Steel Parts Research Articles

Numerical investigation of concrete-filled double skin steel tubular (CFDST) structure subjected to underwater explosion loading

With the increasing applications in the offshore industry such as oil and gas jackets, submarine pipelines and wind turbine foundations, concrete-filled double skin steel tubular (CFDST) structures are encountering the ever-increasing risk of threats to underwater explosions (UNDEX). This study presents a systematical investigation on the structural behaviors and design recommendations of the CFDST structures subjected to UNDEX loadings through finite element analysis (FEA) approaches. Finite element models have been developed, where the non-linear material properties of the constitutive steel and concrete parts and the composite actions in-between have been considered. The FEA models are verified against the experimentally determined shock wave pressure history, the deformation shapes, and the residual strength. The full-range analyses were firstly carried out on the structural responses of CFDST structures, including the typical damage patterns and residual strength of the specimen after UNDEX. Then, the parametric studies show that the cross-section hollow ratio, charge weight, and explosion distance play great roles in determining the residual strengths. Thereafter, damage indexes considering the parameter of the hollow ratio and the scaled explosion distance has been formulated, and design recommendations have been suggested accordingly.

Microstructure and Mechanical Properties of High-Strength, Low-Alloy Steel Thin-Wall Fabricated with Wire and Arc Additive Manufacturing

High-strength, low-alloy (HSLA) steel has attracted much attention in the manufacturing industry because of its good combination of high strength and toughness, low cost, and good formability. Wire and arc additive manufacturing (WAAM) technology can realize the rapid prototyping of HSLA steel parts. This study investigated a 26-layer HSLA steel component fabricated with the WAAM technique. The microstructure of the deposited wall of ER120S-G is mainly acicular ferrite, and there are longitudinal, preferentially growing dendrites along the deposition direction. With the deposition height accumulation, the top sample’s interlayer temperature increases and the amount of acicular ferrite in the microstructure decreases, while the amount of quasi-polygonal ferrite, Widmanstatten ferrite increases. The changes in microhardness were consistent with the corresponding microstructure gradients: the microhardness of the top sample showed a decreasing trend along the deposition direction, while the microhardness of the middle sample was uniform and stable. The present work shows that the mechanical properties of HSLA steel parts deposited using WAAM technology have good strength and toughness. The microstructure gradient of the sample along the deposition direction did not lead to a significant difference in the tensile strength of the sample at different heights. On the contrary, the ductility of the longitudinal sample is slightly lower than that of the transverse sample, indicating some anisotropy in the deposited sample, which is related to the directional growth of grains along the direction of heat flow. From the current work, the thin wall of HSLA steel prepared with the WAAM process has good mechanical properties, which indicates that it is feasible to replace the traditional processing method with the WAAM process to rapidly manufacture an HSLA steel structure meeting the performance requirements.

A lightweight Fe–Mn–Al–C austenitic steel with ultra-high strength and ductility fabricated via laser powder bed fusion

Lightweight Fe–Mn–Al–C steels have become a topic of significant interest for the defense and automotive industries. These alloys can maintain high strength and ductility while also reducing weight in structural applications. Conventionally processed Fe–Mn–Al–C austenitic steels with high Al content (∼9 wt%) demonstrate greater than 1.5 GPa strength with 35% elongation. Several recent studies have demonstrated success in fabricating steel parts using laser powder bed fusion (L-PBF) additive manufacturing (AM), which can generate near-net-shape components with complex geometries and is capable of local microstructural control. However, studies on L-PBF processing of Fe–Mn–Al–C alloys have focused on low Al content (<5 wt%) compositional regimes representing alloys that undergo transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). Here, we present the effects of L-PBF processing on the microstructure and mechanical properties of an Fe–30Mn–9Al–1Si-0.5Mo-0.9C austenitic steel. A process optimization framework is employed to determine an ideal L-PBF processing space that will result in >99% density parts. Implementing this framework resulted in near-fully dense specimens fabricated over a broad range of process parameters. Additionally, two bi-directional scan rotation strategies (90° and 67°) were applied to understand their effects on texture and anisotropy in this material. As-printed specimens displayed considerable work-hardening characteristics with average strengths of up to 1.3 GPa and 36% elongation in the build direction. However, solidification microcracks oriented in the build direction resulted in anisotropy in tensile strength and ductility resulting in average strengths of 1.1 GPa and 20% elongation perpendicular to the build direction. The successful L-PBF fabrication of Fe–30Mn–9Al–1Si-0.5Mo-0.9C presented here is expected to open new avenues for weight reduction in structural applications with a high degree of control over part topology.

