Case-hardened Steel Research Articles

An Efficient Procedure for Identifying the Prediction Model Between Residual Stress and Barkhausen Noise

Residual stress of case-hardened steel samples is predicted in this paper with the linear multivariable regression model. The development of the prediction model is based on the huge set of features calculated from the Barkhausen noise measurement signal among which the most suitable ones are chosen. The selection uses a genetic algorithm with leave-multiple-out cross-validation in the objective function. The original feature set contains collinear features that make the selection task even more complex. Thus a feature elimination procedure based on the successive projections algorithm is studied in this paper. Also the standard genetic algorithm is slightly modified to better serve the feature selection task. The obtained results are good showing that the proposed procedures suit well for residual stress predictions. Also the applied feature elimination procedure is applicable and can be safely used to reduce the dimensionality of the selection problem.

APPLICATION OF X-RAY DIFFRACTION IN DEVELOPMENT OF NEW TYPE OF MOULDS FOR PRODUCTION OF REFRACTORY AND HIGHLY ABRASIVE OBJECTS

Ceramic materials can be used due to their high hardness and chemical stability as both the wear and corrosion resistant coatings. Their deposition on moulds for manufacturing of objects from refractory and highly abrasive materials is challenging, because they are traditionally made from hard-to-blast casehardened tool steels with hardness exceeding 60 HRC. The pressing process imposes further stringent requirements on the coating microstructure; especially in respect to its homogeneity, cohesion and wear resistance. Considering results of laboratory analyses of residual stresses and roughness of blasted surfaces, mould plates from low-carbon C45 steel were sprayed with five different ceramic materials by water stabilized plasma gun. The testing of the moulds with plasma coatings was performed on-site in a factory under standard pressing conditions.

Straightforward Reconstruction of Smooth Concave Diffusivity Profiles from Photothermal Phase

This article introduces a fast and easy way to retrieve smooth concave thermal-diffusivity profiles from the photothermal (PT) response of a semi-infinite solid with concave depth-dependent thermal diffusivity, such as case-hardened steels. The approach is based on the exact asymptotic behavior of the PT phase and on the position, height, and width of the phase maximum. The resulting procedure, which only requires PT phase data at relatively few frequencies, is unambiguous and involves only simple algebraic formulae and no tweaking. The method is successfully applied to the inversion of some simulated profiles, including the demanding piecewise linear one, proving the value of the method.

409 浸炭硬化歯車のピッチング強さに及ぼす表面性状の影響

409 浸炭硬化歯車のピッチング強さに及ぼす表面性状の影響

404 ピーニングを施した浸炭硬化ローラの疲労過程における表面性状の変化

404 ピーニングを施した浸炭硬化ローラの疲労過程における表面性状の変化

Barkhausen noise characterisation during elastic bending and tensile-compression loading of case-hardened and tempered samples

This study examined the Barkhausen noise (BN) response of carburising case-hardened steel with varying tempering stages. The test material was loaded in bending and in alternating loading. The aim of the study was to obtain relevant multiparameter BN data from different loading conditions and to investigate the effect of applied stress on the BN response. The test bar series was made from case-hardened steel. Different tempering parameters were used to vary the surface hardness and the surface residual stresses of the studied series of test bars. In the bending tests, the samples were subjected to incrementally applied loading in the purely elastic deformation region. In addition, uniaxial stepwise loading with tensile and compressive stress was applied to selected samples simultaneously with the BN measurements. The BN measurements were performed under different loading conditions along with X-ray diffraction strain measurements in bending. The results revealed linear behaviour between the reciprocal root mean square value and the stress values obtained with strain gages and X-ray diffraction for the tempered samples.

506 クラウニング歯面を有する浸炭硬化歯車の疲労寿命(機素潤滑設計I)

506 クラウニング歯面を有する浸炭硬化歯車の疲労寿命(機素潤滑設計I)

S112021 同一表面粗さにおける浸炭硬化ローラの疲労寿命に及ぼすキャビテーションピーニングとショットピーニングの影響

S112021 同一表面粗さにおける浸炭硬化ローラの疲労寿命に及ぼすキャビテーションピーニングとショットピーニングの影響

Quantitative prediction of residual stress and hardness in case-hardened steel based on the Barkhausen noise measurement

The aim of this study is to predict residual stress and hardness of a case-hardened steel samples based on the Barkhausen noise measurements. A data-based approach for building a prediction model proposed in the paper consists of feature generation, feature selection and model identification and validation steps. Features are selected with a simple forward-selection algorithm. A multivariable linear regression models are used in predictions. Throughout the selection and identification procedures a cross-validation is used to guarantee that the results are realistic and hold also for future predictions. The obtained prediction models are validated with an external validation data set. Prediction accuracy of the prediction models is good showing that the proposed modelling scheme can be applied to prediction of material properties.

