Peculiarities of Austenite Grain Formation in Improving Steels of Type 45 upon Heating in the Austenitic Region

The features of formation of austenite grains in structural steels 40Kh, 45, 55, and 40 KhNM upon heating from Ac1 to 1250°C are considered. A nonmonotonic character of change in the size of austenite grain with an increase in the heating temperature for quenching is found. It is shown that the first (and strongest) grain refinement in steel 45 occurs upon heating to temperatures of Ac3 and slightly higher. The second, less pronounced, refinement of the austenite grain is observed upon heating in the γ region significantly above the temperature of Ac3 and is accompanied by an increase in impact strength. Outside this interval, the KCU values measured at 20°C decrease with increasing heating temperature for quenching.