Carburized Steel Research Articles

Effect of Carburizing Temperature and Post Carburizing Treatments on Microhardness and Microstructural Evolution of Carburized Low-Carbon Steel

This paper reports the results of an experimental investigation of the effect of carburizing temperature and post carburizing heat treatments on the structural and hardness properties of pack carburized low-carbon steel. The carburizing processes were performed at temperatures of 900°C and 1035°C for 6 hours. After that, two hardening procedures were carried out. In the first hardening procedure, the specimens were directly quenched in oil from carburizing temperatures, while in the second procedure, a double quenching method using brine as a quenching medium was applied. The resultant changes in surface hardness values, carbon content, case depth, microhardness profiles, and microstructural evolution during all processes were tracked and reported. The study showed that the hardness values and carbon content of the carburized specimens increased significantly compared to an untreated specimen, also case depth values increased by two times in some hardened specimens, the increasing in these values were correlated to the changes in microstructures. The obtained results indicated that the structure and the properties of the carburized components are strongly influenced by carburizing temperature and by post carburizing heat treatments; therefore, both variables can be used to altering or modifying surface and core characteristics of the carburized steel, which make it more suitable for engineering components that require a combination of hard surface along with ductile and tough core.

Study on microstructure and wear characteristics of carburized steel at different carburizing times using catalyst strombus turturella shell waste powders

The feasibility of strombus turturella or dog conch shell powder (DCSP) as a catalyst of the carburizing process was investigated. The microstructure and wear characteristics of carburized specimens at various carburizing times were determined and compared. The microstructures and chemical compositions of the carburized specimen were observed by Scanning Electron Microscopy (SEM) machine with a detector energy dispersive spectroscopy (EDS). The wear characteristics were detected by a Pin-on-disk wear testing machine. While the worn surface morphology of carburized specimens was examined by Scanning Electron Microscopy (SEM) machine. The number of martensite structures of carburized specimens increased by increasing the carburization time from 3 to 12 hours. From the results, it is found that the volume loss value of 0.1 mm3, and wear depths value of 0.18 mm were obtained from carburized specimens prepared with 40% DCSP and carburizing time of 12 hours. This result is much better than that obtained by carburizing times of 6, and 3 hours, respectively. Moreover, the worn surface morphology results depicted that the carburized specimens for carburization times of 3, and 6 hours exhibit more severe spalling, wear debris, and extensive adhesion wear and grooves than that achieved of carburized specimens with a carburizing time of 12 hours. The results clearly showed that the wear characteristics of carburized specimens improved with increasing carburizing time.

Effect of notch and stress ratio on Very High Cycle Fatigue characteristics of the carburized 17CrNi high-strength steel and life prediction

In order to investigate the notch effect on the structural characteristics of the carburized 17CrNi high-strength steel in the very high cycle fatigue (VHCF) loading, the axial tests with the stress ratio (R) of ‒1 were performed and the S-N characteristics were studied. The microscopic observation revealed that surface induced failure was the only failure mode. Further, the effect of the notch was investigated: Based on the small crack theory, the calculation of the fatigue notch factor (Kf) was performed and has shown that Kf is slightly less than the theoretical stress concentration factor (Kt). Then, Kf was used to study both the notch effect and stress ratio effect on fatigue life. Finally, the life prediction model associated with R and Kf was established and the calculation results are valid according to the good agreement with the experimental data.

Prediction of surface damage behavior in rolling contacts using torsional fatigue results and surface roughness modeling

This paper presents a novel approach to predict the effect of surface roughness on surface damage in rolling contacts. Rolling contact fatigue (RCF) tests were conducted on AISI 4130 case carburized steel specimens at two different roughness levels, Ra=0.3μm and 0.1μm, under boundary lubrication regime. The RCF experiments were performed using a Thrust Bearing Surface Pitting Rig employing a ball-on-flat configuration. Surface damage was assessed at different combinations of contact pressure and fatigue cycles using optical surface profilometry. Subsequently, the surface damage stress-life (S–N) results were generated at both roughness levels. Torsional fatigue experiments were also performed on the same material. The torsional fatigue S–N results were combined with stress concentrations at the RCF test surfaces due to roughness to predict the surface damage S–N results. A dry circular contact model incorporating the surface roughness was developed and utilized to compute the stress concentration at the contact. The S–N results based on the von-Mises stresses were compared for RCF and torsional fatigue. The predicted results corroborated well with the experimental findings. The approach developed in this investigation illustrates the fundamental relationship between RCF and torsional fatigue.

