The role of hydrogen diffusion, trapping and desorption in dual phase steels

Abstract

Hydrogen embrittlement (HE) of advanced high-strength steels is a crucial problem in the automotive industry, which may cause time-delayed failure of car body components. Practical approaches for evaluating the HE risk are often partially and contradictive in nature, because of hydrogen desorption during testing and inhomogenous hydrogen distributions in, e.g., notched samples. Therefore, the present work aims to provide fully parametrized and validated bulk diffusion models for three dual phase steels to simulate long-range chemical diffusion, trapping and hydrogen desorption from the surface. With one constant set of parameters, the models are able to predict the temperature dependency of measured Choo-Lee plots as well as the concentration dependency of measured effective diffusion coefficients. Finally, the parametrized and validated bulk diffusion models are applied for studying the role of the current density on the permeation time and the role of coatings as effective diffusion barriers. Graphical abstract

Influence of Plastic Deformation on the Hydrogen Embrittlement Susceptibility of Dual Phase Steels

“…Zinc coatings, which are applied after charging, can prevent hydrogen losses during testing, but also cause a decrease of the hydrogen content by desorption during sample handling between charging and galvanization. Furthermore, reliable theories to model the effect of zinc coatings on the hydrogen distribution within the samples and on the measured hydrogen susceptibility are still missing in literature to the authors knowledge [15]. Anyway, the effect of HE was very pronounced in the present investigations using higher strain rates for SSRT, which is partially related to minimum hydrogen losses during sample handling and testing.…”

“…The as-delivered sheets with thickness of 𝑠𝑠 = 1.2 mm were galvanized. Microstructure characterization was performed by etching and LOM as published in a previous work [15]. The martensite area fractions 𝑓𝑓 M are summarized in Table 1.…”

“…It assumes that hydrogen fosters and stabilizes the formation of excess vacancies in the crystal structure and that the accumulation to vacancy clusters causes brittle macroscopic appearance, although significant plastic straining proceeds fracture on the macroscopic scale. DP steels are widely used in the automotive industry and fundamentals of the HE susceptibility of AHSS are well studied [12][13][14][15]. However, since researchers have mostly been focusing on straining pure ferritic iron, lack of knowledge exists with respect to the influence of plastic deformation on HE of industrial relevant DP steels with high strength and reduced ductility.…”

Effect of Tensile Loading and Temperature on the Hydrogen Solubility of Steels at High Gas Pressure

“…Details of the ferritic–martensitic microstructure of the DP steels are given in ref. [48]. The sample size of the 34CrMo4 steels was cubic with an edge length of 4.5 mm, while the DP steel samples had the dimensions 100 × 10 × 1.2 mm.…”

“…For that purpose, gaseous hydrogen contents of different low alloyed steels with a ferritic or martensitic matrix were measured and collected from literature. [13,19,48,[51][52][53] A summary of the literature data is given in a tabular form in Appendix. All measurements were performed using the TDA method after high-pressure hydrogen charging of samples in closed autoclave systems.…”