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

The delta-ferrite to gamma-austenite phase transformation in duplex stainless steels was observed using ultra high-temperature confocal laser scanning microscope, and the orientation relationship between the gamma phase, and precipitate is discussed. Owing to mutual promotion action, the gamma phase was observed at delta/delta grain boundary at the beginning of delta-ferrite ->gamma-austenite transformation, followed by two-dimensional gamma-phase growth at the same speed (0.625 mu m s(-1)) along the grain boundary and into the delta grain matrix. The gamma-phase growth rate decreases to 0.244 mu m 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 gamma phase, and the nucleation and growth of the austenite also promoting the growth of MnS the growth. [GRAPHICS] .