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Twin-electrode GTAW is a novel welding technology in recent years and attracts lots of attention to researchers. However, stainless steel cladding with twin-electrode GTAW has been scarcely reported. This paper investigates the microstructure and mechanical performances of austenite stainless steel cladding by twin-electrode GTAW, and particularly the heat input is concerned. Experimental results of hardness tests, bending tests, and corrosion resistance tests show that both single GTAWand twin-electrode GTAW produce defect-free weld beads which meet engineering standards. Compared to single GTAW, twin-electrode GTAWimproves the welding productivity at a lower heat input because of its higher welding speed and melting rate. Oscillation twin-electrode GTAW cladding also produces fine weld bead formation, but causes excessive heat input due to its very low welding speed and relative large welding currents. During oscillation twin-electrode GTAW, FeCr(Mo) intermetallic compound (· phase) tends to precipitate in the weld bead, which leads to undesirable ferrite content results. [ABSTRACT FROM AUTHOR]

Highly functional and multifunctional material surfaces may be created through fabrication of unusual surface structures. We fabricated mushroom-like nanostructures on a stainless steel surface by simple processes: heat treatment under an atmosphere of low partial pressure of oxygen, followed by electrochemical etching. Island-like titanium oxide was formed on the Ti-containing stainless steel surface by selective oxidation during heat treatment. The titanium oxide became the cap part of the mushroom-like nanostructure and the stem part was fabricated by selective dissolution during electrochemical etching. Detailed analysis revealed that the cap part of the mushroom-like nanostructure was mainly composed of £-Ti3O5, and the stem part was composed of the stainless steel substrate. The contact resistance was significantly reduced by the fabrication of the mushroom-like nanostructures. The protrusions of electrically conductive £-Ti3O5 can contribute to the reduction of the contact resistance. The mushroom-like nanostructures improved the hydrophilicity of the surface without fluorine coating, but improved the hydrophobicity of the fluorine-coated surface. The contact between the stainless steel surface and the water droplet was in the Wenzel state. [ABSTRACT FROM AUTHOR]

The deformation behavior of the Incoloy 926 super-austenitic stainless steel at 1000-1150 °C and 0.001-10 s-1 was investigated. The corrected true stress-true strain curves were obtained by compensating the interfacial friction in the flow stress-strain curves. The interfacial friction increased the flow stress, and this increase was more pronounced at higher strains. According to the constitutive model, the activation energy varied from 328 to 384 kJ mol-1 with respect to strain. The mechanical parameters, peak stress and peak strain, critical stress and critical strain, were described by clearer equations with the temperature and strain rate. Moreover, based on the processing maps and the microstructural observation, the unsafe deformation domain where the localized plastic flow occurred was validated at above 1 s-1,thefavorable process at 1100°Cand0.1s-1 where fine and homogeneous grains can be obtained was determined simultaneously. [ABSTRACT FROM AUTHOR]

Manganese oxides are promising pseudocapacitive materials for electrochemical capacitors, and their capacitance, resistance and frequency response can be characterised using electrochemical impedance spectroscopy. Often, though not universally, the Nyquist plots of these materials evidence a semi-circular feature, which is typically attributed to the pseudocapacitive reaction's charge-transfer resistance. However, we show, for the first time, that the origin of the semi-circle is in fact the oxide-substrate interface resistance. The interface is varied through heat treatment of the manganese oxide and by electrodepositing the manganese oxide on different metals (stainless steel and platinum). Additionally, our novel manganese oxide double-deposition – in which a thin layer of manganese oxide on the interface is heat treated but the bulk of the film is hydrous – separates the interface and pseudocapacitive responses. Films with a low interface resistance (e.g., with a heat-treated interface or deposited on Pt) evidence a 98% smaller semi-circle than those with a poor interface (films deposited on stainless steel with no heat treatment). Conversely, there is no correlation between the amount of psuedocapacitance and semi-circle size. Thus, the Nyquist semi-circle is associated with the interface resistance, and proper modification of this interface can reduce the performance limitations associated with this resistance. Image 1 • Semi-circle in Nyquist plots due to pseudocapacitive oxide-substrate interface. • Electrodeposited manganese oxide on stainless steel has large interface resistance. • Reducing interface resistance through heat-treatment minimizes the semi-circle. • Reducing interface resistance improves high frequency response for the film. [ABSTRACT FROM AUTHOR]

During the stainless steel smelting process, the control of the slag skimming process affects the formation of hexavalent chromium in the stainless-steel slag. However, the hazardous problem of hexavalent chromium in stainless-steel slag has been a major factor limiting its resource utilization. In this paper, by studying the enrichment form of chromium in stainless-steel slag and the formation mechanism of hexavalent chromium, the cooling system and the content of additives were controlled in the slag skimming process to reduce the formation of hexavalent chromium. Different means of characterization including TG-DSC, phase diagram, FT-IR, XPS, potential-pH equilibrium diagram and HJ 687-2014 method were used to characterize the presence and content change of hexavalent chromium in solid and leachate. Results showed that hexavalent chromium formation mechanism was related with the chromium diffusion in two typical Cr-containing components in stainless-steel slag. A slow cooling rate can reduce the emission of Cr(VI) in stainless-steel slag. A lower addition of boron oxide content made a lower emission of hexavalent chromium. [ABSTRACT FROM AUTHOR]

