TRIP型双相钢由于马氏体相变可以平衡强度、提高延展性和提高成形性而受到广泛关注。然而，随着马氏体相变的演化，钢中微观组织和相分布特征不断变化，从而导致复杂的微裂纹形核和扩展。本工作利用SEM、EBSD观察TRIP型双相不锈钢Fe-19.6Cr-2Ni-2.9Mn-1.6Si在拉伸至工程应变为55%时的微裂纹特征，分析由材料微观组织特征(相分布、晶界或相界路径等)导致的微裂纹形核及扩展规律。结果表明，微裂纹主要分布在初始奥氏体与铁素体相界位置，约占总微裂纹数的70%，铁素体相内晶界位置的微裂纹数约占总数的20%，初始奥氏体相内晶界位置的微裂纹数仅占总数的10%左右。微裂纹的形核易发生在多类型界面的交汇位置，主要的微裂纹形核位置可分为3类：相变马氏体/铁素体/残余奥氏体三相的交汇点，相变马氏体/铁素体相界和铁素体晶界交叉点，及相变马氏体/铁素体相界和初始奥氏体晶界交叉点。这些裂纹源在相界附近相变马氏体的影响下，易沿初始奥氏体与铁素体相界或与相界夹角较小(< 30°)的铁素体晶界扩展，而由于马氏体相变松弛了奥氏体相内的应力集中，导致微裂纹不易沿奥氏体晶界扩展。

The transformation-induced plasticity (TRIP) effect considerably enhances the material properties of TRIP-assisted duplex steel due to the martensitic transformation. However, as martensitic transformation progresses, a complex microstructure forms from the intermixing of three phases (i.e., austenite, ferrite, and martensite) in the steel, which results in complex damage behavior, crack nucleation, and propagation characteristics. In this study, under engineering strain up to 55%, TRIP-assisted duplex stainless steel Fe-19.6Cr-2Ni-2.9Mn-1.6Si was characterized to investigate microcrack characteristics. Herein, different types of microcracks were statistically categorized using SEM. Additionally, microcrack nucleation and propagation laws were analyzed in light of microscopic features characterized by EBSD, including phase distribution and grain and phase boundaries. The results show that the majority of microcracks are situated at the phase boundary between original austenite and ferrite, constituting about 70% of all microcracks. The number of microcracks located at the ferrite grain boundary accounts for about 20% of the total, while the number of microcracks located at the original austenite grain boundary accounts for only about 10% of the total. The interface between martensite and ferrite emerged as the primary site for microcrack nucleation. Furthermore, the study identifies three distinct microcrack nucleation sites influenced by various boundary types: at the intersection of martensite, ferrite, and austenite phases; at the junction of martensite/ferrite phase boundary and ferrite grain boundary; and at the cross point of martensite/ferrite phase boundary and the original austenite grain boundary. Therefore, microcracks might propagate along the original austenite/ferrite phase boundary or ferrite grain boundary with a smaller angle (< 30°) to the phase boundary. In addition, microcracks are less apt to propagate along the austenite grain boundary.