Structure-mechanical property relationship in low carbon microalloyed steel plate processed using controlled rolling and two-stage continuous cooling

Controlled rolling followed by two-stage continuous cooling was carried out in-house to study the microstructure and mechanical properties of a low carbon microalloyed steel plate of medium thickness gauge. The objective of the study was to develop a process of obtaining excellent mechanical properties (strength, toughness, and ductility) in a microalloyed steel. The process is industrially viable because it does not require high degree of cooling and large reduction during thermo-mechanical processing. The study demonstrates that it is possible to obtain yield strength, tensile strength, elongation, and percentage reduction in area 585 MPa, 680 MPa, 29.5%, and 55%, respectively, with total deformation reduction of 50% and small first stage cooling rate. The total impact energy at -20 degrees C was 140 J. The microstructure consists of polygonal ferrite and acicular ferrite. The strain-induced 20-30 nm precipitates act as nucleation sites for acicular ferrite. The acicular ferrite contributes to high strength and good toughness, while polygonal ferrite provides excellent elongation. (C) 2013 Elsevier B.V. All rights reserved.