Research on the Lifting Forces of Industrial Plastic Vacuum Cups

Industrial vacuum cups are used for lifting, holding and moving a wide variety of automated applications for handling semi-finished products and parts made of a wide range of materials - metal, glass, plastic, paper, wood, etc. and are used in a variety of industries. This paper presents some of the authors theoretical and experimental research on the maximum lifting force that different types of vacuum cups can achieve. The study was carried out on the basis of sizing recommendations made by manufacturers and dealers of these types of vacuum cups. The specially designed experimental stand was installed on the universal material testing machine LBG 100 kN and allowed the practical determination of these lifting forces provided by various types of industrial vacuum cups. Lifting force measurements were carried out with the AXIS FB 1k digital dynamometer attached to the machine. Vacuum cups of 3 different shapes and made of 3 different materials were used, using different vacuum depressions - 0.3 bar, -0.5 bar, -0.7 bar and -0.9 bar. The research aimed to determine by measurement the maximum lifting force of these types of vacuum cups applied to steel parts. The results obtained for these forces were compared with the calculated theoretical values, with the manufacturer�s recommended dimensioning values, and comparative conclusions were also drawn on the maximum lifting force provided by the different types of industrial vacuum cups studied.

Adaptive sampling for accelerating neutron diffraction-based strain mapping * *This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive,paid-up, irrevocable, world-wide license to publish or reproduce the published form of

Neutron diffraction is a useful technique for mapping residual strains in dense metal objects. The technique works by placing an object in the path of a neutron beam, measuring the diffracted signals and inferring the local lattice strain values from the measurement. In order to map the strains across the entire object, the object is stepped one position at a time in the path of the neutron beam, typically in raster order, and at each position a strain value is estimated. Typical dwell times at neutron diffraction instruments result in an overall measurement that can take several hours to map an object that is several tens of centimeters in each dimension at a resolution of a few millimeters, during which the end users do not have an estimate of the global strain features and are at risk of incomplete information in case of instruments outages. In this paper, we propose an object adaptive sampling strategy to measure the significant points first. We start with a small initial uniform set of measurement points across the object to be mapped, compute the strain in those positions and use a machine learning technique to predict the next position to measure in the object. Specifically, we use a Bayesian optimization based on a Gaussian process regression method to infer the underlying strain field from a sparse set of measurements and predict the next most informative positions to measure based on estimates of the mean and variance in the strain fields estimated from the previously measured points. We demonstrate our real-time measure-infer-predict workflow on additively manufactured steel parts—demonstrating that we can get an accurate strain estimate even with 30%–40% of the typical number of measurements—leading the path to faster strain mapping with useful real-time feedback. We emphasize that the proposed method is general and can be used for fast mapping of other material properties such as phase fractions from time-consuming point-wise neutron measurements.

Investigation of the features of blade processing of steels with ceramic composites based on chromium oxide

An overview of modern cutting ceramic composite materials and possible methods of their production was conducted. An example of the use of composite ceramic materials based on chromium oxide Cr2O3 in blade processing is presented, which makes it possible to improve the quality of processing of the surface layer of steel parts of different hardness. Features of structure formation and properties of the developed cutting material are presented, which, under certain cutting modes, shows higher wear resistance compared to common cutting materials based on aluminum oxide. The effectiveness of dispersed strengthening of the chromium oxide matrix with fine-grained carbides and nitrides of refractory metals is shown.

