Surface Of Austenitic Stainless Steel Research Articles

Corrosion Resistance of Copper Infiltrated on 0Cr18Ni9 Austenitic Stainless Steel by Plasma Surface Technology

Copper is infiltrated on 0Cr18Ni9 austenitic stainless steel surface by Double Glow Plasma technology, the surface copper content is about 3.5%, content of Cr in metal infiltration layer reaches up to 29.2%. Under the conditions of normal pressure and temperature, corrosion resistance of stainless steel samples which copper infiltrated on surface was researched in 1 mol/L NaOH solution by measurement method of electrochemical. The result shows that, corrosion resistance of copper-infiltrated stainless steel is about 1.67 times higher than untreated sample in 1 mol/L NaOH solution.

Cathodic cage plasma nitriding (CCPN) of austenitic stainless steel (AISI 316): Influence of the different ratios of the (N2/H2) on the nitrided layers properties

In this study, we assess how the ratio (N2/H2) – working atmosphere gas mixture – influences the properties of the layers produced on austenitic stainless steel surface by Cathodic Cage Plasma Nitriding (CCPN). The nitriding atmospheres contained nitrogen and hydrogen in three proportions: 20% N2 + 80% H2, 50% N2 + 50% H2, and 80% N2 + 20% H2 delivered at a flow rate of 20 sccm. The effect of 100% N2 was also examined. The morphology, microstructure and electrochemical properties of the layer produced were studied. The samples characteristics were determined by optical microscopy, x-ray diffraction, microhardness test and electrochemical potential curves.

Using an indentation test to evaluate the effect of cavitation peening on the invasion of the surface of austenitic stainless steel by hydrogen

In order to demonstrate the effect that the compressive residual stress introduced by cavitation peening has on suppressing the invasion of the surface of steel by hydrogen, we examined the surface after hydrogen charging using a spherical indenter. It was demonstrated that hydrogen considerably hardens the surface of austenitic stainless steel by 35% and that the surface hardening induced by hydrogen was reduced with increasing compressive residual stress introduced by cavitation peening. Moreover, the surface hardness was restored to its initial state after two weeks due to hydrogen desorption from the charged surface. This shows that the hardening was caused by the invasion of the surface by hydrogen and that the introduction of compressive residual stress suppresses it.

Augmentation of crevice corrosion resistance of medical grade 316LVM stainless steel by plasma carburising

Precipitate free carbon S-phase was produced on the surface of AISI 316LVM medical grade austenitic stainless steel with the use of low temperature direct current and active screen plasma carburising. The treated and untreated alloy was characterised and tested for pitting and crevice corrosion resistance. From this work it can be concluded that when compared to the untreated material, both treatments augment the pitting and crevice corrosion resistance. Using an active screen set-up results in a better surface composition and a higher crevice corrosion resistance than that produced using the direct current plasma carburising treatment.

Efficiency assessment of inhibitors on CaCO3 precipitation kinetics in the bulk and deposition on a stainless steel surface (316 L)

Calcium carbonate (CaCO3) is a common type of scale. Since the beginning of the XXe century, chemical inhibitors, such as PolyphosphinoCarboxylic acid (PPCA), were used to reduce and suppress the scale precipitation, assuming that it would act in the same way on scale deposition on surfaces. Desalination plants and oil industries are currently facing severe restrictions concerning the discharge of oilfield chemicals into the environment. CarboxyMethyl Inulin (CMI), PolyAspartate (PA) and PolyMaleic Acid (PMA) are three inhibitors commonly referred to as “green” products. This paper compares the effect of these inhibitors on the CaCO3 bulk precipitation and deposition on the surface of austenitic stainless steel (316L), at 70°C, under a controlled turbulent flow regime. This study shows that calcium carbonate full inhibition requires higher concentrations for scale deposition than for scale precipitation. Green inhibitors require higher concentrations to reach PPCA inhibition efficiency on both calcium carbonate formation mechanisms.

A Feasibility Study on Increasing Surface Hardness of Austenitic Stainless Steels by Pack Co-Deposition of N and Cr

This study is an attempt to codeposit N and Cr into the surface of austenitic stainless steels by pack cementation process to simultaneously increase their surface hardness and corrosion resistance. The pack powders were prepared using Cr2N powder as a source of both N and Cr, NH4Cl as activator and Al2O3 as inert filler. Specimens of the AISI204 austenitic stainless steel were treated in the 2 wt% NH4Cl activated 15Cr2N-85Al2O3 (wt%) pack at 1100 °C for different times. It was demonstrated that a top Cr2N layer with a Cr enriched zone underneath can be formed on the steel surface via the vapour phase generated in the activated powder pack. The effect of adding Cr powder into the pack powders on the surface layer formation and on the hardness profile at the cross-section of the specimen surface was also investigated. Hardness values of more than 1800 HV were obtained at the outermost surface of the treated specimen.

