The Low Temperature Impact Behavior and Ductile-Brittle Transition of Nanocluster-Strengthened Steel

A series of impact tests within the temperature range of -180~20°C were applied to study the low temperature impact behavior and ductile-brittle transition of the 700MPa nanocluster-strengthened steel. The results clearly demonstrated that temperature had a significant effect on impact properties. As the temperature decreased, the impact absorption energy and shear section ratio were correspondingly reduced, and the micro-morphology was changed gradually from ductile fracture to brittle fracture. The ductile-brittle transition temperature (DBTT) range of was between -80°C and -160°C. The fitting results of the Boltzmann function for the ductile-brittle transition curve were in good agreement with the experimental observations. Specifically, the DBTT was determined to be -110±1°C, which suggested good low-temperature impact toughness. The outstanding low-temperature impact toughness of the test steel is mainly due to its low C content and high Ni content, fine effective grain size (EGS), and a large number of Cu-rich nanoscale precipitates. Furthermore, the effect of temperature on dislocation movement plays a major role in the ductile-brittle transition.