Improved distribution of nickel and carbon in sintered steels through addition of chromium and molybdenum

摘要

Ni rich/C lean ferrite and austenite are frequently found in the microstructure of sintered Ni containing powder metallurgy (PM) steels. These Ni rich areas are soft and prone to fracture during mechanical testing. To improve the microstructure homogeneity and mechanical properties, the influences of Mo and Cr additions were examined. The results showed that when Mo or Cr containing prealloyed powders were used as the base powder, more homogeneous microstructures and improved mechanical properties were attained. With the use of the Thermo-Calc software, the results of thermodynamic analysis indicated that these improvements were attributed to the reduction of the repulsion effect between Ni and C and thus the elimination of the soft Ni rich ferrite and austenite.