The Influence of Galvanizing on the Surface Quality and Part Precision of S235J0 Alloy Machined by Turning

This scientific paper aims to determine the optimal economic roughness of galvanized surfaces by studying the influence of turning surface roughness on the quality of galvanizing. The thickness of the zinc layer, its corrosion resistance, and the precision of the galvanized parts were also examined. S235J0 steel samples were processed using a turning operation to obtain different roughness values. Three galvanizing technologies, galvanic galvanizing, hot dip galvanizing, and hot dip galvanizing with centrifugation, were used in the experiments. The surface evolution from turning to zinc layer deposition was monitored, and parts were subjected to salt spray corrosion resistance testing. Statistical analysis confirmed the stability of the technologies used and the accuracy of the experimental data. Optimal roughness ranges for galvanizing were determined based on the quality of the surface before galvanizing and the galvanizing technology used. The findings show that avoiding small roughness values leads to savings in the machining phases. From the dimensional accuracy perspective, the parts have smaller dimensions after galvanizing, and the dimensional accuracy decreases. The study confirms that steel parts are protected from corrosion, and degradation of the zinc layer is more advanced in sections with less roughness. The optimal surface roughness values before galvanizing were determined to be Ra &lt; 3.657 m in the case of HDG, Ra &lt; 3.344 m in the case of HDG+C, and Ra &gt; 2.928 μm in the case of ZP. The conclusions drawn from this study introduce new directions of research.

Anisotropy of the Surface Energy of Steel and Nickel Alloys in Aviation

The article presents the values of the thickness of the surface layer and the surface energy of steel and nickel parts of the aircraft industry. The thickness of the surface layer for the face (100) is about 1.7 nm, which coincides with the thickness of the surface layer of iron - R(I)=M/ρ = 1.7 nm, since iron in these steels is more than 70%. The R(I) layer contains ≈ 6 iron monolayers. In the [111] plane, the lowest value of the surface energy (~1060 mJ/m2 ) is observed. The average thickness of the surface layer of nickel alloys is R(I) ≈ 2 nm, and the number of monolayers is ≈ 6. This value coincides with the number of iron monolayers. The average value of the surface energy of nickel alloys is greater than that of iron-based alloys. The article shows that the hardness of high-entropy (HEA) coatings and metallic glasses (ML) is approximately the same, but almost 2 times higher than the hardness of steel and nickel coatings. For HEAs and MS coatings, the thickness of the surface layer is also approximately the same. In our opinion, there are many similarities between high-entropy alloys and metallic glasses. The friction of steel and nickel coatings lies at the level of 0.4-0.6. For metallic glasses, the coefficient of friction is higher than 0.2 or more. For HEAs, the coefficient of friction is much less than 0.1.

Mechanism of Residual Stress Generation in Quenched Fe-Ni Alloy Cylinders Using Simulated Strains-Based Approach*

Abstract To elucidate the mechanisms of residual stress generation in quenched steel parts has been a longstanding problem. Qualitative explanations for the changes in the stress distribution in quenched cylinders appeared in the 1930s when it became possible to measure residual stresses in specimens. The explanation at that time used the concept of thermal and transformation stresses, which is still included in current textbooks. This concept is referred to here as the estimated stresses-based approach. To simplify the explanation of stress generation due to the combined effects of temperature change and phase transformations, quenching experiments were devised using Fe-Ni alloys in which only martensitic transformation occurs. On the other hand, since heat treatment simulations provide strains resulting from thermal, phase transformation, plastic, transformation plastic, and creep phenomena, a method to elucidate the mechanism using these strains was devised in the early 2000s and named the simulated strains-based approach. This paper contrasts the estimated stresses-based and simulated strains-based approaches to the mechanism of residual stress generation in quenched Fe-Ni alloy cylinders and highlights the superiority of the latter.

