Case-hardened Steel Research Articles

Enhancing damage prediction in bulk metal forming through machine learning-assisted parameter identification

The open-source parameter identification tool ADAPT (A diversely applicable parameter identification Tool) is integrated with a machine learning-based approach for start value prediction in order to calibrate a Gurson–Tvergaard–Needleman (GTN) and a Lemaitre damage model. As representative example case-hardened steel 16MnCrS5 is elaborated. An artificial neural network (ANN) is initially trained by using load–displacement curves derived from simulations of a boundary value problem—instead of using data generated for homogeneous states of deformation at material point or one-element level—with varying material parameter combinations. The ANN is then employed so as to predict sets of material parameters that already provide close solutions to the experiment. These predicted parameter sets serve as starting values for a subsequent multi-objective parameter identification by using ADAPT. ADAPT allows for the consideration of input data from multiple scales, including integral data such as load–displacement curves, full-field data such as displacement and strain fields, and high-resolution experimental void data at the micro-scale. The influence of each data set on prediction quality is analyzed. Using various types of input data introduces additional information, enhancing prediction accuracy. The validation is carried out with respect to experimental void measurements of forward rod extruded parts. The results demonstrate, by incorporating void measurements in the optimization process, that it is possible to improve the quantitative prediction of ductile damage in the sense of void area fractions by factor 28 in forward rod extrusion.

Separation of Damage Mechanisms in Full Forward Rod Extruded Case-Hardening Steel 16MnCrS5 Using 3D Image Segmentation.

In general, formed components are lightweight as well as highly economic and resource efficient. However, forming-induced ductile damage, which particularly affects the formation and growth of pores, has not been considered in the design of components so far. Therefore, an evaluation of forming-induced ductile damage would enable an improved design and take better advantage of the lightweight nature as it affects the static and dynamic mechanical material properties. To quantify the amount, morphology and distribution of the pores, advanced scanning electron microscopy (SEM) methods such as scanning transmission electron microscopy (STEM) and electron channeling contrast imaging (ECCI) were used. Image segmentation using a deep learning algorithm was applied to reproducibly separate the pores from inclusions such as manganese sulfide inclusions. This was achieved via layer-by-layer ablation of the case-hardened steel 16MnCrS5 (DIN 1.7139, AISI/SAE 5115) with a focused ion beam (FIB). The resulting images were reconstructed in a 3D model to gain a mechanism-based understanding beyond the previous 2D investigations.

Optimized Compound Layer Design for Highly Loaded Nitrided Gears

AbstractNitriding is a thermochemical surface hardening process, which can be used to improve the performance properties of gears. In particular, the tooth flank and tooth root load-carrying capacity can be significantly increased by nitriding. Previous work has shown that tribological dominated failure modes and limits, such as the micro-pitting and wear load-carrying capacity of gears, can be significantly increased by a suitable compound layer structure. In this work, the relationship between compound layer design and macro-pitting load-carrying capacity of nitrided gears is explored based on experimental investigations. For this purpose, the materials EN31CrMoV9 and EN42CrMo4 were nitrided under varying nitriding conditions to produce compound layers with different structures and properties. The characteristics of the compound layer such as phase composition, compound layer thickness and pore seam were extensively characterized by means of metallographic techniques, XRD, GDOES, and EBSD. Experimental investigations of the macro-pitting load-carrying capacity were carried out on an FZG back-to-back gear test rig with center distance a = 52 mm. It was shown that the pitting load-carrying capacity depends to a large extent on the characteristics of the compound layer, in particular on the formation of the pore seam. A minimum pore seam thickness of CLTP ≥ 1.8 µm has a positive effect on the pitting load-carrying capacity. The test results for the pitting load-carrying capacity are above (σH lim ≥ 1690 N/mm2) or, in some cases, significantly above (σH lim = 1979 N/mm2) the strength values specified in ISO 6336-5:2016 for nitrided nitriding steels (σH lim = 1450 N/mm2; material quality ME) and case-hardened alloy steels (σH lim = 1650 N/mm2; material quality ME).

