Effect of the ferrite morphology on hydrogen embrittlement of MAG welded 304 austenitic stainless steel

Ferrite usually plays an important role in the hydrogen embrittlement (HE) of austenitic stainless steel (gamma-SS) weld. However, there are few investigations on the effect of ferrite morphology on HE. In this study, the relationship between the ferrite morphology and HE of metal active gas (MAG) welded 304 austenitic stainless steel is investigated. Hydrogen distribution testing and simulation reveal that the ferrite/austenite interfaces become the hydrogen segregation regions and the degree of hydrogen segregation at the interface is affected by ferrite morphology, which shows the order of lathy ferrite > reticular ferrite > skeletal ferrite. The slow strain rate tensile (SSRT) test indicates that the susceptibility to HE of welds containing lathy ferrite, skeletal ferrite and reticular ferrite reaches 34.6%, 30.7% and 33.2%, respectively. It can be found that the HE resistance shows the order of skeletal ferrite > reticular ferrite > lathy ferrite, which corresponds to the order of increasing hydrogen segregation. Hence, the ferrite morphology influences the resistance to HE of welds by affecting hydrogen segregation at the ferrite/austenite interface. A similar ferrite morphological dependence is observed from the weld fractures.