Effect of nanocarbides and interphase hardness deviation on stretch-flangeability in 998 MPa hot-rolled steels

By performing various laboratory hot-rolling simulation tests, effective rolling conditions for steel with a composition (mass %) of 0.06C–2.0Mn–0.5Si–0.5Cr–0.2(Ti + Nb + V) was studied. Very remarkable mechanical properties were obtained when the coiling simulation temperature was 650 °C: a hole-expanding ratio of 65%, total elongation of 19%, and ultimate tensile strength of 998 MPa were achieved in the hot-rolled state. These results were associated with the Ti–Nb–V multi-microalloyed carbides (10–50 nm in size) precipitated in the ferrite matrix, and with the minimized deviation in interphase hardness.