Research On Precipitation And Solid Solution Behavior Of Ti Inclusions In Bearing Steel

Titanium inclusion in steel is a sharp,angular and brittle inclusion,its edges easily scratch the steel as a source of cracks.These may impact the fatigue life of bearing steel greatly.In order to improve the quality of bearing steel,make further research on titanium in bearing steel,figure out the condition and reason of the formation of titanium and use effective means to reduce the size and number of titanium inclusions are necessary.The calculation of elementals segregation in steel proves the possibility of precipitating titanium inclusions during the solidification of the bearing steel.Through theoretical analysis of precipitation of titanium in bearing steel,thermodynamics of solid solution and kinetics of growth process,the precipitation causes and rules of titanium inclusions in bearing steel have been analyzed.Bearing steels with high content of nitrogen and titanium have been made.After the heat treatment of samples,the size changes of inclusions have been analyzed and that can reflect the law of decomposition and solution of titanium inclusions.The morphology and composition of titanium inclusions have been detected through scanning electron microscope.The results show that:?1?With the existence of elements segregation in steel during solidification,even the contents of Ti and N can be controlled at a low level,titanium inclusions will still precipitate at the end of the solidification.?2?The change of cooling rate has little effect on the segregation of elements but it affects the final size of titanium inclusions.?3?Increasing the nitrogen content in the steel leads to earlier precipitation of titanium inclusions and increases the size of titanium inclusions.The increase of titanium content affects the precipitation of titanium inclusion,but hardly influences the final size.?4?With the increasing of nitrogen and titanium,the temperature that the Ti(C_x N _1-x)inclusions precipitate improves.The change of nitrogen influences the value of x.?5?The heating temperature and holding time have a great influence on the solution behavior of titanium inclusion.Increasing the temperature of heat treatment and extending the holding time appropriately...