Vacuum Carburizing Research Articles

Effect of ultrasonic surface rolling process by disparate static pressure on a carburized layer of 17CrNiMo6 steel

Considering the elevated application requirements for transmission gears in terms of wear and corrosion resistance, this study investigates the impact of different static pressures (0.4 MPa, 0.6 MPa, 0.8 MPa) on the structure and protective properties of vacuum-carburized USRP layers, leveraging the technical advantages offered by vacuum carburizing and USRP. The findings demonstrate that using USRP facilitates fine-grained strengthening, and the thickness of the grain refinement layer increases proportionally with static pressure. The 0.6 MPa static pressure exhibits the most pronounced positive impact on grain refinement. The application of varying static pressures results in different surface integrity and microhardness levels within the carburized layer, thereby impacting the layer's wear and corrosion resistance. The coating exhibits the highest hardness and lowest roughness at a static pressure of 0.6 MPa, thereby demonstrating superior wear resistance. In addition, the 0.6 MPa layer with the lowest roughness has the best corrosion resistance.

Determination of Carbon Potential and Carbon Mass Transfer Coefficient During Vacuum Carburizing of Steel

Determination of Carbon Potential and Carbon Mass Transfer Coefficient During Vacuum Carburizing of Steel

Phase composition and numerical model of low-pressure pulse carburized layer in 15Cr14Co12Mo5Ni2W steel

Aerospace engine gear steel, 15Cr14Co12Mo5Ni2W steel, requires carburizing heat treatment to achieve operational performance. However, predicting the carbon concentration during the vacuum carburizing process poses significant challenges. This paper aims to design and establish a predictive model for the carbon concentration during the vacuum carburizing process of 15Cr14Co12Mo5Ni2W steel. Given the complex phase transformations during the vacuum carburizing process caused by the ultra-high alloy content of 15Cr14Co12Mo5Ni2W steel, vacuum short-term intense carburization and diffusion experiments were designed. Characterization methods such as XRD, scanning electron microscopy, electron probe microanalysis, EBSD, and FIB+TEM were used to study the microstructure, phase composition, phase constituents, and distribution of element concentrations during the vacuum carburizing process. Subsequently, a carbon concentration distribution calculation model considering carbide changes during the vacuum carburizing process of 15Cr14Co12Mo5Ni2W steel was established. Boundary conditions for carbon absorption during the intense carburization process of 15Cr14Co12Mo5Ni2W steel were proposed, and the relationship between surface carbon concentration and boundary conditions was determined through experiments. Using the method of forward calculation with least squares fitting of experimental data, the diffusion coefficient of carbon in the austenite of 15Cr14Co12Mo5Ni2W steel and the rate of carbon exchange between carbides and the matrix were derived, providing a more precise predictive tool for optimizing the vacuum carburizing process of 15Cr14Co12Mo5Ni2W steel.

Enhanced carburization efficiency and performance of vacuum carburized layers by La2O3-doped supersonic fine particle bombardment

In this work, the fabrication of supersonic fine particle bombardment (SFPB)-doped rare-earth pretreatment modified vacuum carburized layers were applied. The SFPB-doped La2O3 pretreated vacuum carburized reinforced layer was explored by common testing methods such as XRD, XPS, SEM, and TEM, focusing on the effects of La2O3-doped SFPB pretreatment on the decomposition, adsorption and diffusion of active carbon atoms and the diffusion mechanism. The composite carburizing behavior of La2O3-doped SFPB pretreatment modified layer under the action of thermal coupling is explored, and the influence law of rare earth modified carburizing and nano-modified carburizing on the thickness, residual stress, impact toughness, tribological properties of the carburized layer were clarified. The mechanism of mass transfer under the coupling role of pre-set surface defects and rare earth pinning was revealed. The case depth of the LSPC layer was increased by 14.3%, and the residual stress was significantly higher. The carbon diffusion coefficients of LSPC were 1.31 times superior to that of the vacuum carburizing layer, which is mainly attributed to the formation of a large number of nanocrystals with high-angle grain boundaries (HAGBs) by the rare-earth doped nanosized pretreatment, and the multiple synergistic strengthening effects of rare-earth oxides and nanocrystals.

