The Study On Microstructures And Properties Of Large Size Grinding Ball With Remaining Heat From Forging For Quenching

In the production of large size grinding ball,remaining heat from forging for quenching has important practical significance in improving the properties of grinding ball,production efficiency and reduce production cost.In this paper,it simulated the temperature field and the average cooling rate of grinding ball made of GN-6A and GN-3A steel in different precooling time,different quenching temperatures,different temperatures of water,different time in the water.Then the optimal process of quenching with remaining heat from forging for quenching was obtained by analyzing the microstructure and mechanical properties of large-scale grinding ball.By the calculation of the temperature field of ?125 mm grinding ball made of GN-6A steel,it determined that the temperature of cooling water was 45°C,and the cooling time is the time until heart temperature reduced to 400°C.Experiment with that process quenching at 860°C showed that compared with the beginning forging at 950°C and 1050°C,the volume hardness increased to 59 HRC from 58 HRC,the impact energy increased 50%,the level of grain size of original austenite increased to 6.5 from 4.5.When the forging temperature began at 1050°C and the pre-cooling time was shortened to 30 s and 60 s,the volume hardness was higher than 59 HRC,the impact energy was higher than 12 J at the 1/2R of the grinding ball.Meanwhile,the matrix was mixed martensite,the original austenite grain was between 5 to 6,and the properties were highter than quenching at 860°C(pre-cooling 95 s).In the industrialized produce of ?125 mm grinding ball of GN-6A steel,the hardness at the surface was higher than 59 HRC,while the center was higher than 57 HRC,and the impact energy was between 13 J to 15 J at the 1/2R,when the temperature of finish forging at 920°C to 950°C and quenching at 860°C to 865°C,the temperature of finish forging at 951°C to 980°C and quenching at 890°C to 895°C,cooling 210 s with the water temperature of 45°C.By the calculation of the temperature field of ?125 mm and ?140 mm grinding ball made of GN-3A steel,it determined the temperature of cooling with water was 45°C,and the cooling time was the time until heart temperature reduced to 300°C.Experiment on ?125 mm grinding ball in the condition of beginning temperature at 950°C and 1050°C,and different pre-cooling time,the volume hardness was higher than 58 HRC,the impact energy was higher than 40 J at 1/2R of the grinding ball,the matrix was martensite.The pre-cooling time has little impact in the properties of grinding ball,but the quenching temperature has lots of impact.The appropriate process was quenching between 860°C to 880°C,and cooling time was 180 s with the water of 45°C.At the same time,experiment on ?140 mm grinding ball in the condition of beginning temperature was 950°C and 1050°C respectively,and different pre-cooling time,quenching at 840°C to 880°C,cooling for 210 s with the water of 45°C,the hardness at the surface was higher than 60 HRC.Besides,the hardness at the central was about 50 HRC,the impact energy was higher than 30 J at 1/2R of the grinding ball,and the matrix at the center has lots of non-martensite.Aboveall,it is importan to produce GN-3A and GN-6A grinding ball in remaining heat from forging for quenching.