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In the present work, the impact of hot top geometry and thermal history on the Columnar-to-Equiaxed Transition (CET) point, of a 12 MT steel ingot was determined using finite element modeling. Experimental validation of the model was conducted on an industrial-size ingot, focusing on temperature, macrosegregation, and shrinkage microporosity. The anticipated Columnar-to-Equiaxed Transition point, influenced by the interaction of solid front rate, thermal gradient, and solid fraction was considered in the analysis. The findings revealed a shift in the CET position in new configurations, up to 56 mm, 63 mm, and 60 mm from the ingot wall in the bottom, middle, and top of the ingot, respectively. The changes are attributed to variations in the kinetics of solidification, particularly the solidification time. Thermo-mechanical phenomena, encompassing mold filling, cooling, solutal convection, and flow driven by shrinkage, were incorporated into the model to predict macrosegregation and the risk of porosity and shrinkage cavity formation for different hot top geometries. A criterion is proposed that allows mitigating macrosegregation and minimizing the risk of porosity and shrinkage cavity.

Computational Fluid Dynamics simulations were used to optimize heating elements placement on the walls of a large size electrical heat treatment furnace in order to reduce temperature gradients within the furnace and uneven temperatures on different faces of the blocks which could result in variabilities in final mechanical properties. Initial evaluations of different layouts highlighted the effectiveness of equipping two side walls. Subsequently, an optimal percentage of side wall coverage was identified through simulations and multi-objective evolutionary optimization. Genetic and pareto search algorithms yielded 10 % and 14.2 % as optimum values, respectively. Implementing an optimal coverage demonstrated significant reductions in surface temperature non-uniformity, surface-to-center temperature differential, and temperature differences between loaded blocks. These improvements suggest a potential for enhanced uniformity in mechanical properties across a batch of products. This approach presents a promising strategy for obtaining consistent and efficient heat treatment cycles in industrial heat treatment furnaces resulting in energy saving and improved product quality.

Abstract Squaring, a wood transformation process, is an operation which consists of introducing the logs into a squaring machine which then uses sharp tools to cut the wood into pieces with high surface quality. Tool steels used in this process experience significant wear, damaging the wood surface and hence leading to substantial scrape rate. This study investigates the wear resistance of three tool steels specifically designed for wood cutting applications: modified AISI A8, modified steels with 0% and 1% tungsten, and powder metallurgy prepared W360 steel. Furthermore, the influence of a PVD coating on the wear resistance of the three alloys was investigated. ASTM G65 abrasive wear tests were conducted using the dry sand/rubber wheel abrasion test. A methodology using a non-contact 3D measurement system and specialized software was developed, allowing for a thorough quantitative assessment of the wear of these steels. The results revealed that the coated A8mod + 1%W steel exhibits the best resistance among the coated steels. Despite the excellent intrinsic resistance of W360 steel, the coating did not provide a significant improvement for this steel, showing only a 10% reduction in wear. Microstructural analysis revealed that the predominant wear mechanisms were abrasion and impact. The relative performance of each steel was quantified and is reported. Field trials conducted under actual cutting conditions, indicate the superiority of W360 steel in terms of resilience to wear and impacts compared to other tested alloys, while confirming the effectiveness of surface treatments in mitigating material wear. However, A8 steel modified with 1% tungsten exhibits increased wear under coating.

The ex-situ incorporation of the secondary SiC reinforcement, along with the in-situ incorporation of the tertiary and quaternary Mg3N2 and Si3N4 phases, in the primary matrix of Mg2Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N2 gas during laser powder bed fusion. This is substantialized based on both the thermal diffusion- and chemical reaction-based metallurgy of the Mg2Si–SiC/nitride hybrid composite. This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing. This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg2Si–SiC/nitride hybrid composite. Consequently, the coefficient of friction of the hybrid composite exhibits a 309.3% decrease to –1.67 compared to –0.54 for the conventional nonreinforced Mg2Si structure, while the tensile strength exhibits a 171.3% increase to 831.5 MPa compared to 485.3 MPa for the conventional structure. This outstanding mechanical behavior is due to the (1) the complementary and synergistic reinforcement effects of the SiC and nitride compounds, each of which possesses an intrinsically high hardness, and (2) the strong adhesion of these compounds to the Mg2Si matrix despite their small sizes and low concentrations.

This study investigates the impact of multi-step austenitization heat treatment on the in-service life of modified AISI A8 cold work tool steel knives used in wood cutting. The knives were subjected to two treatment methods: single quenching and double tempering (SQDT) and double quenching and double tempering (DQDT). Both treatments were followed by physical vapor deposition (PVD) coating to enhance surface properties. The DQDT treatment resulted in a finer microstructure and more uniform carbide distribution. Field tests on 24 knives over 124 h demonstrated up to 130% improvement in wear resistance for DQDT knives, along with superior edge stability and better PVD coating preservation. DQDT knives exhibited ductile fractures characterized by dimples, contrasting with the brittle fracture and cleavage facets in SQDT knives. Residual stress measurements showed higher compressive stresses in DQDT knives (−280 MPa) compared to SQDT knives (−30 MPa), which increased further after field testing. The enhanced performance of DQDT knives is attributed to their refined microstructure, improved carbide distribution, and higher compressive residual stresses, offering significant potential for improving wood cutting tool efficiency and durability.

Development of cracks along the center axis of large high strength steel bars commonly occurs during the forging and leads to excessive part rejections. The present investigation aims to develop a better understanding of the evolution of stress-strain states during the forging operation and in particular the effect of deformation path illustrated by die geometry, on the evolution of damage during the cogging of an AISI H13 steel. Hot compression and tensile tests were performed using Gleeble-3800 thermo-mechanical simulator to develop the optimum material model which was then implemented in the finite element (FE) code Forge NxT 3.2® using a developed user subroutine. Normalized Cockcroft and Latham damage criterion and maximum shear stress (Tresca's) theory of failure were used to predict the damage and failure in the center axis of the shaft through FE analysis with three different die shapes: concave, flat, and convex. A comparative study between the three die geometries was conducted to quantify the effects of each of them on the sensitivity to central burst damage. FE model was validated using industrial data. The lowest and highest damage values were found to occur in the case of cogging with concave and flat die, respectively. The coefficient of variation (CoV) is employed as a measure of heterogeneity and it was found that the concave die provides more uniform deformation and most favorable results for the cogging compared to the flat and convex dies. The novel approach, application of concave die successfully implemented at the industrial scale cogging.

