Abstract
The effect of aging condition on susceptibility to hydrogen embrittlement (SHE) has been investigated by means of tensile tests in vacuum and hydrogen gas for 13Ni-15Co-10Mo maraging steel. The SHE was correlated with the microstructural change as a result of aging. Tensile properties in vacuum were dependent upon the strength level alone, while those in hydrogen were dependent upon both the strength level and aged structure. When aged at temperatures below 475°C and the precipitates were smaller than 40Å, the SHE increased greatly. The increased SHE was considerably reduced by the introduction of small amounts of the precipitates larger than 40Å. Therefore, the abrupt decrease in SHE during aging is considered to be consistent with the microstructure containing a critical amount of the precipitates larger than 40Å. The major increase in SHE in the low-temperature-aging condition may be associated with the accelerated transport of hydrogen by dislocation and the increased adsorption of hydrogen at the metal surface.