Experimental Analysis of Effect of Machined Material on Cutting Forces during Drilling.

Current research studies devoted to cutting forces in drilling are oriented toward predictive model development, however, in the case of mechanistic models, the material effect on the drilling process itself is mostly not considered. This research study aims to experimentally analyze how the machined material affects the feed force (Ff) during drilling, alongside developing predictive mathematical-statistical models to understand the main effects and interactions of the considered technological and tool factors on Ff. By conducting experiments involving six factors (feed, cutting speed, drill diameter, point angle, lip relief angle, and helix angle) at five levels, the drilling process of stainless steel AISI1045 and case-hardened steel 16MnCr5 is executed to validate the numerical accuracy of the established prediction models (AdjR = 99.600% for C45 and AdjR = 97.912% for 16MnCr5). The statistical evaluation (ANOVA, RSM, and Lack of Fit) of the data proves that the drilled material affects the Ff value at the level of 17.600% (p < 0.000). The effect of feed represents 44.867% in C45 and 34.087% in 16MnCr5; the cutting speed is significant when machining C45 steel only (9.109%). When machining 16MnCr5 compared to C45 steel, the influence of the point angle (lip relief angle) is lower by 49.198% (by 22.509%). The effect of the helix angle is 163.060% higher when machining 16MnCr5.

Hybrid methodology development for lubrication regimes identification based on measurements, simulation, and data clustering

The lubrication regimes of a laboratory scale journal bearing were analysed with wide band acoustic emission (AE) measurements. The analysis was supported by data-based clustering of AE data. Digital twin of the journal bearing was generated with Simpack multi-body simulation software to study opportunities for developing a hybrid methodology for more complex systems monitoring. The AE and data-based clustering approach can be effectively used to reveal fundamental lubrication modes, i.e., hydrodynamic (HL), mixed (ML) and boundary (BL) lubrication as a function of Hersey number, which can be evaluated in situ by utilizing digital twin. Besides AE the other parameters monitored were friction torque, bearing temperature, loading, sliding velocity and oil pressure. The materials used in the experiments were case-hardened 18CrNiMo7–6 steel and nitrided 42CrMo7 steel. The tests were lubricated with synthetic extreme-pressure gear oil (SGN 320) and the bearing temperature was kept constant during the tests. The bearing loading and sliding velocity during tests were varied in the wide range resulting in different lubrication situations. The acoustic emission signals power and frequency content was analysed, and essential features were extracted for data clustering. For lubrication regime change identification the parameters such as signal RMS and coefficient of variation (CV) proved to be important, while signal kurtosis showed to be the most sensitive in discovering anomalies. The high sensitivity requires data filtering to remove erroneous peaks and to reveal real trends more clearly. It is also interesting to notice the changes in AE frequency during changing to different lubrication regime. In literature different clustering and classification methods has been proposed and applied for journal bearing status identification. Here the selected unsupervised clustering method was the mean-shift clustering due to fact, that the lubrication regimes in the Stribeck curve form an inseparable continuum. The algorithm does not require specifying the number of clusters in advance, i.e., the clusters are determined by the algorithm with respect to the data. The results were compared to simulations with digital twin. i.e., by comparing simulated digital twin film thickness and measured AE kurtosis relative to measured Hersey number. It was concluded that digital twins can be utilized as virtual sensor for in situ detecting of lubrication regimes, if it is possible to calibrate the simulation with sensitive measurements, e.g., AE. It is obvious that simulations alone cannot predict suddenly appearing anomalies, such as impurities or surface fatigue failures.

