Microstructure refinement strategies in carburized microstructures were evaluated because of their potential for improving the fatigue performance of case carburized components. Commercial 52100 steel was used to simulate the high carbon content in the case. Specimens were subjected to various thermal treatments in a quenching dilatometer. Reheating cycles to austenitizing temperatures were evaluated with respect to both prior austenite grain size (PAGS) and associated martensite and retained austenite refinement. Quantitative stereological measurements were performed to evaluate the micro-geometry of plate martensite and the size distribution of retained-austenite regions. Decreasing the reheating temperature resulted in finer PAGS and multiple reheating cycles resulted in a narrow PAGS distribution. Refinement in PAGS led to a reduction in martensite plate size and finer distribution of RA.