Influence of hydrogen on the static crack resistance of refractory steels

We have investigated the influence of a hydrogen atmosphere under a pressure up to 30 MPa and hydrogen preliminarily absorbed at 623 K on the short-term and long-term static crack resistance of specimens of EP-517 (15Kh12N2MFAV) martensitic steel and EP-700 (10Kh15N27T3V2MR) austenitic precipitation- hardening steel. It has been established that, under the action of hydrogen, the stress intensity factor K (c) decreases 2-3 times, and the thickness of a specimen at which the plane-strain state is realized also decreases. The influence of hydrogen on K (c) is enhanced as the pressure of the hydrogen atmosphere (EP-517 steel) and the concentration of preliminarily absorbed hydrogen (EP-700 steel) increase and the thickness of specimens decreases from 35 to 10 mm. After holding in air at room temperature for 17.5a (TM) 10(4) h, the hydrogen content in the steels decreases, and the values of K (c) increase but are smaller by 20% than those for nonhydrogenated specimens. In long-term static crack resistance tests (for 300 h), we have determined the invariant crack resistance characteristic of EP-700 steel, namely, the threshold value K (IHST) equal to 38 MPa root m.