Risk assessment of hitch pins connecting tractor and trailer to enhance the safety of humans using strain life fatigue approach

Abstract The hitch pin is a critical component between tractor and trailer. The failure of hitch pins is quite frequent and a serious issue which remains unaddressed to a great extent due to limited information on this topic. This paper presents a novel insight into substandard pins manufactured in the informal sector due to non-conformance to any established standard and opens up a new area for further research on this subject. In the present context, risk factors along with reasons of cracks of in-service hitch pins were assessed to enhance the safety of humans. The pin showed signs of a crack, corrosion, scratches, and dents. Notches and scratches acted as stress raisers. Cracks can be seen initiating from the tip of notches. The pin was made of non-standard mild steel and was not heat treated. The study further demonstrates the methods to improve the fatigue life of the pin using numerical simulation. The hardness method was used to collect the cyclic fatigue properties of the commercially available mild steel for different heat-treated samples using the strain life fatigue approach. The casehardened mild steel pin of a case depth of 1.3 mm with a hardness of 30 HRC had considerably increased fatigue properties. Recommendations have been provided to protect humans from these accidents.

Thermal and thermochemical treatments against fretting failure applied to power transmissions

Some power transmission components are subject to the fretting corrosion failure mode, which results in rapid wear of mating surfaces or premature fatigue crack initiation. Fretting corrosion is generated by micro-movements of surfaces in contact. In mechanical transmissions, it is found in particular on shrink-fit connections (bearing rings, for example) and on key and spline connections when they are misaligned or not with the well design fit.The sectoral board for mechanical transmissions and rolling bearings and CETIM is investigating the potential of technical solutions (materials, heat treatment, lubrication, etc.) to prevent fretting. This article presents a study of the impact of thermal and thermochemical heat treatments of steels used in power transmissions on the appearance, morphology and intensity of corrosion fretting.Among the materials and heat treatments commonly used in mechanical transmissions (NF EN 683, ISO 6336-5), the following variants were studied: through-hardened steels (42CrMo4, 100Cr6), surface-hardened steels (42CrMo4), case-hardened steels (20MnCr5) and nitrided steels (42CrMo4). These variants are compared using a standardized ASTM G204 test, which involves oscillating a pressurized, lubricant-free pin (100Cr6) on a plate (the tested variant) for 24 hours. The peak-to-peal slip amplitude range is set at 50µm or 100µm. Tangential forces during testing, then the volume loss of pin and plate after testing, were measured, analysed and compared. The experimental study reveals wear resistance and depend on heat and thermochemical treatment as well as slip amplitudes. Through hardened 100Cr6 has better fretting resistance than nitrided 42CrMo4 for 50µm amplitude, but the results are completely reversed at 100µm amplitude.

Characterization and Separation of Damage Mechanisms of Extruded Case-Hardening Steel AISI 5115 under Cyclic Axial-Torsional Loading

Due to the emerging relevance of topics such as climate change or scarcity of resources, the requirements for energy efficiency, emissions and resource conservation are increasing. In this context, components manufactured by metal forming offer a high potential for lightweight construction, cost effectiveness and resource efficiency. The defects resulting from forming processes e.g. in form of micropores and their growth are currently not taken into account. A commercial design is usually based on mechanical material properties and additional safety factors. The knowledge of the ductile forming-induced damage in the component design enables an improved design. In this study, the influence of different forming process parameters during full forward rod extrusion on the structural damage and the fatigue properties were investigated for the case-hardened steel AISI 5115 (16MnCrS5, 1.7131). The intention was to compare the fatigue properties of different damage states under cyclic axial and axial-torsional loading including the identification and separation of underlying damage mechanisms. A significant effect of superimposed cyclic torsional loading on cyclic axial properties and mechanisms was found, which was associated with a decrease of 38 % in the lifetime. Axial-torsional fatigue tests were conducted at various test temperatures to determine the effect of forming-induced damage and test temperature on the fatigue strength. In addition, differences in microstructure as a result of forming-induced and fatigue-induced damages were validated by using scanning electron microscopy.