Recent work has shown that the strength of fusion welds in alloys 17-4 and 13-8+Mo can be restored by re-precipitation that occurs during subsequent thermal cycles associated with multi-pass welding. The purpose of the current investigation is to develop a more detailed understanding of the precipitation kinetics of these materials during times and temperatures representative of welding thermal cycles. Peak aged samples of each alloy were subjected to a series of short isothermal holds at high temperatures using a Gleeble thermomechanical simulator. Hardness measurements were then recorded to estimate the precipitate dissolution. Additional secondary heating experiments were performed and hardness measurements were recorded to estimate the extent of precipitate growth. The hardness data were then used in combination with the Avrami equation and strengthening considerations to develop a relationship between hardness and fraction transformed of the strengthening precipitates. Light optical microscopy and X-ray diffraction were performed on all samples to determine the evolution of the matrix microstructures. The matrix microstructure had minimal effect on the hardness, while the strengthening precipitates were the primary factor affecting the hardness. Apparent activation energies for precipitation, determined through conventional Arrhenius rate analysis at constant fraction transformed, were calculated as 175 and 132 kJ/mol for 17-4 and 13-8+Mo, respectively. Global fitting of the data, based on a simplifying assumption for the temperature dependence of the Avrami rate constant, was also performed in order to improve the practical utility of the analysis, and provided good correlations between estimated and measured hardness over the full range of times and temperatures. Although additional microstructural characterization is needed to understand the significance of these relationships, the kinetic parameters determined from global fitting are useful for practical estimation of strength restoration procedures in multi-pass fusion welds. [ABSTRACT FROM AUTHOR]

Abstract Precipitation hardened (PH) martensitic grade stainless steels are commonly used in additive manufacturing (AM) processes, but the heat treatment response can vary depending upon the powder feedstock composition. As-built AM 17–4 PH grade stainless steel fabricated using argon and nitrogen atomized feedstocks in separate powder bed fusion systems responded differently to standard heat treatment cycles. Materials fabricated from argon atomized feedstocks, containing low levels of nitrogen (0.01 wt%) and retained austenite (< 1%), responded as expected to standard solutionizing and aging heat treatment cycles. In contrast, materials fabricated from nitrogen atomized feedstocks, containing between 0.06 and 0.12 wt% nitrogen and up to 81% retained austenite, did not display peak aging with standard heat treatments and deviated from the expected overaging response with increasing aging temperatures. At the highest nitrogen and retained austenite levels, peak aging is found to occur at temperatures in excess of 680 °C, even though the material still contains retained austenite levels in the 20% range. These unexpected changes in the heat treat response are closely linked to differences in the nitrogen composition of the powder feedstock. Changes in the Ni and Cr equivalent values determined by other primary alloying elements also impact the heat treat response, even though the alloy compositions still fall within standard alloy element composition ranges. [ABSTRACT FROM AUTHOR]

A downward-facing heating surface under a pressurized condition is expected in some systems, such as in in-vessel retention through the external reactor vessel cooling (IVR-ERVC) or core catcher strategies, that are adopted in nuclear power plants. Because carbon steel is used in the IVR-ERVC strategy and some core catcher candidates, the combined effect of orientation, dimension, pressure and material effects on the CHF results had to be defined. In this study, the combined effects have been addressed with pressure up to 10 bar. The experimental results show that the trends are affected not by an independent parameter, but strongly affected by several environmental conditions. Different trends could be observed between the carbon steel and the stainless steel under high-pressure conditions. In addition, the effect of width on the CHF decreased and sometimes reversed as the pressure increased. Overall CHF on carbon steel is higher than that of the stainless steel at all width, pressure and inclination angle conditions. When the material effect combined with the pressure effect was considered, the trend could be divided into the following two conditions: narrow and wide. Based on the experimental trends, to apply realistic data, operational conditions including pressure condition should be considered, and other parameters such as material properties should also be considered to explain the trends. [ABSTRACT FROM AUTHOR]

Highlights • Thermo-mechanical cyclic experiments of 304SS were performed at large temperature ranges. • The saturated cyclic behavior observed was simulated using a cyclic viscoplastic model with a cyclic hardening parameter. • The saturated behavior was not simulated well by considering temperature dependence of the cyclic hardening parameter. • The saturated behavior was simulated well by assuming maximum temperature dependence of the cyclic hardening parameter. • The micro-structure evolution for cyclic hardening was suggested to be dependent on maximum temperature. Abstract Thermo-mechanical cyclic experiments on 304 stainless steel were performed at several temperature ranges with T min (minimum temperature) of 150 °C and T max (maximum temperature) ranging from 350 °C to 1000 °C. Corresponding isothermal cyclic experiments were also performed at several temperatures. Temperature-history dependent cyclic hardening was thus observed to significantly occur under thermo-mechanical cyclic loading when T max was around 600 °C. In contrast, almost no cyclic hardening occurred when T max was 1000 °C. The observed, thermo-mechanical cyclic hardening behavior was then simulated using a cyclic viscoplastic constitutive model with a cyclic hardening parameter. The simulation focused on the saturated state of cyclic hardening, leading to the following findings. The saturated thermo-mechanical cyclic hysteresis loops were not predicted well by simply taking into account temperature dependence in the cyclic hardening parameter. Then, by assuming the cyclic hardening parameter to be dependent on T max , the saturated thermo-mechanical hysteresis loops were simulated well. These mean that the cyclic hardening parameter of 304 stainless steel should not change with temperature but depend on T max in the saturated state of cyclic hardening under thermo-mechanical cyclic loading. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract The microstructural evolution and its effect on mechanical properties of 27Cr-4Mo-2Ni super ferritic stainless steels during intermediate temperature aging treatment were investigated. Experimental results demonstrated that Laves phase started to nucleate at dislocations and sub-grain boundaries before chi and sigma phase, while the chi phase and sigma phase precipitated at grain boundaries. Laves phase was partially dissolved into the matrix to provide additional Cr and Mo atoms for the rapid coarsening of sigma phase with increasing aging time during 800 °C aging treatment. Meanwhile, the average grain size increased from ~ 68 to ~ 111 µm. Mechanical properties such as RT impact toughness, tensile properties and micro hardness were significantly influenced by the brittle intermetallic and grain coarsening. When the alloy was aged at 800 °C, the rate of microhardness increase was accelerated by the formation and coarsening of sigma phase, and the value of Vickers hardness was positively correlated with the volume fraction of sigma phase. Impact toughness was much more sensitive to brittle precipitates than both the tensile properties and hardness. Precipitation of sigma phase induced brittle fracture during impact testing, especially in the situation where the grain boundaries were completely covered by sigma phase. [ABSTRACT FROM AUTHOR]

