1 30th European Conference on Acoustic Emission Testing & 7th International Conference on Acoustic Emission University of Granada, September Magneto-Acoustic Emission and Barkhausen Noise in A508 Class II Steel Miriam R. NEYRA ASTUDILLO 1, Nicolás NÚÑEZ 1, Isabel LÓPEZ PUMAREGA 1, Darío N. TORRES 1, José RUZZANTE 1,2,3. 1 National Atomic Energy Commission, Av. General Paz 1499, Buenos Aires, Argentina Phone: ; U.T.N., Delta Regional Faculty, National Technologic University, Buenos Aires, Argentina. 3 UNSAM, National University of San Martín, Buenos Aires, Argentina. Abstract When a slowly varying electromagnetic field (through a yoke) is applied on a ferromagnetic material, the motion of the magnetic domain walls is produced. This motion is collected by a pickup coil as a high frequency noise (50 khz khz), on the surface of the material. This is known as Barkhausen Noise (BN). At the same time, the wall domain motion generates elastic waves (very high frequency) recognized as Magneto-Acoustic Emission (MAE). MAE (100 khz - 2 MHz) can provide information of the bulk meanwhile BN is a surface and subsurface technique. Both methods of analysis are applied on a test piece made of A508 Class II Steel, similar to the steel used for pressure vessels. The MBN and MAE results are compared with the information obtained by conventional material characterization: optical, MEB, microscopy, etc. The anisotropy of the material was studied and compared with its material characteristics. Keywords: Barkhausen Noise, Magneto-Acoustic Emission, steel, material characterization. 1. Introduction In ferromagnetic materials, the hysteresis loop is not really a continuous process, if we look inside with a great magnification there are small steps. These discontinuous changes are due to the movement of magnetic domains walls and may be hear using a speaker. The last phenomenon is known as Magnetic Barkhausen Noise (MBN) . Another effect produced by the movement of magnetic domains walls is the Magneto-Acoustic Emission (MAE), also known as Acoustic Barkhausen Effect. These acoustic signals are generated by the sudden and discontinuous changes in magnetization, which involve localized deformations (magnetostriction, volume changes due to magnetization) . These signals are low amplitude and high frequency (50 khz to 1 MHz) and are produced by domain wall movements. Since magnetostriction cannot be produced by 180 domain wall movement, since there is no volume change (magnetization in opposite sense) there is no MAE produced. MBN and MAE are strongly affected by changes in material microstructure and by actual stresses. For these reasons MBN and MAE are techniques applied to nondestructive evaluation of material degradation [2-6]. The material here studied is generally used to construct pressure vessels. They can be the structural component in nuclear reactors, being the most important element considering safety concern. So it is very important to know its chemical composition, its production processes and its metallurgical conditions . In this paper, the microstructure of A508 class II steel block is analyzed through MBN and MAE techniques. Its hardness, electrical conductivity and MBN penetration depth are considered. The inclusions found in this steel are oxides, silicates, manganese sulfides and carbides. The sulfides are softer than the steel, so they can support more strain. On the contrary, the oxides present as inclusions are hard and they do not support strain. The inclusions presented as silicates have an intermediate behavior. Several inclusions were found and they were made visible using the Baumann imprint technique. This technique has the objective to show the locations of sulfide inclusions in the steel. They are on the steel structure as different chemical compounds: Fe sulfides, Mn sulfides (MnS), mix sulfides, etc. . In this paper the influence of soft nonmetallic MnS inclusions is considered in analyzing the strain of the alloy [10-12].
2 2. Experimental tests The metallurgical characterization of the steel block tested is described in the next sections. The chemical composition, metallographic analysis, hardness and results of the Baumann imprint technique are described. The material was analyzed using MBN and MAE techniques and their results were compared with metallurgical characterization Material The block studied is an A508 M Class II alloy obtained by rolling. Its size is 130 mm, 115 mm and 58.4 mm, long, wide, and thickness respectively. In figure 1, a photograph of the block is shown. The arrow indicates the rolling direction and its chemical composition is indicated in table I . The block was divided into 24 zones on different angles, each one in a largest angle (increment = 15 o ). The value 0 o was considered parallel to the rolling direction (white arrow in figure 1). Figure 1. Photograph of the block studied. Table I. Chemical composition (% weight), A508 M Class II C Si Mn P S Cr Mo Ni V Cu Figure 2. Details of Mn sulfide. Figure 3. Details of MnS and FeO x.
