Effects of Cr and B Contents on Volume Fraction of (Cr,Fe)2B and Hardness in Fe-Based Alloys Used for Powder Injection Molding

In the current study, Fe-based alloys were used for powder injection molding (PIM) parts with various qualities and hardness ranges by varying chemical compositions according to thermodynamically calculated phase diagrams. Their microstructure and hardness values were analyzed and compared with those of the PIM specimens made from conventional Fe-based alloy powders or stainless steel powders. The Cr-to-B ratio ( X Cr / X B ) and the sum of Fe, Cr, and B content ( X Fe + X Cr + X B ) were varied to design nine Fe-based alloy compositions based on the composition of Armacor “M” alloy powders (Liquidmetal Technologies, Lake Forest, CA). According to the microstructural analysis results of the cast and heat-treated Fe-based alloys, large amounts of (Cr,Fe) 2 B were formed in the tempered martensite matrix. The volume fraction of (Cr,Fe) 2 B was varied from 42 pct to 91 pct with alloy compositions, and these results were well matched with the thermodynamically calculated volume fractions of (Cr,Fe) 2 B. The hardness of the fabricated alloys was varied from 300 VHN to 1600 VHN with alloy compositions, and this value increased linearly with the increasing volume fraction of (Cr,Fe) 2 B. From the correlation data between the volume fraction of (Cr,Fe) 2 B and hardness, the high-temperature equilibrium phase diagram, which could be used for the design of Fe-based alloys with various fractions and hardness values of (Cr,Fe) 2 B, was made.