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Copyright of Metal Working (1674-165X) is the property of Metal Working Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laser surface alloying is a method used to modify a metal surface to produce a thin surface layer with improved mechanical properties. The results of tests on surface carburizing and boriding of steel 20 using a laser beam are presented. Before laser irradiation, the surface of the material was coated. Two types of coating were used: suspensions of graphite powder and boron carbide. Steel 20 was carburized and borided by melting the coating and the substrate. This processing produced various microstructures in the surface layer, depending on the type of coating used and the processing parameters. The microhardness of the alloyed layers was measured along the depth axis. The surface layer consists of an alloying zone and a heat-affected zone. Some specimens carburized by surface alloying displayed cracking and porosity due to carbon enrichment and high solidification rates. The laser-borated surface has a remelting zone consisting of an eutectic mixture of iron borides FeB, Fe2B, and Fe3B. The dense boride zone located near the surface, while the content of the eutectic mixture of borides and martensite increased toward the base metal. The microhardness of the borated layer was 1200 HV. The alloy layers were tested for abrasive wear. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of the case depth and hardness distribution of carburizing on the rolling contact fatigue (RCF) properties of G20CrNi2MoA steel under deeper carburizing conditions. Four groups of specimens of different case depths are prepared and subjected to RCF tests. A 2D finite element model based on continuum damage mechanics is developed to further analyze these two factors. As the depth of the carburized case increases, the RCF life first increases and then decreases. The optimum case depth is approximately one‐quarter of the thickness of the specimen. A gentler hardness distribution due to a change in the diffusion process parameters ensures a minimal increase (8%) in the RCF performance. The proper case depth has a more notable effect on the RCF life compared with those of the gentle or steep hardness distribution. It is expected that the results can help to promote a better understanding of the heat treatment process of carburized bearings and ensure more reliable carburized bearings are produced. [ABSTRACT FROM AUTHOR]

Copyright of Metal Working (1674-165X) is the property of Metal Working Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The kinetic characteristics of thin-sheet (approx. 1 mm) Zr–1%Nb alloy samples after treatment in a carbon-containing gas medium ( P Ar + C 3 H 8 = 0.106 Pa) in a wide temperature range of 650–850°C and time 1; 5 and 10 h were investigated. The carburizing of the alloy at temperatures of 650 and 750°C occurs according to a law close to linear (n ≈ 1), and at 850°C according to a law close to parabolic (n ≈ 2). The activation energy of the alloy carburizing in the temperature range of 650–850°C at the propane partial pressure p C 3 H 8 = 0.018 Pa was 2.21 kJ/mol. The distribution of microhardness and structure of the near-surface layers of the alloy was shown. The microstructure of the near-surface layers of the alloy after carburizing was determined. The α-Zr and ZrC phase content on the alloy surface after treatment in a carbon-containing gas environment is presented. [ABSTRACT FROM AUTHOR]

The thermodynamics of mass transfer during gaseous carburization and its overall efficiency across various alloyed steels were investigated to discern the influence of alloy content. Quantitative analyses were conducted on the coefficients of mass transfer and carbon diffusivities for EN3, EN35, 20MnCr5, and EN353 steels at a carburization temperature of 930 °C. The study revealed distinct trends in mass transfer dynamics and carbon diffusion rates among the different alloyed steels. For instance, nickel majorly an austenite stabilizer, was found to enhance carbon diffusion in gamma iron, with observed coefficients of mass transfer ranging from 8.85 x 10-6 to 1.87 x 10-5 cm/s. However, EN35 steel exhibited slower mass transfer rates due to weaker atomic interactions, resulting in lower observed coefficients of mass transfer. Conversely, chromium and molybdenum, known carbide-forming elements, facilitated carbon transfer from the gaseous environment to the steel case in 20MnCr5 and EN353 steels, with observed coefficients of mass transfer ranging from 1.39 x 10-5 to 1.55 x 10-5 cm/s. Additionally, the study compared observed carbon diffusivities with those predicted by DICTRA (Diffusion Controlled TRAnsformation) kinetic and thermodynamic datasets, demonstrating excellent consistency. These findings underscore the significance of considering alloy content in achieving consistent carburizing outcomes and suggest potential modifications to existing carburizing methods to improve diffusion depth homogeneity. Overall, the study provides valuable insights into the impact of alloy elements on the carburization process and offers implications for optimizing carburizing practices in alloy steel manufacturing. [ABSTRACT FROM AUTHOR]

In the service process of gears, premature fatigue failure or fracture of gears is often caused by poor surface performance. 20CrNiMo steel is a commonly used material for gears. Laser-shock peening (LSP), carburizing treatment (CT), and hybrid modification of carburizing treatment and laser-shock peening (LSP + CT) were carried out to improve the performance of 20CrNiMo steel. The hardness, residual stress, microstructure, subgrain size, and toughness of the samples were analyzed following various modification methods. It was observed that the properties of the composite-modified gradient structure materials achieved through carburizing and laser-shock peening were superior to those modified using single methods. After the composite treatment of carburizing and laser shocking, the samples exhibited the most significant increase in hardness, up to 916HV0.1, with a surface layer experiencing residual compressive stress as low as −635 MPa. Simultaneously, a gradient microstructure was formed on the surface layer, with 80% of the crystallites being in the nanoscale range. Furthermore, the toughness was notably enhanced. Experimental results confirm the improvement in the properties of 20CrNiMo samples, resulting in the creation of a functionally graded material through the composite treatment of carburizing and laser shocking. [ABSTRACT FROM AUTHOR]

The abnormal grain growth of steel, which is occurs during carburization, adversely affects properties such as heat treatment deformation and fatigue strength. This study aimed to control abnormal grain growth by controlling the materials and processes. Thus, it was necessary to investigate the effects of microstructure, precipitation, and heat treatment conditions on abnormal grain growth. We simulated abnormal grain growth using the cellular automaton (CA) method. The simulations focused on the grain boundary anisotropy and dispersion of precipitates. We considered the effect of grain boundary misorientation on boundary energy and mobility. The dispersion state of the precipitates and its pinning effect were considered, and grain growth simulations were performed. The results showed that the CA simulation reproduced abnormal grain growth by emphasizing the grain boundary mobility and the influence of the dispersion state of the precipitate on the occurrence of abnormal grain growth. The study findings show that the CA method is a potential technique for the prediction of abnormal grain growth. [ABSTRACT FROM AUTHOR]

