Effective Case Depth Research Articles

Simulation of Case Depth of Cementation Steels According to Fick's Laws

The carburizing process is the enrichment of the depth of low carbon steels with carbon. It leads to samples with a combination of high surface hardness and high core toughness and to an impact strength that is required for many engineering parts. The material studied is a low carbon steel. The carbon content is little in this type of steel (wC = 0.2%). The calculation of case depth is very important for cementation steels that are hardened in the carburizing process. The effective case depth is defined as the perpendicular distance from the surface to a place at which the hardness is HV 550. Nowadays, a great number of studies have been carried out on the simulation of effective case depth, but no studies have been conducted to determine the numerical relation between the total case depth on one hand and the carburizing time and the effective case depth on the other hand. The steel specimens were subjected to graphite powder. Then, they were heat treated at 925 °C for about 3, 5, 8 and 12 h, respectively. Then, these parts were quenched in oil. To determine the effective case depth, the microhardness test was performed on the cross-section of specimens. Plotting the case depth vs carburizing time, the required conditions for obtaining the specified case depth were determined. Also, the comparison between the case depths in numerical solution and the actual position in pack carburizing was performed.

Dual-Frequency Approach to Assess Surface Hardened Layer Using NDE Technology

Inspection and quality control of induction hardened parts require a good understanding of the depth of the hardened layer. Traditional destructive methods to determine the case depth are considered to be costly and time-consuming. The eddy current (EC) technique is sensitive to micro-structural changes; hence, it can be used to determine the case depth based on the differences in magnetic properties between the hardened layer and the core of the specimen. In this study, identical rods of AISI 1045 mild carbon steel were surface hardened using induction hardening technique. In order to investigate the applicability of the EC technique, the relations between obtained effective and total case depths and the EC outputs (induced voltage, normalized impedance, phase angle, and their harmonic characteristics) were studied. The results show a maximum of correlation coefficient of 94% in determining case depths by EC technique.

Quality optimisation of induction hardened parts using desirability function

This paper discusses single and multiple characteristics optimisation of induction hardened AISI 1040 steel in rolled condition. Face centred central composite design was used for experimentation. Response surface methodology was used for modelling the responses. Desirability function in conjunction with RSM was used for the optimisation of responses. The results are validated from the existing knowledge of physical metallurgy in general. The solutions, thus developed using different practical and industrial situations, can easily be utilised for tailor-made production of the steel of desired hardness, total case depth and mean effective case depth.

Laser photothermal radiometric instrument for industrial steel hardness inspection

To meet the industrial demand for on-line steel hardness inspection and quality control, a non-contact, non-destructive laser photothermal radiometric instrument (HD-PTR) was developed. The instrument is equipped with a non-liquid-nitrogen-cooled HgCdZnTe (MCZT) detector, a National Instruments data acquisition card with a Dynamic System Analysis (DSA) module, and control software. A series of industrial steel samples which included automotive screws and aircraft gears (flat or curvilinear) were examined. The effective hardness case depths of these samples ranged from 0.21 mm to 1.78 mm. The results demonstrated that three measurement parameters (metrics) can be extracted when using a fast swept-sine photothermal method. These parameters include the phase minimum (or peak) frequency, fmin, the half width, W, and the area, S. It was found that they are complementary for evaluating widely different ranges of hardness case depths. fminis most suitable for large case depths, and W and S for shallower case depths.

Effect of process temperature on the microstructure and properties of gas oxynitrocarburized 35CrMo alloy steel

In the present investigation, 35CrMo alloy steel was gas oxynitrocarburized at 550 °С, 570 °С and 610 °С for 2 h by applying a low-temperature gas multi-elements penetrating system. Microstructure, surface composition, case depth, microhardness, wear and corrosion resistance were analyzed. The compound layer consisting of γ′-Fe 4N and ε-Fe 3N and oxide layer of Fe 3O 4 and Fe 2O 3 were formed on the ground reference surface after treated. Compared with the conventional gas nitrocarburizing, a larger effective case depth was obtained successfully in a short time after treatment. The microhardness and the properties of wear and corrosion resistance were improved obviously and the properties of samples treated at 570 °C are optimum when compared with the samples treated at 550 °С and 610 °С for the same duration.

