Steel Layer Research Articles

Investigation of the surface layer of wheel steel by indentation method

The article considers methods of measurement of microhardness and modulus of elasticity of plasma hardened wheel steel by kinetic indentation method. It provides features of measurement of microhardness, modulus of hardness, elastic recovery, influencing on wear resistance of surface layers of steel. Measurement of these characteristics of material allows estimating and choosing optimum technology of surface modification by surface plasma hardening. It is confirmed that objectivity of determination of microhardness, modulus of elasticity, elastic recovery and flow stress depends on strict observance of imprint depth requirements depending on thickness of hardened layer. It is noted that in spite of the increased amount of factual information, obtained by indentation method, the physical substantiation of hardness micro-mechanisms remains poorly understood, which necessitates substantiation of physical representations of the nature of hardness of metallic materials. It is established that the measurement of microhardness, elastic modulus and elastic recovery by the kinetic indentation method is expedient to use for certification of the surface layer of plasma-hardened wheel steel according to the parameters of physical and mechanical characteristics.

Enhancing the ballistic resistance of steel/aluminum bilayer armor plates through explosive welding

This work presents a comprehensive analysis of the ballistic response of Q235 steel/6061-T6 aluminum bilayer plates fabricated via explosive welding, with a special focus placed on elucidating the mechanisms of ballistic resistance enhancement due to the bonded interface. For comparison purposes, unbonded Q235 steel/6061-T6 aluminum bilayer plates (e.g. being stacked together or spaced with an air gap) were also investigated. Ballistic tests were carried out to compare the residual velocities and failure behaviours of the welded and unwelded bilayer plates. Computational models were built in LS/DYNA and validated with the experiment. Experimental results showed that the ballistic limit velocity of the explosively-welded plate is 13.4% and 9.4% higher than those of the in-contact plate and air-gapped plate. Simulation results suggested that the enhanced ballistic resistance was attributed to its welded interface. On the one hand, the welded interface allowed effective stress attenuation within the steel layer leading to a greater damage tolerance and more energy dissipation during the prolonged response time. On the other hand, when deforming together with the steel layer, the welded interface enforced a uniform indentation on the central region of the aluminum substrate leading to greater energy absorption due to compression and thinning of the material.

Numerical simulations of oscillatory combustion and extinction of a liquid pool fire in a reduced-scale and mechanically-ventilated enclosure

The paper presents a numerical study on an 18 cm-diameter liquid pool fire in a reduced-scale and mechanically-ventilated enclosure. The enclosure walls are made of a calcium silicate layer and a steel layer on five sides, the remaining sidewall is made of heat-tempered glass. The ventilation system is extracted mechanically with free air inlet. Three air renewal rates (ARR) and open atmosphere conditions are considered in the numerical study. Computational Fluid Dynamics (CFD) simulations are carried out with Fire Dynamics Simulator (FDS 6.7.5). The default evaporation model in FDS (i.e., forced convection approach) is compared to a natural convection approach implemented in the source code. The results show that the oscillatory combustion, occurring at ARR = 15 h−1, is best captured by the natural convection approach. It is also found that prescribing the fuel Auto-Ignition Temperature (AIT) is important to capture the fire oscillations and (local) flame quenching. At ARR = 8 h−1, extinction occurs. It is found that prescribing the fuel AIT allows to prevent spurious oscillatory combustion. At ARR = 22.5 h−1, there is a stable steady-state burning regime for which (as well as for open atmosphere conditions) prescribing the fuel AIT is not crucial.

