Papers by Keyword: Pearlite

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Authors: Yoshitaka Adachi, Mayumi Ojima, Naoko Sato, Yuan Tsung Wang
Abstract: The features present in 3D structure have geometric properties that fall into two broad categories: topological and metric. Metric properties are generally the more familiar; these include volume, surface area, line length and curvature. Equally or even more important in some applications are the topological properties of features. The two principal topological properties are number per unit volume and connectivity. In the present study, a change in morphology of pearlite and dual phase microstructures was examined from differential geometry and topology viewpoint. 3D images of eutectoid pearlite and dual phase steels were obtained by reconstructing serial sectioning images. Their metric and topological features were evaluated using The Euler Poincare formula and The Gauss-Bonnet Theorem. In addition, newly developed fully-automated serial sectioning 3D microscope “Genus_3D” will be also introduced.
Authors: T.Y. Hsu
Abstract: In order to diminish the industrial pollution to maintain the sustainable development and to reduce the cost of the steel production, a unified technology combining plastic forming and heat treatment for some steel parts production is suggested. This article mainly concerns part theoretical foundation of such technology, i.e. the thermodynamic and kinetic models of the ferrite and pearlite transformations under external stress. Simulation of the ferrite fraction after continuous cooling under stress in a low-alloyed steel is presented. The effects of stresses on bainitic and martensitic transformations are also briefly introduced. The unified technology seems favorable to be realized in manufacturing practice.
Authors: Ke Han, Jing Ping Chen
Abstract: Large amount of research has been undertaken on the effects of conventional thermomechanical treatment and chemistry variations on the mechanical properties of nanostructured bulk materials developed for wire rod and sheet products. The thermomechanical treatments are selected to refine as much as possible the microstructure to achieve high strength. In most of the cases, the alloy additions are deliberated added to be beneficial to the mechanical properties of the nanostructured materials, especially the tensile strength. In addition to refine the microstructure, both the thermomechanical treatments and chemistry variations may also alter the shape and distribution of the strengthening phases. This article describes the nanostructured composites with face-centered cubic (fcc) copper or body-centered cubic (bcc) ferrite as matrix and discusses several factors that affect the mechanical strength of such materials.
Authors: Anja Oswald, Rosita Schmidtchen, Daniel Šimek, David Rafaja, Rudolf Kawalla, Gunter Lehmann
Abstract: A new method for a fast analysis of heavily deformed, multicomponent ferritic/pearlitic steels microstructure based on XRD measurements had been developed. Its practical application has been examined and proven during wire rod production of a high-strength eutectoid non-alloyed steel grade containing 0.81 weight percent carbon. For individual technological conditions, the lattice strains and their anisotropy were analysed quantitatively by means of fast X-ray diffraction measurements and correlated with the results of comprehensive mechanical testing. Obtained relationships between the microstructure characteristics and mechanical properties were described using physically based models and used to establish a material specific database for prediction of the mechanical properties from X-ray diffraction data. Depending on the deformation state different parameters have to be applied for the material’s macroscopic properties prediction. Additionally, the fast microstructure analysis can provide more detailed information in the case of deviations from the as-required material’s properties due to technological aberrations.
Authors: Goro Miyamoto, Zhao Dong Li, Hirokazu Usuki, Tadashi Furuhara
Abstract: Reverse transformation has been frequently used to refine austenite grain size for refining ferrite, pearlite and martensite structures. However, kinetics and microstructure change during reverse transformation to austenite has not been examined systematically compared with the austenite decomposition reaction. Therefore, alloying effects of 1mass% Mn, Si and Cr on reverse transformation kinetics from pearlite and tempered martensite structures in Fe-0.6mass%C alloys were investigated in this study. Vickers hardness of all the specimens increases with increasing holding time at 1073K because reversely-formed austenite transforms to martensite by quenching. In the reverse transformation from pearlite structure, the kinetics of reverse transformation is hardly changed by the Mn addition while Si and Cr additions delay it. Kinetics of reverse transformation from tempered martensite structure becomes slower than from the pearlite structure in all the alloys. In particular, retarding effect by the Cr addition is most significant among those elements.
