Experimental Study On Surface Wear Of Steels On Multi Working Conditions

This thesis focuses on the wear performances of GCr15 steel under impact load and opposite-sliding conditions. The main contents are as followed.Firstly, on a self-made test rig for small load, the influence of impact load on the wear performance of GCr15 steel by using PAO4 and PB450 lubricants are explored. The results show that inside the wear dent using low viscosity PAO4, micro scratches and plastic deformation are main damage forms while by using PB450 with a higher viscosity, material accumulation and plastic deformation dominate inside the dent.Secondly, on the small load test rig, the impact wear performance of GCr15 bearing steel is investigated by using PAO4 lubricant, seawater and PAO4 mixed with seawater by different ratios. It is found that by using PAO4, micro pits spread over the dent. However, briny corrosive wear plays a major role in seawater lubrication.Then, the impact wear behavior by using PAO4 lubricant, seawater and PAO4 mixed with seawater by different ratios for DLC-coated GCr15 steel is revealed. Using both PAO4 and seawater as lubricants, the number of micro cracks in the surface dents is increased by impact repetition. At higher impact times, the micro cracks are connected into micro dents, showing the feature of fatigue pitting. However, by using PAO4 mixed with seawater by different ratios, the impact damages the metal surface by bulk spalling and new surface substrate is exposed. Or it is shown that the metal is seriously corroded: micro cracks occur in the surface and it is featured by corrosive wear.Furthermore, the impact wear behaviors of DLC-coated GCr15 steel and titanized GCr15 steel lubricated by seawater and PAO4 lubricant are compared. It is demonstrated that the titanized steel GCr15 has a better anti-wear resistance in briny lubrication. The DLC-coated GCr15 steel shows better performance by using PAO4.At last, the anti-wear performance of heat-treated GCr15 steel in dry contact zero entrainment condition is studied. Under the zero entrainment condition, severe stripping and cracks take place in the metal surface. A heat treatment improves the wear resistance of the metal, but does not change the wear mechanism.