Étude de l'aptitude à la rectification des aciers rapides supérieurs : Application aux cylindres de laminage des alliages d'aluminium

Rolled sheet quality depends on microgeometric characteristics of the work roll obtained by grinding operation. However, work roll life and performance characteristics are usually sensitive to surface integrity in grinding in terms of surface topography, residual stresses distribution, microstructure modification, tribological behavior (friction, wear), gradient of properties… So, adjustments of grinding process are necessary to reach the required quality on roll and rolled sheet surfaces. The present study aims to characterize the grindability of new high speed steel used for cold rolling. Given the high hardness of functional surfaces and the particular microstructure, single grit scratch tests were conducted in order to classify several families of abrasive grains and study the grindability of this steel. It was found that superabrasive CBN is the most convenient abrasif, able to grind the high speed. Considering pervious results, the study of the grinding process was conducted using CBN wheels. An experimental approach has been implemented, it allowed to get an overview of the impacts of operating parameters of cylindrical grinding on surface integrity of the ground surface i.e. roughness parameters, surface residual stress and depth . The results show in particular that a combination of the HSS, the CBN wheel and the oil lubrication in finish grinding leads to the generation of compressive residual stresses. In order to understand multiphysical phenomena in the contact wheel-workpiece, numerical simulation of grinding process was conducted using equivalent thermo-mechanical source. Results show, indirectly, that the compressive residual stresses are principally related to metallurgical transformations leading to microstructural change.La qualité des tôles laminées dépend de la qualité microgéométrique du cylindre de laminage. Celle-cià son tour dépend du procédé de rectification qui a permis la réalisation de la surface fonctionnelle. Enfin, la durée de vie des cylindres dépend de l'intégrité de surface à savoir la topographie de surface, la microstructure de la zone affectée, la distribution des contraintes résiduelles, les gradients de propriété, etc… Ainsi, le travail effectué a pour objectif de caractériser l'aptitude à la rectification d’une nouvelle nuance d’acier rapide supérieur, s'est déroulé en trois étapes. Tout d'abord, compte tenue de la dureté excessive des surfaces fonctionnelles et de la microstructure particulière de l’acier, il a été nécessaire de mettre en place des essais de rayage pour classifier plusieurs familles de grains abrasifs et étudier l'aptitude à la rectification de cet acier à l’échelle du grain. On s'est rapidement aperçu que les abrasifs traditionnels ne répondent pas aux exigences attendues. Les essais de rayage avec des indenteurs CBN ont donné de bons résultats. Par conséquent, la procédure de rectification, a été menée directement avec des meules en CBN. Une démarche expérimentale a été mise en place, elle a permis d’obtenir un aperçu sur les impacts des paramètres opératoires de la rectification cylindrique sur l’intégrité de la surface rectifiée à. Les résultats montrent notamment que la combinaison HSS-CBN-huile en rectification de finition mène à la génération des contraintes résiduelles de compression. En vue de comprendre les phénomènes multi- physiques dans l'interface meule/pièce, la simulation par éléments finis du procédé de rectification cylindrique a été menée. Les calculs thermomécaniques réalisés, en utilisant une source thermomécanique équivalente, ont montré indirectement que les contraintes résiduelles de compression viennent essentiellement d’un changement microstructural lié principalement à des transformations métallurgiques et/ ou à un écrouissage fort de la sous couche rectifiée

Fatigue damage accumulation and lifetime prediction of defective C35 steel subjected to block loading

This paper deals with the influence of both defect and loading sequence on fatigue damage accumulation of C35 steel containing artificial defects. Tests were carried out using fatigue samples with artificial spherical defects introduced at the surface. Tests were performed using two blocks loading under increasing and decreasing magnitude. The experimental results were compared to the damage calculated by the Miner rule. In the case of defective material; it is shown in both cases a minor influence of sequence’s effect. A lifetime prediction method is then developed to assess the residual lifetime of damaged defective material. The method is based on a multiaxial endurance criterion used to calculate the equivalent local stress distribution around the defect and to inject it in an uniaxial damage cumulative rule. Finally a comparison between experimental and theoretical results is performed. It is observed that the Mesmacque sequential law gives the most accurate lifetime prediction of defective specimens

Fatigue damage accumulation and lifetime prediction of defective C35 steel subjected to block loading

This paper deals with the influence of both defect and loading sequence on fatigue damage accumulation of C35 steel containing artificial defects. Tests were carried out using fatigue samples with artificial spherical defects introduced at the surface. Tests were performed using two blocks loading under increasing and decreasing magnitude. The experimental results were compared to the damage calculated by the Miner rule. In the case of defective material; it is shown in both cases a minor influence of sequence’s effect. A lifetime prediction method is then developed to assess the residual lifetime of damaged defective material. The method is based on a multiaxial endurance criterion used to calculate the equivalent local stress distribution around the defect and to inject it in an uniaxial damage cumulative rule. Finally a comparison between experimental and theoretical results is performed. It is observed that the Mesmacque sequential law gives the most accurate lifetime prediction of defective specimens

Fatigue damage accumulation and lifetime prediction of defective C35 steel subjected to block loading

