Investigation of the Variations in Microstructure and Mechanical Properties of Dual-Matrix Ductile Iron by Magnetic Barkhausen Noise Analysis

The variations in the microstructure and tensile properties of dual-matrix ductile irons have been investigated non-destructively by Magnetic Barkhausen Noise (MBN) method. Specimens have been intercritically austenitised at 795°C and 815°C for 20 minutes, and then oil-quenched to obtain different martensite volume fractions. Two specimens, namely as-cast and oil-quenched from 900°C, were prepared for comparison purpose. To investigate the effect of tempering, some specimens were tempered at 500°C for 1 h and 3 h. The results showed that there is a good correlation between MBN response and variations in microstructure and mechanical properties. The volume fraction of martensite can be controlled to modify the mechanical properties, and all changes in the microstructure can be nondestructively monitored by MBN.     

Characterization of Austempered Ductile Iron Through Barkhausen Noise Measurements

The outstanding mechanical properties of austempered ductile irons (ADI) are linked to the microstructure of the matrix obtained by subjecting a ductile iron with an appropriate composition to a heat treatment called austempering. Then the microstructure of the matrix consists of bainitic ferrite with different volume fractions of retained austenite. The aim of this work is to use the magnetic Barkhausen noise (MBN) as a nondestructive method for characterizing the microstructure of ADI. First, it is shown that the amplitude and position of the peak-shaped MBN response is quite sensitive to the microstructure of the matrix of ductile irons. Thus each type of constituent (equiaxial ferrite, pearlite, martensite or bainite) exhibits a typical response and, in turn, it can be identified from the MBN response. Furthermore, a good correlation is found between MBN signal parameters and ADI heat treatment parameters, indicating that MBN is also quite sensitive to fine evolutions of the microstructure of ADI. MBN peak position is especially sensitive to the type of bainite, whereas peak amplitude is linked to the progress of the bainite reaction. Hence MBN measurements appear to be a powerful tool to assess some important microstructural features of ADI castings.     

Characterization of Dual-Phase Steels Using Magnetic Barkhausen Noise Technique

The aim of this work is to nondestructively characterize the dual phase steels using the Magnetic Barkhausen Noise (MBN) method. By quenching of AISI 8620 steel specimens having two different starting microstructures, from various intercritical annealing temperatures (ICAT) in the ferrite-austenite region, the microstructures consisting of different volume fractions of martensite with morphological variations have been obtained. The microstructures were first conventionally characterized by metallographical investigations and hardness tests. Then, the MBN measurements were performed using a μSCAN commercial system. Good correlations between the martensite volume fraction, hardness and MBN emission have been obtained. MBN signal height clearly decreased as the ICAT, therefore the volume fraction of martensite increased. The effect of the initial microstructure prior to intercritical annealing has also been differentiated by the MBN measurements. It has been concluded that MBN method can be used as a useful tool for nondestructive characterization of dual phase steels.     

Monitoring the Microstructural Changes During Tempering of Quenched SAE 5140 steel by Magnetic Barkhausen Noise

The aim of this work is to characterize the microstructures of quenched and tempered steels non-destructively by a diverse set of parameters of the Magnetic Barkhausen Noise method (MBN fingerprint, frequency spectra, pulse height distribution, root-mean-square, and total number of pulses). Identical specimens from a SAE 5140 steel bar were prepared. All specimens were austenitized at 860°C for 30 minutes and water-quenched identically. The quenched specimens were then tempered at various temperatures between 200°C and 600°C. The microstructures were characterized by metallographic examinations and hardness measurements. Pulse height distributions, noise signal envelopes and frequency spectra were used to evaluate Barkhausen activity. The results show that as the tempering temperature increases, the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. An excellent correlation was found between Barkhausen parameters and hardness values.     

Comparison of magnetic Barkhausen noise and ultrasonic velocity measurements for microstructure evaluation of SAE 1040 and SAE 4140 steels

The aim of this study is to compare the performance of magnetic Barkhausen noise and ultrasonic methods for the evaluation of the microstructure of commercial steels. Following the austenitization of the specimens made of SAE 1040 and SAE 4140, various heat treatments were carried out to obtain microstructures consisting of martensite, tempered martensite, fine pearlite–ferrite, and coarse pearlite–ferrite. The microstructures were initially characterized by SEM investigation and hardness measurements. The magnitude and position of Barkhausen noise peaks were determined via a commercial system. The propagation rates of longitudinal waves were determined with the ultrasonic pulse-echo technique. Barkhausen noise response and sound velocity goes to minimum for the as-quenched martensite, and both tend to increase in the following sequence: tempered martensite, fine pearlite–ferrite, and coarse pearlite–ferrite. However, the magnetic features are more sensitive to the microstructure variations than to the sound velocity.     

