The vapor film collapse that occurs in the quenching process is complicated and unstable, these affects the heat treatment quality and its distortion. In order to incorporate it into the MBD technology required these days, it is necessary to predict the quality of heat treatment by CAE, shorten the product development period. However, in the past day, in order to formulate the vapor film collapse on a simulation, it was necessary to perform a very large amount of computational calculation (CFD), because of a problem in computer resources and the model of vapor film collapse. In addition, this phenomenon has an complexity behavior of the phenomenon in iterative processing in mass production, which also complicates the calculation. The vapor film collapse phenomenon was visualized by using cellular automaton simulation its include the phenomena of "Vapor film thickness", "Flow disturbance", "Surface step of workpiece". In this study, the Markovian property of vapor film surface vibration was clarified, and the heat treatment deformation instability of ring-shaped parts due to it was predicted.

In the manufacture of steel products, heat treatment plays an influential role in the properties of the steel. During this process, several changes at the microstructure level take place to help achieve the desired properties. One such occurrence is the nucleation, growth, and coarsening of precipitates. Factors such as temperature and time can affect the type of precipitate, its shape, size, number density, etc. in the microstructure. These in turn affect the final mechanical properties. Knowledge of the precipitates formed can be a strategic step in further understanding the microstructure behavior and optimizing the heat treatment parameters.[br] This study focuses on 50CrMo4 martensitic steel with carbide precipitation. 50CrMo4 was subjected to a range of tempering process parameters, i.e., varying tempering temperatures and times. Carrying out detailed experiments to analyze the carbides over a wide range of process parameters is time-consuming and costly. In this case, a physics-based model of the precipitation is sensible to predict the behavior of the metal under a particular heat treatment process. A modeling approach such as JMA (Johnson-Mehl-Avrami) was used to determine parameters like the volume fraction of the carbides during isothermal holding while tempering. The kinetics of the carbides were successfully determined through modeling for a tempering time ranging from a few seconds to hours.[br] Scanning and transmission electron microscopy investigations coupled with image analysis provide experimental data for the carbides in the heat-treated specimens. The physics-based model results are validated using these experimental data. The model results are in accordance with the experimental results. The physics-based model combined with the available experimental data can provide results with increased accuracy. This prediction model provides an additional level of insight into the behavior of 50CrMo4 steel and the necessary heat treatment parameters.

Low pressure carburizing is attracting attention as a technology that can reduce CO₂ emissions because it uses less hydrocarbon gas than conventional gas carburizing. Industrial parts such as gears have different geometries such as tooth flanks, tooth roots, and tooth tops. Since the carbon diffusion field overlaps differently in each area, different carbon concentration profiles can be obtained in each area even with the same carburizing pattern. Therefore, it is of practical importance to estimate an accurate carbon concentration profile for each site for the design of parts such as gears.[br] It has been reported that the carbon concentration distribution at low pressure carburizing in case-hardening steel can be accurately estimated by the following method. The method is a combination of a local equilibrium calculation that takes into account the existence of two phases, austenite (γ-phase) as the matrix phase and cementite (θ-phase) as the precipitating phase, and a time evolution calculation of carbon diffusion, assuming that the carbon activity on the steel surface is 1 (a_C=1) as a boundary condition during the carburizing period. This method is a "Model for Diffusion dispersed System". The growth and disappearance of the θ-phase occur in a very small area, less than a few tens micrometers from the surface, and high spatial and temporal resolutions are required to reproduce them. In addition, when targeting an object with complex overlapping diffusion fields, such as a gear, the computational domain must be at least two-dimensional, and if high spatial resolution is applied to the entire area, the number of elements becomes enormous, making the method impractical in terms of efficiency and computation time. [br] This work investigates an efficient method for predicting 2D carbon concentration distribution assuming gears. To achieve both accuracy and computational time, numerical computations were performed using hierarchical grid refinement, which increases the resolution of the computational grid only where resolution is needed, and parallel computation using GPUs. The calculated and measured values are in good agreement, and it is now possible to efficiently perform carbon concentration distribution not only on the gear tooth flank but also on the tooth tops, tooth roots, and other areas with different geometries in this model. [br]

This study investigates the utilization of laser powder bed fusion for fabricating functionally graded parts using a novel maraging steel named Specialis^®. By manipulating the processing strategy involving single and synchronized dual laser exposures, along with remelting, graded parts are successfully produced. Both the as-built and heat-treated specimens exhibit hardness variations of up to 80 HV across distinct regions. Notably, a reversal of hardness levels occurs after heat treatment, with the originally harder as-built dual laser zone becoming the softest zone following the post heat treatment. This phenomenon is attributed to the early precipitation stage resulting in from the intrinsic heat treatment which occurs during the dual laser processing strategy, which leads to higher hardness in the dual laser as-built condition. However, upon aging, the peak hardness is attained uniformly across all regions. Thus, the higher proportion of austenite present in the dual laser zone, which was identified by means of x-ray diffraction and differential scanning calorimetry, lowers the hardness. Therefore, there is an intriguing shift regarding the area with the highest hardness. These findings offer innovative approaches and eliminate the necessity for complex and time- consuming intrinsic heat treatment steps. Instead, the manufactured parts can be efficiently furnace-hardened while retaining their graded properties. These findings facilitate the production of components with tailored hardness profiles, precisely suited for their intended applications. The versatility of additive manufacturing, combined with the unique capabilities of Specialis ^®, opens a new avenue for creating functionally graded parts with improved mechanical properties.

