Time filter

Source Type

Durango, Spain

Stefanescu D.M.,Ohio State University | Stefanescu D.M.,University of Alabama | Huff R.,Caterpillar Inc. | Alonso G.,Area Ingenieria | And 3 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Extensive SEM work was carried out on deep-etched specimens to reveal the evolution of compacted and chunky graphite in magnesium-modified multicomponent Fe-C-Si alloys during early solidification and at room temperature. The findings of this research were then integrated in the current body of knowledge to produce an understanding of the crystallization of compacted and chunky graphite. It was confirmed that growth from the liquid for both compacted and chunky graphite occurs radially from a nucleus, as foliated crystals and dendrites. The basic building blocks of the graphite aggregates are hexagonal faceted graphite platelets with nanometer height and micrometer width. Thickening of the platelets occurs through growth of additional graphene layers nucleated at the ledges of the graphite prism. Additional thickening resulting in complete joining of the platelets may occur from the recrystallization of the amorphous carbon that has diffused from the liquid through the austenite, once the graphite aggregate is enveloped in austenite. With increasing magnesium levels, the foliated graphite platelets progressively aggregate along the c-axis forming clusters. The clusters that have random orientation, eventually produce blocky graphite, as the spaces between the parallel platelets disappear. This is typical for compacted graphite irons and tadpole graphite. The chunky graphite aggregates investigated are conical sectors of graphite platelets stacked along the c-axis. The foliated dendrites that originally develop radially from a common nucleus may aggregate along the c-axis forming blocky graphite that sometimes exhibits helical growth. The large number of defects (cavities) observed in all graphite aggregates supports the mechanism of graphite growth as foliated crystals and dendrites. © 2016 The Minerals, Metals & Materials Society and ASM International Source

Stefanescu D.M.,Ohio State University | Stefanescu D.M.,University of Alabama | Alonso G.,Area Ingenieria | Larranaga P.,Area Ingenieria | And 2 more authors.
Acta Materialia

Extensive SEM work was carried out on deep etched specimens to reveal the evolution of graphite shape in Fe-C-Si alloys of industrial composition during early solidification and at room temperature. The samples had various magnesium and titanium levels designed to produce graphite morphologies ranging from coarse lamellar to interdendritic lamellar to mixed compacted - spheroidal. The present findings were then integrated in previous knowledge to produce an understanding of the crystallization of lamellar, compacted and spheroidal graphite. It was demonstrated that most forms of graphite grow radially from a common center, most of the time as foliated dendrites (see Figure). The basic building blocks of the graphite aggregates are hexagonal faceted graphite platelets with nanometer height and micrometer width. During solidification, thickening of the platelets occurs through growth of additional graphene layers nucleated at the ledges of the graphite prism. In the magnesium-free irons that graphite platelets assemble into foliated crystals and dendrites, forming graphite plates that grow along the a-axis. In the magnesium-modified melts the graphite platelets stack along the c-axis, producing clusters with random orientation. The clusters are then assembled into quasi-cylindrical shapes connected to more or less curved walls to form tadpole graphite, compacted graphite, or chunky graphite. If enough magnesium is added, conical sectors made of platelets stacked in the c-direction grow from the same nucleus. The conical sectors may occupy the whole volume of the sphere forming a graphite spheroid, or only part of it like in chunky graphite. The large number of cavities observed between the platelets is consistent with growth of foliated dendrites. © 2016 Acta Materialia Inc. Source

Mendez S.,IK4 Azterlan | De La Torre U.,IK4 Azterlan | Larranaga P.,IK4 Azterlan | Suarez R.,Veigalan Estudio 2010 | And 2 more authors.
Metal Casting Design and Purchasing

Researchers were developing ductile iron that features properties similar to austempered ductile iron (ADI), without heat treatment. Researchers first developed a way to achieve the as-cast ausferritic microstructure for a single alloy for a specific casting. Work was needed to develop an experimental model to utilize engineered cooling for a wider variety of parts in real-world applications. The model defined the thickness window in which an ausferritic as-cast microstructure could be achieved without the use of conventional austempering heat treatment by chemical composition adjustments. The model was also validated in a semi-industrial process for the chemical composition range. Source

Natxiondo A.,Veigalan Estudio 2010 | Suarez R.,Veigalan Estudio 2010 | Sertucha J.,Engineering | Larranaga P.,Engineering

Ductile iron casting production is strongly affected by austenite and graphite distribution obtained after the solidification process. At the same time it is accepted that solidification behavior can be considered as hypo-, hyper- or eutectic depending on the chemical composition; there is still some misconception about the growth evolution of graphite nodules and about solid fraction progression. Quenching experiments were performed on two different carbon equivalent compositions using inoculated and non-inoculated thermal analysis standard samples with the aim of freezing the existing phases at different solid fractions for each alloy. As a result of these experiments, it was possible to study the structural features found at different locations of each sample and at different stages of solidification. Additionally nodule evolution during the liquid-solid transformation was also analyzed and discussed regarding the chemical and processing characteristics of the prepared alloys. © 2015 by the authors; licensee MDPI, Basel, Switzerland. Source

Agency: Cordis | Branch: H2020 | Program: SME-1 | Phase: NMP-25-2015-1 | Award Amount: 71.43K | Year: 2016

Workshop managers face daily the challenge to execute their production plans at the lowest product rejection rates and costs. Rejections can be due to multiple kinds of defects in the manufactured piece. Each kind of defect is co-related to the particular parameters of production and the surrounding environment that have converged during the manufacturing process of the defective piece. At modern workshops the number of converging parameters during production can range from several hundreds to thousands. In serial production, defects are more prevalent at the beginning of the production of each new reference, until all production parameters are correctly set-up, but its also frequent to suffer involuntary, environmental or unavoidable modifications of parameters that also cause defective production.The problem of defective production is particularly relevant the higher the value of the workpieces produced and the shorter the production series. The evolution of the industrial production worldwide, and specially in advanced economies like Europe, tend towards a higher customization of products, thus to shorter series of higher cost and value pieces, making the problem of defective production a increasingly relevant issue for the competitiveness of industry.VEIGALAN has developed WORKSHOP4.0, a tool based on big data and artificial intelligence technologies that forecasts in real time the optimum working conditions for production processes involving material melting or fluency. WORKSHOP4.0 is capable to forecast the optimum production parameters at the beginning of a new series and re-calculate the new optimum parameters when unexpected, even un-noticed, defect producing events happen.

Discover hidden collaborations