Sintered Stainless Steel Research Articles

Laser Surface Alloying of Sintered Stainless Steel.

A characteristic feature of sintered stainless steel (SSS) is its porosity. Porosity results in a lower density of steel, making attractive components for producing lightweight structures and materials used in industry (e.g., the automotive industry or aerospace). Scientists also observe that porosity adversely affects steel’s properties, especially its strength properties. One of the proposals for improving the discussed properties is the use of surface treatment of sintered stainless steels, e.g., with the use of concentrated energy sources such as plasma beams or laser beams. However, this proposal is an incidental subject of research, which is not justified from the point of view of the obtained research results presented by a few research groups. In this study, the surface modification (surface treatment) of sintered stainless steel was presented. The authors proposed the use of two surface treatments in order to compare them and obtain the best results. The first treatment was the deposit of Cr3C2–NiCr coatings on SSS surfaces using the atmospheric plasma spraying (APS) method. The second treatment was to create surface layers on SSSs by laser alloying the surface with a CO2 laser. Due to high precision and ease of automation, the most common methods in surface alloying treatment are laser technologies. This research’s main aim was to analyze the microstructure and strength properties of the SSS surface layer. The research confirms that applying the Cr3C2–NiCr coating and modifying the surface layer through the laser alloying method improves the mechanical properties of SSSs.

Influence of plasma sprayed zirconia coating on surface properties of additive manufactured austenitic stainless steel 316 L

The present work was carried out to improve the as-built surface properties of direct metal laser sintered (DMLS) stainless steel AISI 316 L by plasma spray zirconia coating. Layer wise fusion of powder particles in DMLS process led to the nucleation of austenite phases in which the grain boundaries were overlapped each other. The as-built surface morphology exhibited partly fused powder particles on the final layer of laser scan. In order to achieve better surface properties, 100 μm thin layer of zirconia was deposited on the as-built surface. Plasma spray zirconia coating resulted in better surface morphology and led to the disappearance of surface defects. Nano indentation analysis proved substantial enhancement in the surface hardness which exhibited 3942 MPa and 9655 MPa for the substrate and coated layer respectively. Also, zirconia coating headed to significant improvement in the electro chemical corrosion resistance than the substrate which was proven by reduction in the corrosion rate to a percentage of 78.89% in a phosphate buffered saline (PBS) medium.

Torsional Fatigue Failure of Additively Manufactured Stainless Steel of Reduced Specimen Size

The torsional fatigue response of as-built direct metal laser sintered (DMLS) stainless steel (SS) GP1 of reduced specimen size and horizontal build orientation subjected to cyclic loading at a highly plastic shear strain has been investigated. The average shear modulus, G, was found to be 55.36 GPa, with shear stress history revealing cyclic hardening to stabilization and softening to fracture. Findings suggest that stainless steel GP1 of reduced specimen size experiences fatigue crack initiation at voids near the surface, resulting in a star-spline brittle fracture response, and premature torsional fatigue failure within the low cycle fatigue regime. A noninteraction deformation constitutive model through finite element simulations has been used to successfully simulate the deformation response of the gage section under torsional fatigue conditions.

Pit Initiation Behavior at Sulfide Particles in Sintered Stainless Steels

The pit initiation sites for commercial stainless steels have been attributed to sulfide inclusions such as MnS. The chemical composition of the inclusions affects the pitting corrosion resistance of stainless steels. Systematic investigation on the relationship between the chemical composition of the inclusions and the pitting corrosion resistance is required. However, it is difficult to prepare a series of the steel specimens of which the chemical composition of the inclusions is precisely controlled. In this study, spark plasma sintering was used to fabricate stainless steel specimens containing sulfide particles, and a microelectrochemical technique was applied to analyze the effect of the chemical composition of the sulfides on the pitting corrosion resistance of stainless steels. A type 304 stainless steel powder was mixed with a MnS powder to prepare the sintered specimen containing 0.03 mass% S. The particle sizes of the stainless steel and the MnS powder were –100 mesh and –325 mesh, respectively. The mixed powders were loaded into a cylindrical graphite die and were compressed using a hydraulic press. The pressed compact was spark plasma sintered in vacuum, under uniaxial pressure at 30 MPa. The sintered specimen was ground with SiC papers and then was polished with an 1 µm diamond paste. Potentiodynamic polarization was conducted in naturally aerated 0.1 M NaCl (pH 5.5) at 298 K. The specimen surface was masked to make an electrode area of ca. 100 µm × 100 µm containing a sulfide particle. All the potentials reported in this study refer to the Ag/AgCl (3.33 M KCl) electrode (0.206 V vs. standard hydrogen electrode at 298 K). The potential scan rate was 3.8 × 10-4 V/s. The anodic polarization curve was measured in 0.1 M NaCl to characterize the pit initiation behavior at the MnS particle in the sintered stainless steel. Polarization was started at –0.2 V and was stopped after the large increase in the current density was measured. The electrode area was observed using an optical microscope after polarization. The MnS particle partly dissolved, and the pit was found at the boundary between the particle and the steel matrix. This suggests that the large current increase was attributed to the pit initiation at the particle. It is expected that the sintered specimen can be used to investigate the pit initiation behavior at the sulfides in stainless steels.

