•321 stainless steel and Inconel 738 was diffusion bonded using 54Ag-40Cu-5.0Zn-1.0Ni powder-mixture as interlayer.•Effect of holding pressure on metallurgical and mechanical properties of the joint ...was investigated.•The increase in pressure improves the interatomic diffusion and facilitates the formation of a more uniform and wider diffusion affected zone.•An increase in the holding pressure increases the shear strength of the diffusion brazed joints.
The application of 54Ag-40Cu-5.0Zn-1.0Ni powder-mixture interlayer in the diffusion-brazing of Inconel 738 and AISI 321 stainless steel was investigated under a holding pressure variance (1 and 2 MPa). The resultant microstructure, shear strength, and fracture of the brazed joints were investigated. An increase in the holding pressure facilitates better atomic diffusion, uniform thermally-induced reaction layer, and improves the shear strength of the brazed joints. The interfacial reaction layers are made of Cu-rich and Ag-rich phases irrespective of the difference in the holding pressure. Thus, a higher bonding/holding pressure is recommended for the diffusion brazing of Inconel and stainless steels when the brazing medium is a powder mixture.
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•Strain-induced reactivation of a corrosion pit was observed, in-situ.•Pit stability products and 3D pit growth kinetics were estimated.•Applied strain resulted in diffusivity ...parameter (Deff ΔC) of 4.5×10−8molcm−1s−1.•Lacy metal cover fractures were observed.
The reactivation of a corrosion pit under the synergetic effect of strain and electro-chemical polarisation has been observed in a type 304L stainless steel using X-ray computed tomography. The pit reactivation process was associated with the formation of a new pit, directly adjacent to a pre-existing pit. Pit growth kinetics were estimated, revealing an increase of the diffusivity parameter (Deff ΔC) from 3.0×10−8molcm−1s−1 to 4.5×10−8molcm−1s−1 with the application of strain, indicating higher metal dissolution rates. Applied strain resulted in fractured lacy metal covers, and its effect on pit growth kinetics is discussed.
The tensile properties and fracture behavior of lean duplex stainless steel (LDSS) containing Mn–N was investigated through tensile deformation by varying the deformation temperature from 353 K to ...213 K. The ultimate tensile strength (UTS) and yield strength (YS) of the test LDSS increased continuously as the temperature was lowered from 353 K to 213 K. The total elongation (TE) did not decline smoothly as the temperature decreased, instead, the TE peaked at the room temperature (293 K). This temperature-dependent mechanical response was mainly associated with the kinetics of strain-induced martensite transformation (SIMT) in the metastable austenite (γ). A quantitative kinetic model of temperature-dependent SIMT was established, which indicates a positive relationship that the lower the deformation temperature, the faster the SIMT rate. With respect to the nucleation of strain-induced martensite, three modes were clearly manifested by the nucleation mechanism during tensile deformation at different temperature ranges. The first case corresponded to the direct transformation of γ→α′ at 213 K. The second mode of γ→ε→α′ dominated the SIMT at the 213 K–293 K range. The α′-martensite nucleated at the mechanical twinning interactions at 293–333 K, i.e., γ→Twins→α’, which corresponded to the third mode. Notably, as the test temperature was lowered, a continuous fracture mechanism transition gradually emerges from fully ductile to brittle. Microstructural observations from in-situ tensile tests and EBSD showed that damages at the ferrite/martensite (α/α′) interface dominated at 293 K. At 213 K, besides the interfacial fractures that occurred at 293 K, cleavage-type fractures were also found inside ferrite and martensite. Void coalescence was mainly responsible for the ductile fractures over 353 K where SIMT was absent.
The corrosion behaviour of 316 stainless steel in NaCl-KCl-MgCl2 salt vapour at 700 °C under static conditions was investigated in this experiment. Easy-to-peel oxide layers were formed on the ...surface, and their composition and structure changed as exposure continued. The initially formed oxide monolayer was gradually transformed into oxide multilayers, and the outermost layer changed from Cr-Fe oxide to Mg-Cr oxide. The evolution of surface oxide layers was due to the varying diffusion rates of elements in 316 stainless steel as well as to the differing reaction rate of MgCl2 in the salt vapour.
