Effect of Mo on the Precipitation Behavior of FB780 Steel with a High Hole-Expanding Ratio at Different Coiling Temperatures

The investigations conducted on the effect of molybdenum (Mo) on the precipitation behavior of FB780 steel with the high hole-expanding ratio at different coiling temperatures have been limited. In the present study, base steel without the addition of Mo (Nb–Ti steel) and Nb–Ti–Mo steel with the addition of 0.191% (wt.%) Mo was prepared. Different coiling temperatures were selected on the basis of the process used in industrial production. The results indicated that Mo promoted precipitation at low coiling temperatures, while the volume fraction and size of the precipitates were increased and decreased, respectively, exerting a precipitation strengthening effect. The addition of Mo lowered the optimal coiling temperature, which would be beneficial in terms of energy saving. In addition, Mo reduced the row width of the interphase precipitation and improved the performance stability of the FB780 steel with high hole-expanding ratio.