Stainless Steel Research Articles

The Expanded Phases Formed in Stainless Steels by Means of Low-Temperature Thermochemical Treatments: A Corrosion Perspective

Surface engineering of stainless steels using thermochemical treatments at low temperatures has been the subject of intensive research for enhancing the surface hardness of these alloys without impairing their corrosion resistance. By using treatment media rich in nitrogen and/or carbon, it is possible to inhibit chromium compound formation and obtain supersaturated solid solutions, known as expanded phases, such as expanded austenite or S-phase in austenitic stainless steels, expanded ferrite in ferritic grades, and expanded martensite in martensitic grades. These low-temperature treatments produce a significant increase in surface hardness, which improves wear and fatigue resistance. However, the corrosion behavior of the modified surface layers remains of paramount importance. In the international literature, many studies on this topic are reported, but the results are not always univocal, and there are still open questions. In this review, the corrosion behavior of the expanded phases and the modified layers in which they are present is critically analyzed and discussed. The relationships between the phase composition and the microstructure of the modified layers and the corrosion resistance are highlighted while also considering the different test conditions. Furthermore, corrosion test methods are discussed, and suggestions are given for improving the measurements. Finally, perspectives on future directions for investigation are suggested for encouraging further research.

Intermittent polarity inversion of stainless-steel paired electrodes for efficient and durable water electrolysis

Designing robust and cost-effective catalysts through straightforward and replicable techniques is crucial for advancing water electrolysis. In this study, we introduce a dynamic polarization control method for the continuous activation of stainless steel (SS) substrates to achieve high water-splitting performance and durability. By applying periodic inverted current density during high-current–density operation (0.5 or 1 A cm−2) on bare SS adopted as both cathode and anode substrates, a NiFe-based oxide structure favorable for the hydrogen evolution reaction is formed at the cathode, while a Fe-incorporated NiOOH structure with high efficacy for the oxygen evolution reaction develops at the anode. Implemented in an anion exchange membrane water electrolysis system, this inverted polarization approach applied for the SS paired electrolyzer system successfully maintains a cell voltage of approximately 1.9 V for 500 h at a current density of 1 A cm−2 using bare SS for both electrodes.

Circumventing cracking in grading 316L stainless steel to Monel400 through compositional modifications in directed energy deposition

In joining Fe-alloys and Cu-containing alloys to access the high strength of steels and corrosion resistance of Cu-alloy, cracking is widely observed due to the significant Cu microsegregation during the solidification process, resulting in an interdendritic Cu-rich liquid film at the end of solidification. By fabricating functionally graded materials (FGMs) that incorporate additional elements like Ni in the transition region between these terminal alloy classes, the hot cracking can be reduced. In the present work, the joining of stainless steel 316L (SS316L) and Monel400 by modifying the Ni concentration in the gradient region was studied. A new hot cracking criterion based on hybrid Scheil-equilibrium approach was developed and validated with monolithic multi-layer samples within the SS316L-Ni-Monel400 three-alloy system and a SS316L to 55/45 wt% SS316L/Ni to Monel400 FGM sample fabricated by direct energy deposition (DED). The new hot cracking criterion, based on the hybrid Scheil-equilibrium approach, is expected to help design FGM paths between other Fe-alloys and Cu-containing alloys as well.

TiO2 containing glass sealant for protonic ceramic fuel cell applications: Microstructure, strength and stability studied in sealing of BaZr0.1Ce0.7Y0.1Yb0.1O3-δ electrolyte to Crofer 22H interconnect

To address the challenges of protonic ceramic fuel cell (PCFC) stack sealing, a TiO2-containing alkaline silicate glass, named STKN, was utilized to seal the BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolyte and Crofer 22 H stainless steel, achieving a sufficient bonding. The formation of the BaTiSi2O7 reaction layer at the BZCYYb interface is the key to realizing effective joining. Elevating the joining temperature results in a thicker BaTiSi2O7 reaction layer and a concomitant loss of the sealant. The optimal sealing parameter is determined to be 775°C for 30 minutes, yielding a maximum shear strength of 20 MPa. After aging in both oxidizing and reducing atmospheres at 600 °C for 300 h, the microstructure of the joint remained stable, suggesting excellent potential for service stability of the joint.

