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ABSTRACT In this paper, a new type of composite infiltration process was adopted for 20CrNi2Mo steel. Rolling contact fatigue (RCF) tests were carried out on the specimens treated with carburizing (C) and composite infiltration with carburizing and nitriding (C‐N). The results showed that after C and C‐N treatments were performed, the surface microhardness was increased by 78% and 114%, respectively, and the maximum CRS were −220 and −530 MPa. Moreover, the residual austenite volume fraction was controlled to approximately 10% for each treated sample. The fatigue limit of the C‐N sample was 11.3% higher than that of the C sample. The fatigue failure mechanisms are caused by the maximum shear stress distribution and surface roughness. The surface layer of the C‐N sample with higher hardness and more compressive residual stress inhibited the initiation of fatigue cracks, and the appropriate residual austenite in the carbon‐nitrogen infiltrated layer inhibited the propagation of fatigue cracks. [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.)

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]

Atmospheric-controlled induction-heating fine-particle peening (AIH-FPP) was applied to low-alloy, low-carbon steel AISI 4120 to achieve rapid carburizing within minutes and enhance fatigue strength. The shot particles used during AIH-FPP were specifically created by mechanically milling a mixture of steel particles and carbon powders. The specimens were analyzed using laser microscopy, optical microscopy, X-ray diffraction for residual stress measurement, a micro-Vickers hardness tester, and an electron probe micro-analyzer. Axial fatigue tests and fracture surface analyses via scanning electron microscopy and energy-dispersive X-ray spectroscopy were also conducted. AIH-FPP effectively transferred carbon to the treated surface and facilitated its diffusion in a short period, creating a martensite layer with high hardness and compressive residual stress, which resulted in increased fatigue strength. The fatigue strength of the AIH-FPP-treated specimens was influenced by the conditions of reheating and quenching, which altered the prior austenitic grain size and stress concentration at the specimen surface. Notably, specimens treated with AIH-FPP followed by reheating and water-injection quenching exhibited fatigue strength comparable to that of conventional gas-carburized specimens, owing to the formation of a carburized layer with a small prior austenite grain size.

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.)

CSS-42L is a new generation carburized bearing steel for the critical service environment of aero-engine applications. Owing to the complex composition and heat treatment, this steel exhibits unique microstructural features at the subsurface, one of which is the formation of soft austenitic transition layers. So far, a plausible mechanism of this phenomenon is still absent. In this study, a systematic investigation into such austenitic transition layer formation process is conducted. By using various characterisation techniques along with thermodynamic analysis, it is found that the contents of Cr and C in the matrix are dominated by the formation of different types of carbides along depth. With increasing depth, the undissolved carbides vary from M7C3 and M23C6 to M6C and to nil. This is postulated to result in a drastic decrease of martensitic start (Ms) temperature in the M6C region, leading to the formation of austenitic transition layers. The simulations of both microstructure and Ms temperature evolution along depth during heat treatment are performed for different austenitic temperatures and compared against the experimental observation, with good agreement obtained. This study reveals the mechanism of austenitic transition layers for the first time and provides useful instructions for the further microstructural design of such high-performance bearing steels.

ABSTRACTGears are key components of mechanical transmission systems. They need to be carburized and quenched to meet the requirements of internal toughness and external hardness, to obtain higher hardness and wear resistance. Heat treatment engineers can calculate carbon concentration distribution through the finite element analysis method, facing the challenge of high computational cost and high memory requirements. To solve this problem, a real-time prediction method of 1D and 2D carburizing concentration based on a Back Propagation (BP) neural network (BPNN) is proposed. First, carburizing experiments were conducted to verify the accuracy of the carburizing numerical model. Then, by establishing an accurate carburizing model, 37,800 and 177,147 1D and 2D carburizing training samples were generated using the finite element model (FEM) method, respectively. Finally, for 1D carburizing, the average relative error of the training model on the test set is 0.2911%. For 2D carburizing, the average relative error of the reconstructed BPNN model on the test set was 0.4381%, and a real-time performance evaluation was performed. The carbon concentration prediction time for each set of process parameters is only 0.12 s, nearly 175 times faster than FEM calculation, which meets the accuracy and real-time requirements for real-time prediction of carburizing carbon concentration.

AbstractThe 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 × 10−6 to 1.87 × 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 × 10−5 to 1.55 × 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.

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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 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]

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]

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.)

