Nanostructured Eutectoid Steel Synthesized by Mechanical Alloying and Spark Plasma Sintering

Abstract

Blended elemental powders of Fe and C corresponding to the eutectoid composition of Fe–0.8 wt% C are subjected to mechanical alloying in a high‐energy SPEX‐8000 shaker mill. The milled powders and the as‐sintered samples are characterized by X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, and transmission electron microscopy methods for their crystal structure and microstructural features. A supersaturated solid solution phase of ferrite with a body‐centered cubic structure and containing 0.53 wt% C has formed after 15 h of milling. This is followed by formation of the cementite (Fe3C) phase with an orthorhombic structure, and its fraction increases with continued milling for 30 h. Spark plasma sintering of the milled nanocrystalline powders leads to the fabrication of dense bulk nanocrystalline steel samples. The microstructure of the as‐sintered sample has a very fine‐grained structure. On annealing at a high temperature of 900 °C, the expected lamellar structure of pearlite is clearly seen on the polished and etched surface. A lenticular structure of martensite has formed in the water‐quenched sample. The hardness of the samples in different heat‐treated conditions is measured and compared with the reference values.