Effects of Alloy Elements Nb and V on the Microstructure and Expansion Property of 4J32 Austenite

Using optical microscope， scanning electron microscope， and dilatometer etc， this work investigated the effects of alloy elements Nb and V on the austenite microstructure and expansion property of 4J32 alloy. The results indicated that when the addition amount of Nb was 0.1%， the pinning effect on the austenite grain boundaries was not apparent， and abnormal grains growth occurred in the specimens. However， when the addition amounts of Nb reached 0.3% and 0.4%， the microstructure of the specimens was homogeneous， and the average grain sizes decreased by 24.6% and 32.3%， respectively.When the addition amounts of V reached 0.3% and 0.4%， the grain sizes decreased by 14.4% and 16.3%， respectively. The refining ability of Nb on the austenite grains and the homogenization ability of the microstructure of the super Invar alloy were superior to those of V. When the addition amount of Nb reached 0.4%， NbC was mainly distributed along grain boundaries. When the addition amount of Nb was less than 0.4%， NbC distributed in a small amount within grains. The number and size of NbC precipitates increase with the increase in the Nb content. The average linear expansion coefficient α_{20-100 ℃}≤1.0×10^-6/℃ of the experimental alloys with the addition of Nb and V met the application requirements. Overall， the alloys with the addition amounts of 0.3% for both Nb and V showed a more appropriate combination of microstructure homogeneity， grain refinement， and expansion coefficient.