Effects of shielding with various hydrogen-argon mixtures on supermartensitic stainless steel TIG welds

A number of common defects in stainless steel welding result from the presence of hydrogen in the weld. The service life of the stainless steel joints is further significantly dependent on the presence of hydrogen in the respective environment and the susceptibility of various weld microstructures to hydrogen degradation. As a relatively new materials generation, supermartensitic stainless steels (SMSS) are increasingly applied to substitute more expensive alloys, particularly in the oil and gas industries. As a result of their martensitic microstructure these alloys are prone to hydrogen assisted cracking (HAC). The resistance of SMSS to hydrogen assisted stress corrosion cracking (HASCC) during sour service has been extensively studied, predominantly for industrial purposes. Studies are primarily conducted with parent materials based on standard test procedures. The principal hydrogen behavior in welded SMSS microstructures has been less investigated. The central objectives of the study are to determine the hydrogen interactions with the microstructure of a Gas Tungsten Arc (GTA) welded SMSS and hydrogen trapping mechanisms. The interactions of hydrogen with various Tungsten Inert Gas (TIG) welded SMSS microstructures are investigated by means of X-ray diffraction (XRD) and optic (OM) and electronic microscopy (SEM). A number of methods have been employed for the estimation of the quantities of absorbed hydrogen. Hydrogen interaction with structural defects and the characteristics of hydrogen desorption have been studied by means of thermal desorption spectroscopy (TDS), and hydrogen content measurements (LECO analyses). The effects of the respective microstructure on hydrogen absorption and desorption behavior are discussed in detail.