SUS316L stainless steel specimens were fabricated via selective laser melting, followed by stress relieving and solution treatments. Heat treatment conditions of the conventional materials were applied to the specimens. The mechanical properties, microstructure, and corrosion resistance properties of as-built and heat-treated specimens were evaluated. The pitting potential measurements showed that the corrosion resistance of the heat-treated specimens was lower than as-built specimens. Among the heat-treated specimens, no significant difference in corrosion resistance was observed. These results imply that further investigation of appropriate heat treatments is needed for the additively manufactured SUS316L stainless steel.

The patenting process is required to obtain the proper ductility and toughness of high carbon steel for subsequent cold forming by wire drawing or rolling. It is mainly used with lead medium for patenting treatment because the excellent heat transfer properties of lead achieve uniform temperature distribution. Replacing this process with technology that eliminates the use of hazardous lead presents challenges. In this study, our goal is to investigate the relationship between microstructure changes and mechanical properties according to patenting condition (isothermal temperatures and cooling rates) using mixed powder as an alternative to lead medium. After the austenitizing treatment, the microstructure, hardness and friction properties of patented specimens at three isothermal temperatures (460, 560, 660 °C) and three compressed air flow rates (10, 50, 100 l/min) were analyzed to examine the relationship between mechanical properties according to lamellar spacing in pearlite. As the isothermal temperature decreases or the air flow rate increases, not only the lamellar spacing of pearlite decreases, but also the bainite structure is easy to form, which improves the hardness and wear characteristics.

During heat quenching process, temperature transition, microstructure evolution and stress/strain interaction occur simultaneously at different scales. Establishment of a multi-field coupling model need deal with microstructure evolution, thermophysical parameters, and boundary conditions. The specific heat capacity and thermal conductivity of Cr12MoV were obtained using the synchronous thermal analyzer and laser thermal conductivity analyzer. The heat transfer coefficient model of nitrogen was obtained through inverse algorithm. Vacuum Gas Quenching and isothermal quenching were simulated by establishing suitable FEM models. The evolution process of temperature, microstructure, and stress/strain during the quenching process were analyzed. Microstructure evolution during quenching process is predicted successfully. Bainite/martensite multi-phase was formed during isothermal quenching process. The temperature gradient between the surface and center of the cold working die was reduced. The microstructure of samples was compared with FEM simulation results. The comparisons show that the simulation results are consistent with experimental results.

Low-temperature ion nitriding has an excellent performance in improving the surface hardness and wear-resistant of stainless steel by forming the nitriding layer, which can strike a balance between corrosion resistance and wear resistance. In the case of a common treatment temperature of 430°C, for example, after applying ion nitriding for 24 hours in this experiment, the surface hardness of stainless steel increased from 330-360 HV to 1250-1330 HV, and the thickness of the formed nitrided layer was approximately 11-15 μm. Since the nitriding process generated compressive stress on the surface of the material, the residual stress was measured from the surface of nitride layer to the substrate in thickness direction using the Pulstec μ-X360n Residual Stress Analyzer. The residual stress value decreased from -913MPa to -124MPa. When the nitriding temperature exceeded 450°C, the lattice expansion was caused by structural changes. This change would result in the generation of chromium nitride on the surface. The residual stress increased significantly, leading to the rupture of the nitrided layer on the surface. This behavior decreased the corrosion resistance. Furthermore, in this study, the effect of the nitrided layer on the abrasion and residual stresses was investigated. Here, the nitride layer was formed on the surface of 304 and 316 austenitic stainless in different temperatures and treatment times with fixed gas ratios.

A microstructural control for high Ti-rich TiAl was carried out using with Ti-41Al and Ti-45Al binary alloys. By a heat treatment, these alloys showed discontinuous coarsening reactions, forming second lamellar microstructures. However, formation temperature and morphology of second lamellar microstructures differed depending on Al composition.

Recent reports highlight the CoCrFeMnNi high-entropy alloy's (HEA) impressive tensile strength and ductility at low temperatures, but Cantor alloys, including CoCrFeMnNi, tend to exhibit lower hardness compared to typical steel. To address this, surface modification treatment is investigated as an effective method of enhancing Cantor alloys' hardness. This study focuses on varying temperatures with a Ni metal screen to optimize thickening the plasma-nitrided layer in sintered Cantor alloys. Additionally, it aims to assess nitrided layer properties through direct-current plasma nitriding (S-DCPN) treatment, varying the sintered HEA's temperature using a pure Ni screen. Gas-atomized CoCrFeMnNi HEA powder, ball-milled for 10 h, forms the sintered body. S-DCPN treatment is applied at 673-873 K for 15 h, gas pressure at 200 Pa (75% N₂-25% H₂). A pure Ni screen aids uniform heating and increased nitrogen supply. The nitrided samples undergo analyses including X-ray diffraction (XRD), microstructure observation, surface morphology inspection, hardness testing, glow discharge optical emission spectroscopy (GD-OES), corrosion testing, and wear testing. Observations reveal a black modified layer on the nitrided sample's surface, with an edge effect. Surface roughness and SEM images show increased roughness with higher nitriding temperatures. XRD identifies specific compounds, and expanded fcc is noted in the 673 and 723 K samples. After nitriding, HEA sample hardness significantly increases, with GD-OES revealing greater depth of dissolved nitrogen at higher nitriding temperatures.