This study aims to develop a flow rule for evaluating the relaxation and redistribution of residual stresses during the post-weld heat treatment (PWHT) of hydroelectric runners made from low-carbon martensitic stainless steel (13Cr-4Ni composition). During the PWHT, austenite reforms in the filler metal and surrounding areas of the base metal near welded joints. The evolving inelastic strain rate with reformed austenite led to defining two distinct flow rules in the pure martensitic (α′) and austenitic (γ) phases. A linear rule of mixture was then applied to assess global effective stress based on the inelastic strain rate and current austenite fraction during the PWHT. A unified constitutive model incorporating drag stress and back stress, evolving with creep and plastic deformation mechanisms during the PWHT, described the stress–strain behavior. To validate this analysis, a third flow rule was determined in the 18% tempered austenitic microstructure, compared with the rule of mixture’s effective stress contribution from each phase on the inelastic strain rate. Isothermal constant strain rate tests in stabilized crystalline microstructures evaluated constants specific to their respective flow rules. This study demonstrates the stability of reformed austenite at elevated temperatures during slow cooling and its significant influence on the mechanical properties of 13Cr-4Ni steels. The effectiveness of estimating yield stress using the rule of mixture based on individual phase behaviors is also confirmed.

This study is focused on determining the impact of short-time annealing during industrial brazing process. Short-time annealing is commonly used to alleviate residual stresses resulting from the brazing process and represent in this study 30% of the process time. Samples were selected using two designs of experiments with three main parameters which are temperature of brazing, temperature of short-time annealing and time of first cooling for the first, and temperature of brazing for the second. Shear resistance tests allowed to refine the selection of samples for further investigation. EDS views, hardness measurements and residual stress measurements were conducted. From the obtained results, although slight differences were observed in the microstructure, hardness, and residual stresses of the samples, no clear pattern of impacts could be attributed to short-time annealing. In conclusion, this study did not find substantial evidence of short-time annealing having a significant impact on the microstructure, hardness, or residual stresses in the context of industrial brazing for wood cutting tools. Further research could explore other annealing parameters or alternative heat treatment methods to achieve the desired material properties.

The aim of the present research was to study the residual stress variations induced by heat treatment and rough milling operations of large forged steel blocks. The heat treatment process includes quenching and tempering operations. An efficient strategy based on a size sensitivity analysis (SSA) was proposed to reach the actual values of residual stresses in large-size steel blocks by using small-size workpieces in laboratory scale without damaging the blocks. The residual stresses were measured and compared after the first and second tempering and the rough milling. A 3D finite element (FE) model was developed to predict superficial residual stresses and was then calibrated experimentally. The results showed that the residual stresses after the first and second tempering were highly compressive on and near the surface. In addition, the resultants of the residual stresses after double tempering processes were almost equal. Therefore, the second tempering could be omitted from the manufacturing process. It was also found that both surface and sub-surface hoop and radial residual stresses were highly tensile after the rough milling. Finally, the 3D FE model can be used as a predictive tool to predict residual stresses for rough milling to avoid conducting expensive, time-consuming experimentations and measurements.

The influence of hot-top designs with different heat capacities on the distribution of positive and negative macrosegregation was investigated on a 12 metric tonne (MT) cast ingot made using Cr-Mo low-alloy steel. The three-dimensional finite element modeling code THERCAST® was used to simulate the thermo-mechanical phenomena associated with the solidification process, running from filling the mold until complete solidification. The model was validated on an industrial-scale ingot and then utilized to evaluate the influence of the thermal history of the hot-top, a crucial component in the cast ingot setup. This assessment aimed to comprehend changes in solidification time, temperature, and heat flux—all of which contribute to the determination of macrosegregation severity. The results showed that preheating the hot-top had a minor effect on solidification time, while modifications of thermal conductivity in the hot-top region increased the solidification time by 31%, thereby significantly affecting the macrosegregation patterns. The results are discussed and interpreted in terms of the fundamental mechanisms governing the kinetics of solidification and macrosegregation phenomena.

This research study was aimed at investigating the influence of linear friction welding parameters on grain size alteration and temperature distribution of Ni-base superalloy Waspaloy. A 3D finite element model was developed to predict average grain size and peak temperature as responses. The linear friction welding parameters consisted of oscillation amplitude, oscillation frequency, and applied pressure. Initially, the evolution of the average grain size as a function of the most influential process parameters was subsequently modeled based on the Johnson-Mehl-Avrami-Kolmogorov recrystallization model and were then validated with experimental results. Then, D-optimal design of experiments and analysis of variance were conducted to determine the most influential process parameters that affect the average grain size and peak temperature of the welded joint. Thereafter, response surface method was employed to obtain the regression models of the responses. The analysis of variance demonstrated that the P-value of the regression models was smaller than 5% and R2, Radj2, and RPred2 were between 87% and 97%, which showed that the predictive regression models of PT and AGS can be used with a high level of confidence. The regression models were then validated by selecting two extra LFW tests in the space of the DoE. The optimum values of the welding parameters were determined to minimize the responses. The multi-criteria optimization analysis showed that both average grain size and peak temperature were more dependent on pressure than oscillation amplitude and frequency. The developed finite element and regression models can be utilized as a predictive tool for the design of joining industrial components, which minimize expensive and time-consuming experimental tests and measurements.

High-strength steels are pre-heated in gas-fired furnaces before undergoing the open-die forging process. This process increases thermal oxidation on steel surfaces, affecting the interfacial friction between ingot and anvils during deformation. Two medium carbon high-strength steels with different nickel contents were oxidized, and the mechanical characteristics of oxide layers were investigated by micro and nano-indentation methods. It was found that the formed layers on high nickel steel had lower Young modulus and hardness compared to the steel with lower nickel. Finite element modeling and ring tests were used to assess oxide layers' effect on interfacial friction during deformation. The results demonstrated that oxide layers' formation decreased the interfacial friction and deformation load, acting as lubricants at high temperatures.

