Oxide Accelerating Primary Ferrite Nucleation of Austenitic Stainless Steel Weldment

点击翻译按钮获取中文摘要

In this study, we evaluate the accelerating effect of Ti2O3, (Ti,Al)2O3, and MgAl2O4 on TiN formation to promote primary ferrite nucleation. Ti2O3, (Ti,Al)2O3, and MgAl2O4 could all accelerate TiN formation to nucleate δ-ferrite, the specimen with MgAl2O4 showed the optimal effect of δ-ferrite refinement. Ti2O3 and (Ti,Al)2O3 could act as heterogeneous nuclei for TiN because low lattice misfits of 0.6% and 0.6~8.1% could be reached as for Ti2O3 and (Ti,Al)2O3 with orientation relationship of {0001}oxide//{111}TiN and [10-10] oxide//[110]TiN. Spinel type MgAl2O4 was identified to have a fully paralleled orientation relationship with TiN and lead to a 4.8% misfit with TiN in each crystal plane. MgAl2O4 could significantly accelerate TiN formation to form MgAl2O4-TiN with a higher area density of above 250 counts/mm2 compared to 75 counts/mm2 regarding Ti2O3-TiN and (Ti,Al)2O3-TiN. Baker-Nutting (B-N) orientation relationship was confirmed between TiN and δ-ferrite. The formed TiN could nucleate δ-ferrite.The effect of primary ferrite refinement on austenite formation was investigated. When MgAl2O4-TiN was introduced, the primary ferrite was greatly refined with random and multiple orientations, having little relationship with the temperature gradient. The morphology of residual ferrite showed vermicular morphology with fine-dispersed character. The austenite shows columnar morphology because the formation temperature of austenite is higher than the solidus and the austenite nucleated and grew independently to primary ferrite.