This paper investigates the effect of Nb and B microalloying on the wear and corrosion resistance of 20MnCr5 steel after high-temperature carburization at 950 °C. The abrasion and corrosion performance of the steel was compared using electrochemical experiments and dry sliding wear tests. The results show that Nb microalloying reduces the size of residual austenite, thereby improving the wear resistance of 20MnCr5 steel. Furthermore, the combination of Nb and B microalloying reduces the amount of residual austenite, leading to further improvements in wear resistance. Both microalloying methods reduce the wear scar depth and debris accumulation. The corrosion potentials of 20MnCr5, 20MnCr5Nb, and 20MnCr5NbB are 0.645 V, 0.627 V, and 0.675 V, respectively. The addition of Nb to 20MnCr5 steel results in higher corrosion resistance after carburization due to the refinement of needle-like martensite. However, 20MnCr5NbB steel exhibits low corrosion resistance due to the coarsening of needle-like martensite caused by B microalloying. In summary, this study provides new insights into the effects of microalloying elements on the properties of steel. The findings contribute to a deeper understanding of how to design and manufacture gears and other components with superior wear and corrosion resistance.

In this work, TA2 pure titanium was treated by borocarburizing (BC), boriding first and then carburizing (B + C), and carburizing first and then boriding (C + B), and morphology and wear and corrosion properties of these layers were investigated. The results show that the BC layer and B + C layer are composed of TiB, TiB2, and TiC phases, while the C + B layer consists of TiC and TiB2 phases. The wear type of these treated samples is abrasive wear, and wear resistance is in the sequence of B + C layer > BC layer > C + B layer. In 3.5 wt.% NaCl solution, corrosion resistance is in the order of B + C layer > C + B layer > BC layer > TA2. In 5.0 vol.% H2SO4 solution, corrosion resistance is in the order of C + B layer > B + C layer > BC layer > TA2. The B + C treatment can form a layer with gentle hardness gradient, excellent wear properties, and good corrosion resistance, which is most conducive to the bonding between layer and matrix.

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 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]

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]

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]

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.

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.

Austenitic stainless steel is a popular material for its corrosion resistant properties, however it has low hardness which limits its application. Low-temperature carburizing can be used to improve the mechanical properties of the austenitic stainless steel by producing expanded austenite layer. In order to get a high-quality layer and an efficient processing operation, the carburizing process must be optimized. In this research, a Taguchi method was utilized to investigate the effect of processing parameters related to the formation of the expanded austenite layer depth in austenitic stainless steel. Four factors were selected to be optimized namely temperature, gas flow rate, time, and gas composition with three levels each. L9(34) orthogonal array was applied with nine experimental tests to get the diffusion depth value of carbon in the expanded austenite layer. S/N ratio was used to determine the optimum factor combination with nominal-the-better quality characteristic and the most significant factor was obtained by applying the Analysis of Variance. Temperature was found to be the most significant factor with 54.91% contribution. The optimum combination was also successfully defined with temperature at 450°C (level 2), gas flow rate at 15 liter per minute (level 2), time at 12 hours (level 3), and gas composition at 15% CH4 – 5% H2 – 80% N2 (level 3). Clearly, in this study the Taguchi method was proven to be appropriately used as one of robust tools in optimizing the thermochemical treatment process parameters.

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]

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 μm, respectively, and with the use of a graphite powder, they are of 80, 120, 170 μm. 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.

In this study, the effect of thermochemical processes, such as nitriding and carburizing, on the microstructural evolution of superdúplex stainless steel is presented. The objective is to find a correlation between the microstructure and the mechanical properties of the constitutive phases of this stainless steel (i.e., austenite and ferrite) and analyze the diffusion elements influence on the precipitation of secondary phases, such as sigma (σ), chi (χ), nitrides, and carbides. Hardness (H) and elastic modulus (E) maps were obtained by using a high-speed nanoindentation technique. H and E values for the individual phases were determined through the application of Gaussian Mixture Model statistical analysis. Assessments of the mechanical properties of the different phases were achieved by overlaying field emission-scanning electron microscopy micrographs. An excellent correlation between microstructure and small-scale mechanical properties was attained. Secondary phases have been detected and nanoindentation statistics have proven their influence on the mechanical properties. • Impact of thermochemical processes on the microstructure of superduplex stainless steel. • Excellent correlation between constitutive phases and local mechanical properties is achieved using the Gaussian Mixture Model (GMM) method. • Integration of statistical sampling, high-speed nanoindentation techniques, and histograms enhances understanding of the mechanical properties of individual phases. • High-speed nanoindentation proves advantageous over EBDS. [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]