This paper deals with the influence of both defect and loading sequence on fatigue damage accumulation of C35 steel containing artificial defects. Tests were carried out using fatigue samples with artificial spherical defects introduced at the surface. Tests were performed using two blocks loading under increasing and decreasing magnitude. The experimental results were compared to the damage calculated by the Miner rule. In the case of defective material; it is shown in both cases a minor influence of sequence’s effect. A lifetime prediction method is then developed to assess the residual lifetime of damaged defective material. The method is based on a multiaxial endurance criterion used to calculate the equivalent local stress distribution around the defect and to inject it in an uniaxial damage cumulative rule. Finally a comparison between experimental and theoretical results is performed. It is observed that the Mesmacque sequential law gives the most accurate lifetime prediction of defective specimens

Experimental study of morphological defects generated by SLM on 17-4PH stainless steel

For cyclic loading applications and critical structural, the emergence of flaws in additively manufactured components is a key concern. This study highlighted the defects generated by selective laser melting (SLM) to the 17-4 PH stainless steel parts. The defects were quantified using an experimental study: Optical microscope and roughness meter to evaluate surface morphology (roughness and porosity) and microstructure. Tensile tests to evaluate the mechanical performance. The defects recorded take several forms, the most important of which are the rough and heterogeneous surface, prominent bumps on the outer surface in the shape of a hemisphere, cavities inside the spaced and adjacent parts of different shapes, internal cracks perpendicular to the printing direction, undissolved particles confined in the dissolving structure layers, brittle behaviour, non-resistant attractive and heterogeneous structure etc

Mechanical properties of additively manufactured 17-4PH SS ::heat treatment

The effects of the thermal post-treatments on the mechanical properties of SLMed 17-4PH stainless steel are studied. Three thermal post-treatments are carried out: (E0) as received state, (E1 and E2) solution annealing treatment and (E3) aging treatment. Microhardness, impact-strength, and wear tests are carried out to determine the effect of treatment on the mechanical properties of SLMed 17-4PH. The results showed that the hardness of 17-4PH at the E0 state is a greater than the hardness of the powder. This hardness decreases slightly from 418 HV to 384 HV after the solution annealing treatment E2 and increase again after E3 ageing treatment to around 447HV. A hardness difference between the two manufacturing directions was also observed. This difference almost disappears after the E3 ageing treatment. The impact strength results show a huge drop in impact strength for 17-4PH obtained by SLM. An improvement in wear behaviour following heat treatment, especially in the case of ageing

Selective laser melting of stainless-steel ::a review of process, microstructure, mechanical properties and post-processing treatments

Additive Manufacturing (AM) using Selective Laser Melting (SLM) has gained significant prominence across various industries involved in stainless steel part manufacturing. Selective Laser Melting makes it possible to manufacture parts with very complex geometry and with remarkable mechanical and physicochemical properties by controlling the microstructure via the appropriate choice of process parameters. This study presents a comprehensive literature review aiming to provide the scientific and technical communities with an overview of existing knowledge and experimental data regarding the effects of Selective Laser Melting parameters and conditions on the microstructure and mechanical properties of stainless-steel parts. The objective is to highlight the impact of various factors, such as process parameters, building atmosphere, post-heat treatments and initial powder characteristics on phase transformation, porosity and microcracks formation, microstructure evolution and mechanical properties of SLMed stainless steels. Additionally, the integration of emerging Smart Additive Manufacturing (SAM) requires experimental databases, properties prediction and processing parameters optimization to enhance the entire process spanning from design to final product

Simulation numérique de soudage avec un maillage en tétraèdres P1/P1

National audienceLe but de cet article est de montrer la pertinence de l’élément fini P1/P1 pour l’analyse mécanique des métaux solides présentant un comportement élasto-viscoplastique. Une simulation représentative d’un cas de soudage est traitée. Les résultats obtenus se comparent favorablement à ceux obtenus avec un maillage de référence utilisant des éléments hexaédriques du premier ordre à intégration sélective

In-situ monitoring of selective laser melted Ti–6Al–4V parts using eddy current testing and machine learning

Metal laser powder bed fusion (L-BPF) technology is one of the most common and evolved additive manufacturing technologies to fabricate metal components. However, the control of defects generated during the SLM process remains an essential technological challenge for its implementation in production lines. In this work, based on the combination of eddy current testing (ECT) and machine learning (ML) approach, we propose a methodology allowing the in-situ monitoring of LPBF process porosity defects of Ti-6AL-4V components. The present empirical approach is achieved by setting up trained AI algorithms for the in-situ detection of porosity defects generated during the part fabrication. The algorithms are fed with data collected layer by layer using a specific experimental set up composed of an ECT system mounted on the machine recoater of the SLM machine. Comparison between predicted and experimental outcomes shows the effectiveness of the proposed framework which allows the prediction of porosity defects layer by layer with a mean absolute error (MAE) of 0.1% for CNN2D algorithm and 0.11% for LSTM one. The framework developed in this study can be effectively applied to quality control in additive manufacturing

L'influence des écoulements de la matière sur l'évolution des contraintes résiduelles durant le procédé de soudage

International audienceL’objectif de ce travail est de montrer numériquement, au cours du procédé de soudage, l’influence des écoulements de la matière dans le bain fondu sur l’évolution des contraintes résiduelles générées. Ainsi deux approches numériques différentes sont adoptées afin d’assurer le couplage des différents états de la matière liquide et solide, y compris la solidification dans zone pâteuse. Dans la première approche, les écoulements fluides dans le bain fondu sont modélisés, les différents états de la matière sont couplés en se basant sur un formalisme Arbitraire ment Lagrangi en Eulérien (ALE). Dans la deuxième approche, les simulations sont réalisées en adoptant une approche Lagrangienne où les écoulements dans le bain fondu ne sont pas pris en compte