Fabrication Of Stainless Steel Research Articles

Effect of preheat temperature and post-process treatment on the microstructure and mechanical properties of stainless steel 410 made via ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing technology for producing near-net shape metallic parts combining additive ultrasonic metal welding and subtractive machining. Even though UAM has been demonstrated to produce robust metal builds in Al–Al, Al–Ti, Al-steel, Cu–Cu, Al–Cu, and other material systems, UAM welding of high strength steels has proven challenging. This study investigates process and post-processing methods to improve UAM steel weld quality and demonstrates the UAM fabrication of stainless steel 410 (SS 410) builds which possess, after post-processing, mechanical properties comparable with bulk material. Unlike UAM fabrication of softer metals, this study shows that increasing the baseplate temperature from 38∘C (100∘F) to 204∘C (400∘F) improves interfacial strength and structural homogeneity of the UAM steel samples. Further improvement in strength is achieved through post-processing. The hot isostatic pressing (HIP) post treatment improves the shear strength of UAM samples to 344 MPa from 154 MPa for as-welded samples. Microstructural analyses with SEM and EBSD show no evidence of body centered cubic (BCC) ferrite to face centered cubic (FCC) austenite transformation taking place during UAM welding of SS 410. The weld quality improvement of UAM steel at higher baseplate temperatures is believed to be caused by the reduction of the yield strength of SS 410 at elevated temperature. HIP treatment is shown to increase the overall hardness of UAM SS 410 from 204 ± 7 HV to 240 ± 16 HV due to the formation of local pockets of martensite. Nanohardness tests show that the top of layer n is harder than the bottom of layer n+1 due to grain boundary strengthening.

Fabrication of stainless steel 316L/TiB2 composite coating via friction surfacing

Stainless steel 316L/TiB2 composite coatings were fabricated with different TiB2 contents using friction surfacing (FS) on the stainless steel 304 substrate. One or two blind holes were drilled at different positions axially on the cylindrical 316L consumable rods for keeping micron-size TiB2 powder as the reinforcement in the coatings. After FS, TiB2 was found to be embedded into the austenitic matrix and also partially decomposed leading to the formation of FeB2 and FeTi under high temperature and high strain rate. Compared with the friction-surfaced (FSed) 316L coating, the grain size of austenite in the TiB2 reinforced composite coating was refined from 7.8 to 0.64 μm, where austenite grains closed to {111} tends to transform to FeTi. Compared with monolithic 316L coating, the hardness of the FSed 316L/TiB2 coating was significantly increased from 219 to 1056 HV0.2 owing to the presence of TiB2 and intermetallic phases, finer austenitic grains and higher misorientation density. The pitting corrosion resistance of the FSed 316L coating was improved due to the elimination of MnS inclusions whereas the FSed 316L/TiB2 coating possessed lower pitting resistance due to the presence of FeTi. Moreover, the passivity of the 316L/TiB2 coating in 3.5% NaCl solution was preserved but the capability of re-passivation was degraded.

Fabrication of stainless steel based composite by metal injection moulding

Metal injection moulding (MIM) is large scale manufacturing method, for creation of complex shapes and miniature parts by a combination of plastic injection moulding with the flexibility in sintering of metal particulates. In current investigation binder comprised of paraffin wax, polyethylene glycol, stearic acid and low-density polyethylene are developed for moulding of composite powders of SS316L+WC-CrC-Ni, and sintered at 1200°C under hydrogen purged atmosphere. Composites are characterised with respect to rheological, thermal properties and microstructure by scanning electron microscopy, microhardness and density. Properties of sintering temperature and heating rate on the above properties have been evaluated to obtain a defect-free composite.

Application of ultrasonic peening during DMLS production of 316L stainless steel and its effect on material behavior

PurposeAdditive manufacturing (AM) processes involve a layer-by-layer sintering of metallic powders to produce fully functional three-dimensional parts. This layer-by-layer building process provides a unique opportunity to enhance mechanical properties by applying treatments that previously were possible only on the surface in traditional manufacturing techniques. The purpose of the study is to examine the effect of ultrasonic peening (UP) applied during a layer-by-layer direct metal laser sintering (DMLS) fabrication of 316L stainless steel on its mechanical properties and microstructure.Design/methodology/approachUniaxial tensile tests were performed at 1.27 mm/s to determine the effect of UP treatment on the average global behavior of a 316L part, whereas hardness measurements using nanoindentation were performed to determine the modification of local mechanical properties. Compressive buckling tests at a loading rate of 3 mm/min were performed on sample coupons with a large aspect ratio to evaluate the effect of UP on any potential delamination of DMLS layers. Techniques such as optical and scanning electron microscopy (SEM) imaging were utilized to determine the effect of UP on the microstructure.FindingsOverall, significant modification in mechanical properties such as hardness and yield strength, along with microstructure, was observed. Large increases in both the average global and local mechanical properties, as well as a disruption in the columnar grain microstructure, was observed in DMLS parts treated with UP treatment.Originality/valueResults indicate an opportunity for UP to be used as an in-situ process during AM processes for dynamically altering the mechanical behavior, microstructure, and distortion due to residual stress formation, in a tunable fashion.

