Elevated Fracture Resistance of Q&P1180 after Forming and Paint-Baking Treatment

According to precedent studies, many automotive advanced high-strength steel (AHSS) grades obtain reinforced strength yet maintain fracture resistance after forming and paint-baking treatment. Concisely, the mechanism of such behavior is that the Cottrell Atmospheres can only impede the mobile dislocations during the early stage of the plastic deformation and cannot last durable enough to affect the fracture. Nevertheless, a distinctive AHSS grade, Q&P1180, was reported in this work that it obtained some elevated fracture resistance as well as strength after forming and baking. Such a uniqueness was speculated to be caused by 1) no soft ferrite in the microstructure and 2) the transformed fresh martensite being tempered and softened by the paint-baking cycle. To prove this speculation, a series of mechanical experiments were conducted, covering stress-state, strain-rate, and temperature dependencies. Eventually, the test results characterized the elevated fracture resistance of Q&P1180 under various conditions and accordingly further highlighted its promising future in the crashworthiness applications.