Copyright of International Journal of Engineering Research & Development (IJERAD) is the property of International Journal of Engineering Research & Development and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The controversial wear resistance limits the application of the nitro-chromizing process, which is a potential advanced chromizing strategy with a low chromizing temperature and thick strengthening layer. In this study, additional carburizing was proposed to optimize the nitro-chromizing process and the associated wear resistance. Samples of carbon steel were used to evaluate the optimized nitro-chromizing, normal nitro-chromizing, and other relevant processes. Comparative analyses were conducted through XRD composition analysis, microstructure observations, and mechanical property tests.The results confirm that the normal nitro-chromized sample has poor wear resistance due to severe abrasive wear, while the wear rate of the optimized nitro-chromized sample is only about 1/15 of that of the normal nitro-chromized sample. Both the above two samples have similar main phase compositions of Cr2N and Cr7C3. However, the optimized nitro-chromized sample exhibits a lower friction coefficient and better adhesion strength than the normal nitro-chromized sample. The additional carburizing induces the formation of massive fine graphite sheets deposited on porous nitriding structures, which can be in charge of the low friction coefficient and good adhesion strength. [ABSTRACT FROM AUTHOR]

Rotating bending fatigue properties of the gear steel 16CrMnH have been investigated after carburized and re-austenitized at different temperatures with 18-30% of retained austenite in the carburized case. It was found that the fatigue life tended to increase from 105 to 107 cycles with the decrease of the stress amplitude in the range of 1200-1000 MPa. The fatigue limits were higher than 1000 MPa, independent of the fraction of retained austenite. The retained austenite in the carburized case did not transform into martensite after fatigue tests, but the hardness in the carburized case was increased presumably as a result of cyclic hardening of retained austenite. The fatigue limits of the carburized specimens were in good agreement with the calculated values based on the case hardness measured after fatigue tests. Observations of the fracture surfaces of the fatigue specimens showed that the fatigue crack initiated at the non-metallic inclusions or the matrix in the carburized case with a depth of no more 0.6 mm from the surface. Thus, a good fitting of S–N curves could be obtained by taking into consideration of the case hardness after cyclic hardening as well as the non-inclusion sizes. [ABSTRACT FROM AUTHOR]

Carburizing is a commonly employed technique used to improve carbon steel’s surface characteristics, specifically its hardness and ability to resist wear. The introduction of tension during the carburizing process adds complexities that affect the distribution of elements in the material. The research methodology includes subjecting carbon steel samples to carburizing temperatures and applying tensile stress. This approach allows for analyzing the effects of carburization and stress on the carbon steel samples. The focus of the investigation was to analyze the use of the pack carburizing technique at lower temperatures, specifically 700 °C and 750 °C, while also applying proportional-voltage tensile stresses. The study focuses on conducting a comprehensive analysis of changes in the chemical composition throughout the cross-section of the material. Advanced analytical techniques perform mapping and elemental spectrum analysis, such as scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). These techniques enable a thorough investigation of the distribution and composition of elements such as carbon, iron, silicon, magnesium, and phosphorus. According to the research findings, carbon elements were added within the temperature range of 700 °C to 750 °C during the carburization process. The carbon content in the material increased from 0.15 % in its unprocessed state to 0.73 % at a temperature of 700 °C, followed by a further increase to 1.26 % at a temperature of 750 °C. According to the study, it was found that applying tensile loads and reducing carburizing temperatures can enhance the carburizing process and result in higher carbon steel content. This can bring about cost savings and improve overall industrial efficiency. [ABSTRACT FROM AUTHOR]

The carburizing period for tool steel could be significantly shortened by operating at a higher carburizing temperature. However, grain coarsening happens during the carburizing process, and then results in the deteriorated surface properties in 20CrMnTi gear steel, especially at an elevated carburizing temperature. The relationships between grain coarsening and the precipitates in the developed 20CrMnTi gear steel during pseudo-carburizing were established by microstructure characterization, precipitate analysis and in-situ observation to clarify the coarsening mechanism. The results manifested the Baker–Nutting orientation relationship between the (Ti, Mo)(C, N) particles and the matrix, and then testified to the redissolution and ripening of the (Ti, Mo)(C, N) precipitates pre-formed in the α phase during the carburizing. Coarsening in austenite grain during the carburizing process was mainly caused by the rapid redissolution and ripening of the (Ti, Mo)(C, N) precipitates, although this occurred in a very short pseudo-carburizing time. The area density of the dispersed unripe (Ti, Mo)(C, N) particles markedly decreased from 0.389% in as-hot rolled gear steel to 0.341%, and then from 0.279% in carburized steels at 970 and 980 °C, respectively. Additionally, the redissolution and ripening of the (Ti, Mo)(C, N) precipitates were accelerated by the elevated carburizing temperature of 980 °C, at which time the growing rate in austenite grains was 2.34 μm/min during the prior 1 min (0.79 μm/min during the prior 3 min at 970 °C). The temperature then decreased to 0.003 μm/min in the subsequent carburizing process. The results obtained our current work reflected that the particles with excellent thermal stability should play important roles in the limitation of grain coarsening during the carburizing process. [ABSTRACT FROM AUTHOR]

The microstructure and microhardness of multicomponent diffusion boride coatings formed on the surface of prehardened 30KhGSA steel have been studied. Diffusion coatings on prehardened 30KhGSA steel have been obtained by simultaneous diffusion saturation with boron, chromium, titanium, and silicon. Metallographic analysis has been carried out on a Carl Zeiss Axio Observer Z1m metallographic microscope in the ThixoMet PRO software package. The efficiency of the multicomponent boriding process combined with the hardening has been demonstrated. The prehardening of 30KhGSA steel makes it possible to obtain higher microhardness indices as compared with the case of complex boron‒chromium‒titanosiliciding without prehardening. Under thermal treatment, the surface microhardness of the diffusion coating decreases from 1980 to 1160 HV0.1. This is accompanied by an increase in the diffusion-coating thickness by a factor of 3. [ABSTRACT FROM AUTHOR]