Evaluation of gas nitriding process with in-process variation of nitriding potential for AISI H13 tool steel

Gas nitriding under controlled nitriding potential represents one of the important factors in enhancing the service life of dies used in the industry for hot aluminum extrusion. In the present study, AISI H13, a typical material used for hot extrusion dies, is gas nitrided using automated two-stage controlled nitriding process. Prior heat treatment on the material was carried out under the same controlled environment as used for hot extrusion dies to avoid any decarburization. The nitrided layer has been characterized using different techniques including optical microscopy, SEM, XRD, EDS, and microhardness analysis. It was found that controlled nitriding with in-process variation of nitriding potential can efficiently be used to control the morphology of compound layer and diffusion zone, effective case depth, case hardness, and quality of nitrided layer at sharp edges for better die performance. All the results were found in close agreement with established specifications required for improved die performance.

Effect of Alloy Composition on Carburizing Performance of Steel

This paper investigates the effect of alloy composition on the gas carburizing performance of AISI 1018, 4820, 5120, and 8620 steels. The mass-transfer coefficients and carbon diffusivities were calculated from experimental measurements using direct flux integration. Although steels with high concentration of austenite-stabilizing elements (Si, Ni) increased carbon diffusivity in austenite, they significantly reduced the kinetics of carbon transfer from the atmosphere to the steel surface and resulted in lower weight gain. Despite lowering the carbon diffusivities, steels alloyed with carbide-forming elements (Cr, Mo) significantly increased the mass-transfer coefficient in the atmosphere and enhanced the rate of carbon profile evolution. The experimentally determined carbon diffusivities were in good agreement with the carbon diffusivities obtained from the thermodynamic and kinetic databases in DICTRA. Overall, using the concentration dependent mass-transfer coefficient and carbon diffusivity in various alloy steels helped explain the experimentally observed variations in the carbon concentration profiles and the effective case depths. Recommendations are made to help achieve better case depth uniformity within a carburizing workload.

Plasma and gaseous nitrocarburizing of C60W steel for tribological applications

A comparison has been made between plasma and gas nitrocarburizing processes for C60W steel in terms of structural features of the layers and the tribological properties of the specimens. Gaseous treatments were performed in a sealed quench industrial furnace in optimized process cycles. A semi – industrial size unit was operated at a range of process parameters for plasma nitrocarburizing. Experimental results indicate that increasing the treatment time increases the thickness of the compound layer but lowers the wear resistance. Plasma treatment produced a more effective case depth compared with gaseous process, providing a better uniformity. Analysis of X-ray diffraction patterns indicated that the compound layer in gas nitrocarburizing and plasma nitrocarburizing consisted of both ɛ and γ′ phases.

Laser photothermal radiometric instrumentation for fast in-line industrial steel hardness inspection and case depth measurements

A contact-free, nondestructive laser photothermal radiometric instrumentation technique was developed to meet industrial demand for on-line steel hardness inspection and quality control. A series of industrial steel samples, flat or curvilinear, with different effective hardness case depths ranging between 0.21 and 1.78 mm were measured. The results demonstrated that three measurement parameters (metrics) extracted from fast swept-sine photothermal excitation and measurements, namely, the phase minimum frequency f(min), the peak or trough frequency width W, and the area S, are complementary for evaluating widely different ranges of hardness case depth: f(min) is most suitable for large case depths, and W and S for small case depths. It was also found that laser beam angular inclination with respect to the surface plane of the sample strongly affects hardness measurement resolution and that the phase frequency maximum is more reliable than the amplitude maximum for laser beam focusing on the sample surface.

Influence of laser beam size on measurement sensitivity of thermophysical property gradients in layered structures using thermal-wave techniques

The influence of the photothermal laser source beam size on the measurement sensitivity of layered systems using photothermal radiometry (PTR) is presented. Based on an appropriate theoretical model, widely different behaviors of the photothermal amplitude and phase in terms of combinations of thermophysical properties (i.e., thermal conductivity and thermal diffusivity) between a thin coating and the substrate are observed. The beam size effect on PTR measurement sensitivity is theoretically examined and experimentally demonstrated using a carbonitrided C1018 steel sample. The experimental results of using a variable size laser beam for the carbonitrided C1018 sample validate the theoretical prediction, in which an expanded beam exhibits a much larger magnitude change in both amplitude and phase as a function of frequency than measurements with a focused beam. The fitted thermal conductivity and thermal diffusivity based on the assumed industrially relevant range of effective hardness case depth gives the approximate range of the change in thermal conductivity and thermal diffusivity of C1018 steels after the carbonitriding process.

