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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]

A lean duplex stainless steel was friction stir processed at 300 rpm-100 mm/min using a W-Re stirring tool. The microstructural evolution on the advancing side, the center, and the retreating side of the stir zone were studied by a combination of electron microscopy and electron backscattered diffraction. The study indicated that the direction of fiber structure on the advancing side, center, retreating side were 0°, 90°, 45° relative to the processing direction because of the stirring effect of the tool. Given that the strain rate and temperature were different on the advancing side, center and retreating side, the phase fraction, misorientation, texture components varied in different parts of the stir zone. The deformation mostly occurred in the center and retreating side and the material on the advancing side almost did not deform during tensile test. As a result, strain induced martensitic transformation occurred in the center and retreating side. The voids initiated at the interface of ferrite and transformed martensite on the retreating side, and cracks also propagated along this interface during tensile test. Furthermore, because of the 45° direction of the fiber structure on the retreating side, the tensile strength of the FSP sample was slightly less than the base metal. [ABSTRACT FROM AUTHOR]

The high Mn steel (Mn ≥ 20 wt.%) is widely applied because of excellent cryogenic properties. In the fusion-welded high-Mn steel joint, the Mn vapor and segregation degrade the joint quality. Friction stir welding (FSW) produces a high-Mn steel joint without defect, but the nugget zone (NZ) exhibits a poor plasticity. In this work, the preheating was subjected to FSW high-Mn steel to improve the plasticity of the NZ. Compared with the as-welded NZ, the as-preheated NZ contained slightly coarser austenite with lower density of dislocations (6.7 × 1014 m−2), and had a lower stacking fault energy (SFE) (47.18 mJ m−2) at room temperature. The lower SFE caused the deformation mechanism of dislocation slip and active twinning-induced plasticity (TWIP) in the as-preheated NZ owing to the lower back stress and critical twinning stress. Subsequently, a high strength and plasticity product of 62 GPa% was achieved in the as-preheated NZ, which was consistent with high strain hardening rate. At cryogenic temperature of −196 °C, the SFE of the as-preheated NZ decreased to 35.66 mJ m−2, but more active TWIP besides dislocation slip was found during tension. Therefore, the as-preheated NZ exhibited excellent strength and plasticity product of 91.9 GPa%. Furthermore, the yield strength of the as-preheated NZ was slightly reduced, which was attributed to the decreased of dislocation density and grain growth. • The preheating was introduced into the friction stir welded high Mn steel. • The SFE of austenite in the as-welded and as-preheated NZs at room and cryogenic temperature was calculated. • The deformation behavior of the as-welded and as-preheated NZs at room and cryogenic temperature was studied. • The contribution of various strengthening mechanisms to yield strength was evaluated. • The as-preheated-320 NZ presented excellent strength and plasticity product at room and cryogenic temperature. [ABSTRACT FROM AUTHOR]