Favorable Modulation of Microstructural Constituents in Governing Low Temperature Toughness Induced Through a Three-Stage Cooling Trajectory

Abstract

Low temperature toughness continues to be a major challenge and significant efforts are being made in this regard. We address the challenge of scientific and technological gap through the design of a novel process involving a three-stage cooling trajectory during thermo-mechanical controlled processing to process high strength low alloy heavy plates with high low temperature toughness. Interestingly, in contrast to the conventional continuous cooling process, the three-stage cooling trajectory enabled us to obtain a favorable acicular ferrite toughening enhancing microstructure. On the other hand, martensite–austenite islands were characterized by small dot morphology in the three-stage cooling trajectory that restrict crack nucleation and prevent debonding from the matrix. The low temperature impact toughness at − 80 °C exceeded ~ 500% in relation to the conventional process. The mechanism of formation of acicular ferrite and its impact on toughness is critically analyzed experimentally via electron microscopy and electron back scattered diffraction analysis and theoretically discussed in the context of toughening and crack arresting mechanism. Low temperature toughness in heavy steel plates continues to be an aspect of significant concern. We address the challenge of scientific and technological gap through the design of a novel process involving a three-stage cooling trajectory during thermo-mechanical controlled processing (TMCP) to process high strength low alloy (HSLA) heavy plates.