Study on the transformation and microstructure evolution during hot-charging rolling process of a weathering steel

The effect of hot-charging temperature (HCT) on the transformation and microstructure evolution of a weathering steel was investigated by metallography and dilatometry. The results show that the microstructure consisted of ferrite and pearlite in all specimens when the HCT was between 500 ∼ 850 °C. The difference was that pearlite amount increased obviously at 750 °C, which is detrimental to the plasticity of steels. The reason for more pearlite is that ferrite and austenite coexisted at 750 °C, which belongs to the dual-phase region temperature. The reversed transformation of ferrite to austenite happened and the pre-existing austenite became coarse during the secondary austenization. The carbon content in fine reversed austenite was relatively low, while the coarse austenite contained higher carbon content, which decomposed into blocky pearlite in the final cooling process. Therefore, to obtain the desirable ferrite phase, the HCT of about 750 °C should be avoided. The results provide theoretical reference for optimizing hot-charging rolling process parameters.