HYDROGEN EMBRITTLEMENT AND INTERNAL FRICTION OF CARBON STEEL

Abstract

Hydrogen in steel is a harmful element which causes hydrogen-embrittlement phenomena; i.e. white spots, hair-line cracks and pickling embrittlement etc.
Therefore many investigations as to behaviors of hydrogen in steel were previously reported. However even at present, there are many unsolved problems.
Accordingly an experiment on some hypo-eutectoid carbon steels including pure iron and eutectoid steel was made. The authors measured amounts of evolved hydrogen, changes of internal friction as a structure-sensitive quantity and mechanical properties as a measure of actual embrittlement during the evolution (at room temperature) of electrically charged hydrogen, and then investigated the relationships among them.
The results obtained on these steels are summarized as follows. Microscopically speaking, diffusible hydrogen (at room temperature) was much absorbed in free ferrite than ferrite in pearlite, but macroscopically existed in uniform distribution of concentration. This hydrogen evolved with the diffusion process described with the Fick's formula, and the diffusion constant was calculated to be D=3.7×10^-5 cm²/mn. (at room temperature). On the other hand decrease of the elongation and reduction of area in tensile testing, decrease of the impact value, and increase of the internal friction were caused by absorbed hydrogen, but each change took its own form of recovery by aging; i.e. though the recovery of ductility in tensile testing was parallel to hydrogen evolution, the one of internal friction was more rapid than the former and the one of impact value was far more rapid.