Surface Of Austenitic Stainless Steel Research Articles

Enhancements of Passive Film and Pitting Resistance in Chloride Solution for 316LX Austenitic Stainless Steel After Sn Alloying

In the present work, the electrochemical behavior and properties of the passive film of a new Sn-alloyed 316LX austenitic stainless steel were investigated. With the increase in Sn content in 316LX austenitic stainless steel from 0 to 0.21%, the critical pitting temperature value increased from 32.6 to 38.8 °C, and the pitting potential increased from 0.252 VSCE to 0.317 VSCE. Electrochemical impedance spectroscopy results showed that the corrosion resistance of passive film rose with the increase in Sn content, indicating a more stable passive film. The Mott–Schottky measurement revealed an n-type passive film with a decreased carrier concentration on the 316LX austenitic stainless steel surface. The Cr, Sn2+ and Sn4+ (SnO, SnOHCl or SnO2) enrichments were observed in the passive layer by X-ray photoelectron spectroscopy. The enrichment of Sn and Cr in the passive film can account for the enhanced pitting resistance of 316LX austenitic stainless steel in chloride solution.

Hydrogen distribution at twin boundary in austenitic stainless steel studied by scanning Kelvin probe force microscopy

Twin boundary (TB) separation is usually observed on the fracture surface of austenitic stainless steels (γ-SS) under the influence of hydrogen. However, previous studies fell short in determining the hydrogen distribution and diffusion behavior at the TB. Scanning Kelvin probe force microscopy (SKPFM) is used to investigate the hydrogen distribution at TB in thermally hydrogen-precharged γ-SS. It is found that there are many martensite (α′) at TBs in the material. TBs with α′ provide fast paths for hydrogen diffusion and some hydrogen is trapped at these areas, which is proposed to be one of the reasons for the TB separation. In contrast, no clear acceleration of hydrogen diffusion and trapping of hydrogen are found at TBs without α′.

Microstructural characterization and residual stress distribution in a nanostructured austenitic stainless steel

Abstract In this paper, residual stress distribution is investigated by a novel X-ray cosα diffraction technique in a nanostructured austenitic stainless steel after hydrostatic extrusion processes. Hydrostatic extrusion performed at 20°C and with a total true strain of 2.3 leads to the creation of a nanostructure consisting of nanotwins and shear bands. The results reveal that the greatest compressive residual stresses of −1 GPa are found 3 mm from the surface of the nanostructured austenitic stainless steel. These compressive residual stresses restrict crack growth into the material, thereby preventing catastrophic failure.

New insight on early oxidation stages of austenitic stainless steel from in situ XPS analysis on single-crystalline Fe–18Cr–13Ni

In situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure <10 L) leading to the formation of a strongly Cr-enriched Cr3+/Fe3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment.

Ultrasonically generated pulsed water jet peening of austenitic stainless-steel surfaces

In this study, the effects of pulsating water jets were investigated as a surface treatment process using circular and flat nozzles by considering the integrity of a stainless steel (AISI 304) surface. The local energy distribution was controlled by changing the traverse speed and the pulsating water jet (PWJ) effects were assessed in terms of the residual stress and strengthening effect. The strengthening effect of the process was evaluated by measuring the micro-hardness of the treated surface and by studying the impact of the treatment on the surface based on micro-structural analyses using scanning electron microscope (SEM). The residual stress of the subjected area was evaluated using X-ray diffraction technique. Based on the results from the studied samples, it was found that the initial tensile residual stress was relieved and converted to a compressive residual stress. An increase in the hardness of the treated samples was also observed as compared to the untreated samples up to certain depth along the cross-section of the treated region. The micro-structural examination of the samples revealed the plastic deformation that occurred during the treatment process. Additionally, the acoustic emission (AE) generated during the impact was used as an online monitoring tool for observing the behaviour of the elicited signals under different parametric conditions, and as a control mechanism for obtaining better results. The experimental results show that the pulsating water jet constitutes a new potential technology for surface treatment processes.

