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See detailPhase Transformations and Crack Initiation in a High-Chromium Cast Steel Under Hot Compression Tests
Tchuindjang, Jérôme Tchoufack ULg; Neira Torres, Ingrid; Fores, Paulo et al

in Journal of Materials Engineering and Performance (2015), 24(5), 2025-2041

The mechanical behavior of the fully austenitic matrix of high-chromium cast steel (HCCS) alloy is determined by external compression stress applied at 300 and 700 C. The microstructure is roughly ... [more ▼]

The mechanical behavior of the fully austenitic matrix of high-chromium cast steel (HCCS) alloy is determined by external compression stress applied at 300 and 700 C. The microstructure is roughly characterized toward both optical and scanning electron microscopy analyses. Dilatometry is used during heating from room temperature up to austenitization to study the solid-state phase transformations, precipitation, and dissolution reactions. Two various strengthening phenomena (precipitation hardening and stress-induced bainite transformation) and one softening mechanism (dynamic recovery) are highlighted from compression tests. The influence of the temperature and the carbide type on the mechanical behavior of the HCCS material is also enhanced. Cracks observed on grain boundary primary carbides allow establishing a rough damage model. The crack initiation within the HCCS alloy is strongly dependent on the temperature, the externally applied stress, and the matrix strength and composition. [less ▲]

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See detailCharacterization of the Solidification Path, the Solid State Transformations and the Mechanical Behavior of a High Chromium Cast Steel
Tchuindjang, Jérôme Tchoufack ULg; Neira Torres, Ingrid; Habraken, Anne ULg et al

in Proceedings of the 5th Abrasion Conference - 2014 (2014, August)

The mechanical behavior of the fully austenitic matrix of a High Chromium Cast Steel (HCCS) alloy has been determined under external compression stress applied at 300°C and 700°C. The solidification path ... [more ▼]

The mechanical behavior of the fully austenitic matrix of a High Chromium Cast Steel (HCCS) alloy has been determined under external compression stress applied at 300°C and 700°C. The solidification path and the microstructure have been studied, including the nature and the critical temperature ranges for carbides formation, while using Differential Thermal Analysis and both Optical and Scanning Electron Microscopes. The microstructure has been characterized towards both Optical and SEM analyses. Differential Thermal Analysis and Dilatometry were used to study the solid state phase transformations on the one hand, and precipitation and dissolution reactions on the other hand, especially during heating from room temperature up to austenitization, and subsequent cooling down to room temperature. Dilatometry also helps setting the parameters for the preliminary thermal treatments to perform prior to compression tests, in order to allow more or less transition carbides within the stressed microstructure, the other carbides remaining undissolved. Flow stress curves and related work hardening rates were determined for both temperatures. From the compression tests, various strengthening phenomena, such as precipitation hardening and stress induced bainite transformation, and one softening mechanism such as recovery, have been highlighted, while enhancing at the same time the influence of the temperature and the carbide type on the mechanical behavior of the HCCS material. Cracks observed on grain boundaries primary carbides allow establishing a rough damage model. The crack initiation within the HCCS alloy seems to be strongly dependent on the temperature, the external applied stress and the matrix toughness. [less ▲]

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See detailStudy of residual stresses in bimetallic work rolls
Neira Torres, Ingrid ULg; Gilles, Gaëtan ULg; Tchuindjang, Jérôme Tchoufack ULg et al

in Advanced Materials Research (2014), 996

An experimental campaign of compression tests, differential thermal analysis (DTA), differential scanning calorimetry ( DSC), dilatometry and microstructure analysis has been performed, as well as the ... [more ▼]

An experimental campaign of compression tests, differential thermal analysis (DTA), differential scanning calorimetry ( DSC), dilatometry and microstructure analysis has been performed, as well as the identification of the material data set for finite element ( FE) analysis of bimetallic rolls. This article numerically investigates the stress and strain fields after the cooling stage and it checks their effect on the subsequent heat treatment step. As bimetallic rolls have a different material for core and shell, the effect of the roll size and the shell thickness on residual stresses is also studied. [less ▲]

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See detailRapport Final, PROJET RECYLCLAD RW 11-1-7335 : Fabrication de Cylindres Bimétalliques par Rechargement Laser (Laser Cladding) d’Aciers à Outils optimisés sur Axes Réutilisables
Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg; Dedry, Olivier ULg et al

Report (2013)

Le présent rapport contient les résultats principaux des analyses réalisées au sein du laboratoire MMS (Métallurgie et Science des Matériaux) de l’Université de Liège, durant les deux premières années de ... [more ▼]

Le présent rapport contient les résultats principaux des analyses réalisées au sein du laboratoire MMS (Métallurgie et Science des Matériaux) de l’Université de Liège, durant les deux premières années de la recherche, à savoir la période allant du 01/12/2011 au 30/11/2013. Le service MMS est à la fois partenaire et coordinateur du projet RECYLCLAD. [less ▲]

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See detailStudy of phase transformations within bimetallic rolling mills
Neira Torres, Ingrid ULg; Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg et al

Scientific conference (2013, September 10)

With the aim of simulating the cooling behavior after a re-austenitizing stage of bimetallic rolling mills, both materials corresponding to spheroidal graphite iron (core material) and high chrome steel ... [more ▼]

With the aim of simulating the cooling behavior after a re-austenitizing stage of bimetallic rolling mills, both materials corresponding to spheroidal graphite iron (core material) and high chrome steel (shell material) must be characterized through thermo physical and mechanical tests as well as microscopic observations. Dilatometer tests were carried out for both materials in order to determinate thermo physical properties such as thermal expansion coefficient and density. Compression tests were also performed in order to estimate the effect of mechanical stress on martensite phase transformation, especially the nature and the type of martensite and start of transformation temperature. However there are some parameters that are still unknown and that are highly difficult to determinate. Inverse simulations are performed through Lagamine code with the aim of finding an estimated value for these parameters or improved parameters, more accurate than the ones already estimated. [less ▲]

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See detailPrediction of residual stresses by FE simulations on bimetallic work rolls during cooling
Neira Torres, Ingrid ULg; Gilles, Gaëtan ULg; Tchuindjang, Jérôme Tchoufack ULg et al

in Computer Methods in Materials Science (2013), 13(1), 84-91

Bimetallic rolls used in the roughing stands of the Hot Strip Mill require mixed properties as a high wear resistance for the shell material and an enhanced toughness for the core material. The bimetallic ... [more ▼]

Bimetallic rolls used in the roughing stands of the Hot Strip Mill require mixed properties as a high wear resistance for the shell material and an enhanced toughness for the core material. The bimetallic roll studied in this paper is obtained from a vertical spin casting process followed by cooling and subsequent heat treatments. Failure of the compound roll sometimes occurs during the cooling stage of the casting route or later during the thermal treatments. It requires to deeply investigate the thermo mechanical metallurgical interactions generated during cooling and heat treatment in order to find the origin of cracks. For this purpose, a thermo metallurgic mechanical finite element model is used. However these numerical simulations require a high amount of mechanical, thermal and metallurgical parameters. In order to determinate these parameters, a study of available data for estimation of mechanical parameters was performed. Thermo physical parameters were obtained by DTA and DSC methods. Metallurgical characterization by inverse numerical method based on available CCT diagrams was performed to determine the TTT diagrams. First cooling numerical simulations are presented, allowing a rough estimate of residual stresses values and the identification of key parameters for predicting accurate residual stresses by sensitivity analysis. [less ▲]

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