Resistant Stainless Steel Research Articles

Unsupervised learning-enabled pulsed infrared thermographic microscopy of subsurface defects in stainless steel

Metallic structures produced with laser powder bed fusion (LPBF) additive manufacturing method (AM) frequently contain microscopic porosity defects, with typical approximate size distribution from one to 100 microns. Presence of such defects could lead to premature failure of the structure. In principle, structural integrity assessment of LPBF metals can be accomplished with nondestructive evaluation (NDE). Pulsed infrared thermography (PIT) is a non-contact, one-sided NDE method that allows for imaging of internal defects in arbitrary size and shape metallic structures using heat transfer. PIT imaging is performed using compact instrumentation consisting of a flash lamp for deposition of a heat pulse, and a fast frame infrared (IR) camera for measuring surface temperature transients. However, limitations of imaging resolution with PIT include blurring due to heat diffusion, sensitivity limit of the IR camera. We demonstrate enhancement of PIT imaging capability with unsupervised learning (UL), which enables PIT microscopy of subsurface defects in high strength corrosion resistant stainless steel 316 alloy. PIT images were processed with UL spatial–temporal separation-based clustering segmentation (STSCS) algorithm, refined by morphology image processing methods to enhance visibility of defects. The STSCS algorithm starts with wavelet decomposition to spatially de-noise thermograms, followed by UL principal component analysis (PCA), fine-tuning optimization, and neural learning-based independent component analysis (ICA) algorithms to temporally compress de-noised thermograms. The compressed thermograms were further processed with UL-based graph thresholding K-means clustering algorithm for defects segmentation. The STSCS algorithm also includes online learning feature for efficient re-training of the model with new data. For this study, metallic specimens with calibrated microscopic flat bottom hole defects, with diameters in the range from 203 to 76 µm, were produced using electro discharge machining (EDM) drilling. While the raw thermograms do not show any material defects, using STSCS algorithm to process PIT images reveals defects as small as 101 µm in diameter. To the best of our knowledge, this is the smallest reported size of a sub-surface defect in a metal imaged with PIT, which demonstrates the PIT capability of detecting defects in the size range relevant to quality control requirements of LPBF-printed high-strength metals.

Fabrication of High Corrosion Resistant Stainless Steel Containing Mo-rich Grain

Fabrication of High Corrosion Resistant Stainless Steel Containing Mo-rich Grain

Elemental decoration design with metastable cellular substructures for additively manufactured high-strength and high-corrosion resistant austenitic stainless steel

Multi-level chemical-structural heterogeneities extensively exist in additively manufactured (AM) metals due to the intrinsic layer-by-layer non-equilibrium solidification process. Strategies designed with particular metastable substructures aiming at advanced performances are significant for AM counterparts. In this work, Si and Mo additions are conducted based on the regulations of dislocation cell substructures and stacking fault energies for stainless steel (SS) 316L fabricated by laser powder bed fusion (PBF-LB). Their load-bearing performance and corrosion behavior are characterized. Results show that additional Mo segregation at cellular boundaries contributes a stronger strengthening effect than Si, which periodically hinders dislocation slip during deformation. Addition of Si triggers deformation twinning at an early stage due to decreased stacking fault energy, and subsequent dynamic Hall-Petch effects improve strain-hardening capability and plasticity for PBF-LB SS 316L+Si. Meanwhile, addition of Mo enhances pitting corrosion resistance of PBF-LB 316L+Mo SS in chloride-containing solutions, especially the pitting re-passivation, which is opposite in the Si addition case due to the increased quantiy of undesired Si/Mn-rich oxides. Underlying deformation and corrosion mechanisms for Mo/Si-added PBF-LB SSs are discussed. Our work is anticipated to motivate the alloy design concept based on particular metastable substructures for advanced AM alloys.

Bridge for the thermodynamics and kinetics of electrochemical corrosion: Designing a corrosion–resistant HP–13Cr stainless steel by Cu alloying for use in an H2S–containing geothermal environment

The dissolution–ionization–diffusion–deposition (DIDD) model was used for developing a corrosion–resistant stainless steel (SS) by the means of alloying and the guidelines for the process were proposed. The novel HP–13Cr–Cu SS was designed to resist corrosion in H2S–containing geothermal environment. The results indicated that the preferential deposition of CuS promoted the heterogeneous nucleation rate of Cr2O3, FeCr2O3, and FeS, which formed denser corrosion product layer. As a result, this alloy exhibited a low corrosion rate and a high sulfide stress cracking (SSC) resistance. The results were consistent with the theoretical calculation conducted by the DIDD model.

