The distribution of hydrogen near notch tip of austenitic steel 21Cr-7Ni-9Mn-0.25N charging in autoclave under mixed mode loading (I + II and I + III) has been studied with a new method of microregion locating in Ion Microprobe Mass Analyzer (KYKY LT-1A type). It was shown that there were two peaks of hydrogen accumulation, one at notch tip and the other far apart from it, either in cracking direction or in maximum plastic region's(γ_p~(max)), and with the increasing of mode II loading, the peak of hydrogen accumulation of the latter decreased and moved to notch tip. There existed also two peaks of hydrogen accumulation near notch tip under mixed mode I + III loading, with the increasing of mode III component, the two peaks of hydrogen accumulation all decreased and the second hydrogen accumulation peak moving closer to the notch tip. The change of original hydrogen concentration of steel has few effects on the two peaks of hydrogen accumulation near notch tip, Whereas the stress and strain field affect predominantly the formation of the two peaks near notch tip. In order to determine the properties of the two hydrogen accumulation peaks, ADINA non-linear finite element method was used to caculate quantitatively the distribution of hydrostatic stress(σ_h) and eqivalent strain (ε_(eq)) near notch tip, It is shown that with the increasing of distance from the notch tip, σ_h~(max) decrease gradually and move to notch tip. while the (ε_(eq)) decrease griftly. It is revealed by the analysis of comparising hydrogen concentration with stress and strain near notch tip that: The hydrogen accumulation peak at notch tip is caused by trapping effect of dislocation on dissolved hydrogen, while the other one caused by the hydrostatic stress. The interaction between dislocation and hydrostatic stress caused the two hydrogen peaks near notch tip, and the distribution of hydrogen concentration near notch tip is give by: C_H/C_O = f(θ)/r~(1/2) + exp(-A_O) |R - R_O|) - B_O Where, C_0 is hydrogen concentration in absent of stress, A_O, B_O are functions of strain and stress state and material properties.
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