References of "Tchuindjang, Jérôme Tchoufack"
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See detailStructural investigation of solidification and heat treatments influence on High Alloyed Cast Irons Grades with Nb-V-Ti Additions
Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg

in Defects and diffusion forum (2009), 289-292

Two High Alloyed Cast Irons (HACI) were studied, both belonging to the Fe-C-Cr-Si-X system where X was represented by Mo, Nb, Ti or V. One alloy was obtained after adding Nb, V and Ti to the chemical ... [more ▼]

Two High Alloyed Cast Irons (HACI) were studied, both belonging to the Fe-C-Cr-Si-X system where X was represented by Mo, Nb, Ti or V. One alloy was obtained after adding Nb, V and Ti to the chemical composition of the other alloy. Raw materials originated from spun cast rolls for hot strip mill were submitted to different heat treatments routes such as double tempering or quenching, in order to study the influence of alloying elements on the microstructure. Both HACI grades contained a mixture of martensite and retained austenite matrix in the as-cast conditions and after quenching. Differential Thermal Analysis (DTA) was carried out on the heat treated samples in order to determine the phase transformations occurring during re-melting and subsequent solidification sequence. Retained austenite found in the as-quenched HACI without Nb, V and Ti additions exhibited an enhanced stability as confirmed by DTA tests. Various type of martensite were found at the end of heat treatments routes, each having a possible influence on the material behavior while performing re-heating prior to re-austenitisation. Bulky Nb-rich MC carbides precipitating at the beginning of the solidification process strongly influence the nature and the rate of the subsequent phase transformations, particularly for HACI grade with Nb, V and Ti additions. Such NbC carbides were also found to segregate during spin casting process. Quantitative metallography was done to determine graphite, MC carbides, cementite and matrix volume fraction in HACI studied grades. [less ▲]

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See detailInvestigation on retained delta ferrite occurrence and its influence on HSS and Semi HSS Strengthening after thermomecanical routes
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in Proceedings of Abrasion 2008 (2008)

The present work deals with use of DTA tests in order to understand the crystallisation behaviour of semi-HSS and HSS alloys, and to enhance their solid state transformations. Emphasis is laid on the ... [more ▼]

The present work deals with use of DTA tests in order to understand the crystallisation behaviour of semi-HSS and HSS alloys, and to enhance their solid state transformations. Emphasis is laid on the decomposition of the unexpected retained delta ferrite during thermal and thermomechanical treatment. [less ▲]

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See detailASSESSMENT OF RETAINED AUSTENITIC PHASE IN INDEFINITE CHILL CAST IRON MICROSTRUCTURE TOWARDS VARIOUS TECHNIQUES
Tchuindjang, Jérôme Tchoufack ULg; Terziev, Liuben; Sinnaeve, Mario et al

Poster (2007, November 16)

Indefinite Chill Cast Irons also called ICDP when used as rolling mill rolls are high alloyed cast iron alloys belonging to the Fe-Cr-C system. ICDP exhibit improved properties regarding hot oxidation and ... [more ▼]

Indefinite Chill Cast Irons also called ICDP when used as rolling mill rolls are high alloyed cast iron alloys belonging to the Fe-Cr-C system. ICDP exhibit improved properties regarding hot oxidation and wear resistances as their microstructure is a mixture of a martensitic with bulky cementite (M3C) and lamellar graphite fully dispersed into the matrix. Mechanical properties involved depend either on the chemical composition of the alloy or the crystallisation behaviour and the heat treatments performed subsequently in order to lead to the desired microstructure. Thus hardenability of the matrix is of great concern as heat treatments sequence is intended to transform austenite in a more stable structure like martensite or even bainite, depending on Cr content. In fact austenite is known to be unstable during hot working conditions as hot temperature and external stresses could yield transformation of this phase into martensite with major volume distortions and even multiple cracks network on the component involved. To avoid such a hitch in service it is quite necessary to make sure all the austenite is completely transformed into martensite while performing subsequent heat treatments like quenching or tempering on the material obtained after casting process. Various techniques are allowable starting from classical ones (X-Ray Diffraction (XRD), Image Analysis, Vibrating Sample Magnetometer (VSM), Dilatometry) to more exotic one like Conversion Electron Mössbauer Spectroscopy (CEMS). From an industrial point of view, it is important to set a fast and reliable method to assess retained austenite presence into ICDP microstructure at the end of any step of the thermomechanical process. The present work is intended to compare different techniques used for retained austenite assessment in ICDP alloys as a first step prior to the calibration of a classical method like dilatometry. This calibration is to be set starting from complex XRD and CEMS spectrometers analyses. Dilatometry seems to overrate retained austenite volume fraction in the as-cast conditions while good agreements are made on the overall batch of techniques when considering heat treated material where retained austenite transformation occurred [less ▲]