Fabrication and characterization of antimicrobial surface-modified stainless steel for bio-application

We report a photofunctional stainless steel (PSS) that has antimicrobial property which is provided by reactive oxygen species (ROS) generated from the photosensitizer (PS). For the fabrication of the photofunctional stainless steel, the photosensitizer of hematoporphyrin (HP) was covalently bonded to the surface of 316L stainless steel (316LSS) through an esterification reaction. The PSS plate was investigated by x-ray photoelectron spectroscopy (XPS), reflectance UV–Vis absorption, and fluorescence spectroscopy. ROS generation from the PSS plate was studied by using the decomposition reaction of 1,3-diphenyl-isobenzofuran (DPBF). The results suggest that the immobilized photosensitizer molecules on the surface of the PSS plate still possess their intrinsic optical and functional properties including the ROS generation. The antimicrobial property of the PSS plate was successfully demonstrated with the decomposition of biofilm and the suppression of the biofilm formation on the surface of the PSS plate.

A review on nanostructured stainless steel implants for biomedical application

Over the last two decades, many researchers have developed a variety of stainless steel-based medical implant types,taking full advantage of nanostructuring technologies. In this paper the application, fabrication and development of nanostructured stainless steel based materials with new composition for medical implants will be discussed. It is well established that application of severe plastic deformation (SPD) can decrease the grain size of metals and alloys significantly to the nanometer range. Among all the available SPD methods, equal channel angular pressing (ECAP) is very applicable. Stainless Steel became the raw structural material for the majority of the developed medical implants, and several techniques had to be studied and established in order to fabricate a feasible stainless steel-based neural probe. These nanostructured implants present a superior performance mechanically, biologically and electrically, when compared to the conventional implants. Finally, the effect of alloying elements on the bio-interaction of stainless steel will be explained.

Fabrication of Bioactive Stainless Steel by the Function of Apatite Nuclei

Micropores were formed on the surfaces of stainless steel (SUS) by sandblasting methods and Apatite Nuclei (AN) were formed in the pores. By this treatments, a bioactive SUS was fabricated. Apatite-forming ability of the SUS was evaluated by immersing in an acellular simulated body fluid. Formation of bonelike apatite was induced on the surface of the SUS within 1 day. High bonding strength of the bonelike apatite layer was achieved by a mechanical interlocking effect between the bonelike apatite formed in the pores and the SUS specimen.

Possibility of Multi-material Laser Cladding Fabrication of Nickel Alloy and Stainless Steel

There are some applications in the industry for multi-material components, including device engineering and multifunctional surface engineering, having to eliminate a brazing or welding technological step. This study investigates the laser cladding process parameters, related single track geometry and quality of multi-material samples. The optimal process parameters for steel were found of 0.21-0.26 J/mm2 and 0.25 10-2 g/mm under the scanning velocity of 1400-1700 mm/min and powder feeding of 4.2-4.5 g/min. The bimetal thin walls, cylinders and cubes were manufactured within the optimal conditions. The requirements of steel and nickel joining were explored. For the examination, the optical microscopy, SEM, EDX microelement analysis and hardness analysis were involved.

Laser-based continuous monitoring and resolution of steel grades in sequence casting machines

Laser induced breakdown spectroscopy (LIBS) is a well-established technique for on-line industrial applications where robustness, stability, reliability, speed of analysis and operational availability are important topics to be taken into account. In this work, we propose an advanced methodology for in situ analysis of transition as-cast products during continuous casting with the purpose of improving the productivity and cost-efficiency in the fabrication of stainless steel and special steels. We have applied LIBS combined with Artificial Neural Network (ANN) for elemental analysis of casting steels. We have found that the quantitative determination of the material's composition across the slab/billet length is possible and that the intermediate chemical composition between sequential heats can be readily identified.