A Ti–Al alloy phase layer/Ti–Al carburizing composite coating was prepared on the surface of titanium alloy by the stepwise coating method of hot-dip aluminizing and then carburizing. The weight gain results of the composite coating showed that the titanium alloy coated with the composite coating had long-term stability (≥16 days) at 800 °C. The microstructure, phase structure, and composition of the composite coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The composite coating is composed of an alloy phase layer and a carburized layer. The natural transition of four phases (Ti3Al/TiAl/TiAl2/TiAl3) in the alloy phase layer significantly improves the interfacial bonding between the coating and the substrate and slows down the propagation of microcracks through the coating. Al2O3, TiC, and C in the carburizing layer improve the surface hardness of the coating, and TiAl2 and Al2O3 also have excellent oxidation resistance at high temperature. [ABSTRACT FROM AUTHOR]

The object of this work is a study of the microstructure and hardness evolution of LPBF-manufactured biomedical alloy Ti-6Al-4V superficially modified by pack carburization and subsequent laser melting. Carburization was conducted in a powder of (NH2)2CO (20 vol. %), K4Fe(CN)6 (20 vol. %), and a carbon black (60 vol. %) at 1000 (C (7 hours). The laser processing was fulfilled by fiber laser «TruFiber 400» (TRUMPF) of 1064 nm wavelength with a power of 400 W and scanning velocity of 5 mm·sec – 1. The investigations included optical (GX71 OLYMPUS) and scanning electron microscopy observations (JSM-7000F JEOL), energy-dispersive X-ray spectroscopy (INCAx-sight, Oxford Instruments), X-ray diffraction (X'Pert PRO, PANalytical, Cu-Kα radiation) and microhardness measurement (LM700AT LECO, under the load of 0.05 kg). It was found that carburization resulted in a 440-700 μm deep carbon-rich layer of (Ti with an upper thin layer comprising TiC, TiO2, and Al2O3. Carburization led to 720 ± 12 HV in a near-surface layer which is two times the bulk structure (322 ± 32 HV). A consequent laser scanning formed a 60-120 (m wide melted layer followed by the heat-affected zone (having a needle-like (Ti-martensite) extended to (∼0.8 mm depth. The melted layer had a fine-grained structure which included the dispersive particles of an oxycarbide Ti(O0.8C0.2) of both grainy and dendrite-like shapes. Consequently, the hardness of the melted layer rose up to 1000-1200 HV with a further gradual decrease, according to the declining carbon content profile. Laser melting was accompanied by cracks and shrinkage cavities formation. It also led to an increased roughness of the surface caused by its boiling under the laser melting. [ABSTRACT FROM AUTHOR]

Carburizing is one of the leading surface treatments in the industry. For this study, 20MnCr5 steel was gas carburized and quenched in real circumstances and simulated with Simufact software. The research investigated the dimensions and types of bores. A through and blind bore was used in this study to analyze how the geometry affects the created layer and, additionally, it takes into account the placement in the heat treatment furnace. An optical microscope and Vickers hardness tester were used to detect the changes in microstructure and measure the layer thickness. After the experiments, a simulation calculated the same variables to compare and validate the results to each other. It can be stated that the placement in the chamber did not influence the form of the high carbon content layer. The simulation and the measured results were in good agreement. The maximum hardness difference was 17%, but the calculated layer thicknesses were always between the measured data. For example, in the case of a small blind bore, the calculated layer thickness was 1.68 ± 0.18 mm, while the measured value was 1.54 ± 0.37 mm. Additionally, the hardness change in depth was similar in both cases. After this validation process, the residual stresses and plastic strains were determined. The maximum residual stresses were similar for every case, namely around 1900 MPa, while the maximum plastic strain was measured in a small blind bore with a value of 0.18. The minimum plastic strain was 0.04 in the through bore. [ABSTRACT FROM AUTHOR]

By using scanning electron microscope (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD), and hardness and rotational bending fatigue tests, the effect of short-time carburizing treatment on the microstructure and mechanical properties of bearing steel was studied. The results show that when the M50 steel is not carburized, the hardness is 750 HV, the rotational bending fatigue limit is 1100 MPa, and the impact absorption energy is 15.46 J. After short-time carburization with the carbon potential of 0.6%, the maximum hardness in the carburized area, the rotational bending fatigue limit and the impact absorption energy are all increased to be 807.7 HV, 1210 MPa and 16.72 J respectively. When the carbon potential is further enhanced to be 0.8%, the maximum hardness of the carburized area of the steel is further enhanced to be 813.4 HV, but the rotational bending fatigue strength and the impact absorption energy are both decreased to be 1125 MPa and 13.65 J respectively, which has close relations with the increasement of undissolved carbides and the precipitation of acicular carbides. [ABSTRACT FROM AUTHOR]

The results of modifying the surface of austenitic stainless steel by anodic plasma electrolytic treatment are presented. Surface treatment was carried out in aqueous electrolytes based on ammonium chloride (10%) with the addition of ammonia (5%) as a source of nitrogen (for nitriding), boric acid (3%) as a source of boron (for boriding) or glycerin (10%) as a carbon source (for carburizing). Morphology, surface roughness, phase composition and microhardness of the diffusion layers in addition to the tribological properties were studied. The influence of physicochemical processes during the anodic treatment of the features of the formation of the modified surface and its operational properties are shown. The study revealed the smoothing of irregularities and the reduction in surface roughness during anodic plasma electrolytic treatment due to electrochemical dissolution. An increase in the hardness of the nitrided layers to 1450 HV with a thickness of up to 20–25 μm was found due to the formation of iron nitrides and iron-chromium carbides with a 3.7-fold decrease in roughness accompanied by an increase in wear resistance by 2 orders. The carburizing of the steel surface leads to a smaller increase in hardness (up to 700 HV) but a greater thickness of the hardened layer (up to 80 μm) due to the formation of chromium carbides and a solid solution of carbon. The roughness and wear resistance of the carburized surface change are approximately the same values as after nitriding. As a result of the boriding of the austenitic stainless steel, there is no hardening of the surface, but, at the same time, there is a decrease in roughness and an increase in wear resistance on the surface. It has been established that frictional bonds in the friction process are destroyed after all types of processing as a result of the plastic displacement of the counter body material. The type of wear can be characterized as fatigue wear with boundary friction and plastic contact. The correlation of the friction coefficient with the Kragelsky–Kombalov criterion, a generalized dimensionless criterion of surface roughness, is shown. [ABSTRACT FROM AUTHOR]