This study investigates the effects of the treatment temperature and time on the S-DCPN (direct current plasma nitriding with screen) treatment using Ni screens. Austenitic stainless steel SUS304 is used as the substrate, and S-DCPN treatment is performed at treatment temperatures of 673, 723, and 773 K, treatment times of 4 and 16 h, gas pressure of 200 Pa, and treatment gas composition of 75% N₂ and 25% H₂. A Ni mesh is used as the Ni screen. The results of the S-DCPN treatment using a Ni screen on SUS304 after nitridation under each condition confirm that an expanded austenite (S phase) with supersaturated nitrogen solid solution is produced under all conditions, along with a nitrided layer. Ni deposits are formed on the sample surface under all conditions, as suggested by the X-ray diffraction patterns and optical microstructure investigations. The nitrided layer becomes thicker as the treatment temperature and time increase under all conditions. These results indicate that the nitridation efficiency improves upon using the Ni screen.

Induction surface hardening is mainly used in industrial applications to increase the lifetime of components with high efficiency. Improving the predictability of the process is essential for its further development. The current study presents an analysis of a finite element method for an indirect coupled electromagnetic thermal-mechanical simulation to investigate the inductive heating during surface hardening. In particular, the sensitivity of the coupling of electromagnetic and thermal-mechanical simulation was analyzed. An optimized time step was introduced, which reduces the simulation time without affecting the accuracy. More importantly, the study shows that a high time step only leads to small deviations in the resulting temperature profile, which simplifies the simulation of longer and more complex heat treatment strategies, especially for processes below the Curie temperature. Additionally, the results were compared with a commercial program that does not take phase transformations into account. In conclusion, it is possible to simplify simulations of electromagnetic processes by appropriate assumptions, so they are suitable for further applications.

This study investigates the differences between induction hardening and multiline laser surface hardening processes on AISI 4140 quenched and tempered steel to facilitate process selection based on resulting material properties. The microstructures, hardness, and residual stress profiles resulting from the two processes were analyzed, revealing different characteristics. Induction hardening demonstrates rapid processing and uniform hardening but exhibits negative aspects such as edge effects and depth limitations. In contrast, multiline laser surface hardening offers adaptability to different geometries. Due to tempering effects, a layered microstructure was noted with lower hardness in previously processed areas. Favorable compressive residual stresses were measured in the center of the induction-hardened sample, while tensile residual stresses were measured for the multiline surface-hardened sample. This study sheds light on the strengths and limitations of these two surface hardening techniques, providing insight into the selection of optimal processes for enhancing material properties.

Vanadium carbide (VC) coating has been widely used as wear-resistant hard coating on forging dies for its high hardness and good tribological property. In recent years, oxidation resistance is also required for hard coatings in addition to hardness and tribological property, as the processing conditions become more severe such as hot stamping, stamping of high tensile strength steel and processing with poor lubrication. Therefore, applying VC coating for such high-load processing is difficult due to its low oxidation resistance. For improving its oxidation resistance, Vanadium silicon carbide (VSiC) coating was developed by adding silicon (Si), an element that imparts oxidation resistance to the VC coating.
The VSiC coatings was deposited on HSS substrate using the PECVD (Plasma Enhanced Chemical Vapor Deposition) method. The composition, structure and hardness were investigated by using EPMA (Electron Probe Micro-Analyzer), XRD (X-ray Diffraction), Raman spectroscopy and nanoindentation. The oxidation resistance was evaluated by examining the changes in chemical composition and hardness after heating in an atmospheric environment. No significant change in composition and hardness was observed even after being heated to 800℃. This result shows VSiC coating has high oxidation resistance compared with that of VC coating.
Tribological properties of the VSiC coating were evaluated using the ball-on-disk test method with S45C ball. The results showed that VSiC coatings with lower carbon content had higher friction coefficients (≒0.8) and a larger amount of adhesions within the sliding tracks. On the other hand, as the carbon content increased, the friction coefficient decreased (<0.2), and simultaneously, the amount of adhesions within the sliding tracks decreased. The results of Raman spectroscopy for samples with higher carbon content showed the presence of amorphous carbon in the coating. Consequently, it is suggested that amorphous carbon in VSiC coating contributes to suppressing formation of adhesions and attaining excellent tribological property.

DLC (Diamond-Like-Carbon) providing a useful low friction coefficient, is especially suitable for various drive-line applications including automobile parts, but the value of this friction coefficient is often determined under a constant speed sliding environment. However, many of the sliding parts do not always operate at constant speed, hence it is necessary to consider motion from a stationary state. In this study, the effects of mechanical properties (hardness), varied by modification of each film structure, on static/dynamic friction coefficients were evaluated for DLC deposited by plasma-CVD and arc-PVD. A thrust cylinder type friction wear tester was used to measure each friction coefficient. The maximum frictional force at the initial stage of rotation was calculated to give the static friction coefficient, and the friction coefficient at a constant peripheral speed was defined as the dynamic friction force. From the results, satisfactory low coefficients of friction and a reduction in static friction force proved that DLC coating is useful for treatment of sliding parts in drive mechanisms. Furthermore, the film structure and mechanical properties of DLC have a large effect on static/dynamic frictional forces, and the study indicates the need to select the optimum DLC according to the application and expected sliding environment.

To investigate the effects of the number of layers on the mechanical properties of stainless steel, multilayer diamond like carbon (DLC) films with different numbers of layers were deposited after strengthening a stainless steel surface by forming a nitrided layer (S phase) on the surface through direct current plasma nitriding with screen (S-DCPN) treatment. Austenitic stainless steel SUS304 was used as the sample, and S-DCPN treatment was performed at a treatment temperature of 673 K, treatment time of 4 and 16 h, gas pressure of 200 Pa, and a treatment gas composition of N₂:H₂ = 3:1. After S-DCPN treatment, DLC (a-C:H) films with different multilayer structures were deposited using a high-frequency plasma chemical vapor deposition (CVD) system, to achieve a total film thickness of 1.2 μm. The results of this study show that the S-DCPN treatment strengthens the sample surface and improves the adhesion and durability of the DLC film. Further, with 673 K – 4 h nitriding + DLC, the sliding distance increased significantly compared to the untreated substrate, and 4-layers coating had the best durability.

