Effect of hydrogen partial pressure on fatigue crack growth rate of Type304 stainless steel in H2/Ar mixed gas with wide range of pressures

Abstract

Fatigue crack growth testing was carried out on Type304 stainless steel (Type304SS) at room temperature (RT) in mixed gasses controlled to various pressure levels of up to 70 MPa in order to measure changes in embrittlement sensitivity due to hydrogen partial pressure. At PH2 less than 3 MPa, as hydrogen partial pressure decreases, the crack growth rate (da/dN) of Type304SS decreased, and at PH2=5×10-5 MPa (50 Pa), it was 2.8 times higher than that in the air. The hydrogen partial pressure whose da/dN equals the rate in the air, which is the lower limit critical hydrogen partial pressure, was not observed. On the other hand, at PH2=3 MPa or higher, the da/dN reached approximately 20 times higher than in the air. There was an upper limit of the da/dN which no longer increases after hydrogen partial pressure reaches a certain level. From a conservative judgment, it is able to plan the fatigue life considering the da/dN at PH2=3 MPa as the upper limit; approximately 20 times higher than in the air.