New White Etch Cracking resistant martensitic stainless steel for bearing applications by high temperature solution nitriding

White Etch Cracking (WEC) is a severe and unpredictable failure mode that has been frequently observed in, among others, bearings for wind energy applications. In this work a novel, patented, WEC resistant bearing steel solution is developed through high temperature solution nitriding, followed by a custom heat treatment. Conventional medium carbon, 13 wt% Cr martensitic stainless steels were subjected to the novel process to obtain a nitrogen-rich case. A series of soft annealing, austenitization, cryogenic and tempering treatments converted the nitrogen-rich region into a fine-grained case containing nano-sized precipitates. Test bearings and tribometer specimens were treated with the same sequence of treatments. These specimens were tested under two different accelerated WEC failure promoting conditions. In contrast to standard through-hardened bearing steel the nitrided specimens showed no WEC formation, not even after prolonged testing.

Toward High-Pitting Resistance and Low-Cost Austenitic Stainless Steel: The Role of Carbon Alloying

This article investigates the pitting resistance of a newly developed Fe-Cr-Mn-N austenitic stainless steel with 0.14 wt% carbon and its counterpart with 0.02 wt% carbon. By using especially hot-rolled bimetal specimens, we focus on the pitting behavior near the interface between the two alloys and demonstrate that solid solution carbon can significantly improve pitting resistance. The alloyed carbon increases the passive film stability, but the more fundamental reason is that carbon suppresses the active dissolution rate of the matrix, thereby inhibiting the kinetics of pitting growth. These results will highlight the use of carbon alloying in austenitic stainless steel to provide more cost-effective materials with improved corrosion resistance and mechanical strength for the construction industry.

Evaluating shielding gas-filler wire interaction in bi-metallic wire arc additive manufacturing (WAAM) of creep resistant steel-stainless steel for improved process stability and build quality

This study investigates the effect of shielding gases (namely, 98%Ar-2%CO2 and 96%Ar-3%CO2–1%O2) on the bi-metallic wire arc additive manufacturing (WAAM) of creep resistant steel (CRS) and stainless steel (SS). Contrary to the conventional practice of using material-specific gas, i.e., two gases for bi-metallic deposition, the aim here is to find a common shielding gas that creates a favorable mix with alloying elements of each filler wire to facilitate smooth arcing and metal transfer. The appropriateness of the shielding gas is broadly evaluated in terms of two criteria, viz. (a) arc stability and (b) bead uniformity and the penetration pattern. The stability of the arc (in terms of cyclograms, probability density distribution, voltage signal analysis), the accuracy of the bead (visual inspection, X-ray radiography, geometric deviation), and the quality of the deposit (penetration pattern) are first evaluated for single bead-on-plate deposits for the two candidate material and shielding gas pairs. The result of the analysis suggests the appropriate gas, which is then validated by depositing and investigating actual bi-metallic walls of CRS and SS. The change of the gas without alteration of other parameters significantly affects the bead shape, metal-transfer pattern, chemical composition of the welding arc, and bead penetration, all of which contribute to the ability of materials to fuse without any defects at the bi-metallic interface. Higher CO2 and O2 contents in the shielding gas stabilize the welding arc by increasing the metal vapor (i.e., more ionized particles) because of exothermic reaction and reduced surface tension, respectively. The stability leads to bead uniformity and an increase in the weld penetration at the edges and weld dilution, which negates the lack of fusion when two materials are deposited side-by-side to create a bi-metallic wall. The presence of O2 in the gas increases molten metal fluidity, which minimizes the flatness variation on both sides of the bi-metallic wall. The reported results are fundamental and have high significance, serving as guidelines for a wide array of multi-material service components fabricated using WAAM.

Dissimilar welding of super duplex stainless steel (SDSS) and pipeline steel – A brief overview

There are different grades of stainless steels available in the market for its better corrosion resistance but super duplex stainless steel find their name due to the presence of two phase microstructure. Due to the complex metallurgical behavior the welding of super duplex stainless steel is quite difficult as compared to the normal grades of the stainless steel. Austenite and ferrite are the two main phases present in super duplex SS almost in equal proportions. To provide better strength, corrosion resistance and sulfide stress cracking than the normal stainless steels, these super duplex SS (SDSS) are specially designed to meet the requirements of structural and pressure vessel applications. This paper basically study about the dissimilar welding challenges during welding of various grades of super duplex stainless steels. Different secondary phases has been formed in the microstructure of duplex stainless steels (DSSs) when these steels are exposed to higher temperatures. These secondary phases degrade their performance at excessive higher temperatures. To minimize the degradation of the engineering performance of DSSs at higher temperatures various types of isothermal treatments have been used.

