| Torsion bar springs are a key component of modern automotive suspensions.They are made of spring steels and are fixed to the frame at one end and to the suspension at the other.When the vehicle is bumpy,torsion bar springs can absorb the impact energy and play an important role in the smooth operation of the car.With the development of the automotive industry,drivers are demanding more and more smoothness in the driving process of their vehicles.The strength of torsion bar springs needs to be further improved in order to ensure the life of the car and reduce the wear and tear of the car parts.The strength of torsion bar springs is closely related to the strength and toughness of the spring steels.In order to obtain torsion bar springs with excellent performance,the spring steels used should have higher strength and toughness.In this paper,Nb and V are used to micro-alloy torsion bar spring steels and combined with heat treatment process.The microstructure,precipitation and other characteristics of torsion bar spring steels after different microalloying treatments are further analyzed to improve the comprehensive mechanical properties of torsion bar spring steels.The article comparatively investigates the relationship between the properties of Cr-Ni-Mo-V system experimental steels and the three experimental steels with Nb,V and V and C.The experimental steels wrought austenite grain,heat treated martensite lath size,precipitation phase and mechanical properties were analyzed.The discussion investigates the strengthening mechanism of microalloying in the experimental steels,and the main results obtained are as follows:(1)Through the study of the heat treatment process of the experimental steels,it was found that the quenching temperature had a significant effect on both the microstructure and mechanical properties of the base experimental steels.In the quenching temperature range of 840～900℃,the base experimental steels martensite slats at 880℃ quenching is the smallest,the precipitation phase size distribution is more ideal,the strength of 2000 MPa or more,room temperature impact performance of 39 J,relatively better overall performance.Therefore,880℃ can be considered a suitable quenching temperature for this type of torsion bar spring steels.(2)After the addition of 0.035 wt.%Nb,the austenite grains in the forged state of the experimental steels were significantly refined,and the size distribution of the precipitated phases in the heat treatment state was optimized,but the martensitic laths were less refined.The result resulted in a slight decrease in the strength of the experimental steels and some improvement in the impact properties,with the room temperature impact work increasing from 39 J to 44 J.(3)After the addition of 0.36 wt.%V,the refinement of austenite grain and martensite lath size in the forged state of the experimental steels was obvious,and the content of the precipitated phase increased,and a large number of precipitated phases around 15～35 nm were observed.As a result,the tensile strength decreased while the yield strength increased and good impact properties were maintained.Since V depletes the solid solution C content of the steels,further increasing the C content by 0.03 wt%with the addition of V allowed the experimental steels to reach tensile strengths above the 2050 MPa level while maintaining good toughness. |