Ausforming treatments are thermomechanical treatments that consist in plastically deforming a fully austenitized steel, usually leading to either a bainitic or a martensitic microstructure. The effects of the mentioned previous deformation have been mainly studied under compression conditions. However, as widely known, many large-scale processes do not only require the application of deformation under a single mode. For that reason, it is important to assess whether different deformation modes could induce similar effects on the final microstructure. In this work, the effect of the deformation mode was analyzed in a medium carbon high silicon steel. Samples were deformed under compressive and tensile stresses at different temperatures and subsequently subjected to isothermal holding steps in the bainitic range for prolonged times. The final microstructures consisted of bainitic ferrite and retained austenite, where the bainitic ferrite was formed at different stages: a certain fraction was dynamically formed during the deformation step, while the remaining fraction was formed during the isothermal holding. The study of the changes in length observed during these treatments enabled to understand both phase transformations, while the analysis of the final microstructures by different characterization techniques, such as X-Ray Diffraction and Scanning Electron Microscopy, enabled to better understand the effect of the deformation mode at different levels. It was proved that tensile ausforming led to more rapid and intense strain induced transformations than compression ausforming. Moreover, results showed that ausforming led to anisotropic structures, regardless of the deformation mode, where bainitic ferrite plates were aligned with respect to the deformation direction. The effect of the deformation mode on the bainitic ferrite plate thickness, the volume fractions of the different phases, several crystallographic parameters and hardness is also discussed.

This study presents a novel and thorough approach to comprehending and simulating the DRX process while hot compressing steel. To achieve this goal, we studied the high-temperature deformation behavior of a medium-carbon steel through hot compression testing on a Gleeble-3800 thermomechanical simulator over a broad range of strains, strain rates, and temperatures. We also employed an artificial neural network (ANN) to model the thermo-visco-plastic behavior with a flow law. The precision of quantifying the DRX volume fraction is dependent on critical conditions, which are essential for both analytical model evaluation and numerical implementation in finite element software. This study proposes a second ANN, serving as a universal approximator, to fit the data required for DRX critical condition calculations, whereas the Johnson–Mehl–Avrami–Kohnogorov (JMAK) model served as an analytical tool to estimate the DRX volume fraction, which underwent validation through experimental measurements. A numerical implementation of the JMAK model was conducted in ABAQUS software and compared against experimental data by means of microstructure analysis. The comparison revealed a strong correlation between the simulation and experiment. The study investigated the impact of temperature, strain, and strain rate on DRX evolution. The findings showed that DRX increases with rising temperature and strain but decreases with increasing strain rate.

Gas tungsten arc welding (GTAW) is commonly used for joining pipelines; however, it often leads to discoloration in the heat-affected zone (HAZ). In this study, 316L pipes were welded with different concentrations of oxygen present in the argon purge gas during welding. The objective of this study was to investigate the effect of oxygen concentration in the protective gas on the pitting corrosion resistance of welded pipes. The experimental results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas resulted in an increase in pitting corrosion resistance until a critical value, beyond which the resistance decreased. The results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas increased the pitting corrosion resistance until a critical value, beyond which the resistance decreased due to the formation of iron oxide. This study provides valuable insights for improving the corrosion resistance of welded pipes in the oil and gas industry.

The stochastic nature of tool wear during wood machining, owing to the dynamic properties of the biological material and its dependence on various factors, has raised significant industrial and research concerns in recent years. Explicitly, the tool wear is a product of the interaction between wood properties (such as hardness, density, and contamination level) and machining parameters (such as cutting speed, feed rate, and rake angle) alongside ambient conditions (such as temperature and humidity). The objective of this review paper is to provide an overview of recent advancements in the field of wood machining. To begin with, it highlights the important role of wood properties and ambient conditions influencing tool wear. Furthermore, the paper examines the various mechanisms involved in the wood-machining process and discusses their cost implications from an industrial perspective. It also covers technological advancements in the characterization of tool wear and explores the relationship between this parameter and other machining variables. It provides critical and analytical discussions on various methods for enhancing tool wear, including heat treatment, cryogenic treatment, thermochemical treatment, coating deposition, and hybrid treatments. Additionally, the paper incorporates statistical analysis to achieve two objectives. Firstly, it aims to identify the most significant wood property that affects tool wear and establish the correlation between this parameter and wood properties. Secondly, it investigates the effect of heat treatment parameters and carbide characteristics on tool wear as well as their correlation. Lastly, the review provides recommendations based on relevant literature for prospective researchers and industrial counterparts in the field. These recommendations aim to guide further exploration and practical applications in the subject matter.

The influence of stacking patterns, through the different spacer and skid sizes, on the transient temperature distribution uniformity of large-size forgings in a 112-m3 electrical heat treatment furnace was investigated by conducting CFD simulations and real-scale experimental validation. A 3D CFD model of the electrical furnace was generated, including a heat-treating chamber, axial flow fans, large size blocks, skids, and spacers. Real-scale temperature measurements on instrumented test blocks during the heat treatment process were carried out to validate the CFD simulations. Results indicated that the CFD model was capable enough to determine the transient temperature evolution of the blocks with a maximum average deviation of about 6.62% compared to the experimental measurements. It was found that significant temperature non-uniformities of up to 379 K on the surfaces of the blocks due to the non-optimum stacking pattern were experienced by the blocks. Such non-uniformities could be reduced between 24% to 32% if well-adapted spacer and skid sizes were used in the stacking configurations. Based on simulation results and experimental validation work, optimum spacer and skid sizes for uniform temperature distribution were proposed for different stacking patterns.