Characteristic of Low Temperature Carburized Austenitic Stainless Steel

Low temperature carburizing process has been carried out on austenitic stainless steel (ASS) type AISI 316L, that contain chromium in above 12 at%. Therefore, conventional heat treatment processes that are usually carried out at high temperatures are not applicable. The sensitization process due to chromium migration from the grain boundary will lead to stress corrosion crack and decrease the corrosion resistance of the steel. In this study, the carburizing process was carried out at low temperatures below 500 °C. Surface morphology and mechanical properties of carburized specimens were investigated using optical microscopy, non destructive profilometer, and Vicker microhardness. The surface roughness analysis show the carburising process improves the roughness of ASS surface. This improvement is due to the adsorption of carbon atoms on the surface of the specimen. Likewise, the hardness test results indicate the carburising process increases the hardness of ASS.

Permeability Study of Austenitic Stainless Steel Surfaces Produced by Selective Laser Melting

Selective laser melting (SLM) is emerging as a versatile process for fabricating different metal components with acceptable mechanical properties and geometrical accuracy. The process has been used in the manufacturing of several parts (e.g., aerospace or biomedical components), and offers the capability to tailor the performance of several surface and mechanical properties. In this work, permeability properties and surface roughness of stainless steel (SS316L) surfaces were evaluated through experimentation with three different laser scanning patterns (chessboard, meander, and stripe), and different sloping angles between the fabricated surface and the laser beam incident on the process. Results showed that for each scanning pattern, the roughness decreased as the sloping angle increased consistently in all experimental trials. Furthermore, in the case of the permeability evaluation, the manufactured surfaces showed changes in properties for each series of experiments performed with different scanning patterns. The chessboard pattern showed a change of 67° to 107° in contact angle, while the meander and stripe patterns showed a variation in contact angle in a range of 65° to 85°. The different scanning strategies in the SLM process resulted in an alternative method for surface enhancement with different hydrophobicity properties, valuable for designing the most appropriate permeability characteristics for specific applications.

Development and characterisation of novel anti-bacterial S-phase based coatings

It is well-known that biologically active Ag/Cu ions are strong bactericides and silver or copper nanoparticles have been used in polymer-based antibacterial coatings. However, their poor durability has limited their use in tribological applications. This problem has been largely addressed recently by developing novel plasma co-alloying of austenitic stainless steel surfaces with both nitrogen and Ag/Cu to form wear resistant antibacterial S-phase. However, this technology is only applicable to austenitic stainless steel as the S-phase cannot be formed to other materials.In this study, S-phase based anti-bacterial coatings have been, for the first time, developed using magnetron sputtering through co-deposition of austenitic stainless steel with Ag/Cu to form hard S-phase doped with Ag, Cu or both in monolayer and multilayer structures. These coatings were fully characterised using multiple techniques such as SEM, TEM, XRD, GDOES and anti-bacterial tests. It has been found that it is possible to produce dense Ag and Cu doped S-phase layer with significant anti-bacterial efficacy. This was achieved while preserving the advantageous properties of the S-phase microstructure. As opposed to the popular diffusion based S-phase production such as plasma nitriding, this technology can also be applied on all kinds of surfaces, including low-cost steel surfaces, polymers and ceramics.

Thermal management of metallic surfaces: evaporation of sessile water droplets on polished and patterned stainless steel

This communication focus on the evaporation of sessile water droplets on different states of austenitic stainless steel surfaces: mirror polished, mirror polished and aged and patterned by sputtering. The evolution of the contact angle and of the droplet diameter is presented as a function of time at room temperature. For all the surface states, a constant diameter regime (CCR) is observed. An important aging effect on the contact angle is measured on polished surfaces due to atmospheric contamination. The experimental observations are compared to a quasi-static evaporation model assuming spherical caps. The evolution of the droplet volume as a function of time is almost linear with the evaporation time for all the observed surfaces. This is in accordance with the model prediction for the CCR mode for small initial contact angles. In our experiments, the evaporation time is found to be linearly dependent on the initial contact angle. This dependence is not correctly described by the evaporation model

