Technological monitoring of diffusible hydrogen in steels

Diffusible hydrogen (DH) in metals is a part of dissolved hydrogen with high diffusion mobility. It is the main cause of cold cracking of welds and deposited metal. The paper presents the results of technological testing of DH in steels. It has been found that due to low maximum permissible concentrations in high-strength steels, the measurement methods verified for weld metal may give multiple measurement errors. A DH measurement technique is proposed based on the vacuum heating method with mass spectrometric measurement of hydrogen flow from the sample during its analysis. It is proposed to separate the flows of DH and more strongly bound hydrogen during vacuum extraction from the sample using the extraction curve. It is shown that good convergence of results is observed when using this technique, and the measurement time can be significantly reduced compared to the recommendations of standards for weld metal. Based on the comparison of experimental data and standard requirements, it was found that the DH activation energy is no more than 0.3 eV. The extraction time of DH at a fixed analysis temperature depends significantly on the size of the steel sample from which hydrogen is extracted. This does not allow using only the extraction time and temperature when separating DH from bound hydrogen, as recommended by many existing methods for measuring the mass fraction of DH. The obtained results can be used in technological testing of DH in steels.