3 2.2. Metallographic Study The study with SEM (scanning electronic microscope) was made according to the ASTM E- 45, ASTM E-47 standards. The type, morphology, size, composition and orientation were found. The inclusions correspond to silicates, aluminates, MnS and FeO x. Figures 2 and 3 show the micrographics. It was analyzed with EDS (Energy Dispersive Spectrometry) technique in two areas. Results shown in figures 4 and 5 revealed the presence of Al, Fe, S and Mn. Figure 4. EDS spectrum Al precipitate base. Figure 5. Spectrum of MnS.
4 Baumann Imprint Technique With the objective to detect the sulphur segregation the Bauman imprint technique  was applied on all the surface of the block. It is shown in figure 6. The inclusions banded zone, MnS type, can be seen. Some ellipses were draw to highlight the principal directions. Figure 6. Sulfide macro-segregation; the black arrow shows the rolling direction Conductivity Measurements The conductivity ( ) was measured to estimate the MBN penetration. To measure it, a small sample was cut from the block. A known current (HP System Power Supply) was applied on the sample and its voltage was measured with a nanovoltmeter Keithley 2182A, then the conductivity was calculated. Five different currents values (10 A, 20 A, 30 A, 40 A and 50 A) were employed. The average value was = ( ) x10 6 S/m. The conductivity of the material was measured to estimate the skin depth of the magnetic effect (δ). The depth penetration of the MBN depends of the frequency of excitation on the yoke according to equation (1). The same expression is applicable to estimate the maximum depth, which is producing the MBN [14, 15]: 2 (1) f 0 r where µ o is the vacuum permeability; f the analysed frequency on the sensor coil; µ r the relative permeability of the steel; the conductivity; µ o = 4π 10-7 H/m; µ r = 206 ; = 1.64x10 6 S/m. Using the extreme values of the wideband MBN amplifier the corresponding skin depth were calculated. For: f 1 =1 khz δ 1 = 0.07 mm (2) f 2 = 200 khz δ 2 = 0.01 mm (3)
5 These values indicate that MBN is a surface and near surface analysis and they are similar with others found in the literature MBN and MAE Measurements The variable magnetic field was produced on the yoke located on the block surface. A variable voltage generated by a sine wave with a 10 Hz frequency and with 1.25 V amplitude produced by LeCroy Arbstudio 1102, then amplified up to 40 Vpp, was applied on the winding. The yoke was positioned on the block, moving it around a circle marked each 15 (angle measured from the rolling direction). In the middle of the yoke a sensor coil was also located on the block surface. The signal from this coil was then amplified with a bandwidth of 1 khz- 200 khz. To detect the MAE signals an AE resonant sensor (150 khz, PAC, R15I) with a preamplifier included (40 db) was positioned on the bottom surface of the block. The signal was 50 db amplified by an AE system developed at National Atomic Energy Commission. The excitation on the yoke (voltage and current), MBN and MAE signals were measured on a four channels digital oscilloscope (LeCroyWaver Runner 44MXi. The measurement configuration can be seen on figures 7 and 8. The signals were digitized with 1 Ms/s. The MBN and MAE were registered by their RMS (Root Mean Square) values. To take into account the shape of the signals, their statistic parameters Kurtosis (peakedness) and Skewness (asymmetry) were calculated. Figure 7. Complete measurement system scheme.
