It is commonly recognized that for Advanced High Strength Steels (AHSS) the forming limit is mainly controlled by fracture, rather then by localized necking. To date a reliable fracture limit for forming AHSS is not well defined, especially when a practical forming process is under complex strain paths. Hole expansion test has been used by auto industry for assessing fracture-controlled material forming limit. Understanding of crack mechanisms involved in crack initiation and propagation is important for prediction of fracture failure. A dual phase steel with a fine grain and 20–40vol% martensite particles of ∼1μm mean size was used for this study. The results indicate that the hole piercing and blank placement during hole expansion has sensitive impact to the evaluation of edge crack initiation and propagation. Through the comparative study on the “burr up” and “burr down” blank settings the fracture process and the effect of blank preparation, hole expansion, burr geometry effect on crack initiation, and the crack propagation direction and local interaction with microstructure are investigated.

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