Characterization of Green Part of Steel from Metal Injection Molding: An Analysis Using Moldflow

Metal injection molding (MIM) is a quick manufacturing method that produces elaborate and complex items accurately and repeatably. The success of MIM is highly impacted by green part characteristics. This work characterized the green part of steel produced using MIM from feedstock with a powder/binder ratio of 93:7. Several parameters were used, such as dual gates position, injection temperature of ~150 °C, and injection pressure of ~180 MPa. Analysis using Moldflow revealed that the aformentioned parameters were expected to produce a green part with decent value of confidence to fill. However, particular regions exhibited high pressure drop and low-quality prediction, which may lead to the formation of defects. Scanning electron microscopy, as well as three-dimensional examination using X-ray computed tomography, revealed that only small amounts of pores were formed, and critical defects such as crack, surface wrinkle, and binder separation were absent. Hardness analysis revealed that the green part exhibited decent homogeneity. Therefore, the observed results could be useful to establish guidelines for MIM of steel in order to obtain a high quality green part.

Hot Deformation Behaviour of Additively Manufactured 18Ni-300 Maraging Steel

In this article, hot compression tests on the additively produced 18Ni-300 maraging steel 18Ni-300 were carried out on the Gleeble thermomechanical simulator in a wide temperature range (900-1200 °C) and at strain rates of 0.001 10 s-1. The samples were microstructurally analysed by light microscopy and scanning electron microscopy with electron backscatter diffraction (EBSD). This showed that dynamic recrystallization (DRX) was predominant in the samples tested at high strain rates and high deformation temperatures. In contrast, dynamic recovery (DRV) dominated at lower deformation temperatures and strain rates. Subsequently, the material constants were evaluated in a constitutive relationship using the experimental flow stress data. The results confirmed that the specimens are well hot workable and, compared with the literature data, have similar activation energy for hot working as the conventionally fabricated specimens. The findings presented in this research article can be used to develop novel hybrid postprocessing technologies that enable single-stage net shape forging/forming of AM maraging steel parts at reduced forming forces and with improved density and mechanical properties.

Effect of carburizing process on bending fatigue performance of notched parts of 18CrNiMo7-6 alloy steel

Since stress concentration is easily formed at the notch, improving the fatigue performance of notched parts is critical. The carburizing process is widely used to manufacture notched parts. In this research, the effects of carburizing process and notch stress concentration on fatigue performance were analyzed by bending fatigue tests. In addition, the microstructure and hardness evolution processes of the carburized notched 18CrNiMo7-6 specimens were observed quasi-in situ. The results showed that macro-plasticity has little effect on the bending fatigue performance of notched samples and that the improvement in fatigue performance is primarily attributable to the high hardness and residual compressive stress introduced by carburizing. The fatigue notch sensitivity is therefore reduced after carburizing. Compared to the uncarburized specimens, the fatigue limit of the carburized specimens is increased by up to 128%. With the increase of the effective hardening layer depth, the fatigue limit increases first and then decreases. Moreover, the brittle phase transformation product (twinning martensite) of metastable retained austenite is easy to produce stress concentration. Conversely, the 'film-like' retained austenite with an extremely high stability can effectively avoid the phase transformation products.

Influence of the design constraints on the thickness optimization of glass panes to achieve lightweight insulating glass units in cruise ships

The increasing complexity and size in cruise ships demands for lightweight structures and practical but accurate design methods. Conventionally, the focus has been on the steel parts of the ship, as they make most of its weight. However, the proportions of other materials are increasing. Therefore, this study attempts to provide better understanding how one could reach the lightweight designs of insulating glass units (IGUs) in ships. These are windows where at least two glass panes are separated by a hermetically sealed cavity. They are thin-walled structures that benefit not only from the geometrically nonlinear behavior, but also from the load sharing. Considering these effects, their behavior is studied using the nonlinear Finite Element Method and Particle Swarm Optimization. Different design criteria are imposed on the thickness determination of the glass panes with different shapes. Rectangular, triangular, and circular shapes are considered. The results show that the triangular shapes have the least weight for a given area when the deflection criterion is the dominating one. When maximum principal stress is the thickness defining criterion, the shapes perform almost equally well. The ratio between the pane thicknesses had the most influence on the behavior of the IGU. As it increases, i.e., one pane is significantly thicker than the other, the load sharing percentage drops, but it provides the most lightweight solution. Closer it is to 1, more equally the structural stresses are divided between the panes, i.e., redundancy is achieved. Finally, it is possible to establish a simple but effective method for the thickness determination of these IGUs using the results of this study. However, more work is required, including numerical analysis and experimental testing.