Role of the martensitic microstructure in the stabilized residual stresses under cyclic loading and in the fatigue behavior of two steels

The influence of martensitic microstructure on the evolution of residual stresses during cyclic loading has been investigated using X-ray diffraction, both in martensite and in retained austenite. Different microstructures containing retained austenite fractions of 25% and 40% were obtained by vacuum carburizing applied to the 14NiCr11 steel. Additionally, other microstructures, such as quenched or tempered martensite of the 42CrMo4 steel were also studied.The results indicate that, for the same hardness and similar stabilized residual stresses in retained austenite, the greater the longitudinal residual stresses in quenched martensite, the greater the improvement in fatigue strength.From initial biaxial isotropic residual stresses, cyclic loading close to the endurance limit created anisotropic residual stress relaxation in quenched martensite and retained austenite. After cyclic loading, the longitudinal residual stresses were higher than the transverse residual stresses, regardless of the type of loading (bending in the case of 14NiCr11 carburized steel or combined bending and torsion in the case of the 42CrMo4 steel). The high level of longitudinal residual stresses after cyclic loading was correlated with the high retained austenite transformation to martensite in the case of 14NiCr11 carburized steel. The anisotropy of the stabilized residual stresses (after a few 10th of cycles) is due to the metastability of quenched martensite under cyclic loading.

Influence of Chemical Composition on Structure and Mechanical Properties of Vacuum-Carburized Low-Alloy Steels.

This study presents research results concerning the vacuum carburizing of four steel grades, specifically conforming to European standards 1.7243, 1.6587, 1.5920, and 1.3532. The experimental specimens exhibited variations primarily in nickel content, ranging from 0 to approximately 3.8 wt. %. As a comparative reference, gas carburizing was also conducted on the 1.3532 grade, which had the highest nickel content. Comprehensive structural analysis was carried out on the resultant carburized layers using a variety of techniques, such as optical and electron scanning, transmission microscopy, and X-ray diffraction. Additionally, mechanical properties such as hardness and fatigue strength were assessed. Fatigue strength evaluation was performed on un-notched samples having a circular cross-section with a diameter of 12 mm. Testing was executed via a three-point bending setup subjected to sinusoidally varying stresses ranging from 0 to maximum stress levels. The carburized layers produced had effective thicknesses from approximately 0.8 to 1.4 mm, surface hardness levels in the range of 600 to 700 HV, and estimated retained austenite contents from 10 to 20 vol%. The observed fatigue strength values for the layers varied within the range from 1000 to 1350 MPa. It was found that changing the processing method from gas carburizing, which induced internal oxidation phenomena, to vacuum carburizing improved the fatigue properties to a greater extent than increasing the nickel content of the steel.

ОСОБЕННОСТИ ФОРМИРОВАНИЯ ДИФФУЗИОННОГО СЛОЯ СТАЛИ ВНС32-ВИ, СОДЕРЖАЩЕЙ БЕРИЛЛИЙ, ПРИ РАЗЛИЧНЫХ ВИДАХ ХИМИКО-ТЕРМИЧЕСКОЙ ОБРАБОТКИ

A study of the formation features of a diffusion layer in VNS32 — VI steel containing beryllium during vacuum nitriding and carburizing has been carried out. It was established that saturation with carbon and nitrogen made it possible to remove delta ferrite from the structure. The successive combination of nitriding and carburizing due to the formation of a structure more favorable for the diffusion of interstitial elements on the surface of the samples provides an increase in the total thickness of the diffusion layer by 5—10 times more as compared to the thickness values for individual treatments.

Influence of Alloying Elements on the Carburizing Behavior in Acetylene Atmosphere

Three steel types (AISI 1020, AISI 8620, AISI 4120) with similar carbon content and different Cr content were used as test specimens to closely examine the effect of alloying elements for carbon penetration and diffusion on the steel surface during vacuum carburizing. The carbon mass gain according to the carburizing time was measured using a microbalance, and the average carbon flux, which is an indicator of the carbon penetration rate, was calculated using the measured weight as a variable. The outermost surface of the carburized specimen was observed by scanning electron microscopy (SEM) and Raman spectroscopy (RS), and the reason for the change in carburization rate according to the steel type was identified in relation to the equilibrium carbon contents calculated from Thermo-Calc. The overall carbon distribution and distribution of alloy elements on the outermost surface were quantitatively analyzed using an electron probe microanalyzer (EPMA). On the surfaces of the AISI 1020 and AISI 4120 carburized specimens, graphite layers and grain boundary carbide were formed during the carburizing process, which hindered the carburization rate, while no abnormal layer was observed on the surface of the AISI 8620 carburized specimens, so the overall carburization results were excellent.

