高強度鋼の曲げおよびねじり応力下の繰返しSCCき裂発生挙動

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The influences of bending and torsional loading modes on cyclic SCC crack initiation behavior were investigated in a high-strength steel, SCM435, sensitive to hydrogen embrittlement type SCC. Under bending loads, an intergranular cyclic SCC crack by tensile stress is initiated at the bottom of a corrosion pit, and the strength of cyclic SCC is smaller than that of fatigue in laboratory air. Under torsional loads in laboratory air and in a 3.5 % NaCl solution at higher stress levels of τ_<max>≧780 MPa, specimens are fractured by transgranular cracking normal to the longitudinal direction, with no influence of environment on strength. At τ_<max>780 MPa, however, cyclic SCC strength is smaller than fatigue one At 500 MPa≦τ_<max>780 MPa, a longitudinal crack by shear stress, which is considered to be caused by anodic dissolution, is initiated at the bottom of a corrosion pit, and then an intergranular cyclic SCC crack by hydrogen embrittlement at an angle of 45 degrees against the longitudinal direction (45-degree crack), which is dominated by a principal stress, is initiated at the tip of the longitudinal crack. At τ_<max> 500 MPa, however, an intergranular 45-degree crack by hydrogen embrittlement is immediately initiated at the bottom of max a corrosion pit. In the case of bending and torsional loads at τ_<max>< 500 MPa the mechanical condition for crack initiation is determined by the K_<IFSCC> value, which is obtained by assuming corrosion pits as sharp cracks. In a similar way, a longitudinal crack is initiated when a K_<III> value exceeds the K_<IIIFSCC>; a 45-degree crack is initiated when a Mode I stress intensity factor of a longitudinal crack exceeds the K_<IFSCC> value.
社団法人日本材料学会の論文
1988-06-15

高強度鋼の曲げおよびねじり応力下の繰返しSCCき裂発生挙動

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