Study On Bainitic And Martensitic Wear-risisting Liners For Different Work And Digging Conditions

Work and digging conditions for the wear-risisting liner used in Investment Caofeidian port coal conveying system is a complicated system engineering.The service life of wear-risisting liner not only depends on the plate location,but also related to the materials transported.Therefore,studding on the impact and wear resistance of the liners in every location linings would lead to greatly improve for the service life.In this study,the liner containing excellent comprehensive mechanical properties is obtained by designed new material composition and best heat treatment process,which could match the use of industrial conditions.Seven kinds of bainitic and martensitic steels has been designed,and the microstructure,mechanical property and wear resistance has been studied through the different heat treatment processes.Results show that the casting liner exhibits the largest impact toughness when tapping temperature is 1700?,which is the best tapping temperature.Compared with other casting temperature,casting liner at the 1500? casting exhibits similar hardness and impact energy,while shrinkage and segregation is relatively small.Therefore,pouring temperature selects 1500?.In order to decrease segregation,many methods are used,as following: reducing the size of alloy element ore;increasing uniformity of molten steel;increasing cooling rate;adding a small amount of rare earths inoculant,and so on.Rare earth could purify molten steel,improve the cast microstructure,improve the inclusion shape,and effect on alloying,leading to profound improvements in segregation phenomenon.The experimental results show that with the increase of carbon content in the casting bainitic and martensitic liner,hardness increase and impact toughness decrease.Mo can improve the hardness and impact toughness obviously.When the content of C is more than 0.49%,there is a small change in the hardness even adding alloy elements and improve the content of C in the steel.In the air cooling bainitic and martensitic steel,the content of Mn and Si is more than 2%,and containing Mo and Cr elements.When the content of C is between 0.40% and 0.44%,hardness of air cooling liner is more than 50 HRC.When the content of C is between 0.45% and 0.50%,hardness of air cooling liner is more than 55 HRC.The experimental results show that casting and forging(rolling)bainitic and martensitc liners in the same composition and heat treatment process exhibits the same hardness,but the latter exhibit higher toughness and higher wear resistance,which is because microstructure after forging(rolling)is finer,high density,and less defect.Under the low impact absorbing energy,the wear mechanism is mainly cutting mechanism.And under the high impact absorbing energy,the main wear mechanism is plastic deformation and brittle fracture.Compared to the martensitic microstructure,bainitic microstructure exhibits higher plasticity and toughness,and leads to higher wear resistance under the high impact energy.The poor toughness in martensitic microstructure is easy to brittle fracture,and leads to lower wear resistance under the high impact absorbing energy.