Quenching and partitioning (Q&P) steel has gained significant interest in the automotive industry due to its high strength, ductility, and formability [1, 2]. Our investigation into the microstructure characterization and failure mechanisms of Q&P980 steel aims to provide valuable guidance for its production process. The Q&P980 steel in present study consists of five phases, ferrite, fresh martensite, tempered martensite, retained austenite and bainite. We first developed a comprehensive description of microstructure features which including the morphology, phase, precipitates and element distribution via a user-defined EBSD-based phase segmentation tool. Next, the ductile fracture behaviour of Q&P980 under complex stress states was investigated by conducting experiments and microscale characterization tests. We achieved various stress states by designing a number of tensile test specimens with different geometries, such as notched dog bone [3], central hole, smooth dog bone, as well as shear. The results indicate that cleavage fractures are no longer representative of brittle fractures. At higher stress triaxiality, Q&P steel presents a ductile fracture dominated by a cleavage fracture. The inhomogeneity of microstructure will result in stress concentration and failure. Our study highlights the transition from ductile fracture surface morphology of Q&P980 steel under low to high stress triaxiality, revealing its complex microscopic failure mechanism and providing valuable insights into the production process.

References

[1] J. Li, et al. Materials Characterization, 2023. 205: p. 113377.

[2] S. Yan, et al. Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, 2015. 620: p. 58-66.

[3] Z.P., Xiong et al. Scripta Materialia, 2018. 157: p. 6-9.