Surface hardening treatment is used to have strength to mechanical parts, and carburizing and quenching are the most widely used. There are reports on various carburizing efforts to deal with recent environmental issues. The authors have proposed an ultra rapid carburizing above the eutectic temperature, due to realize in-line carburizing. Since this is an unprecedented carburizing treatment method, setting the carburizing conditions that are suitable for efficiency has been the future challenge. In this paper, we investigated a method for predicting the carbon concentration profile in the steel based on the known carburizing reaction mechanism of ultra rapid carburization. In order to predict the carbon concentration profile in the steel, it was calculated by the finite difference method using the carbon penetration rate F, the use of F = 4.04 × 10-11e(1.20 × 10-2 • T), which penetrates from the surface, and the carbon diffusion in the steel based on Fick’s law. In addition, among various carbon diffusion coefficients Dc, the use of Dc(T,C) = 4.53 × 10-7{1+yc(1-yc)}•e{-(-2.221•10-4)(17767-yc•26436)}, which takes into consideration the dependence of carbon concentration, gave a good agreement with the actual measurement results by EPMA. Furthermore, as a result of investigating efficient carburizing conditions using a prediction method, we could minimize the time required to obtain an effective case depth of 0.8 mm. In addition, the amount of carburizing gas used was also reduced. In other words, it suggests that the accumulation of a huge amount of condition data and the condition setting skills are no longer necessary. [ABSTRACT FROM AUTHOR]

The wear characteristics and related mechanisms of the Longwall Shearer Haulage System were investigated. Wear is one of the main reasons for failures and downtimes. This knowledge can help solve engineering problems. The research was carried out at a laboratory station and a test stand. The publication presents the results of tribological tests carried out in laboratory conditions. The aim research was to select the alloy intended for casting the toothed segments of the haulage system. The track wheel was made by the forging method using steel 20H2N4A. Haulage System was tested on the ground using a longwall shearer. Selected toothed segments were subjected to tests on this stand. The cooperation of the track wheel and toothed segments in the tootbar were analyzed by a 3D scanner. Debris chemical composition was also appointed, as well as mass loss of toothed segments. The developed solution toothed segment an increase in the service life of the track wheel in real conditions. The results of the research also contribute to reducing the operating costs of the mining process. [ABSTRACT FROM AUTHOR]

Low carbon steel with carbon content ranging from 0.15% to 0.3% cannot be hardened through quenching and tempering processes and there is little to no martensitic transformation occurring upon quenching. To improve the surface hardness, carburizing is commonly employed. Through this treatment, the surface composition of the low-carbon steel is altered by the diffusion of carbon, resulting in a hard outer casing with good wear resistance. This work investigates the effect of the carburizing treatment temperature and holding time on the crystallographic structure, hardness, and hardened surface layer dimension of commercial low-carbon steel 16NC6. The steel was carburized at 900°C for different holding times of 1, 2, and 3 hours. After the carburizing and quenching processes, the hardness values and the morphology of the crystallographic structure were measured and characterized. [ABSTRACT FROM AUTHOR]

Low-temperature thermochemical treatments are particularly suitable for use in the surface hardening of austenitic stainless steels without impairing their corrosion resistance. In fact, when using treatment media rich in nitrogen and/or carbon at relatively low temperatures (<450 °C for nitriding, <550 °C for carburizing), it is possible to inhibit the formation of chromium compounds and obtain modified surface layers that consist mainly of a supersaturated solid solution, known as expanded austenite or S-phase. It has been observed that this hard phase allows the enhancement of corrosion resistance in chloride-ion-containing solutions, while the results were contradictory for chloride-free acidic solutions. This overview aims to discuss the corrosion behavior of low-temperature-treated austenitic stainless steels, taking into account the different microstructures and phase compositions of the modified layers, as well as the different test environments and conditions. In particular, the corrosion behavior in both chloride-ion-containing solutions and chloride-free solutions (sulfuric acid, sulfate and borate solutions) is discussed. The analysis of the international literature presents evidence that the microstructure and phase composition of the modified layers have key roles in corrosion resistance, especially in sulfuric acid solutions. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the work is a complex review of methods applied industrially as case hardening. The paper contains an overview of scientific and development works on surface case hardening methods, especially carburising and quenching, described in the literature from 2001-2020. Design/methodology/approach: State-of-the-art was reviewed by a critical review of the world literature published in 2001-2022, including theoretical work, scientific research, and industry reports. An additional examination of the state of the art was conducted in terms of patent works. Findings: The period of 2001-2020 was a time of intensive work on the modernisation of case hardening techniques to improve the repeatability and uniformity of the produced layers and minimise deformations after hardening. Developing computing technologies have played a large part in this progress. New technologies have also been developed. Research limitations/implications: The review of papers and patent databases was limited to databases providing English-language content options. Practical implications: Case hardening is a crucial stage of steel heat treatment in almost every industrial branch: mechanical, tool, automotive, railway, and aviation. Originality/value: A synthetic review of case hardening methods was presented, particularly carburizing and quenching methods; it also analysed the possibilities and directions of their development. conducted in terms of patent works. Findings: The period of 2001-2020 was a time of intensive work on the modernisation of case hardening improve the repeatability and uniformity of the produced layers and minimise deformations after hardening. computing technologies have played a large part in this progress. New technologies have also been developed. Research limitations/implications: The review of papers and patent databases was limited to databases Englishlanguage content options. Practical implications: Case hardening is a crucial stage of steel heat treatment in almost every industrial tool, automotive, railway, and aviation. Originality/value: A synthetic review of case hardening methods was presented, particularly carburizing methods; it also analysed the possibilities and directions of their development. Keywords. Heat treatment, hardening, quenching, distortions, carburizing, simulation Reference to this paper should be given in the following way: E. Wołowiec-Korecka, Case hardening development review (2001-2020). [ABSTRACT FROM AUTHOR]