Authors: Harshad K.D.H. Bhadeshia
Authors: Torsten Sjögren, Per Eric Persson, Peter Vomacka
Abstract: During the last years the use of digital image correlation techniques (DIC) has become wide spread within different areas of research. One area in which these techniques are used is in the analysis of deformation of engineering materials. By the analysis of a set of successive images taken during a tensile test DIC makes it possible to determine how the deformation is localized. The observed local strains are often several times higher than the global strain measured by standard strain gauges. In this study, a set of compacted graphite cast irons (CGI) with different ratios of pearlite to ferrite have been examined by the use of DIC. In contrast to the normal use of DIC, where a pattern is sprayed on the tensile test sample as a reference for the determination of deformation taking place between successive images, the materials natural microstructural pattern has been used in this study. The use of the natural microstructural pattern makes it possible to study how the macroscopic deformation is accommodated within the different phases in the CGI studied. It is shown that the graphite phase accommodates a large portion of the strain and that the soft ferrite is strained more than the stronger, less ductile pearlite. The local strain of the observed area might be up to ten times higher than the global strain measured. The use of DIC improves the understanding of the deformation behaviour of compacted graphite cast irons and will be a useful tool when validating future finite element analyses of the micro-mechanical properties of cast irons.
Authors: V.I. Savran, Y. van Leeuwen, Dave N. Hanlon, Jilt Sietsma
Abstract: The first step in the heat-treatment processes for a vast majority of commercial steels is austenitization. There is much less research put in this field comparing to the cooling transformation, but the interest is continuously increasing especially in view of the development of TRIP and Dual-phase steels. The microstructural evolution during continuous heating experiments has been studied for a series of C-Mn steels with carbon contents in the range 0.35-0.45 wt. % using optical and scanning electron (SEM) microscopy. It is shown that the formation of the austenitic phase is possible in pearlitic as well as in ferritic regions, although in the former it proceeds at a much faster rate due to the shorter diffusion distances. Thus a considerable overlap in time of the ferriteto- austenite and the pearlite-to-austenite transformations is likely to occur. Another observation that was made during the experiments is that depending on the heating rate, the pearlite-to-austenite transformation can proceed in either one or two steps. At low heating rates (0.05 °C/s) ferrite and cementite plates transform simultaneously. At higher heating rates (20 °C/s) it is a two-step process: first ferrite transforms to austenite within pearlite grains and then the dissolution of the cementite lamellae takes place.
Authors: H.J. McQueen
Abstract: After 1780, wrought iron (WI) provided a structural material and steel was cherished for its hardness and cutting qualities. When available in quantity after ~1860, steel’s structural strength and wear resistance were recognized in normalized condition in armor plates, rails and drawn wire. The responsible microstructure component was pearlite in which the lamellar spacing of ferrite and carbides could be refined by simple bulk heat treatments that are practiced with small modification until today. The strength and toughness rose as the layer thickness decreased the ferrite slip length and the carbide cracking. In hot working, the strength rises as much as 200% (while ductility falls) with fraction of pearlite; below the transus compared to austenite just above it, strengths are equal at about 0.7C (ductilities equal at 0.35C).
Authors: Juraj Balak, Xavier Sauvage, Duk Lak Lee, Choong Yeol Lee, Philippe Pareige
Abstract: Microstructures of cold drawn pearlitic steel wires were investigated by three-dimensional atom probe (3D-AP) to understand the influence of alloying elements on the decomposition of cementite. Before cold drawing, Si is mostly located in the ferrite phase, while Cr is located in the Fe3C phase and the amount of Mn is similar in Fe3C and in ferrite. Higher Si amount leads to higher dissolution rate of cementite and Cr has a little effect on cementite decomposition during drawing.
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