In the present study, two vanadium-microalloyed 10Mn-18Cr TWIP-type stainless steels with low and high Si contents were designed to achieve a stacking fault energy of 25 mJ/m 2 . Hot deformation behavior was investigated using compression tests in the temperature range 950–1100 °C and strain rate range 0.01–10 s −1 . Microstructural features of the rolled slabs were studied using optical microscopy and those of the hot deformed specimens by electron backscatter diffraction. The low-Si steel possessed a higher hot deformation resistance and a higher activation energy of deformation (507 kJ/mol) compared to the high-Si steel (477 kJ/mol). This unusual trend is attributed to an increasing fraction of soft ferrite in the latter steel with increasing temperature. At lower test temperatures, where partial dynamic recrystallization occurred in the high-Si steel, ferrite possessed high-angle grain boundaries, while the austenite contained dislocation substructures. The hot deformation behavior of the steels was modeled using the dislocation density based Bergström model and the dynamic recrystallization based Avrami model. The rate of increase of Bergstrom's hardening parameter as a function of the Zener-Hollomon parameter is seen to be higher for the high-Si steel. [ABSTRACT FROM AUTHOR]

The ferritic stainless steel AISI 441 (EN 1.4509) is exposed for 1000 h to air - 3% H 2 O on one side and to Ar - 5% H 2 – 3% H 2 O on the other at temperatures 600, 700, and 800 °C. Conditions are chosen to mimic the environment of metallic interconnects in an operating solid oxide fuel cell (SOFC). At 600 °C, ∼25 μm thick Fe 2 O 3 /(Fe,Cr) 3 O 4 forms on large parts of the air side of the samples. Reference samples exposed to air - 3% H 2 O on both sides form thin protective layers of (Cr,Mn) 3 O 4 /Cr 2 O 3 at the same temperature. At higher temperatures, 700 and 800 °C, all samples form protective layers of (Cr,Mn) 3 O 4 /Cr 2 O 3 regardless of exposure to single or dual atmosphere. It is concluded that corrosion resistance in a dual atmosphere has an inverse dependence on temperature. Different hypotheses for the underlying cause for the dual atmosphere effect are discussed and compared to the experimental data. [ABSTRACT FROM AUTHOR]

The microstructure and microtexture of 316L stainless steel fibers (SSFs) after multi-pass cold drawing with intermediate heat treatment were investigated in this study. The crystalline phases of SSFs were identified and quantified using X-ray diffraction (XRD) analysis. Grain orientation and boundary characterization in the mantle and core regions of drawing direction (DD) were analyzed through electron backscatter diffraction (EBSD). The coincident site lattice approach provides beneficial information for defining twin boundary and analyzing the orientation relationship between neighboring grains on the Σ3 segment. Three crystalline phases, γ, α, and σ, could be seen in XRD profiles. The formation mechanism of deformation twins was found, and two types of twin boundaries were observed in the drawn fibers by EBSD. The twin boundary generated between a {112}〈111〉 grain and a 〈100〉//DD grain is believed to nucleate at a high-angle grain boundary and then bulge into the copper grain. [ABSTRACT FROM AUTHOR]

Abstract: This study is focused on stainless steel type 316L produced by selective laser melting (SLM). This steel is very resistant to corrosion in acidic environments and has extremely good strength properties at elevated temperatures. It is also characterized by a very good weldability. These properties allow for various applications of 316L in different fields. The widespread application of 316L opens up various possibilities for production of parts using SLM. Therefore, it is important to characterize the fatigue crack growth behaviour. In the present paper, the crack growth behaviour of SLM 316L stainless steel has been investigated in its as‐built condition and in different heat treatment conditions. The effect of build orientation on the crack growth path is also studied by performing fatigue crack growth tests on compact tension specimens built at 0° and 45° orientations relative to the build direction. A heat treatment above the recrystallization temperature followed by quenching is shown to create compressive residual stresses that improve the resistance against crack propagation considerably. The 45° build orientation shows crack propagation at an angle to the initial notch plane, which reveals that anisotropy still persists after heat treatment. [ABSTRACT FROM AUTHOR]

The influence of chemical composition, temperature, and pressure on the nitrogen solubility of various high alloy stainless steel grades, namely Fe-14Cr-(0.17-7.77)Mn-6Ni-0.5Si-0.03C [wt pct], Fe-15Cr-3Mn-4Ni-0.5Si-0.1C [wt pct], and Fe-19Cr-3Mn-4Ni-0.5Si-0.15C [wt pct], was studied in the melt. The temperature-dependent N-solubility was determined using an empirical approach proposed by Wada and Pehlke. The thus calculated N-concentrations overestimate the actual N-solubility of all the studied Fe-Cr-Mn-Ni-Si-C steel melts at a given temperature and pressure. Consequently, the calculation model has to be modified by Si and C because both elements are not recognized in the original equation. The addition of the 1st and 2nd order interaction parameters for Si and C to the model by Wada and Pehlke allows a precise estimation of the temperature-dependent nitrogen solubility in the liquid steel bath, and fits very well with the measured nitrogen concentrations during processing of the steels. Moreover, the N-solubility enhancing effect of Cr- and Mn-additions has been demonstrated. [ABSTRACT FROM AUTHOR]

F6NM martensitic stainless steel was exposed to 350 °C water condition for 500, 1500, and 2500 h to simulate pressurized water reactor (PWR) condition. The characterization and corrosion behavior of the oxide film were investigated. Results indicate that the exposed steel surface formed a double-layer oxide film. The outer oxide film is Fe-rich and contains two type oxide particles. However, the inner oxide film is Cr-rich, and two oxide films, whose thicknesses increase with increasing exposure time. The oxide film reduces the corrosion behavior because the outer oxide film has many crack and pores. Finally, the mechanism and factors affecting the formation of the oxide film were investigated. [ABSTRACT FROM AUTHOR]