In this study, the surface of industrial pure iron was treated with atmospheric-controlled induction heating fine particle peening (AIH-FPP) using mechanical coating (MC) particles of carbon/steel obtained by mixing carbon powder and fine steel particles using mechanical milling. The surface modification effect and the mechanism of its effect were examined and considered by analyzing of the treated surface. Results showed that a modified layer in which carbon elements were diffused was formed near the treated surface by the AIH-FPP treatment using MC particles. In addition, by examining the influence of the treatment conditions on the formation of the modified layer by the design of experiments, the treatment temperature showed the most significant influence among the treatment temperature, peening time, and gas flow rate. The higher the treatment temperature, the deeper the carbon diffused layer. In addition, when treated at ≥1273 K, the microstructure near the surface became pearlite, and Vickers hardness increased. The time required for carbon diffusion in the AIH-FPP carburizing process using MC particles of carbon/steel was approximately the same as that of a general carburizing treatment using a reactive gas. In the AIH-FPP carburizing process, carbon is considered to be transferred from the particles to the surface, and the grain boundaries and dislocations increased by fine particle peening (FPP) are used as channels to diffuse inside the specimen. This mechanism is entirely different from the conventional carburizing methods. [ABSTRACT FROM AUTHOR]

316L austenitic stainless steel was plasma nitrided and carburized at low temperatures to produce precipitation-free nitrided and carburized layers, respectively. The reciprocation sliding wear performances of the untreated, nitrided and carburized specimens were compared under both unlubricated (dry) and corrosive (in 0.5 M H2SO4 solution) conditions. The results show that under dry sliding conditions, both the nitrided layer and carburized layer can offer good wear resistance to 316L steel. The total material loss (TML) of the steel is reduced by more than two orders of magnitude by low temperature nitriding, while low temperature carburizing offers a reduction in TML by an order of magnitude. The better dry sliding wear performance of the nitrided layer is attributed to its much higher hardness as compared to the carburized layer. However, under corrosive-wear conditions in 0.5 M H2SO4 solution, the wear performance of the nitrided layer is significantly deteriorated, with TML 100% higher than that of the untreated 316L steel. On the other hand, the carburized layer can still offer good wear resistance in the corrosive environment, with a reduction in TML of 316L steel by 40%. This research has practical implication that low temperature nitriding is the most suitable for applications in dry and non-corrosive environments, while low temperature carburizing is more suitable for applications in H2SO4-containing corrosive environments. [ABSTRACT FROM AUTHOR]

To reduce the processing time for in-line carburizing, we performed ultra-rapid carburizing and quenching using induction heating. Conventional gas carburizing and vacuum carburizing (low-pressure carburizing) are treated at 1203-1323 K, which is lower than the eutectic temperature. In contrast, in this study, the carburizing temperature of 1523K was higher than the eutectic temperature for speeding up this process. The SCM420 sample was rapidly heated to the treatment temperature by induction heating. CH4 and N2 were mixed and treated at atmospheric pressure at 5 vol% CH4 and 10 vol% CH4. For ultra-rapid carburizing, the total carburizing depth was proportional to the square root of the carburizing time, following the parabolic law, regardless of the CH4 concentration. We obtained that the amount of carbon penetrating the steel from the atmosphere was proportional to the carburizing time. In other words, the carbon penetration rate was approximately constant during the carburizing process. The processing time for the ultra-rapid carburizing and quenching at 1523K in this study was only 5% of that for the conventional gas carburizing at 1203 K. [ABSTRACT FROM AUTHOR]

Conducting the carburizing process on the surface layer of low-carbon steel and subsequent austempering heat treatment can be implemented to obtain nanobainite microstructure on the surface of steels. In this research, steel with 0.23 wt.% carbon was carburized for 3 h at 900 °C in a liquid salt bath containing sodium cyanide, sodium carbonate, and sodium chloride and immediately quenched to room temperature. The samples were then heated to 900 °C for 30 min and isothermally transformed at three different temperatures of 200, 250 and 300 °C for 72, 24 and 12 h, respectively. It was found that nanostructured bainite was formed on the surface layer and the subunits of bainitic ferrite and high-carbon austenite films were almost 60-300 nm thick depending on the heat treatment temperature. It was also found that the samples austempered at these temperatures contained 18, 21 and 28% volume fractions of retained austenite on the surfaces, respectively. Due to the comparable microstructural characteristics, similar friction coefficients were obtained as for ordinary nanostructured bulk bainitic steels with high-carbon content. [ABSTRACT FROM AUTHOR]

Guide rings and rolling bodies are mainly made of alloy steel with a high chromium content, heat treated, as well as of carburising steel. The efforts to improve the standard of quality of bearing steels are determined by the interest of continuously increasing the adhesion of constructive types. These steels are recommended for large bearings which operate under shock and vibration conditions. Thermochemical treatments are followed by quenching and tempering heat treatments. However, undesirable defects occur sometimes on the surface of the carburised layer and solutions are constantly being sought to identify the causes thereof. [ABSTRACT FROM AUTHOR]

Herein, the carburizing behavior of 20MnCr5 gear steel with different Nb contents after carburizing with the temperature from 900 to 950 °C and the corresponding holding time from 8 to 5 h are investigated. The theoretical results of carbon content and the depth of carburized layer for the two experimental carburizing processes should be the same according to the classical diffusion model. However, the experimental results show that the carbon content of the entire hardened layer increases, and the depth of carburized layer increases by 35% after high‐temperature carburizing. The carbon content of 0.061%Nb steel on the outer surface increases, but the depth of carburized layer remains unchanged. It is found that the theoretical D values at 900 °C and 950 °C are 2.0 × 10−7 and 3.3 × 10−7 cm2 s−1, respectively. However, the experimental D value is much larger than 5.0 × 10−7 cm2 s−1. The carbon diffusion is greatly promoted by high‐temperature carburizing because the number of excess carbides on the outer surface decreases. The diffusion coefficient decreases after the addition of Nb due to forming a large number of small particles of Cr7C3 and NbC, but the effect is only obvious on the outer surface. [ABSTRACT FROM AUTHOR]

