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The Austempering heat treatment is a well-known solution to improve the mechanical properties of ductile cast irons, therefore being referred as 'ADI' (Austempered Ductile Iron). The improved mechanical properties of ADI's with respect to conventional ductile iron is attributed to its resulting microstructure, which contains mainly carbide-free bainite with stabilized retained austenite. More recently, ductile cast irons were submitted to another heat treatment, known as 'Quenching and Partitioning' (Q&P). In this case, the ductile cast iron is austenitized, quenched to a temperature between Mf and Ms temperatures and subsequently heated to a temperature above Ms in order to partition the carbon from the martensite to the remaining austenite. The resulting microstructure comprises mainly low carbon martensite, austenite (stabilized by the carbon partition) and carbide-free bainite. Such microstructure resulted in equal or better properties than ADI.

This work consists in a study on the influence of gray cast iron graphite shape on the localized wear occurrence in engine block cylinders. The four cylinder automotive spark ignition internal combustion engine has been submitted to a complete dynamometer engine durability test. The tested engine is the one equipped with the flexible fuel technology, which is capable to work with both gasoline/ethanol fuels, in any mixture proportion. The specimen taken from the end-of-test engine block has been submitted to a 2D profilometer analysis, where region of localized wear at top dead center (TDC) zone was identified. The local wear region has been properly prepared epared and characterized through both scanning electronic microscopy (SEM) and metallography technics.

The present work aims to characterize the microstructure of valvetrain camshaft lobes that are currently applied in the automotive industry, obtained by different processing routes. The cam lobe microstructure has been assessed by microscopy, whereas the mechanical properties by hardness profile measurements on the surface region. Microconstituents type and form, composing the final microstructure at the cam lobe work region, are defined by the casting route and/or post-heat treatment process other than alloy chemical composition, so that knowledge and control of processing route is vital to assure suitable valvetrain system assembly performance and durability. Most of the mechanical solicitations on the part occur at the interface between cam and follower; the actual contact area is significantly smaller than the apparent area. As a result, the microstructure at and near the surface performs a direct role on the performance of the valvetrain, cam lobe and its counterpart.

The so-called Modified Martempering discussed in this work differs from the standard martempering by that the temperature of the quenching bath is below the Ms point. In spite of the fact the lower temperature increases the severity of quenching, this also usually avoids the bainite formation, and by this reason, it is possible to make a fair comparison between different processes, which result in different microstructures. The present study shows the results in terms of mechanical properties, impact resistance in special of a cold work tool steel class, after being heat treated by the isothermal modified martempering process, as well as a comparison with the conventional quenching and tempering process and the austempering as well.

A ring on block lubricated sliding wear test was used to study severe adhesive wear or scuffing between cam and cam-follower materials. The scuffing resistance was measured at constant 4,85 m/s disk velocity. DIN 100Cr6 quenched and tempered rings were tested against DIN 16MnCr5 blocks treated to obtain two different surface conditions: a) carburized;, b) carburized and nitrocarburized with predominantly carbonitride layer. The worn surfaces were characterized using scanning electronic microscopy (SEM). The phases present at the nitrocarburized layer were characterized using GDS. The role of the layer on the scuffing resistance was evaluated. The nitrocarburized specimens had better scuffing resistance than carburized one. The friction power intensity criterion was used to define the capacity of the material to resist to scuffing. A low FPI (friction power intensity) has a high scuffing resistance.