Mechanical properties of low carbon steel hardened by the Fe ₂SiTi phase at high volume fraction

The addition of Si and Ti to low carbon steel allows to obtain a nanometric precipitation of an ordered intermetallic phase, Fe₂SiTi, with a volume fraction of the order of 6%; which is much higher than usual for microalloyed steels and more comparable to the situation encountered in aluminum alloys. The resulting precipitation hardening leads to extremely high mechanical properties, depending on the optimization of metallurgical route, which makes these materials very promising for the development of innovative, weight saving automotive solutions. In this contribution the precipitation sequence and kinetics are studied in details by a combination of experimental techniques including small angle neutron scattering and scanning or transmission electron microscopy. Some properties (yield stress, strain hardening, strain to fracture) are discussed in view of the measured precipitate characteristics, notably their size and volume fraction. The fracture mechanism, and particularly the occurrence of brittle fracture, is discussed in view of the state of precipitation.