Carburized Steel Research Articles

Effect of Stress Ratio and Evaluation of Crack Sizes on Very-High-Cycle-Fatigue Crack Propagation Life Prediction of Carburized Cr-Ni Steel

Carburized Cr-Ni steel is widely used in the manufacture of components in many fields due to excellent performance, of which the service life has been a concern. In order to investigate the high-cycle-fatigue and very-high-cycle-fatigue properties of carburized Cr-Ni gear steel, axial loading fatigue tests were performed by QBG-100 with stress ratios of −1, 0 and 0.3. The Generalized Pareto distribution was used to evaluate the inclusion size of carburized Cr-Ni gear steel. Based on the stress ratio and the evaluated crack size, a new fatigue life prediction model for carburized Cr-Ni gear steels was constructed. The results show that the S–N characteristics of carburized Cr-Ni gear steel represent the continuously descending tendency. Based on the long crack propagation threshold and the instability propagation threshold of carburized Cr-Ni gear steel, the sizes of FGA, fisheye and surface smooth area (SSA) can be evaluated, respectively. In addition, the maximum size of surface and interior inclusion of carburized Cr-Ni gear steel are 17.50 μm and 6.46 μm with a cumulative probability of 99.9%. By validating the new established model, the prediction result is acceptable according to the good consistency between the predicted life and the experimental life.

Determination of plastic properties of surface modification layer of metallic materials from scratch tests

A new test method was proposed to extract plastic parameters, i.e., yield stress and strain hardening index, and interfacial coefficient of friction of metallic materials via scratch tests with a pyramid indenter based on dimensional analysis and finite element analysis. Yield stress and strain hardening index of scratched materials can be calculated with scratch width, residual scratch depth and normal force obtained from the scratch tests. Interfacial coefficient of friction between the scratched materials and scratch tip can be determined by the ratio of tangential force and normal force. The accuracies of the proposed formulas were verified by comparing the results of uncarburized and carburized 18CrNiMo7-6 alloy steel obtained by conventional methods with those by scratch tests. This work provides a convenient method to determine plastic parameters and interfacial coefficient of friction of metallic materials simultaneously, which is important for the mechanical analysis, design and safety evaluation of mechanical parts.

Study on Friction and Wear Properties of 23CrNi3Mo Carburized Steel under Water Lubrication

In this paper the friction and wear of 23CrNi3Mo carburized steel under water lubrication were studied. The friction and wear properties of carburized steel sliding with stainless steel, GCr15, Al2O3 and ZrO2 balls were analyzed by tribometer, 3-D topography and SEM. The results show that compared with other materials, ZrO2 and carburizing steel have better tribological properties. Compared with Al2O3, the wear depth of carburized steel sliding with ZrO2 is reduced by 41% at the load of 2 N and 50% at the load of 10 N. In the load range of 2N-10N, the wear rate of carburized steel is the lowest when rubbing with ZrO2, and it gradually decreases when the load increases. Combined with SEM and Raman spectrum analysis, Oxide film was formed on the surface of carburized steel during the sliding test of ZrO2 and carburized steel. This oxide film was mainly composed of Fe3O4 and Fe2O3, which effectively reduces the friction coefficient and wear rate of 23CrNi3Mo carburized steel under water lubrication.

Study Experimental the Effect of Normalizing Treatment and Galvanic Pack Carburizing Process on Mechanical Properties of Low Carbon Steel

Steel is the type of metal most often used in engineering. This study aimed to improve the mechanical properties of mild steel in terms of hardness, ductility, and other mechanical properties and to compare the hardness of carburized steel by galvanic treatment with non-galvanic carburizing of the steel. This research was carried out by varying the heat treatment process, namely carburizing with galvanic heat treatment and carburizing without galvanic, where the carburizing process uses activated carbon coconut shell charcoal with a weight percentage of 80% and 20% of K2CO3 (Potassium Carbonate) at a temperature of 9000C with a holding time of 60 minutes, 120 minutes and 180 minutes. The results obtained from this study indicate that the mechanical properties (hardness) of carbon steel increase at a temperature of 9000C with a holding time of 1 hour on the galvanic heating method with a better hardness value than the hardness of steel on the non-galvanic method. The hardness value obtained in the galvanic method is 94.06 HRB, while in the non-galvanic method, it is 76.4 HRB. And the pearlite phase is formed, increasing the hardness value on the surface of the specimen.

