The decomposition of austenite in an experimental UHSS Cr-MoMo(VI) ions-V was analyzed by dilatometric analysis and continuous and controlled cooling conditions at different rates: 0.016, 0.083, 0.250, and 0.416 °C s−1. During the analysis, it was observed that exists two behaviors during the decomposition of austenite depending on the cooling rateCooling Rate; at a very low rate (0.016–0.083 °C s−1), the decomposition of austenite occurs in two stages of transformation, and with a low rate (0.250–0.416 °C s−1), decomposition occurs in a single transformation stage. The phases associated with a very low cooling rateCooling Rate were ferrite and bainite, and the phase associated with a low cooling rateCooling Rate was bainite. From the dilatometric analysis, the critical austenite decompositionAustenite Decomposition temperaturesTemperature were determined by \(A{r}_{3}\) , \({B}_{s}\) , and \({B}_{f}\) , and the continuous cooling transformation diagram was constructed, indicating the corresponding phase fields during the austenite decompositionAustenite Decomposition stage. Finally, the microstructureMicrostructure was analyzed by optical microscopy, relating to measurements of Vickers microhardnessMicrohardness dependent on the cooling rateCooling Rate, observing an increase in microhardnessMicrohardness with increasing cooling rateCooling Rate.