Study On Precise Control Of Forging ?140mm B3 Steel Ball

The production technology of China's wear-resistant steel ball is backward,and the quality of the produced ball is poor and its service life is short,which greatly aggravates the consumption of mining industry.Therefore,the preparation of high-performance grinding balls has very important economic and social significance.This paper aims at the defects of cracks and excessive hardness gradients(?5 HRC)which occurred in the process of producing?140 mm B3 forging ball in a factory.The metallographic observation,SEM microscopic topography observation,raw material composition energy spectrum analysis,and mechanical property testing were applied to discuss and study on the causes of defects of trial-produced B3 steel balls.We studied the austenite transformation temperature,heating temperature,quenching temperature,cooling medium concentration,and cooling medium flow rate to analyze their effects on the microstructure and properties of the materials.The heat treatment process of B3 ball was optimized to produce high performance large diameter B3forging balls by using orthogonal test method.The results showed that B3 steel raw material organizations are pearlite and a small amount of ferrite,no ribbon organization,containing a small amount of holes and inclusions,but the size of inclusions in the normal range does not affect the use of steel.The surface structure of the trial-produced small-batch B3 forging balls consists mainly of acicular martensite and a small amount of ferrite.In addition to Martens in vitro,a certain amount of massive agglomerated tortoise and large feather-like babe are also present in the heart tissue.The macroscopic morphology of the crack mainly extends from the vertical surface to the center and ends near the center of the sphere,and the microscopic morphology expands along the grain boundary and the coarse bainite.The defect of cracks occurred at the process of martensitic transformation during the later quench cooling.The heat treatment process has a significant effect on the performance of the forged ball.Among them,cooling medium velocity and quenching temperature are the main reasons for cracks and uneven hardness.The crack defect ratio was low with uneven hardness when the quenching temperature was high and cooling medium velocity was fast.On the contrary,the crack defect ratio was high,but hardness was evenly.The final preparation process of?140 mm B3 forged ball optimized by orthogonal test method is as follows:blanking(?100×183 mm)—heating(1050°C,40 s)—750 kg air hammer forging forming(hemisphere anvil hammering 35-40times)—air cooling(along the raceway,3 min20 s)—quenching(810°C,fast water cooling)—effluent(120~150°C),stay for 5s—secondary cooling(2 min15 s)—effluent(70~90°C)—entry—tempering(180°C,10~20 h)—storage.Compared with the condition of trial-produced forged balls,the optimized B3 steel ball has no cracking but more uniform organization,and more fine needle martensite can be obtained.The hardness is high and the hardness gradient is small(the hardness of heart is?57 HRC,the hardness of surface?60 HRC,maximum hardness difference?3 HRC).The impact toughness is also good(impact toughness?27 J/cm~2).