Vacuum Carburizing Research Articles

Influence of the Temperature of Vacuum Carburizing on the Thickness of the Carburized Layer and Properties of Steel Parts

The properties of steel parts after carburizing in low-pressure acetylene are studied. The thickness of the carburized layer, its hardness, the microstructure, and the hardness of the core are determined after carburizing at 900 – 960°C with simultaneous shortening of the process from 104 to 44 min. The data obtained for the diffusion of carbon make it possible to predict the profiles of carbon distribution over the thickness with good enough accuracy.

Effect of Mo in Combination with Nb on Austenite Grain Size Control in Vacuum Carburizing Steels

Vacuum carburizing with high-pressure gas quenching is increasingly employed to reduce near-surface intergranular oxidation and reduce quenching distortion. Vacuum carburizing can be conducted at higher operating temperatures, as high as 1100 °C, to reduce the processing times and increase furnace productivity. However, processing at elevated temperatures may result in excessive austenite grain coarsening, leading to the degradation of fatigue performance. Microalloying to form small carbo-nitride precipitates is one effective method to limit austenite grain growth during carburizing. In this study, the effects of microalloying a carburizing steel with molybdenum (Mo) and niobium (Nb) on microstructural grain refinement in the core have been investigated. Additions of Nb alone are found to provide some control of abnormal austenite grain growth. Additions of Mo in combination with Nb provide enhanced resistance to austenite grain growth, especially at high carburizing temperatures up to 1050 °C. The enhanced control is attributed to solute and precipitation effects.

Effect of Surface Condition on the Torsional Fatigue Behaviour of 20MnCr5 Steel

Torsional fatigue behaviour of steel is influenced by various significant factors on the surface of steel such as the stress state, the metallurgical conditions and the surface roughness etc. This research presents the results of the studies conducted on the torsional fatigue life of steel for different surface stresses, conditions and microstructures. Based on the results, inferences were derived out of the factors and conditions which are instrumental in increasing the fatigue performance. This research is done with the purpose of increasing the fatigue performance of power train shafts processed through vacuum carburizing followed by second tempering. The fatigue tests were conducted using a bi-directional torsional cyclic loading in a MTS make torque testing machine. Various researches has been conducted in this paper to find out the impact of surface roughness, second tempering, inter granular oxidation and carbon case depth on the transmission shafts. The existence of surface retained austenite has not yielded a notable enhancement in fatigue performance in the power train shaft whereas existence of martensite with minimum fraction of retained austenite enhanced the fatigue performance significantly from 12,000 to 35,000 cycles on ± 3100 N m torque load.

Resource-saving optimal control of energy-intensive process of work part thermochemical treatment

Paper discusses approach to the resource-saving optimal control algorithms development, which includes problem oriented mathematical modeling of the process, determination of the tolerance limits for controlling action changes and condition of thermochemical treatment process as a subject under control, optimality criteria formalization and determination. Specified and solved critical problems for resource-saving optimal control of energy-intensive thermochemical process of work parts treatment on the maximum accuracy and speed of operation criteria. Alternance optimization method was used for optimal control problems solution, which allows to determine not only interval of constancy size but also maximum achievable control accuracy in every subset of intervals. Analytical mathematical model of vacuum carburizing in an acetylene atmosphere with variable coefficients of mass transfer was developed, which takes into consideration different mechanisms of carbon mass transfer from the atmosphere into the work part surfaces at the saturation and diffusion stages. Dependences of the carburization accuracy on the optimal control parameters were constructed. Influence of the technological constraints on the control quality was analyzed. Suggested approach demonstrated high energy efficiency.

Vacuum Carburization of a Transmission Shaft

Abstract Tests conducted on vacuum carburized and quenched shafts identify variables that increase distortion and the magnitude of residual stresses.

Influence of quenching temperature of the individual quenching method on the geometrical dimensions of the elements

The quenching process is related to the internal-stress phenomena, resulting in geometric changes (distortions). In this paper, the impact of hardening temperature on the quenching distortions occurring during low-pressure carburizing with gas quenching using the individual quenching method was analyzed. The reference elements were subjected to carburizing at 980°C, followed by gas quenching at temperatures of 860°C, 920°C and 980°C. The geometrical measurements of the elements were made before and after the chemical treatment and the size of the quenching distortions of their geometrical parameters was determined: external and internal diameters as well as ring thickness. The study examined whether there is a statistically significant difference between the geometrical dimensions of the elements before and after the thermo-chemical treatment for the elements in three temperature groups. It was shown that for the ring thickness parameter there are no significant differences between the groups of elements before and after heat treatment for the temperature 980°C, while for the temperature 860°C and 920°C these changes are significant. However, for external diameter bottom, there is always a difference regardless of temperature. For the single piece-flow vacuum carburizing with gas quenching using the individual quenching method, it is advisable to use the highest possible quenching temperatures to reduce quenching distortions.

