The effect of complex modification on the structure and properties of gray cast iron for tribotechnical application

Abstract

Introduction. An approach based on the complex modification of cast irons makes it possible to improve its mechanical properties by changing the structure of the metal matrix, as well as the shape of graphite and its distribution. The aim of this work is to study the influence of alloying elements on the structure and mechanical properties of gray cast irons obtained for operation under friction wear conditions. Research methods. The paper describes the process of obtaining complex modified gray cast irons. Fractographic investigation of dynamically destroyed samples is carried out. Structure’s features of SCh35, ChMN-35M and SChKM-45 gray cast irons are studied. Tribological testing under sliding friction conditions is carried out. Results and its discussion. It is established that the complex modification of SCh35 gray cast iron with molybdenum, nickel and vanadium makes it possible to increase its hardness to 295 HB and tensile strength to 470-505 MPa. Alloying with nickel (0.4-0.7 wt.%), molybdenum (0.4-0.7 wt.%) and vanadium (0.2-0.4 wt.%) leads to a decrease in the interlamellar distance of perlite by 2 times, as well as to the metal matrix grain refining. The length of graphite lamellas of modified cast irons is reduced by 3-5 times. An additional effect on the tensile strength of cast iron is due to the alloying of ferrite with molybdenum and vanadium, which is fallen out along the boundaries of graphite inclusions. Alloying of ferrite with molybdenum and vanadium increases the level of its microhardness by 1.4 times in comparison with the α-phase of SCh35 serial cast iron. The results of tribotechnical tests of the designed materials are presented. Conclusions. It is established that the wear of specimens made of SChKM-45 cast iron is approximately 20-30% lower compared to cast iron SCh35 cast iron and 10-15% lower compared to ChMN-35M cast iron. Fractographic studies show that complex alloying with molybdenum, vanadium and nickel, contributing to the refining of pearlite colonies, leads to a decrease of the size of the cleavage facets.