Fundamental relationship between rolling contact fatigue driven surface damage and torsional fatigue

This paper presents fundamental findings on equivalence of rolling contact fatigue (RCF) driven surface damage and torsional fatigue modes of failure. Fatigue experiments were conducted for both modes of failure using AISI 4130 case carburized steel specimens. A Thrust Bearing Surface Pitting Rig (TBSPR) was designed and developed to perform RCF tests on flat test specimens using thrust ball bearings. The experiments were conducted in boundary lubrication regime, simulating the contact conditions in tribological machine components. The current investigation presents a novel approach where the effect of contact pressure and number of fatigue cycles on the initiation of surface damage was characterized by surface profilometry of the wear track after each test to generate a stress-life (S-N) map. The S-N map provides unique insights to early detection of RCF driven fatigue damage. The S-N map was utilized to generate the surface damage S-N curve. Torsional fatigue experiments were conducted on the same material, and the S-N curves of both failure modes were compared. The comparison shows key similarities between the two S-N curves, as they differ by a simple scaling factor. This investigation demonstrates that RCF driven surface damage characteristics can be predicted by conducting much simpler, and faster, torsion fatigue tests. This paper also presents a novel methodology to determine contact pressures to avoid incipient micropitting/microdenting damage.

RESEARCH OF THE CURRENT STATE AND TECHNOLOGICAL OPPORTUNITIES OF ELECTROLYTE-PLASMA CHEMICAL HEAT TREATMENT OF STEELS

In the modern world, one of the most important requirements for the production of structural steel parts in machine building is improved hardness and wear resistance. Electrolyte-plasma chemical-thermal treatment is one of the best solutions for this problem, as the surface of steel is modified while the core of the part remains in a ductile state for resistance to impact loading, and this method is resource-saving due to the saving of energy and material consumption. In the present work the questions of technological possibilities of the method of electrolyte-plasma chemical heat treatment of steels are considered. The research results of other authors have been studied, and the analysis of the influence of technological parameters on the change of structural-phase state and improvement of microhardness at electrolyteplasma chemical heat treatment has been given. Electrolyte-plasma carburizing of 20X steel was carried out at the electrolyte-plasma chemical heat treatment unit. A solution of 10% soda ash (Na2CO3), 20% urea (CH4N2O) in 70% distilled water was used as an electrolyte. It was found that the cross section of steel after electrolyte-plasma carburizing has a zonal structure, so the modified layer with a thickness of ⁓50 μm consists of α-Fe, α'-Fe, Fe3C. After electrolyte plasma treatment of 20X steel, the microhardness increased ⁓3.5 times compared to the initial state.

Determination of Optimum Ratio of Selected Carbonaceous Materials on Mechanical and Corrosion Behavior of Carburized Mild Steel

This work is centred on the determination of optimum ratio of selected carbonaceous materials of A(40% Snail shell + 40% Animal bone), B(60% Snail shell + 20% Animal Bone), C(20% Snail shell + 60% Animal bone), D(50 Snail shell + 30 Animal bone) and E(30 Snail shell + 50% Animal bone), the mechanical properties and corrosion behaviour of carburized mild steel. Which were carburized at single austenitic temperatures of 1000°C, soaked at single carburizing time of 5hr, at the treatment temperature and samples were then quenched in water. Before the carburization process, standard test specimens were prepared from the received sample for testing hardness, tensile strength, wear, and microstructure analysis. After the carburization process, the test samples are subjected to standard testing to generate data on the ultimate tensile strength and wear rate of the carburized samples. Research shows that the mechanical properties of mild steel are strongly influenced by each of the mixed ratios of the carbonaceous material (Such as Snail shell and Animal Bone). An improved hardness values in all the samples were observed, with sample A having the highest hardness value of 59.05 RHC while sample B and sample C have the highest wear resistance value of 0.090. The samples were immersed in 0.3M H2SO4 solution for potentiodynamic studies. There results show that sample E had the least corrosion rate of 8.1809 mpy hence is less prone to corrosion attack in acidic environment than others. These samples are found to be useful in automobile industry.

