The modelling of microstructure evolution and final properties for Nb microalloyed steels

The production of Nb HSLA steels by hot rolling may entail a number of metallurgical processes. These can be broadly categorized by recrystallization, grain growth, transformation and precipitation. However each of these processes may in turn involve complex interactions. For example, the reheat temperature affects the state of the precipitates which in turn influences the recrystallization kinetics and subsequent grain growth. The recrystallization may also be either static, dynamic or metadynamic depending on the deformation and thermal history. In this paper individual models have been developed for each of these processes. These have then been assembled into a total microstructure development model which can then be incorporated into a process model for a given rolling mill. This has then been used to simulate the microstructure development during the hot rolling of plate, strip, gar and structurals. The model also predicts the final tensile properties and hence can be used to evaluate the effects on these of changes in composition and processing route