基于巴克豪森效应的无损检测技术应用现状

基于巴克豪森效应的无损检测技术可用于应力、硬度、晶粒度、磨削烧伤等的检测,因其具有快速、无损、定量等优点而受到关注。综述了巴克豪森效应国内外研究现状。围绕基于巴克豪森效应的无损检测技术,介绍了其在应力、硬度、晶粒度、磨削烧伤检测上的应用情况,并给出了应力、应变、硬度、晶粒度及磨削烧伤与磁巴克豪森噪声信号之间的关系。简述了MBN传感器设计要点。     

Magneto-mechanical properties evolution of Fe–C alloy during precipitation process

Evolution of magneto-mechanical properties of 160 ppm Fe–C alloy due to carbides precipitation during isothermal annealing at 473 K (up to t=50×10³ s) was studied by means of classical Barkhausen noise (HBN) and mechanical Barkhausen noise (MBN) effects. The MBN was measured for the torsion mode of load with a torque motor. Also the B(H) hysteresis loop and the coercive field H_c were evaluated using a low-frequency magnetisation set. Magnetic hysteresis losses ΔW₁ were compared with the integral ΔW₂ of HBN intensity over one period of magnetisation and the integral ΔW₃ of MBN intensity over one period of the mechanical load. The internal stress distribution function and the resulting mean level of internal stress parameter σ_i were evaluated from the MBN ‘first load’ data. It was revealed that a correlated increase of ΔW₁ and ΔW₂ parameters exists. However, the relative increase of ΔW₃ is much lower than the relative increase of ΔW₁. The relationship between H_c and σ_i was found to be parabolic. This dependence explained by Néel’s model of the impact of the residual stress level on H_c. The presence of precipitates of type was confirmed by scanning electron microscopy.     

Isothermal aging effect on the microstructure and dry sliding wear behavior of Co–28Cr–5Mo–0.3C alloy

In this study, an attempt to investigate the role of isothermal aging on the microstructure and dry sliding wear behavior of Co–28Cr–5Mo–0.3C alloy was made. Regarding the results, it is clear that isothermal aging at 850 °C for 8 and 16 h contributed to the formation of lamellar type carbides (γ-fcc + M₂₃C₆) at the grain boundary regions. Moreover, at higher aging times (24 h), the lamellar type carbides decreased whereas severe precipitation of carbides was found to occur on the stacking faults. Furthermore, according to X-ray diffraction results, 24 h isothermal aging of solution treated specimens did not lead to complete fcc → hcp transformation. The wear properties of as-cast and heat treated samples were determined at 0.5 ms⁻¹ speed several under normal applied loads such as 50, 80, and 110 N. At the lowest load applied (50 N), isothermally aged specimens for 8 and 16 h have higher wear resistance probably due to more volume fraction of lamellar-type carbides when compared to as-cast for both 4 and 24 h aged specimens. But, at higher applied loads (80 and 110 N) due to the formation of adhesive oxide layer on the as-cast specimen surface, the wear rate of as-cast samples is lower compared with all heat treated specimens.     

Magnetic Barkhausen Noise, Metal Magnetic Memory Testing and Estimation of the Ship Plate Welded Structure Stress

Using the Magnetic Barkhausen Noise (MBN) technique in combination with the Metal Magnetic Memory (MMM) technique, the stress in a welded steel ship plate was investigated. As part of this, the three dimensional image of the self-leakage magnetic field was obtained. In addition, MBN measurements were made in the same test area. The stress distribution, as deduced from the MBN measurements was found to correspond well with the MMM self-leakage image. As a consequence of this positive result, a new testing procedure using the combined MBN and MMM technique is proposed. First, the region with high residual stress is located rapidly using the MMM technique. Then, the actual level of residual stress is determined using the MBN technique, based on prior calibration using specimens made from the same material. This method combining with the X-ray testing method, the damage degree of the ship welded structure which suffered the navigation vibration and environment impact and so on is comprehensively estimated. This test method can not only reduce the workload of the non-destructive testing, but also improve the accuracy of the stress testing.     