A medium-carbon Cr--Mo--V martensitic steel was thermally processed by quenching (Q) at 890 °C and tempering (T) at increasing temperatures from 650 °C to 720 °C and the effect of tempering temperature, Tt, on sulfide stress cracking (SSC) behaviors was estimated mainly via double cantilever beam (DCB) and electrochemical hydrogen permeation (EHP) tests and microstructure characterization. The results indicate that the threshold stress intensity factor for SSC, KISSC, increased with increasing Tt. The overall and local H concentration around the inclusions decreased with increasing Tt, due to reductions in the amounts of solute atoms, grain boundaries and dislocations, which effectively prevented SSC initiation. Also, increasing Tt caused an increased fraction of high-angle boundaries, which evidently lowered the SSC propagation rate by more frequently diverting the propagating direction and accordingly restricted SSC propagation. The overall SSC resistance of this Q&T--treated steel was therefore significantly enhanced. [ABSTRACT FROM AUTHOR]

The laser powder bed fusion (L-PBF) technique builds parts with higher static strength than the conventional manufacturing processes through the formation of ultrafine grains. However, its fatigue endurance strength σf does not match the increased monotonic tensile strength σb. This work examines the monotonic and fatigue properties of as-built and heat-treated L-PBF stainless steel 316L. It was found that the general linear relation σf = mσb for describing conventional ferrous materials is not applicable to L-PBF parts because of the influence of porosity. Instead, the ductility parameter correlated linearly with fatigue strength and was proposed as the new fatigue assessment criterion for porous L-PBF parts. Annealed parts conformed to the strength-ductility trade-off. Fatigue resistance was reduced at short lives, but the effect was partially offset by the higher ductility such that comparing with an as-built part of equivalent monotonic strength, the heat-treated parts were more fatigue resistant. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel is extensively used in industries that operate at elevated temperatures. This work investigates the high-temperature microstructure stability as well as elevated-temperature properties of 304L stainless steel fabricated using the selective laser melting (SLM) process. Significant microstructural changes were seen after a 400°C aging process for as little as 25 h. This dramatic change in microstructure would not be expected based on the ferrite decomposition studied in conventional 304L materials. The as-built additively manufactured alloy has much faster kinetic response to heat treatment at 400°C. An investigation of the structures which occur, the kinetics of the various transformations, and the mechanical properties is presented. The impact of this on the application of SLM 304L is discussed. [ABSTRACT FROM AUTHOR]

The present study is to investigate the effect of post heat treatment on the microstructures and mechanical properties of a submerged-arc-welded 304 stainless steel. The base material consisted of austenite and long strips of delta-ferrite surrounded by Cr-carbide, and the welds consisted of delta ferrite and austenite matrix. For the heat treatment at 850 °C or lower, Cr-carbides were precipitated in the weld metal resulting in the reduction of elongation. The strength, however, was slightly reduced despite the presence of Cr-carbides and this could possibly be explained by the relaxation of internal stress and the weakening of particle hardening. In the heat treatment at 1050 °C, the dissolution of Cr-carbide and disappearance of delta ferrite resulted in the lower yield strength and higher elongation partially assisted from deformation-induced martensitic transformation. Consequently, superior property in terms of fracture toughness was achieved by the heat treatment at 1050 °C, suggesting that the mechanical properties of the as-weld metal can be enhanced by controlling the post weld heat treatment. [ABSTRACT FROM AUTHOR]

Cubic specimens from AISI 316 stainless steel were multiaxially forged to 15 passes and annealed at 1200 °C for 1, 2, and 3 h and finally sensitized at 700 °C for 24 h. Examination of samples indicated that the hardness of the annealed samples was reduced from 153 to 110, 81, and 74 HV for as-received sample and under 1, 2, and 3 h of annealing, and increased from 245 to 288 HV for samples forged at 3 and 7 passes. However, no significant changes were observed in a large number of passes and at about 300 HV. Degree of sensitization of samples was increased to approximately 27.3% at 3-h annealing but reduced to 1.23% by 15 passes of MF. The potentiodynamic polarization test shows that the breakdown potentials decreased with annealing time from 0.6 to − 102 (mV/SCE) for as-received and 3-h annealed specimen. These potentials increased to approximately − 16.5 mV with the increase in MF passes to 15. These observations indicated that the chromium carbide deposition affects Cr-depleted zone, which can subsequently affect the degree of sensitization and pitting corrosion resistance of AISI 316 austenitic stainless steel. [ABSTRACT FROM AUTHOR]

This paper aims at improving the hardness and wear resistance of Austenitic 316L Stainless Steel (SS) by Plasma-assisted Low Temperature Carburizing (PLTC) process. The process has been employed in austenitic 316L SS for achieving carbon supersaturated phase, the so-called 'S Phase'. The microstructure of the treated specimens was characterized by Optical microscopy, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The results showed evidences of expanded austenite phase and formation of 'S phase' at a temperature of 460C with 10% of methane (CH and 90% of hydrogen (H at a pressure of 1mbar for a time period of 20h. The hardness of the specimen was evaluated as 1030HV using Vickers microhardness setup. The wear behavior of plasma treated specimen was studied using pin on disc test at ambient condition and the results are discussed. Wear rate in PLTC 316L SS was observed to be low when compared with the wear rate of the untreated 316L SS specimen. The PLTC 316L SS specimen is subjected to ASTM A262 oxalic acid etch test to study the intergranular corrosion behavior. The 'step' formation was observed in the SEM micrographs which reveal the retention of corrosion resistance in the specimen. [ABSTRACT FROM AUTHOR]