In the present work, a critical analysis of the most-commonly used analytical models and recently introduced ANN-based models was performed to evaluate their predictive accuracy within and outside the experimental interval used to generate them. The high-temperature deformation behavior of a medium carbon steel was studied over a wide range of strains, strain rates, and temperatures using hot compression tests on a Gleeble-3800. The experimental flow curves were modeled using the Johnson–Cook, Modified-Zerilli–Armstrong, Hansel–Spittel, Arrhenius, and PTM models, as well as an ANN model. The mean absolute relative error and root-mean-squared error values were used to quantify the predictive accuracy of the models analyzed. The results indicated that the Johnson–Cook and Modified-Zerilli–Armstrong models had a significant error, while the Hansel–Spittel, PTM, and Arrhenius models were able to predict the behavior of this alloy. The ANN model showed excellent agreement between the predicted and experimental flow curves, with an error of less than 0.62%. To validate the performance, the ability to interpolate and extrapolate the experimental data was also tested. The Hansel–Spittel, PTM, and Arrhenius models showed good interpolation and extrapolation capabilities. However, the ANN model was the most-powerful of all the models.

Abstract In the present study, the effect of homogenization and solution treatment times on the elevated-temperature (650 °C) mechanical properties and the fracture mechanisms of Inconel 718 (IN718) superalloy fabricated by laser powder bed fusion (LPBF) was investigated. Homogenization times between 1 and 7 h at 1080 °C were used, while solution treatments at 980 °C were performed in the range from 15 to 60 min. The as-printed condition showed the lowest strength but the highest elongation to failure at 650 °C, compared to the heat-treated conditions. After heat treatments, the strength of the IN718 alloy increased by 20.3–31% in relation to the as-printed condition, depending on the treatment time, whereas the ductility decreased significantly, by 67.4–80%. Among the heat treatment conditions, the 1 h homogenized conditions at 1080 °C (HSA1 and HSA2) exhibited the highest strength and ductility due to the combined effects of the precipitation hardening and sub-structural changes. Further increases in the homogenization time to 4 and 7 h led to a decrease in the strength and significant ductility loss of the LPBF IN718 due to the considerable annihilation of the dislocation tangles and a greater precipitation of coarse MC carbide particles. Furthermore, it was found that the solution treatment duration had a crucial influence on the mechanical properties at 650 °C due to the increase in the grain boundary strength through the pinning effect of the intergranular δ-phase. In addition, the fracture mechanism of the LPBF IN718 was found to be dependent on the heat treatment time. Finally, this investigation provides a map that summarizes the effect of homogenization and solution treatment times on the high-temperature mechanical behavior of LPBF IN718 by relating it to the corresponding microstructural evolution. This effort strives to assist in tailoring the mechanical properties of LPBF IN718 based on the design requirements for some specific applications.

It has been well established that austenite can partially transform into ferrite during thermomechanical processing. The laboratory-scale strip and plate rolling simulations in the literature suggest that both forward and backward dynamic transformation (DT) can occur above the equilibrium Ae3 temperature. In this work, a five-pass Steckel mill rolling schedule (isothermal deformation) of an X70 high Nb steel was simulated using a torsion testing machine. Four different roughing schedules with a strain of 0.4 per pass were employed at 1100 °C before the application of finishing passes. A total of five finishing passes were simulated at 900 °C with pass strains of 0.3, strain rate of 1.0 s−1, and interpass time of 10 s, followed by isothermal holding varying from 1 to 270 s. The level of the flow curves depicted activation of softening phenomena, which was shown to be the formation of DT ferrite by means of optical and scanning electron microscopy images. The volume fraction of DT ferrite increases with increasing the number of roughing passes due to retained work hardening. Moreover, the DT ferrite retransforms back into austenite during the 10 s pass interval and holding after last strains, as shown by phase fraction measurement before and after each pass. Thus, the interpass time and holding intervals after the simulations play a significant role in reducing the amount of ferrite after the process. It seems that the presence of Nb in the alloy affects both the forward and backward transformation. The present investigation can be used to estimate the amount of formed and retransformed ferrite during Steckel mill operations in order to have a better metallurgical understanding of the process. This may result in better dimensional and quality control during the manufacturing of X70 pipeline steels.

Open-die forging is a critical step in the manufacture of large numbers of components used in the transportation and energy industries. Dynamic recrystallization, dynamic transformation, and dynamic precipitation take place during the hot deformation process and significantly affect microstructure conditioning, which ultimately influences the service properties of the component. In the present work, using a Gleeble 3800 thermomechanical simulator, the open-die forging of a large-size ingot made of a modified AISI 6140 medium carbon high-strength steel is investigated. Deformation temperatures ranging from 950°C to 1,250°C and strain rates ranging from 0.01 to 1 s−1, representative of the actual process, are considered in the analysis. The generated true stress–true strain curves are used as a basis for the development of a constitutive model predicting the occurrence of softening and strengthening phenomena as a function of thermomechanical conditions. The corresponding activation energy is determined to be about 374 kJ mol−1 and is compared against the values reported in the literature for other high-strength steels. Dynamic recrystallization kinetics is studied using the t50 model, and the influence of temperature and strain rate is quantified and discussed. The interaction between dynamic precipitation and dynamic recrystallization is discussed, and the deformation conditions under which such interactions occur are determined. The thermomechanical results are validated by microstructure examination, including laser confocal microscopy, field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy. The present study focuses on reproducing the deformation cycle applied during the open-die forging process of a vanadium-containing high-strength steel used in the industry with special attention to the interaction between dynamic recrystallization and precipitation processes.

The effect of the hot top height on the formation of positive and negative macrosegregation patterns, the ingot quality, and the material yield during solidification of a 12 MT cast ingot made of a Cr-Mo-low alloy steel was investigated. A 3D numerical simulation of the process was conducted using finite element modeling. A full-size 12 MT ingot was cut off from its center in the longitudinal direction, and a large cross-section was sliced into small samples. The chemical mapping of all the elements in the steel composition was obtained for all samples and compared with the model predictions for validation purposes. The influence of the increase in hot top height on the liquid metal velocity field, size and shape of vortexes, cooling rate of the liquid, and liquidus temperature was determined. Results revealed that increasing the hot top height by 165 mm increased the solidification time, fluid velocity in regions including the hot top and ingot bottom, and decreased the local liquidus temperature. The combination of all the above resulted in an overall decrease in positive and negative macrosegregation of more than 6% and an increase in ingot quality. The results are interpreted based on the interactions between the transport of solute and heat coupled with the flow driven by thermo-solutal convection and shrinkage-induced flow.

