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Abstract：
The effects of Y on the solidification process of 7Mo super austenitic stainless steel (7MoSASS) under low cooling rate conditions (10 °C/min) were investigated using high-temperature confocal laser scanning microscopy (HT-CLSM). The in situ observation results indicate that Y samples promote an increase in austenite nucleation density. After 10 s of nucleation, the nucleation density increased by 149.53/mm2 for the Y sample. Furthermore, variance analysis indicated that Y addition improved the uniformity of the 7MoSASS solidification microstructure under low cooling rate conditions. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory results showed that when the solid phase ratio was 0.5, the nucleation mode of the Y sample transitioned from saturation site nucleation to saturation site nucleation + Avrami nucleation. YAlO3 has a low lattice disregistry value with austenite, making it a suitable heterogeneous nucleation core for promoting the early nucleation of austenite. During the late stages of solidification, Y accumulates in the residual liquid phase, providing a greater degree of compositional undercooling. SEM-EDS analysis showed that Y contributed to the refinement of the 7MoSASS solidification microstructure, with the proportion of precipitated phases decreasing by approximately 7.5%. Cr and Mo were the main elements exhibiting positive segregation in 7MoSASS, and the Cr segregation ratio increased in the Y sample, while the Mo segregation ratio decreased.
摘要：
利用高温共聚焦激光扫描显微镜(HT-CLSM)研究了Y对低冷却速率条件(10℃/min)下7Mo超级奥氏体不锈钢(7MoSASS)凝固过程的影响。原位观察结果表明，Y样品促进了奥氏体成核密度的增加。成核10秒后，Y样品的成核密度增加了149.53/mm2。此外，方差分析表明,Y的加入提高了低冷却速率条件下7MoSASS凝固组织的均匀性。Johnson-Mehl-Avrami-Kolmogorov(JMAK)理论结果表明，当固相比为0.5时，Y样品的成核模式从饱和位点成核过渡到饱和位点成核+Avrami成核。YAlO3与奥氏体的晶格失准值低，使其成为促进奥氏体早期形核的合适异质形核。在凝固的后期,Y积聚在残留的液相中，提供更大程度的成分过冷。SEM-EDS分析表明Y有助于7MoSASS凝固组织的细化,析出相的比例降低约7.5%。Cr和Mo是7MoSASS中表现出正偏析的主要元素，Y样品中Cr偏析率增加，而Mo偏析率下降。