Wear Behavior of Surface Treated Alloy Steel with Assorted Blends of Fine Particles by Using Plasma Spray Process

Surface treatment is a new improved treatment procedure which espouses the mitigation of root cause of failures and improves the internal properties of case-hardened alloy steel. Coating is one of the Surface treatment processes applied on the case hardened alloy steel by which a sign of tremendous improvement is shown in wear resistance. This is due to increase in hardness by coating fine particles of oxides of ceramics (OC) and tungsten carbide (WC) on the surface of alloy steel. The coating makes the surface of alloy steel completely devoid of retain austenite formation which is usually formed in other conventional heat treatment processes. An analysis has been made on the surface treated alloy steel which is coated with diverse blends of fine particles of OC and WC. The investigation of coating consists of numerous metallurgical processes to identify the coating powder specification, coating process, coating characteristics, micro-structure and wear resistance property for the surface treated alloy steel. The exploration reveals the best alternative among the coating blends of fine particles which are taken for analysis on base alloy steel.

The influence of manufacturing method on the running-in of gears

Striving for higher gear transmission efficiency by using a low-viscosity transmission lubricant affects the lubricant film thickness. To keep the Λ-ratio (the ratio between the film thickness and the surface roughness) intact, more effort must be put on the surface topography. This paper presents a study of how running-in affects the dry elastic contact area ratio in spur gears using real surface topographies from three common manufacturing methods (green-shaving, honing, and grinding). The test gears were manufactured in case-hardened steel, similar to 20MnCrS5. Surface topography measurements were used as input to a contact analysis boundary element software program. An important hypothesis used in this work is that the dry elastic contact area ratio, i.e. the ratio between real and nominal contact area, can be used as a measure of the contact conditions in gears. It is concluded that running-in differs significantly for the studied manufacturing methods and that the dry elastic contact area ratio gives a consistent description of these changes. The shaved gears have the highest dry elastic contact area ratio after running in, where the ground gears have the lowest dry elastic contact area ratio. The increase in dry elastic contact area ratio is about 30 per cent for the shaved gears, 12 per cent for the honed gears and less than 5 per cent for the ground gears. Extreme value parameters, such as Rp and Rz, showed relatively good correlation to dry elastic contact area ratio. However no genuine correlation could be found between dry elastic contact area ratio and two-dimensional (2D) surface roughness parameters. Furthermore, traditional gear metrology form parameters do not serve as a good measure on the changes occurring during the running-in.

Effect of elasto-plastic loading on the magnetic characteristics of steel 20 hardened with gas case-hardening

The evolution of the magnetic characteristics of case-hardened Steel 20 under the influence of elasto-plastic tensile, compressive, and torsional strains is analyzed. The field dependence of the differential magnetic permeability is shown to reflect a three-layer nature of the obtained micro-structure: a hardened surface layer, a transition zone, and a ferrite-pearlite core. It is proposed to evaluate the level of the applied stresses on the basis of the peak field and the height of the differential magnetic permeability peaks of corresponding layers of the case-hardened steel.

818 微粒子ピーニングを施した浸炭硬化ローラの疲れ寿命(機素潤滑設計III)

818 微粒子ピーニングを施した浸炭硬化ローラの疲れ寿命(機素潤滑設計III)

Case-hardening inspection of steel using photothermal phase maxima

Starting from the exact solution for the photothermal signal in semi-infinite materials with an exponential and with a piecewise linear thermal conductivity profile, a set of equations valid for a broad class of profiles is derived for the direct computation of the conductivity profile depth and surface conductivity from the properties of the photothermal phase maximum alone. By virtue of the usual anticorrelation between conductivity gradient and hardening gradient, this can be used for the assessment of case depth and surface hardening of case-hardened steels. The results compare very well with the results of Vickers hardness tests. The methodology only applies to concave conductivity profiles, excluding e.g., sigmoidal shapes.

BARKHAUSEN: A study on laser-processed grinding burn simulation and analysis based on Barkhausen noise measurement

Barkhausen noise (BN) is widely used as a quality control method for grinding burn detection in ferromagnetic materials such as the case-hardened steels used in gears. The study of grinding burns with BN equipment requires, however, a calibration reference sample with a known BN response. The demand for better calibration samples is well recognised. In this study, artificial grinding burns with laser processing were produced in case-hardened steel. The laser was selected because it is a surface-sensitive heating method and it accurately simulates the heat generation during grinding between the grinding wheel and work-piece. A test series was made by changing the laser input power and traverse rate to process the surface of a ground gear wheel sample. The laser-processing parameters were optimised experimentally. The BN measurement data was used in the modelling of selected quality measures: hardness and residual stress (RS). The BN measurement device provided some features from the time-domain analysis of the signal and a new feature, BN entropy, was also used. The modelling was done with Matlab® using linear regression. The results showed that laser processing had a clear effect on the BN features and residual stresses.

