Search

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]

[Display omitted] • A low-cost composite (LMC-CS) was designed, which simultaneously exhibited high strength and low HE susceptibility. • Austenitic layer blocks and absorbs the majority of hydrogen, maintaining ductile failure in LMC-CS after fracture. • Semi-coherent composite interface is generated inside DRX grains by the limited element diffusion. • The semi-coherent composite interface deeply trapped hydrogen, thereby hindering hydrogen-induced crack initiation. High-strength metallic materials with low hydrogen embrittlement (HE) susceptibility have always been regarded as ideal commercial materials in the hydrogen energy field. This work proposed a low-cost laminated metal composite (LMC-CS) consisting of austenitic stainless steel (ASS) layer and martensitic steel (MART) layer, which simultaneously achieved high mechanical strength with excellent HE resistance. The ASS layers provide additional strain-hardening capability and the MART layer contributes high strength to LMC-CS after H-charging. Additionally, the composite interface displays semi-coherent characteristics, and the atomic arrangement on both sides follows the Kurdjumov-Sachs orientation relationship with (1 1 ¯ 0) α-Fe // ( 1 ¯ 1 1 ¯ ) γ-Fe and [1 1 1] α-Fe // [1 1 0] γ-Fe and the Nishiyama–Wassermann orientation relationship with ( 1 ¯ 1 ¯ 0) α-Fe // ( 1 ¯ 11) γ-Fe and [0 0 1] α-Fe // [ 01 1 ¯ ] γ-Fe., which coordinates deformation between layers and hinders hydrogen-induced cracks initiation at the interface. The as-designed LMC-CS achieves an ultimate tensile strength of 1102 MPa and an elongation loss of 14.8% after long-time hydrogen charging with sides sealed, outperforming a wide range of metallic materials. This work provides a fresh perspective on developing commercial materials with high strength and superior HE resistance for application in severe hydrogen environments. [ABSTRACT FROM AUTHOR]

Hydrogen-induced damage is an inevitable challenge in pipeline safety applications, especially, the fusion welded joints owing to microstructure heterogeneity caused by welding process. In this work, X100 pipeline steel was subjected to friction stir welding (FSW) at rotation rates of 300–600 rpm under water cooling, and the relationship among the microstructure, hydrogen diffusivity, and hydrogen embrittlement (HE) behavior of the nugget zone (NZ) were studied. The NZ at 600 rpm had the highest effective hydrogen diffusion coefficient (D eff) of 2.1 × 10−10 m2/s because of the highest dislocation density and lowest ratio of effective grain boundary. The D eff decreased with decreasing rotation rate due to the decrease of dislocation density and the increase of ratio of effective grain boundary, and the lowest D eff of 1.32 × 10−10 m2/s was obtained at 300 rpm. After hydrogen charging, the tensile strength of all specimens decreased slightly, while the elongation decreased significantly. As the rotation rate decreased, the elongation loss was obviously inhibited, and ultimately a lowest elongation loss of 31.8% was obtained at 300 rpm. The abovementioned excellent mechanical properties were attributed to the fine ferrite/martensite structure, low D eff , and strong {111}//ND texture dramatically inhibiting hydrogen-induced cracking initiation and propagation. • FSW of X100 steel was performed in water cooling, producing defect-free weld. • The diffusion behavior of hydrogen in the NZ was studies. • The effect of hydrogen on deformation and fracture behavior was analyzed. • The NZ with fine ferrite/martensite present high HE resistance. [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]

The medium-Mn steels with high strength and ductility can be used as a potential material in the engineering fields. However, the weld in the medium-Mn steel joint has extremely low ductility due to the existence of full martensite. In this work, a superior tensile strength of 1453 MPa and elongation of 32.7% was obtained in the weld of friction stir welded (FSWed) medium-Mn steel. This should be related to high volume fraction of austenite (24.4%) far higher than that of basal metal (15.1%). The formation mechanism of exceptionally high fraction of austenite was studied based on the transformation kinetics. The volume fraction of austenite in the weld predicted by classical model was only 15.4% much lower than the experimentally measured value, indicating that this model is not suitable for FSW. We applied various assumptions about the diffusivity of Mn in austenite and ferrite during simulation. Consequently, when the Mn diffusivity of austenite and ferrite was multiplied by 4000 and 1500 times, respectively, the simulated austenite volume fraction was well consistent with the experimental results. This was attributed to that the high density of dislocations introduced by strong plastic deformation of FSW promoted the Mn diffusion and the austenitic reverse transformation. • The weld contained a high volume fraction of austenite (24.4%) far higher than that of the basal metal. • The formation mechanism of exceptionally high fraction of austenite was studied based on the transformation kinetics. • A superior tensile strength of 1453 MPa and elongation of 32.7% was obtained in the weld of FSW medium-Mn steel. • The contribution of various strengthening mechanisms to yield strength was evaluated. [ABSTRACT FROM AUTHOR]

In this study, the crystallography of the nugget zone of bainitic steel was examined by applying friction stir welding (FSW) and submerging in various cooling mediums. In air, the variants mainly occurred in a single Bain group because of the plastic accommodation of transformation strain. However, in water and a mixture of water and CO 2 , the variants generated in two and four close-packed (CP) groups, respectively, and this was attributed to the self-accommodation of transformation strain. In this case, the variant selection was inhibited by both the severe deformation during FSW and low temperature of cooling medium. Furthermore, the reduced cooling-medium temperature resulted in refined bainitic and martensitic blocks with an increased fraction of high-misorientation variant pairs owing to the increased transformation driving force. • Previous studies on the FSW bainitic steel were focused on the phase transformation, and the crystallography was ignored. • The crystallographic characteristics and its effect on microstructure refinement for FSW bainitic steel was studied. • In air, the plastic deformation in austenite easily accommodates the transformation strain, causing the variant selection. • In water and water+CO 2 , refined blocks were obtained with an increased fraction of high-misorientation variant pairs. [ABSTRACT FROM AUTHOR]