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See detailFractography survey on high cycle fatigue failure: Crack origin characterisation and correlations between mechanical tests and microstructure in Fe-C-Cr-Mo-X alloys
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in International Journal of Fatigue (2007), 29(4), 713-728

Raw materials were cast from different specific processes in order to produce cleaner steels with a reduced amount of inclusions. Studied materials that are HSS hardened alloys belonging to the Fe-Cr-C-X ... [more ▼]

Raw materials were cast from different specific processes in order to produce cleaner steels with a reduced amount of inclusions. Studied materials that are HSS hardened alloys belonging to the Fe-Cr-C-X system were shared out in four groups depending on the tempering temperature and the presence of secondary and primary carbides. Both inclusions and carbides were roughly assessed by means of Image Analysis. Forging was done on all studied materials with different reduction ratios in order to highlight the texture influence oil mechanical properties. High cycle fatigue tests were made using the boundary method to allow a quick evaluation of results. Fractographic analyses carried out on broken samples led to the definition of four failure modes depending on the nature and the location of the point from which the crack was initiated in one hand, and the roughness of striations in the propagating area over and around the initiation point. Internal and surface crack initiation points were found, the latter being more harmful than the first ones. Though oxides appeared to be more detrimental than other inclusions, primary carbides were also found to be both crack initiation candidates and crack propagation enhancers. Various parameters likely to influence high cycle fatigue failures were finally defined, the most significant one dealing with the nature and location of embedded precipitates and the forging reduction ratio. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailImprovement in HSS grade for early stands of hot strip mills - Metallurgical features and mechanical properties assessment
Ernst, Roger; Breyer, Jean-Pierre; Tchuindjang, Jérôme Tchoufack ULg et al

in Proceedings of the 43rd Seminar of Rollings (2007)

Aurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X system, where X is a strong carbide former element of the V, Mo or W type. Both alloys were metallurgically characterised prior ... [more ▼]

Aurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X system, where X is a strong carbide former element of the V, Mo or W type. Both alloys were metallurgically characterised prior to their comparison. Metallurgical analyses involved phases identification and carbides quantification by using Scanning Electron Microscopy and Energy Dispersive X rays. Differential Thermal Analysis was performed to allow a better understanding of the solidification sequence of studied alloys while mechanical tests performed were compressive at room temperature and bulk hardness at usual service temperatures. An attempt was made in order to connect experimental results to the good behaviour in operation of Aurora grade. In fact Aurora grade appeared to exhibit strong metallurgical differences when compared to Kosmos grade, especially as concern in nature and amount of carbides. [less ▲]

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See detailMetallurgical assessment of two HSS rolls grades for Hot Strip Mill
Lecomte-Beckers, Jacqueline ULg; Delaunois, Fabienne; Breyer, Jean-Pierre et al

in AISTech-Proceedings of the Iron and Steel Technology Conference (2007)

Aurora and Kosmos grades are HSS alloys used for the manufacturing of rolling mill work rolls for early finishing stands of Hot Strip Mills. Both alloys were metallurgically assessed using Electron ... [more ▼]

Aurora and Kosmos grades are HSS alloys used for the manufacturing of rolling mill work rolls for early finishing stands of Hot Strip Mills. Both alloys were metallurgically assessed using Electron Microscopy, X Rays analysis on carbides and Differential Thermal Analysis. These methods allow a better understanding of the behaviour of the studied alloys during solidification and cooling. Some mechanical tests were also performed. A connection between the laboratory results and the performance in operation of both grades is performed. The strong metallurgical differences especially as concern the nature and amount of carbides allow to explain the good behaviour in service of Aurora. [less ▲]

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See detailUse of Microscopy for identification of complex MC, M2C, M6C, M7C3 and M23C6 carbides in high speed-steels
Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg

in GIT - Imaging and Microscopy (2005), 2

High-speed steels (HSSJ rofis are useci in front finishing stands of hot strip mils. Good wear resistance and hardness at high temperature are defining features of HSS. Many types of carbides are present ... [more ▼]

High-speed steels (HSSJ rofis are useci in front finishing stands of hot strip mils. Good wear resistance and hardness at high temperature are defining features of HSS. Many types of carbides are present in these alloys, each having different effect upon the final properties of HSS. As a resuit, nature, morphology and amount of these carbides are factors of important concern. Identification and characterisation of HSS carbides are realised with optical microscopy comhined with electron microscopy. [less ▲]