Influence of magnetizing parameters on the magnetic Barkhausennoise

Magnetic Barkhausen noise (MBN) measurements were made on a sample of pipeline steel as functions of magnetizing frequency and AC flux density in the sample. The observed MBN responses suggest a strong dependence on these magnetizing parameters. With increasing flux density in the sample, the MBN activity initially increases but finally begins to decrease at higher magnitudes of flux density. The MBN activity also increases with increasing magnetizing frequency. Pulse-height distribution analysis of the MBN waveforms suggests that the dependence of MBN activity on these magnetization parameters is more complex than appears from the rms voltage measurements     

Quantitative Prediction of Surface Hardness in 12CrMoV Steel Plate Based on Magnetic Barkhausen Noise and Tangential Magnetic Field Measurements

Both magnetic Barkhausen noise (MBN) and tangential magnetic field (TMF) strength can be applied in the quantitative prediction of surface hardness of ferromagnetic specimens. The prediction accuracy depends on the selected model and the input parameters of the model. In this study, the relationship between the surface hardness of 12CrMoV steel plate and the measured MBN and TMF signals is investigated with multivariable linear regression (MLR) model and BP neural network technique. A comparative study between the MLR and BP model is conducted. The external validation results show that the BP model utilizing four MBN features as the input nodes has a smaller average prediction error (3.7%) than that of the MLR model (13.2%). Features extracted from the MBN and TMF signals are combined together as the input parameters of the BP model in order to achieve high accuracy. After adding two more TMF features into the input nodes of the BP network, the external validation results suggest that the average prediction error is decreased from 3.7 to 3.5%.     

Applicability of the Magnetic Barkhausen Noise Method for Nondestructive Measurement of Residual Stresses in the Carburized and Tempered 19CrNi5H Steels

There exist no materials and/or structures of technical importance without residual stresses. The residual stress management concept has gained importance in industrial applications aiming to improve service performance and useful life of the product. Thus, the industry requests rapid, reliable, and nondestructive methods to determine residual stress state. The aim of this article is to investigate the applicability of the Magnetic Barkhausen Noise (MBN) method to measurement of surface residual stresses in the carburized steels. To comprehend the differences in the surface residual stress state, 19CrNi5H steel samples were carburized at 900°C for 8 and 13 hours, and then, tempered in the range of 180°C and 600°C. The MBN measurement results were correlated with those obtained by the X-ray diffraction (XRD) measurements. Microstructural investigations and hardness measurements were also conducted. For this particular study, it was concluded that both techniques give similar qualitative results for monitoring of the residual stress variations in the carburized and tempered steels. Since the MBN method is much faster than the XRD method, from the industrial point of view it is a very strong candidate for qualitative monitoring of residual stress variations. With an appropriate pre-calibration by considering the effect of microstructure, the MBN method may give reliable quantitative results for residual stress.     

The effect of microstructure and applied stress on magnetic Barkhausen emission in induction hardened steel

The influence of elastic deformation on the emission of magnetic Barkhausen noise (MBN) was investigated for induction-hardened low alloy steel with two different treatments: a standard temper (ST) and an over temper (OT) heat treatment. The rectified MBN profiles were found to be reversible with respect to loading and unloading, i.e., a profile that was changed by application of stress was recovered when the stress was removed. Characteristics of the profiles (peak height V _p, peak position I _p and half-width W _p) were recorded as a function of applied stressσ. Plots of V _p versus σ were S-shaped, with V _p reaching a maximum on the tensile side of the graph and a minimum on the compression side. In a more restricted stress range, between −500 and 1,000 MPa, V _p was an approximately a linear function of σ. The OT specimens showed greater sensitivity to stress than the ST specimens. Another difference was that the OT specimens produced an MBN profile with two overlapping peaks when under compression. The other profile characteristics showed a relationship with stress that ran counter to that of V _p, i.e., where V _p increased with increasing stress, I _p and W _p decreased. The observations are discussed in the light of established models of Barkhausen noise.     

Induction Hardened Layer Characterization and Grinding Burn Detection by Magnetic Barkhausen Noise Analysis

The quality of the ball screw shafts used in the aeronautical sector has to be controlled and certified with the most advanced non-destructive techniques. The capacity of magnetic Barkhausen noise (MBN) as a non-destructive technique to control the quality of ball screw shafts by assuring the appropriate induction hardened layer depth and detecting local overheated regions, known as grinding burns, which may occur during grinding processes is shown in the present work. Magnetic Barkhausen noise measurements were made with a system designed and implemented by the authors and the derived parameters were compared with microhardness measurements made at various depths after the different induction hardening treatments and the grinding processes were applied. A multiparametric study of the MBN signal as a function of the magnetic field in the surface of the sample is done in order to estimate the thickness of the hardened layer and to detect the grinding burns produced during grinding processes. The hardened layer thickness can be characterized with an error of ±200 \(\upmu \)m in the range between 150 and 2500 \(\upmu \)m by the position of the first peak of the MBN envelope in terms of the tangential magnetic field measured at the surface and the grinding burns can be detected with the position of the second peak of the MBN envelope in terms of the tangential magnetic field measured at the surface.     

