amount of high-melting point compounds(ZrO₂) formed in the alloy with the addition of 0.081% Zr(mass fraction). Based on the theory of lattice misfit,the lattice misfit between(001) surfaces of ZrO₂ and the Fe-36Ni matrix is 0.77%,which is relatively low. Therefore,ZrO₂ could serve as the effective core of heterogeneous nucleation,resulting in remarkably shorter and thinner columnar grains,which increases the proportion of equiaxed grains and refines the solidification structure. The alloy has a bad hot ductility below 1050℃,which is mainly attributed to weaker boundaries and grain boundary sliding. However,the hot ductility of the alloy is highly enhanced at 950~1000℃ because of the addition of 0.081% Zr,which could refine grain sizes to hinder grain boundary sliding,strengthen grain boundaries,and promote grain boundary movement.The alloy has a good hot ductility over 1050℃ for the existing of dynamic recrystallization.