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 conditionsat temperatures of 950, 1050, 1150, and 1250 °C. High-temperature laserscanning confocal microscopy enables in situ observations and quantification ofthe 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 to120 ppm. The quantified mean grain sizes are further applied for the parame-trization of the Nb-induced solute drag effect and the Smith–Zener pinning forcesdue to Nb(C,N) in a grain growth kinetics model in MatCalc 6.04. In the first stepthe three Fe–C–N ternary reference alloys without Nb addition are used todetermine the effective GB mobility for the base material. Then, the results ofNb-containing alloys with a wide variation of Nb and N serve for the parame-trization of solute drag and pinning forces. The experimentally obtained resultsalign strongly with simulation predictions for grain growth kinetics, supportingthe model’s applicability in describing pinning effects in the austenitic region.RESEARCH ARTICLE lwww.steel-research.desteel research int. 2025, 2500095 2500095 (1 of 15) © 2025 The Author(s). Steel Research International published by Wiley-VCH GmbH