The influence of grinding conditions on surface roughness parameters of 20MnCr5 steel vacuum-carburised by single-piece flow method

The purpose of the experimental tests described in the article was to determine the effect of selected abrasive machining conditions on the value of surface roughness of 20MnCr5 steel samples. The samples were subjected to vacuum carburising (LPC) using the ‘single-piece flow’ method and high-pressure gas quenching (HPGQ) in a 4D Quenching chamber to obtain an effective case depth (ECD) of 0.4 mm. Next, the samples were ground with a Norton Vortex corundum grinding wheel. Cooling and lubricating fluid was delivered to the grinding zone using the flooding method (WET) and with the minimum quantity lubrication method (MQL). The samples were ground in one pass of the grinding wheel using two grinding depths – ae = 0.01 mm and ae = 0.02 mm. For each grinding test, surface roughness measurements were made using a stationary laboratory profilometer T8000 from Hommel Werke. These measurements enabled the determination of the 2D and 3D roughness parameters. Analysis of the measurement results showed that for the adopted test conditions, the use of the MQL method resulted in a decrease in surface roughness compared to the surface ground using the WET method. This property applies to both tested grinding depths.

Effect of vacuum carburizing on surface properties and microstructure of a tungsten heavy alloy

Vacuum carburizing of the R2M tungsten alloy was carried out to obtain a carburized layer that improves the surface properties. The effects of various carburizing temperatures and times on the structure and hardness were studied by Optical microscopy(OM), x-ray Diffraction(XRD) and Scanning electron microscope(SEM). In this work, the microstructure of the carburized layer, the relative content of the surface layer, the depth of the layer and the microhardness of the carburized sample were studied. The results show that the microstructure exhibited three layers from the surface to the bulk of the sample after carburizing. The outside layer comprised a 40 ∼ 60 μm deep WC carburized layer. The hardness of the surface layer (396 HV) was significantly higher than that of the substrate (282 HV). As the carburizing temperature and time increased, the WC and W content of the surface layer of the sample gradually increased, and the depth of the carburized outer layer increased.

Features for formation of diffusion layers during vacuum carburizing of 12Kh2N4A-Sh and 20Kh3MVF-Sh steels

The patterns reflecting the influence of controlling technological parameters on the characteristics of the carburized layer during vacuum carburizing of 12Kh2N4A-Sh and 20Kh3MVF-Sh steels are considered. The need is shown to take into account the presence or absence of active carbide-forming elements in the composition of carburizing steels when developing of vacuum carburizing modes.

The influence of carburization technology on performance properties of high-loaded gear wheels

The purpose of the study is to develop a technology for vacuum carburization of heat-resistant steels, taking into account the requirements for the structure of the carburised layer to ensure the operational properties of gears.The paper describes the issues of improving the operating characteristic of heavily loaded gears made of high-strength steels. Information on the modes of vacuum cementation is given. A technological process has been developed that ensures the presence of carbides on the tooth profiles, the absence of a carbide mesh in the cemented layer and the optimal mechanical properties of the gears. Recommendations on the choice of modes of diffusion saturation to ensure wear resistance, contact endurance, bending strength of gears made of heat-resistant steels are proposed.

