804 昇温脱離水素分析を用いた高強度ステンレス鋼の水素ぜい化割れ特性評価

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  • Evaluation of Hydrogen Embrittlement Cracking Properties in High Strength Stainless Steel by Thermal Desorption Hydrogen Analysis

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The influences of dynamic loading conditions on the environmentally induced cracking have been investigated in a newly developed ultra-high-strength martensitic stainless steel, HSL180. The corrosive environment used was a 3% NaCl+3g/L NH_4SCN solution at 25℃. The tests were conducted at the free corrosion potential and the cathodically charged condition with a constant cathodic current of 3mA/(cm)^2. The SSRT (slow-strain rate testing) strength at the free corrosion potential was slightly lower than the tensile strength obtained in laboratory air. However, under the cathodically charged condition, the SSRT strength decreased to about a half of the tensile strength. The Kiscc value obtained at the free corrosion potential was about 10 MPa・m^<1/2>. The dynamic SC crack growth rates were accelerated at lower stress intensity indicating that the small vibratory stresses superimposed at a high R promote the HE crack growth. The fatigue crack growth rate at a stress ratio R of 0.1 and a stress cycle frequency of 0.1Hz was enhanced at the free corrosion potential compared with that in dry air. This crack growth acceleration was conspicuous when tested under a cathodically charged condition, or under a negative pulse waveform. The hydrogen evolution rate obtained by thermally desorption analyses, was increased by the cathodic charging, with a lower temperature peak. The fracture surfaces were closely examined with a field emission type, high-resolution scanning electron microscope, and the fracture mechanisms are discussed.

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