The bainitic ferrite plate thickness is the main parameter that controls the strength of this type of microstructures. Such thickness has been proved to mainly depend on the austenite yield strength, the driving force for the transformation and the transformation temperature. However, no research has focused on how these parameters evolve throughout the transformation and how this evolution can affect the outcome. In this study, thermal and thermomechanical treatments have been performed in three selected steels. The treatments have been designed in such a way that all the mentioned parameters are comparable, aiming to obtain similar microstructures in terms of bainitic ferrite plate thickness. However, significant differences have been found among the microstructures, with variations in plate thickness larger than 100 nm. These results indicate that there might be other factors that take part in the scale of bainitic microstructures. To explain these differences and based on the kinetics of the transformation and on the carbon content of austenite at the end of the transformation, a possible explanation has been proposed.

Reliable inspection of large steel forgings is a significant problem across multiple industries. When the dimensions of forgings are at least 1000 mm in each direction, ultrasonic phased array inspection becomes difficult because conventional probes are not designed to transmit and focus acoustic energy over such large distances. Using simulations and experiments, this article aims to discuss the possibilities and limitations of phased array imaging of large forged steel ingots. Simulations were used to design a transducer based on the reflected amplitude, as well as the lateral and axial resolutions of defects in a 1000 mm thick block. It was shown that when limiting the aperture to allow easy handling in an industrial inspection setting, the lateral resolution and the reflected amplitude were the main limitations. Increasing the element width maximizes the energy transmitted into the material, but it also moves elements away from each other, thus reducing the lateral resolution. Based on the simulations, an experimental phased array transducer was manufactured with eight elements of 9.25 × 22.5 mm. The probe was used to perform measurements and generate total focusing method images of three different at a depth of 370 mm in a 776 mm forged steel block.

In the present work, the influence of filling rate on macrosegregation in a 40-Metric Ton (MT) ingot of a high-strength low-carbon steel was studied using finite element (FE) simulation. The modelling of the filling and solidification processes were realized with a two-phase (liquid-solid) multiscale 3D model. The liquid flow induced by the pouring jet, the thermosolutal convection, and the thermomechanical deformation of the solid phase were taken into consideration. Two filling rates were examined, representing the upper and lower manufacturing limits for casting of large size ingots made of high strength steels for applications in energy and transportation industries. The evolution of solute transport, as well as its associated phenomena throughout the filling and cooling stages, were also investigated. It was found that increasing the filling rate reduced macrosegregation intensity in the upper section, along the centerline and in the mid-radius regions of the ingot. The results were analyzed in the framework of heat and mass transfer theories, liquid flow dynamics, and macrosegregation formation mechanisms.

The present research work aimed to study the effects of cutting environments and conditions on tool wear and residual stresses induced by orthogonal cutting of AA6061-T6. Cutting environments included dry- and flood-coolant modes and cutting conditions consisted of cutting speed and feed rate. A 2D finite element (FE) model was developed to predict tool wear and residual stresses and was validated by experimental measurements including machining forces, tool wear, and residual stresses. This was obtained by exploring various magnitudes of the shear friction factor and heat transfer coefficient and choosing proper coefficients using the calibration of the predicted results with the measured ones. The experimental results showed that the effect of cutting environment including dry and flood-coolant modes was negligible on machining forces. The experimental investigation also demonstrated that increasing feed rate raised machining forces, tool wear and residual stresses in both cutting environments. Low Speed Cutting (LSC) led to the highest value of tool wear and High Speed Cutting (HSC) provided the lowest values of resultant machining forces and residual stresses in both modes. Flood-coolant mode reduced tool wear and slightly decreased tensile residual stresses in comparison with dry mode. As a result, low feed rate and high-speed cutting under flood-coolant mode were proposed in order to improve tool wear and residual stress in orthogonal cutting of AA6061-T6.

Comprehensive unsteady analysis of large size forged blocks heating characteristics in a gas-fired heat treatment furnace was carried out employing experimentally measured temperatures and computational fluid dynamics (CFD) simulations. Heat and fluid flow interactions, consisting of turbulence, radiation and combustion, were simultaneously considered using k-ε, DO and EDM models in a three dimensional CFD model of the furnace, respectively. Applicability of the S2S radiation model was also evaluated to quantify the effect of participating medium and radiation view factor in the radiation heat transfer. Temperature measurements at several locations of an instrumented large size forged block and the furnace chamber were performed. A maximum deviation of about 7% was obtained between the model predictions and the experimental measurements. Results showed that despite the unloaded furnace had uniform temperature distribution, after loading, product surfaces experienced different heating rates, resulting in temperature differences up to 200 K. Findings were correlated with furnace geometry, vortical structures and flow circulations around the workpiece. Besides, S2S model demonstrating reliable results highlighted the importance of radiation view factor optimization in this application. The study could directly be employed for optimization of the heat treatment process of large size steel components. Keywords: Heat treatment, CFD simulation, Gas-fired furnace, Temperature measurement, Heating uniformity, Radiation modeling

In this study, a new method is developed to predict an accurate convective heat transfer coefficient (HTC) during quenching of large size steel blocks, using a combination of 3D Finite Element (FEM) simulations and a progressive artificial neural network (ANN).The HTC profile of the first inputs used for FEM simulations were acquired from the literature to calculate the cooling temperature profiles at specific locations. The training of the ANN was set up between HTCs and their corresponding FEM-calculated temperature. Experimental validation was carried out by instrumenting a large size forged steel block during the quench process. The experimental cooling curves were used for validation of the FEM simulation, as well as for the prediction of new HTCs by simulating the ANN. Results show that the proposed method provides progressively more accurate predictions than the existing ones reported in the literature.A mean absolute percentage error (MAPE) of 1.47% was found between experimental and calculated cooling curves for the predicted HTC, further demonstrating a better prediction ability of the proposed method. Keywords: Heat transfer coefficient of steel quenching large forged blocks, FEM simulation, Artificial Neural Network, TTT, Phase transformation

