A nanostructured dual-phase microstructure has been achieved by a quenching–partitioning–tempering treatment of a high-carbon super bainitic steel. Observations showed that the nanostructured steel consisted of fine martensite, retained austenite and carbides. The hardness reached up to approximately 700 HV1. X-ray diffraction analysis indicated that carbon was partitioned into austenite after martensitic transformation, creating a mixture of carbon-depleted martensite, carbon-enriched retained austenite and fine carbides, with a hardness that exceeds even that of low-temperature super bainite.