Herein, it is proposed to obtain a favorable combination of microstructure and mechanical properties of martensitic stainless steel 14Cr14Co13Mo5 by prenitriding method before carburizing and appropriate heat treatment processes. The result indicates that the effective hardened layer depth is increased by 32% to 0.66 mm, and the hardness is significantly improved by prenitriding. The confocal laser scanning microscope and electron backscattered diffraction show that the prenitriding can effectively refine the martensite substructure of the carburized layer after quenching due to the refinement of prior austenite grain. In addition, plenty of second‐phase particles M2N with finer size appear at the same case layer depth instead of coarse M23C6 in the specimen prenitrided, which optimize the microstructure of the case layer. [ABSTRACT FROM AUTHOR]

In this paper, a new low-carbon alloy gear steel is designed via Si/Al alloying. The carburizing and austempering, at a temperature slightly higher than the martensitic transformation point (Ms) of the surface and much lower than the Ms of the core, for different times, were carried out on the newly designed gear steel. After heat treatment, a series of different microstructures (superfine bainitic ferrite + retained austenite, superfine bainitic ferrite + martensite + retained austenite, and martensite + retained austenite) were obtained on the surface, whilst the low-carbon lath martensitic microstructure was obtained in the core. The microstructure of the surface was examined using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The phase composition was analyzed using X-ray diffraction (XRD). The hardness and wear resistance of the surface as well as the hardness distribution of carburizing layer of the samples with different microstructures were studied. The results show that the Si/Al-rich gear steel, after carburizing and austempering at 200 °C for 8 h, not only has excellent mechanical properties but also has high wear resistance, which meets the technical requirements of heavy-duty gear steel. The research work in this paper can provide a data reference for the application of carburized steel with mixed microstructures of bainitic ferrite and martensite in the design of heavy-duty gear. [ABSTRACT FROM AUTHOR]

The article reviews and analyses the current scientific research in the field of surface treatment of metal surfaces with concentrated energy fluxes (CEF) -- the electric-spark (in the literature, known also as electrospark) alloying (ESA), which makes it possible to obtain surface structures with unique physical, mechanical and tribological properties at the nanoscale. The ESA method with a graphite electrode (electrospark carburizing -- EC) is based on the process of diffusion (saturation of the surface layer of a part with carbon), and it is not accompanied by an increase in the size of the part. In this article, the influence of the EC parameters on the quality of the carburized layer is investigated. The microstructural analysis shows that the three characteristic zones could be distinguished in the structure: the carburized ("white") layer, the finely dispersed transition zone with fine grain, and the base metal zone. The analysis of the results of the durometric studies of the coatings is carried out. To achieve the required parameters of dimensional accuracy and roughness of the working surface of the part after the EC process, it is necessary to use the method of non-abrasive ultrasonic finishing (NAUF). In addition, because of applying the NAUF method, the surface roughness is decreased, the tensile stresses are changed to the compressive ones, and the fatigue strength is increased too. In addition, to reduce the roughness of the treated surface, it is proposed to apply the EC technology in stages, reducing the energy of the spark discharge at each subsequent stage. In order to increase the quality of the carburized layer obtained by the EC process, it is proposed to use a graphite powder, which is applied to the treated surface before alloying. The comparative analysis shows that, after the traditional EC process at Wp = 4.6 J, the surface roughness of steel 20 is Ra = 8.3-9.0 µm, and after the proposed technology, Ra = 3.2-4.8 µm. In this case, the continuity of the alloyed layer increases up to 100%; there increases the depth of the diffusion zone of carbon up to 80 µm as well as the microhardness of the "white" layer and its thickness, which increase up to 9932 MPa and up to 230 µm, respectively. The local micro-x-ray spectral analysis of the obtained coatings shows that, at the EC process carried out in a traditional way, the applying Wp = 0.9, 2.6, 4.6 J provides the formation of the surface layers with high-carbon content depths of 70, 100, 120 pm, respectively, and with the use of a graphite powder, they are of 80, 120, 170 pm. While deepening, the amount of carbon is decreasing from 0.72-0.86% to the carbon content in the base metal -- 0.17-0.24%. In the near-surface layer formed with the use of the new technology, the pores are filled with free graphite, which could be used as a solid lubricant to improve the operating characteristics of the friction-pairs parts processed thereby. [ABSTRACT FROM AUTHOR]

To investigate the microstructure and damage of friction-fatigued carburized martensitic steels for the reliability of remanufacturing parts, the retained austenite (γ) phase and residual stress were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). We evaluated their changes before and after roller pitching tests, and before and after the operation of the gear parts. In the roller pitching tests, the retained γ phase decreased with increasing load and number of cycles, presumably due to martensitic transformation caused by the cyclic load. The residual stress ratio (after/before the test) was significantly lower at high loads than that before testing, which was ascribed to the appearance of surface microcracks and the resultant release of internal stress. From SEM observations of the cross-section of the friction surface, we confirmed that the changes in the retained γ phase and residual stress ratio reflect the process of formation of multiple microcracks in the 10µm surface layer. The decreases in both the retained γ phase ratio and the residual stress ratio would therefore appear to rule out reuse. A decision on the potential for gear reuse can be made by means of non-destructive testing, i.e., investigating the relationship between the retained γ phase ratio and the residual stress ratio. [ABSTRACT FROM AUTHOR]