Investigation in Gas Carburizing of AISI 4140, EN36, and 16MnCr5 Steels Using the Grey Incidence-Based Taguchi (GIBT) Method

Gas carburizing is an effective surface treatment process for improving the hardness and wear resistance of different class of steels. The study reports an application of grey-incidence based Taguchi (GIBT) method in gas carburizing of case-hardening steels like AISI 4140, EN36, and 16MnCr5 which are widely employed in precision levers, transmission shafts, and pinions. Carburizing trials are performed using Taguchi’s L9 orthogonal array by varying the design parameters like carburizing temperature, soaking time, and tempering temperature. Surface hardness (SH), diffusion depth (DD), and wear loss (WL) are studied as process responses at the completion of various carburizing trials with replications. Optimal design variables are identified using grey incidence grade as a performance index in the GIBT method. The contribution of individual parameters is also studied using the analysis of variance (ANOVA). Microscopic examination and SEM images of the treated surface are also studied after validating the method of GIBT.

Effect of process parameters on hardness and microstructure of 18CrNiMo7-6 carburized steel in high-speed cylindrical grinding

Effect of process parameters on hardness and microstructure of 18CrNiMo7-6 carburized steel in high-speed cylindrical grinding

ОСОБЕННОСТИ СТРУКТУРЫ ТОНКИХ ОБРАЗЦОВ ИЗ СТАЛИ 20ГЛ, ПОЛУЧЕННЫХ ЛИТЬЕМ ПО ГАЗИФИЦИРУЕМЫМ МОДЕЛЯМ

The work is devoted to the study of carbon liquation in cast steel samples with a thickness of 8 mm obtained by a special method of casting according to gasified models (LGM). In the course of the work, steel castings with a thickness of 8 mm were obtained. The microstructure of castings was studied both before heat treatment and after TO (annealing). Studies have shown that in the process of pouring metal during the destruction of expanded polystyrene, intensive carburization of steel occurs not only in the surface area, but also throughout the cross-section of the samples. Traditional heat treatment of steel castings (annealing) does not have a significant effect on the redistribution of carbon in the volume of the casting, that is, it does not reduce the carbon liquation along the sample cross-section.

Exploration on the fatigue behavior of low-temperature carburized 316L austenitic stainless steel at elevated temperature

The fatigue behavior of low-temperature carburized 316L austenitic stainless steel at elevated temperature was investigated. Uniaxial tensile tests and rotating bending fatigue tests were performed on untreated and carburized 316L austenitic stainless steel at 300 °C, 400 °C, 500 °C and ambient temperature. Results show that carburized case can improve the fatigue strength at both ambient and elevated temperatures significantly. The improvements of tensile strength and endurance limit by carburized case at elevated temperature are even higher than those at ambient temperature. Moreover, the higher improvement of fatigue performance at elevated temperature is mainly due to the better strengthening effect of carburized case on the strength, the brittleness reduction and the redistributions of carbon content of carburized case. Based on the observation of fracture morphologies, fatigue fracture mechanisms of untreated and carburized specimens at different temperatures were analyzed. For untreated specimens, fatigue cracks always initiate from the surface at both ambient and elevated temperatures. For carburized specimens, fatigue cracks initiate at subsurface near the boundary between carburized case and substrate at ambient temperature. At elevated temperature, fatigue cracks initiate near the boundary under the high applied stress while under low applied stress, fatigue cracks initiate from the inclusions.