Surface durability of WC/C-coated case-hardened steel gear

The purpose of this study is to investigate the influence of tungsten carbide/carbon (WC/C) coating on the surface durability of casehardened steel gear. Two kinds of WC/C coatings were deposited on the ground gear pair made of chromium molybdenum steel with carburizing and quenching. One is the conventional WC/C coating, and the other is WC/C coating with about 1 μm CrN interlayer. Here, the WC/C-coated test pinion and the WC/C-coated one with CrN interlayer are represented by WT and ST, respectively. Non-coated test pinion is represented by NT. The surface roughness along the tooth profile direction of WT and ST was almost the same as that of NT. A spur gear test was carried out with an IAE power circulating type gear test rig under EP gear oil lubricating condition. The fatal failure mode of the test pinions was pitting due to surface cracking. The fatigue life of WT was longer than that of NT under a maximum Hertzian stress pmax=1700 MPa. On the other hand, under pmax=1900 MPa, that of WT was as long as that of NT due to the peeling occurrence of the coated layer. Under the comparatively low load condition without peeling occurrence, the surface roughness of WT decreased with the increasing number of cycles, and their fatigue life became longer than that of NT. On the contrary, in the case of ST, the peeling of the coated layer occurred at a comparatively early stage of the gear test, and the dedendum was worn by tens of micrometers. Therefore, in the case of ST, the effect of the WC/C coating disappeared at a comparatively small number of cycles.

Variable amplitude fatigue behavior and life predictions of case-hardened steels

Fatigue behavior of case-hardened steel specimens were investigated under variable amplitude loading conditions including two-level load tests, periodic overload tests, and service load history tests. Fatigue life predictions were made using a two-layer model based on case and core material fatigue properties and compared to the experimental results. Both standard strain-life curve based on constant amplitude data as well as effective strain-life curve based on periodic overload data were used for life predictions. The effective strain-life curve showed that periodic overloads have a strong effect on fatigue life of case-hardened specimens. In service load history tests with plastic deformation, the fatigue damage caused by the small cycles in the load history is larger than the damage calculated from the standard strain-life curve. For periodic overload or variable amplitude service load history, the linear damage rule (LDR) resulted in reasonably good life predictions, while for high–low step loading tests the damage curve approach (DCA) resulted in better predictions.

Metal magnetic memory effect caused by static tension load in a case-hardened steel

For investigating the magnetic abnormality influenced by stress in ferromagnetic materials, static tension tests on a case-hardened steel were carried out. Different loads, which covered tensile elastic loads up to plastic deformation and break, were applied. Meanwhile, the normal component of magnetic flux leakage, H p( y), was measured by metal magnetic memory testing. The results indicate that H p( y) values change with the tensile loads and positions. There exists a relationship between k, which is the inclination of the linear amplitude-locus magnetic flux leakage curve, and static tension load. A simple model is derived. Additionally, the mechanism of the magnetic memory effect can be explained by the theory of the interaction between dislocations and domains. The research provides the potential possibility of quantitative inspection for metal magnetic memory testing.

Magnetic characterization of surface-hardened steel

Case depth measurements of surface-hardened steel parts are important for quality control. Here, the magnetic properties of two sets of carefully characterized 25-mm-diameter case-hardened steel rods were studied with the aim of developing new methods to evaluate the case depth nondestructively. Induction-hardened 4140 steel and carburized 8620 steel rods were studied. Each set contained control samples (heat-treated but not surface-hardened) and samples hardened to three different nominal depths. After fabrication, the microhardness profiles of the rods were measured and the data analyzed to obtain the mid-hardness depth in each case. These measurements were compared with optical micrographs that reveal the microstructure of the samples as a function of depth below the surface. By the analysis of measured magnetization curves and hysteresis loops, the differential permeability and saturation magnetization of the rods were extracted. It was found that differential permeability increases with increasing case depth at a certain strength of the applied field (1350–1450 A/m) for both hardening mechanisms, but only significantly for induction-hardened rods. Saturation magnetization M s was evaluated using the ‘law of approach’ and was observed to decrease as the depth of case hardening increases, for both induction-hardened and carburized steel rods. The observed behavior is described adequately by a simple model in which M s for the rod is represented as a volume-weighted sum of saturation magnetization values in the core and in the surface layer.

Characterisation of case-hardened gear steel by multiparameter Barkhausen noise measurements

Renewable energy sources have become nowadays very popular. Wind energy is one of the most promising renewable energy sources of the future. Due to the booming energy markets and increasing production of wind turbines, the requirement for long-lasting and reliably working windmills has emerged. The Barkhausen noise (BN) method is a world-leading technique in the quality control of industrial grinding processes, for example in windmill gear production. The main goal for this study is to create a profound approach to the multiparameter Barkhausen noise measured and to compare the measured values to the absolute values obtained with other research methods such as residual stress measurements by X-ray diffraction, hardness measurements and microstructural studies. A test bar series was made from a case-hardened steel used in wind turbine gears. Different tempering parameters were used to vary the surface hardness of the test bars. A stepwise loading was done simultaneously with the BN measurements to obtain relevant multiparameter BN data and to investigate the effect of applied stress on the BN signal. The results indicate clearly that the response of the studied material is mainly consistent with the known BN relations, but there exist some unequal BN stress correlations in the tempered test bars.