Corrosion fatigue crack propagation of a duplex stainless steel X6 Cr Ni Mo Cu 25-6 in air and in artificial sea water

摘要

Fatigue crack growth behavior of a duplex stainless steel has been investigated at a stress ratio of 0.1, in air environment at room temperature and in artificial sea water heated to 70℃. Growth rates generated under constant load amplitude at a frequency of 0.1 Hz under corrosion fatigue were found to be about 1.7 orders of magnitude higher than those generated in air environment. The study of the crack propagation under both conditions has revealed a significant change in fracture mechanisms between both environments. In air environment, microscopic growth rates in austenite measured by striation spacing in SEM were found to be very close to the macroscopic growth rates whereas in sea water, cyclic cleavage of the ferrite controls the macroscopic growth rales for ΔK between 20 and 60 MPam~(1/2). The cyclic cleavage is induced by hydrogen embrittlement of the ferrite which is produced by an electrochemical reaction between the material and sea water.