Modélisation de la fissuration à froid dans un acier ferritique de type 16MND5

Abstract : This thesis is aimed at studying the hydrogen induced cold cracking (HICC) in the heated affected zone (HAZ) of weldments and at proposing a criterion to predict this phenomenon. HICC is attributable to three factors: i) a susceptible microstructure; ii) hydrogen concentration; and iii) a critical stress. To this end, first tensile tests on smooth specimens charged with hydrogen were performed to investigate hydrogen embrittlement of martensite. According to these results, a ductile-brittle damage model is proposed in order to establish a HICC criterion. In order to validate this criterion, we performed the modified Tekken tests. The Tekken test was chosen because one can control the welding parameters in order to induce cold cracking. The modified Tekken tests have then been modeled using a fully coupled thermo-metallo-mechanical-diffusion model using the finite element method. This model allows to compute martensite’s portion, residual stress level and hydrogen concentration in the HAZ. By applying the HICC criterion to these tests, cold cracking phenomenon has been correctly predicted.
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Qianqiang Chen. Modélisation de la fissuration à froid dans un acier ferritique de type 16MND5. Sciences de l'ingénieur [physics]. ENSTA ParisTech, 2015. Français. ⟨tel-01144540⟩

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