Effect of Hot-Forging Heating Temperature and Time on the Austenite Grain Size of Pseudo-Carburized 20CrMnTi

In this work， the phase transformation and precipitation behavior of 20CrMnTi steel after forging and the morphology of the prior austenite grain after isothermal normalizing and pseudo-carburizing under different forging heating processes were investigated. Results show that， for the conventional hot-rolled bars， the normal prior austenite grain morphology after carburizing can be obtained under the forging heating process of 1 220 ℃×2， 3， 5 and 10 min. Using the pretreatment， i.e.， homogenized by 1 000 ℃×2 h， deformed at 950 ℃ and then furnace-cooled from 700 ℃ to room temperature， （Nb， Ti）C fully precipitated from the hot-rolled state. In order to avoid the abnormal growth of the prior austenite grain after the same isothermal normalizing and carburizing process， the forging heating time at 1 220 ℃ should be no less than 5 min.Under the design of titanium reduction on the surface of test steels with different compositions， ensuring the sufficient re-dissolution of microalloyed carbonitrides through the heating temperature and time before forging can also achieve no mixed grains in the 960 ℃ pseudo-carburizing process. Maximizing the avoidance of excessive precipitation of microalloyed carbonitrides in hot-rolled bars can reduce the temperature and time required for the re-dissolution of microalloyed carbonitrides during the forging heating process in downstream forging plants.