Enhanced upper shelf energy by ultrafine elongated grain structures in 1100 MPa high strength steel

The ultrafine elongated grain (UFEG) structure with strong <1 1 0>//RD fiber deformation texture was produced by warm caliber-rolling at 500 °C and final tempering at 550 °C, namely tempforming in the 1100 MPa medium carbon-low alloy steel with ultralow phosphorus and sulfur concentrations. Charpy impact tests were performed at temperature range of −196 °C to 150 °C on the UFEG structure along with a conventional quenched and tempered (QT) structure. A remarkable increase in upper shelf energy of 150 J was obtained in the UFEG structure without delamination, while that of QT structure was 97 J. The UFEG structures tempered at higher temperatures of 625 and 700 °C showed remarkable increase in Charpy absorbed energy from 150 J to 187 J and 203 J. Also, the QT structure absorbed almost same energy as UFEG structure at 700 °C. The enhanced toughness was discussed with tensile ductility, void nucleation and growth, and their relations to microstructure including the <1 1 0>//RD fiber deformation texture.