日本金属学会誌

J. Japan Inst. Metals, Vol. 65, No. 12 (2001),
pp. 1082-1090

Determination Method of Weibull Shape Parameter for Evaluation of the Hydrogen Embrittlement Susceptibility of High Strength Steel

Shusaku Takagi1,, Tadanobu Inoue1, Kaneaki Tsuzaki1 and Fumiyoshi Minami2

1Materials Engineering Laboratory, National Institute for Materials Science, Tsukuba 305-0047
2Department of Manufacturing Science, Osaka University, Suita 565-0871

Abstract:

An experimental method to obtain the shape parameter m in the Weibull stress for evaluation of hydrogen embrittlement (HE) was examined in a commercial JIS SCM440 steel with the tensile strength of 1403 MPa. The stepwise HE tests were performed by using circumferentially notched round-bar specimens with the stress concentration factor of 4.9 after hydrogen pre-charging and homogenization treatments. The applied stress of the first step loading was set at 702 MPa and the stress increment from the second step was 14 MPa. The holding time was over 12 h for the first step and over 2 h for each step from the second step. It was conformed by acoustic emission measurement that the first cracking and final fracture occurred in the same step. The diffusible hydrogen content was measured by thermal desorption analysis immediately after fracture. The distribution of stress and hydrogen content near notch root was calculated by FE-analysis. By this procedure, it was able to obtain the distribution of critical Weibull stress under the condition that the local diffusible hydrogen content in fracture process zone was constant. The shape parameter m was determined to be 46 for the present steel. In the discussion part, it was confirmed that the evaluation of the HE susceptibility based on the local approach is appropriate and it was pointed out that the hydrogen content distribution in the fracture process zone must be taken into account for evaluating the HE.


(Received July 2, 2001)

Keywords:

hydrogen embrittlement susceptibility, Weibull stress, Weibull shape parameter, delayed fracture, martensitic high strength steel, acoustic emission, local approach, evaluation method, stepwise hydrogen embrittlement test


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