Total Case Depth Research Articles

Effect of gas nitrocarburizing post oxidation on electrochemical behaviour of AISI 4140 steel in neutral medium

Medium carbon AISI 4140 steel samples were oxidized immediately after gas nitrocarburizing. The treated samples were characterized using scanning electron microscopy, micro hardness tester, X- ray diffraction, X- ray photoelectron spectroscopy and electrochemical polarization. The thickness of the compound layer was found in the range of 19–20 µm and total case depth ∼ 355 µm. Surface Hardness was found to be increased from ∼740 HV to ∼885 HV. XRD investigations revealed the formation of nitrogen richer ε- Fe2-3(C,N) at the surface and γ' - Fe4(C, N). The corrosion rate was found to be 0.01 mpy significantly lower than that of untreated steel. XRD and XPS investigations pointed out and confirmed the formation of magnetite. This layer, being passive, protects the steel by anodic protection mechanism.

The study on mechanical properties of pack carburized low carbon steel using BaCO3 as energizer

Machine components such as crankshaft and gear require hard surface and ductile core characteristics. One method to obtained such characteristics is pack carburizing. This research concern to compare the mechanical properties of carburized low carbon steel under different carburizers; GBC (80% goat bone charcoal + 20% BaCO3) and BC (80% bamboo charcoal + 20% BaCO3) and derived from reference. Pack carburizing was carried out by heating up to a temperature of 950°C, holding for 4 hours and quenching in the oil. The results showed that hardness, yield strength, tensile strength and modulus elasticity of carburized steels increased significantly, however, there was a decrease in elongation. The closer to the core the lower of hardness obtained until reach a total case depth of 1.5 mm and 2 mm for carburized using BC and GBC, respectively. The use of carburizer GBC produces carburized steel with a higher yield strength (51.75 kg.mm−2), tensile strength (74.58 kg.mm−2), and elongation (5.78 %) than carburizer BC but lower in hardness (558.13 HV1), modulus elasticity (256.79 GPa), and effective case depth (0.33 mm). The mechanical properties of carburized low carbon steels have fulfilled requirements as the material of gear or shaft.

Surface Characteristics and Distortion Analysis of the Case-Hardened Helical Gears: A Comparison of Different Case-Hardening Treatments

In this study, the effect of different case-hardening treatments on microstructure, hardness distribution, surface roughness parameters, and dimensional changes was investigated for helical-toothed gears made of 16MnCr5 and 21NiCrMo2 steels. Gas carburizing, gas carburizing–double quenching, low-pressure carburizing, and plasma-nitriding treatments were performed as case-hardening processes. The surface characteristics and distortion analyses of the case-hardened helical gears were examined using an optical microscope, hardness tester, profilometer, and micrometer. In order to ensure adequate pitting and bending strength, the required minimum effective case depth and minimum total case depth values were provided by the performed case-hardening treatments. In the gears, the largest dimensional increase after the heat treatments occurred at the end of the gas carburizing due to the long treatment times at high processing temperatures. The surface roughness values obtained through all performed case-hardening treatments necessitated the finishing processes.

Characterisation of case depth in induction-hardened medium carbon steels based on magnetic minor hysteresis loop measurement technique

The magnetic hysteresis behaviours of ferromagnetic materials vary with the heat treatment-induced micro-structural changes. In the study, the minor hysteresis loop measurement technique was used to quantitatively characterise the case depth in two types of medium carbon steels. Firstly, high-frequency induction quenching was applied in rod samples to increase the volume fraction of hard martensite to the soft ferrite/pearlite (or sorbite) in the sample surface. In order to determine the effective and total case depth, a complementary error function was employed to fit the measured hardness-depth profiles of induction-hardened samples. The cluster of minor hysteresis loops together with the tangential magnetic field (TMF) were recorded from all the samples and the comparative study was conducted among three kinds of magnetic parameters, which were sensitive to the variation of case depth. Compared to the parameters extracted from an individual minor loop and the distortion factor of the TMF, the magnitude of three-order harmonic of TMF was more suitable to indicate the variation in case depth. Two new minor-loop coefficients were introduced by combining two magnetic parameters with cumulative statistics of the cluster of minor-loops. The experimental results showed that the two coefficients monotonically linearly varied with the case depth within the carefully selected magnetisation region.