6 Exciting coil Sample MAE sensor Figure 8. Complete measurement system photograph. A total of 26 MBN and MAE digitized files were obtained at different angles with increment equal to 15 (see figure 1). Figure 9 shows an example of 4 MBN signals and the corresponding MAE signals. Both signals look different in waveforms and amplitudes. Figure 9. MBN and MAE signals, 0 angle. To estimate the error in the measurement processes, MBN and MAE values were repeated 10 times for 0, 45 and 90. Their mean standard deviations were 0.3 mv for MBN, and 3.4 mv for MAE. The RMS values, supplied by the oscilloscope, for MBN and MAE were represented in figure 10 on a polar graph. In figures 11 to 13, the mean statistical parameters, kurtosis and skewness were graphed on a polar system. The mean values were calculated taking into account the 4 signals of each screen of the oscilloscope as it is shown in figure 9.
7 Figure 10. Polar map of MBN (left) and MAE (right), RMS values. Figure 11. Polar map of mean value of MBN (left) and MAE (rigth). Figure 12. Polar map of the mean Skewness, MBN (left) and MAE (rigth).
8 Figure 13. Polar map of mean Kurtosis of MBN (left) and MAE (right). All these graphs for MBN and MAE showed some type of anisotropy at 30 o angle. 3. Discussion There are two types of inclusions: i) softer sulfides (SMn) deformed in lamination direction, and ii) harder silicates with oxides (Aluminum, Silica, Iron, etc.) which are more fragile than the previous, breaking during higher plastic deformation. The inclusions, sulfide, oxide, and nitride type, are formed during fabrication steel process, and they are unavoidable and it is impossible to eliminate them totally. The deformation mechanism of soft inclusions during the steel fabrication processes was widely discussed. The deformation of soft inclusions follows the deformation trend of the matrix . The imprint Baumann technique showed a distribution of Manganese sulfide inclusions in a preferential direction on the block surface (see the banded of figure 6). In figures 14 a) and b) the RMS values for MBN and MAE are overlapped with Baumann image. a b. Figure 14. Comparison between Baumann technique and RMS of a) MBN (left); b) MAE (right).
9 The symmetry axis of MBN polar graph coincides with the inclusion distribution direction, at The symmetry axes for MAE polar distribution is move up to 60 0, perhaps this is due to that MAE responds to the bulk emission of elastic waves. It is worth noting that MBN detects the changes of magnetic domain walls only near surface (see equations 2 and 3). 4. Conclusions The graph of mean values, skewness and kurtosis for MBN showed anisotropy around 30 o. The same behavior (for 60 o ) is seen for MAE, except for kurtosis. The symmetry axes of the statistic parameters (skewsness and kurtosis) for MBN are orientated as the inclusion distribution direction (30 o ). In the case of MAE the same behaviour was seen for near 80 o. It is clear that the MBN signals are originated at near surface and MAE is captured from the bulk, so this may explain their differences. At the polar graphs the orientation of the maximum values of MAE and MBN coincide in between, but with a 30 o rotation. MBN and MAE are sensible to the anisotropy of the banded inclusions segregation. Acknowledgements To National Agency for Scientific and Technological Promotion, ANPCyT, Argentina, PICT- CNPq : Emisión Acústica y Efecto Barkhausen. To Lic. Daniel Rodríguez, Micro and Nano Technology, National Atomic Energy Commission, Argentina. To Ricardo Montero, for the metallographic characterization, Materials Department, National Atomic Energy Commission, Argentina. To Eng. G. Anteri, for his rich comments, Materials Department, National Atomic Energy Commission, Argentina. References 1. D. Jiles, Introduction to Magnetism and Magnetic Materials, Chapman and Hall, K. Ono, Magneto-Acoustic, ISSN X, Actas Primer Encuentro del Grupo Latinoamericano de Emisión Acústica, E-GLEA 1, pp , 6-10 Septiembre, M. Shibata, K. Ono, Mae- New method for Nondestructive Stress Measurement, NDT International, vol. 5, pp , S. Roman, Maharshakk, G. Amir, Magnetomechanical Acoustic Emission: A Nondestructive Characterization Technique of Precipitation Hardened Steels, Journal Acoustic Emission, vol. 2, p. 64, D. O. Sullivan, M. Cotterell, S. Cassidy, D. A. Tanner, I Meszaros, Magneto-acoustic emission for the characterization of ferritic stainless steel microstructural state, Journal of Magnetism and Magnetic Materials, vol. 271, pp , A. Ruiz, R. Piotrkowski, M. I. López Pumarega, J. Ruzzante, "Ruido Magnético Barkhausen y Emisión Magneto Acústica para la caracterización de materiales ferromagnéticos", Materia, vol. 13, pp.12-22, abril, Beatriz Acosta Iborra, Desarrollo y Validación de una Nueva Técnica de Ensayo no Destructivo, Basada en el Potencial Termoeléctrico, Para el Conocimiento del Envejecimiento de los Aceros de Vasija de Reactores Nucleares, Tesis Doctoral, Universidad Politécnica de Madrid, Escuela Técnica Superior de Ingenieros Industriales, Bermudes Olivares, Maria Dolores, Practicas de Ciencias de Materiales, I.S.B.N: , Secretario de Publicaciones, Universidad de Murcia, pp 31-35, 1992.