Effect of low-temperature plasma carbonitriding on the fretting behaviour of 316LVM medical grade austenitic stainless steels

Abstract An optimized low-temperature plasma carbonitriding process at 430 °C for 15 h was used to treat the surface of 316LVM medical grade austenitic stainless steel. By using a servo-hydraulic dynamic test machine, the fretting behaviour of both as-received and the surface-treated 316LVM plate samples against martensitic stainless steel balls was studied in the Ringer's solution at various displacement amplitudes. The experimental results demonstrate that the optimized low-temperature plasma surface treatment can produce a precipitate-free, C/N supersaturated S-phase layer. Such layer revealed a hardness of 5 times that of 316LVM substrate. The formation of S-phase can protect the 316LVM from corrosion in the Ringer's solution, and the hard surface-treated layer can significantly improve the fretting wear resistance of 316LVM material. When fretted in a mixed regime, a sharp drop of friction force was observed for untreated 316LVM after fretting for about 1000 cycles, which was mainly caused by the penetration of Ringer's solution into the contact area of the fretting pairs. As a comparison, no friction drop was observed through the fretting process on the surface-treated samples. Due to the high ratio of elastic modulus to hardness (E/H) of untreated sample, the main damage mechanism on untreated sample was adhesive and abrasive wear during the fretting process. However, because of the high hardness and low E/H ratio of the surface-treated sample, the main damage mechanism was mild abrasive wear. In conclusion, the low temperature plasma surface treatment can effectively improve the fretting wear properties of 316LVM stainless steel, which could pave the way to develop the high-performance, long-life body implants.

Low Temperature Nitriding of a Martensitic Stainless Steel

Nitriding is as an effective technique applied for many years to improve the surface hardness and wear resistance of low carbon and tool steels [1]. In the case of stainless steels, increase of surface hardness and wear resistance accompany by a drop in corrosion resistance due to the precipitation of CrN. In this respect, many attempts have been made to modify the surfaces of austenitic stainless steels to increase their surface hardness and wear resistance without scarifying the corrosion resistance [2-6]. It is finally concluded that, nitriding at temperatures lower than conventional nitriding process (which is generally about 550°C) has potentiality to produce a nitrogen expanded austenite (also known as S-phase), on the surface without formation of CrN. Due to the superb properties of the S-phase, the low temperature nitrided austenitic stainless steels exhibit very high surface hardness, a good wear resistance, and more importantly, an excellent corrosion resistance. Recently some attempts have been made to apply low temperature nitriding to martensitic stainless steels, which are widely used in the industries of medicine, food, mold and other civil areas [7-9]. In these works, where nitriding has been conducted by plasma processes, superior surface hardness, along with excellent wear and corrosion resistances have been reported for AISI 410 and AISI 420 grade martensitic stainless steels. This work focuses on low temperature gas nitriding of AISI 420 grade martensitic stainless steel in a fluidized bed reactor. In this respect the microstructures, phase compositions, hardness, wear and corrosion behaviours of the original and nitrided martensitic stainless steels have been compared.

Characterization of stress–strain behavior of a cast TRIP steel under different biaxial planar load ratios

This paper investigates the stress–strain curves of different load paths and the initial yield surface of a metastable austenitic stainless cast steel under biaxial planar loading using cruciform specimens. These tests were carried out on a 250 kN biaxial servohydraulic tension-compression testing machine. The laborious stress determination was undertaken with a new testing method by using global elastic unloading to measure the local stiffness. Isotropic yielding and mainly isotropic strain hardening were found. To evaluate the microstructure, the martensite formation was detected by use of a ferrite sensor and scanning electron microscopy and electron backscatter diffraction were applied.

High-corrosion-resistant Al2O3 passivation-film formation by selective oxidation on austenitic stainless steel containing Al

We have developed Al2O3 passivation film having very high anticorrosion resistance on the surface of austenitic stainless steel containing 3 wt % aluminum. Al2O3 passivation film is formed by selective oxidation of aluminum in the austenitic stainless steel in the Ar and H2 ambient including a small amount of H2O at predetermined temperatures. Al2O3 film is obtained at temperatures higher than 750 °C in the Ar and H2 ambient, where the partial pressure ratio of H2 and H2O is set higher than 2×103. Al2O3 films have been confirmed to exhibit very high anticorrosion resistance for various halogen gases and various plasma ambients (Cl2, H2, and O2) with ion-bombardment energies less than 100 eV at temperatures less than 150 °C. In the case of fluorine-gas plasma, the Al2O3 film surface has been converted to AlF3 with a depth of 15 nm, where AlF3 film is thermodynamically stable, as well as Al2O3, resulting in an excellent passivation film exhibiting very high anticorrosion capability. Moreover, the Al2O3 film surface has been confirmed to exhibit no catalytic activity for various specialty gases at temperatures less than 150 °C.

