Na atualidade, o estudo da transformação martensítica é de grande importância na área acadêmica e tecnológica, devido à aplicação de aços e ferros fundidos com estruturas martensíticas. O estudo dos fenômenos da transformação martensítica envolve vários pesquisadores no mundo e é objeto de eventos como o ICOMAT e ESOMAT. O presente trabalho acompanhou a transformação martensítica por meio de técnicas experimentais a temperaturas sub-zero em um aço AISI D2 e uma liga Fe-Ni-C previamente austenitizadas. A literatura indica que o tratamento a temperaturas sub-zero pode melhorar propriedades dos aços temperados e revenidos. Foi explorado o uso dos métodos de ruído magnético de Barkhausen (MBN), para detectar a transformação de fase da austenita para a martensita durante o resfriamento sub-zero das amostras, usando três diferentes configurações: a emissão de ruído Barkhausen convencional estimulada por um campo magnético alternado; o método de Okamura que é a emissão de ruído magnético medido embaixo de um campo fixo (DC); e uma nova técnica experimental, que mede a emissão magnética espontânea durante a transformação na ausência de qualquer campo externo. Os fenômenos associados com a transformação de fase também foram medidos por resistividade elétrica e as amostras resultantes foram caracterizadas por microscopia óptica e eletrônica de varredura. Medições MBN no aço ferramenta AISI D2, austenitizadas a 1473K (1200C) e resfriadas a temperatura de nitrogênio líquido apresentaram uma mudança próximo de 225K (-48C) durante o resfriamento, que corresponde à temperatura Ms, como foi confirmado por medidas de resistividade. As medições da emissão de ruído magnético espontâneo, realizadas in situ durante o resfriamento da amostra imersa em nitrogênio líquido, mostraram que poderia ser detectado um fenômeno de estouro individual (burst), de forma similar às medições de emissão acústica (AE), o qual foi confirmado com a liga Fe-Ni-C. Este método de caracterização Spontaneous Magnetic Emission (SME) pode ser considerado uma nova ferramenta experimental para o estudo de transformações martensiticas em ligas ferrosas. Foi acompanhado o inicio da transformação martensítica por SME, em função do tamanho de grão, já que é conhecido pela literatura que o inicio da transformação martensítica (Ms), muda com a variação do tamanho de grão. / Martensitic transformations are of special interest both as an academic topic and as a technological issue, due to importance of steels and cast irons with martensitic structures. Studies of martensite transformation phenomena involve researchers all over the world and specific conferences and meetings, as ICOMAT and ESOMAT. The present work followed the martensitic transformation using different experimental techniques, during cooling at cryogenic temperatures samples of a AISI D2 cold work tool steel and also a Fe-Ni-C, previously austenitized. There are plenty of references in the literature suggesting that sub-zero cooling treatments could ameliorate the properties of quenched and tempered steels. The Magnetic Barkhausen Noise (MBN) method was applied during cooling to subzero temperatures of austenitic samples of a AISI D2 cold work tool steels (previously quenched from 1200ºC) and to a Invar-type Fe-Ni-C alloy. MBN is a non-destructive technique based on the detection of the signal generated when ferromagnetic materials are subjected to an oscillating external magnetic field. In order to study the austenite to martensite transformation, three different configurations were tested: conventional Barkhausen using an oscillating magnetic field, a method proposed by Okamura, which uses a fixed magnetic field and a new method that detects spontaneous magnetic emissions (SME) on the absence of any applied magnetic field. Other phenomena associated with the transformation were followed using electrical resistivity measurements, optical microscopy and X-ray diffraction. MBN measurements on a cold work tool steel AISI D2, austenitized at 1473K (1200ºC) and quenched to room temperature, made during further cooling to liquid nitrogen temperature, presented a clear change of signal intensity near 225K (-48ºC), corresponding to Ms temperature, as confirmed by resistivity measurements. The SME in situ measurements during cooling of samples in liquid nitrogen were able to detect single burst (landslide nucleation and growth) phenomena, in a manner similar to the Acoustic Emission (AE) measurements; these results have been confirmed also with measurements on a Fe-Ni-C alloy. The new Spontaneous Magnetic Emission (SME) characterization method can be considered a new experimental tool for the study of martensitic transformations in ferrous alloys. The beginning temperature for the martensitic transformation detected using SME, electric resistivity and MBN were compared with estimates using the Andrews empirical equation (linear, 1965) for the Ms temperature. The effect of the austenite grain size on the beginning of the martensitic transformation was studied using SME, as it is known that the Ms temperature depends on the austenite grain size.