Development of Stainless Steel (SS316L) Foam with Different Composition Using Compaction Method

<span><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3"> </span> <p><span style="font-size: medium;" size="3"><span style="font-family: Times New Roman;" face="Times New Roman">Powder metallurgy stainless steels are retains unique benefits in preparation of porous metals due to its low cost, better wear, precise size control and corrosion resistance which are significant quality displays. In this study, the fabrication of open cellular stainless steel (SS316L) foams by using a crystalline sugar via compaction method was investigated. In this work, we show a promising method of SS316L preparation with crystalline sugar as space holder particles. Then, the foams will be given to consider the properties of SS316L foam after sintering process. Powder metallurgy process needs to go through the mixing, pressing, sintering and analysis. The selected composition of SS316L was 50 wt % and 55 wt % SS316L while the remaining percentages are foaming agent or binder. Then, sintering process was conducted in the tube furnace. The SS316L foams were characterised using X-Ray Diffraction (XRD) and Energy Diffraction X-ray (EDX). The results of this study indicate that, the XRD was detected Austenite stainless steel. Then, the detected elements in the SS316L foam were O, K, Mn, Cr, Fe, Mo and Al.</span></span></p> <span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3"> </span>

Fabrication of Porous Stainless Steel by Flame Spraying of Semimolten Particles

In this study, porous 316L deposits were processed by flame spraying under different spray conditions aimed at controlling deposit microstructure. Scanning electron microscopy (SEM) was used to characterize the microstructure of the deposits and deposit porosity was estimated from its cross section by image analysis. Results showed that porosity of 316L deposits ranged from 20 to 55% with change in spray particle melting degrees, resulting from alteration of spray parameters. To understand the deposition mechanism, the velocity of spray particles was quantitatively measured before impact and the morphology of isolated particles deposited was characterized by SEM and three-dimensional (3D) laser microscopy to estimate the melting degree of spray particles. The relationships between melting degree, spray conditions, and deposit porosity were established. The examination showed that porous steel deposits with 3D through-deposit pore-nets were fabricated through interbonding of solid cores of semimolten spray particles. It was found that the welding of particles by the molten fraction of semimolten spray particles forms large bonding necks between deposited particles, which improved the compression strength of the porous deposits over that fabricated by other conventional processes.

Fabrication of Nanostructured Medical-Grade Stainless Steel by Mechanical Alloying and Subsequent Liquid-Phase Sintering

This article focuses on the microstructure of medical-grade P558 (ASTM F2581) stainless steel produced by mechanical alloying and liquid-phase sintering. Rietveld X-ray diffraction and transmission electron microscopy reflect that the mechanically alloyed stainless steel powder is a nanocrystal dispersed amorphous matrix composite. Mn-11.5 wt pct Si eutectic alloy as additive improves densification of the synthesized P558 alloy via liquid-phase sintering mechanism. X-ray mapping shows that after sintering at 1323 K (1050 °C) for 1 hour, a uniform distribution of dissolved Mn and Si is achieved. Moreover, the development of a nanostructured, fully austenitic stainless steel after sintering at the same temperature is realized by X-ray diffraction and transmission electron microscopy.

The Effect of the Welding on the Residual Contact Stress in the Expanded Zone of Expanded-Welded Tube-to-Tubesheet Joints

The fabrication of stainless steel tube-to-tubesheet joints of heat exchangers consists of welding after hydraulic expansion. Here, this process is simulated by use of the finite element method, which is carried out in a sequentially decoupled analysis: the welding temperature field is solved by a transient thermal analysis, and subsequently, a nonlinear elastic plastic stress analysis is carried out. The effect of the unexpanded zone length with reference to the expanded zone of the joints is investigated. The results indicate that welding after the expansion will produce a shrinkage deformation in the tube end. This further reduces the magnitude of the contact stress in the expanded zone and moves it toward the tubesheet secondary surface. The percentage reductions of the contact stress and the contact area are introduced to quantitatively describe the effect of the welding on the expansion zone of the joint. The results show that these reductions decrease linearly with change in the unexpanded zone length, and that the effect of the welding on the contact stress in the expanded zone cannot be neglected. Therefore, a reduction of the influence of the welding on the structural integrity of tube-to-tubesheet joints should be taken into account when utilizing the technique of welding after hydraulic expansion.

Analysis of machining characteristics in electrochemical etching using laser masking

Electrochemical etching using laser masking (EELM), which is a combination of laser beam irradiation for masking and electrochemical etching, allows the micro fabrication of stainless steel without photolithography technology. The EELM process can produce various micro patterns and multilayered structures. In this study, the machining characteristics of EELM were investigated. Changes in characteristics of recast layer formation and the protective effect of the recast layer according to the laser masking conditions and electrochemical etching conditions were investigated by field emission scanning electron microscopy (FE-SEM), focused ion beam (FIB) and X-ray photoelectron spectroscopy (XPS). The oxidized recast layer with a thickness of 500 nm was verified to yield a superior protective effect during electrochemical etching and good form accuracy. Finally, micro patterns and structures were fabricated by EELM.

Role of residual stresses induced by industrial fabrication on stress corrosion cracking susceptibility of austenitic stainless steel

Effect of residual stress generated during tube fabrication, roll expansion and machining of stainless steel on the stress corrosion cracking (SCC) susceptibility was studied by testing fabricated tubes, tube–tube sheet joint and heavily machined plate of austenitic stainless steel (SS) in boiling MgCl 2. U bend samples of machined plate were exposed to acidified SO 4 + Cl − environment at room temperature to study its ambient temperature SCC behavior. The results correlate the SCC behavior of the SS tubes and roll expanded joints to the nature and magnitude of residual stresses present. The study also highlights the distinct difference in ambient temperature SCC behavior of machined vs. nonmachined surfaces.