•Corrosion process of 316 SS in NaCl-KCl-MgCl2 salt vapor was investigated at 700 °C.•Loose oxides layers were formed on 316 SS surface in the molten salt vapor.•Composition and structure of oxides layers evolved with vapour exposing time.•Oxide layer evolution reveals the corrosion mechanism of 316 SS in salt vapor.
The microstructures and mechanical properties of friction stir processed 2507 super duplex stainless steel were examined. Experimental results revealed that there is an optimum traverse speed for a ...given rotational speed that gives minimum grain size. The individual and synergistic effects of FSP parameters such as heat input, strain rate and strain on the grain size of the material were evaluated. The results indicate that counteracting effect of heat input and the combined effect of strain rate and strain results in achieving minimum grain size at an intermediate traverse to rotation speed ratio. The twin boundaries (particularly Σ3 CSL boundaries) in the stir zone of friction stir processed material reduced considerably compared to that in the base material. Both the base material and the friction stir processed material with the smallest grain size achieved were subjected to tensile testing at ambient and elevated temperatures under different strain rates. The results obtained are presented and discussed here.
The long-term thermal aging behavior of a 316L austenitic stainless steel welds containing ∼12% of δ-ferrite was investigated using the nano-scale (nanopillar compression), micro-scale ...(micro-hardness and small punch), and macro-scale (tensile and J-R) mechanical property testing methods. Specimens were aged at 343, 375, and 400 °C for up to 20,000 h. The thermal aging activation energies were estimated based on the various mechanical test results using two fitting methods. The activation energies vary from 124 to 300 kJ/mol, depending on fitting and mechanical testing methods. Among the mechanical properties, the nanopillar and J-R test results showed similar activation energies lower than those from other mechanical properties. The similarities and discrepancies among the estimated activation energies were discussed in view of the contribution of embrittled δ-ferrite to the fracture and deformation of test specimens.
•Thermal aging activation energies were evaluated for 316L weld with 12% of δ-ferrite.•Activation energies vary from 124 to 300 kJ/mol depending on test and fitting methods.•Nanopillar and J-R tests showed similar activation energies, lower than those from others.•Nanopillar test on δ-ferrite could represent embrittlement kinetics of bulk J-R test.
Pre-straining at different strain-rate is usually carried out during forming of 304L stainless steel (SS) which can affect its corrosion behaviour. A systematic study on the effect of strain-rate in ...conjunction with pre-strain on electrochemical corrosion behaviour of 304L SS is elucidated for the first time. Prior deformation (10% and 30%) resulted in either beneficial or detrimental effect on the corrosion and pitting resistance depending up on the imposed strain-rate. A novel observation of improved corrosion resistance at higher strain-rate is attributed to differences in strain-rate dependent evolution of microstructure and substructure. This work suggests that the corrosion behaviour of 304L SS is a stronger function of strain-rate compared to the strain and from the microstructure viewpoint, it depends on the complex interplay between dislocation density, deformation-induced martensite, coincidence site lattice (CSL) boundary and, crystallographic texture.
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•Novel observation on the domination role of strain-rate on corrosion behavior of 304L SS is demonstrated.•Corrosion behavior was studied using Potentiodynamic Polarization and EIS tests.•Higher dislocation density and deformation-induced martensite are detrimental for pitting resistance.•CSLboundaries and crystallographic texture close to end orientation are favourable for pitting resistance.•Overall pitting resistance depends on the complex interplay of microstructure, dislocation density and texture.
•Infusing hydrogen leads to higher strains in the austenite than the ferrite.•The strains perpendicular to the surface are highest and tensile.•Hydrogen-induced lattice strain development is ...heterogeneous.•Most lattice strain evolution occurs at the near surface.•The austenite supports the ferrite against hydrogen embrittlement.