CO2-neutral Process Heating for Carburizing Furnaces – an Ecological Analysis*

Abstract In order to achieve the goal of a massive reduction of CO2-emissions, fossil fuels have to be substituted. In Germany, continuous carburizing furnaces for high capacities are almost exclusively fired by natural gas due to the lower energy costs. Electrical heating and hydrogen combustion are obvious alternatives. While electrical heating elements are state-of-the-art for these types of furnaces, hydrogen combustion has not been investigated. Furthermore, these two alternatives strongly depend on the specific energy mix, which determines the CO2-emissions. This case study compares different process heat generation options for continuous ring hearth furnaces for carburizing automotive steel parts by a quantitative approach. The investigated alternatives are natural gas/air heating as the reference, electrical heating and hydrogen/air heating. Besides the energy balances, primary energy consumption and resulting CO2-emissions are calculated. Furthermore, possible developments until 2050 are analysed. The results show that both alternative cases have a high potential to decrease CO2-emissions which strongly depend on the development of the energy mix and, therefore, the future expansion of renewable energy sources.

Influence of aging treatments on 17–4 PH stainless steel parts realized using material extrusion additive manufacturing technologies

The most relevant criticalities of parts produced by material extrusion additive manufacturing technologies are lower mechanical properties than standard material performances, the presence of pores caused by the manufacturing method, and issues related to the interface between layers and rods. In this context, heat treatments can be considered an effective solution for tailoring the material behavior to different application fields, especially when using precipitation hardening stainless steels. In this work, aging treatments were conducted on parts realized using three different extrusion-based processes: Atomic Diffusion Additive Manufacturing, bound metal deposition, and fused filament fabrication. Two conditions of direct aging (H900 and H1150) were considered with the aim of comparing the response of properties in the opposite conditions of peak-aged and overaged. The hardness tests revealed that H900 aging significantly influenced hardness (max increase of 52%), and porosity (− 34.3% with respect to the as-sintered condition). On the other hand, the H1150 aging decreased the hardness (− 18% max) and porosity (− 32.2% max). Substantial differences among the microstructures due to grain size and δ-ferrite were illustrated. A statistical test was included to better highlight the influence of the heat treatment on the investigated properties.

Digital Image Correlation for Measuring Full-Field Residual Stresses in Wire and Arc Additive Manufactured Components

This study aims to demonstrate the capability of the digital image correlation (DIC) technique for evaluating full-field residual stresses in wire and arc additive manufactured (WAAM) components. Investigations were carried out on WAAM steel parts (wall deposited on a substrate) with two different wall heights: 24 mm and 48 mm. Mild steel solid wire AWS ER70S-6 was used to print WAAM walls on substrates that were rigidly clamped to H-profiles. DIC was used to monitor the bending deformation of WAAM parts during unclamping from the H-profiles, and residual stresses were calculated from the strain field captured during unclamping. Residual stresses determined from the proposed DIC-based method were verified with an analytical model and validated by the results from established residual stress measurement techniques, i.e., the contour method and X-ray diffraction.

