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Hardness of a material refers to the ease with which it fractures under load. Stainless steels have a hardness of HRC 32 and above, which means that they are susceptible to hydrogen embrittlement (HE) under plating processes that introduce hydrogen into the material. They can also experience long-term failures due to accumulation of hydrogen over time from cathodic protection and other sources in service. These failures typically manifest as brittle cracking below the expected proof or yield strength.
The HE susceptibility of stainless steels is mainly influenced by their crystal structure and the rate at which hydrogen can diffuse and deformation mechanisms operate. However, the effect can be further aggravated by the conditions under which fatigue tests are conducted and the microscopic morphology of the resulting fatigue crack. This article discusses the influence of various factors on the susceptibility to HE in fatigue and methods suggested for preventing HE.
Hydrogen embrittlement (HE) is a phenomenon that reduces the ductility of metals and increases their crack growth rates under cyclic loading. This degradation of fatigue properties is a consequence of the interaction between atomic hydrogen that can penetrate and combine with solid phases to form molecular hydrogen gas, and the mechanical stress acting to promote crack growth.
The severity of HE is a function of temperature and most metals are immune to it at temperatures above 150 °C, although the sensitivity can increase at lower temperatures. It is also known that the presence of pre-existing a’-martensite in a hydrogen charged tensile sample reduces its sensitivity to HE, but the impact of notch bluntness is not well understood.