Improving the sliding properties of plastic materials adds significant industrial value. Diamond-like carbon (DLC) is well known for its exceptional characteristics as a coating material, offering remarkable attributes such as low friction and high wear resistance. It has been the subject of extensive study. Therefore, this study attempts to investigate the effect of DLC coating on plastic materials. Among plastic materials, engineering plastics were selected as the base material because of their superior mechanical properties and heat resistance. However, because it is necessary to consider temperature when depositing films on plastic materials, DLC with different source gases was deposited via low- temperature treatment utilizing plasma chemical vapor deposition. After deposition, the effects of the low-temperature treatment and its effects on the adhesion, mechanical properties, and friction and wear properties of the DLC films to the plastic substrate were investigated. The results revealed that the deposition speed was independent of the processing temperature. Moreover, as the percentage of elements impeding carbon bonding in the raw deposition gas decreased, the resulting DLC film exhibited superior performance in terms of friction and wear resistance.

The adhesion resistance of PVD films on blasted substrates were investigated. For comparison, samples without blasting were also evaluated. In the PVD method, TiN, TiCN, CrN, AlTiN, and AlCrN were respectively deposited. A ball-on-disk friction tester was used to evaluate adhesion resistance. SUJ2, Al and Zn balls were used in the friction test. After the friction test, the wear marks of the specimens were observed with an optical microscope. The presence or absence of adhesion was determined by optical micrographs.
In SUJ2 balls, adhesion occurred in TiN blasted with SiC, CrN blasted with alumina and SiC, and AlCrN blasted with SiC. In Al balls, adhesion occurred in all the blasted specimens. The average friction coefficient of TiCN film without blasting treatment was as low as about 0.2, but the average friction coefficients of the other specimens were as high as about 0.6 to 0.7 due to the occurrence of adhesion. In the case of Zn balls, adhesion occurred in all films blasted with SiC. Specimens blasted with glass or alumina tended to have smaller sliding widths. For CrN and AlTiN, blasting treatment with glass or alumina improved the adhesion resistance to Zn.

Stainless steel is known to undergo pitting corrosion when it exposes to media solutions containing chloride ions. In this study, ZrTiAgN multilayer coatings were applied to the surface of 316L stainless steel using a cathodic arc deposition (CAD) process and the bias parameters were varied to explore the effect of different bias voltages (-60V, -120V, and -180V) on the coating microstructure and the corrosion behavior of the coated stainless steel. Two media containing chloride ions, NaCl and HCl solutions, were used for the corrosion tests. In addition, EPMA, XRD, and SEM were used to analyze the chemical composition, microstructure, and morphology of the coatings.
The experimental findings indicated that as the bias value increases, the silver (Ag) content decreases. The coatings consisted of a multilayer structure composed of ZrN and TiN phases, with only minimal amounts of amorphous Ag (0.04-0.1 at.%) doped into the film structure. All three different bias coatings exhibited well adhesion (HF1-HF2). In the corrosion test, the polarization test conducted with a NaCl solution revealed that the ZrTiAgN coating enhanced the corrosion resistance of 316L stainless steel. The specimens treated with a bias of -180V displayed the highest polarization resistance value, indicating the best corrosion resistance. Similarly, the ZrTiAgN coating significantly improved the corrosion resistance of 316L stainless steel in the HCl solution immersion test, with the best results observed in the bias -180V specimen. This outcome aligns with the findings from the polarization test.

In this study, the effects of the tube temperature and gas flow rate on diamond synthesis using tubular hot foil chemical vapor deposition (CVD) were investigated. CH₄ (concentration = 1%) and H₂ were employed as the process gases. The tube was heated using resistance heating at a temperature range of 1500°C–1650°C, and the H₂ gas flow rate was varied from 500 to 1000 SCCM. The film quality decreased with increasing the gas flow rate. The deposition rate increased with the tube temperature, achieving a maximum deposition rate of 13.5 μm/h at a temperature of 1650°C and a H₂ gas flow rate of 1000 SCCM. Thus, tubular hot foil CVD can be used to obtain diamond films at deposition rates higher than 10 μm/h.

Nitrocarburizing is a thermochemical process used to enhance wear-, corrosion- and fatigue resistance in steels in wide variety of applications. Due to the complex atmosphere and relatively high temperature, 540 – 580°C, many challenges are presented when attempting to monitor it and control for a specific outcome. Monitoring ammonia (NH₃) is of particular interest due to its strong correlation to the nitriding potential, which in turn can be related to the metallurgical outcome. Current methods to monitor NH₃ rely on two main methods: 1) extracting the furnace gas to a separate measuring station outside the furnace where NH₃ is measured, or 2) estimating NH₃ indirectly through measurements of N₂, H₂ and CO/CO₂. Risks associated with extractive methods pertains to the formation of salts that clog the extraction pipes, owning to water condensation. While estimating NH₃ from other gases avoid the risk of salt formation, there are concerns regarding the accuracy of these estimates. The present study evaluated an alternative measuring setup, using tunable diode laser absorption spectroscopy (TDLAS), which allowed for direct measuring of NH₃ content without extractive analysis. The study was conducted in an industrial environment, and the results obtained from TDLAS were compared to measurements done by Fourier transform infrared technique (FTIR) and estimates based on the furnace's hydrogen sensor. Overall, TDLAS showed good agreement with FTIR measurements, indicating its accuracy in directly measuring NH₃ content. Additionally, it was found that directly measured NH₃ deviated significantly from estimated NH₃. It is thus concluded that measured NH₃ should be preferred when controlling the furnace using nitriding potential. To this end, TDLAS can provide a cost-efficient method for measuring NH₃ directly in industrial environments.