In the present study, multi-objective optimization is employed to develop the optimum heat treatments that can achieve both high-mechanical performance and non-distinctive crystallographic texture of 3D printed Inconel 718 (IN718) fabricated by laser powder bed fusion (LPBF). Heat treatments including homogenization at different soaking times (2, 2.5, 3, 3.5 and 4 h) at 1080 °C, followed by a 1 h solution treatment at 980 °C and the standard aging have been employed. 2.5 h is found to be the homogenization treatment threshold after which there is a depletion of hardening precipitate constituents (Nb and Ti) from the γ-matrix. However, a significant number of columnar grains with a high fraction (37.8%) of low-angle grain boundaries (LAGBs) have still been retained after the 2.5 h homogenization treatment. After a 4 h homogenization treatment, a fully recrystallized IN718 with a high fraction of annealing twins (87.1%) is obtained. 2.5 and 4 h homogenization treatments result in tensile properties exceeding those of the wrought IN718 at both RT and 650 °C. However, considering the texture requirements, it is found that the 4 h homogenization treatment offers the optimum treatment, which can be used to produce IN718 components offering a balanced combination of high mechanical properties and adequate microstructural isotropy.

The severe deformation and temperature paths in the stir zone, also called weld nugget, of friction stir welded joints result, at very local levels, in significant microstructural variations, such as major differences in grain size or precipitation. One of the most common features of friction stir welds is the presence of successive material layers, known as onion rings; however, little data is available on the mechanical properties of the different regions of the weld nugget, and particularly within the onion ring bands. Such information becomes very important for the integrity of large size friction stir welded structures. In the present study, a comprehensive characterization of onion rings produced during friction stir welding of a 6082-aluminum alloy was carried out. Advanced techniques such as in-situ SEM nanoindentation, EBSD, and high-resolution EDS were used to validate and compare the characteristics of the different bands in the onion rings. The analyses consisted of quantifying variations in grain size, precipitate composition and distribution, crystallographic orientations, and mechanical properties in each band. Furthermore, the tensile strengths of different regions of the weld nugget were evaluated using shear punch testing and correlated with those for the onion ring region in order to determine the impact of the presence of onion rings on weld nugget mechanical properties. The main difference between the alternate bands in the onion ring was found to be due to the difference in their grain size, misorientation, and precipitate content. It was also observed that the bands originate from the base metal and stir zone successively due to the nature of the stirring process, which pulls BM into SZ. Comparison of the shear punch testing results in different regions of the nugget revealed that, in spite of having local differences in the hardness of alternate bands in the onion ring, the presence of onion rings has no significant impact on the deterioration of the mechanical properties of the weld nugget.

To meet the requirements for high-performance products, the aerospace industry increasingly needs to assess the behavior of new and advanced materials during manufacturing processes and to ensure they possess adequate machinability, as well as high performance and an extensive lifecycles. Over the years, industrial research works have focused on developing new alloys with an increased thermal conductivity as well as increased strength. High silicon content aluminum (Al–Si) alloys, due to their increased thermal conductivity, low coefficient of thermal expansion, and low density, have been identified as suitable materials for space applications. Some of these applications require the use of intricate parts with tight tolerances and surface integrity. These challenges are often tied to the machining conditions and strategies, as well as to workpiece materials. In this study, experimental milling tests were performed on a rapidly solidified (RS) Al–Si alloy with a prominent silicon content (over 50%) to address challenges linked to material expansion in deep space applications. The tests were performed using a polycrystalline cubic boron nitride (PCBN) tool coated with amorphous diamond to reduce tool wear, material adhesion, surface oxidation, and particle diffusion. The effects of cutting parameters on part surface roughness and microstructure were analyzed. A comparative analysis of the surface with a conventionally utilized Al6061-T6 alloy showed an improvement in surface roughness measurements when using the RS Al–Si alloy. The results indicated that lower cutting speed and feed rate on both conventional and RS Al–Si alloys produced a better surface finish. Reduced vibrations were also identified in the RS Al–Si alloy, which possessed a stable cutting time at low cutting speeds but only displayed notable vibrations at cutting speeds above 120 m/min.

In the present study, Inconel 718 (IN718) superalloy fabricated by laser powder bed fusion (LPBF) has been characterized focusing on the effect of both homogenization and solution treatment time on grains structure, crystallographic texture, precipitates formation/dissolution and material hardness. For this purpose, a heat-treatment time window with a wide range of soaking times for both treatments was established aiming to develop the optimal post-treatment conditions for laser powder bed fused IN718. It was found that the as-printed IN718 is characterized by very fine columnar/cellular dendrites with Laves phase precipitating at the grain boundaries as well as inter-dendritic regions, which differs from the microstructure of wrought and cast materials and requires special heat-treatment conditions different from the standard treatments. The results reveal that the relatively short homogenization treatment at 1080 °C for 1 h was not enough to significantly change the as-printed grain structure and completely dissolve the segregates and Laves phase. However, a completely recrystallized IN718 material and more Laves phase dissolution were obtained after homogenization treatment for 4 h. A further increase in time of the homogenization treatment (7 h) resulted in grain growth and coarsening of carbides precipitates. The solution treatment time at 980 °C did not cause noticeable changes in the crystallographic texture and grain structure. Nevertheless, the amount of δ-phase precipitation was significantly affected by the solution treatment time. After applying the heat-treatment time window, the hardness increased by 51–72% of the as-printed condition depending on the treatment time due to the formation of γ′ and γ″ in the γ-matrix. The highest material hardness was obtained after 1 h homogenization, whereas the prolonged time treatments reduced the hardness. This study provides a comprehensive investigation of the post heat-treatments of the laser powder bed fused IN718 that can result in an optimized microstructure and mechanical behavior for particular applications.

