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The interaction of hydrogen with various tungsten-inert-gas-welded austenitic stainless steels’ (AUSS) microstructure is studied by means of desorption/absorption analysis and microstructure observations. One of the limitations of welding is created by the presence of hydrogen in the weld, which can shorten the steel’s service life. The local hydrogen concentration, trapping, and its distribution along the welded samples were studied by thermal desorption spectrometry and were supported by X-ray diffraction (XRD) and electronic microstructural observations. Hydrogen content demonstrated a dependence on the welding zone. It was found that hydrogen distribution, and accepted microstructure during welding, played a significant role in the trapping mechanism of 316L AUSS. XRD analysis revealed residual stresses which were caused due to the presence of hydrogen in c-phase. It was shown that the austenite microconstituents inside 316L can have a crucial effect in preventing hydrogen-assisted cracking phenomenon. The effects of AUSS microstructure on hydrogen absorption and desorption behavior are discussed in detail.
Fatigue crack propagation investigations have been performed in austenitic-ferritic duplex stainless steel H22N5M3 in air and during hydrogen charging, using various frequencies of loading. Strong differences of crack propagation velocity depending on the test conditions were noticed. Lower frequency with applied hydrogen charging led to the huge increase of crack propagation velocity compared to the tests performed in air. To understand such a behaviour in each case and characterize crack mode, the samples were observed using electron back-scattered diffraction (EBSD). It was shown that in air, the fatigue crack propagation involved plastic deformation and the resulting cracks had ductile character. The presence of hydrogen led to more brittle mode of cracking. This effect was also connected with frequency of loading: lower frequency, which assured longer time for hydrogen-crack tip interaction, resulted in the highest crack propagation velocity and the brittle cracking mode with lower amount of plastic deformation. The performed observations indicated that the path of the crack went mostly transgranularly through both austenite and ferrite phases. Phase and grain boundaries were not the preferred paths for crack propagation.
The hydrogen influence on the microstructure of the austenitic-ferritic Cr22-Ni5-Mo3 stainless steel was investigated. Cathodic hydrogen charging was performed electrochemically from aqueous solution of 0.1M H2SO4 with hydrogen entry promoter addition. The aim of this study was to reveal microstructural changes appearing during the hydrogen charging and particularly to clarify the occurrence of phase transformations induced by hydrogen. The specific changes in both phases of steel were observed. In the ferritic phase, strong increase of dislocation density was noticed. Longer time of hydrogen charging leaded also to the strips and twin plates formation in ferrite phase. In the austenitic phase, the generation of stacking faults, followed by the formation of α' martensite was remarked.