Reduction of the production cycle of case-hardened parts

The possibilities of reducing the production cycle for the manufacture of case-hardened steel parts are being studied. The use of turning of hardened cylindrical parts with a mineral-ceramic tool (ВОК-60) and a 50 % reduction in manual labor (loading, unloading, marking, sandblasting) can reduce the production cycle by 35÷40 %. Keywords: case-hardened steel, processing, mineral ceramics, production cycle. bsv_sfmai@mail.ru

Experimental Investigation of Tribology-Related Topography Parameters of Hard-Turned and Ground 16MnCr5 Surfaces

Several surface topography parameters are available for the quantification of tribological properties of machined surfaces. Although these parameters and their influences are widely studied, there are contradictory findings due to the nature of the topography parameters, i.e., the behavior of different materials and cutting tool interactions lead to relatively varying numerical results. A comprehensive study of these interactions can contribute to more exact industrial machining applications. In this study, tribology-related 3D topography parameters of hard-machined (hard-turned and ground) surfaces were analyzed. The machining experiments were carried out based on a detailed design of the experiment; the analyzed material was case-hardened low-carbon content steel, which is widely used for automotive, industrial components such as bearings or gears. From the topography data, response function, correlation, and relative deviation analyses were carried out for the analyzed topography parameters, and tribology maps were created to support the selection of optimal cutting parameter values.

Observation of Transition Area Origin Cracks on Fracture Surfaces of Carburized JIS SCM415 Bars

Under high cycle and very high cycle fatigue, high strength steels break as a result of internal fracture from inclusions. In order to understand this fracture, “Fisheye” crack has been investigated. In our previous work we found that cracks grew from the boundary between the hard surface and soft core of case-hardened S45C, SUJ2 and SCM415 steel bars under rotating bending fatigue. These cracks were called “Transition area origin (TRO)” cracks. In this study, we closely observed the fracture surface of TRO crack areas in carburized JIS SCM415 specimens (under 734, 776 and 865 MPa). We found three features of the TRO cracks: outside of the TRO cracks had asperities; the shapes of TRO cracks were almost circular, and were different from those in S45C and SUJ2 steels; and the HAZ-TRO area which was located at hardened layer had some ridges, and the Core-TRO area at unheat-treated layer was smooth and flat.

Detectability of Thermomechanical Surface Damages on Quenched and Tempered, Nitrided and Case-Hardened Steels by Barkhausen Noise Analysis

Abstract Magnetic Barkhausen noise analysis is an already industrially used method for the detection of grinding burn and offers several advantages over the established nital etching test with respect to objectivity, cost savings as well as occupational safety and environmental protection. Studies on the detectability of damages and influencing factors such as the condition of the surface zone prior to grinding have so far only existed in isolated cases and mostly limited to a few widely used case-hardened steels. For this reason, various steel grades used in particular in the aerospace sector were considered in this study. For one quenched and tempered, one nitrided and two case-hardened steels, the detectability of damages by means of Barkhausen noise and the influence of different heat treatment parameters were investigated. It was shown that the use of Barkhausen noise analysis is also possible on these steel grades and enables more reliable damage detection than nital etching.

DLC-Coated Thermoplastics: Tribological Analyses under Lubricated Rolling-Sliding Conditions

The goal of this work is to evaluate the potential of diamond-like carbon (DLC) coatings on thermoplastic polymers for friction and wear reduction in highly stressed rolling–sliding contacts. Therefore, hydrogen-containing DLC coatings were deposited on the polymer surface by a low-temperature high power pulsed magnetron sputtering (HPPMS) physical vapor deposition (PVD) process. The rolling-sliding contact between coated polyamide 66 (PA66) or coated polyether ether ketone (PEEK) against case-hardened steel 16MnCr5 is investigated in a twin-disk tribometer at normal loads up to FN = 1,000 N, sum velocities between 1 m/s ≤ vΣ ≤ 16 m/s and slip ratios up to s = 50%. Results show a friction reduction with the application of DLC on the considered polymers compared to uncoated polymers under specific lubrication conditions. High solid losses caused by the polymer’s internal damping properties dominate the temperature behavior of the polymer, even when coated with DLC. Regarding the wear behavior, DLC coatings show potential especially under severe mixed lubrication conditions with high-solid load portion and sliding. The knowledge gained about coated polymers can be used to improve the overall tribological performance in terms of friction and wear of thermoplastic machine elements like gears.

