| Automobile leaf spring is one of the important parts of automobile suspension system.It plays a role in reducing and absorbing vibration in the process of automobile driving,which greatly affects the braking stability and safety of automobile when it runs at high speed and smoothly.With the continuous development of the national economy,the traffic is increasingly busy,the automobile market is booming,and the demand for automobile leaf spring is increasing.At present,the carbon content of spring steel is about 0.45 ~ 0.65%,which belongs to medium and high carbon steel.There is obvious decarburization problem in the process of heat treatment,which greatly affects the quality and reliability of automobile leaf spring.In recent years,the awareness of environmental protection is gradually awakened,energy conservation and emission reduction policies are gradually implemented,the traditional spring steel such as 60Si2 Mn,55Cr Mn A needs quenching and tempering production process,resulting in great production pollution,so the development and design of new energy-saving and green automobile leaf spring steel has become an urgent problem to be solved.In order to obtain high-performance automobile leaf spring,researchers at home and abroad have done a lot of work and achieved good research results,but the main research direction is still to add some alloy elements to improve the existing steel grades,and the quenching process is still needed.Bainitic steel can obtain better strength toughness ratio and better comprehensive properties under certain microstructure.Therefore,the development and design of bainitic steel for automobile leaf spring has become a new research direction and is of great significance.The material studied in this paper is a new type of bainite automobile leaf spring steel independently developed and designed by Xihua University.The steel was forged into automobile leaf springs with thickness of 30 mm,40mm and 45 mm respectively by forging process,and their microstructure and properties were studied.The results show that bainite structure can be obtained in air-cooled environment,and its structure is carbon free bainite;XRD and EDS test results show that the phase composition of three kinds of thickness bainite steel leaf spring is single-phase structure,the purity of steel is high,and there is no obvious impurity;three kinds of thickness bainite leaf spring have good mechanical properties,and the yield strength is as high as 1200 MPa,the tensile strength is as high as 1400 MPa,the yield strength ratio is as high as 0.84,the elongation and the reduction of area is 16% and 40% respectively,the impact strength is as high as 91.5J·cm-2 at room temperature,and the impact strength of 30 mm bainitic steel leaf spring is as high as 104.8 J·cm-2,with excellent strength toughness combination.Three kinds of bainitic steel leaf springs with different thickness were tempered for different time length to study the effect of tempering time on their microstructure and properties.The results show that the microstructure of three kinds of thickness bainitic steel leaf spring has no obvious transformation after tempering heat treatment,and it is still lath bainite and granular bainite,which indicates that the structure stability is good;XRD diffraction analysis shows that there is no carbide precipitation in the tempering process,and the phase composition is relatively stable,which indicates that it has good anti tempering stability;when tempering for 4h,the bainite is stable The steel leaf spring has the highest impact strength.Tempering treatment improves the tensile properties of the leaf spring,and the yield strength and tensile strength are slightly enhanced.The corrosion resistance of bainitic steel leaf spring was tested by means of immersion and polarization curves under simulated coastal environment.The coastal area is an important economic zone in China,and the transportation industry is developed.The results show that the bainite leaf spring has good corrosion resistance. |
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