Papers by Keyword: Cementite

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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: Alexander V. Evteev, Elena V. Levchenko, Irina V. Belova, Graeme E. Murch
Abstract: Molecular dynamics is employed to investigate carbon diffusion in cementite. An approximation that carbon atoms can interact with each other only indirectly (via neighbouring iron atoms) is used. The interstitial mechanism of carbon diffusion in cementite is elucidated. The formation energy of defects (a carbon atom on an interstitial position and a vacant site on a regular carbon position) as well as the migration energy of carbon atoms are estimated in the temperature range 1273–1373 K.
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: Makoto Egashira, Toshihiro Tsuchiyama, Setsuo Takai
Authors: Elena V. Levchenko, Alexander V. Evteev, Irina V. Belova, Graeme E. Murch
Abstract: . In this paper, carbon diffusion in cementite is studied by molecular dynamics simulation. An assumption that carbon-carbon interaction occurs only indirectly via neighbouring iron atoms is used. An interstitial mechanism of carbon diffusion in cementite is revealed. The principal tracer diffusion coefficients and activation parameters of carbon diffusion in cementite are calculated for the temperature range 1223-1373 K and compared with the available published experimental data.
Authors: Jay Chakraborty, Tias Maity, Mainak Ghosh, Goutam Das, Sanjay Chandra
Abstract: Despite numerous investigations in the past, mechanism of cementite dissolution has still remained a matter of debate. The present work investigates cementite dissolution during cold wire drawing of pearlitic steel (~ 0.8wt% carbon) at medium drawing strain (up to true strain 1.4) and the role of dislocations in the ferrite matrix on the dissolution process. Quantitative phase analysis using x-ray diffraction (XRD) confirms more than 50% dissolution of cementite phase at drawing strain ~ 1.4. Detail analysis of the broadening of ferrite diffraction lines confirms presence of strain anisotropy in ferrite due to high density of dislocations (~ 1015m-2) at drawing strain 1.4. The results of the analysis shows that the screw dislocations near the ferrite-cementite interface are predominantly responsible for pulling the carbon atoms out of the cementite phase leading to its dissolution.
Authors: Meilinda Nurbanasari, Panos Tsakiropoulos, Eric J. Palmiere
Abstract: The cementite precipitation behavior in the martensite and banite of the H21 tool steel under high temperature axisymmetric compression test and double temper was investigated. The main purpose on this work is to develop a better understanding regarding the transformation mechanism of bainite and martensite in a H21 tool steel. The selected deformation temperatures were 1100 oC and 1000 oC and the double temper process was carried out at 650 oC for 1 hour respectively. The results showed that the cementite was sensitive to the stress. The applied stress has affected the Fe3C precipitation behaviour by decreasing the number of variants carbides in tempered martensite and decreasing the number of a single variant carbides in tempered lower bainite. The results were in agreement with a displacive mechanism of martensite and bainite transformation. It was also found that hot deformation temperatures selected in this work have the same contribution in decreasing number of variant carbides in tempered martensite and decreasing number of single variant carbides occurred in tempered lower bainite.
Authors: Feng Fang, Xian Jun Hu, Shao Hui Chen, Jian Qing Jiang
Abstract: Lamellar cementite will be spheroidized in drawn pearlitic steel wire during galvanization process. To understand the evolution of the microstructure in this process, effects of isothermal time on microstructure of drawn pearlitic steel wires were investigated by using scanning electron microscope (SEM), transmission electron microscope (TEM) and DSC Technique. Experimental results showed that the lamellar cementite would transform to spheroidized cementite during the isothermal treatment. During the heating process, no endothermic or exothermic peak existed in pearlitic strand, while an obvious exothermic peak appeared in cold drawn pearlitic wire at about 380°C. It results from the spheroidization of lamellar cementite. The dislocation density was very low in pearlitic strand, but the dislocation density increased shapely after drawing. During the isothermal treatment at 450°C, the high dislocation density zone disappeared and some cementite became spheroidized. The cementite spheroidization phenomena first began at the boundary of pearlitic blocks or grains, and then in the high dislocation density zone in pearlitic blocks.
Authors: Minoru Umemoto, Zhi Guang Liu, D.Y. Liu, H. Takaoka, Koichi Tsuchiya
Authors: Minoru Umemoto, Yoshikazu Todaka, T. Takahashi, P. Li, R. Tokumiya, Koichi Tsuchiya
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