Abstract
The pinning effect is useful for restraining austenite grain growth in low alloy steel and improving heat affected zone toughness in welded joints. We propose a new calculation model for predicting austenite grain growth behavior. The model is mainly comprised of two theories: the solute-drag effect and the pinning effect of TiN precipitates. The calculation of the solute-drag effect is based on the hypothesis that the width of each austenite grain boundary is constant and that the element content maintains equilibrium segregation at the austenite grain boundaries. We used Hillert’s law under the assumption that the austenite grain boundary phase is a liquid so that we could estimate the equilibrium solute concentration at the austenite grain boundaries. The equilibrium solute concentration was calculated using the Thermo-Calc software. Pinning effect was estimated by Nishizawa’s equation. The calculated austenite grain growth at 1473–1673 K showed excellent correspondence with the experimental results.
Highlights
High heat input welding is often employed in industrial fields such as ship building and civil engineering for low alloy steel structures
A fine heat affected zone (HAZ) microstructure is effective for obtaining high HAZ toughness, and some technical proposals, such as the pinning effect and intragranular ferrite (IGF), have been proposed in this regard
This paper describes a method for predicting austenite grain growth behavior that considers both the solute-drag and pinning effects
Summary
High heat input welding is often employed in industrial fields such as ship building and civil engineering for low alloy steel structures. The austenite grain size in the area becomes coarse, and the toughness of the HAZ is generally lower than that of the base metal.[1,2,3] A fine HAZ microstructure is effective for obtaining high HAZ toughness, and some technical proposals, such as the pinning effect and intragranular ferrite (IGF), have been proposed in this regard. Oxides such as TiO,[4,5,6] MnAl2O4,[7,8] Ti2O3,[9] Ti2O3-TiN-MnS,[10,11,12]. In previous research into simulating austenite grain growth, Burke proposed the following grain growth equation:[21]
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