Effect of prestrain and strain path on Retained Austenite transformation and eventual fracture behavior of Q&P steels

Post-forming fracture behavior of Quenched & Partitioned (Q&P) steel grades can be compromised because of reduction of available Retained Austenite (RA) and formation of fresh martensite during stamping. A study was undertaken to characterize the post-forming fracture behavior of two Q&P steel grades of tensile strength 980MPa and 1180MPa. Using the Marciniak test, samples were formed to different strain levels under plane strain and balanced biaxial conditions. Following forming, samples were extracted to determine the fracture strain using the VDA238-100 bend test with Digital Image Correlation (DIC). In both steels, it was found that while the post-forming fracture strain had a strong dependence on the remaining RA after pre-straining, the strain path had a lower influence.