Effect of cold work and aging on mechanical properties of a copper bearing HSLA-100 steel

Influence of cold working and aging on the mechanical properties of a Cu-bearing HSLA-100 steel has been studied. The steel was given solution treatment at 1000°C, followed by cold rolling to 25, 50 and 80 pct deformations and aging at 600°C for various durations. Substantial improvement in hardness and UTS was observed in the peak aged condition of various treatments, but at the expense of ductility and impact-energy. Extensive scanning electron microscopic studies carried out on impact and tensile fracture surfaces suggest that poor impact energy and low ductility in peak aged condition could be associated with inhomogeneous deformation caused by the existence of coherent precipitates. Other parameters adversely affecting toughness and ductility in various stages of cold work and aging may include high stress concentration at high density dislocation network and dislocation-precipitate interface. Overaging in various treatments resulted in higher impact energy and ductility, presumably due to existence of incoherent precipitates and reduction in stress concentration at dislocation cell boundaries. It is observed that a good combination of high hardness and UTS with high impact energy and ductility could be obtained by a treatment suitable to cause coexistence of coherent and incoherent precipitates.