NiTi endodontic rotary instruments have increased flexibility and strength compared with stainless steel instruments, but they seem to be vulnerable to fracture in clinical situations. Heat treatment (thermal processing) is one of the most fundamental approaches toward adjusting the transition temperatures of NiTi alloys and affecting the fatigue and torsional resistance of NiTi endodontic files. In recent years, novel thermo-mechanical processing and manufacturing technologies such as controlled memory wire (CM-wire), M-Wire and electrical discharge machining (EDM) have been developed to optimize the microstructure of NiTi alloys and their mechanical properties. Aim of this work was to investigate the torsional resistance (maximum torque load, and angular rotation) of NiTi instruments made by different thermo-mechanical and manufacturing processes. For this purpose, a torque device able to perform static and dynamic tests of Ni-Ti instruments for root canal treatment was designed and realized, by performing this device through the design and optimization of the single components and on the system globally. [ABSTRACT FROM AUTHOR]

Failure investigation was done on a 321 stainless steel charge heater tube which failed in a refinery unit processing heavy crude oil. Crude oil was the charge in the radiant and convection sections; while saturated stripping steam is present in convection section. After a leak was detected, visual inspection revealed that nine convection tubes had black oil/coke deposits on their external surfaces. The deposits were seen on the first three rows of tubes. When one of the tubes was lightly ground at the black colored area, a circumferential crack was visually observed. The investigation revealed that long-term aging, coupled with localized deposition of salts and coke from the heavy crude led to sensitization of the tube surface layers. This in turn resulted in sulphidation of the internal surface grain boundaries, formation of grooves, and cracking of the material. Thus, cracking was intergranular in nature in the initial stage, but became transgranular at later stages. It was concluded that cracking was due to chloride stress corrosion cracking catalyzed by the presence of sulphur-bearing species. It was recommended that the desalter operation be improved and frequent decoking and scale removal be carried out, with emphasis on the convection section at the refinery. [ABSTRACT FROM AUTHOR]

Laser cutting is the popular unconventional manufacturing method widely used to cut various engineering materials. In this work CO2 laser cutting of AISI 314 satinless steel has been investigated. This paper focus on the investigation into the effect of laser cutting parameters like laser power, assist gas pressure, cutting speed and stand-off distance on surface roughness, hardness and kerf dimensions like kerf width, kerf ratio and kerf taper in CO2 laser cutting of AISI 314 stainless steel. [ABSTRACT FROM AUTHOR]

The duplex stainless steel 2205 was heat treated at 750 °C, 850 °C, and 900 °C for increasing durations of up to 10 h. The samples were investigated through light microscopy (LM), transmission electron microscopy (TEM), and x-ray diffraction (XRD) to characterize the volume fraction and morphology of the precipitated secondary phases. The samples were then tested via flat-top cylinder indenter for mechanical characterization (FIMEC) testing to determine the yield stresses that were found to be significantly affected by the different heat treatments. The yield stress evolution with heat treatments resulted in being correlated to both the relative volumes of the secondary phases and the morphology of the σ phase. The FIMEC test proved to be capable of detecting the effects of small amounts of secondary phases on yield stress in DSS 2205 and seems to be a promising technique for industrial applications. [ABSTRACT FROM AUTHOR]

The high-temperature austenite phase of a high-interstitial Mn- and Ni-free stainless steel was stabilized at room temperature by the full dissolution of precipitates after solution annealing at 1523 K (1250 °C). The austenitic steel was subsequently tensile-tested in the temperature range of 298 K to 503 K (25 °C to 230 °C). Tensile elongation progressively enhanced at higher tensile test temperatures and reached 79 pct at 503 K (230 °C). The enhancement at higher temperatures of tensile ductility was attributed to the increased mechanical stability of austenite and the delayed formation of deformation-induced martensite. Microstructural examinations after tensile deformation at 433 K (160 °C) and 503 K (230 °C) revealed the presence of a high density of planar glide features, most noticeably deformation twins. Furthermore, the deformation twin to deformation-induced martensite transformation was observed at these temperatures. The results confirm that the high tensile ductility of conventional Fe -Cr-Ni and Fe-Cr-Ni-Mn austenitic stainless steels may be similarly reproduced in Ni- and Mn-free high-interstitial stainless steels solution annealed at sufficiently high temperatures. The tensile ductility of the alloy was found to deteriorate with decarburization and denitriding processes during heat treatment which contributed to the formation of martensite in an outermost rim of tensile specimens. [ABSTRACT FROM AUTHOR]

The influence of grain size and irradiation defects on the mechanical behavior and the corrosion resistance of a 316 stainless steel have been investigated. Nanostructured samples were obtained by severe plastic deformation using high pressure torsion. Both coarse grain and nanostructured samples were irradiated with 10 MeV 56 Fe 5+ ions. Microstructures were characterized using transmission electron microscopy and atom probe tomography. Surface mechanical properties were evaluated thanks to hardness measurements and the corrosion resistance was studied in chloride environment. Nanostructuration by high pressure torsion followed by annealing leads to enrichment in chromium at grain boundaries. However, irradiation of nanostructured samples implies a chromium depletion of the same order than depicted in coarse grain specimens but without metallurgical damage like segregated dislocation loops or clusters. Potentiodynamic polarization tests highlight a definitive deterioration of the corrosion resistance of coarse grain steel with irradiation. Downsizing the grain to a few hundred of nanometers enhances the corrosion resistance of irradiated samples, despite the fact that the hardness of nanocrystalline austenitic steel is only weakly affected by irradiation. These new experimental results are discussed in the basis of couplings between mechanical and electrical properties of the passivated layer thanks to impedance spectroscopy measurements, hardness properties of the surfaces and local microstructure evolutions. [ABSTRACT FROM AUTHOR]