Asymmetric Height Distribution of Surfaces Machined by Hard Turning and Grinding

The asymmetric height distribution of a machined surface can be useful from a tribological point of view in several cases. The purpose of this study is to analyze this asymmetry based on the 3D surface texture parameter skewness, providing technological parameter values that help in achieving favorable surfaces. A 16MnCr5 case-hardened steel (62–63 HRC) was machined by hard turning and grinding based on a comprehensive design of experiments and the topography of the surfaces was measured and analyzed. The texture parameter that informs about the height distribution of the surface points (skewness, Ssk) was compared to the volume parameters peak material volume (Vmp) and valley void volume (Vvv). The main finding is that negative Ssk values are found at low Vmp and Vvv values, which confirms the favorable tribological properties.

Early Detection of Subsurface Fatigue Cracks in Rolling Element Bearings by the Knowledge-Based Analysis of Acoustic Emission.

Aiming at early detection of subsurface cracks induced by contact fatigue in rotating machinery, the knowledge-based data analysis algorithm is proposed for health condition monitoring through the analysis of acoustic emission (AE) time series. A robust fault detector is proposed, and its effectiveness was demonstrated for the long-term durability test of a roller made of case-hardened steel. The reliability of subsurface crack detection was proven using independent ultrasonic inspections carried out periodically during the test. Subsurface cracks as small as 0.5 mm were identified, and their steady growth was tracked by the proposed AE technique. Challenges and perspectives of the proposed methodology are unveiled and discussed.

Wear mechanisms and wear resistance of austempered ductile iron in reciprocal sliding contact

Austempered ductile irons (ADIs) are used in applications commonly exposed to severe contact conditions, and as a consequence wear damage frequently followed by failure of components. Hence, wear resistance of the material governs the final life time of a component. In the present work, the sliding wear resistance of two ausferritic spheroidal graphite ductile irons ADI1 and ADI2 used commonly in mining and construction equipment was investigated. ADI1 and ADI2 were heat treated to a similar strength, the volume fraction of the carbon-rich austenite in ADI1 and ADI2 was around 30% and 16%, respectively, and they both contained 10 – 13% nodular graphite. The wear tests were performed using a slider-on-flat-surface (SOFS) tribometer. Case-hardened steel plates made of a high strength steel, 22NiCrMo12–F, were used as the counterface. The wear tests were conducted under lubricated sliding contact at normal loads of 50, 100, 200 and 300 N, and at each load level sliding at 100, 200 and 300 m. The friction force between contacting surfaces was continuously monitored during sliding. The lubrication used in the present investigation was a mineral-oil-based paste commonly used in applications where high frictional heating is generated. Wear mechanisms of the tested specimens were investigated by means of optical and scanning electron microscopy and X-ray diffraction, and the wear damage was quantified using a 3D-profile optical interferometer. The main wear mechanisms, severe plastic deformation and surface delamination, were discussed concerning test conditions and material properties. The ADI1 grade with the higher volume of carbon-rich austenite displayed better resistance to sliding wear at high normal loads. The higher normal loads promoted larger deformation at and beneath the contact surface and initiated austenite transformation into hard martensite. Thus, it was concluded that the increase of wear resistance in ADI1 was due to the formation of marteniste. On the other hand, the ADI2 grade with higher silicon content showed lower wear resistance at high normal loads. This was associated with cracking of the proeutectoid ferrite presented in ADI2.

Formation of structure and properties of surface layer of case-hardened steel by electromechanical surface hardening

The researching results of the structure and microhardness of the surface layer of steel 20 after vacuum cementation of cylindrical samples to a depth of 1,0 mm and their hardening by volumetric heat treatment in comparison with electromechanical surface hardening are presented. The maximum microhardness of the surface layer of cemented steel 20 is at a depth of 0,05 mm and corresponds to 9650 HV MPa, and gradually decreases within the hardened layer to 8190 HV MPa at a depth of up to 0,75 mm after electromechanical surface hardening has been experimentally established. There isn’t decarbonized layer after the electromechanical surface hardening of cemented steel samples 20. The reaserch practical significance is associated with the possibility of improving the quality and reducing the cost of parts producting from cemented steels by replacing heat treatment after cementation with the technology of hardening the working surfaces by electromechanical surface hardening.

