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.