The effects of building orientation and post-fabrication heat treatment (solution annealing plus peak-aging) on fully-reversed strain-controlled fatigue behavior of 17-4 precipitation hardening (PH) stainless steel (SS) fabricated via Selective Laser Melting (SLM) is investigated. For this particular alloy, post-SLM heat treatment was found to be necessary in order to improve its tensile strength and fatigue behavior in low cycle fatigue (LCF), where the effects of microstructural impurities are less pronounced. However, the selected heat treatment was found to have detrimental influence on the SLM 17-4 PH SS high cycle fatigue (HCF) performance. The heat treatment resulted in precipitation hardening, allowing the SLM parts to become more sensitive to impurities in HCF, where the crack initiation stage dominates the total fatigue lifetime. Building orientation played a significant role on fatigue behavior in both LCF and HCF, owing to the relative orientation of deposited layers with respect to applied load. Un-melted regions (i.e. inter-layer cavities/voids), resulting from insufficient fusion or low laser penetration depth, were found to be the most detrimental type of defects on fatigue strength of SLM 17-4 PH SS due to their relatively large size and irregular shape. These specific regions that formed during fabrication of vertically-orientated samples were more detrimental than those of horizontally-built ones as they provided more stress concentration under loading, leading to lower fatigue strength. Although the process parameters were optimized based on maximizing density, the results of this study imply that this criterion is not sufficient for improving fatigue behavior, as the split-shaped un-melted regions, containing a large area with small volume, cannot be taken into account through conventional density measurements. [ABSTRACT FROM AUTHOR]

The deformation behavior of alumina-forming austenitic heat-resistant steels at high temperatures was studied to elucidate their hot workability using two types of alloys, i.e. AFA and MAFA. Uniaxial compression tests were performed between the temperature range of 800–1100 °C with strain rates of 0.005–5.0 s − 1 . From the constitutive relationship between flow stress, temperature and strain rate, the activation energies for hot deformation were estimated. Both of the investigated alloys exhibited higher activation energies (AFA: 618.8 and MAFA: 711.1 kJ/mol) than other conventional alloys under similar conditions. Processing maps based on dynamic material model and microstructures after the tests indicated that the hot working of both alloys became more efficient and stable with increasing temperature and decreasing strain rate, which was attributed to more active operation of restoration processes such as dynamic recovery and recrystallization. In both alloys, secondary NbCs were precipitated during the test. Due to their pinning effect on dislocations, grain and sub-grain boundaries, the progress of restoration processes was hindered, which contributed to their high activation energy. In spite of the common types of restoration processes, MAFA with increased Nb and C content exhibited degraded hot workability due to more extensive precipitation of NbC. [ABSTRACT FROM AUTHOR]

Tearing as a factor that restricts formability of sheets and tubes is determined by forming limit diagram (FLD). The aim of the current study is to present a novel approach to achieve FLD of a metallic tube using hydroforming process. Here, for 304 stainless steel tubes, various loading conditions, namely free loading, bulging with axial feeding and bulging with closed end, were considered. Along with loading condition, die geometries with different corner radius and deformation width were studied on the strain path and plastic instability. The effects of process parameters on the strain path have been evaluated and simulated using ABAQUS/Explicit. Meshed tubes were bulged under controlled loading, and the FLD was drawn after measuring the major and minor strains close to the tearing location. Finally, the evaluation of the current method has been investigated by using the obtained FLD in the forming of an industrial part (i.e., the cam-shaped tube). The results revealed that the proposed approach has the capability to predict the formability of industrial components. [ABSTRACT FROM AUTHOR]

The phenomenon that a heating structure vibrates itself due to the behavior of vapor bubbles generated under subcooled boiling has been known as “Subcooled Boiling-induced Vibration (SBIV)”. As one of such a heating structure, fuel assemblies for Boiling Water Reactors (BWR) are utilized in subcooled boiling of water, and those for Pressurized Water Reactors (PWR) may face unexpected subcooled boiling conditions in case of sudden drop of the system pressure or loss of water flow, though they are utilized in single phase of water under normal operating conditions. As studies on SBIV, some researchers have conducted demonstrative experiments with a partial array of fuel rods simulating the actual BWR fuel assembly in a flow test loop, which showed no significant influences of the SBIV to degrade the integrity of the fuel rods. In addition, in order to investigate the fundamental phenomenon of the SBIV, pool boiling experiments of the SBIV on a single heater rod were performed in other studies with a simplified apparatus of a water tank in laboratory size under atmospheric pressure. In the experiments, behavior of bubbles generated under various degree of subcooling were observed, and the acceleration of the SBIV of the heater rod was measured. The present study, as a series of the above experiments for the fundamental phenomenon of the SBIV, the two thin walls made of stainless steel were installed in parallel to interleave the heater rod with the gap distance of 1 mm or 3 mm to each of the two walls, which was expected to provide useful results to investigate effects of the parallel walls configuration to the SBIV of the heater rod. The results obtained in the experiments suggested that bubbles growing largely in the gap influenced on the SBIV of the heater rod, with the remarkable behavior such as slide of the large bubbles on the surface of the heater rod towards the open region, interference and coalescence between large bubbles. [ABSTRACT FROM AUTHOR]

Heat-to-heat variation in creep life has been investigated for the 9 heats of JIS SUS 304HTB (18Cr–8Ni steel) and also for the 9 heats of JIS SUS 347HTB (18Cr–12Ni–Nb steel) in the NIMS Creep Data Sheets, mainly taking the effect of Nb into account. The heat-to-heat variation in creep life of 304HTB is mainly caused by the variation in precipitation hardening due to fine NbC carbides at short times, while it is mainly caused by the variation in available nitrogen concentration, defined as the concentration of nitrogen free from AlN and TiN, at long times. The heat-to-heat variation in creep life of 347HTB is mainly explained by the variation of boron concentration, 3–27 ppm, but not by the variation of solution temperature, Nb/C atomic ratio and phosphorus concentration. Boron reduces the coarsening rate of fine M23C6carbides along grain boundaries, which enhances the grain boundary precipitation hardening. [ABSTRACT FROM PUBLISHER]