The aim of this work is to nondestructively characterize the industrial dual phase (ferritic-martensitic) steels (DPS) by 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 and morphology have been obtained. The microstructures, strength properties and hardness values were determined by conventional metallographic and mechanical tests. The measurements of the Magnetic Barkhausen Noise (MBN) were performed by using both Rollscan and &amp / #956 / SCAN sensor connectors. A good correlation between the martensite volume fraction, hardness and MBN signal amplitude has been obtained. MBN emission decreased as the ICAT, therefore the volume fraction of martensite increased. Moreover, MBN emission decreased as the martensite morphology become thinner. It has been concluded that MBN method can be used for nondestructive characterization of industrial dual phase steels.

This aim of this thesis is to examine the possibility of using Magnetic Barkhausen Noise (MBN) technique in characterizing the microstructures of quenched and tempered low alloy steels as well as annealed low carbon steels. To determine the average grain size by MBN, SAE 1010 steel consisting of dominantly ferrite was used. The specimens were slowly cooled in the furnace after austenitizing at different time and temperature variations. By metallographic examination the average ferrite grain size of specimens was determined. The magnetic parameters were measured by a commercial MBN system. With increasing ferrite grain size, the magnetic Barkhausen jumps caused by the microstructure were decreased due to the reduction in grain boundary density per unit volume. A clear relationship has been observed between average grain size and the magnetic Barkhausen noise signals. SAE 4140, 5140 and 1040 steels were used to characterize the microstructures of quenched and tempered specimens. After austenitizing and quenching identically, the specimens were tempered at various temperatures between 200oC and 600oC. Formation of the desired microstructures was ensured by metallographic examinations and hardness measurements. The results show that as tempering temperature increases the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. It has been shown that MBN is a powerful tool for evaluating the microstructures of martensitic and annealed steels.

High Pressure Torsion (HPT) is one of the most widely used severe plastic deformation methods which enable to obtain a crack free ultra-fine grained bulk material with improved mechanical properties like increased strength and toughness. In the process, a disc shaped sample is pressed between two anvils and deformed via surface friction forces by rotating one of the anvils. The aim of this study is to nondestructively characterize the variations in the deformation uniformity of the severely deformed steel disks. Two sets of low carbon steel samples were obtained by applying the unconstrained and constrained HPT process up to 6 turns. Magnetic Barkhausen Noise (MBN) method was used in order to evaluate the samples in a nondestructive manner via a commercial device. The results of the MBN measurements were verified with those of conventional methods such as / x-ray diffraction (XRD), metallographic examination and hardness measurements. The initial stages of HPT revealed the effects of conventional plastic deformation on MBN / however with further straining, grain size refinement prevailed and caused increase in MBN signals.

The purpose of this study is to estimate the residual stress state in steel weldments by using Magnetic Barkhausen Noise (MBN) technique. For obtaining accurate, fast and continuous residual stress measurements a set up for single pass welded plates was designed and used. In order to convert the MBN values to residual stress values a calibration set up was also designed and a procedure for obtaining calibration curves was developed. After welding of low-C steel plates, residual stresses on heat affected zone (HAZ) and parent metal were measured by MBN technique. The results were verified by the hole drilling method. Microstructural investigation and hardness measurements were also conducted.