Friction Property under Lubrication for Case Hardening Steel Subjected to Combined Thermomechanical Treatment with Excess Vacuum Carburizing and Subsequent Severe Plastic Deformation and Induction Hardening

Friction Property under Lubrication for Case Hardening Steel Subjected to Combined Thermomechanical Treatment with Excess Vacuum Carburizing and Subsequent Severe Plastic Deformation and Induction Hardening

Influence of surface nanocrystallization pretreatment on high-temperature vacuum carburizing behavior

Abstract The supersonic fine particles bombarding (SFPB) pretreatment is adopted to assist vacuum carburizing for refining the microstructure and improving the mechanical properties of carburized layer. The microstructures, micrhardness and tribology properties of SFPB carburized sample and vacuum carburized sample were studied. The results showed that SFPB pretreatment could form random oriented, ultrafine-grained microstructure and high density dislocations in AISI 9310 steel, leading to the increase of case depth of carburized layer, the refinement of grain size and the promotion of the formation of twin martensite and carbides in carburized layer. Besides, the surface microhardness, maximum residual compressive stress and wear rate of carburized layer were enhanced by SFPB pretreatment, which was attributed to the formation of twin martensite, grain refinement, dispersion strengthening of carbides and the increase of high misorientation angle grain boundary.

High cycle fatigue behavior of a low carbon alloy steel: The influence of vacuum carburizing treatment

The present investigation attempts to explore the influence of vacuum carburizing treatment on the high cycle fatigue behavior of a low carbon alloy steel 20Cr2Ni4 by using rotating bending fatigue test. The same heat steel subjected to conventional quenched & tempered (QT) treatment was used for comparison. It was found that the vacuum carburizing treatment significantly promoted the formation of a particular area of granular bright facet in the vicinity of non-metallic inclusion in the fatigue crack initiation region with fatigue life beyond ~106 cycles and thus caused mainly an interior inclusion-induced failure mode compared with the QT treatment. Both the high cycle fatigue strength and the threshold value of stress intensity factor range controlling macroscopic crack growth were significantly enhanced on condition that the crack initiation site was still within the carburized case layer. These beneficial enhancements are mainly ascribed to the introduction of a case layer with much higher hardness and compressive residual stress.

The effect of grit-blasting on the formation of a carburized layer in the vacuum carburizing

The effect of grit-blasting on the formation of a carburized layer in the vacuum carburizing

Carburization induced extra-long rolling contact fatigue life of high carbon bearing steel

For the first time, vacuum carburization surface treatment was applied to high carbon bearing steel 100Cr6. The rolling contact fatigue (RCF) life and the wear behavior of 100Cr6 with and without carburization were compared and the microstructure was characterized. The carburization results in 30 vol% cementite and ~20 vol% retained austenite in the surface layer, significantly higher than those processed by the conventional heat treatment. RCF life (L10) is significantly enhanced by more than 10 times from 1 × 107 cycles to ≥1 × 108 cycles by carburization. This enhancement is attributed to plate/rod cementite and retained austenite.

Study of the Catalytic Strengthening of a Vacuum Carburized Layer on Alloy Steel by Rare Earth Pre-Implantation.

Conventional carburizing has disadvantages, such as high energy consumption, large deformation of parts, and an imperfect structure of the carburizing layer. Hence, a rare earth ion pre-implantation method was used to catalyze and strengthen the carburized layer of 20Cr2Ni4A alloy steel. In this study, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive microanalysis (EDS), transmission electron microscopy (TEM), and Rockwell/Vickers hardness testing were used to analyze the microstructure, phase composition, retained austenite content, hardness, carburized layer thickness, and carbon diffusion. The results showed that lanthanum and yttrium ions implanted into the 20Cr2Ni4A steel formed solid solutions of rare earth ions and a large number of dislocations, which improved the diffusion coefficient of carbon elements on the carburized surface and the uniformity of the carbon distribution. Simultaneously, rare earth ion implantation improved the structure and hardness of the vacuum carburized layer. Compared to the lanthanum ion implantation, yttrium ion implantation caused the structure of the carburized layer to be finer, and the carbon diffusion coefficient increased by 1.17 times; in addition, the surface hardness of the carburized layer was 61.8 HRC.

Experimental study on carbon flux in vacuum carburizing

Traditional oxygen sensing probes fail to work in low-pressure vacuum carburizing processes. Currently, there is no effective sensing device that can directly measure the carbon potential in a vacuum furnace. Therefore, the accurate measurement and calculation of carbon flux is an important and urgent issue to be solved for the development of low-pressure vacuum carburizing. In this work, the process of carbon atom diffusion into metal is discussed by theoretical and experimental analyses, and a test method applicable to the determination of carbon flux in low-pressure vacuum carburization is investigated. At the carburizing pressure of 300 Pa and the carburizing temperature of 930 °C, the carbon flux is measured in a self-developed low-pressure vacuum carburizing furnace with the change in carburizing time from 0 to 64 s. The effects of carburizing pressure and carburizing temperature on surface carbon flux are investigated under different carburizing pressures of 100 Pa, 200 Pa, 300 Pa and different carburizing temperatures of 930 °C, 950 °C, 980 °C. With the examination of the temperature influence on the carbon flux, a carbon flux model is established for the low-pressure vacuum carburization of 12Cr2Ni4 steel.