Inconel 718 (IN718) superalloy samples fabricated by selective laser melting (SLM) were submitted to different heating cycles and their microstructural characteristics were investigated. The selected heating rates, ranging from 10 °C/min to 400 °C/s, represent different regions in the heat-affected zone (HAZ) of welded additively manufactured specimens. A combination of differential thermal analysis (DTA), high-resolution dilatometry, as well as laser confocal and electron microscopy were used to study the precipitation and dissolution of the secondary phases and microstructural features. For this purpose, the microstructure of the additively manufactured specimen was investigated from the bottom, in contact with the support, to the top surface. The results showed that the dissolution of γ″ and δ phases were delayed under high heating rates and shifted to higher temperatures. Microstructural analysis revealed that the Laves phase at the interdendritic regions was decomposed in specific zones near the surface of the samples. It was determined that the thickness and area fraction of these zones were inversely related to the applied heating rate. A possible mechanism based on the influence of heating rate on Nb diffusion in the interdendritic regions and core of the dendrites is proposed to interpret the observed changes in the microstructure.

The impact of microsegregation models on thermophysical properties and solidification behaviors of a high strength steel was investigated. The examined microsegregation models include the classical equilibrium Lever rule, the extreme non-equilibrium Scheil-Gulliver, as well as other treatments in the intermediate regime proposed by Brody and Flemings, Clyne and Kurz, Kobayashi and Ohnaka. Based on the comparative analyses performed on three representative regions with varied secondary dendrite arm spacing sizes, the classical equilibrium Lever rule and non-equilibrium Scheil scheme were employed to determine the thermophysical features of the studied steel, using the experimentally verified models from literature. The evaluated thermophysical properties include effective thermal conductivity, specific heat capacity and density. The calculated thermophysical data were used for three-dimensional simulation of the casting and solidification process of a 40 metric ton steel ingot, using FEM code Thercast®. The simulations captured the full filling, the thermo-mechanical phenomena and macro-scale solute transport in the cast ingot. The results demonstrated that Lever rule turned out to be the most reasonable depiction of the physical behavior of steel in study in large-size cast ingot and appropriate for the relevant macrosegregation simulation study. The determination of the model was validated using the experimentally measured top cavity dimension, the thermal profiles on the mold outside surface by means of thermocouples, and the carbon distribution patterns via mass spectrometer analysis.

A five-pass torsion simulation of the roughing passes applied during hot plate rolling was performed in the single-phase austenite region of a Nb-microalloyed steel under continuous cooling conditions. The deformation temperatures were approximately half-way between the Ae3 and the delta ferrite formation temperature (i.e., 250 °C above the Ae3) in which the free energy difference of austenite and ferrite is at maximum. The microstructures in-between passes were analyzed to characterize and quantify the occurrence of deformation-induced dynamic phase transformation. It was observed that about 7% of austenite transforms into ferrite right after the final pass. The results are consistent with the calculated critical strains and driving forces which indicate that dynamic transformation (DT) can take place at any temperature above the Ae3. This mechanism occurs even with the presence of high Nb in the material, which is known to retard and hinder the occurrence of DT by means of pinning and solute drag effects. The calculated cooling rate during quenching and the time–temperature–transformation curves of the present material further verified the existence of dynamically transformed ferrite.

High-speed blow forming (HSBF) is a new technology for producing components with complex geometries made of high strength aluminum alloy sheets. HSBF is considered a hybrid-superplastic forming method, which combines crash forming and gas blow forming. Due to its novelty, optimization of the deformation process parameters is essential. In this study, using the finite element (FE) code ABAQUS, thinning of an aluminum component produced by HSBF under different strain rates was investigated. The impact of element size, variation of friction coefficient, and material constitutive model on thinning predictions were determined and quantified. The performance of the FE simulations was validated through forming of industrial size parts with a complex geometry for the three investigated strain rates. The results indicated that the predictions are sensitive to the element size and the coefficient of friction. Remarkably, compared to a conventional power law model, the variable m-value viscoplastic (VmV) model could precisely predict the thickness variation of the industrial size component.

The effect of filling velocity on positive macrosegregation in large size steel ingots was studied. Macrosegregation and macro/microstructures were characterized on the hot-tops and a portion of the upper section of two ingots. The measurements revealed that segregation features in the two ingots varied as a function of the alloying elements, and that the severity of positive macrosegregation in the casting body was reduced when the filling rate was increased. It was also found that at the higher filling rate, grain morphologies in the first solidified zones of the ingot changed from columnar to equiaxe, and secondary dendrite arm spacing (SDAS) became slightly smaller in the intermediate and final solidified zones. The experimental findings were analyzed in the framework of diffusion and convection-controlled solidification, as well as liquid metal flow theories. The solute dependence of segregation features was related to the difference in the solid-liquid partition coefficient and diffusion capability of each element in the liquid iron. Calculation of Reynolds numbers (Re) during the filling process, for both ingots, showed that higher filling velocity caused more instable movement of the liquid metal in the initial solidification stage, resulting in the modification of grain morphology, as well as accelerated solidification rate.

The effect of isothermal tempering on retained austenite decomposition and carbide precipitation were investigated in a medium-carbon low-alloy bainitic steel. High-resolution dilatometry was used to perform isothermal tempering at 350 °C, 550 °C and 600 °C for different holding times up to 16 h. The decomposition of retained austenite, morphology and composition of carbides were investigated by analyzing the dilatometric curves and were confirmed through scanning and transmission electron microscopy observations. The decomposition behavior of retained austenite varied significantly as a function of the tempering temperature with a full decomposition observed at 600 °C. It was also found that by increasing the tempering temperature from 550 °C to 600 °C, carbides precipitate approximately twice as fast, and evolve from M3C type to Cr7C3 and Cr23C6 after 16 h of tempering at 600 °C.

In this paper, water quenching of large ingots was simulated using FORGE NxT 1.1® Finite Element code. Simulations were carried out for as-forged medium-carbon low-alloy steel. A novel method is proposed to simulate the different parts of a large size forged block with different chemical compositions and grain sizes using the multiple materials method. The effects of macrosegregation, grain size variation and cooling rate on phase distribution through the volume of the forged block were investigated. The delay in transformation kinetics, which is due to the effect of grain size variation and carbon content, was analyzed. Results show that macrosegregation and grain size variations significantly influence transformation start points and the volume fraction of phases that are present in each location of the forged ingot. The proposed prediction method was validated using high-resolution dilatometry experiments and X-ray diffraction measurements to evaluate accurately the volume fraction of martensite, bainite and the percentage of retained austenite for each condition.