Fin-pass rolls are the latest series of rolls in electric resistance welding (ERW) pipe production lines that form the sheets to tubular shape and adjust the edges of the sheet for welding. The rolls (made of AISI 8622 steel) lose their proper function after about 10 years of operation due to severe wear and change of their original surface profile. The worn portions were removed by grinding and replaced by an AISI D2 high carbon steel ring to repair these rolls. After a short time of service (about one year), the edge of the repair ring was exposed to severe spalling and fracture. The present study investigated the causes of the rapid failure of the AISI D2 repair ring and proposed a solution to the problem. The surface morphology, hardness, and wear resistance were studied. Moreover, the stress analysis of fin-pass rolls was studied using ABAQUS 6.14 finite element software for the closer investigation of the failure mechanism. The leading cause of spalling was the inherent brittleness of the AISI D2 steel and the presence of a high-stress concentration at the edges of the repair ring. To overcome this problem, carburized AISI P20 steel, case hardened AISI 4140 steel, and hard chromium electroplated AISI 4140 steel were replaced, and the resulting properties were studied. The highest resistance to spalling and wear occurred with carburized AISI P20 steel because of the high surface hardness and the gradual increase of toughness from the surface to the depth in the carburizing process, increasing the wear resistance and retarding the growth of fatigue cracks. [ABSTRACT FROM AUTHOR]

This study concerns the improvement of performance of resistance to wear phenomena of the Ti-6Al-4V alloy surface by means of Gaseous carburizing thermochemical treatment. Three-thermochemical treatment durations (2h, 4h, and 6h) were chosen for investigation of the effect of such treatment on this alloy. The hardness test under an indentation load of 0.05 kgf with a Vickers pyramidal indenter revealed that the surface hardness is 335 HV for the untreated samples. The hardness reaches approximately 1500 HV during gas cementation at 930 °C for variable times (2h, 4h, 6h) followed by quenching at 840 °C in an oil medium, which was accompanied by a significant improvement in wear resistance. The characterization of the modified surface layers was studied by means of a microscopic analysis and by X-ray diffraction. The case-hardening made it possible to obtain a wear resistance greater than that of the alloy not treated, minimal loss of mass by dry friction and an improvement in roughness as well as a good coefficient of friction. [ABSTRACT FROM AUTHOR]

The work aims to study the influence of carburizing and nitriding on fatigue properties of 18Cr2Ni4WA high strength steel in very high cycle fatigue regime. Very high cycle fatigue tests were carried out on 18Cr2Ni4WA Steel after carburizing and nitriding respectively. The micro morphology of fatigue fracture was observed by scanning electron microscope, the failure mode and failure mechanism were discussed. The relationship between fatigue life and defect size, FGA size, fish eye size of fracture was analyzed. The characteristic size of defects is evaluated by Gumbel, Weibull and GEV distribution functions, and a modified Akiniwa fatigue life prediction model considering the relationship between FGA size and inclusion size was established. The results showed that, nitriding and carburizing treatment improve the surface fatigue limit of the steel. The fatigue life decreases with the increase of internal defect size and FGA size. After carburizing and nitriding treatment, the internal fatigue strength of the specimen decreases slightly. When the failure probability is 99%, the internal defect sizes of nitrided specimens calculated by Weibull, Gumbel and GEV distributions are 141.5 µm, 148.4 µm and 211.7 µm respectively. The calculated internal defect sizes of carburized specimens are 47 µm, 67.8 µm and 40 µm respectively. Compared with the experimental data, the fatigue strength predicted by GEV is the most appropriate. carburizing and nitriding treatment can improve the surface fatigue strength of 18Cr2Ni4WA steel, but slightly reduce the internal fatigue strength. The prediction result of the new model is conservative when the failure probability is 99%, which is suitable for engineering application. [ABSTRACT FROM AUTHOR]

The boundary conditions for describing the mass transfer of carbon from a low-pressure oxygen-free atmosphere into steel under vacuum carburizing are analyzed. Experimental results and thermodynamic calculations are used to determine the numerical value of the activity of carbon in an environment of low-pressure acetylene. The calculated value of the carbon potential is used in the boundary condition of kind III in the form of a Langmuir expression applied to a mathematical model of vacuum carburizing based on numerical solution of the diffusion equation. The calculated concentration profiles are shown to describe adequately the experimental results. Different nonequilibrium processes of vacuum carburizing of steels are shown to have similarity. [ABSTRACT FROM AUTHOR]

To investigate the microstructure and damage of friction-fatigued carburized martensitic steels for the reliability of remanufacturing parts, the retained austenite (γ) phase and residual stress were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). We evaluated their changes before and after roller pitching tests, and before and after the operation of the gear parts. In the roller pitching tests, the retained γ phase decreased with increasing load and number of cycles, presumably due to martensitic transformation caused by the cyclic load. The residual stress ratio (after/before the test) was significantly lower at high loads than that before testing, which was ascribed to the appearance of surface microcracks and the resultant release of internal stress. From SEM observations of the cross-section of the friction surface, we confirmed that the changes in the retained γ phase and residual stress ratio reflect the process of formation of multiple microcracks in the 10μm surface layer. The decreases in both the retained γ phase ratio and the residual stress ratio would therefore appear to rule out reuse. A decision on the potential for gear reuse can be made by means of non-destructive testing, i.e., investigating the relationship between the retained γ phase ratio and the residual stress ratio. [ABSTRACT FROM AUTHOR]

Ametallographic study of advanced low-carbon martensitic steel with high resistance of the supercooled austenite to the transformations by pearlitic and bainitic mechanisms under continuous cooling is performed. The critical temperatures of the transformations occurring under heating and cooling are determined. The kinetics of the isothermal transformation of the austenite in the temperature range of 300 – 400°C is analyzed. The possibility of successful implementation of isothermal quenching of the steel after carburizing is demonstrated. [ABSTRACT FROM AUTHOR]

