Control of precipitation morphology in the novel HSLA steel

Vickers hardness data revealed that, in specimens isothermally held at 650 °C without hot deformation, the range of hardness distribution was 180-320 HV 0.1 after 5 min of isothermal holding, and 170-250 HV 0.1 after 60 min. For specimens isothermally held at 650 °C with 20% hot deformation at 900 °C, the range of the hardness distribution was 200-260 for 5 min of isothermal holding, and 210-240 for 60 min. Therefore, the average microhardness decreased with the isothermal holding temperature and time, and a narrower range of hardness distribution occurred in specimens that underwent hot deformation. The narrower Vickers hardness distribution reflects more uniform precipitation in each ferrite grain.