A modelling approach is presented to identify the deformation mechanisms of 316L stainless steel produced by laser powder bed fusion (LPBF). The approach incorporates the evolution of dislocations, ...forming a forest, and of twins, which develop a back-stress. The overall plasticity behaviour is described in terms of dislocation multiplication and annihilation progress with strain. The modelling is matched up with detailed electron microscopy observations; the combination of both demonstrates the deformation behaviour of LPBF builds is intrinsically different to that of wrought alloys. LPBFed samples undergo three stages of deformation, with the first developing twins, which formation quickly saturates; the second sees a dramatic increase in dislocation forest hardening, combined with dislocation recovery; and the third undergoes dynamic recrystallization taking place around heavily twinned sections. Opposite to wrought alloys, LPBFed specimens decrease their density of statistically stored dislocations throughout deformation, and it is shown that this behaviour is replicated by other LPBFed metals, including high-entropy alloys. The intrinsic behavioural differences in LPBF plasticity is thought to be due to the presence of a residual stress; this promotes dislocation recovery from the onset of deformation.
•Plastic deformation mechanisms of laser powder bed fused 316L stainless steel are modelled.•Dislocation forest, twinning, recovery and recrystallization progress during room temperature deformation are modelled.•Statistically stored and geometrically necessary dislocation evolution are modelled and their progress is opposite to wrought alloys.•Residual stress promotes dislocation recovery from the onset of deformation, making additively manufactured alloys plasticity intrinsically different.
Carbon steels are widely used in the oil and gas industry from downhole tubing to transport trunk lines. Microbes form biofilms, some of which cause the so-called microbiologically influenced ...corrosion (MIC) of carbon steels. MIC by sulfate reducing bacteria (SRB) is often a leading cause in MIC failures. Electrogenic SRB sessile cells harvest extracellular electrons from elemental iron oxidation for energy production in their metabolism. A previous study suggested that electron mediators riboflavin and flavin adenine dinucleotide (FAD) both accelerated the MIC of 304 stainless steel by the Desulfovibrio vulgaris biofilm that is a corrosive SRB biofilm. Compared with stainless steels, carbon steels are usually far more prone to SRB attacks because SRB biofilms form much denser biofilms on carbon steel surfaces with a sessile cell density that is two orders of magnitude higher. In this work, C1018 carbon steel coupons were used in tests of MIC by D. vulgaris with and without an electron mediator. Experimental weight loss and pit depth data conclusively confirmed that both riboflavin and FAD were able to accelerate D. vulgaris attack against the carbon steel considerably. It has important implications in MIC failure analysis and MIC mitigation in the oil and gas industry.
The attachment, biofilm formation and control of biofilm formed by Vibrio parahaemolyticus (VP) ATCC 17802 on four stainless steel (SS) coupons which are different in type or finishing, 316L, 304, ...430 with 2B finish and 304 with BA finish, were studied. SS coupons were subjected to surface roughness measurement using Atomic Force Microscope and Scanning Electron Microscope. The surface of 316L/2B was the roughest surface while 403/2B and 304/BA were the least roughness surface. VP were able to attach on all SS surfaces immediately after contact. They tended to attach on the rougher surface of the SS samples better than the smoother ones. They could be released from surfaces into liquid medium and grew very fast, after contact. Attached cells formed multilayer clumps within 72 h. Cells in biofilms survived on all SS surfaces under dry condition for more than 72 h. The 0.02% benzalkonium chloride (BAC) completely eliminate 8 log10 CFU mL−1 planktonic cells immediately after contact, but it took more than 1 min to eliminate viable cells of 24 and 72h biofilms from 304/2B and 316L/2B. The viable cells in biofilm on the rougher surfaces showed more resistance to the BAC than those on the smoother ones.
•V. parahaemolyticus attached on the stainless steel surface immediately after contact.•V. parahaemolyticus cells in biofilm survive under dry condition for at least 72 h.•V. parahaemolyticus cells were released and increased very fast after contact to liquid NB.•0.02% BAC was able to eliminate viable cells in 24 and 72 h biofilms after 1 min contact.•The highest number of V. paraheamolyticus attached on the surface of 316L/2B coupons.
2205 duplex stainless steel (DSS) is a kind of complex structure stainless steel, which has advantages of both austenitic and ferritic stainless steel. Compared with 300 series stainless steel, it ...has better performance and can be used in more severe environment. Bulk 2205 DSS with heterogeneous composite structure is prepared via aluminothermic reaction. The volume percentage of ferrite phase is 32.3%, that of austenite phase is 59.7%, and σ phase is 8.1%. Average grain size of nanocrystalline and ultrafine austenite is 20.9 nm, accounting for 74.2%. The relatively mechanical properties deteriorate, which belongs to brittle fracture. The joint action mechanism of dual-phase structure and micro/nanostructure is analyzed by fracture observation. At present, the tensile strength and fracture elongation of as-cast heterogeneous composite structure 2205 DSS are poor. Therefore, different rolling and annealing systems are needed to coarsen grains and adjust mechanical properties through structure design.
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•Grain boundary engineering of large size materials via warm-rolling and annealing.•The large size 316 after GBE has even distributed high proportion of CSL boundaries.•Formation of ...the long twin boundary chains is a prominent characteristic of GBE 316.
A new thermomechanical processing of warm rolling by a low deformation followed by annealing, which was specially developed for grain boundary (GB) engineering of large-size materials, was performed on a large-size 316 stainless steel. To examine usefulness of the thermomechanical process, the GB-networks before and after this process were quantitatively compared, and intergranular attack susceptibility was measured. Results clearly demonstrate that the GB-engineered 316 has higher proportions of coincidence site lattice boundaries, larger grain-clusters, longer twin boundary chains, and lower susceptibility to intergranular attack, indicating a successful process for GB-engineering. Additionally, a new parameter called twin boundary chain was proposed to evaluate the GB-network optimization.