Physics-coupled Data-driven Design of High-Temperature Alloys

We present a materials design loop, which streamlines physics-coupled machine learning (ML) surrogate models to discover new alloy chemistries with improved properties. The efficacy is demonstrated by discovering a high-temperature alumina-forming austenitic (AFA) stainless steel with enhanced creep, followed by experimental validation. The ML models have been trained using a well-curated, highly consistent experimental dataset augmented with synthetic microstructural features from a computational thermodynamic approach. We have populated a large number of hypothetical AFA alloys to explore the high-dimensional composition space and have predicted their creep properties by providing the same synthetic input features obtained from the trained ML models. Uncertainties from the ML training were taken as thresholds for truncating predicted results to identify alloys with improved or deteriorated creep. Individual elemental compositions have been determined via probability density distribution analysis from the group of alloys at the top and bottom of the predicted creep values for further virtual and experimental validations. We anticipate that this workflow can be applied to screen desired conditions, such as chemistry and processing parameters, in high-dimensional space through physics-guided data analytics.

Exploring bracket torque expression: A comparative in vitro study of new self-ligating bracket designs and archwire geometries

This in vitro study aimed to evaluate the torque expression efficiency when it is integrated into the bracket slot versus the bracket base. Additionally, the impact of archwire geometry (rectangular vs. rhomboid) on torque expression has been examined. The torque expression was evaluated in a full arch printed maxillary model, focusing on tooth #11, which was positioned within an alveolus filled with Typodont wax. Three different types of brackets were utilized: conventional metallic bracket (Minidiamond™), self-ligating bracket with torque in base (Damon Q2™), and a new self-ligating bracket design with torque in slot (Damon Ultima™). Two variations of archwires were used: rectangular and rhomboid stainless steel, measuring 0.019×0.025 inches and 0.019×0.0275 inches, respectively, from ORMCO™. The study included seven groups: six experimental groups and a control group, with 15 measurements in each group, totaling 105 torque measurements. Optical impressions were taken of the tooth's original position and its final position after torque expression. STL files were superimposed using GEOMAGIC software to calculate the percentage of torque expression. The self-ligating bracket with torque in slot (Damon Ultima™) shows significantly higher torque expression than the self-ligating bracket with torque in base (Damon Q2™) with a rectangular stainless steel archwire (P=0.00015). The Ultima™ bracket also demonstrates higher torque expression than both the Q2™ and conventional 22° brackets with a rhomboid stainless steel archwire (P<0.003). No significant difference in torque expression was found between the rectangular and rhomboid stainless steel archwires for any bracket group (P>0.05). The self-ligating bracket with torque in slot shows comparable torque expression effectiveness to the conventional bracket, outperforming the self-ligating bracket with torque in base. Archwire geometry does not significantly impact torque expression.

Influence of arc energy on the microstructure and corrosion behavior of ER2209 duplex stainless steel deposited on Q345B low-alloy steel by GMAW

In order to eliminate the complex effects of thermal cycling and the thermal effects of the next pass on multi-layer multi-pass welding of low-alloy steel and duplex stainless steel, ER2209 welding wire was single-layer single-pass deposited on the surface of Q345B hot-rolled plate by gas metal arc welding (GMAW). The microstructure and corrosion resistance of welded joints were studied by different arc energies. The results showed that the arc energy had a significant impact on the “tongue-shaped” morphology and the width of heat affect zone in the welded joint, which in turn affected the corrosion performance of the welded joints. Due to the least distribution of “tongue-shaped” morphology and minimum width of heat affected zone in the welded joint with arc energy of 0.645kJ/mm, it owned the best corrosion resistance. The weld metals of the welded joints were composed of ferrite and austenite phases. The ferrite phases were distributed along grain boundaries and intergranular. As the heat input increases, the distribution of ferrite phase along grain boundaries gradually decreased. The corrosion products and corrosion morphology of the welded joint were also investigated and the corrosion mechanism was discussed in detail. The research results of this article provide a theoretical basis for improving the corrosion performance of multi-layer multi-pass welded joints of low-alloy and duplex stainless dissimilar steels.

Unveiling deformation microstructure during cyclic straining of 316 L stainless steel at 873 K

Cyclic plastic deformation behaviour of 316L steel with an average grain size ∼ 30 μm was investigated at high temperature (873K) under completely reversed straining at ±0.5% strain amplitude with a constant total strain rate of 3 × 10−3S−1. Maximum true tensile stress initially increased due to cyclic hardening until 100 cycles, then stress saturation occurred and finally failed at 1250 cycles. Deformation microstructure varied significantly with imposed fatigue cycles. Occurrence of planar glide and isolated dislocation walls were observed in the initial hardening stage, while dislocation walls accompanied by connected equiaxed dislocation cells were predominant in the saturation stage. The deformation microstructure at failure stage mainly composed of elongated dislocation cells and diffusive dislocation walls. Dislocation densities estimated by X-ray diffraction were ∼ 1013m-2.