Evaluation of effective case depth in heat treated steel products using photothermal radiometry

A quantitative calibrated methodology based on photothermal radiometric (PTR) depth-profilometry for non-contact, non-intrusive determination of effective case depth in heat treated case-hardened steel products was developed. Several types of heat-treated C1018 industrial steel screw products (with hexa- gonal, cylindrical and spherical heads) were statistically evaluated using the case-depth – induced interferometric thermal-wave phase minima. Calibration curves for each type of sample were established with the help of conventional destructive indenter measurements. It is shown that PTR thermal-wave interferometric phase minima can be used as a fast, on-line inspection methodology of industrial steel products for non-destructive quality control of heat treating processes.

Characterization of hardened cylindrical samples using photothermal radiometry

The evaluation of the hardness case depth and the measurement of the thermophysical properties of cylindrical C1018 heat-treated steel rods has been demonstrated. By using a cylindrical two-layer model and a multi-parameter fitting algorithm, the effective case depth and the corresponding thermal conductivity and thermal diffusivity of the hardened layer are obtained for a nominal 0.04′′ case depth hardening. The measurement results from different samples in the same batch of heat treated cylinders are consistent with each other and are also consistent with mechanical indentater test results in the sense of yielding an effective case depth within the discrete two-layer thermal-wave approximation.

Characterization of hardened cylindrical C1018 steel rods (0.14%–0.2% C, 0.6%–0.9% Mn) using photothermal radiometry

Frequency-domain photothermal radiometry has been used for the evaluation of the hardened case depth and the measurement of the thermophysical properties (thermal conductivity and diffusivity) of cylindrical C1018 heat-treated steel rods. The measurement results of several steel cylinders nominally hardened identically during a common heat-treating process were consistent with each other and also with mechanical indentation hardness test results. The application of the two-layer composite cylinder thermal-wave theory yielded an effective case depth within the discrete two-layer thermal-wave approximation. This technique provides a relatively simple noncontact and nondestructive method for evaluating the thermophysical parameters of layered cylindrical samples. The good fit of the experimental frequency scans to the two-layer thermal-wave model was shown to constitute a reasonable method for calibrating actual continuously decreasing hardness depth profiles by means of abrupt two-layer-equivalent profiles.

Case depth determination in heat-treated industrial steel products using photothermal radiometric interferometric phase minima

A quantitative calibrated methodology based on photothermal radiometric (PTR) depth-profilometry for non-contact, non-intrusive determination of effective case depth in heat-treated case-hardened steel products was developed. Several types of heat-treated C1018 industrial steel screw products (with hexagonal, cylindrical and spherical heads) are statistically evaluated using the case-depth-induced interferometric thermal-wave phase minima. Calibration curves for each type of sample are established with the help of conventional destructive indenter measurements. It is shown that PTR thermal-wave interferometric phase minima can be used as a fast, on-line inspection methodology of industrial steel products for non-destructive quality and feedback control of heat-treating processes.

A method to predict effective case depth in ion nitrided steels

Ion nitriding is one of the most promising thermochemical surface treatments to improve surface properties such as wear and corrosion resistance and fatigue strength. The prediction of effective case depth before nitriding treatment is very important and useful particularly from the perspective of the manufacturers in practice. In this study, ion nitriding parameter (INP), which is only a function of effective case depth and activation energy, has been suggested for the prediction of effective case depth in ion nitriding and the applicability of this approach has been verified. There is a good correlation between the progress of effective case depth and a proposed time-temperature compensated parameter. The results of proof tests have indicated that a reasonable agreement with 10% deviation was found between the experimental data and effective case depth values, which were predicted by using the parametric approach of INP for the steels AISI 4140, H13 and D3.

Estimation method for the fatigue limit of case hardened steels

It is well known that estimation of fatigue limit and optimum effective case depth are an important area of interest to the design engineer. In this study, simple expressions for the case hardened steels have been proposed to estimate the bending fatigue limit and optimum case depth values. Validation of the proposed expression was carried out several nitrided low alloy and carburised steels with different case depths. Results showed that the proposed analytical methods have good agreement with the experimental fatigue limit, and estimated optimum effective case depth values are favourable from the practical point of view. In case of considering 23 different effective case depth values of the steels with core hardness values are in range of 190–290HB, the calculated absolute mean deviation in estimating fatigue limit is 5.5%.

