Effects of Chromium Addition on Preparation and Properties of Bulk Cementite

Bulk cementites with the Cr contents of 0, 3. 01, 6. 03, 8. 22, and 11. 51 mass% were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The results indicated that when the Cr content was low (3. 01 mass%), the phases were composed of cementite with a small amount of α-Fe at a sintering temperature of 1 173 K, but the microstructure became single-phase alloyed cementite as the Cr content was further increased. It showed that microaddition of Cr was beneficial for promoting the formation of cementite. Furthermore, the mechanical performance of cementite can be greatly affected by the variation of Cr content. The hardness, elastic modulus and elastic recovery presented a remarkably increasing tendency with the addition of Cr, and the maximum micro-hardness and elastic modulus values reached 1 070. 74 HV and 199. 32 GPa, respectively, which were similar to the precipitation phase (cementite) obtained by melting and casting techniques. Moreover, when the Cr content was below 11. 51 mass%, the crystal structure of Fe₃C-type cementite would not change with increasing the Cr content. A Cr atom replaced an Fe atom in the lattice of the cementite, and voids appeared when Cr was doped into the cementite at content of about 11.51 mass%, causing the relative density to decrease.