Effect of interrupted accelerated cooling on mechanical properties and structure of vanadium and titanium microalloyed steel bars

Abstract

The effect of interrupted accelerated cooling, in the range from finish rolling temperature to 600°C at rates up to 17 K s⁻¹, on the mechanical properties and structure of V and Ti microalloyed steel bars was investigated. The influence of reheating temperature, in the range 1000–1250°C, and finish rolling temperature (starting cooling temperature), in the range 800–1000°C, was also studied. Interrupted accelerated cooling caused a double enhancement of grain refinement and an increase of precipitation strengthening resulting in increases of yield strength up to 750 MN m⁻² and elongations greater than 25%. Increasing the reheating temperature to 1100 and 1250°C for V and Ti steels, respectively, enhanced the increment of precipitation strengthening due to accelerated cooling, but had no effect on grain refinement. Interrupted accelerated cooling was found to be most effective for improving yield strength when it is started at higher temperatures in the γ region. Accelerated cooling effectively inhibited bainite formation and produced very fine grain size at high finish rolling temperatures. This technique is therefore very attractive for processing of microalloyed steels because of the possibility of attaining very fine grains without decreasing the finish rolling temperature, thus reducing the process time.

MST/1180