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See detailMelting and crystallisation behaviour of multi-component Fe-C-Cr-X alloys : microstructural aspects
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in Proceedings of the 13th European Microscopy Congress (2004)

Studied materials are of the Fe-C-Cr-X multi-component system where X represents a group of strong carbides formers as Mo, V, or Nb. These alloys are used for wear components. Differential Thermal ... [more ▼]

Studied materials are of the Fe-C-Cr-X multi-component system where X represents a group of strong carbides formers as Mo, V, or Nb. These alloys are used for wear components. Differential Thermal Analysis (DTA) was used to determine the melting and solidification behaviour of these materials. Raw material has a thermomecanical history that involved casting, heat treating and hot forming, which could be investigated by the melting sequence of the DTA trial. [less ▲]

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See detailStructural investigations of HSS rolls for hot strip mill
Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg; Ernst, R. et al

in Proceedings of the 41st Rolling Seminar Processes, Rolled and Coated Product (2004)

High Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills (HSM). Good wear resistance and hardness at high temperatures, are defining features of HSS. Previous experience has ... [more ▼]

High Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills (HSM). Good wear resistance and hardness at high temperatures, are defining features of HSS. Previous experience has shown that HSS rolls containing mainly hard MC carbides have a high friction coefficient, which is detrimental for the rolling power consumption and for the strip surface quality. On the other hand, HSS rolls containing eutectic rod shaped carbides are brittle and more susceptible to spalling. To overcome these problems, a suitable grade, called HSS7, that gives the best compromise between a low friction coefficient and a high crack propagation and wear resistance was developed. That alloy contains well-dispersed hard VC carbides improving wear, and non-interconnected eutectic carbides of the M2C and M7C3 type, hindering crack propagation. All the metallurgical factors affecting the performance and damage of under rolling condition in front finishing stands are reviewed: wear resistance, friction coefficient, resistance to rolling incident, and oxide film formation. The effect of nature, morphology and amount was for each of the carbides studied and connected to the factor affecting the behaviour of the new grade developed. Different techniques are used such as: differential thermal analysis, optical and electron scanning microscopy and image analysis. A correlation with mechanical properties was also performed. [less ▲]

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See detailStudy of complex carbides obtained after solidification and thermal treatment in High Speed Steels
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in Proceedings des journées annuelles de la Société belge de physique SBP-BSP (27 et 28 mai 2003) (2003, May)

High-speed steels (HSS) rolls are used in front finishing stands of hot strip mills. Good wear resistance and hardness at high temperature are defining characteristics of HSS. Many carbides are present in ... [more ▼]

High-speed steels (HSS) rolls are used in front finishing stands of hot strip mills. Good wear resistance and hardness at high temperature are defining characteristics of HSS. Many carbides are present in these alloys, each having different effects upon the final properties of HSS. As a result, the nature, the morphology and the amount of these carbides are factors of important concern. Optical microscopy combined with electron microscopy lead to quicker identification and characterization of HSS carbides. [less ▲]

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See detailInclusions and Carbides characterisation in High-Speed Steels
Tchuindjang, Jérôme Tchoufack ULg; Lecomte-Beckers, Jacqueline ULg

in Proceedings de la journée de la société belge de microscopie (SBM-BVM), RUCA, UA (2003)

Prior to assessment of inclusions and carbides is the identification of thes particles. The present survey shows how we determine the nature of inclusions and carbides, while using Scanning Electron ... [more ▼]

Prior to assessment of inclusions and carbides is the identification of thes particles. The present survey shows how we determine the nature of inclusions and carbides, while using Scanning Electron Microscopy and Energy Dispersive Spectroscopy with X-Rays. [less ▲]

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See detailDevelopment of a new high-speed steel with optimized carbide composition for mill rolls
Lecomte-Beckers, Jacqueline ULg; Tchuindjang, Jérôme Tchoufack ULg; Pirard, Eric ULg et al

in Stal' (2003), 2

High Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills. Good wear resistance and hardness at high temperatures, are defining features of HSS. Many types of carbides are ... [more ▼]

High Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills. Good wear resistance and hardness at high temperatures, are defining features of HSS. Many types of carbides are present in these alloys, each having different effect upon their final properties. As a result, nature, morphology and amount of these carbides are factors of important concern. Identification and characterisation of carbides were realised. MC, M2C, M7C3 carbides were found. Some relationships with mechanical properties were obtained especially in the field of the solidification sequence that affects grain size and carbides dispersion. [less ▲]

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