Application of Microalloying for Controlling Recrystallization and Grain Growth During Downstream Steel Processing

Abstract Downstream processing of steel products involves a large variety of heat treatments in the ferrite as well as in the austenite phase. Different from austenite conditioning in the upstream processing stage, deformation and temperature schedules are usually decoupled in downstream processing. Fundamental characteristics of microalloying elements regarding their effects on recovery, recrystallization, phase transformation, and grain growth during downstream processing will be reviewed. Relevant characteristics of microalloying elements are the atom size, the solubility and temperature stability of related carbides or nitrides, the tendency of segregating at grain boundaries, dislocations and point defects, as well as the diffusivity. The various interactions and resulting microstructural effects will be demonstrated for several industrial steel developments. The selected examples cover microalloy effects in ferrite and austenite phases, under slow and fast thermal cycles, as well as during short and long heat treatment times. Based on the observations and the related interpretation, a qualitative understanding of the microalloy interactions will be developed that is generally applicable despite the considerable variation of processes and products. It will also be highlighted how appropriate process and microalloy adaptations resulted in remarkable product optimization under industrial conditions.