Experimental observations of nucleation and crack growth paths of hydrogen-induced cracking in pipeline steel

The microstructural features that favor hydrogen-induced cracking (HIC) in internal, middle, and external layers of pipeline steels were investigated. The electrochemical cathodic charging was used to induce HIC, and straight beam ultrasonic inspection was identified in which steel layers HIC nucleate and grow. The cracked plates were examined by optical microscope and scanning electron microscope (SEM). The hydrogen microprint technique (HMT) was used to visualize the site of high hydrogen concentrations. Electron backscatter diffraction (EBSD) was used to analyze the role of crystallographic texture in HIC pathways. The results revealed that HIC nucleation and growth are influenced by the segregation degree and inclusion contents, which are higher in the internal surface layer of our studied steels but not consistently so in the middle thickness layer. Further, HIC nucleated in cuboidal and spinal inclusions and propagated along ferrite/pearlite bands with high misorientations. The HMT results showed that hydrogen is present in pearlite colonies, grain boundaries, and non-metallic inclusions. The results indicated that HIC is not solely controlled by the crack geometry.

Evolution of the oxide layers of an aluminum-forming austenitic heat-resistant steel with high-Mn substitution for Ni: Experiment and first-principle calculations

High Mn (8 wt%) was used to save Ni resources to replace 10 wt% Ni in Aluminum-forming austenitic (AFA) heat-resistant steel; the changes in oxidation resistance and morphology evolution of multiple oxide scales for the 8Mn-AFA steel were then studied. The 8Mn-AFA steel formed a three-layer scale on the surface oxidized at 750 °C for 100 h: inner dense Al2O3 sub-layer closed to the austenite matrix, intermediate Cr2O3 sub-layer with partial Cr substituted by Mn, and outer loose Mn2O3 + Mn3O4 sub-layer with FeMnO3 surface nodules. Mn from the matrix to the α-Al2O3 diffusion is spontaneous. However, Mn moving from an α-Al2O3 to α-Cr2O3 leads to partial Cr in the Cr2O3 sub-layer was substituted by Mn. When the 8Mn-AFA steel oxidated at 750 °C for 360 h, the Mn oxides, including Mn2O3, Mn3O4 and FeMnO3, increased significantly with the prolongation of the oxidation time. First-principle calculations based on density functional theory (DFT) also confirmed the diffusion of Mn did not destroy the dense Al2O3 scale. The oxidation weight gain of 8Mn-AFA steel oxidized at 750 °C in the air for 360 h follows a parabolic law, and the oxidation rate constant is 2.65 × 10−4.

Learning from the Past: The Reconstruction of the Original Damascus Steel. Experimental Study

The original method of manufacturing Damascus steel has been forgotten over time. Due to differences in the raw material used and the manufacturing techniques, some of the current attempts at replicating Damascus steel have failed. The study of Damascus steel provided the opportunity to observe in detail the laborious process of manufacturing this material, which involves the free forging and welding of different layers of steel to obtain a particularly strong and durable final product. To carry out this research, high-quality materials were selected from a catalogue of steels, with a particular focus on achieving the best results. In this case, two types of steel were chosen to create Damascus steel: AISI 1095 and 15N20 steel. Both materials have been selected for their individual properties, such as mechanical resistance and durability, which contribute to the ultimate quality of Damascus steel. This rigorous selection of materials ensured a high-quality and authentic product. Throughout this study, a functional furnace was built capable of contributing to the welding and forging processes of these two different materials. This furnace played a crucial role in obtaining true Damascus steel. By applying a complex process of heating and forging and then repeating this process, the layers of steel were welded together, resulting in a final material that is extremely strong and has a unique aesthetic appearance. Processing and laboratory tests were carried out on the obtained Damascus steel to evaluate its mechanical properties, including the processing of the results using Autodesk Inventor Professional 2023 and simulation in Ansys 2023.

Effect of machining processes on the quenching and tempering surface layer of ultra-high strength steel

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes.

