Wear resistance of centrifugal casting isothermally quenched ductile iron bushing

In addition to Si, Mn and C elements, a certain amount of Cu is added to nodular cast iron. Cu can stabilize austenite, promote the formation of bainite and refine the acicular structure of bainite to a certain extent. Cu can also improve the austenitizing speed of Austempered Ductile Iron and reduce the austenitizing time and heat treatment cost. Reasonable casting, spheroidization and isothermal quenching processes can ensure that austempered ductile iron has good spheroidization rate and a large number of spherical graphite. Bainite preferentially forms and grows around the graphite ball, so it can provide more bainite nucleation positions to form a large number of evenly distributed bainite. The internal stress, microcrack, microstructure uniformity and thermal stability of bainite are better than those of martensite, which makes austempered ductile iron have better mechanical properties and wear resistance.

In the friction and wear test, Austempered Dutile iron sample showed excellent anti-wear and antifriction properties. A large number of fine needle like lower bainite and martensite in the microstructure of Austempered duct iron sample improve the hardness and wear resistance of Austempered duct iron sample. The friction extrusion in the friction process leads to the transformation of residual austenite on the surface of austempered ductile iron sample into martensite, thus forming a high hardness “shell” on the material surface and improving the wear resistance of the matrix. Under the action of stress, the internal residual austenite deforms plastically, relaxes the stress concentration, and prevents the generation and propagation of cracks. During the wear process, the graphite in the Austempered conductive iron sample will peel off and separate, and enter the friction interface. Graphite is a common solid lubricant. These graphite balls are in the free state, which plays an isolation role between the friction pairs, reduces the friction coefficient and reduces the wear, so that the Austempered duct iron shows good self-lubricating performance. Under the condition of oil lubrication, the holes formed after the graphite ball falls off can store lubricating oil, and play the role of lubrication together with lubricating oil, further improving the wear resistance of the material.

The samples were prepared by centrifugal casting

The ductile iron bushing of excavator has fine structure after being treated by austempered ductile iron, which is mainly composed of acicular lower bainite, spherical graphite and retained austenite. Under the condition of dry friction, the friction coefficient of Austempered Dutile iron sample is about 2 / 3 of that of 45 steel, and the wear amount is 1 / 6 of that of 45 steel; Under the condition of oil lubrication, the friction coefficient of Austempered duct iron sample is only 1 / 4 of that of No. 45 steel, and the wear amount is only 1 / 10 of that of No. 45 steel. It has excellent wear resistance and self-lubricating performance, and meets the performance requirements of excavator bushing.

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