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  1. Oct 2019
    1. Hydrogen embrittlement (HE) of metals has remained a mystery in materials science for more than a century. To try to clarify this mystery, tensile tests were conducted at room temperature (RT) on a 316 stainless steel (SS) in air and hydrogen of 70 MPa. With an aim to directly observe the effect of hydrogen on ordering of 316 SS during deformation, electron diffraction patterns and images were obtained from thin foils made by a focused ion beam from the fracture surfaces of the tensile specimens. To prove lattice contraction by ordering, a 40% CW 316 SS specimen was thermally aged at 400 °C to incur ordering and its lattice contraction by ordering was determined using neutron diffraction by measuring its lattice parameters before and after aging. We demonstrate that atomic ordering is promoted by hydrogen, leading to formation of short-range order and a high number of planar dislocations in the 316 SS, and causing its anisotropic lattice contraction. Hence, hydrogen embrittlement of metals is controlled by hydrogen-enhanced ordering during RT deformation in hydrogen. Hydrogen-enhanced ordering will cause the ordered metals to be more resistant to HE than the disordered ones, which is evidenced by the previous observations where furnace-cooled metals with order are more resistant to HE than water-quenched or cold worked metals with disorder. This finding strongly supports our proposal that strain-induced martensite is a disordered phase.

      En resumen, se realizaron pruebas de tracción a temperatura ambiente (RT) en un acero inoxidable 316 (SS) en aire e hidrógeno de 70 MPa. Con el objetivo de observar directamente el efecto del hidrógeno en el pedido de 316 SS durante la deformación, se obtuvieron patrones e imágenes de difracción de electrones a partir de láminas delgadas hechas por un haz de iones enfocado desde las superficies de fractura de las muestras de tracción. La fragilización por hidrógeno es un tipo de corrosión en la cual el hidrógeno atómico se difunde en el material y se deposita en la estructura reticular del metal. La fragilización por hidrógeno ocurre frecuentemente durante la soldadura y electrogalvanización de aceros debido a que se forma hidrógeno en el acero catódico. La recocción de bajo hidrógeno (templado) contrarresta esto.

    2. The Role of Hydrogen in Hydrogen Embrittlement of Metals: The Case of Stainless Steel

      "El papel del hidrógeno en la fragilización por hidrógeno de metales: el caso del acero inoxidable"