engleski

Inluence Of Sub-Zero Treatments On The Properties Of Austempered Ductile Cast Iron

A deep cryogenic treatment (DCT) is a heat- treatment procedure where the material is subjected to subzero temperatures before tempering to obtain dimensional stability, but also to improve the abrasive, fatigue and wear resistance. DCT is very popular in research, with reports covering tool steels, maraging steels, cast irons, annealing steels, hard metals, aluminum, and others. The main mechanisms contributing to the improvement of mechanical and tribological properties of steel are the completion of austenitic transformation and the precipitation of nanometric eta-carbides evenly dispersed by the martensitic matrix. Recent studies have provided a more detailed insight into the mechanisms mentioned, including the formation of nano-martensite during the DCT and the plastic deformation of the primary martensite that follows the martensitic conversion with the partial dissolution of the carbide and the formation of carbon clusters. ADI has become an important engineering material in recent years due to its interesting combination of properties, such as very good strength-to-weight ratio, good toughness, high wear resistance, and excellent fatigue strength in combination with the low cost, design flexibility, and good machinability. As a result of these properties, which are a consequence of the ADI’s specific microstructure that consists of needle-like bainitic ferrite (αB) and high- carbon austenite (γHC), ADI is increasingly used in the automotive industry as a substitute for steel and aluminium parts. The study investigated the influence of a deep cryogenic treatment on the abrasive wear resistance of ADI austempered in the upper ausferrite area as well as the microstructural changes that occurred during the deep cryogenic treatment and the subsequent tempering. The obtained results show that the DCT, in combination with different tempering temperatures, affects the matrix microstructure of the ADI, which leads to an increase in both the abrasion wear resistance and the hardness.

austempered ductile cast iron, deep cryogenic treatment, microstructure, wear resistance

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