Shot peening is a cold-working process by which residual compressive stresses are being induced in the surface region to increase the fatigue strength and the resistance to stress-corrosion cracking. This study covers non-destructive measurement of surface residual stresses in the shot-peened steel components by a micro-magnetic technique, named as Magnetic Barkhausen Noise (MBN) method. For this purpose, various low alloy steel specimens were prepared by a controlled shot peening process with different intensity, impact angle and coverage values. The measurements showed that a clear relationship exists between residual stresses and the MBN signals. Residual stress values determined by MBN technique were also verified by X-ray diffraction measurements.

A study of gouges and dents in the context of pipelines has been completed, using the non-destructive evaluation (NDE) techniques of magnetic flux leakage (MFL) and magnetic Barkhausen noise (MBN). The research is part of an ongoing effort by the Applied Magnetics Group (AMG) at Queen's University to improve the interpretation of the MFL signal, which is used extensively by industry for defect detection and evaluation. The gouges were found to have distinctive MFL signatures depending on their orientation relative to the magnetization axis. Features in the MFL signal were identified as superpositions of geometry-related effects and strain or work hardening of the surface material. A qualitative magnetic permeability distribution in the material near a gouge has been proposed. The distribution is expected to vary in magnitude and extent according to the defect severity. The MFL results of the dent studies, on samples made available by Gaz de France (GdF), largely agreed qualitatively with previous research of dents. However, the differences pointed to the need for study of more varied dent shapes; new signal features were observed that suggested tensile residual strain in the dent rim is more prominent than earlier studies and modeling have predicted. Additionally, upgrades made to the MFL scanning system used by the AMG and a novel approach for building computer models are detailed. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-24 17:13:12.775

This thesis aims to examine the possibility of using Magnetic Barkhausen Noise technique in characterizing the ferritic-martensitic microstructure of hypoeutectoid steels quenched from the intercritical temperature range. For this purpose, rectangular specimens were prepared from SAE 1020, 1040 and 1060 steels. The specimens were heated at different temperatures within the intercritical temperature range and then quenched into water. Microstructures of the specimens were characterized by metallographic examinations and hardness measurements. The measurements of the Magnetic Barkhausen Noise (MBN) were performed by using both Rollscan and &amp / #956 / SCAN sensor connectors. It was seen that, for specimens having identical carbon content, Barkhausen emission decreased as the heating temperature increased. Moreover, in specimens heated at the same temperature, Barkhausen emission decreased as the carbon content of the specimen increased. In both cases, the decrease in Barkhausen emission is associated with the increase in martensite content. The results indicate that MBN is inversely proportional to hardness and that MBN is very sensitive to the microstructural condition of the material. It has been shown that using MBN is a powerful tool for evaluating the microstructure of hypoeutectoid steels quenched from the intercritical temperature range and that the use of this technique could be extended to characterize industrial dual phase steels.