Sustainable carburization of low carbon steel using organic additives: A review

Mild steel is made of iron and other elements, the chief among which is carbon. It is considered one of the most notable alloys in engineering applications because of its high tensile strength advantage and low cost. However, mild steel essentially lacks the hard surface quality which is considered key to many structural and industrial applications. This review explores various aspects of the carburization of mild steel which is targeted at providing the hard surface quality it lacks. This work critically reviews the mechanisms of different carburization methods, factors affecting carburization quality, and the potential of organic additives for carburizing low-carbon steel. Furthermore, this review article provides new insights into organic energizers and their benefits to both the handlers of carburizing operations and the environment in which they are carried out, following the United Nations' Sustainable Development Goal number 12 on sustainable production and consumption. Finally, this review concludes by providing directions for future research on organic additives-based mild steel carburization.

The Influence of Repeated Heat Treatments on The Propagation of Fatigue Cracking of Medium Carburized Steel

The issue of metal fatigue emerged as one of the major issues in a variety of engineering designs, and the design engineers were forced to take metals' fatigue resistance into account. In this paper, multiple quenching mediums and varied heat treatments were utilized to examine the effects of various heat treatments on the development of fatigue cracking in steel. The model that was carburized, quenched in distilled water and tempered before being quenched once more in distilled water and tempered a second time had the best outcomes, the fewest cycles needed to cause the model to fail, and a correlation between the rate of fatigue crack propagation and the length of the crack, according to the results. Additionally, the analytical findings demonstrated that this model, as opposed to models with fixed stress intensity factors, has a fatigue crack growth rate. The model that was carburized, quenched in coolant, then tempered and quenched again without performing the tempered appearance failed very rapidly. The high rate of the stress intensity factor with fatigue crack propagation is shown by the data analysis. The results show a reduction in the growth amount tendency of fatigue crack in the linear region mode-III.

The Effects of Ultrasonic Impact Modification on the Surface Quality of 20CrNiMo Carburized Steel

Ultra-high residual compressive stress can be introduced via the ultrasonic impact on the basis of transformation hardening, and further enhance the overall performance of 20CrNiMo carburized steel. In order to achieve the best surface quality of 20CrNiMo carburized steel, ultrasonic impact modification testing with varying static loads (900 N, 1200 N, and 1500 N) and rounds (1, 3, and 6) was conducted. By characterizing microhardness, microstructure, the surface roughness and residual compressive stress, the influence of ultrasonic impact modification parameters on its surface quality were analyzed. The experimental results indicated that the static loads and rounds of ultrasonic impact modification had a significant impact on the surface quality. The best surface quality could be obtained after six rounds of ultrasonic impact modification under a static load of 1200 N. In addition, the surface roughness decreased from 0.40 μm to 0.04 μm, the surface microhardness increased from 679 HV0.1 to 1086 HV0.1, and the maximum residual compressive stress of 1195.36 MPa was formed. Furthermore, the surface quality would deteriorate when the static load and ultrasonic impact rounds were increased.

Fatigue Behaviors of High-Strength Carburized Steel under Different Stress Ratios: Evaluation of Competitive Failure and Prediction of Very Long Life

Abstract As a metal material with superior mechanical properties, high-strength carburized steel is of great value for the production and manufacture of components in various fields. In this work, based on axial loading tests at stress ratios of −1, 0, and 0.3, the fatigue behaviors of high-strength carburized steels from high cycle to very high cycle are systematically investigated. For defect-fine granular area (FGA)-fisheye induced failure exhibiting long fatigue life, it is verified that the transition sizes between small and long cracks can be approximately equivalent to FGA size. Combined with extreme value estimation, a new mathematical model based on Weibull distribution was proposed to describe the competition among different failure modes. The results show that the probability of interior failure will decrease significantly with the increase of the maximum surface defect size under the condition that the maximum stress exceeds about 900 MPa. Additionally, larger surface defects are more beneficial to the occurrence of surface failure. Finally, combined with the stress correction factor proposed for optimizing the data with large dispersion, the fatigue life is predicted based on the crack initiation and propagation behavior, and the prediction results are in good agreement with the experimental results.

