ABSTRACT
Carbide-free bainite steels have been extensively studied because of their excellent tensile strength and toughness. Caballero and Bhadeshia (Bhadeshia 2013a, Bhadeshia 2013b, Lonardelli et al. 2012) designed a new kind of carbide-free bainite steel, which was called the “nanobainite steel” based on the theory of phase transformation strengthening. By isothermally treating at 200 °C for 5 days, the ultrafine microstructure with a thickness of 20-40 nm can be obtained. Nanobainite consists of a mixture of two phases, namely bainite ferrite and carbon-enriched retained of austenite. The ultimate strength of nanobainite steels is 2.5 GPa, and Vickers hardness is more than 600 HV. The best way of developing low-alloy high-strength steels is by using nanobainite because of its remarkable comprehensive mechanical properties, low cost and simple processing technique.