Non-destructive direct current potential drop assessment of forming-induced pre-damage in AISI 5115 steel

Due to efficient material utilization and reproducible high-quality level, metal forming processes, such as forward extrusion, meet the requirements of resource-saving and economical production. However, the performance of workpieces is considerably affected among others by the occurrence of forming process-induced damage. So far, there are only few investigations available on the influence of process-induced pre-damage on fatigue behavior. With the knowledge of damage influence on the component durability, components can be designed specifically and enable optimization of loading capability and lightweight construction. Also, the degree of process-induced pre-damage after forming is currently measured by time-demanding destructive analyses in scanning electron microscopy (SEM). Electrical resistance measurement (DCPD) could offer the opportunity for a time-efficient non-destructive assessment of ductile damage. The aim was to develop a method for damage characterization that allows conclusions to be drawn about the expected lifetime of components. Therefore, a highly accurate resistance-based sensor system for the evaluation of forming process-induced damage and loading-induced cyclic damage, and for the analysis of their interaction has been established and validated. The measurement technology required for damage detection was adapted and optimized to round specimens and should lead to highest possible reproducibility. The measurement parameters, such as applied current and duration of current pulse, were optimized with the aid of statistical experimental design. The new sensor system was tested on specimens of case-hardened steel AISI 5115 (16MnCrS5, 1.7139) with different damage states. The signal acquisition could be optimized by the measurement parameter variation by a factor of more than 100 compared to initial measurements. By using the delta mode, the thermoelectric effects could be eliminated during the measurement. A significant influence of deformation-induced damage on the electrical resistance measurement was validated. Specimens with less forming-induced damage showed lower electrical resistance. The results were validated with recordings by destructive testing in SEM. Thus, a cost-effective non-destructive method for forming-induced damage analysis was developed, providing the capability for process monitoring in future.

Abrasive Wear, Scuffing and Rolling Contact Fatigue of DLC-Coated 18CrNiMo7-6 Steel Lubricated by a Pure and Contaminated Gear Oil.

Due to extreme working conditions of mining conveyors, which contaminate gear oil with solid particles, their transmissions are exposed to intensive abrasion, scuffing, and even rolling contact fatigue (pitting). These effects shorten gear life. To prevent their occurrence, a wear-resistant coating can be deposited on gear teeth. The resistance to abrasive wear, scuffing, and pitting was investigated and reported in the article. Simple, model specimens were used. Abrasive wear and scuffing were tested using a pin-and-vee-block tribosystem in sliding contact. A cone–three-ball rolling tribosystem was employed to test pitting. The material of the test specimens (pins, vee blocks, cones) was 18CrNiMo7-6 case-hardened steel. Two types of DLC (Diamond-like Coatings) coatings were tested, W-DLC and W-DLC/CrN. The vee blocks and cones were coated. Two industrial gear oils were selected to lubricate the specimens: one with a mineral and one with a synthetic PAO (polyalphaolephine) base, as pure oil or contaminated with solid particles from a coal mine. The results show that, to minimize the tendency to abrasion, scuffing, and pitting of specimens made of 18CrNiMo7-6 steel, the W-DLC/CrN coating should be deposited. This coating also gives very good protection when the lubricating oil is contaminated.

Correlation Modeling Between Peening-Induced Hardness, Residual Stress and Roughness in Case-Hardened High Strength Steels

The present paper is focused on the investigation of the correlation modeling of hardness and compressive residual stress on the surface and subsurface regions of case-hardened 18CrNiMo7-6 steels subjected to shot peening. The results exhibit that the relationship between hardness and compressive residual stress can reasonably well be approximated by an inverse linear model. The analysis suggests that the slope and y-intercept of the inverse linear trend line can be related to the compressive residual stress level and the initial material hardness, respectively. It is further revealed that the negative effect brought by the peening-induced roughness on the measurement of experimental data computed on the surface can be compensated by performing the normalization using the roughness parameter called the maximum valley height (Sv).