Abstract: he effects of three environments of3.5% NaCl solution(SW), distilled water(DW)and air(AIR)and two stress ratios of R=0.1 and 0.5 on corrosion fatigue crack initiation life(FCIL)are experimentally investigated in the present study ior 300M steel,an ultra-high strength steel used in airplane structure. Experimental results show that the two corrosive envi- ronments SW and DW used in the present study, without exception,significantly reduce the fa- tigue strength and FCIL of 300M steel, and when the values of equivalent stress amplitude(Δσeqv)in test are identical to each other for the above mentioned three environments, the se- quence of FCIL(Ni)indecreasing order of magnitude is that(Ni)AIR>(Ni)DW>(Ni)SW. When the values ofequivalent stress amplitude are identical for the ahove mentioned ratios,the CF crack initiation life of 300M steel in SW increases as increasing stress ratio. The concepts of FCIL loss factor DL and Fatigue crack initiation strcngth loss factor Ds induced by corrosive environ- ments are also introduced in this paper Furthermore,several quantitative expressions of Ni vs Δσeqv,Ds vs Ni and DL vs Δσeqv are also given in this paper

Key words: corrosion resistance, crack initiation, environmental tests, stress ratio