Fracture toughness determination for the surface-modified layers of carburized 18CrNiMo7-6 alloy steel via the compact tension method

Anti-fatigue manufacturing technology is the latest manufacturing technology to control surface integrity and modification. Surface modification techniques have been used to construct surface-modified layer (SMLs) on the workpiece surface. In this study, to accurately characterize and measure the fracture toughness of SMLs, a characterization method was proposed for evaluating the J-integral of fracture toughness of SMLs. The elastic–plastic parameters of the SMLs, such as the strain hardening index and yield strength, were obtained via peeling-layer tensile testing. The effect of n was considered when deriving the plasticity factor (ηp). The J-integral of the SML of 18CrNiMo7-6 alloy steel was obtained from single edge notched tension tests and finite element simulations. The results show that the fracture toughness of the SMLs can be accurately characterized using the proposed method.

Role of Precipitates on the Grain Coarsening of 20CrMnTi Gear Steel during Pseudo-Carburizing

The carburizing period for tool steel could be significantly shortened by operating at a higher carburizing temperature. However, grain coarsening happens during the carburizing process, and then results in the deteriorated surface properties in 20CrMnTi gear steel, especially at an elevated carburizing temperature. The relationships between grain coarsening and the precipitates in the developed 20CrMnTi gear steel during pseudo-carburizing were established by microstructure characterization, precipitate analysis and in-situ observation to clarify the coarsening mechanism. The results manifested the Baker–Nutting orientation relationship between the (Ti, Mo)(C, N) particles and the matrix, and then testified to the redissolution and ripening of the (Ti, Mo)(C, N) precipitates pre-formed in the α phase during the carburizing. Coarsening in austenite grain during the carburizing process was mainly caused by the rapid redissolution and ripening of the (Ti, Mo)(C, N) precipitates, although this occurred in a very short pseudo-carburizing time. The area density of the dispersed unripe (Ti, Mo)(C, N) particles markedly decreased from 0.389% in as-hot rolled gear steel to 0.341%, and then from 0.279% in carburized steels at 970 and 980 °C, respectively. Additionally, the redissolution and ripening of the (Ti, Mo)(C, N) precipitates were accelerated by the elevated carburizing temperature of 980 °C, at which time the growing rate in austenite grains was 2.34 μm/min during the prior 1 min (0.79 μm/min during the prior 3 min at 970 °C). The temperature then decreased to 0.003 μm/min in the subsequent carburizing process. The results obtained our current work reflected that the particles with excellent thermal stability should play important roles in the limitation of grain coarsening during the carburizing process.

Effect of bio-mineral oil blend quenchant on the mechanical properties of carburized mild-steel

In this study, the effect of bio-mineral oil blend quenchants on the mechanical properties of carburized mild steel was experimentally studied and reported. The tensile, hardness, impact, and microstructural test specimens were prepared in line with ASTM standards. Prepared specimens were then buried in a 50:50% ratio mixtures of eggshell/date-seed particulates as carburizing medium in a sealed packed cylindrical crucible. The carburization was then carried out in a muffle furnace at 950 oC for 3 h soaking time at 5 °C/min heating rate and thereafter quenched in different percentage blends of bio-mineral oils. Before the mechanical test and microstructural examination, samples were tempered at 200 oC for 1 h.Results from the experimental findings revealed that water and bio-mineral oil blend quenchants significantly influenced the mechanical properties and microstructure of carburized mild steel in varying degrees depending on the quenching media. Specimen quenched in 100% groundnut oil yielded the maximum yield tensile strength (805.43 MPa) and hardness at the surface edge (173.8 HV) equivalent to 106.7 and 87.66 percentage increment however, the best combination of mechanical properties (tensile strength 738.66 MPa, strain 17.12%, hardness 169.5 HV and impact strength 51.1 J) was obtained in the specimen quenched in 60/40% groundnut oil and SAE40 oil blends respectively. The enhancement in the mechanical property was due to the grain refinement in the microstructure of the bio-mineral oils quenched specimen. The 60/40 groundnut/SAE40 oil blend is therefore recommended for metallurgical heat treatment of mild steel for critical industrial applications.

Evaluation of Retained Austenite in Carburized Bearing Steel Using Magneto-Inductive Method

The present work explores the magneto-inductive method to evaluate different levels of retained austenite content in carburized 20NiCrMo7 bearing steel while comparing the corresponding measurements by X-ray diffractometry and image analysis by optical microscope. The content of retained austenite in carburized 20NiCrMo7 steel was modified with additional tempering to yield three samples with distinct ranges of retained austenite profiles in the carburized region of the steel. The retained austenite measured at different depths in these samples using the magneto-inductive method had an outcome comparable to other methods. Further discussion based on data suggests that the magneto–induction method yields precise (with an average deviation of 0.5%) results with sufficient sensitivity at different levels (including below 5 vol. %.) of retained austenite.

