2026 Agbedo CA6NM Transformation Temperatures

Accurate prediction of the critical transformation temperatures Ac1 and Ac3 is essential for the heat treatment of CA6NM cast martensitic stainless steel. This study quantifies the influence of alloy composition, heating rate, and prior austenite grain size on the critical temperatures through dilatometric measurements and statistical modeling. Six heat treatment conditions varied prior austenite grain sizes from 75 to 247 µm. Results indicated that grain size variations produced only minor changes in Ac1 and Ac3, showcasing a weak dependence of transformation temperatures on grain size within the investigated range. Conversely, both chemical composition and heating rate significantly affected the critical temperatures, with increases of approximately 100°C for Ac1 and 115°C for Ac3 as the heating rate rose from 0.1 to 10 °C/s. A regression-based predictive model incorporating alloy composition and heating rate was developed and validated, demonstrating strong agreement with experimental measurements (R² = 0.972, RMSE = 4.78 °C) and markedly improving prediction accuracy compared to thermodynamic calculations using Thermo-Calc and previously published empirical models. The findings provide a refined framework for predicting transformation temperatures in CA6NM under continuous heating conditions.