UDC 669.131.7:669.112.227 MICROSTRUCTURE AND TRIBOLOGICAL PROPERTIES OF SPHEROIDAL GRAPHITE CAST IRONS WITH NANOADDITIVES © J. Kaleicheva PhD, associate professor, Technical University of Sofia, Sofia, Bulgaria The microstructure and tribological properties of spheroidal graphite cast iron with nanosized additives of titanium nitride + titanium carbonitride (TiN + TiCN), titanium nitride TiN and cubic boron nitride cBN are investigated. <...> Samples of spheroidal graphite cast iron are put under austhempering at the following conditions: heating at 900 °С, 1 h and isothermal retention at 380 °С, 2 h with the aim to achieve a upper bainite structure. <...> The microstructure of the iron is investigated by metallographic and X-Ray analyses. <...> The Vickers hardness testing and wear resistance at fixed specimen study are carried out. <...> The influence of the nanosized additives on the microstructure, mechanical and tribological properties of the iron is investigated. <...> INTRODUCTION Nanosized particles added to the cast iron melt in a small quantity increase the graphite quantity and change its morphology. <...> The austempering is a type of a heat treatment leading to the ductile iron metal base bainitic transformation and to the enhanced strength, increased durability and toughness. <...> The aim of the present paper is to investigate the microstructure, mechanical and tribological properties of austempered ductile iron (ADI) samples containing nanosized additives of titanium nitride + titanium carbonitride (TiN + TiCN); titanium nitride TiN and cubic boron nitride cBN respectively. 2.MATERIAL AND INVESTIGATION METHOD The composition of the spheroidal graphite cast iron samples is: Fe-3,55C-2,67Si-0,31Mn-0,009S-0,027P0,040Cu-0,025Cr-0,08Ni-0,06Mg wt%. <...> The TiN, TiCN and cBN, nanosized particles are coated by electroless nickel coating EFTTOM-NICKEL [7] prior to the edition to the melt. <...> The austempered ductile iron samples’ microstructure is observed by means of an optical metallographic microscope GX41 OLIMPUS. <...> Microstructure of spheroidal graphite cast irons: a – sample 1; b – sample 2; c – sample 3; d – sample 4 Проблемы машиностроения и автоматизации, № 2 – 2014 59 treated with 2 vol. % HNO3 – C2 hardness testing is performed by Vickers method. <...> The austempered ductile iron samples are tested by H5 X-Ray diffraction analysis to examine the retained austenite quantity in the structure <...>