Research On Heat Treatment Process And Microstructure Properties Of High Strength Spring Steel Wire For Automobile

Spring materials for shock absorption systems are mainly used in the automobile manufacturing industry,and their consumption accounts for more than 90%of the total output.At present,the highest strength level of suspension spring materials for shock absorption systems at home and abroad is 2000 MPa.The demand for lightweight development and energy saving and emission reduction of automobiles is becoming more and more urgent,and higher requirements are put forward for the strength and toughness of automobile springs.For this reason,it is necessary to develop higher-level high-strength suspension spring materials.At present,domestic research on suspension spring materials is mainly focused on materials such as 60Si2CrV and 55Si Cr,while there are few reports on the research on high-strength automotive spring steel 65Si2CrV.Therefore,the research results of this article will effectively fill the gaps in this part of the country and play a certain guiding role in actual production.This paper takes 65Si2CrV high-strength quenched and tempered spring steel wire as the research object,using X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),backscattered electron diffraction(EBSD),energy spectrum(EDS),etc.Characterize the structure evolution of 65Si2CrV spring steel wire under different heat treatment process parameters,and test the corresponding mechanical properties through Vickers hardness and tensile tests.The main work and results are reflected in:(1)The structure evolution law of 65Si2CrV during the austenitization process under different process parameters was studied.The size of the original austenite grains is calculated by the method of electrochemical hydrogen charging to observe the fracture.The results show that:the size of the original austenite grains gradually grows with the austenitization temperature and holding time;micro Vickers hardness With the extension of the holding time,it firstly drops,then rises sharply,then slowly rises to the apex,and finally drops;the best austenitization parameter is 940?for 5 min,at this time the original austenite grain size is8.59?m.(2)The Gleeble 3800 thermal simulation test machine was used to measure the static CCT curve of 65Si2CrV.The results show that only martensite transformation occurs when the 65Si2CrV cooling rate exceeds 10?/s during quenching;the temperature of the quenching medium rises from 0°C to 20°C,the retained austenite content increases from6.56%to 8.13%,and the dislocation density is 4.6-5.0 In the interval of×10¹⁵m^-2,the thickness of the martensite slab is increased from 100-150 nm to 200-300 nm.The best quenching medium temperature is 20?.Afterwards,by setting different tempering temperatures and tempering times,the results show that the tensile strength is reduced from the highest 2240 MPa at 400°C to 2136 MPa at 430°C,and the best tempering temperature for comprehensive strength and plasticity is 420°C;The tensile strength,yield strength and microhardness all decrease with the extension of holding time.The tempering time with the best comprehensive performance is 150 s-200 s.(3)Through the 65Si2CrV heat treatment production experiment,the influence of the quenching medium temperature on the structure and properties of 65Si2CrV was studied.The field experiment results show that the tensile strength is 2090 MPa when the quenching medium temperature is 50?,and the tensile strength reaches 2123 MPa when the quenching medium temperature is 20?;the calculation of the strength contribution to the quenching medium temperature of 20?shows that 65Si2CrV strengthens The mechanism is mainly dislocation strengthening and precipitation strengthening.Among them,the contribution of dislocation strengthening is 815 MPa,and the contribution of precipitation strengthening is887 MPa.