Effect of polyurethane matrix and steel fiber in combination with glass fiber or basalt fiber on the properties of hybrid composite laminates

Abstract Polyurethane is a versatile polymer with a high degree of toughness and ductility used in a wide variety of applications. In this study, two-part thermoset polyurethane was used as a matrix material to prepare hybrid and non-hybrid composites. Hybrid laminates were prepared by combining either glass fiber or basalt fibers with steel fibers. The mechanical properties of prepared composite specimens were characterized and scanning electron microscope (SEM) observation was performed around the fracture region of the tested specimens. The results revealed a significant increment in tensile strength, and flexural strength in BS1-PU (8 layers of basalt-1 layer of steel) hybrid laminate by 357.74 % and 64.59 %, respectively, compared to steel fibers reinforced polyurethane composites. Furthermore, GS4-PU hybrid composite (5 layers of glass-4 layers of steel) achieved an improvement in tensile strain by 12.07 %, flexural strain by 25.32 %, and absorbed energy by 18.21 %, compared to glass fibers reinforced polyurethane composite. Moreover, the SEM observations revealed that the replacement of some basalt and glass layers with steel layers leads to a positive hybridization effect of the overall produced hybrid composites.

Fatigue crack propagation of the gradient surface-modified layer of high-strength steel

A gradient modified layer can be produced on the high-strength steel surface by carburizing heat treatment. In this study, microstructure characterization and fatigue crack propagation test were carried out on the gradient surface-modified layer of the 18CrNiMo7-6 high-strength steel. With increasing depth of the surface-modified layer, the yield strength and the kernel average misorientation value decrease, and the equivalent grain size of the slatted martensite structure and the number of the large-angle boundaries increase. The orientation difference angle of the point to point pre- and post-fatigue at the crack of the transition layer and the matrix layer increases from less than 2° to approximately 10° and about 4°, respectively. With the increase of the depth of the surface-modified layer, the degree of deformation inside the martensitic packet decreases, while the extent of macroscopic deformation of the material increases. Deformation occurs inside the martensitic packet at the main crack, and there is essentially no deformation inside the martensite packets away from the main crack. On both sides of the main crack, a large number of extrusions parallel to the martensitic lath appear. The large-angle boundaries of the original austenite grain boundary and martensite boundary hinder the propagation of the fatigue crack.

Influence of Temperature on the Behavior of Sandwich Panels

AbstractSandwich panels in the construction industry are used as roof and facade elements and usually consist of two thin face layers of steel and a thicker core of polyurethane (PU) or mineral wool in between. The PU core material is constantly being further developed. In addition to improvements in the physical properties, this further development also leads to changes in the mechanical properties. As a result, the design rules that were established for older foam systems must be reviewed at regular intervals. There is a great need for research into the temperature‐dependent behavior of the foam system. As these elements are used as roof and facade elements, they are directly exposed to climatic conditions. High temperatures are generated on the cover sheets due to solar radiation. The PU rigid foam changes its mechanical properties in this temperature range. Tests on small parts and components show a change in the stiffnesses and strengths, as well as the load‐bearing behavior under elevated temperature. Consideration of the temperature in the design is therefore of great importance. In view of the continuous further development of the foam system, statements regarding the core material from older research must be reconsidered.

Effects of pulsed laser hardening of cylindrical surfaces on fatigue behavior

The issues of the of laser hardening of the plain bearing effects on the fatigue strength of the crankshaft neck journal are discussed in this article. The crankshaft destruction of the crankshaft leads to catastrophic consequences, especially for heavy diesel engines. The article substantiates the assertion of a decrease in the fatigue strength of steels after pulsed laser hardening treatment of the friction surface to increase the wear resistance of a plain bearing. The process of formation of a surface hard layer of steel and the formation of dimple-shaped stress concentrators on it after interaction with a laser pulse is studied. Factors affecting the fatigue behavior of materials are analyzed. Particular attention is paid to the formation of a residual stress state in the surface layer and the role of surface defects on the fatigue behavior of steel. The assumption about the possibility of reducing the decrease in fatigue strength by optimizing the technological parameters of laser processing is substantiated. On the basis of the study, it is proposed to limit the energy of the laser pulse, preventing the surface from melting.