205404 ナノ秒レーザにより表面加工したステンレス鋼の静的・動的濡れ性評価(一般01 材料科学・材料力学5)

Austenitic stainless steel (SUS316L) surfaces were processed with a Nano-second Laser System (NLS). Changing processing parameters such as defocus distance, scanning rate and path intervals caused different effects on topography of the surfaces. The processed surface showed unique surface microstructure with complicated micro holes. The wettability of the surfaces was also examined by measuring a static and dynamic contact angle. The contact angles were changed from 0° to 137°, and the contact angle histereses decreased to 3.6° depending on the processing parameters. This suggests that the wettability of SUS316L steel surfaces can be controlled by NLS processing.

Steel research int. 1/2011

Cover Photo: The cover shows a confocal microscopy image (“confocal height maps”) of the surface of a metastable austenitic stainless steel (1.4301) with a grain size of approx. 20 mm. More on topological surface changes during tensile deformation of steels can be found in the paper by S. Hoffmann and W. Bleck on page 32 of this issue.

Surface microstructure and antibacterial property of an active-screen plasma alloyed austenitic stainless steel surface with Cu and N

Antibacterial modification of medical materials has already been developed as a potentially effective method for preventing device-associated infections. However, the thin layer generated, often less than 1 µm, cannot ensure durability for metal devices in constant use. A novel stainless steel surface with both a quick bacterial killing rate and durability has been developed by synthesizing Cu and a supersaturated phase (S-phase) using a new active screen plasma alloying technology. This paper investigated the microstructure of a multilayer (using EDS/WDS, SEM, TEM and XRD) and the viability of bacteria attached to biofunctional surfaces (using the spread plate method). The experimental results demonstrate that the plasma alloyed multilayered surface case consists of three sublayers: a nano-crystalline (Fe, Cr, Ni)3N deposition layer (∼200 nm), a unique Cu-containing face-centred cubic (f.c.c.) γ′-M4N (M=Fe, Cr, Ni, Cu) layer and a Cu/N S-phase layer. The thicknesses of the total treated case and the Cu-containing layers are 15 and 8 µm, respectively. Copper exists as substitutional atoms in the γ′-M4N (with a constant concentration of about 5 at%) and in the S-phase lattice (reduces from 5 to 0 at%). The crystal constant of the Cu/N S-phase layer ranged from 0.386 to 0.375 nm, which is expanded by γ from 4.4% to 7.5%. An effective reduction of 99% of Escherichia coli (E. coli) within 3 h was achieved by contact with the homogeneous Cu alloyed surface. No viable E. coli was found after 6 h (100% killed).

Development of Polymer Coatings for Coronary Stents

The aim of this study is to examine some key properties of medical polyurethane coatings on coronary stents such as thickness and size of pores on the surface of austenitic stainless steel (316L). Plates were used as carrier instead of real stents, because they are too expensive and difficult to work with. The carriers were dipped into the solution of polyurethane and tetrahydrofuran. Solutions of 1 to 5 wt % were prepared for the experiments and the numbers of the dipping were changed. The coatings were examined with Atomic Force Microscope (AFM). In contact mode detailed images with good contrast were made about the coatings. These images were processed with image processing algorithms in MATLAB and with the image analysis software belonging to the AFM instrument.

Out-of-plane magnetic patterning on austenitic stainless steels using plasma nitriding

A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks.

X-ray diffraction characterisation of expanded austenite and ferrite in plasma nitrided stainless steels

The S phase, known as expanded austenite, is formed on the surfaces of austenitic stainless steels that are nitrided under low temperature plasma. A similar phase was observed for nitrided ferritic stainless steels and was designed as expanded ferrite or ferritic S phase. The authors treated samples of austenitic AISI 304L and AISI 316L and ferritic AISI 409 stainless steels by plasma nitriding at different temperatures and then studied the structural, morphological, chemical and corrosion characteristics of the modified layers by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and electrochemical tests. For both austenitic AISI 304L and AISI 316L stainless steels, the results showed that a hard S phase layer was formed on the surfaces, promoting an anodic polarisation curve displacement to higher current density values that depend on the plasma nitriding temperature. A layer having a high amount of nitrogen was formed on the ferritic AISI 409 stainless steel. X-ray diffraction measurements indicated high strain states for the modified layers formed on the three stainless steels, being more pronounced for the ferritic S phase.