Global attention is focused on carbon neutrality. In the future, new carburizing methods are required for sustainable and environmentally friendly heat treatment. To address this need, ultra-rapid carburization has been developed. This method is significantly faster than conventional carburization owing to the rapid temperature rise by induction heating and carburization above the eutectic temperature. This development considerably enhances the efficiency of the process. Previous studies have clarified the carburization reaction mechanism for ultra-rapid carburization, and verified that the reaction is rate-controlled by the decomposition of methane gas, the raw material. However, some problems must be solved for the industrial application of this technology. Therefore, we investigated a countermeasure against the coarsening of prior austenite grains caused by high-temperature treatment, and then considered and verified the method of setting the heat-treatment conditions. Consequently, we found that prior austenite grain size could be refined to approximately #9 by cooling after ultra-rapid carburization to form a single layer of martensite, and subsequent re-quenching. In addition, we calculated the optimal conditions that yielded a surface carbon concentration of 0.6 mass% and an effective hardened layer depth of 0.8 mm based on the carburization reaction mechanism and Fick's second law, and then calculated the amount of carbon diffusion in the steel. Finally, we verified our results experimentally.

The concentrated energy sources, such as intense pulsed electron beams (IPEB), to modify the surface properties of machine parts and tools allows flexible regulation of the structural-phase state of materials in a wide range. The current research aims to create a functional layer on the surface of L6 steel by subsequent electron beam processing (EBP) of a diffusion boride layers by the IPEB of a megawatt power level. The EBP of a diffusion layer based on boron and aluminum on L6 steel leads to the transformation of the layer by remelting and crystallization of the upper zone of the diffusion layer up to 220 µm deep. Meanwhile the thickness of the whole diffusion layer is 580-620 µm. The microstructure of the layer has become more compact (pores have disappeared) and the roughness has decreased. The maximum microhardness on the surface of the diffusion layer reaches 870 HV. The hardness distribution is uneven, which indicates alternation of hard and soft components in the layer, and lower hardness on the surface indicates predominantly aluminized zone. Microhardness of the modified layer after EBP has increased to 1400 HV.

Surface hardening treatments such as nitriding can improve the mechanical properties to extend the applicability of austenitic stainless steel (ASS) fine and precise machining. Improving these characteristics without changing the design and material is highly advantageous, particularly for medical and surgical instruments. In particular, an improved bending rigidity of medical injection needles is desirable because a small needle diameter reduces invasiveness. However, no method has yet been reported for improving the bending strength of ASS without reducing its corrosion resistance. It is known that the low-temperature nitriding and carburizing generated expanded austenite (S phase) that can be hardened while maintaining the corrosion resistance of austenitic stainless steel. It would be very beneficial if these techniques could be applied to thin pipes with a small diameter such as medical injection needles. In the present study, low-temperature active-screen plasma nitriding (ASPN) and active-screen plasma carburizing (ASPC) are applied to improve the bending rigidity of an ASS pipe with a small diameter.

Fine Particle peening is a method to obtain surface modification effects, such as fatigue strength improvement, by bombarding the work material with particles at high velocity. However, there are many factors that affect the surface modification effect, making it difficult to select the optimum conditions. The particle velocity and particle flight behavior have not been clarified due to the large number of flying particles in addition to the extremely high particle velocity. Therefore, in this study, in addition to air flow analysis inside and outside the nozzle, particle velocity analysis using the particle method was conducted. ANSYS was used for the airflow analysis, and Particle Works was used for the particle method. The nozzle diameter and nozzle - work distance were varied. The nozzle diameter was varied from 3 to 10 mm. The nozzle - work distance was 50, 100, and 150 mm. The pressure at the nozzle entrance was set to 0.2 MPa, and air flow analysis was performed under incompressible fluid conditions. The particle method used iron-based particles with a particle diameter of 100 μm as a model for analysis. The results of the airflow analysis showed that the potential core area increases as the nozzle diameter increases. This was attributed to the shear layer caused by the wall resistance inside the nozzle. Next, particle velocity analysis showed that particle velocity tended to increase with increasing nozzle diameter. In addition, it was found that the particle velocity increased with increasing nozzle - work distance. Next, the particle flight behavior was analyzed, and it was found that the particles accelerated most at the parallel part of the nozzle and continued to accelerate after the nozzle exit.

To improve the surface properties of magnesium alloys, shot peening was used to joined dissimilar metal foils. The joining of magnesium alloys with dissimilar metal foils was investigated to improve the surface properties. In the experimental method, the metal foils were pure titanium, pure copper, pure nickel, pure iron and stainless steel. The thickness of the metal foil was 0.2 to 0.4 mm. Shot peening was performed on a centrifugal shot peening machine. The shot media was cast steel with an average diameter of 1.0 mm. The peening velocity and peening time were 60 m / s and 10 s, respectively. After joining, no voids or cracks were observed at the joining interface. In bending test, the metal foil did not peel off even when the substrate was broken. In addition, the bondability of dissimilar metal foils was improved by heat treatment at 450 °C. Wear resistance was also improved by the joining of stainless steel foil. This method was effective for surface modification of magnesium alloys.