Corrosion and Microhardness Behavior Improvement of 316L Stainless Steel via Fiber Laser Surface Treatment

This study investigated how fibre laser surface treatment affects stainless steel 316L’s microhardness and corrosion resistance. The laser parameters utilized in this investigation were four different readings of laser power applied at a constant frequency and scanning speed to stainless steel 316L specimens. A digital micro-Vickers hardness tester was used to measure the microhardness of the samples before and after laser treatment. The TAFEL cyclic potentiodynamic polarization technique was employed to study corrosion behaviour. The microstructure of the base metal and the effect of laser power were investigated using optical microscopy. The phases before and after laser treatment were identified through X-ray diffraction, and the cross section of the heat-affected zones and the molten pool’s depth were examined using a scanning electron microscope. Results revealed that laser treatment affected microstructural transitional phase alterations. Compared with the average microhardness of the base metal, the microhardness of the laser-treated specimens improved to 78.23% as the laser power increased. The increase in microhardness considerably enhanced corrosion resistance to 36.13% relative to that of the base metal.

Creep-fatigue interactive behavior and damage mechanism of TP321 stainless steel under hybrid-controlled conditions

In this study, Hybrid-controlled creep-fatigue (HCCF) tests were conducted on TP321 austenitic stainless steel under a variety of test conditions. The effects of strain amplitude, holding time, holding stress and temperature on the creep-fatigue behavior of TP321 austenitic stainless steel were not only analyzed in detail but also revealed the creep-fatigue damage interactive mechanism. The results demonstrated that a rise in test temperature and load holding time markedly induced creep deformation, resulting in a notable reduction in failure life. Additionally, an increase in test temperature led to the cessation of the cyclic hardening phenomenon. Secondly, the analysis of fracture morphology and X-ray computed tomography (X-CT) scanning results demonstrated that the transgranular cracks expanded inwards and connected with the intergranular voids under creep-fatigue interaction, forming a mixed intergranular and transcrystalline fracture mode. The presence of large creep cavities impeded the propagation of fatigue cracks when creep damage was the dominant phenomenon. Subsequently, the damage evolution mechanism was elucidated through microstructural analysis, which revealed that the impact of the slip bands on the triangular grain boundaries and the precipitation of carbides facilitated the nucleation of voids and the internal formation of intergranular microcracks, thereby causing creep-fatigue damage interaction. Finally, the TP321 austenitic stainless steel creep-fatigue damage interactive mechanism diagram was proposed in conjunction with the fracture morphological characteristics and microstructure.

A prediction model for the mechanical properties of SUS316 stainless steel ultrathin strip driven by multimodal data mixing

Constructing a mapping relationship among material preparation process, microstructure, and mechanical properties is a challenge in material research and development. In this work, a deep learning framework for multimodal data fusion is constructed that couples a multi-layer perceptron (MLP) and a residual neural network (ResNet) to predict mechanical properties of SUS316 stainless steel ultrathin strips. Specifically, the MLP branch is used to extract the rolling process data features, and the ResNet with the addition of a convolutional block attention module (CBAM) is used to extract the microstructure features. Six models are constructed for comparison under the comprehensive consideration of factors such as unimodal network, the multimodal network and input form of image samples. The results show that the multimodal data model fused with the ResNet and MLP after adding the CBAM using both rolling process data and four types of microstructure image data as model inputs has the most accurate prediction results. The R2, MAPE, RMSE and MAE are 0.998, 0.727, 4.440 and 3.359, respectively. In addition, the proposed model is used for predicting yield strength and elongation, and the results show that the R2 values of both models on the test set are greater than 0.980, fully confirming that the multimodal data model has high prediction accuracy and good generalizability.

