Studies on mechanical and wear properties of alloyed hypereutectic gray cast irons in the as-cast pearlitic and austempered conditions

摘要

The mechanical and wear behavior of a series of as-cast gray iron alloys were compared with properties obtained after austempering at 360℃. The austempered alloys showed equivalent or moderately enhanced mechanical strength than the as-cast pearlitic gray irons. The specific wear rates of all the austempered alloys decreased significantly by 7-15 times and friction coefficient reduced by 30-50% compared to pearlitic alioyed gray irons. The dry sliding wear studies of as-cast alloys against high carbon l%Cr through-thickness hardened steel shows that the specific wear rate ranged from 5.6 to 19.1 (× 10~(-7)) g/Nm with friction coefficient from 0,55 to 0.7. While, the austempered alloys showed wear rates from 0.5 to 2.6 (× 10~(-7)) g/Nm with friction coefficient ranging from 0.23 to 0.4. The improved wear resistance was attributed to the layer wise surface phase transformation associated with strain induced mar-tensite formation of the stabilized austenite in the austempered matrix, lubrication of the interface by the flake graphite and better heat conduction from the rubbing interface by higher volume fraction of the graphite. Cast iron alloyed with Ni shows enhanced mechanical properties and wear resistance. The tensile strength shows decreasing trend with increase in carbon equivalent and graphite volume. The specific wear rate and friction coefficient shows decreasing trend with increase in hardness and graphite flake volume.