Character of adsorptive weakening of steel by hydrogen-containing gases

Abstract

Under normal conditions, the hydrogen-containing gases reduced the initial value of 7 (8"102 J/m 2) of the steel by 25% (H2), 50% (H2S), 25% (HCI), and 20% (CH~). In helium, A7 = 0. The reduction of Y in all cases occurred immediately after admission of the gas into the working chamber containing the specimen, subsequently remaining nearly constant over time. Holding specimens in the gas for i00 h with subsequent testing in the vacuum did not change the initial value of y. Both the above results and the temperature dependence of Ay obtained earlier [5] in gaseous hydrogen (Fig. i) can be explained only by the specific features of the adsorptive interaction of hydrogen and steel in the investigated temperature range. This presumption is also supported by the following considerations: i. An increase in test temperature from 120 to 300~ undoubtedly intensifies the diffusion of hydrogen in the steel, and the greater embrittlement of the metal with increasing temperature (Fig. I) maybe explained by the large amount of hydrogen having penetrated the metal. However, a further increase in temperature should have further embrittled the metal, but the test results show the opposite effect. Thus, the hydrogen absorbed by the metal cannot be considered responsible for the reduction in 7 for the metal. 2. The decrease in A7 with an increase in temperature to 420~ (Fig. i) could be due to some additional tempering of the metal during its testing. As is known [6], the increase in the ductility of the metal that occurs during tempering makes it less sensitive to the effects of the medium. We therefore conducted tests to obtain the dependence of A 7 for the steel on the preliminary tempering temperature. The resultant data (Fig. 2a) (7 was determined at room temperature) shows that additional tempering, even at 500~ has almost no effect on the degree of hydrogen embrittlement of the metal. Thus, we explain the reduction in the strength of the steel by the action of gaseous hydrogen in the investigated temperature range first of all in terms of its chemisorptive effect on the metal at the tip of a developed crack (Rebinder effect). However, the character of the adsorptive process facilitating embrittlement of the metal remains unclear.