Researchers discover how hydrogen causes embrittlement of steels

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In a world first, University of Sydney researchers have identified the cause of  hydrogen embrittlement in steels. The discovery is described as one of the missing pieces of the hydrogen economy puzzle, paving the way for steel tanks and pipelines to play a vital role in the distribution and storage of this ubiquitous element.

Hydrogen embrittlement refers to the process by which certain metals become susceptible to early fracture due to the absorption of hydrogen. In the case of steel, hydrogen is making the metal brittle leading to catastrophic failures. However, comprehending the behavior of hydrogen in steel and other alloys has been limited due to the difficulty of observing tiny, light and mobile hydrogen atoms.

The University of Sydney scientists have tackled the challenge of identifying the exact location of hydrogen atoms in two common steels using a sophisticated imaging technique called cryo-transfer atom probe tomography. Working in partnership with CITIC Metal, the researchers were able to directly observe hydrogen at microstructures in steels and show that hydrogen is pinned to various interfaces in the steels thanks to Microscopy Australia’s state-of-the-art custom-designed cryogenic atom probe microscope.

The research, published in the journal Science, showed hydrogen accumulates inside the carbon-rich dislocations and grain boundaries separating steel crystals. This accumulation weakens the steel along these features, leading to embrittlement.

In another breakthrough, the researchers have found the first evidence that preventing steel embrittlement is possible. They found that clusters of niobium carbide within the steel trap hydrogen in such a way that it cannot readily move to the dislocations and crystal boundaries. This effect has the potential to be used to design steels that can resist embrittlement.

Lead researcher Yi-Sheng Chen from the Australian Centre for Microscopy and Microanalysis and Faculty of Engineering at the University of Sydney said these findings were an important step to finding a safe solution to produce, store and transport hydrogen.

“These findings are vital for designing embrittlement-resistant steel; the carbides offer a solution to ensuring high-strength steels are not prone to early fracture and reduced toughness in the presence of hydrogen,” Chen said.