Three-dimensional crack propagation behavior in hydrogen-related fracture of high-strength martensitic steel

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Relationship between Three-dimensional Crack Morphology and Macroscopic Mechanical Properties of Hydrogen-related Fracture in Martensitic Steel

International audienceIn the present study, several parameters related to crack morphology in the case of hydrogen embrittlement were estimated by X-ray computed tomography and correlated with the macroscopic mechanical responses (J-integral and tearing modulus) obtained from the fracture mechanics tests. Even when the hydrogen content was high up to 4.00 wt ppm, unstable premature fracture did not immediately occur, and a certain crack-growth resistance could be confirmed. The three-dimensional crack morphology was not continuous with the formation of un-cracked ligaments in the uncharged specimen. In contrast, the hydrogen-related intergranular crack propagated more continuously with a smaller crack opening-displacement. The J-integral value monotonically increased with increasing estimated values of the surface area divided by the projected surface area on the macroscopic crack plane, indicating that crack meandering and branching increased the fracture energy. We defined crack-propagated thickness (standard deviation of the crack surface area at each section (parallel to the macroscopic crack plane) divided by the crack surface area) as a parameter representing crack meandering. The tearing modulus increased as the crack-propagated thickness increased, suggesting that crack meandering also increased the crack-growth resistance

Local crack arrestability and deformation microstructure evolution of hydrogen-related fracture in martensitic steel

International audienceIntergranular cracks in the uncharged specimen were arrested at low-angle prior austenite grain boundary (PAGB) segments of several micrometers. In contrast, even small, low-angle PAGB segments with sub-micrometer sizes impeded the propagation of hydrogen-related intergranular crack. At the hydrogen-related quasi-cleavage crack tip, the crystallographic orientation changed abruptly, and deformation microstructures developed, including the formation of low-energy dislocation structures. A certain degree of crack growth resistance (intrinsic crack growth resistance) in the hydrogen-related fractures could be attributed to the intense localized plastic works involved in the arrest of intergranular cracks and the propagation of quasi-cleavage cracks