Minimizing Deformations in High-Temperature Vacuum Carburizing.

This article presents the results of a study on reducing deformations resulting from high-temperature vacuum carburizing and post-carburizing heat treatment. The idea was to increase the strength of steel at elevated temperatures by pre-carburizing at heat-up to the process temperature (SC-stage carburizing). It has been shown that the use of carburizing in stages from a lower temperature to the target temperature, compared to traditional vacuum carburizing at a constant temperature (Constant-Temperature Carburizing-CTC), has a significant impact on the chemical and phase composition of the technological layer, surface after the process and, consequently, on its mechanical properties. It was shown that the retained austenite content after stage carburizing was reduced by approximately 45%, as was the thickness of the gear teeth measured at the pitch diameter. Additionally, uniform stress distribution was demonstrated for the SC process. Carbon saturation of austenite increases the yield strength, and therefore the dimensional stability of steel heat-treated at elevated temperatures also improves, which effectively permits high-temperature treatment of critical steel parts such as, for example, gear wheels, for which high dimensional accuracy is required.

Effects of thermo-chemical treatment and grinding process of external cylindrical surfaces on residual stresses in 13CrMo4-5 steel

This paper presents a study aimed at determining the effect of the carburizing treatment process and the subsequent grinding process on the residual stresses occurring in ring-shaped specimens made of 13CrMo4-5 steel.During the tests, vacuum carburizing was used, achieving an effective case depth ECD = 0.5 mm. Subsequently, the cylindrical outer surfaces of the samples were ground by conventional plunge grinding and with innovative kinematics using a test stand based on a conventional flat-surface grinding machine. As part of the study, microhardness and residual stresses were measured before and after grinding. Measurements were carried out to a depth of 1 mm. The main component of the stand is an original special device that allows the cylindrical specimen to be clamped. Then the angle between its axis of rotation and the axis of rotation of the grinding wheel is set with respect to the plane of the grinding machine’s magnetic table. In the described tests, the axis of rotation of the cylindrical specimen was deviated from its original position by 15 and set at an angle of 75 to the axis of rotation of the grinding wheel. The specimens were ground with a grinding wheel of noble electro-corundum marked 38A60K8V. In both kinematic cases of the grinding process, a machining allowance of 0.01 mm was removed.Grinding using innovative kinematics did not cause any significant changes in the microhardness distribution, either for vacuum or conventional carburizing. In addition, residual stress measurements using the Dawidenkov-Sachs method showed that innovative grinding enables a more favourable distribution than those obtained after conventional plunge grinding.Further research will focus on, among others, selecting the angular settings of the workpiece axes relative to the grinding wheel axes depending on their dimensions. Grinding guidelines should include coverage ratio, infeed value, grinding time, and peripheral speeds. In addition, the plan for future research includes measuring the components of the grinding force and the geometric structure of the surface.Grinding process is a crucial stage of steel treatment in almost every industrial branch. In sustainable manufacturing, it is extremely important to produce high-quality items while reducing the cost of manufacturing and taking care of the environment and workers’ health.The proposed test stand, together with the authors’ device, makes it possible to conduct machining of the external surfaces of cylindrical workpieces on a flat surface grinder. In this case, the innovation of the grinding process consists of the non-parallel alignment of the cylindrical rotational axis of the specimen and the rotational axis of the grinding wheel with respect to the plane of the magnetic grinding table.

Carburizing Rate of Pyrolysis Furnace Tube in Long-term Service

The high-temperature working environment of ethylene pyrolysis furnace tubes makes carburization one of the main damage mechanisms, and carburization also leads to the degradation of tube material properties and failure. It is important to study the carburization rate of long-term service furnace tubes for the evaluation of long-cycle use and carburization detection. In this paper, the relationship between carburization rate and carburization time is studied by low-pressure vacuum carburization of Cr35Ni45Nb alloy tubes with different service life (new tubes, two years, three years, and six years) in the field, aiming to provide a scientific basis for the remaining life prediction and carburization inspection for the tube material.

