An Answer to the Structure of Carbon Cluster in Low-Temperature Aged Ferritic Low-Carbon Steel

The morphology and structure of carbon cluster in a low temperature aged low-carbon ferritic steel were examined by transmission electron microscopy and atomically-resolved scanning transmission electron microscopy. The needle-like carbon cluster was found parallel to<001> direction to the matrix. The crystal structure of the carbon cluster was determined as martensite-like body-centered tetragonal structure via measurement of lattice constant of them, which suggested that the carbon cluster was supersaturated with carbon atoms occupying specific octahedral sites orderly. The carbon content of the carbon cluster was estimated as 0.11 mass%, five times larger than the solubility of carbon in the alloy.