The very high cycle fatigue (VHCF) properties of case hardening steel 18CrNiMo7-6 after carburizing and pseudo-carburizing have been investigated by means of ultrasonic fatigue tests. Results showed that the pseudo-carburized specimens with the hardness of 442 HV did not show VHCF fracture, and fatigue fracture did not occur even after 109 cycles when the applied stress amplitude was lower than the high cycle fatigue limit of 650 MPa obtained at 107 cycles. When carburized thoroughly with the hardness of 700 HV, the experimental steel showed VHCF phenomenon, and it might fracture even at nearly 109 cycles when the stress amplitude was about 600 MPa. Observations of the fracture surfaces of the fatigue specimens showed that after carburizing, the fatigue crack initiation sites changed from martensite matrix to nonmetallic inclusions, forming granular bright facet (GBF) and fish-eye before final abrupt fracture. The stress intensity factor at GBF area, which was calculated to be 3.5 MPa m1/2, could be used as a critical value for VHCF fracture for the carburized specimens of the experimental steel. The VHCF fracture of the carburized specimens of the experimental steel could be related to the high hardness and large amount of retained austenite as a result of carburizing. [ABSTRACT FROM AUTHOR]

As a novel manufacturing technology, additive manufacturing (AM) has many advantages such as energy saving, reduced material waste, faster design-to-build time, design optimization, reduction in manufacturing steps, and product customization compared to conventional manufacturing processes. Heat treatment is widely used to improve the properties of conventional manufactured steel parts. The response of additively manufactured steel parts to heat treatment may be different from conventionally manufactured steel parts due to variations in the as-deposited alloy microstructure. An understanding of heat treatment processes for additively manufactured steel parts is necessary to develop their heat treatment process parameters. In the present work, 20MnCr5 steel was selected to investigate the carburizing heat treatment of additively manufactured parts. These parts were fabricated by selective laser melting (SLM) for the carburizing study. It was found that the AM parts fabricated by the SLM process show the microstructure of tempered martensite, while the microstructure of as-received wrought part is ferrite and pearlite. It was also experimentally found that the SLM process decarburizes the entire SLM part. Before carburizing, a normalization process was conducted on both SLM and wrought 20MnCr5 parts to reduce the effect of the pre-carburizing microstructure. The objective of this project is to determine the carburizing performance of additively manufactured steel parts. The results for the SLM parts in terms of carbon concentration and microhardness profiles are compared with the results for the wrought steel. It was found that the carburized SLM part in the present work has higher carbon concentration near the surface, deeper case depth, and higher total carbon flux than the carburized wrought part. [ABSTRACT FROM AUTHOR]

Microstructure refinement strategies in simulated carburized microstructures were evaluated because of their potential for improving the fatigue performance of case-carburized components. Commercial 52100 steel was used to simulate the high-carbon content in the case. Specimens were subjected to various thermal treatments in a quenching dilatometer. Reheating cycles to austenitizing temperatures were evaluated with respect to both prior austenite grain size (PAGS) and associated martensite and retained austenite (RA) refinement. Quantitative stereological measurements were performed to evaluate the microgeometry of plate martensite and the size distribution of RA regions. Decreasing the reheating temperature resulted in finer PAGS, and multiple reheating cycles resulted in a narrower PAGS distribution. Refinement in PAGS led to a reduction in martensite plate size and finer distribution of RA. Additionally, interrupted quenching below martensite start (MS) temperature was evaluated. This processing route results in a refinement of martensite plates and more stable RA. The stabilization of austenite may be mechanical or chemical in nature, owing to the deformation of austenite during primary transformation, or due to partitioning of carbon into austenite similar to quenching and partitioning steels. [ABSTRACT FROM AUTHOR]

In the present study, we have examined the wear properties of the sintered pure iron subjected to two distinct heat treatments such as nitriding-quenching (NQ) and carburizing-quenching (CQ). Based on our current observations, the martensite layer was formed on the surface layer following each treatment, whereas the hardness of the NQ martensite was much higher than that of the CQ one. The wear of the CQ specimen was slightly smaller than that of the NQ martensite, despite the lower value of the initial hardness. Meanwhile, the hardness of the CQ surface after the sliding tests significantly elevated relative to the NQ surface resulting in the better wear resistance. EBSD analysis demonstrated that the plastic deformation on the CQ surface along the sliding direction. Furthermore, the micro area X-ray diffraction along the surface layer of the CQ surface showed that a small amount of the retained austeite which reduced locally during the test. Therefore, the CQ-treated surface showed the excellent wear resistivity due to the surface hardening by the stress-induced transformation of the retained austenite dispersed in the martensite, in addition to the strain hardening of the martensite itself. In contrast, the worn surface of the NQ specimen showed slight plastic deformations of the ferrite grains beneath the martensite layer, but not in the surface martensite layer. This deformation under the martensite layer was due to the hardness gap between inward and the heat-treated surface, and might contribute to form the concave profile on the sliding surface. Consequently, this study could demonstrate such the difference in the wear mechanisms between the CQ and the NQ specimens. [ABSTRACT FROM AUTHOR]

Carburizable martensitic stainless steels (MSSs) are attractive candidates for bearings due to their high corrosion resistance, high hardness, and high temperature performance. Wear performance in tribocorrosion applications is strongly influenced by the surrounding environment. Electrochemical testing was used to evaluate three different surface treatments on AMS 5930 steel developed for advanced gas turbine engine bearing applications: low temperature (LTT), high temperature (HTT), and carbonitrided (CN). HTT had a higher corrosion rate that increased with time, whereas LTT and CN had lower corrosion rates that were stable over time. Accelerated testing revealed that surface treatment significantly influenced how corrosion propagated: HTT was more uniform; conversely, LTT and CN showed localized attack. Degradation mechanisms developed from electrochemical methods provide rapid insight into long-term wear behavior. [ABSTRACT FROM AUTHOR]

Functionally graded WC–Co cemented carbides (FG WC–Co) with plate-like WC grains were fabricated by carburizing of cemented carbides with no η phase. The phase composition and microstructure of FG WC–Co were investigated by XRD, SEM and EDX. The results showed that a cobalt-deficient layer was formed due to difference in affinity among carbon and other alloying elements. WC grain size increased while the ratio of side length to thickness decreased slightly in the surface zone due to difference of growth rate between different planes of WC grains. Moreover, FG WC–Co possessed an 80 μm deep cobalt-deficient layer, and showed excellent mechanical properties with a surface hardness of 1748 HV and fracture toughness of 9.6 MPa · m1/2 in the surface zone. [ABSTRACT FROM AUTHOR]