Effect of Hydrogen Diffusion on Hydrogen Embrittlement of 18%Ni Maraging Steel

The purpose of the present study is to clarify effects of hydrogen diffusion on hydrogen embrittlement of 18%Ni maraging steel. Thin plate specimens were machined after being solution-treated under recrystallizing and unrecrystallizing conditions for austenite. An electrochemical transportation method was carried out in order to measure hydrogen diffusion coefficient D of structure-controlled specimens. The values of D decreased with prior-austenite grain size for the specimens solution-treated under recrystallizing condition for austenite. On the other hand, for the specimens solution-treated under unrecrystallizing condition for austenite, there was almost no influence of the grain sizes on the D values and besides these values were smaller than the recrystallized specimens. The above results were quite consistent with the effects of the prior-austenite grain sizes on the crack growth rate in the stage II region. Consequently it was elucidated that the hydrogen diffusion predominantly controlled the crack growth rate of the hydrogen embrittlement for the maraging steel.