Net shape fabrication of stainless steel–alumina composite micro parts

This paper presents a successful method to fabricate high-quality composite micro parts. The fabrication process starts with producing SU-8 aster moulds using photolithography technique, mirror replication of PDMS soft moulds, preparing composite slurry using super fine 316-L stainless steel (5 µm) and α-alumina powder (⩽400 nm) in 2.5, 5, 7.5 and 10 wt%, filling the moulds, obtaining the green parts, de-binding and sintering. A new method was used in this research to homogenize the alumina particles in a stainless steel composite slurry. Stainless steel and alumina powders were dispersed separately in distilled water and dispersant. Then, the two dispersed powders were mixed together to form a homogeneous composite slurry. The process resulted in high-quality composite micro parts which retain the very details of the SU-8 master moulds. The internal structures of the green and sintered micro parts showed homogeneous distribution of alumina particles in a stainless steel matrix. The density and micro hardness of the sintered parts were also investigated in detail for different stainless steel alumina compositions.

Stainless steel in concrete structures and in the fastening technique

AbstractThis paper summarises the state of the art in the application of stainless steel in concrete structures as well as in the fastening technique. Fabrication and application of stainless steel in civil engineering has been undergoing development for many years. Today this material is available in different alloy compositions and has an excellent long‐time resistivity in natural environments and in contact with wet construction materials, which offer a technically attractive and also economical approach for civil engineering, primarily for corrosion endangered bearing construction elements. The higher initial cost of using stainless steel can be justified on the basis that the increase in total project cost is small and is easily overtaken by the benefits of lower maintenance and repair costs. Actually stainless steel has been used in reinforced concrete and in fastening techniques for many years. The current concerns of research is the application of high‐strength stainless steel in prestressed concrete structures.

Fabrication and properties of Lotus-type porous nickel-free stainless steel for biomedical applications

Lotus-type porous Fe–25 wt.%Cr, Fe–23 wt.%Cr–2 wt.%Mo alloys and type AISI 446 stainless steel were fabricated by continuous zone melting technique in pressurized hydrogen and helium gas. The porosity of the samples varied in the range 44–48% and the mean pore size values obtained (145–374 μm) are in the biomedical field desired range. The fabricated Lotus-type porous nickel-free stainless steel was nitrided at high temperature up to the nitrogen concentration of 1.0 wt.% and this amount resulted to be sufficient for maintaining almost single-phase austenitic structure at room temperature. The combination of very small magnetic susceptibility, light weight, mechanical properties close to the human cortical bone, together with the known good enough corrosion resistance of high nitrogen nickel-free stainless steel, makes this Lotus-type porous Fe–Cr–N alloys very attractive for bone implant applications.

Microstructure characterisation and process optimization of laser assisted rapid fabrication of 316L stainless steel

In the present study, laser assisted fabrication of 316L stainless steel has been attempted using a high power (1.5 kW) continuous wave diode laser. The main process variables for the present study were applied power density, scan speed and powder feed rate. A detailed microstructural study of the surface and cross-section of the fabricated layer were carried out using optical and scanning electron microscopy to understand the influence of laser parameters on microstructure of the surface and interface between the successive layers. The microstructure of the top layer was equiaxed, the near substrate region was fine dendritic, however, at the interface between two successive layers, it was coarsened. The morphology and degree of fineness of the microstructure was found to vary with laser parameters. The range of grain size (maximum grain size–minimum grain size) was taken as a measure of homogeneity. It was found that with increasing the scan speed, the range of grain size was minimized. Micro-porosities were present in the microstructure that reduced with increasing scan speed and found to be minimum at a medium powder feed rate. The optimum processing conditions have been established by correlating the characteristics of the fabricated layer with process parameters.

Fabrication of stainless steel and aluminum fibers by PDME method

A pendent drop melt extraction (PDME) equipment was designed and fabricated to produce metallic fibers. The suitable work coils in our PDME unit were two or three turns type. The fiber formed by PDME method tends to be round as the diameter of the metallic fiber decreases. The final microstructure of the fiber significantly depends on the cooling rate of the melt drop. Solid nucleus was generated on the contact region of the cooling disc and grew in radial direction to the opposite side in relatively large diameter of the fiber. However, homogeneous and fine dendrite structure was observed in small diameter of the fiber. Optimum processing conditions for the fabrication of 40 and 100μm in diameter of stainless steel and aluminum fibers were 6–8, 14–21mm/min of specimen feeding speed, 400, 450–600rpm of cooling disc revolution in inert argon atmosphere, respectively.