Investigation of Egg Shell Waste as an Enhancer in the Carburization of Mild Steel

This work has investigated the possibility of utilizing egg shell waste which is a rich source of calcium carbonate as an enhancer or energizer in the case hardening of mild steel using organic solid wastes like sugar cane, melon shells and aracaceae flower droppings as the carbon source. The mild steel specimens were inserted in carburizing boxes containing the carburizing material and carburized at a temperature of 920°C for 5 hours. They were then quenched in water, after which they were prepared for hardness test using Rockwell hardness tester, and for microscopic examination. The result showed that the carbonaceous organic waste used improved the case hardness of the steel. The result also showed that egg shell containing carburizing material produced higher case hardness on the steel than those carburizing materials without egg shell. Sugar cane waste produced a case hardness of 45.1HRC, with egg shell the case hardness became 45.5HRC. Melon shell waste produced a case hardness of 47.8HRC, and with egg shell the case hardness became 52.6 HRC. This hardness corresponded to an effective case depth of 0.65mm. Aracaceae flower wastes produced a case hardness of 56 HRC on the mild steel this corresponded to an effective case depth of 0.7mm, with egg shell the case hardness became 56.6 HRC with an effective case depth of 0.75mm. The calculated total case depth based on carburizing parameters was 1.34mm. The effect of egg shell waste as an enhancer in the carburization of mild steel has been established the result of the work has clearly shown that egg shell waste can be used in place of calcium carbonate to improve on the hardness value of mild steel during carburization. The success of this work has created another outlet for reducing the waste burden attributed to these solid wastes

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.

Modeling and Microstructural Analysis of Induction Hardened Parts

In the present article, an effective procedure of response surface methodology (RSM) is utilized to find the optimal values of process parameters for induction hardening of AISI 1040 steel under three different conditions of the material to predict total case depth. The three material conditions are untreated as-received (rolled), normalized, and tempered. Various process parameters, such as feed rate, current, dwell time, and gap between the workpiece and induction coil are experimentally explored. The experimental results show that the proposed mathematical models can predict the total case depth within the limits of the factors being investigated. The optimal values of process parameters have been verified by confirmation experiments. After ascertaining the optimal sample (corresponding to the best setting of induction hardening process parameters), tensile strength tests were performed so that the comparison could be done between the optimal induction hardened material and material without subjecting to induction hardening. It was concluded that the tempered is the most favorable raw material for making shafts, axles, or other automobile components during induction hardening process as almost finely distributed martensite was observed during scanning electron microscope (SEM) analysis.

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.

Influence of Combined Processes between Gas Soft Nitriding and Carburizing to Hardness of Low Carbon Steel

Low carbon steel is widely used in industries due to its low cost and easy to recycle. However, the low carbon steel is also known that easily attacked by environment and low strength compared with other kinds of steel. Therefore, several surface coating and treatment techniques are employed to improve its properties. This study was aimed to investigate influence of combined processes between gas soft nitriding and gas carburizing on the hardness of low carbon steel. The specimen was normalized by normalizing and shot blasting. Then the specimen was treated by gas carburizing, gas carbonitriding and combined processes between gas soft nitriding and gas carburizing. It was found that the combined processes yielded the good surface hardness and total case depth compared to other conditions. The most advantage of the combined processes could be considered to be very small variation of hardness.

Influence of laser hardening on the tribological properties of forged steel for hot rolls

The influence of laser hardening on the tribological behaviour of a forged steel for hot profiled rolls is evaluated using a customary test rig which provides the rolling–sliding contact between the roll and a C40 plain carbon steel counterpart. Samples treated with different lasers and processing parameters were considered. Starting from a base value of 300 HV the surface hardness was increased up to 800 HV and the total case depth ranged from 1.2 to 2 mm. The benefits of the laser treatment could be clearly observed at low test temperature, due to the positive influence of a hard martensite microstructure in preventing severe metallic wear by adhesive fracture. The influence of laser hardening was less evident at high temperature, where the tendency of different microstructures towards the formation of wear protective oxide layers could result in a better or worse resistance compared to the base steel, respectively. The capability of the roll material to produce wear particles and their entrapment within the contact interface resulted of fundamental importance for the formation of oxide glazes.

