Control of grain size and sub-structure in plain carbon and high strength low alloy (HSLA) steels—the problem and the prospect

Abstract

The energy crisis has created the need to develop steels with better strength-toughness combinations than ever before to meet the stringent criteria for various applications in the energy production, transportation and usage. “Effective” grain size being one of the main factors that can simultaneously improve strength as well as toughness, the control of the final microstructure and the substructure of the steels has received considerable attention, particularly in the last few years. As a result many new thermochemical treatment techniques and compositional modifications have evolved to control the austenite grain size and morphology and in turn to control the final ferrite grain size and substructure. The paper reviews the state of art of structural improvement of plain carbon and HSLA steels discusses the underlying principles and mechanisms, points out the limitations of the present theoretical knowledge with reference to its application to commercial steels particularly, in the area of predicting the final structure when multiple alloying additions and/or complex thermomechanical processing techniques are involved. Potential areas of research are indicated. Finally the work being carried out at Laval in the area of structural control of carbon and HSLA steels are briefly discussed.