Microstructures of SUS304 Stainless Steel after Long-Term Service in Vacuum Carburizing Quenching

The microstructural changes and crack propagation in the carburized layer of SUS304 stainless steel due to repeated vacuum carburizing quenching as a heat treatment basket were investigated in this paper. As a result, beneath a graphite scale formed on the outermost surface, it was revealed that there were three types of carburized layers with different morphologies: M7C3 layer, M7C3/M23C6 mixed layer, and M23C6 layer (M = Cr, Mn, Fe). In addition, the surface was found to be uneven due to the occurrence of metal dusting. Besides, repeated heating and quenching caused the formation of voids in carbides and matrix in the carburized layer, and micro cracks appeared in the surrounding areas. Under the loading stress during vacuum carburizing quenching, these voids, micro cracks, and the uneven surface are considered to be the initial points for cracking.

Carbon-induced magnetic properties and anomalous Hall effect in Co2Mn2C thin films with L10 -like structures

${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$ thin films were synthesized via vacuum carburization of the host CoMn alloy films based on a conventional gas-solid reaction to demonstrate the effect of C, a common light element, on the magnetic and spintronic materials. The crystal structure transitioned from the disordered face-centered-cubic CoMn to the $L{1}_{0}$-like ${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$, for which the lattice constant increased from 0.356 to 0.378 nm. The C $1s$ x-ray photoemission spectra of the ${\mathrm{Co}}_{2}{\mathrm{Mn}}_{2}\mathrm{C}$ film indicated hybridization in C-Co and C-Mn and a homogeneous concentration of C in the film. The enhancement of both the saturation magnetization and the anomalous Hall conductivity (${\ensuremath{\sigma}}_{xy}$) was induced by C, attributing to the magnetic transition to the ferrimagnetic spin order. The surface flatness and high ${\ensuremath{\sigma}}_{xy}$ are promising characteristics for spintronic applications such as the spin-anomalous Hall effect. The atom- and spin-resolved density of states (DOS) via first-principles calculations revealed that face-centered Mn(II) and Co could be significantly influenced by C because of p-d hybridization, resulting in enhanced spin polarization of the DOS at the Fermi level of \ensuremath{\sim}0.82. These results demonstrate that the use of C could be an essential way to boost material properties in the future.

Machine learning based optimization method for vacuum carburizing process and its application

This paper develops an optimized prediction method based on machine learning for optimal process parameters for vacuum carburizing. The critical point is data expansion through machine learning based on a few parameters and data, which leads to optimizing parameters for vacuum carburization in heat treatment. This method extends the data volume by constructing a neural network with data augmentation in the presence of small data samples. In this paper, the database of 213 data is expanded to a database of 2116800 data by optimizing the prediction. Finally, we found the optimal vacuum carburizing process parameters through the vast database. The relative error of the three targets is less than that of the target obtained by the simulation of the corresponding parameters. The relative error is less than 5.6%, 1%, and 0.02%, respectively. Compared to simulations and actual experiments, the optimized prediction method in this paper saves much computational time. It provides a large amount of referable process parameter data while ensuring a certain level of accuracy.

Effect of the Atmosphere for Heat Treatment on Carbon Flux in Ultra-Rapid Carburizing

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 1523 K 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 1523 K in this study was only 5% of that for the conventional gas carburizing at 1203 K.

Enhanced impact and wear properties of gear steel by supersonic fine particle bombardment modification technology

In this work, the wear resistance and impact toughness of the carburized layer were improved by rare earth (RE) doped supersonic fine particle bombardment (SFPB) pretreatment assisted vacuum carburizing. On the surface of 17CrNiMo6 steel, vacuum carburizing (VC), SFPB vacuum carburizing (SC), and CeO2 doped SFPB vacuum carburizing (CSC) layers were formed, respectively. The effect of SFPB and CeO2 doping SFPB pretreatment on microstructure, impact toughness and wear resistance of carburized layers were investigated in detail. Results show that the microstructure of the CSC layer changes obviously, and equiaxed martensite and nano carbide are formed on the surface. The surface impact toughness and wear resistance of the SC layer and the CSC layer are significantly improved, compared with that of the VC layer. In particular, the impact absorbed energy of CeO2 doping SFPB carburized (CSC) (60.8 J) was 30.8% higher than that of the VC (46.5 J), which is attributed to the refinement of martensite and austenite by pretreatment. Among the carburized layers, the modified carburized layer doped with CeO2 (CSC) had the minimum wear rate (9.45 × 10−15m3N−1 m−1), indicating the strongest resistance to wear. Meanwhile, the wear rate of the CSC layer was increased by 11% compared to that of the VC layer. Moreover, the main wear mechanism of various carburizing layers was abrasive wear.