Optimization of Thick 22MnB5 Sheet Steel Part Performance through Laser Tempering

Press Hardening offers the possibility to obtain a wide range of mechanical properties through microstructural tailoring. This strategy has been successfully applied in thin sheet components, for instance, through differential cooling strategies. The application of these added value features to truck components implies adapting the process to the manufacture of thick sheet metal. This introduces an additional layer of complexity, but also opportunity, in a process where the final microstructure and, thus the mechanical performance is generated in the press shop. This work presents a study on optimizing the crash worthiness and impact energy absorption on a press hardened thick 22MnB5 steel sheet. Different microstructure design strategies have been studied, including ferrite-Pearlite (representative of a differential heating and austenitization strategy), in-die generated Bainite (representative of differential cooling) and Tempered Martensite (generated through laser tempering), keeping a fully hardened martensite as a reference condition. The material performance has been compared in terms of the monotonic properties, useful for anti-intrusion performance, and Essential Work of Fracture, a well-suited parameter to predict the crash failure behavior of high strength steels. The results show that laser tempering offers properties similar to Bainite-based microstructures and can be a successful replacement in components where the sheet thickness does not allow for the fine control of the in-die thermomechanical evolution.

Bmpti Corrosion Inhibition for API 5L X70 Steel in Saline Medium

In this work, electrochemical test was applied on API 5L X70 steel in NaCl 3% wt solution to observe the effect on the corrosion process of the material with the addition of BMPTI (C17H18IN3O). The steel parts were exposed to open circuit potential (OCP) test, electrochemical impedance spectroscopy (EIS) and polarization curves (CP) with different concentrations of inhibitor (5, 20 and 50 ppm); from these test the action of the inhibitor, its efficiency, the effect on the corrosion rate and a thermodynamic analysis to determine the mechanism of action of the inhibitor.

Microstructure-electrochemical behavior relationship in post processed AISI316L stainless steel parts fabricated by laser powder bed fusion

AISI316L stainless steel components produced via additive manufacturing techniques have quickly found new applications across several industrial sectors. However, parts manufactured through this method generally exhibit poor surface quality and performance in the as-built state. This work addresses the influence of laser polishing and water jet assisted recirculating shot peening on the surface quality, microstructure and electrochemical properties of AISI316L samples produced by the laser powder bed fusion method. To do so, surface roughness analysis, residual stress measurement, scanning electron microscope and electron backscatter diffraction analysis were employed along with electrochemical tests, including cyclic potentiodynamic polarization, electrochemical impedance spectroscopy and Mott-Schottky analysis. Laser polished samples exhibited a smooth surface with high tensile residual stress on the surface, which led to the reduction of pitting potential and formation of passive layers, including more crystal defects. Microscopical analysis evidenced that the higher density of lattice defects and local microstrain on the surface of the shot peened samples promoted surface hardness and induced compressive residual stress. Therfore, the shot peened samples exhibited a wider passive range in cyclic potentiodynamic polarization measurements, higher polarization resistance in electrochemical impedance spectroscopy measurements, and less defective passive film in Mott-Schottky analysis. Moreover, it was calculated that the passive film thickness of the shot peened sample was slightly larger than the other samples. Low surface roughness, high crystal defect density, and compressive residual stresses enhanced the passive layer's resistance to defect transport, lowered the point defect concentration in the passive film, and improved the pitting resistance of the samples.

Surface Finish Analysis of Gradient Voltage Electrochemical Polishing of 316L Stainless Steel Parts Forming by Laser Powder Bed Fusion.

Laser powder bed fusion (LPBF) of complex-structure 316L stainless steel (316L ss) parts has a wide application prospects in aerospace, biomedical, and defense industry fields. However, the surface roughness (Ra) of the LPBF sample is unsatisfactory due to the process characteristics of layer-by-layer selective melting and cumulative forming, which limits its applications in the engineering field. Herein, a gradient voltage electrochemical polishing strategy is proposed based on the characteristics of electrochemical polishing technology, which can polish complex structures. The mechanisms of polishing process parameters and polishing strategy on the surface finish of LPBF parts are investigated. The gradient voltage polishing strategy is extended to complex structures, and the Ra of the inner surfaces of square and round tubes are successfully reduced to about 1 μm. The gradient electrochemical polishing process for surface finish post-treatment of LPBF parts can broaden the engineering applications of complex-structure metal parts.