Extending powder lifetime in additive manufacturing: Chemical etching of stainless steel spatter

• Chemical etching can eliminate most oxides from 316 L spatter. • A reduction in oxide coverage from 7–0.7% was possible. • Removal is thought to occur via initial dissolution of oxide-surrounding metal. • Etched spatter powder performed better in LPBF. • Reduced slag layer, and better wetting was seen for LPBF etched spatter. In laser powder bed fusion, unconsolidated metal powder on the build plate tends to comprise a proportion of oxidised powder after repeated use. This is generally caused by the generation of oxidised spatter particles during processing which can contaminate the powder bed, and be incorporated into future builds, ultimately undermining part integrity. Oxidised metal powder often results in porosity, poor layer-layer bonding and detrimental oxides in the printed part. This work uses a new chemical etching approach to remove oxides from the surface of oxidised stainless steel spatter powder. It was shown that a ten-fold reduction in oxide area coverage on spatter powder was possible through submersion in a solution of heated Ralph's etchant for one hour. Oxide removal is thought to occur mostly via dissolution of the metal surrounding and underneath oxide islands on the powder, allowing more aggressive oxide removal. LPBF processing was performed using spatter, etched and virgin powder sieved to an identical powder size range. Etched spatter showed a reduced oxide slag layer on track surfaces compared to spatter. In addition, incorporation of powder into tracks appeared improved after chemical etching of the powder. This work demonstrates that chemical etching has the potential to be used to increase the re-usability and lifetime of spatter or heavily used powder from widely used and corrosion resistant stainless steel powder.

Construction of corrosion resistant stainless steel mesh and the design for protecting optical window free from biofouling

Bio-fouling impedes widespread application of sensors for marine environmental monitoring. It is an issue to develop a simple and mitigating membrane fouling attachment device. In this work, an antifouling and corrosion resistant 316ss mesh combining with 3D printing was used to develop a novel device model for protecting the optical window free from biofouling under sea water. The Ag coating 800# 316ss mesh exhibited the most antifouling effect on protecting the glass not only among the different pore size, but also comparing with the naked mesh at the same pore size in natural water. However, the corrosion occurred on the Ag coating 316ss mesh in the seawater. After Al2O3 pre-deposited on 316ss mesh prior coating Ag film, the multilayered Al2O3/Ag 316ss mesh were prepared successfully. To simulate experiment of protection optical window in the sea, a proper device was designed through 3D printing combined with the functional 316ss mesh, which exhibited an outstanding antifouling capacity as long as 30 days and without corrosion. This strategy demonstrated a realistic paradigm of combining 3D printing technology with the antifouling materials to design a simple and mitigating membrane fouling attachment device for commercially available sensors in the further application.

Preparation & Characterization of Complexes Containing Beta Lactam & Study of the Effect of Corrosion Inhibition Using Iron Resistant Stainless Steel

Metal (II) complexes of Co, Ni, Cu and Zn with Amoxicillin derivative (L) were synthesized and identified by elemental analysis CHNS Uv-Vis, FTIR, TGA, metal analysis AA, magnetic susceptibility and conduct metric measurement. by analysis the ligand behaves as a bidentate. All complexes that have nickel, copper , cobalt and zinc ions were proposed as octahedral geometry shape. Protection study of the corrosion behavior of carbon steel surface was conducted with several of the zinc derivative concentrations. Experimentally, the inhibition efficiencies (%IE) in the saline solution 3.5% NaCl was examined using measurements of potentiometric polarization. The outcomes revealed that the %IE of carbon steel corrosion by amoxicillin Derivatives was 72.87%. Keywords: corrosion resistance, elemental analysis CHNS , Uv-Vis and FTIR spectroscopies, Amoxicillin derivative

Adhesive transfer operates during galling

In order to reduce cobalt within the primary circuit of pressurised water reactors (PWR’s), wear-resistant steels are being researched and developed. In particular interest is the understanding of galling mechanisms, an adhesive wear mechanism which is particularly prevalent in PWR valves. Here we show that large shear stresses and adhesive transfer occur during galling by exploiting the 2 wt.% manganese difference between 304L and 316L stainless steels, even at relatively low compressive stresses of 50MPa. Through these findings, the galling mechanisms of stainless steels can be better understood, which may help with the development of galling resistant stainless steels.

