Embrittlement due to hydrogen in ferrite and martensitic structural steels

AISI 420 steel test-pieces were submitted to hydrogen discharge by electrolyzation at a constant current density (8 mA cm−2) under a constant load (14 daN mm−2), with different charging times (from 3600 to 450,000 s). Two test-pieces were hydrogenated simultaneously, then one was tensioned by a tensile machine, while the other was tested by a hydrogen analyzer. Tensile tests results have shown that as the charging time increases, the material toughness (obtained by the value of reduction in area) decreases, passes through a minimum value and then later tends to recover its original value. Hydrogen-analyzer results have highlighted that, in parallel with the decrease and the recovery in material toughness, there is an increase and a decrease in the amount of hydrogen extractable at 400 °C, respectively, while at 600 °C and 800 °C respectively, it remains practically constant and subsequently increases. This phenomenon has been confirmed by fractographic analysis.