MICROSTRUCTURE AND FRICTION PARAMETERS OF THE SURFACE LAYER OF SINTERED STAINLESS STEELS

Sintered stainless steel (SSS) is manufactured using the powder metallurgy technology (PM). SSSs are characterized by a two–phase structure which can be obtained by mixing different proportions of the main structural components (i.e. austenite and ferrite). Taking into account the improvement of functional properties of SSSs, a number of surface modifications have been proposed. This study proposes a method to improve functional properties by formation of chromium carbide coating and alloying the surface by the gas tungsten arc welding (GTAW) process. The results of light optical microscopy and scanning electron microscopy (SEM/EDX), roughness parameters, hardness, and the coefficient of friction are presented.

Mechanical Characterization and Modeling of Direct Metal Laser Sintered Stainless Steel GP1

The additive manufacturing (AM) process is unique in that it can facilitate anisotropy because of the layer-by-layer deposition technique intrinsic to this process. In order to develop a component for a desired application, it is necessary to understand the mechanics that facilitate this material behavior. This study investigates how build orientation affects the mechanical performance of as-built direct metal laser sintered (DMLS) stainless steel (SS) GP1 (also referred to as 17-4PH) through strain-controlled monotonic tension and completely reversed low-cycle fatigue (LCF) testing. The anisotropic behavior of DMLS SS GP1 is assessed for samples built along the horizontal plane. Fracture surfaces were found to exhibit ductile responses that were consistent with the σ–ε curves. Constitutive models (i.e., Ramberg–Osgood, Hahn) based upon linear elasticity and nonlinear plasticity are presented and used to simulate the monotonic discontinuous stress–strain yielding response of this material, which are found to be in agreement with the experimental data. A collection of low-cycle fatigue tests reveals initial strain hardening to stabilization, followed by softening to fracture. Tensile and fatigue material constants determined from experimental findings are also presented in this study. Plasticity effects on the life of varying build orientations are explored.

Bending Behavior of Porous Sintered Stainless Steel Fiber Honeycombs

A novel porous honeycomb-type substrate has been developed using solid-state sintering stainless steel fibers. The porous sintered stainless steel fiber honeycombs (PSSSFH) are composed of a skeleton of sintered stainless steel fibers, three-dimensionally interconnected porous structures and multiple parallel microchannels. The bending behavior of the PSSSFH is investigated using three-point bending tests. Four stages, including an elastic stage, a yielding stage with a plateau, a hardening stage and a failure stage, are observed during the bending process of the PSSSFH. In the initial yielding stage, the bending forces increase slowly with displacement increasing, and then a yielding plateau follows, which is unique compared with other porous materials. Moreover, the structure parameters of the PSSSFH are varied to investigate the influence on the bending strength. It is determined that the multiple parallel microchannels can enhance the bending strength of porous stainless steel fiber sintered substrates (PSSFSS) and do not influence the variation trend of bending strength of PSSFSS with porosity increasing. The open ratio is conducive to increasing the bending strength, and the microchannel diameters ranging from 0.5 mm to 1.5 mm have little influence on the bending strength. In addition, both the increasing of sintering temperature and sintering time can strengthen the PSSSFH.

