Critical Hydrogen Concentration for Hydrogen-Induced Cracking of Type 321 Stainless Steel Available to Purchase

The effects of hydrogen concentration (C_H) on ductility and fracture of type 321 (UNS S32100) stainless steel (SS) were studied. A linear relationship was obtained for C_H and ductility reduction. C_H increased logarithmically with hydrogen charging current. Elongation of the type 321 SS decreased linearly with increasing C_H or logarithmically with charging current (i_C). A critical hydrogen concentration $(CH*)$ existed for hydrogen-induced fracture (HIC). This concentration was ~ 74 wppm for the applied conditions, below which non-HIC occurred but hydrogen-induced ductility loss did occur. Hydrogen introduced in the specimen during corrosion in boiling 42% magnesium chloride (MgCl₂) solution was determined. The amount was ~ 32 wppm when the specimen was exposed in a solution of pH = 1 for 200 h. The environment could cause a 25% elongation reduction but not HIC. The critical concentration for hydrogen-induced ductility loss was below the critical value for HIC.