mathematical modelling of NbC precipitation in ferrite and prediction of tensile strength of hot rolled Nb added steels

초록

mathematical modelling was performed to desciribe the precipitation behaviour during γ/αtransformation and to predict the tensile strength of hot rolled Nb-containing microalloyed steel. The classical nucleation and growth theories were applied to analyze the kinetics of NbC precipitation which occurs not only on the moving γ/α phase boundary but in the ferrite matrix. It was found that the isothermal precipitation kinetics of interface and matrix precipitations exhibited the typical C- shape curve. Using the calculated results,the time-temperature-transformation-precipitation and the continuous cooling transformation-precipitation diagrams were constructed. For the prediction of tensile strenth, the strengthening effects of precipitation were formulated in the Hall-Petch type equation, and the predicted tensile property variation was analyzed based on the microstructural changes.