Evolution of the corrosion layer of Q235 steel in simulated fire‐scene smoke

AbstractThe ability to accurately identify fire patterns is the fundamental requirement for fire investigations. The corrosion layers of steel in fire scenes exhibit three distinct characteristics. First, due to steel's nonflammable nature, steel patterns can be preserved better at the fire site than patterns formed on other combustible materials; second, both the high temperature and the smoke during the fire affect the high‐temperature oxidation process; and third, the corrosion layer of steels inevitably undergoes further evolution after the fire because of the subsequent room‐temperature corrosion. This study focuses on investigating Q235 steel because of its extensive use in construction and vehicles. The pattern evolution processes of high‐temperature oxidation at elevated temperatures in air, polyethylene (PE), and polyvinyl‐chloride (PVC) combustion smoke and the corresponding subsequent corrosion at room temperature were systematically investigated from the perspective of macroscopic and microscopic morphology. The results showed that the smoke atmosphere played an important role in the formation of the corrosion layer of Q235 steel. Compared with samples oxidized in air, samples oxidized in PE combustion smoke exhibited a uniform and dense oxide layer on the surface, which inhibited the corrosion at room temperature further. The PVC combustion smoke accelerated the high‐temperature oxidation of the sample, and its influence on the subsequent room‐temperature oxidation process was closely correlated with the temperature of the high‐temperature oxidation. The results of this study provide important references for understanding the formation of the corrosion layer of Q235 steel for fire investigations.

Determination of ef ective thickness of cemented steel layer

The problems of increasing the strength of high-loaded steel parts of transmissions of energy-saturated machines are considered. It is noted that, along with hardness, an important parameter of the hardened cemented steel layer is its effective thickness the distance from the surface of the sample (part) to the zone with hardness 50 HRC (529 HV0.5). It is shown that great infl uence on accuracy of its defi nition have unavoidable banding of metal in the area of hardness measurement and an instrumental error of hardness measurement. A method of increasing the accuracy of determining the effective thickness of the cemented layer, based on interpolation by polynomial of the second degree of distribution of experimentally measured hardness values HV0.5 in an extended range of changing distances from the surface of the article to the hardness measurement HV0.5 is offered. Error of defi nition of an effective thickness of the cemented layer is reduced at the expense of expansion of area of change of hardness HV0.5 in an analyzed zone with approximation of its monotonous change in this area and the subsequent solution of the received square equation. Approximating polynomial statistically correctly refl ects the character of hardness change HV0.5 of cemented steel in the analyzed area depending on the distance from the workpiece surface to the hardness measurement place. The effectiveness of the method was confi rmed when determining the effective thickness of the grouted layer of a sample of 18CrNiGt steel after carburizing and hardening. The obtained results will be useful in the development of optimal regimes of carburizing of high-loaded gearwheels of automobile and tractor transmissions.

Durability and Performance of Poly(norbornene) Membranes and Ionomers in Alkaline Electrolyzers

Ion conducting polymer electrolytes provide an enabling technology for low-temperature alkaline electrolyzers. The critical parameters of solid polymer electrolytes include ionic conductivity, ion selectivity, chemical resistance and dimensional stability in the presence of excess water. High pH operation using anion conductive polymer electrolytes has several potential advantages over acid-based polymer devices including low-cost catalysts, hydrocarbon (non-perfluorinated) polymer, and low cost cell components.In this study, a family of hydroxide conducting, poly(norbornene) solid polymer electrolytes were synthesized and used in high-performance, durable membrane electrode assemblies for fuel cells and electrolyzers. In addition to membranes, covalently bonded, self-adherent, hydroxide conducting ionomers were used to form high-performance, durable membrane electrode assembly for water electrolysis. The self-adhesive ionomers and membranes are based on hydroxide conducting poly(norbornene) polymers. The effect of porous transport layer material and porosity was examined. High performance electrolysis with very low degradation rates was achieved using stainless steel and nickel porous transport layers and flow-channels

