Development Of The Suspension Swing ARM Casting Steel For Heavy-duty Car

As an important bearing and transmitting component,the suspension system of heavy vehicle has significant influence on it's driving reliability and riding comfort.At present,forging molding method also is the main forming process for the suspension system components.To reduce manufacturing costs of the suspension swing arm parts,the possibility of producing these parts through casting technique is explored in this study.Firstly,on the basis of analyzing the components' working conditions and performance needs,a new type of bainitic steel which called ZG20CrMnSiNi2Mo is designed.Furthermore,the effects of different heat treatment processes on microstructures and properties of the materials are studied.Results show that the microstructures are mainly composed of granular bainites by using different normalizing processes.Under the experimental conditions,the martensite and austenite islands(M-A islands)range from massive structures to strip structures and the particals become finer with the increasing of normalizing temperature or normalizing time.With the increasing of normalizing temperature,the tensile strength is decreased,the hardness firstly is increased and then decreased.And the impacting toughness of materials is increased with the increasing of normalizing temperature.With the normalizing time increasing,the tensile strength and hardness of the materials is gradually decreased,but the impacting toughness is slightly increased.The excellent combined mechanical properties can be obtained when the normalizing heat treatment processes are 960?×60-180 min.The microstructures of different tempering heat treatment processes are composed of ferritic phases and austenite phases.When the tempering temperature increasing from 200 ? to 700?,the amount of retained austenites are decreased and the number of M-A islands become more.The microstuctures range from strip structures to granular or massive structures with the increasing of tempering temperature,their distribution become very dispersive but be limited to the same direction.When the tempering time increasing from 0.5h to 6h,the tensile strength and hardness is slowly decreased,the microstuctures of materials have the same trend.And the impacting toughness is firstly decreased then increased.When the tempering heat treatment processes are 200?×120 min,the excellent comprehensive properties of experimental materials can be obtained.The microstructures of the specimens are strip bainites by the process of Air-Cooling and Window-Cooling after austeniting process.The structures or microstructures of Oil-Cooling and Water-Cooling processes are consisted of strip martensites and residuary austenites.Moreover,the martensite laths taper off,the residuary austenites are distributed between martensites laths and laths.Comparing with Air-Cooling process,the residuary austenite contents of Water-Cooling are enormous.The effects of different complex heat treatment processes on microstructures and properties are studied.The results show that the microstructures become finer by operating on some preparation-heat-treatment processes such as high tempering temperature heat treatment process,quenching and annealing heat treatment process before normalization or by using ultra-high temperature normalization,which could improve toughness and eliminate the genetic of microstructures.For the present materials the best comprehensive mechanical properties can be obtained and the microstructures are mainly contained bainites and residuary austenites when the isothermal quenching temperature is 360?.Fixed isothermal temperature 360?,the contents of retained austenites are decreased with the increasing of isothermal quenching time.And the strength,hardness,impacting energy of the experimental materials have downward trend.The morphology fractures of the different isothermal quenching time belong to brittle fractures,their forms are mainly cleavage and quasi-cleavage.The casting process of heavy automobile suspension swing arm is designed and improved,the filling process and solidification process of lost-foam casting are simulated by ProE and AnyCasting softwares.The results show that both products can obtain qualified castings by adopting top pouring system and local adding cold iron methods.