3D printing externally reinforced layers for high-speed railway brake discs: Adaptability of SLM processes for manufacturing gradient materials

In this paper, the quasi-continuous ratio gradient alloy steel for the high-speed railway brake disc is prepared by selective laser melting (SLM). While maintaining the strength of the 24CrNiMo alloy steel at the core, it significantly improves the external wear and corrosion resistance of the material. The composition of the designed gradient alloy steel is x% 24CrNiMo + (1-x)% wear-corrosion resistant stainless steel (x is 100, 65, 35 and 0). Through the 20 groups of processes, the optimal process parameters of each gradient are summarized. Besides, the density, surface roughness and residual stress of the material are systematically characterized. The scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) are used to study the types of defects and formation mechanisms in the SLM process. The results show that the optimal laser energy density (LED) range for gradient alloy steel is 56 J mm−3 to 47.8 J mm−3. With the increase of LED, the density of the alloy first increases then decreases, and the type of defects changes from spheroidization defects to cracking. The sample with the best process parameter has a good metallurgical bonding between the gradients, which lays a good foundation for the subsequent analysis of wear resistance and corrosion resistance.

Enhancement of Anodically Treated Stainless Steel by NiFeP-Catalyst Electrodeposition as Bifunctional Electrodes for Water Electrolysis

Electrochemical water splitting, using bifunctional and easily scalable electrodes made of abundant materials, is one of the most important milestones towards the storage of intermittent energy generated from renewable sources. In this work, we demonstrated the synthesis of amorphous NiFeP catalysts for H2 and O2 evolution using a very simple and scalable electrodeposition method. Corrosion resistant stainless steel was used as substrate, which is subject of improvement by a facile anodic treatment in an electrolyte comprised of sulfuric acid and glycerol. This treatment increased the surface area approx. six-fold by dissolving parts of the stainless steel substrate. Electrodes with NiFeP catalyst supported on pretreated substrates reported overpotentials of 305 and 210 mV at ∣10∣ mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The electrodes were stable for 24 h at a current density of 400 mA cm−2, which resembles real operation for alkaline electrolyzers, with a slight increase in the overpotentials due to the accumulation of bubbles at the surface.

Effect of Zircoat-M coating on SS304L for designing high temperature process chamber in selective laser sintering

Selective laser sintering (SLS) process is one of the most useful additive manufacturing techniques used, because it has the ability to readily generate complicated structures. The quality of parts made by SLS process directly depends on controlling heat transfer to powder bed. High temperature process chamber is specially designed for high temperature plastics and metal powders (PEEK and Aluminium). With the exception of aluminium, Zircoat - M is a Zirconia-rich refractory coating compound with a high proportion (63%) of Zirconia and is best suited for ferrous and non-ferrous metals and refractories. Metals and refractories are protected by Zircoat-M from corrosion erosion and flue gases escaping from heating chambers. An attempt was made to develop a high temperature build chamber and pre-heating system to manufacture prototypes using materials having maximum melting/ fuse temperature of 800°C. PEEK and Aluminium may be used to produce light weight products for multiple sectors such as bio-medical, automobile and aerospace. A high temperature resistant stainless steel 304L grade was chosen, along with SS304L coated with Zircoat-M for Build chamber and Pre-heating system. Experimental analysis such as Thermal Expansion, Thermal Conductivity and Corrosion resistance for the coated and uncoated specimen was carried out. Coefficient of Linear Thermal Expansion of uncoated specimen is 16 × 10-6 /°C and coated specimen is 14 × 10-6 /°C. Thermal conductivity for the Ceramic coated Zircoat-M on SS304L for 100 °C is 0.280 W/mK. Thermal conductivity of SS304L at 100 °C is 16.3 W/mK. Both the specimen has very good corrosion resistance.

SOLID INSULATION DISTRIBUTION TRANSFORMER

Underground transformers with insulating oil as insulating and cooling medium have been used since the early 1960s. It adopts mineral oil, ester oil and silicone oil and the enclosure is made of corrosion resistant stainless steel. Underground, submersible and environmental conditions in which the transformer is installed are exposed to sewage, rain and surrounding chemicals. If liquid filled transformers leak due to corrosion or other damage to the tank the liquid can contaminate the surrounding soil and underground water and restoration costs can be higher than installing a new transformer. In addition, the potential risk of explosion and fire caused by the transformer failures play a role of spreading the fire, which further increases safety concerns. There has been a demand for new technology to solve these problems. This document provides technical information of a new underground, solid insulation distribution transformer (SIDT) for building a safe and eco-friendly underground distribution system.

