An Investigation On The Microstructural Evolution Of ER8C During Sliding Wear Process

The MRH-5A ring-block machine is used for dry pure sliding wear of ER8C steel and U71Mn steel.The microstructure evolution and wear properties of ER8C steel are analysized by optical microscope,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.And the formation mechanism of white etching layer?WEL?under dry pure sliding conditions is discussed.The results show that with the increase of cycles,wear loss of ER8C increases almost linearly,while wear loss of U71Mn increases dramatically at first and then kept stability essentially.With the enhancement of rotational speed and test force,wear loss of ER8C growths.The wear mechanism consist of abrasive wear,adhesive wear and fatigue wear.When the test force keeps constant,fatigue wear on ER8C gradually get worse with the increase of rotational speed and adhesive wear gradually reduced.Meanwhile,the specimen deformation layer thickness decreases.The worn surface at 450 r/min is mainly plastic diformation layer.When the rotating speed increases to 600 r/min,WEL distributes unevenly on surface and the thickness of WEL increases at 750 r/min.With the increase of test force on the condition that rotating speed gets constant,the primary wear mechanism turns to abrasive wear.The thickness of deformation layer decreases as opposite as the thickness of WEL.The hardness of deformation layer increased gradually from matrix to the surface.When the speed increases from 450 r/min to 600 r/min,the maximum hardness of deformation layer increases significantly.But when the speed increases from 600 r/min to750 r/min,the maximum hardness of deformation layer basically remained unchanged.WEL is featureless layer after etched by nitric acid alcohol with hardness of 900 HV_{0.0 1}.WEL is composed by nanocrystalline ferrite which is basicly equiaxed shape and nano-size caibides.The formation process of WEL is as follows:The plastic deformation of original pearlite lamellar and proeutectoid ferrite under the action of stress makes proeutectoid ferrite and pearlite parallel to the sliding direction gradually.With the increase of deformation,the interface between pearlite and proeutectoid ferrite and pearlite boundary disappear,cementite gradually breaks into pieces and ferrite changes to strips;With the further increase of deformation,cenmentite fragements and dissolives completely with not quite obvious directivity,and distribute around ferrite,which recrystallize to become equiaxed nano-grains.Meanwhile,WEL has formed.