Experimental Analysis of the Nb(C,N) Pinning Effects on Austenite Grain Growth Coupled with Mean-Field Simulations

The pinning forces of niobium carbonitrides (Nb(C,N)) on grain boundary (GB) migration in austenite (γ-Fe) are studied under isothermal annealing conditions at temperatures of 950, 1050, 1150, and 1250 °C. High-temperature laser scanning confocal microscopy enables in situ observations and quantification of the grain size evolution in 12 Fe–Nb–C–N alloys, each containing 0.15 wt% C, with Nb content ranging from 0 up to 0.08 wt% and N content ranging from 60 to 120 ppm. The quantified mean grain sizes are further applied for the parametrization of the Nb-induced solute drag effect and the Smith–Zener pinning forces due to Nb(C,N) in a grain growth kinetics model in MatCalc 6.04. In the first step the three Fe–C–N ternary reference alloys without Nb addition are used to determine the effective GB mobility for the base material. Then, the results of Nb-containing alloys with a wide variation of Nb and N serve for the parametrization of solute drag and pinning forces. The experimentally obtained results align strongly with simulation predictions for grain growth kinetics, supporting the model's applicability in describing pinning effects in the austenitic region.