The influence of hardening medium in the vacuum carburizing process on the distortion of machine elements used in the automotive industry

Purpose: As part of this study, the influence of the hardening medium on distortions of FineCarb® carburized rollers used in the automotive industry as elements of fuel pumps has been examined. The analysis was carried out for the process of quenching in gas at different pressure of cooling gas and quenching in oil at variable delay time of oil mixers. Design/methodology/approach: The research was carried out on real elements used in the automotive industry as elements of fuel pumps. FineCarb® vacuum carburizing technology was used in order to obtain optimal parameters of the surface layers. During quenching a variable related to the parameters of the quenching medium was introduced. For quenching in gas it was the pressure at which nitrogen was introduced into the cooling chamber, while for quenching in oil it was the time of mixers delay. The sample batch was laid out in accordance with the PPAP (Production Part Approval Process) requirements for the automotive industry. Microhardness and radial runout measurements were carried out on the samples and subjected to statistical analysis. Findings: The analysis of each hardening processes has showed that depending on the cooling medium used, different distortion values are obtained. The distortion value is significantly influenced by the parameters of the hardening process – gas pressure/oil mixers delay. With the proposed quenching parameters, there is no relationship between the location of the sample in the furnace chamber and the distortion value. The smallest hardening distortions were obtained as a result of the hardening process in gas at a gas pressure of 3 bar. Hardening in gas was characterized by the smallest scatter values of obtained results of radial runout. Research limitations/implications: Basing on the studies and analyses carried out in this work, it can be concluded that the introduction of gas quenching technology instead of oil quenching technology is justified qualitatively and economically alike. Hardening in gas was also characterized by the smallest scatter values of obtained results of radial runout. This is an extremely important technological and economic aspect, due to the cost of grinding processing. Practical implications: The automotive and aviation industries are putting ever greater demands on the quality of manufactured components while reducing costs. Volume 94 • Issues 1-2 • May-June 2019 It requires optimization of technological processes from co-operators. In the case of hardening plants, the most important aspect is obtaining repeatable, precisely planned parameters of the carburized layer, as well as minimizing the negative phenomena that cause dimensional changes after hardening of elements. The tests allowed to determine the most effective hardening conditions in terms of obtained distortions and costs of eliminating distortions. However, the selection of the optimal parameters depends on whether the core hardness requirements are also determined. Originality/value: The conducted tests allowed to determine the most effective hardening conditions in terms of obtained distortions, costs of levelling distortions and a complete technological process for the automotive industry.

Technological Features of Vacuum Carburizing of Low-Alloyed Steels

Technological factors are studied for the vacuum carburizing of low-alloy steels. The features of vacuum carburizing cyclic modes caused by a changing carbon layer structure formed on the saturated surface as a result of the catalytic dissociation of acetylene molecules are considered. Different variants of the process are proposed. The advantages of vacuum carburizing, which provides an improvement in the operating properties of the treated parts in mechanical engineering, are stated.

Tribological performance of GLC, WC/GLC and TiN films on the carburized M50NiL steel

To improve the tribological performance of M50NiL aero-bearing steel, the TiN, GLC and WC/GLC films were deposited on the M50NiL steel treated by low pressure vacuum carburizing. GLC and WC/GLC films were prepared using unbalance magnetron sputtering system, and TiN films were deposited by magnetic filtered cathode vacuum arc system. The microstructures and mechanical properties of the films were evaluated. The tribological properties of the films were investigated in different environments including dry sliding and #4010 aviation lubricant. The results show that, in dry sliding, WC/GLC film exhibits better tribological performance than GLC film under the load ranging from 5 N to 15 N, while as the load increases to 20 N, the wear rate of WC/GLC film is about 10% higher than that of GLC film. In #4010 aviation lubricant, under the full load ranging from 5 N to 30 N, TiN film shows lower friction coefficient than GLC film, and WC/GLC film performs the best tribological performance. Moreover, the wear mechanisms of TiN, GLC and WC/GLC films were analyzed.