The states of hydrogen and hydrogen embrittlement susceptibility of precipitation hardened SUS630 stainless steel

To elucidate the influence of precipitates on the states of hydrogen and hydrogen embrittlement susceptibility of SUS630, solution treatment, sub-aging (410 °C, 1 h), peak-aging (470 °C, 1 h), and over-aging (550 °C, 1 h) methods were used to prepare specimens. States of hydrogen were analyzed by thermal desorption analysis (TDA). Hydrogen embrittlement susceptibility was evaluated using tensile tests. Specimens were electrochemically precharged with hydrogen and then tensile tests were carried out simultaneously with hydrogen charging under the same conditions as those after precharging. Susceptibility was evaluated as the elongation ratio with/without hydrogen. The solution-treated and sub-aged specimens displayed a single peak near 100 °C, whereas peak- and over-aged specimens displayed two peaks, one near 100 °C and the other near 200 °C. The peak near 100 °C corresponded to hydrogen desorbed from the matrix and the peak near 200 °C corresponded to hydrogen desorbed from Cu precipitates. Ductility of peak- and over-aged specimens with hydrogen did not decrease, however, that of solution-treated and sub-aged specimens with hydrogen did. These findings indicate that specimens containing hydrogen with a higher temperature peak associated with Cu precipitates showed less hydrogen embrittlement susceptibility than those containing hydrogen with only a lower temperature peak.