Local strain development in the microstructure of a commercial 25Cr-7Ni super duplex stainless steel was mapped using high-energy x-ray diffraction during cathodic hydrogen charging under constant uniaxial load. The infusion of hydrogen resulted in tensile strains in austenite grains, one order of magnitude larger than those in the ferrite. Most strain evolution occurred at the near-surface, with compensating compressive forces developed in underlying regions, with up to two-times more compression occurring in the ferrite than the austenite. The strains along the loading axis were more pronounced than in the transverse direction, in which mostly compressive strains developed in the ferrite.
This paper presents the development and background information of the web crippling design provision proposed for cold-formed stainless steel square and rectangular hollow sections (SHS and RHS) ...incorporated in the recently revised ASCE/SEI 8-22 Specification. The provision was derived based upon reliability requirements as regulated by the ASCE/SEI 8-22 using experimental data from the literature on cold-formed SHS and RHS of austenitic, ferritic, and austenitic-ferritic (duplex and lean-duplex) stainless steel types of various grades including UNS S30400, S30153, S43940, S40977, S32101, and S32202. The accuracy and consistency of the design provisions in the ASCE/SEI 8-22 and SEI/ASCE 8-02 specifications were compared. In addition, the possible extension of validity limits of the new ASCE/SEI 8-22 provision was assessed by utilizing additional finite-element results generated in this study as well as those reported in the literature. It is shown that the validity limits of the new provision could be further extended. Moreover, the direct strength method (DSM) proposed by the authors for web crippling design of cold-formed ferritic stainless steel SHS and RHS was evaluated to check its applicability to other stainless steel types and grades. A modified DSM with updated coefficients is proposed in this study using the format that in line with DSM for members in shear as per ASCE/SEI 8-22. It is shown that the modified DSM can provide well-predicted resistances for cold-formed stainless steel SHS and RHS undergoing web crippling.
Ce-doped TiO2 coatings were applied by electrodeposition on a low-nickel austenitic stainless steel (AISI 201) bearing 8 wt% Mn to improve the electrochemical properties in acidic chloride solutions. ...Characterization of the Ce-doped TiO2 coatings was performed by a scanning electron microscope equipped with energy dispersive X-ray spectroscopy (EDS) to study the tiny features. The corrosion behavior of the bare and coated steel was evaluated in aqueous acidic chloride solutions mixing with different chloride concentrations, 1 mol·L−1 H2SO4 with 0–1.5% NaCl. Potentiodynamic polarization tests were conducted to evaluate the corrosion characteristics, corrosion potential Ecorr and corrosion current density icorr. Further study concerning the weight loss (WL) using immersion tests for the long-term was conducted to determine the bare and corresponding coated steel's equivalent corrosion rates.
It was found that the electrodeposited Ce-doped TiO2 coatings with a layer thickness of ~1 μm enhance the corrosion resistance of the coated steel in the acidic chloride solutions compared to its counterpart, the bare steel. The polarization tests showed that the icorr of the Ce-doped TiO2 coated steel significantly declined to a half value of the bare steel. The Ecorr for all coated specimens shifted to a more positive value when compared with those of the bare steel. The WL measurements displayed that the bare AISI 201 steel experiences intensive corrosion degradation in the presence of a low concentration of chloride ions. However, the Ce-doped TiO2 coatings significantly resist the aggressive chloride ions and consequently increase the corrosion resistance of the steel.
•A ceramic coating of Ce-doped TiO2 was electrodeposited on medium-Mn AISI 201 steel.•The coating morphology shows a dendritic pattern with a uniform thickness of ~1 μm.•The coating constitutes a protective passive film in acidic chloride solutions.•Slow degradation in acidic chloride media due to high stability of Ce-doped TiO2•Pitting and corrosion layers were promoted on the bare steel during corrosion tests.
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