Nanolath martensite-austenite structures engineered through DQ&P processing for developing tough, ultrahigh strength steels
Sumit Ghosh, Ilkka Miettunen, Mahesh C. Somani, Jukka Kömi, David Porter
Abstract
A novel processing route comprising thermomechanical rolling followed by direct quenching and partitioning (DQ&P) was designed for developing tough, ductile, ultrahigh strength steels using 0.4 wt% carbon steels. A preliminary characterization of a laboratory-rolled, high-silicon DQ&P steel revealed an excellent combination of mechanical properties comprising high yield and tensile strengths (~1025 and ~2137 MPa, respectively), besides reasonable elongation (≈ 12%) and good impact toughness (T28J temperature ≈ −10 °C). The high mechanical properties are attributed to the formation of desired nanolath martensite-retained austenite (≈ 15%) structures. Features such as nano-twinned martensite, interlath austenite etc. were comprehensively characterized through high-resolution transmission electron microscopy. Attempts have been made to detect possible existence of metastable hexagonal omega phase within the boundaries of nano-twinned martensite and understand its nature of formation.