Abstract
An academic methodology based for experimental evaluation of materials treatment is presented. The study is centered in an educational research emphasis about microstructure evaluation and heat treatments in steels samples machined according to ASTM E8 specifications. The uses of metallographic techniques and hardness/tensile tests for analyzing experimental variations due to structural changes are included. Different thermal treatments were applied on AISI-SAE 1018 steel specimens by raising the temperature until it reached the austenization state. Images were obtained with a Nikon NIS Elements computer programming, in order to observe the microstructure and identify the phases involved in each of the thermal treatments. For the hardness analysis, the round indenter of 1/16 in of Tungsten Carbide with a preload of 100 kg was used. A grain diameter of 3 to 4 µm was observed in both annealed and normalized sample, so it is assumed that the cold rolled or reference sample had a normalized condition. Both 41 and 67% in elongation and area reduction percentages, respectively, in the normalized samples were observed. The results allow identifying the correlation between microstructures and mechanical properties, providing an engineering educational approach for metallographic analysis and heat treatment schemes focused on the grain size interpretation, resilience and stress-strain curves. The described methodology provides an academic reference for the didactic evaluation of the main techniques associated with the treatment of materials for physics and mechanical engineering training. Key words: Heat treatments, microstructure, tensile test, hardness, educational research.
Highlights
Since the beginning of civilization, materials have been used by humanity to improve their standard of living, being it the substances that make up any structure or product (Daunton et al, 2012; Whitesides and Wong, 2006)
The study is centered in an educational research emphasis about microstructure evaluation and heat treatments in steels samples machined according to ASTM E8 specifications
The results allow identifying the correlation between microstructures and mechanical properties, providing an engineering educational approach for metallographic analysis and heat treatment schemes focused on the grain size interpretation, resilience and stress-strain curves
Summary
Since the beginning of civilization, materials have been used by humanity to improve their standard of living, being it the substances that make up any structure or product (Daunton et al, 2012; Whitesides and Wong, 2006). Engineers design most products and the processes required for their manufacture are invoiced, so students of engineering must get acquainted with the internal structure and properties of the materials, as well as the techniques of thermal treatments, stress tests, hardness and metallographic analysis The thermal treatments constitute procedures to improve materials properties or achieve characteristics for specific purposes (Calik, 2009; Kuśtrowski et al, 2005; Fadare et al, 2011; Daramola et al, 2010; He et al, 2010) and these in turn, depend on the structure and the type of material in a piece, which is achieved with the precise handling of temperature and cooling rate. A description about the main heat treatment problems can be found in ASM Handbook, chapter 1 (ASM Handbook, 2014)
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