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Characterization of diffusible hydrogen in high strength steels coated with Al-Si alloy(AluSi)

Muhammad, Afsar
(2018)

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Afsar_15751601_2018.pdf
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Details

Supervisors
Jacques, Pascal
Faculty
Ecole polytechnique de Louvain
Degree label
Master [120] : ingénieur civil en chimie et science des matériaux
Abstract
The ever-increasing demand of weight reduction of the vehicles in automotive industry without compromising on properties has lead to the development of high/ultra-high strength steels. Meanwhile, new forming techniques allowing production of thinner components with near net shapes are researched. 22MnB5 is an ultra-high strength steel developed for this purpose and is used with thermo-mechanical process of hot stamping. Hot stamping is an elevated temperature forming process, in bare steels it results in problems like oxidation and decarburization during the heating which reduces the final properties. These issues are addressed by several ways, one of which is by applying coating of Al-Si alloy also called AluSi. However, the major challenge for high strength steels is hydrogen embrittlement. In this work evolution of micro-structure in AluSi coating during hot stamping process is characterized with techniques like scanning electron microscopy(SEM), energy dispersive x-ray spectroscopy (EDX), glow discharge optical emission spectroscopy (GD-OES), X-ray diffraction (XRD) and interferometry. In parallel, diffusible hydrogen content in AluSi coated 22MnB5 (hydrogen causing embrittlement) is quantified by thermal desorption analysis (TDA). The values of apparent diffusion coefficient of hydrogen in AluSi coated 22MnB5 at different temperatures are calculated using hot gaseous permeation. With results obtained from mentioned techniques, effect of micro-structure evolution of AluSi on hydrogen uptake and hydrogen diffusion coefficient is explored for 22MnB5 steel coated with AluSi. This work will enable to understand hydrogen diffusion behavior at elevated temperature, which can be used to prevent hydrogen induced failures in automotive industry. It will also enable to predict possible failures conditions for high strength steels.