Corrosion and abrasion behavior of high-temperature carburized 20MnCr5 gear steel with Nb and B microalloying

This paper investigates the effect of Nb and B microalloying on the wear and corrosion resistance of 20MnCr5 steel after high-temperature carburization at 950 °C. The abrasion and corrosion performance of the steel was compared using electrochemical experiments and dry sliding wear tests. The results show that Nb microalloying reduces the size of residual austenite, thereby improving the wear resistance of 20MnCr5 steel. Furthermore, the combination of Nb and B microalloying reduces the amount of residual austenite, leading to further improvements in wear resistance. Both microalloying methods reduce the wear scar depth and debris accumulation. The corrosion potentials of 20MnCr5, 20MnCr5Nb, and 20MnCr5NbB are 0.645 V, 0.627 V, and 0.675 V, respectively. The addition of Nb to 20MnCr5 steel results in higher corrosion resistance after carburization due to the refinement of needle-like martensite. However, 20MnCr5NbB steel exhibits low corrosion resistance due to the coarsening of needle-like martensite caused by B microalloying. In summary, this study provides new insights into the effects of microalloying elements on the properties of steel. The findings contribute to a deeper understanding of how to design and manufacture gears and other components with superior wear and corrosion resistance.

Analytical model for predicting coverage in suspension waterjet shot peening and its influence on fatigue

Suspension waterjet peening is an emerging technology for surface modification. Coverage is a key factor affecting the integrity of a modified material surface, however such an experimental method that can be utilized for precise control has not yet been established. To determine the numerical value of coverage after surface peening treatment, In this paper, a coverage analytical method was proposed and then verified by the results through experiments. Furthermore, to explore the impact of high coverage on surface integrity, a large-scale coverage peening modification was performed on 18CrNiMo7-6 carburized steel specimens using a specialized suspension waterjet equipment. The results indicate that coverage has a significant impact on roughness and compressive residual stress field, with the highest improvement on surface and their maximum values reaching 51.6% and 24.7%, respectively. It is shown that the fatigue performance of the specimens can be significantly enhanced.

Explicit microstructural and electrochemical study of value-added carburized mild steel with coconut shell ash and CaCO3 nanoparticles derived from periwinkle shell

Explicit microstructural and electrochemical study of value-added carburized mild steel with coconut shell ash and CaCO3 nanoparticles derived from periwinkle shell

レーザピーニングが浸炭鋼の表面特性および曲げ疲労特性に及ぼす影響

To investigate the effects of laser peening (LP) on the surface and bending fatigue properties of carburized steel (JIS SCM420), surface roughness measurements, residual stress measurements, retained austenite measurements, and four-point bending fatigue tests were conducted. After LP, the compressive residual stress was introduced on the surface, with the effect extending to a depth of more than 1 mm. Due to the high compressive stress, the bending fatigue strength of LP specimen was 1.46 times higher than that of the as-heat-treated specimen even though the surface roughness was increased by LP. Notably, the amount of retained austenite was 10.9％ at the top surface of LP specimen, and high-density twins were observed in the lath martensite structure. This can be attributed to high strain rate deformation by LP.

Failure behavior of a roller in automotive flywheel manufacturing

The failure behavior of a carburized 18CrNiMo7-6 steel roller from a roll forming mill used to manufacture automotive flywheels is investigated. Microstructural observations using optical and scanning electron microscopy are carried out, and the hardness determined using a Vickers hardness testing machine. The carburized layer is mainly comprised of fine tempered martensite, small carbides and retained austenite. The depth of the carburized layer around the roller groove is thinner than the required standard. The decrease in microhardness with increasing distance from the surface to the core is found to be due to the different carbon concentrations. However, a pronounced variation of the microhardness value is detected around the roller groove surface. This is related to the formation of an inhomogeneous microstructure during quenching after the carburizing process. The results indicate that the crack nucleates at the bottom surface of the roller and propagates along the direction vertical to the roll forming with a transgranular character.