Determine The Suitable Heat Input Range for Butt Joint Made by Heat Resistance Stainless Steel SUS316L by Using the Numerical Simulation

One of the methods for reducing the production costs to increase competitiveness is to minimize waste products as well as the cost of testing products, and numerical simulation is a useful tool to solve this task. In this study, the authors use SYSWELD software to compute in advance the suitable heat input range to weld specific layers in heat-resistant stainless steel butt welded joints in chemical plants, oil and gas, and energy. The simulation results show that with the butt-welded joint made by SUS316L steel in 8 mm thick and welded by the MIG welding process, the appropriate heat input of the root pass is 506 J/mm ≤ qđl ≤ 650 J/mm and the heat input suitable for cap pass is 754 J/mm ≤ qđl ≤ 1066 J/mm.

DESIGN AND FABRICATION OF MULTI-PURPOSE MINERAL LEACHING EQUIPMENT

With much amount of money the nation had invested into the extractive sector of the economy, minerals are still mined and exported out of the country for beneficiation which results into much economic losses in the mining and extractive industries. The need to reduce the huge amount of losses expended on extracting valuable metals from ores by local miners and out springing cottage industries motivates this work. This report covers the design and construction of a laboratory size leaching equipment suitable for dissolution of clean pulverised minerals in acid and alkaline media via agitation and in-situ leaching techniques in single operation system. The dissolved metals are easily recovered from the solution by other techniques. The design and fabrication is based on the fundamentals of stoichiometric calculations and chemical reactions, engineering design drawings using AUTOCAD and INVENTOR softwares, material selection and safe environmental ethics. The equipment is produced from combination of highly corrosion resistant plastic materials, mild steel, stainless steel and other components. For the purposes laboratory studies, the machine can process about 320-350 kg mineral feeds charged manually and in batches for working period of 1 to 8 hours per day. The estimated fabrication cost is about N194,500.00.

Slip band interactions and GND latent hardening in a galling resistant stainless steel

Slip activation, slip band interactions, and GND densities in iron-base, galling resistant alloy Nitronic 60 have been characterised at the grain length scale using small-scale mechanical testing with high resolution digital image correlation and high-angular resolution electron backscatter diffraction. By correlating the two measurement techniques, new insight into slip band interactions, the generation of lattice curvature and the corresponding accumulation of geometrically necessary dislocations (GNDs) is provided. Multiple discrete slip bands are typically active within single grains, resulting in significant slip band interactions. Crossing slip bands were found to generate accumulations of GNDs. Regions where slip bands block other slip bands were associated with the highest GND densities, in excess of three time the densities of crossing slip bands. Representative crystal plasticity modelling investigations have demonstrated that discrete slip blocking events are responsible for locally elevated GND density. This behaviour is rationalised in terms of lattice curvature associated with the differing levels of constraint provided by the crossing or blocking-type behaviours. Ferrite grains are also found to contribute to the generation of GNDs. Together, these two effects provide significant work hardening mechanisms, likely to be key to the development of future iron-base hard facing alloys.

Interface Quality Indices of Al–10Si–Mg Aluminum Alloy and Cr18–Ni10–Ti Stainless-Steel Bimetal Fabricated via Selective Laser Melting

Bimetallic materials are important in many industries (aerospace, medicine, etc.) since they allow the creation of constructions that combine specific functional properties, for example, low density (aluminum alloy) and high corrosion resistance (stainless steel), due to layering fabrication of the bimetallic joint. On the other hand, the difference in thermophysical properties of the dissimilar material layers leads to residual stresses, which cause deformation and destruction of such a bimetallic joint produced via the methods of surfacing or additive technologies. This article discusses the methods based on the gray relational analysis and generalized desirability function for the quality assessment of Al–10Si–Mg aluminum alloy and Cr18–Ni10–Ti stainless-steel bimetal fabricated via selective laser melting (SLM). There are four main parameters (quality indices) of the quality generalized assessment, which determine the degree of Al penetration into the steel substrate and Fe into the deposited layer, the difference in microhardness values on both sides of the interface boundary, and the resistance to mechanical destruction of the bimetallic joint. According to the results obtained, the best set of quality indices corresponds to the SLM technological modes with an energy density of 105 and 147 J/mm3. The greatest functionality of the bimetals is determined by the quality index associated with its strength. Therefore, methods of gray relational analysis and desirability function make it possible to form a generalized assessment for the bimetallic joint quality and, consequently, to select the best technological mode.