In-situ observation of interaction between precipitates and austenite during δ→γ phase transformations

The δ-ferrite to γ-austenite phase transformation in duplex stainless steels was observed using ultra high-temperature confocal laser scanning microscope, and the orientation relationship between the γ phase, and precipitate is discussed. Owing to mutual promotion action, the γ phase was observed at δ/δ grain boundary at the beginning of δ-ferrite→γ-austenite transformation, followed by two-dimensional γ-phase growth at the same speed (0.625 µm s−1) along the grain boundary and into the δ grain matrix. The γ-phase growth rate decreases to 0.244 µm s−1 when precipitate stops growing. In the process of grain growth at high temperature, the precipitated pinning grain boundary will slow the movement speed of the grain boundary.The mutual promotion action leads to preferential nucleation of the γ phase, and the nucleation and growth of the austenite also promoting the growth of MnS the growth.