In the present research work, corrosion behavior of post-weld heat-treated (PWHT) AISI 316L (X2CrNiMo 17-13-2) specimens joined by gas metal arc welding is compared with as-welded samples by using potentiodynamic polarization technique. Welded samples were PWHT at 1323 K for 480 s and quenched. Mechanical properties, corrosion behavior and microstructures of as-welded and PWHT specimens were investigated. Microstructural studies have shown grain size refinement after PWHT. Ultimate tensile strength and yield strength were found maximum for PWHT samples. Bend test have shown that PWHT imparted ductility in welded sample. Fractographic analysis has evidenced ductile behavior for samples. Potentiodynamic polarization test was carried out in a solution composed of 1 M HSO and 1 N NaCl. Corrosion rate of weld region was 127.6 mpy, but after PWHT, it was decreased to 13.12 mpy. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) technique was used to study the oxide film formation of 316LN stainless steel (SS) in high temperature aqueous environment. The morphology and chemical compositions of oxide films of 316LN SS base metal and weld were also investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The results indicated that 316LN SS weld had a higher oxidation resistance than that of base metal due to higher amount of chromium and nickel in the weld material. AE activity and intensity were high during the oxide film formation and decreased gradually with increasing immersion time. The evolution of AE hits was consistent with the oxidation kinetics of 316LN SS base metal and weld. The formation of Cr-enrichment layer and Ni(OH)2 contributed to the enhancement of oxidation resistance, leading to a continuous decrease of AE activity and intensity. Two types of AE waveforms were detected and the frequency spectra of both types mainly ranged from 0.3 to 0.6 MHz. According to the analyses of AE based b-values and parameters, it could be deduced that AE sources during oxide film formation were the plastic deformation of base metal/weld and oxide film. [ABSTRACT FROM AUTHOR]

The serrated chip produced in high-speed machining of martensitic precipitation-hardening stainless steel is inevitably tore up into isolated segments due to adiabatic shear fracture with the further increase of cutting speed. The induced mechanism of adiabatic shear fracture and the corresponding damage process in high-speed machining are investigated through quick-stop tests and chip morphology examinations. The isolated segments generated due to adiabatic shear fracture which is found in the rate-related process of adiabatic shear evolution is a cyclic process of energy convergence and release with ductile-brittle damage transition. The fracture energy of adiabatic shear band approaches a stable saturation limit with the increases of cutting speed and feed. On the basis of saturation limit model, the critical fracture energy is predicted by cutting conditions and compared with the experimental results. [ABSTRACT FROM AUTHOR]

Austenitic steels 304 L and 316 L are used extensively as nuclear structural materials. The objective of this study is to determine if their corrosion behavior can be improved by developing an Al-containing surface layer by a complex surface treatment, including substrate modification by growth of oxide layers using anodic oxidation, cyclic voltammetry and autoclaving in water, as well as a micro-arc oxidation (MAO) treatment in 0.1 M NaAlO2 aqueous solution. The processes and structures obtained by MAO under various experimental conditions were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectrometry analysis. The corrosion behavior, studied by Tafel potentiodynamic polarization, was correlated to the microstructure and the chemical composition of the surface layers which are strongly dependent on the treatment parameters. An overall description of the electrochemical processes involved in the growth of aluminum coating, the surface properties improvement, together with some consideration about the new materials development for energy technologies are presented. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to provide a theoretical foundation for improving the selective laser melting (SLM) surface roughness. To improve the part’s surface quality during SLM process, the upper surface roughness of SLM parts was theoretically studied and the influencing factors were analyzed through experiments.Design/methodology/approach The characteristics of single track were first investigated, and based on the analysis of single track, theoretical value of the upper surface roughness would be calculated. Two groups of cubic sample were fabricated to validate SLM parts’ surface roughness, the Ra and relative density of all the cubic parts was measured, and the difference between theoretical calculation and experiment results was studied. Then, the effect of laser energy density on surface roughness was studied. At last, the SLM part’s surface was improved by laser re-melting method. At the end of this paper, the curved surface roughness was discussed briefly.Findings The SLM upper surface roughness is affected by the width of track, scan space and the thickness of powder layer. Measured surface roughness Ra value was about 50 per cent greater than the theoretical value. The laser energy density has a great influence on the SLM fabrication quality. Different laser energy density corresponds to different fabricating characteristics. This study divided the SLM fabrication into not completely melting zone, balling zone in low energy density, successfully fabricating zone and excessive melting zone. The laser surface re-melting (LSR) process can improve the surface roughness of SLM parts greatly without considering the fabricating time and stress accumulation.Originality/value The upper surface roughness of SLM parts was theoretically studied, and the influencing factors were analyzed together; also, the LSR process was proven to be effective to improve the surface quality. This study provides a theoretical foundation to improve the surface quality of SLM parts to promote the popularization and application of metal additive manufacturing technology. [ABSTRACT FROM AUTHOR]

Hot compression tests were performed to study the hot deformation characteristics of 13Cr-4Ni stainless steel. The tests were performed in the strain rate range of 0.001-10 s and temperature range of 900-1100 °C using Gleeble® 3800 simulator. A constitutive equation of Arrhenius type was established based on the experimental data to calculate the different material constants, and average value of apparent activation energy was found to be 444 kJ/mol. Zener-Hollomon parameter, Z, was estimated in order to characterize the flow stress behavior. Power dissipation and instability maps developed on the basis of dynamic materials model for true strain of 0.5 show optimum hot working conditions corresponding to peak efficiency range of about 28-32%. These lie in the temperature range of 950-1025 °C and corresponding strain rate range of 0.001-0.01 s and in the temperature range of 1050-1100 °C and corresponding strain rate range of 0.01-0.1 s. The flow characteristics in these conditions show dynamic recrystallization behavior. The microstructures are correlated to the different stability domains indicated in the processing map. [ABSTRACT FROM AUTHOR]