Electrochemical behavior and microstructure of diffusion welding of zirconium alloy and super duplex stainless steel

In this study, the effect of welding temperature on interface microstructure, mechanical properties, and electrochemical behavior of diffusion welded joints (DWJs) of zirconium alloy (ZrA, Zr702 grade) and super duplex stainless steel (2205 duplex stainless steel grade) were investigated. Alloys were welded in a vacuum atmosphere at four different temperatures (800, 850, 900, and 925 °C) for 75min under 4MPa compressive pressure. The optical, scanning electron microscopy, electron probe micro-analyzer, and X-ray diffraction techniques were used to characterize the interfacial microstructure of the DWJs. Layers of intermetallics were formed along the welded interface at 850 °C and above welding temperatures. At 850 °C, a single reaction layer (phase mixture of ZrFe2+ZrCr2) was observed; however, bilayers (ZrFe2+ZrCr2 and Fe2Zr+FeZr3 phase mixtures), and triple layers (ZrFe2+ZrCr2, Fe2Zr+FeZr3, and β-Zr+FeZr3 phase mixtures) were observed at the welded interface of the joints processed at 900 and 925 °C, respectively. Width of the reaction layer (phase mixtures) increases with an increase in the welding temperature. The DWJs processed at 900 °C reach the maximum joint strength of ~312MPa along with ~6.4% ductility. For corrosion analysis, studies of the base alloys and DWJs in 0.1mol/L HCl and 0.1mol/L NaOH solutions separately using electrochemical techniques, such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization were undertaken.

Experimental study on local buckling capacity of stub column with welded cross-sections based on stainless steel S35657

Experimental study on local buckling capacity of stub column with welded cross-sections based on stainless steel S35657

Cost effective reduced graphene oxide/polyaniline composite coated SSM cathode for bio-electrochemical desalination: Advancing desalination via cathodic improvement

The microbial desalination cell (MDC) has emerged as a fascinating and green desalination process. However, cathode limitation restricts its practical implementation. An efficient catalyst layer for the cathode can improve such deficiencies significantly. The study, for the first time, investigated reduced graphene oxide (rGO) and polymerized aniline (PANI) composite catalysts to improve cathodic performance in MDC. Different rGO layers were achieved on stainless steel mesh (SSM) by varying rGO concentrations, followed by fixed PANI layer deposition. The XRD, FTIR and SEM analysis confirmed the successful formation of PANI on top of rGO on SSM with the nano-fibrous structure having rGO-characteristic XRD peak at 11.7° with OH, (-C=O), (-C-O), C = C groups. The effect of rGO was optimized by fine-tuning of rGO mass deposition on SSM. The cyclic voltammetry (CV) results have verified that PANI-rGO1.0-SSM (1 mg/mL rGO deposition) was electrochemically the best-performing composite with the highest CV current (2.1 mA). Therefore, three PANI-rGO1.0-SSM composite cathodes were prepared with 15, 30, and 45 deposition cycles to apply in MDC to study the desalination and bio-electrochemical performances. The 30-deposition cycle cathode showed the best improvement among desalination rates (i.e., 40.5 % higher) and internal resistance (i.e., 96 % low) compared to the controlled cathode. Cost estimation revealed that the electro-deposition is a low-cost coating method for PANI-rGO1.0 on SSM (US $6) and is advantageous compared to the platinum coating processes. Future research should optimize rGO and PANI loading rates and coating process to achieve better cathodic improvement for PANI-rGO composite.

Effectiveness of airborne particle monitoring technique for assessment of wear progression of mechanical components

For effective implementation of smart machine technology, there is a great demand for real-time monitoring of the wear progression of machine components. In this work, the effectiveness of assessing wear by monitoring the airborne wear particles was investigated. Sliding wear tests were performed using different combinations of stainless steel (SUS304) and alumina material pairs while monitoring the size distribution and the number of particles using a particle counter. The results showed that particles less than 2 μm in size accounted for more than 83% of the total number of airborne particles. However, particles greater than 2 μm account for 95% of the volume of airborne particles. Additionally, in the case of wear volume, the total wear volume, which is the sum of the plate and the ball wear volumes, should be similar to that of the total airborne particle volume. For the SUS304/SUS304 pair, the total wear volume and the total airborne particle volume were very similar. However, in the case of alumina/SUS304 and alumina/alumina, the total wear volume and total airborne particle volume were not similar, and the total wear volume was significantly higher than the total airborne particle volume. The effectiveness of the airborne particle monitoring technique depended strongly on the material pairs. This was due to the fact that particle dispersion behavior varied with respect to the wear mechanisms of the materials.

