Abstract
Stress corrosion tests were conducted on the notched compact tension specimens of quenched-tempered SNCM 439 steel in three kinds of environmental solution: distilled water, 3.5%NaCl, and 0.1N H2SO4. The crack nucleation behavior was analysed from a view point of fracture mechanics. The results obtained are summarized as follows;
(1) Time to crack nucleation tn of the notched specimens with various root notch radii was determined by a parameter of Kρ/(ρ+ρ0)1/2, where Kρ is the apparent stress intensity factor, ρ is the notch root radius and ρ0 is the intrinsic notch root radius. The life got shorter as the hydrogen content became larger in the order of distilled water, 3.5%NaCl, and 0.1N H2SO4.
(2) Stress corrosion cracks were formed from the notch on three different planes: the original notch plane and two inclined planes to the notch. The crack plane changed depending on environments, notch-root radii and stress levels. Two inclined planes of crack initiation from the notch agreed with the plane of the maximum shear stress.
