Mechanical behavior and microstructure evolution of a quenched and partitioned steel during drop weight impact and punch testing

In this work, a Fe-0.25C-3.0Mn-1.5Si-0.023Al-0.015Cr (wt. %) steel was subjected to the Q&P treatment, and its mechanical behavior and microstructure evolution during drop weight impact testing and quasi-static punch testing were thoroughly analyzed. It is shown that the 1 mm thick Q&P steel sheet can withstand 110 J impact energy without any (micro) cracking, which is well above the impact resistance of DP 1180 steel. The local true plastic strain can reach 53.4% in biaxial stretching showing excellent formability of the material. The microstructure characterization shows that the volume fraction of retained austenite decreases exponentially with increasing plastic strain under dynamic biaxial stretching. Scanning electron microscopy analysis of cracks formed after drop weight impact testing with 120 J energy reveals a ductile fracture surface consisting of elongated dimples formed by MnS inclusions which are surrounded by fine chisel-point type dimples. The potential of Q&P treated steels for application in the automotive industry is discussed.