Friction and Wear Properties of New Low Alloy Ductile Iron under Oil Lubrication Condition

A kind of low alloy ductile iron was prepared by melting casting after adding 0.5wt% chromium and 0.01wt% bismuth elements to the existed QT600-3 cast iron. The microstructure and friction and wear properties under different loads (400,800,1 200 N) and different wear times (3, 6, 9, 12 h) of the ductile iron under oil lubrication condition were studied and compared with those of QT600-3 cast iron and alloy gray cast iron. The results show that the microstructure of the low alloy ductile iron was composed of graphite, martensite and carbide. The graphite was spherical, and the graphite spheres were smaller, more numerous and more rounded comparing to those in QT600-3 cast iron. Low alloy ductile iron had more carbide content than those of alloy gray cast iron and QT600-3 cast iron. The volume wear rate of low alloy ductile iron increased with the increase of load, and first increased, then decreased, and then increased with the extension of wear time. Under the load of 1 200 N and wear time of 12 h, the volume wear rate of low alloy ductile iron was 10.7×10⁻¹³ mm³ · N⁻¹ · m⁻¹, which was 25% and 78% lower than those of alloy gray cast iron and QT600-3 cast iron, respectively, and low alloy ductile iron had the best wear resistance. The wear mechanism of low alloy ductile iron was mainly abrasive wear. A large number of fine carbides in the microstructure could resist the expansion of the furrow and reduce the degree of the abrasive wear, while the graphite spheres with higher sphericity could reduce the possibility of the material spalling and cracking.