Abstract: The fatigue crack growth rates of 30CrMnSiNi2A high-strength steel were studied at room-temperature (22±2℃) in standard laboratory air (40 ±10% R. H. ),low humidity air (<10% R. H. ),high humidity air (40±10% R. H. ) ,3.5% sodium chloride (NaCl) solution and synthetic sump water environments. The results show that there is no influence of moisture on da/dN. The SEM examination of specimens tested in air showed some typical features of intergranular fracture,but individual transgranular fracture was observed in moist air. There is no effect of frequency on da/dN in air. Varying R from 0.1 to 0.6 has little contribution to da/dN in region Ⅱ in lab air. In saltwater under free-corrosion conditions and at f = 10Hz the da/dN were in agreement with the results in air, otherwise at f = 1Hz the da/dN increased up to a factor of 4 dependent on ΔK primarily at mid-range. The fracture surfaces showed classic intergranular fracture mixed with patches of transgranular fracture which was similar in both 10Hz and 1Hz. The result is attributed to that the high strength steel is susceptible to hydrogen embrittlement. In general, the test results in freely corroding sump water are similar to that in saltwater. However, at f = 10Hz there was a small plateau over a relatively low ΔK values where the crack growth rates were independent of ΔK and decreased up to a factor of 3 than that in air. The corrosion fatigue crack growth process is mutually competitive of mechanical fatigue, hydrogen embrittlement and corrosing-products-induced wedge effect.

Key words: environmental tests, corrosion fatigue, crack propagatione