Methods of evaluation degraded parts
2015
Kusmierczak, S., Jan Evangelista Purkyne Univ. in Ústí nad Labem (Czech Republic)
This article deals with degradation of foundry cores in the casting process of automotive pistons, where the change in the properties of the cores results in deterioration of the quality of the resulting castings, resulting in economic losses. Moulds and cores are components that are exposed during casting temperature changes. Therefore, as their product alloyed steels for hot working are used. Steels for hot working should have increased resistance to tempering, high hardness and strength while maintaining relatively high toughness. This is achieved by alloying elements such as Cr, Mo and V. A further increase of the resistance of the material against this loading contributes to creating a hard surface layer, e.g., by nitriding. The aim of this work is to show on a definite example the necessity of complex approach to dealing with situations, where limit states and subsequent degradation occurred. This means that from already present degradation retrospectively its cause is determined using available metallographic methods and standardized test materials. As the material of cores steel by CSN 41 9522 was used, after hardening, nitriding, with surface hardness 50 ± 5 HRC. Chemical composition was analyzed spectrophotometrically at the equipment Tasman Q4. Evaluation of hardness according to ČSN EN ISO 6507 – 1 was carried out by Shimadzu hardness tester. The material was complexly evaluated microscopically using the methods of light and electron microscopy.
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