Research On New Heat-Treatment Technology And Failure Mechanism Of Cadi Grinding Ball

Carbidic austempered ductile iron,so-called CADI,is a new kind of wear resistant material that derived from ADI in recent years.It has a good application and prospect in Metallugical and Mine Industries.This work focuses on the research of new-heat treatment technology and failure mechanism of CADI grinding ball. It mainly includes: 1) Research on cooling capacity of salt-bath quenching medium; 2) Determination of the heat-transfer coefficient between the CADI thermal probe and the salt; 3) Experimental investigation of the new heat-treatment technology on CADI grinding ball; 4) Stress numerical simulation of CADI grinding ball during the falling sphere test;5) Research on failure mechanism of CADI grinding ball.The result showed: 1) In the test range(0~2%),as water in the salt-bath increased,the cooling capacity of the salt was intensified at the same temperature ; In the test range(250℃~350℃),the cooling capacity of the salt weakened at the same temperature as the austempering temperature enhanced; 2) The cooling curves of the quenching medium can not display the surface information of the thermal probe,but it has special uses; 3) The heat-transfer coefficient between the CADI thermal probe and the salt was determined under the one-dimensional heat transfer model by ANSYS program and the result was reliable; 4) The temperature field of the CADI grinding ball during the austempering was simulated by ANSYS program and the necessary time for the balance of the temperature field was derived; 5) In the test range(4min~150min),as the salt-bath austempering time increased,the hardenability of the CADI grinding ball enhanced while the hardness and impact toughness of the ball showed the same trend;6)In the new heat-treatment test,the mechanical properties of theφ100mm CADI grinding ball with the salt-bath austempering time of 480s were: AVH 54.1HRC, impact toughness 8.5J/cm2. It can be inferred that the new heat-treatment technic reached the level of the austempering technic excluding the impact of experimental error. 7) In the test range(1%~3%), as water in the salt-bath increased, the hardness at different depth of the grinding ball enhanced while the impact toughness of the ball decreased; 8) During the single drop in the falling sphere, the peak value of shear stress appeared in the area slightly deviated from the center of the contact interface while the maximum of equivalent stress just at the center of the contact interface.The peak of residual equivalent stress and residual shear stress both appeared in the neighboring extrusion zone of collision.9) The existence of slag in the subsurface of the ball was the real reason that caused the failure of the grinding ball in the ball mill.According to the research, it is practical to replace the austempering technology with the new technique of"salt-bath and electrical resistance furnace quenching", and the labour productivity was enhanced significantly while guaranteeing the heat-treatment quality.The auther believed that surface spalling failure of the CADI grinding ball resulted from the fatigue damage of the material that caused by the accumulation of the residual stress,stress-induced martensitic transformation,etc.At the same time, material and metallurgical quality really had effect on the spalling failure of the grinding ball.The existence of slag in the subsurface of the ball was the real reason that caused the spalling and the roundless failure of the CADI grinding ball.