Effect of atmospheric-controlled induction-heating fine particle peening on electrochemical characteristics of austenitic stainless steel

Atmospheric-controlled induction-heating fine particle peening (AIH-FPP) using Cr and Mo shot particles in a N2 atmosphere was introduced to improve the electrochemical characteristics of AISI 316 austenitic stainless steel. The surface microstructure of the AIH-FPP-treated specimen was characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). AIH-FPP can be used to form transferred and diffused layers of shot particles on the surface of austenitic stainless steel. The thickness of the diffusion layers of Cr shot particles tended to increase with the heating time in the AIH-FPP process, whereas the Cr concentration at the surface tended to decrease. Electrochemical polarization tests were performed in 3wt% NaCl+H2SO4 and 20wt% NaCl environments at 343K using a three-electrode electrochemical cell connected to a computer driven potentiostat to examine the corrosion resistance of austenitic stainless steel treated with AIH-FPP. The pitting potential of the AIH-FPP-treated specimen was higher than that of the untreated specimen. In particular, there was clear improvement in the pitting potential of austenitic stainless steel by AIH-FPP with Cr shot particles following peening with Mo shot particles. AIH-FPP using Cr and Mo shot particles in a N2 atmosphere is an effective method of improving the electrochemical characteristics of austenitic stainless steel.

Influence of laser shock peening on irradiation defects in austenitic stainless steels

The laser shock peening process can generate a dislocation network, stacking faults, and deformation twins in the near surface of austenitic stainless steels by the interaction of laser-driven shock waves with metals. In-situ transmission electron microscopy (TEM) irradiation studies suggest that these dislocations and incoherent twin boundaries can serve as effective sinks for the annihilation of irradiation defects. As a result, the irradiation resistance is improved as the density of irradiation defects in laser-peened stainless steels is much lower than that in untreated steels. After heating to 300 °C, a portion of the dislocations and stacking faults are annealed out while the deformation twins remain stable, which still provides improved irradiation resistance. These findings have important implications on the role of laser shock peening on the lifetime extension of austenitic stainless steel components in nuclear reactor environments.

Wear and corrosion behaviors of duplex surface treated 316L austenitic stainless steel via combination of boriding and chromizing

Surface of low carbon austenitic stainless steel (AISI 316L) was modified by duplex surface treatment to improve its wear behavior, without compromising corrosion resistance of the steel. The duplex surface treating process composed of pack boriding (B) and pack chromizing (Cr) stages. Some specimens were duplex surface treated by boriding followed by chromizing (B–Cr), while some others were treated via chromizing followed by boriding (Cr–B), to evaluate the effect of duplex treatment sequence on wear and corrosion resistances. Microstructural studies, phase identification, wear and corrosion behaviors of the specimens were evaluated by scanning electron microscope (SEM), X-ray diffractometer (XRD), pin-on-disc wear test, and potentiostat electrochemical test. The results show that the precedence of boriding stage to chromizing stage makes significant improvement in wear and corrosion resistances of the duplex coating, whereas B-Cr coating provided superior wear resistances (up to 49%) and reduced corrosion rate (up to 4.5 times) in comparison to Cr-B and boriding coatings. Corrosion resistance of B-Cr coating was comparable to that of the stainless steel.

CVD graphene transfer procedure to the surface of stainless steel for stem cell proliferation

Graphene is an attractive material for tissue engineering due to its good interaction with cells (adhesion and proliferation) and its ability to protect the surface of biomaterials against corrosion. CVD graphene is a suitable candidate among the various types of graphene since it can cover large areas, however, the transfer process to the target substrates still involves several steps including the etching of metal used in chemical vapor deposition. Here, a new route of CVD graphene transfer process to the surface of austenitic stainless steel (ASS) is presented taking the advantage of not requiring an etching step. The structural stability of graphene transferred to the ASS surface was evaluated in SBF (simulated blood fluid) as well as for stem cell attachment and proliferation. CVD graphene was successfully transferred to a stainless steel surface in two steps: 1) Directly from a polymer film without the etching of copper (Direct Dry Transfer method - DDT); 2) Graphene transfer from the polymer to the ASS surface using temperature and pressure and the removal of the polymer by solvent. The area covered by graphene on the ASS surface varied according to the transfer parameters (pressure and time) and roughness of the substrate. Raman mapping results showed that graphene transferred to ASS surfaces presents a distinct structural stability in SBF of up to 28days. All samples tested allowed mesenchymal stem cell attachment and their proliferation. The success of the transfer procedure, the structural stability presented by the graphene under ASS, its attachment capacity, and proliferation of cells provides new opportunities for graphene as a covering material for tissue engineering.

