Magnetic and mechanical properties of Cu-strengthened aged HSLA-100 steel

Magnetic and mechanical properties were evaluated for various heat-treated Cu-strengthened HSLA-100 steels. After austenitizing at 1183K for one hour and then water quenching, the material was aged at different temperatures ranging between 623K and 973K for one hour. Scanning and transmission electron microscopes with an energy dispersive X-ray attachment were used for microstructural analysis. Nanosize coherent copper precipitates caused an
increase in hardness with increase in ageing temperature. The steel exhibited maximum hardness at 773K followed by decrease in hardness with over-ageing. Copper precipitates coarsened and lost coherency during over-ageing. Ageing
behaviour again exhibited an increase in hardness at 973K due to the formation of new martensite islands. Magnetic hysteresis loop and magnetic Barkhausen emissions techniques were used to characterize the aged materials. No correlation was observed between the magnetic parameters and hardness. The results were explained by the fact that nanosize Cu precipitates, the size of which is much
smaller than the domain wall width, did not influence the magnetic domain
dynamics.