Application of quenching–partitioning–tempering process and modification to a newly designed ultrahigh carbon steel

Graphical abstract: - Highlights: • The novel process "quenching–partitioning–tempering" was applied to ultrahigh carbon steel for the first time. • The novel multi-component modifier has excellent effect on the solidification microstructure. • The heat treatment cycle of homogenization is greatly shortened. • UHCS with excellent comprehensive properties has been obtained under industrial conditions. - Abstract: The applicability of quenching–partitioning–tempering (Q–P–T) process to an ultrahigh carbon steel (UHCS) has been investigated by means of optical microscopy (OM), scanning electronic microscopy (SEM) combined with energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and mechanical property tests. The molten steel was modified with a multi-component modifier-rare earth and a low melting point alloy (Al–Bi–Sb) before casting into iron molds. Observations showed that the carbide exists as partly isolated and fine blocky structure in as-cast microstructure, indicating good effect of modification. After the Q–P–T treatment, carbon was partitioned into austenite from martensite, creating a mixture of carbon-depleted martensite, carbon-enriched retained austenite and fine carbides. This kind of microstructure leads to a much higher impact toughness, 32 J/cm2, in comparison with the value, i.e., no more than 20 J/cm2, of the conventional quenching and tempering (Q–T) treatment at the same hardness level. Furthermore, wear-resisting property of the steel has also been investigated. It showed that the Q–P–T treated steel has better abrasive wear resistance, about 18% increased, compared with the Q–T treated alloy under high load conditions