Immobilization of heparin/poly-l-lysine microspheres on medical grade high nitrogen nickel-free austenitic stainless steel surface to improve the biocompatibility and suppress thrombosis

Thrombosis formation, restenosis, and delayed endothelium regeneration continue to be a challenge for coronary artery stent therapy. To improve the hemocompatibility of cardiovascular implants and to selectively direct vascular cell behavior, a novel heparin/poly-l-lysine microsphere was developed and immobilized on a dopamine-coated surface. We chose medical grade high nitrogen nickel-free austenitic stainless steel as the stent material since it has better biocompatibility. The stability and structural characteristics of the microspheres changed with the heparin: poly-l-lysine concentration ratio. Antithrombin III binding was significantly enhanced. Furthermore, for plasma coagulation tests, the activated partial thromboplastin time and thrombin time were prolonged and depended on the heparinfunction. The modified exhibited excellent stability and anticoagulant activity, and efficiently accelerated endothelialization and anticoagulation. This work has potential application for the design of coronary artery stent surfaces tailored for vascular cell behavior.

Computer Simulation of Laser Welding Technology of Chrome-Nickel Steels in Automotive Industry and its Verification by Means of Electron Microscopy

Numerical simulation of technological processes enables their exact description and it makes possible to get closer to the real process courses. The described method uses mathematical models transformed into the finite element method. The processes of interaction of the laser beam with the surface of austenitic stainless steel are first observed on simple geometrical models. Hereby the basic parameters of the processes are analyzed, and individual welding stages are described as dynamic fluid systems, in which steel is in a liquid state and it behaves as an incompressible fluid, while it is simultaneously loaded by the heat flux from the laser beam. Subsequently, three-dimensional models are analyzed using thermal and structural elements. Due to the high density of heat flow in the material, an orthotropical material model with equivalent coefficients of thermal conductivity of steel has to be used. The results obtained by numerical analyzes represent a sufficient picture of the behavior of the material when exposed to the laser beam, and they show the distribution of temperature, velocity and stress fields during welding. The acquired knowledge can be suitably used both in the automotive industry and also in many other industry branches.

Characterization of AISI 316L Stainless Steel Pattern via DC Plasma Nitriding

Aiming to produce a pattern on the surface of austenitic stainless steel, AISI 316L, cylindrical samples were plasma nitrided with copper grids (the same are used in Transmission Electron Microscopy (TEM)) accommodated on the surface. Samples were positioned at the cathode and process was performed according to following constant parameters: temperature of 400 °C, pressure of 3 Torr and treatment time of 2h. In order to evaluate the difference in the pattern produced, three different gas mixtures were used: poor in nitrogen (5% N2/95% H2), rich in nitrogen (95% N2/5% H2) and a gas mixture with addition of argon (80% N2/10% H2/10% Ar). After nitriding, samples were characterized by optical interferometry (OI), scanning electron microscopy (SEM), optical microscopy (OM), micro hardness test and, X-ray diffraction (XRD). The results showed the presence of a mask (TEM grid) promotes the surface patterning of steel. This patterning is associated with high residual compressive stress induced by the introduction of a large amount of nitrogen.

