日本金属学会誌

J. Japan Inst. Metals, Vol. 48, No. 2 (1984),
pp. 144-150

The Effect of Tempering Temperature on Susceptibility to Hydrogen Embrittlement of Chromium Molybdenum Steel

Mitsunori Tsutsui1, Takashi Yamada1 and Rikuro Otsuka2

1Nagoya Municipal Industrial Research Institute, Nagoya
2Nagoya Institute of Technology, Nagoya

Abstract:

The purpose of the present study is to investigate the effects of heat treatment on the hydrogen embrittlement of chromium molybdenum steel containing 0.35%C, 1.05%Cr and 0.15%Mo. The specimens were deformed at a constant slow stress rate with cathodic hydrogen charging simultaneously.
The susceptibility to the hydrogen embrittlement of the specimens was evaluated from the loss in strength caused by hydrogen absorption. On the other hand, the hydrogen content was estimated as a function of tempering temperature by means of the electrochemical permeation technique.
The results are as follows:
(1)  The susceptibility to hydrogen embrittlement of chromium molybdenum steel varied with tempering temperature. The tensile strength of the specimens tempered below 823 K decreased markedly by hydrogen charging. The maximum loss in strength was obtained at tempering temperature of 673 K.
(2)  The diffusion coefficient of hydrogen increased with increasing tempering temperature, and the content of hydrogen decreased conversely.
(3)  The tensile strength of hydrogen charged specimens recovered to the same level as that of the hydrogen free specimen by leaving them in air for 345.6 ks after hydrogen charging.
It is suggested that the hydrogen embrittlement is not caused by hydrogen, which is fastened tightly at trap sites, but by diffusible hydrogen.


(Received 1983/07/30)

Keywords:

chromium molybdenum steel, susceptibility to hydrogen embrittlement, tempering temperature, slow stress rate technique, cathodic hydrogen charging, diffusion coefficient of hydrogen, hydrogen content, diffusible hydrogen


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