10 9. M. A. Linaza, S. Martín, l. San Martín, J. L. Romero, J. M. Rodríguez Ibabe y J. J. Urcola, Influencia de las Inclusiones No Metálicas en la Tenacidad de Aceros de Media Alta Resistencia en la Zona De Transición, Anales de Mecánica de la Fractura, Vol II, pp , Chunhui Luo, Ulf Stahlberg, Deformation of Inclusion During Hot Rolling of Steels', Jounal of Materials Processing Technology, Vol 114, pp 87-97, R Rodriguez, J Toribio y F. J. Ayaso Defectos Microestructurales que Gobiernan la Fractura Anisótropa en Aceros Fuertemente Trefilados, Anales de Mecánica de la Fractura 26, Vol. 1, pp , F. Vodopivec, M. Gabrovsek, Relative Plasticity of Manganese Sulphide Inclusions in Steel, Met. Technol. 7, pp , Adrián A Ruiz, Ruido Barkhausen y Emisión Magneto Acústica: Desarrollo de un Sistema de Medición y Aplicación a la Caracterización Microestructural y al Estado de Tensiones, Master Tesis, Universidad Nacional de General San Martín, Comisión Nacional de Energía Atómica. Abril Jiles, D. C. Dynamics of Domain Magnetización and the Barkhausen Effect, Chezchoslovak, Journal of Physics, Vol. 50, No 8, pp , M. Isabel López Pumarega, Ruido Magnético Barkhausen y Emisión Magneto Acústica en probetas de aleación Fe-1 wt % Cu, VII Congreso Regional de Ensayos No Destructivo, CORENDE, Memorias del Congreso, ISBN: , Rosario, Santa Fe, Argentina, de Noviembre 2009.
Voice Coil Impedance as a Function of Frequency and Displacement Mark Dodd 1, Wolfgang Klippel, and Jack Oclee-Brown. 3 1 KEF Audio UK (Ltd),Maidstone,Kent,ME15 6QP United Kingdom. Mark.dodd@KEF.com Klippel
Properties of Electrons, their Interactions with Matter and Applications in Electron Microscopy By Frank Krumeich Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 817 AlN Thin Film Electroacoustic Devices BY GONZALO FUENTES IRIARTE ACTA UNIVERSITATIS UPSALIENSIS UPPSALA 2003
HALL EFFECT SENSING AND APPLICATION MICRO SWITCH Sensing and Control 7DEOHRI&RQWHQWV Chapter 1 Hall Effect Sensing Introduction... 1 Hall Effect Sensors... 1 Why use the Hall Effect... 2 Using this Manual...