This study is concerned with the reactivity between SiC particles and 410L stainless steel alloy. An interval of sintering temperatures (900, 1000, 1100, and 1180℃) was scoped in order to study the temperature influence on the interface reaction under different compaction pressures (400, 800, and 1200 MPa). SiCp/410L SS composites were produced by powder metallurgy. Interface area fraction (%) results and microstructural characterization showed that the interface reaction is strongly dependent on temperature. At 900℃ no reaction SiCp/410L SS was found. At 1000℃ SiCp reacts with 410L SS matrix and with increasing temperature the extent of reaction becomes higher. However, at 1180℃ SiCp dissolves completely leading to specimen deformation. The higher interface area fraction was obtained at a sintering temperature of 1100℃ and a compaction pressure of 1200 MPa. This study presents an advantageous and original combination of materials and process that allows combining compaction pressure and sintering temperature in order to control the interface. [ABSTRACT FROM AUTHOR]

Effects of post weld heat treatment (PWHT) on mechanical properties and corrosion behavior of NiTi shape memory wire, laser welded to the 304 stainless steel wire were investigated. The results showed that PWHT at 200 °C increased corrosion resistance and tensile strength of the joint up to ~1.8 times that of the as-weld joint, with no heat treatment. On the contrary, precipitation of neoteric intermetallic compounds like FeTi, CrTi, FeNi, NiTi, and TiNi in the welded region deteriorated these properties, when PWHT was conducted at 400 °C. Due to the vital effects of the PWHT performed after the laser welding, careful control of the PWHT temperature was found to be a prerequisite for achievement of desirable properties in the dissimilar NiTi-304 stainless steel laser-welded wires. [ABSTRACT FROM AUTHOR]

Results of research on the effect of stainless steel (SS) surface roughness on the amount and microscopic structure of milk impurities, formed under the influence of high-temperature milk processing are presented. Three types of plates of different roughness were used in the study: Ra = 0.028 μm; Ra = 0.174 μm; Ra = 0.445 μm. The plates were immersed in raw milk and heated at 85-90°C for 30 min, imitating pasteurisation conditions. As a result of this action, a milk sediment difficult to remove was created. The structure of impurities was determined by the Confocal Scanning Laser Microscope CSLM method. The analysis of the microscopic structure of formed milk impurities enabled their classification into three types depending on their structure and way of their bonding to the surface. The research results suggested that the roughness plays a prominent role in the level of fouling and probably in cleaning effectiveness. [ABSTRACT FROM AUTHOR]

This paper examines the metallurgical evolution of AISI Stainless Steel 321 (SS 321) during multi-step forming, a process that involves cycles of deformation with intermediate heat treatment steps. The multi-step forming process was simulated by implementing interrupted uniaxial tensile testing experiments. Evolution of the mechanical properties as well as the microstructural features, such as twins and textures of the austenite and martensite phases, was studied as a function of the multi-step forming process. The characteristics of the Strain-Induced Martensite (SIM) were also documented for each deformation step and intermediate stress relief heat treatment. The results indicated that the intermediate heat treatments considerably increased the formability of SS 321. Texture analysis showed that the effect of the intermediate heat treatment on the austenite was minor and led to partial recrystallization, while deformation was observed to reinforce the crystallographic texture of austenite. For the SIM, an Olson-Cohen equation type was identified to analytically predict its formation during the multi-step forming process. The generated SIM was textured and weakened with increasing deformation. [ABSTRACT FROM AUTHOR]

The effect of systematical Mo, Ti, Al and Ca alloying of corrosion-resistant maraging steels of type Kh11N10M2T and of the modes of their heat treatment on the phase composition, combination of properties and resistance to brittle fracture is studied. It is shown that the structural strength of the steels can be raised by additional alloying with copper and formation of a regulated content of metastable retained austenite. [ABSTRACT FROM AUTHOR]

A novel, low-cost, simple liquid-phase process has been developed for preparing highly aligned carbon nanotube (CNT) arrays (HACNTAs). Highly pure HACNTAs with heights of ∼10 μm were grown perpendicular to a preheated stainless steel substrate in ethanol solution by liquid-phase electrical resistance heating process without the addition of any growth catalyst for CNTs. In this paper, the effects of preheating conditions of the substrate before the synthesis on the morphology of the resulting CNTs are discussed. The optimum conditions were preheating temperature of 500 °C and preheating duration of 30–180 min in air for the substrate to form HACNTAs. The preheating brings Fe-rich oxide layer on the substrate surface and generates numerous Fe catalyst nanoparticles that promote HACNTA growth at following liquid-phase resistance heating process. In addition to ethanol, methanol and 1-butanol were also tested as carbon sources; however, the HACNTAs from those sources did not grow homogeneously on the substrate surface and contained many impurities compared with those prepared from ethanol. This unique HACNTA synthesis method is simple, since it requires neither a vacuum nor an external catalyst preparation process, and it is environmentally friendly, because it only uses ethanol and stainless steel substrates for the synthesis. [ABSTRACT FROM AUTHOR]

An abstract of the article "Effect of Chemistry and Heat Treatment on the Pitting Corrosion Resistance of Three Duplex Stainless Steel Alloys" by Ethan Edwards, Daniel Hodgkinson, and Myrissa Maxfield is presented.

The laser welding of AISI 316L stainless steel plates was carried out with a CO2 laser and the welding properties were related to the flexural characteristics of the welded plates. In testing the welded plates the shift in the position of the natural frequency of the flexural motion is evaluated for characterization of the welded structures. An experimental configuration was interfaced with the LabVIEW software's virtual instrument (VI) to capture the natural frequency of the welded plate which is subjected to a cantilever configuration. Effect of laser welding parameters is analysed and it is found that laser welding modifies the elastic modulus of the plates, which can be efficiently used to characterize the weld. The flexural motion analysis indicates that the weld section is free from defect sites. [ABSTRACT FROM AUTHOR]