Abstract
In the present paper, authors have demonstrated how a localized induction heat treatment can be advantageously applied, controlled, and mechanically characterized on a specific part—i.e., on steel hose fittings for hydraulic applications. More specifically, the study shows how this specific type of heat treatment facilitates significant localization effects on mechanical properties, and how such a treatment could act as a powerful tool for material optimization in diverse applications. The instrumented micro-indentation test was adopted as the investigation method for mechanical characterization and, due to the reduced amount of material required for the test, has the double advantage of retrieving potential spatial gradients of the mechanical properties without causing permanent damage to the analyzed parts. A measurement of both Vickers hardness and plastic work are required in order to make the indentation necessary to quantify the strength and ductility capability of the parts’ materials. In addition, a customized tensile test, based on a strains measurement obtained through an optical full-field method—i.e., digital image correlation (DIC)—was developed with the aim of identifying and quantifying the correlation between the material properties attainable through a conventional tensile test and those measured by the instrumented micro-indentation test. Finally, it was demonstrated that the proposed customized tensile test, due to the localized heat treatment, is capable of retrieving potential spatial gradients of the material properties.
Highlights
Heat treatments always represented a powerful tool to improve the performance of the materials in several industrial applications, allowing to attain specific mechanical properties without modifying the chemical composition of the materials [1]
3.1 Reference specimens subjected to instrumented micro‐indentation test Specimens #0, #1, and #2 were initially tested to evaluate reference values of the mechanical parameter and to understand the potential existence of their spatial gradients
Due to the complex stress state induced by this type of test, mechanical properties directly usable for design purposes and typical obtained by a standard tensile test – i.e. yield and tensile strength, ductility and plastic flow parameters – cannot be measured straightforwardly
Summary
Heat treatments always represented a powerful tool to improve the performance of the materials in several industrial applications, allowing to attain specific mechanical properties without modifying the chemical composition of the materials [1]. Stress and strain at the necking limit resulted to be correlated to the plastic deformation work of indentation, whereas the mathematical relation can be assumed linear, provided that the range of the considered values is not too wide The evaluation of this type of relationship has the advantage to provide important mechanical properties and their gradients typically obtained by expensive and destructive tests – i.e. tensile test – by quite less invasive and cheaper experimental procedures – i.e. indentation tests –, implementable in industrial environment without the need of highly skilled operators. The study showed how the developed methods allow to quantify and control the properties’ magnitude and gradient, with the aim to advantageously fit the parts in the whole production cycle
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