Correlation of mechanics degradation and thermal aging damage defects in Z3CN20.09M cast austenitic stainless steels

Microstructural characterization and mechanical testing were performed on 400℃ thermally aged Z3CN20.09M cast austenitic stainless steels. A quantitative mathematical model is introduced for the relationship between aging defects and mechanical properties. Charpy impact energy was used as a characteristic mechanical parameter, and the short-range order of the Cr element segregation that induced by spinodal decomposition was chosen as the characteristic defect parameters. The macroscopic mechanical properties and the microscopic thermal aging defects was quantitatively correlated in this model, which has a great reference significance in safety assessment and lifetime prediction of the reactor structural materials.

Corrosion behavior of 17–4 PH stainless steel manufactured by laser powder bed fusion: Effect of graphene coating and heat-treatment

Corrosion behavior of 17–4 PH stainless steel manufactured by laser powder bed fusion: Effect of graphene coating and heat-treatment

Effect of solution aging treatment on corrosion resistance and erosion resistance of laser metal deposition 17-4PHss

Slurry erosion and cavitation erosion are the primary causes of failure in pass flow components, and preventive maintenance can effectively extend their service life. In this paper, 17-4PH stainless steel was prepared using laser metal deposition (LMD) technology and aged to investigate the effect of solution treatment on its microstructural transformations. The microhardness, electrochemical corrosion behavior, slurry erosion resistance, and cavitation erosion behavior of the as-built and solution-treated, aged samples were analyzed, with traditional forged specimens used as controls. During heat treatment, the microstructure fully transformed to martensite, and NbC precipitated as a second phase. Solution treatment led to microstructural coarsening, while aging significantly refined the microstructure and produced partial reverted austenite. Microhardness analysis showed that the microhardness of the solution-treated and aged samples increased to 465.5 ± 8.6 HV0.2 due to the combined effects of finer and more uniformly distributed NbC precipitation and grain refinement. The solution aging samples exhibited the lowest corrosion current density and the highest corrosion potential, influenced by the presence of reverted austenite. Slurry erosion results indicated that the corrosive environment accelerated mass loss due to the synergistic effects of mechanical abrasion from gravel and brine corrosion. Meanwhile, the solution aging samples demonstrated superior resistance to slurry erosion, with mass losses in clear water and brine slurry of only 69 % and 63 % of those observed in the traditional forged samples. In the cavitation erosion experiment, the solution aging sample showed the lowest cumulative mass loss (3.54 ± 0.18 mg), and the work-hardening of the reverted austenite further enhanced the cavitation erosion resistance of the solution aging sample.

Electrodeposition of Ag-doped diamond-like carbon films on stainless steel for supercapacitor applications

Electrodeposition of Ag-doped diamond-like carbon films on stainless steel for supercapacitor applications

Design and development of wire-mesh packed bed liquid desiccant dehumidifier to reduce pressure-drop and carryover

In response to the high air-pressure drop and desiccant carryover experienced in liquid desiccant-packed bed dehumidifiers, which adversely affect the room environment and system economics, this study explored various modified wire-mesh packed bed designs. It experimentally evaluated dehumidification efficiency, and thermal performance across different corrugated wire-mesh packings, introducing a new design for cost-effective moisture removal while reducing pressure drop and desiccant carryover. Three specially designed packings (P-1, P-2, and P-3) were tested against standard commercial options like Celdek (7090, 6090, 5090) and Mellapak 250Y, focusing on optimizing performance. At a constant optimal concentration of the desiccant solution, the effects of airflow rates (ma), solution flow rates (ms), and solution temperatures (Ts) on the performance of the system was analyzed. The findings indicated that P-1 performed better than others, particularly in terms of condensation rate (CR) and moisture effectiveness (εm). Specifically, it outperformed the acrylonitrile butadiene styrene (ABS) (benchmark) packing by 22.1 % and 8 % respectively at a solution concentration of 40 wt% and ma of 0.025 kg/s under ambient conditions of nearly 0.02921 kg/kg specific humidity and 31 °C temperature. Increasing the void fraction led to a reduction in air pressure drop while enhancing the wettability, and dehumidification efficiency. The packing, P-1, made of stainless steel (SS340) with 0.3 cm mesh was finally proposed to obtain better performance for dehumidification applications in buildings. Additionally, its potential to reduce air-pressure drop and desiccant carry-over can provide improved energy efficiency and enhanced air quality, making it a practical choice for sustainable building cooling solutions.