Nonlinear analysis of reinforced concrete slabs using a quasi-3D mixed finite element formulation

This study presents an efficient quasi-3D mixed finite element (MFE) formulation for the materially nonlinear analysis of reinforced concrete (RC) slabs based on a refined layered global–local plate theory. The cross-section of the RC slab is divided into a series of concrete and steel layers. Each layer is treated as a plate structure and mechanical properties of the steel and concrete materials are individually applied to each layer. In addition to unknown variables of the displacement field, out-of-plane stress components are also assumed as independent field variables in the presented MFE formulation. It makes it possible to obtain the out-of-plane shear stresses at each node directly from constitutive equations with the enough accuracy. A four‐node rectangular element ensuring the C1‐continuity is used for discretizing the domain of the RC slab. The governing equations are derived based on a partially mixed-field variational principle. The accuracy and efficiency of the presented MFE have been investigated through some benchmark examples. Numerical tests show that the presented MFE yields results with sufficient accuracy at a low computational cost.

Fracture toughness determination for the surface-modified layers of carburized 18CrNiMo7-6 alloy steel via the compact tension method

Anti-fatigue manufacturing technology is the latest manufacturing technology to control surface integrity and modification. Surface modification techniques have been used to construct surface-modified layer (SMLs) on the workpiece surface. In this study, to accurately characterize and measure the fracture toughness of SMLs, a characterization method was proposed for evaluating the J-integral of fracture toughness of SMLs. The elastic–plastic parameters of the SMLs, such as the strain hardening index and yield strength, were obtained via peeling-layer tensile testing. The effect of n was considered when deriving the plasticity factor (ηp). The J-integral of the SML of 18CrNiMo7-6 alloy steel was obtained from single edge notched tension tests and finite element simulations. The results show that the fracture toughness of the SMLs can be accurately characterized using the proposed method.

Influence of combined electromechanical processing modes of 40Kh steel on its structure and hardness

The paper considers the effect of combined electromechanical processing in three different modes on the structure and hardness of the surface layers of 40Kh steel, which was in a normalized state (the original structure). The modes differ from each other by the different applied load and the number of pulses. The applied load in modes 1 and 2 (current strength 39 kA, pulse time 0.02 s, number of pulses 1) is 100 and 250 MPa, respectively. A distinctive feature of mode 3 compared to mode 2 is a greater number of pulses (two). Metallographically it was established that in all three cases a hardened surface layer of different thickness (from 300 to 1200 μm) with a hardness of 593 – 598 HV is formed, consisting of two zones (a surface zone with a structure of fine-needle martensite; a transition zone smoothly transitioning into the initial ferrite structure). The transition zone (treatment according to mode 1) in its structure contains martensite and ferrite. The transition zone (mode 2 processing) consists of a Widemannstett structure. A more substantial surface heating zone according to this mode (700 μm) in comparison with the processing according to mode 1 (300 μm) in combination with intensive heat removal contributed to the formation of a Widmanstett structure, which is defective and unacceptable for operation. The transition zone with the processing according to mode 3 has the structure of martensite and ferrite. The formation of a defective Widmanstett structure in the transition zone does not occur, since 2 times more pulses are used during processing than in mode 2. This contributes to the heating of the surface layer to a greater depth (1200 μm), and, consequently, the structure formation in the transition zone occurs from the intercritical interval Ag3 – Ag1 .

