Nanostructured/ultrafine multiphase steel with enhanced ductility obtained by mechanical alloying and spark plasma sintering of powders

A nanostructured/ultrafine steel with a complex microstructure comprising bainitic ferrite, austenite and martensite was obtained by mechanical alloying and spark plasma sintering of powders. Transmission electron microscopy and X-ray diffraction analysis were employed to investigate the microstructural morphologies and the nature of bainitic ferrite and retained austenite formed during sintering process. The presence of a complex microstructure with elongated ferritic lamellae separated by thin layers of retained austenite was revealed. Some ferritic equiaxed grains are also present. The steel displays a large uniform plastic deformation, thanks to its work hardenability provided by the microstructural characteristics: the bimodal distribution of ferrite, the multiphase microstructure and the TRIP phenomenon provided by austenite.