Effect of Addition of Carbon on Sintering Behavior of Fe-Ni Compacts Shaped by Injection Molding

The effect of C addition affecting sintering behavior and mechanical properties of sintered bodies on Fe-4%Ni compacts made by injection molding has been studied. Specimens were made of carbonyl Fe(0.05 mass% C, 0.2 mass% O) and carbonyl Ni powder having average diameters of 5 and 2 mu m, respectively, and the amount of C powder added to the specimens was from 0 to 0.8 g per 100 g of Fe-4%Ni mixed powder. The compacts were debound in air at temperatures ranging from 503 to 553 K for 7.2 ks. They were then sintered in a reduced pressure of 1 Pa at 1523 K for 7.2 ks. It was found that there exists a critical debinding temperature above which oxides precipitate in sintered bodies and below which no oxide is formed. As the amount of added C is increased, the critical temperature becomes higher. C addition strongly affects the densities and mechanical properties of sintered bodies. Below the critical temperature, for instance, C addition increases the tensile strength and it lowers the elongation.