Numerical Simulation and Surface Properties of 42CrMo Steel Treated by Plasma Nitriding and Laser Quenching

In this study, we investigated the nitriding and laser quenching composite modified layers of 42CrMo steel. MATLAB was used to fit the nitrogen concentration distribution during nitriding, and the laser temperature field was fitted using ABAQUS finite element simulation software. Two groups of simulation results were integrated to fit the modified layer depth under different processes, and the nitriding and laser quenching experimental results were compared with the simulation results, which indicated that the simulation results agreed well with the experimental results. The depth of the nitriding–laser quenching composite layer greatly improved compared with the nitriding or laser hardening layers. The austenitizing temperature of the 42CrMo steel was reduced to 577 °C by nitriding. Therefore, the depth of the austenitized layer of the 42CrMo steel heated with the same laser power significantly increased. Under the same laser process conditions, more austenitic phase transformation was observed in the nitriding layer than in the non-nitriding layer, so martensitic phase transformation was more likely to occur in the subsequent cooling process. After plasma nitriding at 460 °C for 16 h and laser quenching, the modified layer depth of the 42CrMo steel reached 990 μm, and the average surface hardness of the 42CrMo steel reached 625 HV0.1. The friction coefficient of the modified layer was the lowest, with a value of 0.433, and the minimum wear value was 1.024 mm3. Double hardness and thickness of the modified layer could be obtained by nitriding and laser quenching composite processes.

Determination of Toughness Variation and Cohesive Zone Parameters for De-bonding of Adhesively Bonded PMMA and Steel Using the Shaft-loaded Blister Test

ABSTRACT In this work, the shaft-loaded blister test (SLBT) is employed to investigate the de-bonding of a poly-metha-methyl-acrylate (PMMA) layer adhesively bonded to a steel layer. During de-bonding, the mode-mixity does not remain constant in this test; hence, the variation of mode-mixity with the change in de-bond size (blister radius) and the out-of-plane displacement of the PMMA layer is established through Finite Element Analysis (FEA). Experiments are performed in which the load, load-point displacement, and de-bond size is recorded synchronously. Three different thicknesses of PMMA layer are considered in experiments. The variation in toughness as a function of mode-mixity is evaluated. FE simulations with embedded cohesive zone model (CZM) are carried out, and the mixed-mode cohesive zone modelling parameters are identified by comparing the numerical results with experimental observations. By using this approach, the toughness variation as a function of mode-mixity and the CZM parameters is determined using the SLBT.

Methodology for Determining the Effective Thickness of the Cemented Layer of Steel

Highly loaded transmission gears are cemented and hardened. An important parameter of the hardened cemented layer is its effective thickness hef . Metal banding and the unavoidable instrumental error in hardness measuring have a great influence on the reliability of hef determination. The purpose of this article was to develop a methodology to improve the reliability of determining of the effective thickness hef of the hardened layer in steel after carburizing and quenching.The value of hef is the distance h from the surface of the product to the hardness zone of 50 HRC. The article substantiates that approximation of hardness change from the distance h to the product surface will allow to obtain a more reliable dependence of hardness change in the investigated area when making hardness measurements in a wider range of distance h. Therefore, to increase the reliability of hef determination, results of the HV0.5 hardness measurement in an extended range of changes in h in the vicinity of the analyzed zone were used. The HV0.5 measurement results are converted to HRC hardness values using the formula recommended by the international standard. The HRC(h) distribution of HRC hardness values in the measurement area is interpolated by a second-degree polynomial which physically correctly reflects the change in metal hardness in the analyzed area. The resulting polynomial is used to determine of the distance hef at which the hardness takes on a value of 50 HRC. The methodology was used to determine the hef of an 18KhGT steel gear wheel after carburizing and quenching. It is shown that results of two independent measurements of the hef sample differ from each other by 0.003 mm. This is significantly less than the permissible error of 0.02 mm of the hef determination according to the standard technique. The error of hef determination is reduced by extending the range of variation of h and statistically valid interpolation of the monotonic change in hardness with the distance from the surface of the item in the measurement area. The developed method of determining the effective thickness hef of the hardened steel layer consists in determining the distribution of its hardness in the expanded vicinity of the hef area, approximating the obtained dependence by a polynomial of the second degree and solving the square equation obtained with its use. The technique provides a significant reduction in the influence of the structural banding of the metal and the inevitable error in measuring hardness on the result of determining the hef . Its application will allow to optimize the cementation regimes of gear wheels to increase their service life.