Simulated Coarse Grain Heat-Affected Zone Transformation Behavior of Newly Developed Zr-Ti-RE Deoxidized High-Strength Low-Alloy Steels with Extremely High Impact Toughness

The continuous cooling transformation behavior of the Zr-Ti-RE deoxidized high-strength low-alloy steel in the simulated coarse grain heat-affected zone at different cooling rates (corresponding to different t(8/5)) is investigated by a Gleeble 3800 thermomechanical simulator in combination with microstructure and mechanical properties analysis. The continuous cooling transformation curve in the simulated heat-affected zone is plotted, and the transformation law of M/A constituents is systematically investigated. It is found that with the increase of the cooling rate, the dominated microstructure is transformed from pearlite + ferrite into granular bainite and, finally, into lath bainite with the further refinement of M/A constituents. The steel exhibit excellent V-notch Charpy impact properties at -20 degrees C under typical heat inputs (20, 100, 500 kJ cm(-1)). Moreover, acicular ferrite formed on spherical Zr-Ti-RE composite inclusions are observed at the heat input of 100 kJ cm(-1). The low-temperature impact absorbed energy gradually decreases with the increasing heat input due to the coarsening of the microstructure, larger effective grain size, and the reduction in the number of high-angle variant pairs.