Advanced High Strength Steels (AHSS) have a better combination between strength and ductility than conventional HSS and higher crash resistances are obtained in concomitance with weight reduction of car structural components. These steels have been developed in last decades and their use is rapidly increasing. Notwithstanding, some their important features have to be still understood and studied in order to completely characterize their service behavior. In particular, the high mechanical resistance of AHSS makes hydrogen related problems a great concern for this steel grades. This paper investigates the hydrogen embrittlement (HE) of four AHSS steels. The behavior of one TRIP, two martensitic with different strength levels and one hot stamping steels have been studied using Slow Strain Rate Tensile (SSRT) tests on electrochemically hydrogenated notched samples. The embrittlement susceptibility of these AHSS steels has been correlated mainly to their strength level and to their microstructural features. Finally, the hydrogen critical concentrations for HE, established by SSRT tests, have been compared to Hydrogen contents absorbed during the painting process of Body In White (BIW) structure, experimentally determined during a real cycle in an industrial plant.

A detailed qualitative and quantitative examination of the microstructure and mechanical properties of three different classes of DP600 and DP450 dual-phase (DP) steels was carried out. The tested DP steels are characterized by different alloying elements: aluminum, boron, and phosphorus. Among them, aluminum DP steels showed the lowest percentages of hard phases, while phosphorus DP steels exhibited the highest resistance values. The Hollomon, Pickering, Crussard-Jaoul (CJ), and Bergstrom models were used to reproduce the strain hardening behavior of DP steels. Relationships that correlate the fitting parameters with the chemical composition and the thermal cycle parameters were found, and the predictive abilities of different models were evaluated. The Pickering equation, among the tested models, is the best one in the reproduction of the experimental stress-strain data.

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The purpose of the present work is the implementation and validation of a model able to predict the microstructure changes and the mechanical properties in the modern high-strength dualphase steels after the continuous annealing process line (CAPL) and galvanizing (Galv) process. Experimental continuous cooling transformation (CCT) diagrams for 13 differently alloying dual-phase steels were measured by dilatometry from the intercritical range and were used to tune the parameters of the microstructural prediction module of the model. Mechanical properties and microstructural features were measured for more than 400 dual-phase steels simulating the CAPL and Galv industrial process, and the results were used to construct the mechanical model that predicts mechanical properties from microstructural features, chemistry, and process parameters. The model was validated and proved its efficiency in reproducing the transformation kinetic and mechanical properties of dual-phase steels produced by typical industrial process. Although it is limited to the dual-phase grades and chemical compositions explored, this model will constitute a useful tool for the steel industry.

The present paper aims at analyzing the flow curves of DP and TRIP steels obtained by uniaxial tensile tests by proposing a strain hardening prediction model. This has been built by using a very simple interpolation formula based on a third‐order polynomial whose parameters have been determined by linear regression analysis on the basis of chemical composition and mechanical properties. The chosen interpolating formula has demonstrated to very effectively reproduce both the stress‐strain curve and its derivative, thus providing a easy tool to predict the strain hardening behavior of DP and TRIP multiphase steels that could be usefully used in industrial application for the simulation of drawing processes.