Wear characteristics of flat die in flat die pellet mills based on Glycyrrhiza uralensis

During granulation, a serious wear problem may be found in flat die as a key component of a flat die pellet mill. Specific to this problem, Glycyrrhiza uralensis was selected as the wear-causing material to investigate the wear mechanism of the flat die. Additionally, carburizing steel (20Cr and 20CrMnTi) and stainless steel (4Cr13) commonly used in flat die were adopted to conduct wear tests. To explore the influence of Glycyrrhiza uralensis powder and rods on friction and wear properties of the above three types of steel materials, a CFT-I general-purpose tester for surfaces was applied under dry friction conditions. Moreover, x-ray diffractometer (XRD), three-dimensional profilometry, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were used to analyze the phase compositions, surface morphologies, and elementary compositions of the samples. As demonstrated by relevant results, the influence of Glycyrrhiza uralensis on the flat die is primarily embodied in abrasive, adhesive, and fatigue wear, and a thermal oxidation reaction occurs on the surface of the flat die. By comparing the wear conditions of the three steel materials between the powder and rods of Glycyrrhiza uralensis, it is found that flat die damages caused by glycyrrhiza rods are more severe than those of its powder. Additionally, the lowest friction coefficients are generated by 20CrMnTi, which are 0.40 and 0.88, respectively. In terms of the mean wear depth, its values are 1.2 and 2 μm, which are below those of 20Cr and 4Cr13. The results herein reveal that flat die made of 20CrMnTi have excellent wear and ductile fracture resistance characteristics. Hence, this study may provide a theoretical guide for selecting flat die materials.

Duplex Heat Treatment of a Precipitation Hardening Carburising Steel

Abstract This article reports the microstructural development of a molybdenum and copper alloyed steel by different thermochemical heat treatments for gears and shafts in automotive applications. The case hardening is compared to a duplex heat treatment consisting of carburising, ageing and plasma nitriding. This study evaluates the microstructure, the surface hardness and hardness profiles. For all applied heat treatment routes, the ageing conditions have a minor influence on the case and core hardness compared to the influence of the carbon concentration. Retained austenite fractions decreased to < 5 % in all duplex heat-treated samples without cryogenic treatment. Material characterisation with optical light microscopy and scanning electron microscopy indicate unwanted phases of nitrogen and carbon-rich precipitates at the grain boundaries after duplex heat treatment. Therefore, the sequence of duplex heat treatment is changed to carburising followed by solely plasma nitriding where the unwanted precipitates are detected only up to a depth of 15‒20 μm from the compound layer.

Structural-phase transformations and changes in the properties of AISI 321 stainless steel induced by liquid carburizing at low temperature

Structural and phase transformations occurring due to the supersaturation of austenite with interstitial atoms (carbon and/or nitrogen) are the key priority in the study of AISI 300 series austenitic steels. It is also very important to achieve a greater hardening depth by nitriding or carburizing. For this purpose, a method of salt bath carburizing at low temperature was proposed. The aim of this work is to perform a detailed analysis of structural-phase transformations and their effect on the properties of AISI 321 austenitic steel subjected to liquid carburizing at a temperature of 780°С. Optical and scanning electron microscopy, optical profilometry, X-ray diffraction analysis, energy-dispersive microanalysis, electron backscatter diffraction analysis, instrumented microindentation and microhardness measurement are used as methods of investigation. It has been discovered that, along with carbon-rich (up to 0.46 wt% C) austenite, chromium carbide Cr23C6, cementite Fe3C, ε-martensite, and α-martensite are formed in the surface layer of the carburized AISI 321 steel. Carbides are present both at the grain boundaries and within the austenite grains. Martensite formed in the carburized AISI 321 steel is induced by deformation, and the martensitic transformation path is γ → ε → α′ (two-stage transformation). In its turn, plastic deformation occurs during cooling that follows carburizing, and this is a relaxation mechanism of high thermal stresses. Liquid carburizing of AISI 321 steel also multiplies the microhardness of the steel surface from 200 ± 7 to 890 ± 110 HV0.025, with the total hardening depth being about 500 μm. The hardened layer is gradient and characterized by increased resistance to elastic-plastic deformation, this being important for increasing the contact endurance and wear resistance of the steel. It has also been found that, due to high carbon concentration, the corrosion resistance of the carburized steel does not deteriorate significantly.

