Investigation of high temperature wear behavior of for boro-tempered ductile iron

In this thesis, the effects of boro-tempering heat treatment on microstructure and hightemperature wear properties of ductile iron were investigated. Wear samples weremachined from Y-block castings and subjected to boro-tempering heat treatment. Inthe case of boro-tempering, the samples were boronized in a solid medium containingcommercial Ekabor®2 powder under atmospheric pressure at a temperature of 900 ºCfor 1, 3 and 5 h. This was followed by quenching in a molten salt bath at differenttemperatures of 250 ºC, 300 ºC, 350 ºC, or 450 ºC for 1 h. and finally, cooled down toroom temperature in air. After the boro-tempering treatment, all samples were cleanedwith water and dried. Boro-tempered samples were subjected to ball-on disc wear testsat the different ambient temperatures (room temperature, 150 ºC, 300 ºC and 450 ºC).Alumina balls of 8 mm in diameter were used as an abrasive. The following conditionswere chosen for wear tests; 10 N of load, 0.3 m/s of sliding speed and 1000 m ofsliding distance. After the wear tests, wear tracks were examined by scanning electronmicroscopy (SEM) and EDX point analyses. Selected area of wear tracks were used forsuch analyses. Hard boride layer was produced on the surface of ductile iron by borotemperingheat treatment while a matrix of ausferritic structure. Tribological testsindicated that boro-tempering treatment increased the wear resistance of ductile iron.Boro-tempered samples showed lower wear rate than that of as-cast ductile iron at alltest temperatures. Worn surface examinations revealed that the wear started in the closevicinity of nodular graphite. As the coating layer on the graphite fractured under thealternating loading, resulting debris may cause abrasive wear.Keywords: Ductile Iron, Boro-tempering, Microstructure, High Temperature WearProperties