EXPERIMENTAL STUDY ON MICROSTRUCTURAL EVOLUTION AND DYNAMIC PROPERTIES OF A LOW-CARBON STEEL

In this study, dynamic tensile experiments were performed at a wide range of loading speeds from 1 mm/s to 1000 mm/s to investigate the microstructural evolution under high rates and ractccte-dependent behavior of mechanical properties of SM490 structural steel.The evolution of microstructure under different loading speeds or strain rate levels was observed.At a loading speed of 1 mm/s, partially broken original ferrite grains under the applied tensile loading resulted in the formation of smaller ferrite grains and packets of dislocation debris.The debris could be observed to be located inside original ferrite grains, while pearlite grains tended to move closer together, becoming the thin layers of pearlite.At the highest loading speed, pearlite thin layers were fully developed leading to the formation of the layers of ferrites.The averaged grain size tended to decrease with the further increase of loading speed.Both yield stress ( y ) and tensile strength ( u ) displayed rate-dependent behavior, in which higher y could be observed at higher loading speed levels.In contrast, the work hardening () showed different behavior. exhibited a slight increase when the loading speed increased from 1 mm/s to 10 mm/s, and then gradually decreased with the increasing speed of loading.Another plastic property () showed a decrease from 10.7 to 5.28 with increasing loading rate from 1 mm/s to 1000 mm/s.Finally, strain rate sensitivity values of 0.0428 from the y data and 0.0226 from the u data were well determined and reported for the tested material.