분말야금 스테인리스 스틸의 산화특성에 미치는 조성 및 조직변화의 영향

As well-known wrought stainless steel, sintered stainless steel (STS) has excellent high-temperature anti-corrosion even at high temperature of , and exhibits good corrosion resistance in air. However, when temperature increases above , the corrosion resistance of STS begins to deteriorate and dramatically decreases. In this study, the effects of phase and composition of STS on high-temperature corrosion resistances are investigated for STS 316L, STS 304 and STS 434L above . The morphology of the oxide layers are observed. The oxides phase and composition are identified using X-ray diffractometer and energy dispersive spectroscopy. The results demonstrate that the best corrosion resistance of STS could be improved to that of 434L. The poor corrosion resistance of the austenitic stainless steels is due to the fact that oxides forming poor adhesion between the matrix and oxide film increase the oxidation susceptibility of the material at high temperature.

Enhanced sintering of austenitic stainless steel powder AISI 316L through boron containig master alloy addition

It is well known that boron is widely used in order to enhance sintering process for obtaining high density of sintered iron alloys. It was found that even a small amount of elemental boron added to iron based powder compacts, produces significant increase in densification rate upon formation of a liquid phase. Due to the attractive characteristic the use of boron has also been actively investigated for enhancing sintering stainless steels powders. In present research boron was added as a part of master alloy, which has been designed to provide the formation of wetting liquid phase, with accomplished characteristics for manufacturing controlled densification of sintered austenitic stainless steels powders AISI 316L. In this paper the influence of sintering atmosphere and the boron in 0,1; 0,2; 0,3 and 0,4 wt. % amount on the density, microstructure and selected properties of sintered austenitic stainless steels were reported. Green compacts obtained by cold compaction at 600 MPa reached densities around 6,2 g/cm3. The sintering process was carried out both in pure dry hydrogen atmosphere and in vacuum at temperature 1240°C using dilatometer Netzsch DIL 402C. In order to interpret the influence of sintering atmosphere and boron content on the sintering behaviour of boron alloyed austenitic stainless steels powders during heating and isothermal holding, the evolution of the dilatometric curves have been discussed. The as-sintered microstructures were characterized under the SEM (EDS), while the pore morphology by the image analysis. In conclusion it could be affirmed that the addition of the master alloy containing boron to austenitic stainless steels powders, produces a permanent liquid phase that enhances densification compacts during sintering, in particular in hydrogen atmosphere. For this reason the results are promising from a technological point of view, because boron addition could extend applications of sintered stainless steel both with respect to lower sintering temperature and shorter time necessary to obtain well rounded pores which are desirable with respect to mechanical properties and corrosion resistance.

Electro-microfiltration of the mineral particles in dairy processing

Two sintered stainless steel (SSS) microfiltration membranes (5 &mgr;m and 25 &mgr;m pore size respectively) were used for separating Alamin particles found in dairy processing. An external electric field was applied upon the membrane to provide a combination of rejective coulomb force, fluid shearing force and the bubbling rejection to the foulant. The electric field can be applied in two ways: 1) to mitigate the fouling deposit, and/or 2) to clean the fouled filtering surface. The divergence of pH in the retentate and permeate was studied.

Experimental study of fouling and cleaning of sintered stainless steel membrane in electro-microfiltration of calcium salt particles.

Sintered stainless steel (SSS) microfiltration membranes, which served as electrode directly, were used for the experiment of separating Alamin, a calcium salt and protein containing particles, found in dairy processing. Fouling and cleaning of the SSS membranes under the application of an external electric field were studied. The imposed electric field was found, diverging the pH of permeate and retentate. This in turn altered the solubility of the calcium salt and impacted the performance of electro microfiltration membrane. Using electric field as an enhanced cleaning-in-place (CIP) method in back flushing SSS membrane was also studied.

Mechanical Properties of Sintered and Non Sintered Stainless Steel Wools: Experimental Investigation and Modelling

AbstractEntangled fibrous materials have a common point with cellular solids: the architecture is at the millimetric scale. However, they present one extra degree of freedom which is the connectivity on the constituents: while compressing a fibrous structure, the number of contacts between fibers is variable, by contrast to cellular solids where the building lock is the cell. In this respect, fibrous entangled solids can span a whole range of mechanical behavior depending on the possibility offered to fibers to create new contacts: from the felt where they are totally free, to the fully sintered wool where their relative motion is constrained by irreversible contacts. The purpose of this paper is to investigate the mechanical properties of this class of materials, based on micro tomography observations for the number of contacts, and on a physically based model for fiber bending and collective reorganization. The material studied is a stainless steel wool. The properties investigated are the loading curves for sintered and non sintered wools. Qualitative differences introduced by sintering motivate a modification of the classical Toll model, which will be presented together with the experimental results.

