Investigation on the hot ductility of Fe-36Ni invar alloy with cerium addition

The hot ductility of Fe-36Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850-1,050 degree Celsius, and the improvement mechanism of the hot ductility was analyzed using a combination of SEM, EDS, and OM. The results indicated that Fe-36Ni invar alloy exhibited poor hot ductility below 1,050 degrees Celsius, which was mainly attributed to weak grain boundaries and the action of grain boundary sliding. However, the alloys with cerium contents of 0.016% and 0.024% both demonstrated substantial improvement in the hot ductility over the entire testing temperature range. The observed improvement of the hot ductility of the alloy with 0.016% cerium at 950 degrees Celsius and the alloy with 0.024% cerium at 900 degrees Celsius was associated mainly with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of cerium reduced the segregation of sulfur at grain boundaries and refined the grain structure.