The paper presents the results of investigation concerning the strength properties of the vermicular and the nodular cast iron both in the as-cast state and after the heat treatment held according to a couple of various options. The nodular cast iron exhibited almost 100% nodular graphite precipitates and the purely pearlitic matrix. The graphite precipitates in the vermicular cast iron were almost 100% vermicular ones, embedded in the pearlitic-ferritic matrix (50%/50%). The heat treatment of the examined cast iron types differed with respect to the temperature. The austenitization process was performed either at 900°C or at 960°C, while austempering was held either at 290°C or at 390°C. Both the austenitizing and the austempering time was constant and set to 90 min. Both the as-cast specimens and the heat-treated ones were subjected to mechanical testing which allowed to determine their properties, namely Rm, Rp0,2, A5, and hardness. The change of the initial matrix to the ausferritic one resulted in the increase in mechanical properties, however the results were diversified depending on the type of graphite precipitates occurring in the material.Keywords: Nodular cast iron, vermicular cast iron, austempering, AVGI, ADI
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