A multi-physical finite element model for the induction hardening of a 50CrMo4 steel rod was implemented in Abaqus, including an electromagnetic, thermal, mechanical, and metallurgical model describing the individual phenomena taking place during the process. For induction heating, a linearization scheme for the nonlinear permeability of steel was implemented. The model was validated by recreating a previously published experiment with the model and using the calculated residual stress data as a comparison to the measured stresses. To ensure a valid comparison, the sample preparation process and measurement methodology were considered for the simulation and a good agreement between the measured and calculated stress distributions was obtained. Thus the distribution and time evolution of several quantities such as temperature, phase fractions and plastic strain can be examined to gain insight into the formation of residual stresses.

Surface hardening is commonly used to modify mechanical properties of crankshaft bearings. In this work, residual stress and hardness distributions across the crankshaft bearings cross-sections are evaluated using synchrotron high-energy X-ray diffraction and hardness testing. It is shown that the measured hardening depth correlates with a point of sudden sharp reversal of the stress gradient from compressive to tensile. This point is linked to the microstructure and does not shift with subsequent tempering or trimming of the sample. The superimposed data is used to interpret the evolution of stresses during the quenching and tempering cycle and gain understanding of the hardening process for such complex geometries. Within the hardened zone retained austenite is found to increase with depth to over 15 %, which is attributed to reduced quenching effects as the material is further away from the surface. All measured properties agree in the determined hardening depth of 3.5 mm to 4.5 mm, which in turn fits well with optical evaluation of metallographic microsections.

This work investigates the in-depth residual stress distribution and retained austenite content in plates that were wire eroded from one locally quenched and one locally quenched-tempered 50CrMo4 cylinders by the means of high-energy X-Ray synchrotron transmission techniques. The main challenge was to interpret the results from all diffraction angles to obtain meaningful validation data for future computer simulations of induction hardening and tempering. The results were discussed in relation to hardness distribution. With the help of the applied measurement technique, even the effects of macro-segregation near the longitudinal sample axis can be detected. In inductively heated and quenched cylindrical specimens of 50CrMo4 specimens, macro-segregations near the longitudinal sample axis lead to a reduced retained austenite content, which shifts the axial stresses towards tensile stresses. Comparing the results with those from the literature, it can be seen that variations in the chemical composition of the sample within the specification range of the steel grade have less influence on the residual stress distribution in the induction hardened samples than the sample geometry and/or the quenching rate.

Surface heat treatment and quenching are commonly used to modify mechanical properties of crankshaft bearings. In this work, hardness and residual stress distributions across the crankshaft bearings cross-sections are evaluated using hardness testing and synchrotron high-energy X-ray diffraction. It is shown that the measured hardening depth correlates with a point of sudden sharp reversal of the stress gradient from compressive to tensile. This point is also connected to the microstructure and does not shift with subsequent heat treatment or trimming of the sample. The superimposed data is used to interpret the evolution of stresses during the quenching and tempering cycle and gain understanding of the hardening process for such complex geometries. In further research, superimposed datasets of diverse properties can be used to validate finite element analyses of the heat treatment process, particularly where material models build upon one another and any errors are cumulative.

This work describes an indirect determination method for magnetic flux density-field strength. (B-H) hysteresis measurement. Several electromagnetic measurement methods determining and analysing specific material properties are already established, but these are meant for laboratory measurements using small samples having only limited application possibilities. Such methods are the vibrating sample magnetometer, ring sample method, Epstein frame and other indirect methods, which are until now under continuous development. In the present work, a combination of the mentioned measurement setups based on a yoke setup was designed to measure magnetic behaviour of industrial samples in an indirect measurement setup having a wide range of application possibilities. This was realised using various corrections and a reluctance model for the magnetic circuit. Using a min. 70 vol-% pure iron particle filled flux conducting paste at the contact positions, the H-field loss called demagnetisation and caused by stray fields became insignificant. Interestingly, finite element model and experimental estimation result in about half of demagnetisation of the setup as the validation indicated. For validation purposes, a comparison with the results of a direct electromagnetic measurement method was established. Using the adjusted demagnetisation, the results were reasonably in line with the validation.

This work investigates the effect of different initial microstructures on the electromagnetic magnetisation curves/hysteresis of 50CrMo4 steel and technically pure iron introducing a novel measurement method. Surprisingly little is known about the relationship between microstructure and the magnetic properties, although this is of great importance for a better understanding and multi-physics modelling of induction heat treatment. Analysis of the magnetic hysteresis and Distortion Analysis of Magnetic Excitation (DAME) are important techniques to characterise magnetic behaviour of materials. To perform these measurements, a specific measurement setup based on excitation circuit/yoke with secondary coils was implemented. Using these methods, the characterization of the effect of mechanical properties (i.e.: hardness) and different microstructures on electromagnetic magnetisation curves/hysteresis is possible with high precision. The effect of the eddy-currents on the B-H hysteresis shows a systematic behaviour, which opens the possibility for a new kind of categorisation of these effects. DAME shows a closely linear relationship with the assumed precipitation size allowing indirect analysis of the microstructure, also at elevated temperatures.

