Structural investigation of solidification and heat treatments influence on High Alloyed Cast Irons Grades with Nb-V-Ti Additions

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 ▲]

Benefits of thixoforging hot-crack-sensitive aluminium alloys at high solid fraction

in Proceedings of The 13th Esaform Conference on Material Forming (2010) - semi-solid processing (2009)

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular microstructure helps to decrease forming load. But the introduction of a liquid phase in the material is a source of defects that limit mechanical properties of thixoforged parts. One of these defects is the hot cracking for some hot crack-sensitive wrought aluminium alloys. Hot cracking occurs because of strain and deformation during last step of solidification. This paper shows how thixoforging process helps to lower hot cracking tendency without modification of the alloy composition by decreasing strain and deformation due to shrinkage. Different experimental tests by extrusion of 7075 aluminium alloys are used. [less ▲]

Physique des matériaux : partim 2 polymères

Learning material (2009)

Recherche sur la frittabilité de l'Inconel 718

Report (2008)

Fabrication de feuilles minces métalliques par dépôt sous vide

Report (2008)

Alloy Characterization to Adapt Steels to Thixoforming: Study of a High Chromium High Carbon Steel

in Solid State Phenomena (2008), 141-143

This paper deals with the examination of the influence of alloying elements on the thixoformability of a Cr steel. It focuses on the liquid fraction curves of different Cr steels with modifications of ... [more ▼]

This paper deals with the examination of the influence of alloying elements on the thixoformability of a Cr steel. It focuses on the liquid fraction curves of different Cr steels with modifications of composition. The effect of composition modifications was observed. The solid fraction versus temperature has been obtained by a thermodynamics software (MTData) and by Differential Scanning Calorimetry (DSC), limited to low heating rates. MTData permits to obtain information on the influence of alloying elements, with the advantage of the possibility to change the chemical composition very easily. The DSC tests determine the influence of the heating rate on these curves. [less ▲]

Influence of Alloying Elements on the Thixoformability of a Chromium Steel

in International Journal of Material Forming (2008), 1(1), 997-1000

This paper deals with the examination of the influence of alloying elements on the thixoformability of a chromium steel. It focuses on the liquid fraction curves of various chromium steels with and ... [more ▼]

This paper deals with the examination of the influence of alloying elements on the thixoformability of a chromium steel. It focuses on the liquid fraction curves of various chromium steels with and without modification of composition. The liquid fraction versus temperature has been obtained by MTData, a thermodynamic prediction package, and by Differential Thermal Analysis (DTA), limited to low heating rates. The correlation between liquid fraction and temperature has been studied. The effect of modifications of composition and of heating rate was observed. First, the thermodynamical calculations allow the study of the influence of alloying elements with variations in chemical composition. Secondly, the DTA tests offer the possibility to observe the influence of heating rate on liquid fraction curve parameters. All these results lead to the identification of the initial parameters necessary to perform inductive heating and quenching tests, and so to approach the industrial process. [less ▲]

Extrusion tests of 7075 aluminium alloy at high solid fraction

in International Journal of Material Forming (2008), 1(1), 1019-1022

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<fs<1). 7075 aluminium alloy has been used as a feedstock for thixoforging in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. Higher solid fraction of 7075 alloy is less sensitive to a drop in temperature, avoids metal splash at high speed, allows laminar flow at high speed. Hot tool is used to slow down the solidification rate of the high solid fraction metal by decreasing thermal exchanges. To determine the best parameters to achieve maximum mechanical properties in thixoforging of 7075 aluminum alloy, we need to consider the impact of some parameters such as tool temperature, shear rate. For this, we use extrusion tests with constant speed [1] where these parameters are known. The result of this study is that each parameter has its level of impact on the thixoforging: the temperature of the tool and the deformation rate shouldn't be high to avoid cracks. Thermal exchanges between the material flow and the tool have to be reduced to avoid high solidification rate [2]. [less ▲]

Optimization of the formulation and post-treatment of stainless steel for rapid manufacturing

in Journal of Materials Processing Technology (2008), 196(1-3), 160-164

Rapid prototyping process called Optoform shapes functional parts from a photocurable paste. This paste contains metal powder, resin, UV photoinitiator and wetting agent. After processing on the Optoform ... [more ▼]

Rapid prototyping process called Optoform shapes functional parts from a photocurable paste. This paste contains metal powder, resin, UV photoinitiator and wetting agent. After processing on the Optoform machine, a post-treatment is applied (debinding+sintering). During the post-treatment, the residual carbon coming from the resin modifies the composition of the metal and its melting point. This modification affects densification mechanisms, which leads to a residual porosity that lowers mechanical characteristics. We will present theoretical consideration leading to the optimization of the formulation. To improve the process, bimodal powder is used and thermal treatment is adapted. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

Investigation on retained delta ferrite occurrence and its influence on HSS and Semi HSS Strengthening after thermomecanical routes

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 ▲]