This study proposes a new calculation model for predicting the prior-austenite grain size in the weld heat affected zone (HAZ) of Ti bearing steel. The model considers the solute-drag effect of multi-element systems based on the theory of grain boundary movement by elemental transition. The pinning effect of TiN is also taken into account. Additionally, for modeling, the grain boundary segregation of each element and the weakening of the pinning effect due to the dissolution of TiN during the thermal cycle are taken over. The prior-austenite size in HAZ of 0.05C-0.14Si-1.6Mn-0.012Ti was calculated using the proposed model during thermal cycle heated at a temperature ranging from 1473 to 1673 K. The calculation was also conducted using the conventional theoretical model. Furthermore, the grain growth behavior was experimentally examined in the simulated HAZ test specimen. As a result, the theoretical grain growth estimated by the proposed model was consistent with the experimental grain growth. In particular, at a thermal cycle of over 1623 K, which dissolves TiN, the proposed model properly describes the actual grain growth behavior in HAZ of low alloy steel bearing Ti compared with the conventional model. Additionally, the calculation considering temperature gradient in the area from the fusion line to 0.5 mm HAZ was performed. This calculation method was found to provide a good analysis of the austenite grain growth behavior.
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