Microstructure and Properties of Nanoduplex Bainite-Austenite Steel for Ultra-High-Strength Plates

Basing on experimentally determined continuous cooling transformation (CCT) and time-temperature-transformation (TTT) diagrams, examination of microstructure by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques and measurements of mechanical properties an optimized chemical composition of a nanostructured bainite-austenite steel intended for production of plates is proposed. The optimized composition enables to manufacture ultra-high-strength plates up to 15mm in thickness at relatively low cost of alloying elements and with characteristics facilitating industrial production. Experimental flat bars manufactured in semi-industrial conditions of the developed steel containing 0.56% C, 2.00% Mn, 1.76% Si, 1.29% Cr, and 0.76% Mo after transformation at 225 degrees C for 60-72 h show good combination of mechanical properties: ultimate tensile strength over 1.9 GPa, yield strength in the range of 1.3-1.4 GPa, total elongation about 15% and hardness at the level of 600 HV.