Thermomechanical processing(TMP) or disciplined hot deformation has had a dramatic effect on structural steels over the last quarter-century. It is now well-recognized that both the strength and the resistance to brittle fracture can be improved, in virtually any steel, through the use of proper TMP. Improvements in conventional steel and the development of new steels have been the benefits of the widespread application of TMP. The principal goal of TMP is to achieve microstructural refinement in the as-rolled austenite prior to transformation. Grain refinement is based on controlling the kinetics of recrystallization and subsequent grain coarsening which occur during the interpass time between deformations in a multi-pass schedule. The resulting effects of recrystallization and grain coarsening, and their influence on grain size, are determined by the balance struck between the operative driving forces and retarding forces. In general, only steels with certain definite characteristics can be easily processed by TMP. While plain carbon and most low alloy steels are not suitable for TMP, they can be made so through the addition of the microalloying elements Nb, Ti or V. This paper will discuss modem TMP, the retarding forces which are critical to its success, and the microalloying required for successful implementation. Examples of successful application of TMP will be given.
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