The effect of dissolved hydrogen (DH) content and zinc addition on the corrosion behavior of type 316 stainless steel was investigated in the primary water environment of pressurized water reactors. ...The coupled effect, as well as the individual effect of increasing DH concentration and zinc addition, was investigated. Increasing DH from 25 (normal) to 50 (high) cc/kg-H2O resulted in 3 times thicker oxide layer. With the addition of 30 ppb zinc, the oxide layer became substantially thinner in both normal and high DH conditions. The measured electrochemical properties of oxide layers were in agreement with the observed corrosion behavior such that the zinc incorporated oxide film showed significant increase in reaction resistance and bode impedance value. Meanwhile, both reaction resistance and bode impedance slightly decreased with increasing DH concentration. Overall, the best corrosion resistance was observed in the simulated PWR environment with normal DH concentration and zinc addition.
In this work, a semi-continuous functionally graded material (FGM) between an austenitic and a super duplex stainless steel was obtained. These materials are of great interest for the chemical, ...offshore, and oil and gas sectors since the austenitic stainless steel type 316L is common (and not so expensive) and super duplex stainless steels have better mechanical and corrosion resistance but are more expensive and complex in their microstructural phases formation and the obtention of the balance between their main phases. Using directed energy deposition, it was possible to efficiently combine two powders of different chemical compositions by automated mixing prior to their delivery into the nozzle, coaxially to the laser beam for melting. A dense material via additive manufacturing was obtained, with minimum defectology and with a semi-continuous and controlled chemical compositional gradient in the manufactured part. The evolution of ferrite formation has been verified and the phase fraction measured. The resulting microstructure, austenite/ferrite ratio, and hardness variations were evaluated, starting from 100% austenitic stainless-steel composition and with variants of 5% in wt.% until achieving 100% of super duplex steel at the end of the part. Finally, the correlation between the increase in hardness of the FGM with the increase in the ferrite phase area fraction was verified.
Open cell 316L stainless steel foam (SSF) of varying porosities have been developed through powder metallurgy route using evaporative spherical urea particles (UP) as a space holder. Stainless steel ...powders (SSP) were cold compacted under 500 MPa pressure and sintered at 1200 °C for 1 h in a high vacuum atmosphere (10−4 mbar). Detailed Energy dispersive X-ray spectroscopy (EDS) analysis and X-ray diffraction pattern (XRD) conformed that no residue of space holder (urea) in sintered samples. The compressive deformation behavior of sintered foam samples with varying relative densities (ρrd) was conducted at 0.01s−1 strain rate. The yield strength, elastic modulus (Ef), plastic modulus, average plateau stress (σpl) and energy absorption (Eab) of the foam increases with increases in the relative density and these follows power law relationship with relative density. On the other hand, densification strain (ɛd) decreases with increases relative density. This has been discussed with the deformation mechanism of the stainless steel foam (SSF). Deformation of SSF is associated with cell wall (CW) bending, CW collapse due to bulking followed by shearing and facture of cell wall layer by layer.
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•Urea can be used as an excellent evaporative space holder for making SSF.•Cell sizes are almost related to the size of the space holder.•The mechanical properties of SSF follow standard relationship.•Deformation behavior of SSF is strong as a function of relative density.
Selective Laser Melting (SLM) is a metal additive manufacturing process wherein a laser beam is used to melt and fuse metal powder layer by layer to create a part. This technique involves the ...interaction of various process parameters such as laser power, scanning speed, powder layer thickness and scan strategy. In this study, the effects of two different scan strategies were investigated and the 17-4PH stainless steel samples fabricated using these strategies, both in as-fabricated and heat-treated conditions, were characterized in terms of relative density, microstructural phase composition and micro-hardness. It was found that the samples printed with double scan strategy showed improvement in the relative density as compared to that printed with single scan strategy. Moreover, it was observed that the samples fabricated using the double scan strategy showed higher hardness than the samples printed using single scan strategy which was attributed to the high phase distribution of martensite than the retained austenite in these samples. In addition, the heat treatment of the as-fabricated samples produced uniform distribution of tempered martensite-dominant phase with negligible retained austenite, resulting in improved hardness as comparable to the heat-treated wrought sample.
The effects of hydrogen on the tensile properties and fracture surface morphologies of Type 316L stainless steel were investigated using virgin and prestrained specimens. Hydrogen gas exposure at ...10 MPa and 250 °C for 192 h resulted in its uniform distribution in the specimens. Such internal hydrogen degraded the tensile ductility of the specimens. Cup–cone fracture occurred in the non-, Ar-, and H-exposed specimens. The fracture surfaces were covered with large and small dimples. The H-exposed specimens exhibited larger small-dimple areas than the non- and Ar-exposed ones. The diameter of the large dimples decreased with increasing small-dimple area. Three-dimensional analysis of the dimples showed that the small-dimple regions were void sheets produced by local shear strain. Hydrogen accelerated nucleation of voids and formation of the void sheets by enhancing localization of shear deformation, thereby reducing the average size of the dimples.
•Hydrogen content slightly increased with increasing prestrain.•Cup–cone fracture occurred in non-, argon-, and hydrogen-exposed specimens.•All fracture surfaces were covered with large and small dimples.•The small dimples were void sheets produced by local shear strain.•Formations of the void sheets were accelerated by hydrogen.
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