Accumulation of uranium, transuranium and fission products on stainless steel surfaces. I. A comprehensive view of the experimental parameters influencing the extent and character of the contamination

The surface contamination by uranium and transuranium (Pu, Am, Cm) nuclides in the primary circuit of pressurized water nuclear reactors is a fairly complex problem as (i) different chemical forms (molecular, colloidal and/or disperse) of these atoms can be present in the boric acid coolant, and (ii) only limited information about the extent, kinetics and mechanism of uranium and transuranium (TRU) accumulation on constructional materials is available in the literature. A comprehensive program has been initiated in order to study the accumulation of uranium and TRU species on some structural materials used at Soviet made VVER-type pressurized water reactors (such as heat exchanger tube of steam generators and stainless steel canister material). This paper, which is the first part of a series of two, provides a comprehensive view on the main experimental parameters influencing the extent and character of the surface contamination by uranium and TRU nuclides. Specifically, we give a brief summary of relevant literature data on the chemistry of uranium and TRU elements and review the dominant chemical forms and their relative sorbability on austenitic stainless steel and Zr(Nb) alloy surfaces. Moreover, some findings on the distribution of uranium, plutonium, americium, and curium species in a model solution of boric acid coolant obtained by the VisualMINTEQ computer code are also presented and discussed.

Surface pretreatment of austenitic stainless steel and copper by chemical, plasma electrolytic or CO 2 cryoblasting techniques for sol–gel coating

The surface pretreatments of the austenitic stainless steel and copper surfaces for the sol–gel coating were carried out by chemical, plasma electrolytic or CO 2 cryoblasting techniques. With the austenitic stainless steel the smoothest surfaces were obtained with plasma electrolytic cleaning, after which the measured contact angles of water were clearly decreased revealing improved hydrophilicity. As well with the copper samples the smooth surface and improved hydrophilicity was obtained with the plasma electrolytic cleaning, but oxide layer formed to the copper surface immediately after the treatment. CO 2 cryoblasting provided rough surface with wetting properties close to the original surface both for austenitic stainless steel and copper surfaces. CO 2 cryoblasting provided best appearance for the copper surface because no oxidation happened with that treatment. XPS and SIMS studies showed that with the plasma electrolytic treatment the surface layer of the austenitic stainless steel enriched of chromium and the oxide layer formed on the surface was less than 10 nm thick. With the chemical cleaning and CO 2 cryoblasting, the chromium enrichment to the stainless steel surface was less. However XPS and SIMS studies showed that chemical treatment provided thinner oxide layer to copper surface than plasma electrolytic treatment.

Study of the S Phases Formed on Plasma-Nitrided Austenitic and Ferritic Stainless Steels

An expanded austenite layer is formed on the surfaces of austenitic stainless steels that are nitrided under low-temperature plasma. This S phase is an iron alloy metastable phase supersaturated with nitrogen. We have identified a similar expanded ferrite or ferritic S phase for nitrided ferritic (BCC) stainless steels. Samples of austenitic AISI 304L and AISI 316L and ferritic AISI 409L stainless steels were plasma-nitrided at 350, 400, 450 and 500°C, and the structural and corrosion characteristics of the modified layers were analyzed by X-ray diffraction (XRD) and electrochemical tests. For the austenitic AISI 304L stainless steel, the results showed that a hard S phase layer was formed on the surface, without corrosion resistance degradation, by using low plasma temperatures (350 and 400°C). A similar behavior was observed for the austenitic AISI 316L stainless steel: the modified layers formed at 350 and 400°C were constituted mainly by the S phase. Plasma-nitriding treatment of the ferritic AISI 409L stainless steel caused the formation of a layer having high amount of nitrogen. XRD measurements indicated high strain states for the modified layers formed on the three stainless steels, being more pronounced for the ferritic S phase.

Characteristics of austenitic stainless steel nitrided in a hybrid glow discharge plasma

A nitriding process based on two distinct nitrogen glow discharge modes, with sample temperatures ranging from 380 0C to 480 0C, was employed to treat the surface of austenitic stainless steel (SS 304). The temperature is controlled exclusively by switching the operation conditions of the discharges. First mode of operation is the conventional one, named cathodic, which runs at higher pressure values (1 mbar) in comparison to the second mode, named anodic, which runs at the pressure range of 10-3 - 10-2 mbar. Cathodic mode is used to quickly heat the sample holder, by the high ion flux. On the other hand, in the anodic mode, due to the lower operation pressure, higher effective ion acceleration takes place, which allows deeper ion implantation into the sample surface. This hybrid process was thoroughly explored regarding the duty cycle and conditions of operation, to achieve optimal performance of the treatments, which led to the attainment of surface hardness for samples of AISI SS 304 as high as 20 GPa and improvements including higher elastic modulus and resistance against corrosion. Detailed comparison among samples treated by this process with others treated by conventional method was done using nanoindentation, Auger Electron Spectroscopy (AES) and corrosion resistance testing.