Conventionally, induction heating coils, the main components of induction hardening equipment, are manufactured using many technologies such as cutting, bending, and brazing in the process to completion. To avoid this time-consuming and costly method, we have applied metal additive manufacturing, which has recently attracted attention as a new manufacturing technology, to manufacturing induction heating coils. By metal additive manufacturing equipment using electron beam melting (EB-AM, shortly), we successfully fabricated pure copper moldings equivalent to oxygen-free copper C1020. Using this molding method, we manufactured two different types of coils, one with less brazing joints, and the other with a complicated inner cooling channel that was difficult for the conventional method. Comparing the results of induction hardening experiments on those coils and the coil manufactured by the conventional method, it was confirmed that the hardening property provided by the EB-AM coils was comparable to the coil of the conventional method. In addition, it was found that the EB-AM coil with less brazing joints showed less deformation after the induction heating process than the coil of the conventional method with many brazing joints. Also, temperature measurements and simulations on the coils during the induction heating process revealed the EB-AM coil showed lower temperature, smaller deformation, and little fluctuation of the air gap between the coil and the workpiece than the coil of the conventional method.

Funnel feeding tank and spiral pipe enable micro component evenly contact quenching oil and flow into system. Gas in the collecting tank blows micro component through filter so that won’t be stuck in the filter, also removes quenching oil. This design facilitates collecting rate and yield rate reach 95%.[br] The objective of this study is to evaluate the heat treatment processes of micro-precision components using a continuous heat treatment equipment. To conduct this heat-flux coupling analysis, specific computational fluid dynamic models were established based on the Cradle/scFLOW, a commercially available software. [br] To maximize the productivity during the continuous heat treatment process, the ultimate goal is to uniformly heat up these micro-precision components, such as up to 1173 K, in the shortest process cycle and maximum conveyer speed. Two major tasks including the construction of the furnace heat up model and the feeding of the micro-component within the furnace were developed. The corresponding experimental tests were also conducted to ensure the reliability of the simulation models and consequently, to improve the processes by using these digital technologies. This study successfully established a finite-volume based computer aided engineering methodology and enabled the integration of virtual simulations and practical applications for the micro-component heat treatment industry. Through these simulation models, the thermal power from associated thermal resistances can be adjusted and managed properly. As a consequence, the concerns about high energy consumption can be reduced and the low carbon green energy manufacturing goal can be reached.

In recent years, it is required to improve productivity and reduce environmental load in the heat treatment process. Since aqueous polymer quenchants pose little danger of fire, it is possible to unify production lines with pre- and post-processes, which is expected to improve productivity. In addition, it is expected to reduce CO₂ emissions. On the other hand, aqueous polymer quenchants have a longer vapor blanket stage length and a faster cooling rate near the martensite transformation point than quenching oils, so there are concerns about changes in hardness, quenching crack, and increased distortion. In this study, we developed aqueous polymer quenchants with oil-like cooling properties and investigated the effect on the quenching quality with conventional aqueous polymer quenchants. The hardness and distortion of conventional aqueous polymer quenchants, developed aqueous polymer quenchants, water and quench oils were investigated, and examined whether the developed aqueous polymer quenchants could improve the hardness and distortion. As a result of quenching round bars of different materials, the developed aqueous polymer quenchants has the same hardness as oil regardless of the material, while the conventional aqueous polymer quenchants have the same hardness for chromium molybdenum steel , but lower hardness for carbon steel. It is considered that the developed aqueous polymer quenchants did not decrease in hardness because the vapor blanket stage length was shortened, so cooling proceeded without passing through the pearlite nose. In the quenching of C-type chromium molybdenum steel test pieces, there was no crack with the developed polymer quenchants, while crack occurred when quenching with the conventional polymer quenchants and water. When a heat treatment simulation was performed, there was a correlation between the actually measured residual stress and the maximum principal stress, which could be used to predict quenching crack. The distortion change of the developed aqueous polymer quenchants were as small as that of the quenching oils compared to the conventional aqueous polymer quenchants. Visualization and multi-point cooling performance evaluation experiments confirmed that the aqueous polymer quenchants had less uneven cooling than the conventional one. It is considered that the shortening of the vapor blanket stage length suppressed uneven cooling and reduced distortion.

Heat treating oils are composed of base oil and additives, with the heat treating oils composed mainly of the base oil. Therefore, the properties of the base oil significantly affect the quality of the heat treating oil. Base oil is classified into mineral oil and synthetic oil, and mineral oil is generally used for heat treating oil. Mineral oils are classified according to the degree of refining. In recent years, due to improved refining technology, highly refined base oils, known as Group III base oils, have been produced and distributed in the market. The demand for high quality base oils has caused a decrease in the production of Group I base oils, which are lower in degree of refining, due to the closing of older refineries and the impact of newer processes. These backgrounds require the use of Group III base oils for heat treatment oils. Heat treating oils are used at high temperatures, in contrast to general petroleum products. The oxidation stability test specified for heat -treated oil was compared with the oxidation stability test for general lubricating oil. The results for Group III base oils showed oxidation progress under heat-treated oil conditions, unlike the results for general lubricating oils. Therefore, it is difficult to compose a heat treating oil using only Group III base oil. In this paper, in order to improve the oxidation stability of heat treating oils, a study was conducted to determine the most suitable composition by adding a Group I base oil to a Group III base oil. The addition of Group I base oil to Group III base oil gave good results. The sulfide in the Group I base oil was found to be a factor.