Na atualidade, o estudo da transformação martensítica é de grande importância na área acadêmica e tecnológica, devido à aplicação de aços e ferros fundidos com estruturas martensíticas. O estudo dos fenômenos da transformação martensítica envolve vários pesquisadores no mundo e é objeto de eventos como o ICOMAT e ESOMAT. O presente trabalho acompanhou a transformação martensítica por meio de técnicas experimentais a temperaturas sub-zero em um aço AISI D2 e uma liga Fe-Ni-C previamente austenitizadas. A literatura indica que o tratamento a temperaturas sub-zero pode melhorar propriedades dos aços temperados e revenidos. Foi explorado o uso dos métodos de ruído magnético de Barkhausen (MBN), para detectar a transformação de fase da austenita para a martensita durante o resfriamento sub-zero das amostras, usando três diferentes configurações: a emissão de ruído Barkhausen convencional estimulada por um campo magnético alternado; o método de Okamura que é a emissão de ruído magnético medido embaixo de um campo fixo (DC); e uma nova técnica experimental, que mede a emissão magnética espontânea durante a transformação na ausência de qualquer campo externo. Os fenômenos associados com a transformação de fase também foram medidos por resistividade elétrica e as amostras resultantes foram caracterizadas por microscopia óptica e eletrônica de varredura. Medições MBN no aço ferramenta AISI D2, austenitizadas a 1473K (1200C) e resfriadas a temperatura de nitrogênio líquido apresentaram uma mudança próximo de 225K (-48C) durante o resfriamento, que corresponde à temperatura Ms, como foi confirmado por medidas de resistividade. As medições da emissão de ruído magnético espontâneo, realizadas in situ durante o resfriamento da amostra imersa em nitrogênio líquido, mostraram que poderia ser detectado um fenômeno de estouro individual (burst), de forma similar às medições de emissão acústica (AE), o qual foi confirmado com a liga Fe-Ni-C. Este método de caracterização Spontaneous Magnetic Emission (SME) pode ser considerado uma nova ferramenta experimental para o estudo de transformações martensiticas em ligas ferrosas. Foi acompanhado o inicio da transformação martensítica por SME, em função do tamanho de grão, já que é conhecido pela literatura que o inicio da transformação martensítica (Ms), muda com a variação do tamanho de grão. / Martensitic transformations are of special interest both as an academic topic and as a technological issue, due to importance of steels and cast irons with martensitic structures. Studies of martensite transformation phenomena involve researchers all over the world and specific conferences and meetings, as ICOMAT and ESOMAT. The present work followed the martensitic transformation using different experimental techniques, during cooling at cryogenic temperatures samples of a AISI D2 cold work tool steel and also a Fe-Ni-C, previously austenitized. There are plenty of references in the literature suggesting that sub-zero cooling treatments could ameliorate the properties of quenched and tempered steels. The Magnetic Barkhausen Noise (MBN) method was applied during cooling to subzero temperatures of austenitic samples of a AISI D2 cold work tool steels (previously quenched from 1200ºC) and to a Invar-type Fe-Ni-C alloy. MBN is a non-destructive technique based on the detection of the signal generated when ferromagnetic materials are subjected to an oscillating external magnetic field. In order to study the austenite to martensite transformation, three different configurations were tested: conventional Barkhausen using an oscillating magnetic field, a method proposed by Okamura, which uses a fixed magnetic field and a new method that detects spontaneous magnetic emissions (SME) on the absence of any applied magnetic field. Other phenomena associated with the transformation were followed using electrical resistivity measurements, optical microscopy and X-ray diffraction. MBN measurements on a cold work tool steel AISI D2, austenitized at 1473K (1200ºC) and quenched to room temperature, made during further cooling to liquid nitrogen temperature, presented a clear change of signal intensity near 225K (-48ºC), corresponding to Ms temperature, as confirmed by resistivity measurements. The SME in situ measurements during cooling of samples in liquid nitrogen were able to detect single burst (landslide nucleation and growth) phenomena, in a manner similar to the Acoustic Emission (AE) measurements; these results have been confirmed also with measurements on a Fe-Ni-C alloy. The new Spontaneous Magnetic Emission (SME) characterization method can be considered a new experimental tool for the study of martensitic transformations in ferrous alloys. The beginning temperature for the martensitic transformation detected using SME, electric resistivity and MBN were compared with estimates using the Andrews empirical equation (linear, 1965) for the Ms temperature. The effect of the austenite grain size on the beginning of the martensitic transformation was studied using SME, as it is known that the Ms temperature depends on the austenite grain size.

The purpose of this thesis is non-destructive determination of residual stress state in the multi-pass welded steel plates by Magnetic Barkhausen Noise (MBN) technique. To control the effectiveness of the developed procedure, continuous MBN measurements on the heat affected zone and parent metal of the welded plates were performed. In the experimental part, various steel plates were welded with different number of weld passes. Various series of samples were prepared for residual stress and for angular deflection measurements. Microstructural investigation and hardness measurements were also conducted. The results were discussed to evaluate the effectiveness of MBN measurements to monitor the changes in the residual stress state in the welded components as a function of weld pass number.