不同冷却速度下双相不锈钢δ/γ相变过程的原位观察

IN-SITU OBSERVATIONS OF FERRITE/AUSTENITE TRANSFORMATIONS IN A DUPLEX STAINLESS STEEL AT VARIOUS COOLING RATES

利用共聚焦激光扫描显微镜原位观察不同冷却速度下双相不锈钢中高温铁素体(δ)向奥氏体(γ)转变的全过程。结果表明,冷却速度较高时,γ优先在δ晶界上析出并迅速向δ内部长大,其形状以针状为主;冷却速度较低时,γ优先在δ晶界上析出,呈片状,γ端面在向δ内部长大的同时,其侧面也不断长大,相变过程中伴随着δ晶界的迁移。利用固态相变形核理论和扩散控制长大理论分析讨论了不同冷却速度下δ→γ的相变行为。

Transformation of δ→ γ in a duplex stainless steel was observed in-situ by using a confocal scanning laser microscope at various cooling rates. It was found that at higher cooling rate, the γ-phase precipitated first at the δ grain boundaries and spread sharply into the initial δ grain, and the main shape of γ-phase was sword-like patterns. While at lower cooling rate, the γ-phase precipitated first at the δ grain boundaries with sheet patterns, and then spread into the initial δ grain along the longitudinal direction as well as its flank augmenting, and the δ grain boundaries migrated at the course of transformation. The reason for the transformation behaviors of δ→γ T at various cooling rates was discussed in the light of the solid state transformation nucleation theory and diffusion controlled growth theory.