Evaluation of hole expansion ratio of ultra-high strength martensitic steels produced with various processing routes

Abstract Hole expansion ratio of hot rolled ultra-high strength martensitic steels with tensile around 1000 MPa was evaluated. Steels were produced direct quenching and traditional reheat processes final thickness 3 mm. Achieved yield values (R p0.2 ) varied between 918 – 1068 depending on the processing route. Mean hole ratios (HER) in direct-quenched (DQ) tempered (DQT) conditions 22 36 %, no clear improvement seen after tempering treatment compared to quenched variant. HER for (RQ) reheat, (RQT) variants 31 49 highest achieved RQT steels, which at 600 °C. Based field emission scanning electron microscope backscatter diffraction (FESEM-EBSD) analysis/characterization martensite grain size, more uniform structure discovered RQ could be reason improved properties. also test results (uniform elongation, true strain), formability maps constructed. However, only minor correlation found strain values.