The mechanical properties of a bainitic microstructure with slender ferrite plates (20-65 nm in thickness) in a matrix of carbon-enriched retained austenite have been characterized. The microstructure is generated by isothermal transformation at temperatures in the range 200-300ºC. A yield strength as high as 1.5 GPa and an ultimate tensile strength between 1.77 to 2.2 GPa has been achieved, depending on the transformation temperature. Furthermore, the high strength is frequently accompanied by ductility ( ≤ 30%) and respectable levels of fracture toughness (< 45 MPa m 0.5). This unusual combination of properties is attributed to the exceptionally fine scale of the carbidefree bainitic microstructure and the associated retained austenite.
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