Refined and Uniform Microstructure with Superior Mechanical Properties in Medium Plate Microalloyed Steel with Reduction in Mn-Content during Ultrafast Cooling

We describe here the relationship between electron microscopy and mechanical property studies in industrially processed titanium bearing microalloyed steel plates that involved processing using the recently developed ultrafast cooling (UFC) approach. Given that the segregation of manganese is generally responsible for microstructural banding in low-alloy steels, which can deteriorate the tensile property in the direction of thickness, the manganese-content was reduced by ~0.6-0.8% with the objective to obtain uniform microstructure across the thickness of the steel plate. Besides, non-uniform distribution of accelerated cooling along the thickness direction also leads to inhomogeneous microstructure across the plate thickness. In order to obtain near-uniform microstructure and similar mechanical properties from the surface to the center of plate, fast and effective cooling process is necessary. In this regard, refined and uniform microstructure that was free of microstructural banding was obtained via UFC process across the plate thickness, with strict control and faster cooling rate on the run-out table. Furthermore, grain refinement and random precipitation in the ferrite matrix contributed ~100 MPa toward yield strength. The study underscores the potential of processing medium and heavy plates of titanium bearing microalloyed steels plates with uniform and refined microstructure across the thickness via thermo-mechanical controlled processing (TMCP) involving UFC.