The bearing outer ring is often non-uniformly deformed after quenching. The ellipticity of the bearing is also an evaluation indicator for quality control. In this paper, the cooling curves of the inner and outer surfaces of the bearing outer ring were measured separately. Based on the measured cooling curves, the cooling rates were calculated, and the heat transfer coefficients at the measurement points on the inner and outer walls of the bearing outer ring were calculated using the inverse analysis method. The heat transfer coefficients at measurement points on the inner and outer walls of the bearing ring were calculated under different quenching postures, revealing the non-uniform heat transfer mechanism during the bearing quenching process. Through experiments, thermal physical properties such as the phase transformation plasticity coefficient of GCr15 material were measured., the quenching processes of GCr15 materials, were simulated according to the metal thermodynamics theory and the multi-field coupling calculation method. Through the simulation, the results of distortion of the bearing sleeve after quenching were obtained, and the ellipticity values of the bearing sleeve after quenching were obtained according to the distortion results to verify the distortion mechanism of the bearing sleeve during the quenching process.

Medium-manganese steels are promising candidates for use as air-hardening forging steels, thus eliminating the need for subsequent heat treatment steps. This publication deals with the influence of the main alloying elements, namely, carbon, silicon, manganese, and chromium, on the transformation behavior during continuous cooling of medium-manganese steels. Therefore, dilatometer-tests, microstructure characterization by SEM and EBSD and in addition, hardness and retained austenite measurements were performed to derive CCT diagrams. The substitution of 1% manganese with 1% chromium in the steel 0.2C1Si4Mn results in a similar transformation behavior except for a higher M_s temperature (335°C instead of 303°C) and a slightly lower hardness. In general, all 4% manganese steels and the 3% manganese + 1% chromium steel show relatively high hardness values after slow cooling, which makes them suitable for use as air-hardening steels. All steels exhibit increasing retained austenite fractions with decreasing cooling rates, which can be attributed to autopartitioning. It could be shown that ferrite formation starts significantly earlier than the 1% transformation line in the classical CCT-diagram indicates, which is suspected to affect toughness.

In gas nitriding of steel, a compound layer is formed on the surface of the steel, which is composed of ε-phase and γ'-phase of iron nitrides. It is known that the mechanical properties improved depend on which of these phases is formed more. The compound layer obtained by gas nitriding of iron can be predicted by the Lehrer diagram, which shows the relationship between temperature, nitriding potential KN, and the stable phase in the Fe-N system. However, in industrial steels, ε-phase and γ'-phase may be mixed in a complex phase composition due to the influence of alloying elements such as C and Cr. The result is not always consistent with the phase composition shown in the Lehrer diagram. Therefore, further study is needed on the stability of the phase composition of the compound layer of industrial steels.
In this study, the effect of the temperature history following nitriding treatment on the phase composition of the generated compound layer was investigated for industrial steel SCM. In the experiments, specimens were gas nitrided at KN for a predetermined time, moved to the low temperature zone in a nitriding atmosphere, held for a predetermined time, and then quenched to room temperature. The phase composition of the compound layer at each temperature history was analyzed by EBSD. As a result, it was confirmed that the phase composition in the compound layer changed by holding at low temperatures, specifically, the ratio of ε-phase decreased and γ'-phase increased. This change in phase composition occurred in a relatively short period of time, from 10 to 30 minutes. In addition, the C and N distribution of the ε-phase and γ'-phase in the compound layer before and after low temperature holding was analyzed by EPMA. The C enrichment in the ε-phase after low-temperature holding was particularly pronounced compared to that before holding. The phase stability of the ε-phase in the Fe-C-N system was estimated by the computational phase diagram. The results show that for the ε-phase to be stable at low temperatures, C must be more enriched than when held at high temperatures. This implies that the change in phase composition of the compound layer due to holding at low temperatures is caused by the redistribution of C and N, driven by the change in phase stability of the ε-phase and γ'-phase due to the temperature change.

The aim of this study is to characterise the microstructure of plate-like lower bainite and the effect of carbon on this microstructure using Fe–C alloys. The carbon content in the specimens ranged from 0.6 to 1.4 in mass percentage. The specimens were heat-treated at 573 K after austenitisation, followed by water cooling. The specimens were observed using optical microscopy and scanning electron microscopy, and their crystal orientations were analysed using electron backscatter diffraction. Microstructural observations and crystallographic analysis show that plate-like lower bainite contains a packet and block structure within the prior austenite grains, similar to lath martensite and lath-like bainite. The most frequently observed crystallographic orientation relationship between the bainitic plates is the one 20° away from the twin orientation relationship, i.e., the V1/V6 relationship. The paired variants compose a microstructure unit and the bundled bainitic plates have similar long directions. The morphology of the interface is different from those of lath martensite and upper bainite. The variant pairing and paired block morphology, including interface shape, are considered distinct features of plate-like lower bainite.