Influence of Nb Addition on Microstructure and Creep Property of Heat-Resistant Cast Steel in Vacuum Carburizing and Quenching

The relation between microstructure and creep property of austenitic heat-resistant cast steels with and without Nb addition under the condition of repeated vacuum carburizing and quenching was investigated. Cr-carbide scale is formed on the sample surface by a carburizing reaction, resulting in the depletion of Cr in the matrix adjacent to the scale. A carburized layer consisting of various fine carbides is observed below the Cr-depleted layer, and the carburized layer depth is suppressed by Nb addition. When process of vacuum carburizing and quenching is repeated, formation of voids caused by heating and rapid cooling is more remarkable in primary Cr carbides than in primary Nb carbides. As the carburized layer depth increases, creep rupture time of both cast steels shifts to the shorter time side; however, Nb addition is effective for extending creep rupture time at 1303 K.

The Effect of Vacuum Carburizing on the Mechanical and Wear Properties of Fe–C–Cu Composite Materials Produced via Powder Metallurgy

The Effect of Vacuum Carburizing on the Mechanical and Wear Properties of Fe–C–Cu Composite Materials Produced via Powder Metallurgy

Multi-field coupling simulation of vacuum carburizing and high-pressure gas quenching process

Vacuum carburizing and high-pressure gas quenching process is being widely used in the heat treatment industry. There is an urgent need for a mature technology to predict the influence of carbon content and quenching gas flow on the microstructure and mechanical performance of workpieces. In this paper, a coupling simulation system of the flow field, temperature field, phase field, and stress-strain field was established. And simulations and experiments were carried out for an 18CrNiMo cylindrical sample and a 20CrMnTi gear hub. The results prove that this system can realize the synchronous coupling simulation of the above physical fields, and the simulation results are accurate and applicable to complex shape parts, therefore can guide the design of the process control scheme of the vacuum carburizing and high-pressure gas quenching process.

Surface Hardening Behavior of Advanced Gear Steel C61 by a Novel Solid-Solution Carburizing Process

During vacuum carburizing, coarse reticulated carbides tend to precipitate along grain boundaries due to high-carbon-potential conditions. This phenomenon is often one of the main factors in the failure of conventional gear steels. In this paper, a novel solid-solution carburizing process was proposed to achieve nano-carbide formation in the surface of the carburizing layer, and the conventional carburizing process and material thermodynamic calculations were combined to study the carburized layer by changing the parameters of the carburizing process, and to optimize the microstructure and properties of the carburized layer. The results showed that the high carbon potential or the long-time boost carburizing process could easily cause the enrichment of many carbon atoms in the traditional carburization, thus forming a carbide network and decreasing the carburization efficiency. The minor increase in large-sized M7C3 carbides did not significantly improve the surface hardness and wear resistance. However, the presence of small and dispersed M2C carbides was the main factor in improving the microhardness and mechanical properties. The novel solid-solution carburizing process could improve the carburizing efficiency and transform reticulated carbides into nano-dispersed M2C carbides. The surface carbon content and microhardness of 1.07% and 875 HV, respectively, increased 17.7 and 2.4% compared to conventional carburizing processes at 1100 °C. On the other hand, the surface’s ultimate tensile strength was found to be 1900 MPa by mini-tensile testing, and the core had a good match of strength and toughness. It was concluded that the novel solid-solution carburizing process could dissolve the carbon network and thus effectively increase the surface carbon content, achieving fully nanosized carbide on the surface. Modifying the size, morphology, and distribution of the nano-M2C carbides dispersed within the lath-martensite after tempering the test steel was found to be the main factor in improving the mechanical properties.