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Description
Multiphase steels combine the strengths of different microstructural components, offering both mechanical strength and ductility for lighter designs and lower vehicle emissions. Quenching and Partitioning (QP) steels are a 3rd generation Advanced High-Strength Steel (AHSS) used in vehicles, featuring low-carbon martensite and retained austenite for an excellent strength-ductility balance. It poses significant questions that currently limit its adoption in the automotive industry, primarily to their inherent vulnerability to Hydrogen Embrittlement (HE) and delayed fracture.
In this study, the interaction between hydrogen and QP1180 AHSS was examined. Hydrogen diffusivity and trap energies were evaluated using Devanathan-Stachurski permeation and Thermal Programmed Desorption (TPD) tests on both commercial and pre-deformed QP1180 samples. Additionally, Slow Strain Rate Tensile tests (SSRT) were conducted on electrochemically hydrogen-charged smooth specimens, with the effective hydrogen content measured via the hot extraction method for each specimen. Metallographic analyses and micro-hardness tests were performed to characterize the material microstructure and quantify retained austenite content.
Fractographic examinations using scanning electron microscopy revealed the influence of hydrogen on fracture behavior, showing a transition from ductile to predominantly brittle fracture modes at elevated hydrogen concentrations, with the transition threshold varying based on the specimen orientation with respect to the sheet rolling direction.