Magnetization Rate Dependence of the Barkhausen Noise in JRQ Steels

The magnetic Barkhausen noise (MBN) in JRQ reference steel was measured under varying magnetization rate. The scaling properties of the avalanche size distribution were determined experimentally as a function of the excitation frequency. We have found that the exponent decreases and the scaling region extends as the excitation frequency increases in accordance with theoretical expectations. The average avalanche energy, size, and frequency were found to have power law dependence on the excitation rate. The temporal analysis has shown that the MBN noise generation starts earlier and develops a more symmetric character with the increase of the excitation frequency. These changes with the excitation rate can not be accounted for only by the overlap of individual MBN avalanches, but reveal a change of the dynamics of the MBN process.      

Evaluation of thermal recovery of neutron-irradiated SA508-3 steel using magnetic property measurements

The Vickers microhardness and magnetic properties have been used to investigate irradiation effects and thermal recovery characteristics of neutron-irradiated SA508-3 reactor pressure vessel steel specimens irradiated to a neutron fluence of 5.5×1017 n cm-2 (E>1 MeV) at 70°C. Two recovery stages were identified from the hardness results during isochronal annealing and the mechanism responsible for the two stages was explained using the results of Barkhausen noise on the basis of the interaction between radiation-induced defects and the magnetic domain wall. The neutron irradiation caused the coercivity to decrease, whereas the maximum magnetic induction increased. Barkhausen noise parameters associated with the domain-wall motion were decreased by neutron irradiation and recovered with subsequent heat treatments. From the sensitive changes in the Barkhausen noise upon annealing heat treatment, it is suggested that the Barkhausen noise measurements may be used as a useful tool for monitoring the early stage of the thermal recovery behaviour of neutron-irradiated reactor pressure vessel steels. This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of Lüders bands on magnetic Barkhausen noise and magnetic flux leakage signals

Lüders bands, which occur during the onset of tensile plastic strain in most steels, are localized regions of high plastic strain within a specimen, bounded by regions that have undergone mainly elastic deformation. This study was conducted to understand the dependence of magnetic Barkhausen noise (MBN) and magnetic flux leakage (MFL) signals on Lüders banding in mild steel. MBN and MFL measurements were made on tensile samples of hot-rolled mild steel, in which Lüders bands were deliberately nucleated by applying tensile stress. The results indicate that the MBN activity increases in the region of Lüders bands. A strong magnetic anisotropy was also observed on these bands with the generation of dual magnetic easy axis. The MFL results indicate that magnetic flux leaks out into the air from regions with Lüders bands due to decreasing permeability in these regions owing to localized plastic deformation.     

Influence of high-pressure torsion and hot rolling on the microstructure and mechanical properties of aluminum–fullerene composites

In this study, we investigate the impacts of working process, high-pressure torsion (HPT) and hot rolling (HR) on the microstructure and mechanical performance of aluminum-based nanocomposites containing fullerenes. HPT caused severe plastic deformations that generate numerous dislocations and lattice strains, and this stimulated the formation of aluminum carbides (Al₄C₃) and reduced the hardness during heat treatment. In contrast, the HRed specimens experienced dynamic recovery, and their initial dislocation densities and lattice strains were lower than those of the HPTed specimens. Thus, the HRed composites formed supersaturated aluminum phases as well as aluminum carbides during the heat treatment. The supersaturated phases provided high-density dislocations and severe lattice strains, resulting in an increase in the hardness during the heat treatment. This comparison suggests that the mechanical properties of aluminum–fullerene composites can be controlled by working processes in practical situations.     

Surface decarburisation of steel detected by magnetic barkhausen emission

The effect of decarburisation of the surface layer on magnetic Barkhausen noise (MBN) emission was investigated in quenched and tempered steel containing 0.67% carbon. The MBN profile of intensity versus energising current from the un-decarburised material showed a single peak typifying the martensite structure. After decarburisation, a profile with a double peak was obtained. The presence of the decarburised layer produced a second, overlapping peak at a lower field value. The height of the second peak increased with increasing depth of decarburisation and its position moved to increasingly lower field values.     

Rejuvenation heat treatment’s influence on the microstructure and properties of superalloys

Rejuvenation heat treatment is an important technology to restore damaged microstructure and properties of superalloys. This investigation is conducted to figure out the effect of rejuvenation heat treatment on the superalloys. The microstructure and micro-hardness of K002 and DZ125 superalloys after different heat treatment procedures were evaluated. The results show that the heating temperature mainly affects the solubility of the carbides and γ′ phases, while the cooling rate has an effect on the morphology of secondary γ′ phase. Owing to the transition of carbides during the work process, rejuvenation heat treatment temperature has little effect on the amount of carbides in damaged alloys. Suggestions for rejuvenation heat treatment are proposed.