High Strength High Ductility Low Alloyed Steel

Annealed Martensite Matrix (AMM) concept was studied on two steel grades with low alloyed base composition of Fe-C-Mn-Si and two levels of Nb. Conditions for the thermal treatments were selected based on the experimental dilatometry tests and thermodynamic calculations. Annealing trials with short austempering holding were performed in the laboratory salt pots. Mechanical properties of heat treated steels have been investigated by tensile tests. Associated microstructures have been analyzed using Scanning Electron Microscopy as well as magnetization saturation method for measuring retained austenite fractions. Excellent strength-ductility balance was obtained due to the ultra-fine multiphase structure and high amount of stable retained austenite.