The double differentiation method overestimates the critical stress associated with the initiation of dynamic transformation (DT) because significant amounts of the dynamic phase must be present in order for its effect on the work hardening rate to be detectable. In this work, an alternative method (referred to here as the free energy method) is presented based on the thermodynamic condition that the driving force is equal to the total energy obstacle during the exact moment of transformation. The driving force is defined as the difference between the DT critical stress (measured in the single-phase austenite region) and the yield stress of the fresh ferrite that takes its place. On the other hand, the energy obstacle consists of the free energy difference between austenite and ferrite, and the work of shear accommodation and dilatation associated with the phase transformation. Here, the DT critical stresses in a C-Mn steel were calculated using the free energy method at temperatures ranging from 870 °C to 1070 °C. The results show that the calculated critical stress using the present approach appears to be more accurate than the values measured by the double differentiation method.

In this work, the microstructure, texture, phases, and microhardness of 45° printed (with respect to the build direction) homogenized, and hot isostatically pressed (HIP) cylindrical IN718 specimens are investigated. Phase morphology, grain size, microhardness, and crystallographic texture at the bottom of each specimen differ from those of the top due to changes in cooling rate. High cooling rates during the printing process generated a columnar grain structure parallel to the building direction in the as-printed condition with a texture transition from (001) orientation at the bottom of the specimen to (111) orientation towards the specimen top based on EBSD analysis. A mixed columnar and equiaxed grain structure associated with about a 15% reduction in texture is achieved after homogenization treatment. HIP treatment caused significant grain coarsening, and engendered equiaxed grains with an average diameter of 154.8 µm. These treatments promoted the growth of δ-phase (Ni3Nb) and MC-type brittle (Ti, Nb)C carbides at grain boundaries. Laves phase (Fe2Nb) was also observed in the as-printed and homogenized specimens. Ostwald ripening of (Ti, Nb)C carbides caused excessive grain growth at the bottom of the HIPed IN718 specimens, while smaller grains were observed at their top. Microhardness in the as-fabricated specimens was 236.9 HV and increased in the homogenized specimens by 19.3% to 282.6 HV due to more even distribution of secondary precipitates, and the nucleation of smaller grains. A 36.1% reduction in microhardness to 180.5 HV was found in the HIPed condition due to γ ″ phase dissolution and differences in grain morphology.

Phase transformations during non-isothermal tempering of bainitic or martensitic microstructures obtained after quenching of a medium-carbon low-alloy steel was studied. The microstructures correspond to different locations of an as-quenched large-sized forged ingot used as a die material in the automotive industry. High-resolution dilatometry experiments were conducted to simulate the heat treatment process, as well as to investigate different phenomena occurring during non-isothermal tempering. The microstructures were characterized using optical and scanning electron microscopy. Dilatometry analyses demonstrated that tempering behavior varied significantly from bainitic to martensitic microstructures. Retained austenite, which exists between bainitic ferrite sheaves, decomposes to lower bainite causing a remarkable volume increase. It was found that this decomposition finishes below 386 °C. By contrast, martensite tempering was accompanied with a volume decrease due to the decomposition of medium-carbon martensite to low carbon martensite and carbides.

The authors wish to make the following corrections to the main text in the published paper [1]. In this paper, the weight of CuCl2 should be changed from 5 mg to 5 g to provide accurate recipe for the IN718 etchant.[...]

3D printing results in anisotropy in the microstructure and mechanical properties. The focus of this study is to investigate the structure, texture and phase evolution of the as-printed and heat treated IN718 superalloy. Cylindrical specimens, printed by powder-bed additive manufacturing technique, were subjected to two post-treatments: homogenization (1100 °C, 1 h, furnace cooling) and hot isostatic pressing (HIP) (1160 °C, 100 MPa, 4 h, furnace cooling). The Selective laser melting (SLM) printed microstructure exhibited a columnar architecture, parallel to the building direction, due to the heat flow towards negative z-direction. Whereas, a unique structural morphology was observed in the x-y plane due to different cooling rates resulting from laser beam overlapping. Post-processing treatments reorganized the columnar structure of a strong {002} texture into fine columnar and/or equiaxed grains of random orientations. Equiaxed structure of about 150 µm average grain size, was achieved after homogenization and HIP treatments. Both δ-phase and MC-type brittle carbides, having rough morphologies, were formed at the grain boundaries. Delta-phase formed due to γ″-phase dissolution in the γ matrix, while MC-type carbides nucleates grew by diffusion of solute atoms. The presence of (Nb0.78Ti0.22)C carbide phase, with an fcc structure having a lattice parameter a = 4.43 Å, was revealed using Energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) analysis. The solidification behavior of IN718 alloy was described to elucidate the evolution of different phases during selective laser melting and post-processing heat treatments of IN718.

In the present paper, tool wear and the rate of wear during friction stir welding (FSW) of Ti-6Al-4V alloy are investigated. A conical tungsten carbide tool was used to produce butt-type friction stir welded joints in two-millimeter thick Ti-6Al-4V sheets. An original design of a movable pin allowed for the examination of the tool damage for each process condition. The influence of tool degradation on the quality of the welded joints and the damage brought to the microstructure are examined and discussed. For this purpose, optical and scanning electron microscopies as well as EDX analyses were used to examine the tool wear and the resulting macrostructures and microstructures. The type and nature of the defects are also analyzed as a function of FSW processing parameters. Important geometry and weight variations were observed on the pin and shoulder for all welding conditions, in particular when low tool rotation and travel speeds were used. Experimental results also show that the radial wear of the pin is not uniform, indicating the presence of important frictional temperature gradients through the thickness of the joint. The maximum wear was measured at a location of about one millimeter from the pin root center. Finally, tool rotation was determined as the most significant process parameter influencing both tool wear and microstructure of the joints.