Researchers from University of Lyon assessed the impact of hydrogen charging on the nucleation and growth of microdamage in austenitic stainless steels
Austenitic stainless steel is a specific type of stainless steel alloy with an austenite crystalline structure. This type of stainless steel finds application in automotive trim, cookware, food and beverage equipment, and industrial equipment. It is also used in components installed in high-pressure hydrogen refueling stations and embarked in fuel cell vehicles. However, austenitic stainless steel is prone to hydrogen-induced degradation. Hydrogen can easily penetrate into the material and lead to hydrogen embrittlement—a process by which hydride-forming metals such as titanium, vanadium, zirconium, tantalum, and niobium become brittle and fracture due to the introduction and subsequent diffusion of hydrogen into the metal. Therefore, in-depth understanding of hydrogen-induced degradation is necessary for safe use of components such as vessels, valves, regulators, and metering devices that are exposed to high-pressure hydrogen gas environment.
Now, a team of researchers from University of Lyon evaluated the effect of hydrogen charging on nucleation and growth of cavities in ductile materials. Two types of austenitic stainless steels were investigated: AISI316 and AISI316L, in this study. The in situ tensile experiments were conducted at the European Synchrotron Radiation Facility (ESRF), using the tomography setup available at the ID19 beamline to analyze the fracture process of charged and uncharged samples.
The aspect ratio of the cavities demonstrated a crack shape in the hydrogen-charged AISI316, which led to earlier macroscopic fracture. This in turn explains the reduction in ductility. The team found that hydrogen charging does not have a significant impact on both nucleation and growth, which suggests that the microscopic evolution of damage is not increased due to presence of hydrogen. Cavities rapidly transformed into cracks that were perpendicular to the tensile axis in AISI316, which led to early fracture. Moreover, hydrogen charging reduces the ductility in the sample. According to the findings, 316L is a potential option in vehicle tanks. The research was published in the journal MDPI Materials on May 1, 2019.