Influence of Dissolved Hydrogen on Stress Corrosion Cracking Susceptibility of Nickel Based Weld Alloy 182 Luciana Iglésias Lourenço Lima, Mônica Maria de Abreu Mendonça Schvartzman, Marco Antônio Dutra
1 Linear Motor for Multi Car Elevators: Design and Position Measurement Cagri Gurbuz, Ender Kazan, Ahmet Onat and Sandor Markon Abstract Multi-car elevator is an emerging technology consisting of two or
NDT 2010 Conference Topics Session 2B (2) Novel Techniques Chairman Dr R A Smith 14.30 A new and novel inspection system for Titanium billets Authors - Harshad V. Patel, Xiaoming Jian, Simon Woods, Ian
Evaluation of In-Place Strength of Concrete By The Break-Off Method By Tarun Naik Ziad Salameh Amr Hassaballah Evaluation of In-Place Strength of Concrete By The Break-Off Method By Tarun R. Naik Associate
Primer XYZs of Oscilloscopes Analog Oscilloscope Delay Line Vert Amp Amp Display Trigger Horiz Amp Digital Storage Oscilloscope Amp A/D DeMux Acquisition µp Display Memory Memory Display Digital Phosphor
REMARKS ON SURFACE INTEGRITY OF ELECTRIC DISCHARGE MACHINED SURFACES: A STATE OF ART REVIEW Bülent EKMEKÇİ, email@example.com Karaelmas University, 67100, Zonguldak, Turkey Abdulkadir ERDEN, firstname.lastname@example.org
Nuclear Magnetic Resonance as a Tool for On-Line Catalytic Reaction Monitoring Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der Rheinisch-Westfälischen Technischen Hochschule Aachen
5 Matter Waves Chapter Outline 5.1 The Pilot Waves of de Broglie De Broglie s Explanation of Quantization in the Bohr Model 5.2 The Davisson Germer Experiment The Electron Microscope 5.3 Wave Groups and
How to Read MTF Curves by H. H. Nasse Carl Zeiss Camera Lens Division December 28 Preface The rules of optics are complex and nasty! This is a nice, honest sentence from an internet discussion about How
Michael Levin Metropolitan Computing Corporation, East Hanover, New Jersey, U.S.A. INTRODUCTION This article is designed to facilitate the understanding of the general principles of tablet press instrumentation
Institut für Theoretische Physik Fakultät Mathematik und Naturwissenschaften Technische Universität Dresden Spectroscopy of Discrete Breathers Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften
Magnetron Theory of Operation Theory of Operation A magnetron is a high power microwave oscillator in which the potential energy of an electron cloud near the cathode is converted into r.f. energy in a
ITU Department of Mechanical Engineering MANUFACTURING PROPERTIES of ENGINEERING MATERIALS Lecture Notes Prof.Dr.Ahmet Aran 2007 CONTENTS 1. Engineering Materials and Their Properties 1.1. Classification
The Free High School Science Texts: A Textbook for High School Students Studying Physics. FHSST Authors 1 December 9, 2005 1 See http://savannah.nongnu.org/projects/fhsst Copyright c 2003 Free High School
premio tesi di dottorato 37 PREMIO TESI DI DOTTORATO Commissione giudicatrice, anno 2012 Luigi Lotti, Facoltà di Scienze Politiche (Presidente della Commissione) Fortunato Tito Arecchi, Facoltà di Scienze
TAGUCHI APPROACH TO DESIGN OPTIMIZATION FOR QUALITY AND COST: AN OVERVIEW Resit Unal Edwin B. Dean INTRODUCTION Calibrations to existing cost of doing business in space indicate that to establish human
The 10 th International Conference of the Slovenian Society for Non-Destructive Testing»Application of Contemporary Non-Destructive Testing in Engineering«September 1-3, 2009, Ljubljana, Slovenia, 415-421
Measuring Rev. Adv. Mater. and analyzing Sci. 29 (2011) leakage 31-53 current for outdoor insulators and specimens 31 MEASURING AND ANALYZING LEAKAGE CURRENT FOR OUTDOOR INSULATORS AND SPECIMENS Dionisios
IEEE TRANSACTIONS ON MEDICAL IMAGING, VOL. 29, NO. 12, DECEMBER 2010 1959 Coupled Nonparametric Shape and Moment-Based Intershape Pose Priors for Multiple Basal Ganglia Structure Segmentation Mustafa Gökhan