1. School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang, Henan 471023, China
2. Henan Collaborative Innovation Centre of Non-Ferrous Generic Technology, Luoyang, Henan 471023, China
3. Third Assembly Plant, China First Tractor Group Co. Ltd., Luoyang, Henan 471004, China
Abstract：The drilling-ability of HT250 and QT450 used in front brackets of tractors has been evaluated in terms of thermal conductivity, chip shape, surface roughness in the drill hole, temperature of drill top and drilling load (torque, feeding force). The relationship between the drilling-ability and microstructure is analyzed. Experimental results show that drilling load of two front brackets was roughly same. Compared with the HT250 tractor front bracket, the one of QT450 has a larger surface roughness in the drill hole and a higher temperature of drill top. This is mainly because QT450 has a weaker graphite segmentation effect to matrix and a higher ferrite content, there is certain difficulty in chip breaking and chip removal during drilling, which leads to the larger surface roughness in the drill hole of QT450. The smaller heat conductivity coefficient and severer friction between the drill and chip result in the higher temperature of drill top. Moreover, QT450 has a smaller cutting force and a larger friction force between the drill and chip. Under the comprehensive function of the two forces, QT450 has nearly the same drilling load as HT250.
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2018, Vol. 39 