Acicular martensite induced superior strength-ductility combination in a 20Cr2Ni2MoV steel

The super combination of ultrahigh strength and good ductility is in high demand for the gear steels. Here we improved the mechanical properties of a micro-alloyed gear steel through the fabrication route composed of carburizing and re-quenching. The results showed that the different re-quenching temperatures significantly affect not only the sizes and morphologies of precipitates and martensite but also the ratio of low-angle grain boundaries to high-angle grain boundaries as well as dislocation densities. The maximum ultimate tensile strength up to 2420 MPa was obtained after re-quenching at 780 °C, while the steel re-quenched at 820 °C exhibited the highest yield strength of 1500 MPa despite of the decreased ultimate tensile strength of 2145 MPa. Especially, a good ductility of 8.5% was maintained in the carburized steel processed after 780 °C re-quenching. The spherically nanosized precipitates together with the high ratio of low-angle grain boundaries were beneficial for the simultaneously improved strength and ductility.

Tribofilm properties and microcrack morphologies for a carburized SCM420 steel under high-pressure rolling sliding contact fatigue with lubricants containing high sulfur- and phosphorus-additives

Tribofilms and microcracks developed on a carburized SCM420 steel through a two-roller-type pitting test were characterized. Tribofilms composed mainly of calcium phosphate, iron phosphate, and iron oxide were generated on the contact surface. The tribofilms were homogeneously distributed on the contact surfaces that exhibited a longer life, suggesting that the tribofilm distribution affects the rolling sliding contact fatigue (RCF) life. Compounds including the elements from the lubricant were also generated on the surfaces of microcracks formed on the contact surface, suggesting that lubricant flowed into the surface microcracks during the test. The martensitic microstructure at the specimen subsurface was dynamically reconstructed to an ultrafine-grained microstructure during RCF, which resulted in the residual stress relief, especially on the contact surface. After the residual stress release, the fluid pressurization accelerated the formation of a mixed-mode microcrack of mode I and mode II with a high angle to the surface in the later stage, while a shallow microcrack in mode II developed during the early stage.

Study on mechanical properties of pack carburizing ASTM A36 steel with energizer pomacea canalikulata lamarck shell powder

In the present study material low carbon steel ASTM A36 were treated with pack carburizing with carburizing agent, a mixture of gigantochloa apus (Schult.F.) Kurz charcoal (GAC) and pomacea canalikulata Lamarck shell powder (PCSP). The composition of carburizing agent PCSP-GAC was varied at 10%: 90%, 15%: 85%, and 20%: 80%. The process done at carburizing temperature various 875, 900, 930 ℃ and soaking time for 2 hours. The surface hardness test and an impact test was carried out to determine changes in the surface hardness number and impact toughness. From the results of the study, it was concluded that pack carbrizing with carburizing agent, a a mixture of PCSP and GAC increased the hardness number but decreased the impact toughness of the specimen. The highest hardness number is 537.48 Kg/mm², the lowest impact toughness is 158.33 Joules, at a pack carburizing temperature of 930 ⁰C, the composition of the carburizing agent 20% PCSP : 80% GAC. Microstructural characterization indicates that high toughness of the carburizing steel subjected to the cooling heat treatment process results from a proper multiphase microstructure transition from the surface to the matrix of the steel.

Microstructure Characteristics and Wear Performance of a Carburizing Bainitic Ferrite + Martensite Si/Al-Rich Gear Steel

In this paper, a new low-carbon alloy gear steel is designed via Si/Al alloying. The carburizing and austempering, at a temperature slightly higher than the martensitic transformation point (Ms) of the surface and much lower than the Ms of the core, for different times, were carried out on the newly designed gear steel. After heat treatment, a series of different microstructures (superfine bainitic ferrite + retained austenite, superfine bainitic ferrite + martensite + retained austenite, and martensite + retained austenite) were obtained on the surface, whilst the low-carbon lath martensitic microstructure was obtained in the core. The microstructure of the surface was examined using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The phase composition was analyzed using X-ray diffraction (XRD). The hardness and wear resistance of the surface as well as the hardness distribution of carburizing layer of the samples with different microstructures were studied. The results show that the Si/Al-rich gear steel, after carburizing and austempering at 200 °C for 8 h, not only has excellent mechanical properties but also has high wear resistance, which meets the technical requirements of heavy-duty gear steel. The research work in this paper can provide a data reference for the application of carburized steel with mixed microstructures of bainitic ferrite and martensite in the design of heavy-duty gear.