Deep-hole carburization in a vacuum furnace by forced-convection gas flow method

Carburization in the deep hole with high aspect ratio is a great challenge for the metallurgist. In this paper, the deep-hole carburization of JIS SCM415 as well as SNCM 220 steel with an aspect ratio of beyond 30 has been developed in a two-chamber vacuum furnace under low-pressure acetylene atmosphere by virtue from the forced-convection gas flow carburizing method. The proposed experiment was performed at 950–1050 °C for 15 or 30 min to evaluate the specimens on the uniformity of the carburized layers for the inner surface of the holes through the hardness distribution profiles and the effective case depth (ECD) of the hardened layers. Additionally, the exterior ECD of the specimens was also determined for comparison. With the experimental results, it is shown that a uniform carburized layer was formed in the surface of the deep hole. Furthermore, the diffusion coefficient of carbon atoms was then determined through this study. This paper surely contributes the approach to carburize the deep hole with high degree of uniformity regardless of the aspect ratio.

Deep-hole carburization in a vacuum furnace by forced-convection gas flow method

Carburization in the deep hole with high aspect ratio is a great challenge for the metallurgist. In this paper, the deep-hole carburization of JIS SCM415 as well as SNCM 220 steel with an aspect ratio of beyond 30 has been developed in a two-chamber vacuum furnace under low-pressure acetylene atmosphere by virtue from the forced-convection gas flow carburizing method. The proposed experiment was performed at 950–1050 °C for 15 or 30 min to evaluate the specimens on the uniformity of the carburized layers for the inner surface of the holes through the hardness distribution profiles and the effective case depth (ECD) of the hardened layers. Additionally, the exterior ECD of the specimens was also determined for comparison. With the experimental results, it is shown that a uniform carburized layer was formed in the surface of the deep hole. Furthermore, the diffusion coefficient of carbon atoms was then determined through this study. This paper surely contributes the approach to carburize the deep hole with high degree of uniformity regardless of the aspect ratio.

The influences of alloy elements on the carburized layer in steels using vacuum carburization in an acetylene atmosphere

In this article, three commercial steels, JIS SCM 415, JIS SNCM 220 and AISI 1008 were carburized in a two-chamber vacuum furnace at temperature ranging between 900 and 1050 °C in an acetylene atmosphere. Steel SCM 415 consists of mainly 0.12% C, 1.0% Cr and 0.17% Mo, steel SNCM 220 consists of 0.18% C, 0.55% Mo, 0.42% Cr and 0.17% Mo, while steel AISI 1008 is a 0.058% C plain carbon steel. The carburized specimens were characterized for the hardness distribution and the microstructure of the carburized layers using thermodynamic analysis. Experimental results show that, under the same treatment conditions, the SNCM 220 steel exhibited the best performance in both the effective case depth (ECD) and total case depth (TCD) of the carburized layers. However, the carbon concentration in the carburized surface of the SCM 415 steel was higher than that for the SNCM 220 steel. The AISI 1008 steel was the worst among the steels investigated. Furthermore, the carbon potential of the atmosphere for the SCM 415 steel should be controlled lower than that for the SNCM 220 steel if the same carbon concentration in the work surface is an essential requirement. The plain carbon steel AISI 1008 required the highest carbon potential among the three steels.

天然ガスを有効利用した鋼の表面熱処理

The gas carburizing atmosphere for surface treatment of steel can be regulated using the carbon potential, which is obtained by measuring the dew point, oxygen concentration or carbon dioxide concentration. The carbon potential which is calculated with carbon dioxide concentration is consistent with the carbon content of carburized steel foil. However, since a zirconium oxide oxygen sensor is easier to handle and its response is better than others, it is generally used for controlling the carbon potential, Methane is the main component of natural gas and it is stable at high temperature, so that the majority of tends to remain in the furnace. Since the retained methane decomposes on the oxygen sensor tip, the oxygen concentration around it decreases. Therefore the measurement of carbon potential with an oxygen sensor has been considered to be difficult when natural gas is used as the enriched gas. In this study, the carbon potential is regulated by taking account of the difference of the carbon potentials which are calculated with carbon dioxide concentration and with oxygen concentration; therefore the carbon potential can be controlled by the oxygen sensor, using natural gas for enriched gas. Target surface hardness and effective case depth are obtained when gas carburizing is carried out using this method, In addition, when the carrier gas is generated with natural gas and air, the carbon oxide concentration is 20.5 volume%, and the hydrogen concentration is 39.0 volume%; therefore the carburizing speed is higher than that when the carrier gas is generated with propane or butane.