Process control in surface hardening depends greatly on the repeatability of the results. Induction heating facilities stand out in this aspect but challenges arise when it comes to the verification of the expected temperatures. In-situ temperature measurement of a workpiece may be made impossible due to it moving through an enclosed, automated induction facility that lacks built-in sensors. This paper uses transition patterns in the microstructure of the hardened region to reconstruct isothermal contour lines of the temperature field during austenitisation. It does so based on a continuous cooling transformation phase diagram and a time-temperature-austenitisation diagram of the considered steel. The presented method serves as a practical approach to validate simulations of the inductive austenitising process and supports simulations of the heat treatment of the work piece. Once these simulations have been iterated upon and validated thoroughly, they may then yield a reconstruction of the entire temperature field during the heat treatment process.

Abstract This paper deals with a methodology for a characterisation of inductive heat treatment plants to allow comparison of their practical electromagnetic behaviour with conventional simplifying assumptions used in simulations of the heating process. The impact non-sinusoidal currents and non-linear B-H curves on the simulation are specifically dealt with here. A Rogowski coil and digital oscilloscope are used to read in current signals in various induction plants and compare their total harmonic distortion (THD). In the course of parameter studies, the different current signals were used in simulations of induction to compare heating effects. This yielded positive correlations with the THDs.

Induction heat treatment facilities have a wide application range for heat treatment of cylindrically shaped materials in the steel processing industry due to their reduced process-time and high throughput. The adjustment of the heat treatment process usually aims at reaching a desired hardness. However, the question arises whether the full potential of the applied material is actually exploited. Therefore, this work systematically investigates the influence of the primary microstructure, austenitisation and tempering conditions to the resulting notch impact energy and flow behaviour of a 50CrMo4 quenched and tempered steel, with normalised and soft-annealed prior microstructures. The heat treatments, performed with a laboratory induction heat treatment facility, show that low austenitising temperatures lead to a distinct yield point with reduced strain hardening, while increasing the tempering heating rate results in the precipitation of smaller carbides and a significant increase in tensile strength. Austenitising needs to be adjusted to the primary microstructure to reach an optimum solution state to exploit the hardness and notch impact energy potential.

Objective. Strength is one of the preferred parameters used in dentistry for determining clinical indication of dental restoratives. However, small dimensions of CAD/CAM blocks limit reliable measurements with standardized uniaxial bending tests. The objective of this study was to introduce the ball-on-three-ball (B3B) biaxial strength test for dental for small CAD/CAM block in the context of the size effect on strength predicted by the Weibull theory.Methods. Eight representative chairside CAD/CAM materials ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Specimens were prepared with highly polished surfaces in rectangular plate (12 x 12 x 1.2 mm(3)) or round disc (empty set = 12 mm, thickness = 1.2 mm) geometries. Specimens were tested using the B3B assembly and the biaxial strength was determined using calculations derived from finite element analyses of the respective stress fields. Size effects on strength were determined based on results from 4-point-bending specimens.Results. A good agreement was found between the biaxial strength results for the different geometries (plates vs. discs) using the B3B test. Strength values ranged from 110.9 MPa (Vitablocs Mark II) to 1303.21 MPa (e.max ZirCAD). The strength dependency on specimen size was demonstrated through the calculated effective volume/surface.Significance. The B3B test has shown to be a reliable and simple method for determining the biaxial strength restorative materials supplied as small CAD/CAM blocks. A flexible solution was made available for the B3B test in the rectangular plate geometry. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

OBJECTIVE:Strength is one of the preferred parameters used in dentistry for determining clinical indication of dental restoratives. However, small dimensions of CAD/CAM blocks limit reliable measurements with standardized uniaxial bending tests. The objective of this study was to introduce the ball-on-three-ball (B3B) biaxial strength test for dental for small CAD/CAM block in the context of the size effect on strength predicted by the Weibull theory. METHODS:Eight representative chairside CAD/CAM materials ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Specimens were prepared with highly polished surfaces in rectangular plate (12×12×1.2mm3) or round disc (Ø=12mm, thickness=1.2mm) geometries. Specimens were tested using the B3B assembly and the biaxial strength was determined using calculations derived from finite element analyses of the respective stress fields. Size effects on strength were determined based on results from 4-point-bending specimens. RESULTS:A good agreement was found between the biaxial strength results for the different geometries (plates vs. discs) using the B3B test. Strength values ranged from 110.9MPa (Vitablocs Mark II) to 1303.21MPa (e.max ZirCAD). The strength dependency on specimen size was demonstrated through the calculated effective volume/surface. SIGNIFICANCE:The B3B test has shown to be a reliable and simple method for determining the biaxial strength restorative materials supplied as small CAD/CAM blocks. A flexible solution was made available for the B3B test in the rectangular plate geometry.