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The susceptibility to hydrogen embrittlement behavior was investigated in an interstitial Mn–N austenitic steel HR183 and stainless steel 316L. Hydrogen was introduced by cathodic hydrogen charging at 363 K. HR183 has stronger austenite stability than 316L despite its lower nickel content, the addition of manganese and nitrogen inhibited martensitic transformation during the slow strain rate tensile deformation. Due to the diffusion of hydrogen being delayed by the interstitial solution of nitrogen atoms and the uniform dislocation slips, hydrogen permeates more slowly in HR183 than 316L, contributing to an 84.79 μm thinner brittle fracture layer in HR183 steel. Hydrogen charging caused elongation losses in both 316L and HR183 steels associated with the hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanism. However, the hydrogen embrittlement susceptibility of HR183 is 3.4 times lower than that of 316L according to the difference in elongation loss between the two steel after hydrogen charging. Deformation twins trapped a lot amount of hydrogen leading to brittle intergranular fracture in 316L. The multiple directions of slip in HR183 steel suppressed the strain localization inside grains and delayed the adverse effects conducted by HELP and HEDE mechanism, eventually inhibiting server hydrogen embrittlement in the HR183 steel. This study is assisting in the development of low-cost stainless steel with excellent hydrogen embrittlement resistance that can be used in harsh hydrogen-containing environments. [Display omitted] • SIM was suppressed by adding manganese and nitrogen with low nickel content. • Interstitial nitrogen affected the solubility of hydrogen in FCC lattice and slowed down the permeation of hydrogen. • The HELP and HEDE mechanism conducted hydrogen embrittlement in interstitial Mn–N austenitic steel. • Multiple directions of slip alleviated the adverse effect of HELP and HEDE mechanism. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement (HE) susceptibility in nickel-economized austenitic stainless steels (NEASSs) with varying manganese content was explored based on the statistical results of hydrogen-induced cracks (HICs) characterization after slow strain rate tensile (SSRT). With almost the same initial microstructure, manganese modifies the deformation patterns of NEASSs by adjusting stacking fault energy, which essentially influences the initiation and propagation mechanisms of HICs and eventually results in different brittle fracture modes. Additionally, different ways of HIC initiation and propagation caused significant differences in brittle-fracture areas and HICs lengths after SSRT tests, which resulted in great variations in HE susceptibility between NEASSs. [Display omitted] • The hydrogen-induced cracking behavior in nickel-economized austenitic stainless steels is systematically explained. • A Higher Mn alloying leads to a lower strength/elongation loss in NEASSs. • The hydrogen embrittlement performance of NEASS is essentially influenced by its deformation mode during SSRT tests. • The fracture mode of the brittle-fracture zone is determined by the initiation and propagation behavior of HICs • For NEASSs with plastic deformation dominated by dislocation slip exhibit lower HE susceptibility. [ABSTRACT FROM AUTHOR]

The effect of grain boundary character distribution (GBCD) on hydrogen-induced cracks (HICs) initiation and propagation in nickel-saving austenitic stainless steel was investigated at different strain rates with electrochemical hydrogen charging. The fracture strength and elongation of specimens decreased as the strain rates decreased due to more hydrogen atoms being transported by mobile dislocations. HICs are more likely to initiate at random grain boundaries (RGBs) because of poor deformation coordination of adjacent grains at RGBs after hydrogen charging. Special boundaries (SBs) deflected HICs and hindered the propagation of HICs owing to a more stable boundary structure and less strain localization during slow strain rate tensile (SSRT) deformation with hydrogen charging. Furthermore, highly efficient distributions of SBs contribute to great resistance to hydrogen embrittlement. • Higher content of SBs reduced the elongation and strength degeneration of material after H-charging. • With the increase of SB, the fracture mode changes from intergranular to quasi-cleavage. • SBs are beneficial to delay hydrogen permeation. • HICs prefer to initiate on RGBs due to poor deformation coordination after H-charging. • HICs are deflected and terminated by special boundaries, a higher fraction of f J2 /(1-f J3) effectively inhibit HICs propagation. [ABSTRACT FROM AUTHOR]

AISI 201 stainless steel plate was friction stir processed (FSP) at rotation speeds in the range of 500–1000 rpm with traverse speed of 100 mm/min, and rotation speed of 1000 rpm with traverse speed of 50 mm/min using W-Re stirring tool. The microstructural evolution was studied by optical microscopy, scanning electron microscopy, electron backscattered diffraction, electron probe micro analyzer and transmission electron microscopy. The results suggested that the final grain structure in the stir zone (SZ) originated from the competition between continuous recrystallization (CDRX) and discontinuous recrystallization (DDRX). The grain size and the content of δ-ferrite in SZ were closely related to the processing parameters, and a band structure contained 6.5% δ-ferrite formed. Furthermore, the δ-ferrite formed in SZ significantly promoted the occurrence of DDRX and strong (111) [112] annealing texture formed in δ-ferrite. No sigma phase was observed in the SZ, and the density of dislocations and sub-structures was found to be seriously affected by the processing parameters and locations of SZs. The relationship between mechanical properties and structure is elucidated. [ABSTRACT FROM AUTHOR]