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The scope of this study is to characterize the mechanical properties of a novel Transformation‐Induced Plasticity bainitic steel grade TBC700Y980T. For this purpose, tensile tests are carried out with loading direction 0, 45 and 90° with respect to the L rolling direction. Yield stress is found to be higher than 700 MPa, ultimate tensile strength larger than 1050 MPa and total elongation higher than 15%. Low‐cycle fatigue (LCF) tests are carried out under fully reverse axial strain exploring fatigue lives comprised between 102 and 105 fatigue cycles. The data are used to determine the parameters of the Coffin–Manson as well as the cyclic stress–strain curve. No significant stress‐induced austenite transformation is detected. The high‐cycle fatigue (HCF) behaviour is investigated through load controlled axial tests exploring fatigue tests up to 5 × 106 fatigue cycles at two loading ratios, namely R = −1 and R = 0. At fatigue lives longer than 2 × 105 cycles, the strain life curve determined from LCF tests tends to greatly underestimate the HCF resistance of the material. Apparently, the HCF behaviour of this material cannot be extrapolated from LCF tests, as different damage, cyclic hardening mechanisms and microstructural conditions are involved. In particular, in the HCF regime, the predominant damage mechanism is nucleation of fatigue cracks in the vicinity of oxide inclusions, whereby mean value and scatter in fatigue limit are directly correlated to the dimension of these inclusions.

The problem of hydrogen embrittlement in ultra-high-strength steels is well known. In this study, slow strain rate, four-point bending, and permeation tests were performed with the aim of characterizing innovative materials with an ultimate tensile strength higher than 1000 MPa. Hydrogen uptake, in the case of automotive components, can take place in many phases of the manufacturing process: during hot stamping, due to the presence of moisture in the furnace atmosphere, high-temperature dissociation giving rise to atomic hydrogen, or also during electrochemical treatments such as cataphoresis. Moreover, possible corrosive phenomena could be a source of hydrogen during an automobile’s life. This series of tests was performed here in order to characterize two press-hardened steels (PHS)—USIBOR 1500® and USIBOR 2000®—to establish a correlation between ultimate mechanical properties and critical hydrogen concentration.

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Demanding structural applications require a detailed knowledge of the materials response up to the very late stages before failure. Ductile high-strength steels may undergo pronounced necking over the majority of their straining life; this makes a reliable stress–strain characterization difficult, especially at dynamic rates, because the self-heating from fast adiabatic dissipation may promote thermal effects interplaying with the strain rate effects. Further complications arise in deriving the postnecking flow curves when the material is a metal sheet due to geometrical issues intrinsic in the prismatic flat shape of the specimens. This paper focuses on the experimental derivation of the flow curves of DP1000 and MS1700 steels at strain rates ranging from 1 to 500/s. In addition, the moderately high temperatures achieved due to the self-heating at dynamic rates are imposed at static rates for separately investigating thermal and dynamic effects. Digital Image Correlation (DIC) and pixel counting optical techniques are used together with postprocessing procedures based on standard criteria and on physical considerations proposed by the authors. The resulting hardening curves are compared to each other and the advantages of the proposed method are discussed.