Lattice Plane Spacing Change in Hardened Layer of Chrome Molybdenum Steel after Carburizing and Quenching

Block specimens of chrome molybdenum steel with 0.20 mass% C, SCM420, were carburized in carrier gas and quenched in oil bath. The hardness and carbon content gradients in the hardened layer were measured experimentally. The carburized surface of one block specimen was gradually removed by electrolytic polishing. Ten thin plates were cut from the total case depth of the other block specimen. An experimental method to determine the stress-free lattice plane spacing of the hardened layer was examined using x-ray and neutron radiations. As a result, the stress-free lattice plane spacing change in the hardened layer could be determined successfully by measuring neutron diffraction peaks from Fe-211 of the thin plates during rotating ±90° around the specimen axis. Using x-ray, the stress-free lattice plane spacing at the carburized surface could be also determined by measuring the 2θ-sin2ψ diagrams of either removed surface of block specimen or thin plate. However, under the carburized surface, the Kα2 diffraction from the heat-treated eutectoid phase was superimposed on x-ray diffraction peak because the subsurface microstructure was composed of martensitic and heat-treated eutectoid phases. The stress-free lattice plane spacing under the carburized surface could not be determined using x-ray. Furthermore, the stress-free lattice plane spacing of Fe-211 was found to decrease with increasing the distance from the carburized surface and be expressed by the cubic function of the carbon content in the hardened layer.

Nitriding of Aluminum Extrusion Die: Effect of Die Geometry

Nitriding of complex-shaped extrusion dies may result in non-uniform nitride layers and hence a required hardness may not be achieved in some regions of the bearing area. The present study is carried out to assess the effect of extrusion die profile on the characteristics and growth behavior of nitride layers so that the critical die design feature can be identified to enhance the uniformity of the nitride layer. For this purpose, AISI H13 steel samples have been manufactured with profiles similar to those of hot extrusion dies. The samples were then gas nitrided under controlled nitriding potential. The uniformity and depth of nitride layers have been investigated in terms of compound layer and total nitride case depth for selected die features. The results of this study indicated the need to include the effect of profile on the nitride layer for the optimal die design with improved service life.

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.

外部ヒータを併用した鋼のプラズマ窒化処理

In the plasma nitride processing that uses direct current glow discharge, the sample is heated and ruggedness is generated on the sample surface because the ions in plasma bombard against the sample surface. To minimize the ruggedness, we heated the sample by an external electric heater during plasma nitride processing. The sample material was SACM 645 steel. NH3 gas was used for nitriding. We examined the generation of nitrified layers and surface roughness under various conditions of NH3 gas composition from 20 to 60%, nitriding temperature from 743 to 843K and nitriding time from 1.8 to 43.2ks. In general, higher nitriding temperature led to higher surface hardness. Moreover, the total case depth hardened by nitriding became from 0.2 to 0.3mm. Longer nitriding time led to higher surface hardness and the total case depth hardened by nitriding became from 0.075 to 0.35mm. No layer of nitrides of iron was generated until the NH3 gas composition became 40%. When the NH3 gas composition was 60%, 1.3μm layer was generated and the surface roughness was Rz 0.24μm. No nitride was identified by X-ray diffraction. However, higher NH3 gas composition led to larger half value width of α-Fe at peak. This suggested that nitrides mainly composed of minute nitride chromium were being precipitated.

Kinetics of Plasma Nitriding and Renitriding of 3% Cr-Mo-V Steel

Kinetic studies of plasma nitriding of 3% Cr-Mo-V DIN 39CrMoV13.9 steel were performed at 538, 510, and 483 °C. It was found that the process obeys a parabolic law of diffusion for total case depth and is slower than parabolic for effective case depth formation. The kinetics of renitriding was found to be a continuation of the preexisting case growth. Mathematical equations were developed for the relationships. Long exposure to the nitriding temperatures had a negative effect on the hardness of the steel.

Some effects of the plasma nitriding process on layer properties

The layer properties of AISI 722M24, AMS 6472 and AISI H13 materials plasma nitrided under various conditions were defined. The materials were plasma nitrided at temperatures between 510 and 590 °C for times ranging between 4 and 100 h in a dissociated ammonia atmosphere. The effects of duration, temperature, chemical composition and the shape of sample on the layer properties were determined. It was determined that the total case increased with treatment time and temperature increases the white layer thickness and the effective case depth. The increase in the white layer thickness is very sharp up to a total case depth of 0.3 mm, but it is very slow between 0.3 and 0.75 mm total case. The chemical composition of the material also affects the depth and hardness of the case. High alloy steels have higher hardness but thinner case than low alloy steels. Although the γ'-Fe 4N single-phase compound layer was formed on 722M24 steel, a thick and mixed ϵ- γ' (Fe 2−3N+Fe 4N) phase was produced on H13 steel. The hardness distributions from curved and flat surfaces to the core of the test material exhibit different profiles.