Effects of nitrogen ion implantation on the corrosion characteristics of Cu-electroless plated and sintered stainless steel

Electrochemical tests were used to investigate the effects of N+2 implantation on the corrosion characteristics of Cu-electroless plated and sintered stainless steel (SSS) in H2SO4, H2SO4+KSCN, and HCl solutions. Stainless-steel compacts containing Cu (2–10 wt%) were prepared using the electroless Cu-plating (ELCP) method. N+2 implantation was carried out using N2 gas as the ion source of the feed materials. The ions were embedded by an accelerator with an energy of 130 keV to a dose of 3.0×1017 ions cm−2 on the SSS at 25 °C in a 2×10−5 Torr vacuum. In the case of N+2 implanted 316LSSS, the corrosion potential increased, and the passive current density decreased. As the Cu content increased, the corrosion potential of N+2 implanted 316LSSS drastically increased, with the exception of a slight decrease in the passive current density. The reactivation peak of N+2 implanted and unimplanted SSS did not appear (not sensitized), but the activation current density decreased. The pitting potential of N+2 implanted 316LSSS was higher than that of the implanted 304LSSS due to the synergistic effect of Mo and N, and the inhibition of NH+4 against Cl−. The pitting resistance increased as the Cu content increased, due to the formation of CuCl2·3Cu(OH)2, CuO and Cu2O on the surface.

Corrosion Behaviour of Sintered Stainless Steel in Sulphuric Acid and Sodium Chloride Solutions

Corrosion Behaviour of Sintered Stainless Steel in Sulphuric Acid and Sodium Chloride Solutions

ChemInform Abstract: Effect of Cu Addition on the Corrosion Behaviour of Sintered Stainless Steel in H2SO4 Environment.

Chemischer InformationsdienstVolume 17, Issue 17 Physical Inorganic Chemistry ChemInform Abstract: Effect of Cu Addition on the Corrosion Behaviour of Sintered Stainless Steel in H2SO4 Environment. D. ITZHAK, D. ITZHAKSearch for more papers by this authorP. PELED, P. PELEDSearch for more papers by this author D. ITZHAK, D. ITZHAKSearch for more papers by this authorP. PELED, P. PELEDSearch for more papers by this author First published: April 29, 1986 https://doi.org/10.1002/chin.198617017Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue17April 29, 1986 RelatedInformation

ChemInform Abstract: Effect of Sn Addition on the Corrosion Behaviour of Sintered Stainless Steel in H2SO4.

AbstractEine Sn‐Zugabe von O.5‐3 Gew.‐% verstärkt die Verdichtung von heiß‐ gepreßten, gesinterten Edelstahlproben der Type 316; die Anzahl offener Poren wird verringert, wodurch die Korrosionsbeständigkeit in H2SO4 verbessert wird.

The Effect of Oxides Additives on Anti-corrosion Properties of Sintered 316L Stainless Steel

<p>As wrought stainless steel, sintered stainless steel (STS) has excellent high-temperature anti-corrosion even at high temperature of 800ºC and exhibit corrosion resistance in air. The oxidation behavior and oxidation mechanism of the sintered 316L stainless was reported at the high temperature in our previous study. In this study, the effects of additives on high-temperature corrosion resistances were investigated above 800ºC at the various oxides (SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, MgO and Y<sub>2</sub>O<sub>3</sub>) added STS respectively as an oxidation inhibitor. The morphology of the oxide layers were observed by SEM and the oxides phase and composition were confirmed by XRD and EDX. As a result, the weight of STS 316L sintered body increased sharply at 1000oC and the relative density of specimen decreased as metallic oxide addition increased. Compared with STS 316L sintered parts, weight change ratio corresponding to different oxidation time at 900oC and 1000oC, decreased gradually with the addition of metallic oxide. The best corrosion resistance properties of STS could be improved in case of using Y<sub>2</sub>O<sub>3</sub>. The oxidation rate was diminished dramatically by suppression the peeling on oxide layers at Y<sub>2</sub>O<sub>3</sub> added sintered stainless steel.</p>