Effect of Residual Stress Distribution on the Rotating Bending Fatigue Properties of Shot Peening Treated Carburized Steel

Effect of Residual Stress Distribution on the Rotating Bending Fatigue Properties of Shot Peening Treated Carburized Steel

Fatigue limit estimation for carburized steels with surface compressive residual stress considering residual stress relaxation

The mechanism of residual stress relaxation for carburized steels was elucidated and their fatigue limit was estimated. The compressive residual stress in the carburized steel after rotating bending fatigue tests is mainly influenced by the relaxation during the compressive loading phase, although it increases at the early stage. The fatigue limit of carburized steels can be estimated according to the modified Goodman diagram considering the residual stress relaxation. The proposed equation shows the maximum value of the fatigue limit (1013 MPa) of carburized steel and the maximum value of the compressive residual stress contributing to the increased fatigue limit.

Evolution of Microstructure and Wear Resistance of Carburized Low Carbon Steel

The main aims of this present work were to investigate the microstructure and wear resistance of AISI 1020 during the pack carburization. The samples were prepared in a rectangular shape with a dimension of 5 mm X 25 mm X 2 mm for microstructure and hardness studies. Another set of samples with a dimension of 4.0 cm x 2.5 cm x 0.5 cm was prepared for the wear resistance performance. Both sets of samples were packed in the steel container which was tightly sealed. The carburizing atmosphere in the container was prepared by using mixtures of powdered charcoal and tamarind catalysts. The carburizing temperature of 950 °C with a fixed carburizing time of 2 hours was controlled for the pack carburizing treatment. The results exhibited that in the fresh condition, AISI 1020 mostly contained ferrite. Nevertheless, after carburization, quenching, and tempering process were carried out, the microstructures of the samples were changed from ferrite to pearlite and then martensite. An increase in the carbon content after carburization plays a major role in the evolution of the high hardness layers which subsequently enhanced the hardness and the wear resistance performance of AISI1020 after quenching and tempering.

Low Temperature Carburizing of Stainless Steels and the Development of Carbon Expanded Austenite*

Abstract Low-temperature carburizing dramatically enhances the inherently low wear resistance of austenitic stainless steels due to the formation of a carbon-supersaturated solid solution, i.e. expanded austenite. The formation of expanded austenite from low-temperature carburizing has been intensively investigated. However, the influence of chemical composition of the stainless steel on the carburizing response has not received the same interest. This contribution addresses the effect of the chemical composition on low-temperature carburizing in terms of carbon solubility, decomposition of expanded austenite upon exceeding the solubility limit and the elasto-plastic accommodation of the carbon-induced lattice expansion. The results demonstrate that the carbon solubility increases with an increasing Cr-equivalent and that higher Cr- and Ni-equivalents favor the formation of Cr-based M7C3 over Fe-based Hägg (M5C2) carbide.

Fretting tribological performance of DLC, TiAlN and DLC/TiAlN coatings deposited on carburized 18CrNi4A steel

To improve the fretting wear performance of 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings were deposited on the surface of carburized 18CrNi4A steel, respectively. The microstructure morphologies, chemical compositions, and mechanical properties of these coatings were evaluated. The fretting tribological properties of pad/flat contact pairs for carburized 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings were investigated in different lubricant environments including dry sliding and #RIPP 7254 aviation grease. The results show that DLC, TiAlN and DLC/TiAlN coatings deposited on the carburized 18CrNi4A steel surface can improve surface roughness, hardness, fracture toughness and resistance to plastic deformation. DLC, TiAlN and DLC/TiAlN coatings deposited on the surface of carburized 18CrNi4A steel can make the surface of the substrate have excellent fretting wear properties. DLC and DLC/TiAlN coatings have lower coefficient of friction and better fretting wear resistance than TiAlN coatings in dry sliding condition, and DLC/TiAlN coatings have the lowest wear rate in #RIPP 7254 grease lubrication condition. In addition, the wear mechanisms of carburized 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings in dry sliding and #RIPP 7254 aviation grease conditions were analyzed.