An investigation of the properties and wear behaviour of plasma-nitrided hot-working steel (H13)

The microstructural properties and wear behaviour of AISI H13 steel which had been plasma nitrided at 530 and 550 °C for times between 4 and 100 h have been investigated. The effect of treatment temperature and time on the microstructure have been examined. The wear behaviour of material treated for 4 and 100 h has also been observed. It was seen that a total case depth of 0.55 mm with a hardness of 1000 HV can be achieved in 100 h. However, the white layer thickness is increased to 17 μm while the core hardness is reduced to 480 HV at 550 °C. The wear rate of the sample treated at 550 °C for 100 h is higher than that of the sample treated at 550 °C for 4 h.

Characteristics of alloying and phase composition of nitrided austenitic steel 03Kh17N8G5MFAB

1. Austenitic stainless steel 03Kh17N8G5MFAB was developed for nitrided precision friction parts and also the optimal heat treatment. The steel has a stable austenitic structure at low temperatures and high stresses. 2. The optimal nitriding conditions for steel 03Kh17N8G5MFAB are 600–620° for 30 h with 30–40% dissociation of ammonia. After this treatment the case depth is 0.22 mm, the hardness HV5∼800–900, and the case is corrosion resistant down to a depth amounting to ∼50% of the total case depth. 3. Carbon promotes formation of γ′ phase in the surface zone of the case, stabilizes austenite, and reduces the overall case depth. The high concentration of carbon in austenite and γ′ phase may be one of the reasons for the low corrosion resistance of the surface zone of the case on steels with 0.05–0.08% C.

Nitriding of low-carbon martensitic stainless steels 03Kh11N10M2T and 03Kh12N10MT

1. The nitrided case on steels 03Kh11N10M2T and 03Kh12N10MT, from the surface to 50–70% of the total case depth, has high corrosion resistance in a humid atmosphere and in salt spray. 2. Tempering before nitriding, which ensures a good combination of mechanical properties of the core and the case and high stability of the structure and the dimensions during nitriding and operation, should be conducted at 580° for 10h or 640° for 4 h+580° for 10 h (steel 03Kh11N10M2T) and at 570° for 6h (steel 03Kh 12N10MT). 3. The nitrided case on steels 03Kh11N10M2T and 03Kh12N10MT does not fracture when subjected to tensile stresses as high as the proof stress of the core. 4. Retained austenite formed in steels 03Kh11N10M2T and 03Kh12N10MT during tempering and nitriding is stable at negative temperatures as low as -196° and also when subjected to tensile stress as high as the proof stress at temperatures as low as -196°. 5. After nitriding, σb=100–120 kgf/mm2 for steel 03Kh11N10M2T; with a case depth of 0.20–0.25 mm, the ductility and toughness are superior to those of widely used nitriding steels 30Kh3VA and 38KhMYuA with a case depth of 0.45 mm and it is recommended for nitrided machine parts operating at temperatures from-70 to +450°. 6. Nitrided stainless steel 03Kh12N10MT has high toughness and ductility in combination with high strength at cryogenic temperatures, and it can be recommended for nitrided machine parts operating at temperatures from -253 to +350°.

The Influence of Residual Stress on the Fatigue Strength of Carburized Hardened Steels

Carburizing is a favored process to improve the fatigue strength and wear resistance of automobile gears and many other machine parts. Despite many years of studies and reports on the properties of carburized hardened steels, there still remain many problems to be solved in this respect where production is concerned.The values of surface hardness, core hardness and case depth are known as main factors which influence the strength of carburized hardened steels. Among these, case depth and core hardness are variable extensively according to the differences in chemical composition, hardenability, and methods of carburizing and quenching, even if the parts are of the same quality. Moreover, those values vary widely depending on the hardenability of steels, even when the same type of steel is treated at the same temperature.There have been many reports in which comparisons are made among the types of steels and the methods of carburizing and hardening but very few reports are obtainable concerning the investigations that dealt with these two factors at a time, especially on one type of steel.Therefore, we investigated the influences of case depth, core hardness and residual stress on the fatigue strength of carburized hardened steels. The materials tested are chrome-molybdenum case hardening steels (SCM 21 & 22) of various hardenabilities.The following points were made clear as the results of these tests. The fatigue strength of carburized hardened steel is influenced by the case depth and core hardness, both of which have optimum values to cause the maximum endurance. When the core hardness is low and the case depth is thin, crack initiates from case-core boundary (fish-eye). The depth of this fish-eye from the surface is almost equal to the total case depth. The decrement of residual stress during the fatigue test is rather small, and comparatively large residual stress is observed even after the test.The surface residual stress of carburized hardened specimens first increases, then tends to decrease as the case depth is increased, and this can be considered to be one of the main causes for the behavior of maximum endurance of carburized hardened steels.From those results, it seems necessary that further studies are pursued to ascertain the effect of residual stress, in order to attain high fatigue strength even for production parts.