In this study, to improve the hardness of CoCrFeNi-Si alloys, CoCrFeNi-Si alloy powders prepared by gas atomization (Co_28.5Cr_15.5Fe_28.5Ni_15.5Si₁₂, Co₂₈Cr₁₅Fe₂₈Ni₁₅Si₁₄, and Co₂₂Cr₂₂Fe₂₂Ni₂₂Si₁₂) were processed by ball milling (BM) (t = 0 h, 25 h and 50 h) followed by spark plasma sintering (SPS, 1073 K, 50 MPa, holding for 10 min). BM 0 h of Co_28.5Cr_15.5Fe_28.5Ni_15.5Si₁₂, Co₂₈Cr₁₅Fe₂₈Ni₁₅Si₁₄, and Co₂₂Cr₂₂Fe₂₂Ni₂₂Si₁₂ powders identified the main fcc phase, and silicide Co₂Si by X-ray diffraction (XRD). The XRD results of the BM 25 h and 50 h powders of Co_28.5Cr_15.5Fe_28.5Ni_15.5Si₁₂, Co₂₈Cr₁₅Fe₂₈Ni₁₅Si₁₄, and Co₂₂Cr₂₂Fe₂₂Ni₂₂Si₁₂ reveal that a single fcc phase was formed. The BM also caused the Co₂Si compound to dissolve, and all elements were completely solid- soluted in the fcc matrix. According to the XRD results of the sintered samples after the SPS process, the sintered samples of Co_28.5Cr_15.5Fe_28.5Ni_15.5Si₁₂, Co₂₈Cr₁₅Fe₂₈Ni₁₅Si₁₄, and Co₂₂Cr₂₂Fe₂₂Ni₂₂Si₁₂ exhibited an fcc phase and contained FeSi and Co₂Si compounds. The hardness results showed that the Co₂₈Cr₁₅Fe₂₈Ni₁₅Si₁₄ sample was the hardest of the three sintered samples, because the higher the mixing entropy ΔS_mix (closer to the isoatomic composition), the higher the Si content, the higher the increase in hardness. Furthermore, the hardness of the three alloys increased with BM time; in this case, the increase in hardness can be attributed to the introduction of more transitions rather than the BM plastic working.

Generally, brazing is completed when the brazing filler metal penetrates the gap by uniform wetting. It is believed that the joining process is completed with the formation of joint defects "voids" in the process of uniform wetting. However, previous studies have shown that what occurs when brazing is performed is non-uniform wetting. It is suggested that this non-uniform wetting is the cause of void generation.[br]In this experiment, new specimen was created. It is called us “V-groove specimen”. Specimens were created with two base metals. They are pure copper and lead-free brass in which bismuth was used as an alternative element. In order to do in situ experiments, it was not possible to observe the inside of a conventional electric furnace. Therefore, a new furnace was produced with a window for in-situ observation and experimented with it. Two types of brazing filler metals. They are BAg-7 and BAg-8. As a result of experiments with V-groove specimens, it was found that there are two types of wetting of brazing filler metal. they are called "primary wetting" and "secondary wetting". It was evaluated these two types of wetting and investigated the wetting of the brazing filler metal. It was found that the wetting of the molten brazing filler metal was different for each base metal.

The exhaust gas recirculation (EGR) cooler uses stainless-steel brazing. The EGR cooler is a heat exchanger that cools exhaust gases, rendering these cooled gases useful for optimizing combustion. This application considerably benefits from stainless steel due to its excellent heat and corrosion resistance. In this context, stainless-steel brazing is achieved by applying various forms of brazing filler metal tailored to different brazing conditions and joint designs. Nickel-based brazing filler metals are classified into foil and powder forms. Foil-type brazing filler metal is known for its propensity to induce interfacial reactions, even below the conventional brazing temperature. Previous studies have shown a pronounced correlation between the boron content, a primary constituent of brazing filler metal, and brazing and liquidus temperatures. Heightened boron content has been empirically proven to decrease brazing and liquidus temperatures. Therefore, the effect of boron addition on brazing is investigated using coessential observations and assessments of joint strength. Ferritic stainless steel (SUS444) was used as the base metal, whereas brazing metal is a nickel-based foil-type augmented with varying boron concentrations. The brazing procedure entails assembling components using a stainless-steel jig, followed by brazing under vacuum conditions at 1050 °C for 10 min with a heating rate of 20 K/min. Post-brazing protocols encompass vaporizing binders at 600 °C for 15 min, succeeded by air cooling. Subsequent evaluations encompass visual inspections of the fillet, cross-sectional microstructural analyses conducted via optical microscopy, and tensile testing. This multifaceted investigation provides insights on the impact of boron content on the brazing process and delves into the structural and mechanical integrity of the brazed joints.

Austempering is a heat treatment process used in the automotive industry. In contrast to case hardening, austempering results in a bainitic microstructure with only slightly lower hardness and significantly higher fatigue strength. For economic reasons, the heat treatment is carried out in batch processes, usually with several components being quality tested.
Extensive sensor data is available for each batch, but the variance is low due to the stability of the series process. At the same time, quality control using Vickers hardness testing is subject to measurement uncertainty, especially when only a few indentations are measured, as is common in production. Deviations within a batch further limit the prediction accuracy for an individual part. The prediction quality of a machine learning (ML) model is limited by the quality of the data. One way to better model the process, is to use simulation data in a hybrid model. An additional approach is Uncertainty Quantification, which provides an indication of how confident the model is that the prediction is accurate. Many of these models are also more robust and have higher prediction accuracy.
The aim of this work is the implementation of several Uncertainty Quantification methods for a hybrid model as well as the comparison of these models and a recommended action for hybrid models in production. The ML models with Uncertainty Quantification are better suited for data with a higher uncertainty (e.g. measurement uncertainty). These models learn next to the labels how reliable the predictions are. This is particularly important in production and can be used as an additional criterion in quality control. The developed model will be evaluated with production data to assess its performance.

Gas carburized quenching process exhausts much CO₂ because fossil fuels is burned. For this reason, reducing CO₂ is one of the urgent tasks for this process. “carburizing gas regenerator” is an equipment, including polyimide hollow-fiber membrane filter, which allows H₂ to permeate therethrough. As H₂ is generated during carburizing process, by circulating carrier gas using this equipment, H₂ is eliminated by filter, and H₂ eliminated carrier gas is able to reuse to the furnace.
Using carburizing gas regenerator enables to reduce total amount of carrier gas and CO₂ emissions up to 50%, and get less variation of hardness and carbon concentration among carburized quenching specimens.