Effect of annealing process on the abnormal grain growth behavior during carburizing of 20CrMnTi steel

Abnormal grain growth (AGG) as an important physical metallurgical behavior is to be avoided during carburizing due to its adverse effect on properties such as fatigue, impact toughness and the quenching distortion. In this work, two types of annealing process which produce different morphology of precipitated particles were conducted to investigate its effect on the subsequent austenite grain growth behavior during carburizing of 20CrMnTi steel. Calculation from Humphreys' model exhibited a good agreement with experimental observations, which indicates the large sized particle from high temperature annealing led to the locally insufficient pinning force for the blockage of grain boundary migration and is therefore responsible for the AGG. The isothermal precipitation kinetics for TiC particles is able to be described by the diffusional growth and LSW coarsening models with reasonable accuracy provided with the transition time from growth to coarsening stage. Design of microalloying and pre-treatment processing to suppress AGG can be assisted with the combinatory application of Humphrey's model and precipitation kinetics model.