Austenite Grain Growth and its Equation in the Austenitizing Process for 700 MPa Grade High-Strength Steel

Austenite grain growth behavior in the austenitizing process for 700 MPa grade high-strength steel was investigated. The results revealed that the austenite grain size is increased from 25.4 & mu;m to 52.8 & mu;m with the increase of heating temperature from 1150 & DEG;C to 1250 & DEG;C at holding time of 6 min. Austenite grains grow up with the increase of holding time and are not as significant as heating temperature. The number of undissolved precipitates decreases, and the precipitate size increases with the increase of heating temperature. Additionally, equations for predicting the austenite grain size and their distribution were fitted. The predicted austenite grain sizes and their distribution agree well with the measured data with R-2 of 0.968 and RMSE of 4.15 & mu;m. Combining the contour maps of w and austenite grain size under different heating conditions, the optimum heating conditions can be obtained as a heating temperature of 1423 K and a heating time of 1123-1200 s if the grain size needs to be controlled as 45-48 & mu;m, providing guidance for obtaining uniform and fine initial austenite grain size.