Cover Picture: Materials and Corrosion. 8/2016

Cover:EUROCORR, the annual event of the European Federation of Corrosion, is the premier Corrosion Congress in Europe. EUROCORR2016, organized by CEFRACOR in cooperation with Chimie ParisTech, will take place in Montpellier, France, from 11 to 15 September 2016. It will cover all aspects of corrosion science, technology, and engineering, with emphasis on a main theme: Advances in linking science to engineering.This theme is illustrated on the cover by a new multi‐technique platform designed to study in situ the evolution of material surfaces during their interaction with gaseous or liquid environments. It combines, into a unique machine, in situ electron spectroscopy for chemical analysis, in situ scanning tunneling and atomic force microscopies, electron diffraction, electrochemistry, and surface preparation facilities. The background is a STM image with atomic resolution of an austenitic stainless steel surface.

Effect of Cold Work on Cavitation Resistance of an Austenitic Stainless Steel Coating

Machining procedures of welding deposits are usual and result on cold work hardened surfaces. The cold work effect on cavitation erosion of an austenitic stainless steel surface is assessed. FeCrMnSiB coatings were processed by PTA on AISI 304 plates. Specimens were grouped as the cold work deformed surface (CWHS) and the undeformed polished surface (UPS) specimens. Top surface and transverse section of coatings were analysed for slip lines and hardness changes by light microscopy and Vickers microhardness measurements. Ultrasonic cavitation tests were conducted in accordance to ASTM G32-10. CWHS specimens exhibited slip lines and hardened surfaces while UPS specimens did not show traces of slip lines and had insignificant changes on microhardness. Cold work prior to cavitation indirectly increased the nominal incubation time and reduced the maximum erosion rate. Cold work increases the duration of the acceleration period postponing the onset of the maximum erosion rate and enhancing cavitation resistance.

Cover Picture: Materials and Corrosion. 7/2016

Cover:EUROCORR, the annual event of the European Federation of Corrosion, is the premier Corrosion Congress in Europe. EUROCORR2016, organized by CEFRACOR in cooperation with Chimie ParisTech, will take place in Montpellier, France, from 11 to 15 September 2016. It will cover all aspects of corrosion science, technology, and engineering, with emphasis on a main theme: Advances in linking science to engineering.This theme is illustrated on the cover by a new multi‐technique platform designed to study in situ the evolution of material surfaces during their interaction with gaseous or liquid environments. It combines, into a unique machine, in situ electron spectroscopy for chemical analysis, in situ scanning tunneling and atomic force microscopies, electron diffraction, electrochemistry, and surface preparation facilities. The background is a STM image with atomic resolution of an austenitic stainless steel surface.

Synergetic effect of thicker nanocrystalline structure with high amount of strain induced martensite on surface characteristics of plasma nitrided austenitic stainless steel

Abstract Severe shot peening is a simple and effective method to synthesize nanocrystalline layer on metallic surfaces. A new reactor to synthesize thicker nanocrystalline layers on metallic surfaces by shot peening is presented. In this cylindrical reactor air enters inside the reactor tangentially, propels shots on the specimen to be shot peened and leaves the reactor after multiple rotations. Air vortex and very high turbulence formed inside the reactor dissipate heat generated during shot peening and thus suppress dynamic recovery which promotes formation of refined and thicker nanocrystalline structure on a metallic surface. Experiments were conducted on 5specimens of austenitic stainless steel with different shot velocities in the reactor. Characterization (X-ray diffraction profiles, cross-sectional optical micrographs, TEM and micro-hardness profiles) of shot peened surfaces showed that thicker nanocrystalline/nano-twinned layers were developed during all peening conditions used in the experiments. Microstrain in the lattice, dislocation density and volume fraction of strain induced martensite observed to increase with rise in shot velocity. Specimens with thicker nanocrystalline layers were prepared. These specimens contained high amount of strain induced martensite deep down the surface. Plasma nitriding of these pre-shot peened specimens were done at 425 °C and 500 °C for six hours. Presence of thicker nanocrystalline layer with high amount of martensite at the surface of austenitic stainless steel observed to have synergetic effect and significantly influenced kinetics of nitriding process leading to higher surface hardness and 6-fold thicker nitrided layers compare to untreated nitrided surface. Presence of nanocrystalline structure, however, also effects on precipitation of chromium nitrides during nitriding.