The 2000MPa high-stress plate spring steel jointly developed by the rolling technology and continuous rolling R&D team of CQHY Automotive Suspension Technology Group and DBDX Special Steel Technology Group has successfully passed various performance tests, and its performance indicators have reached foreign advanced leaf springs. At the end of October 2020, the road test of passenger car models was successfully completed, and the test results all met user requirements, providing technical support for Chinese bus companies to upgrade high-stress leaf spring products.
Leaf springs, also known as leaf springs, are often used in suspension systems of various commercial vehicles and engineering vehicles because of their simple structure, easy maintenance and low cost. When the vehicle is running, the leaf spring bears the load impact of the wheel on the frame, reduces the severe vibration of the vehicle body, and maintains the stability of the vehicle and its adaptability to different road conditions. During the running of the vehicle, the spring member for vehicle suspension repeatedly bears the stress load, therefore, the fatigue durability of the leaf spring is extremely important. At the same time, in order to improve the comfort of commercial vehicles, it is usually desirable to reduce the stiffness of the leaf spring, which requires the leaf spring to have a high stress load bearing capacity. In addition, the lightweight requirements of commercial vehicles also require thinning of the thickness of each piece of the leaf spring member to achieve the effect of reducing the weight of the suspension system, and the stress level of the leaf spring is further improved. In summary, the design stress level of leaf springs for some models is as high as 1300MPa. Therefore, it is necessary to develop the next generation of spring steel materials for high-stress leaf springs and the corresponding leaf spring manufacturing technology.
Commonly used spring flat steel products now mainly include 60Si2Mn, 50CrV, 52CrMnMoV, etc. The yield strength is mainly 1200~1500MPa, the tensile strength is 1300~1800MPa, and the design of medium and high carbon alloys leads to poor toughness of the material, which can no longer meet the requirements of automobiles. The demand for high-stress plate spring steel.
Based on the research and development of 2000MPa hot stamping steel, DBDX uses vanadium microalloying design combined with unique heat treatment process, and uses nano-level vanadium carbide precipitation to greatly improve the toughness of spring steel martensite matrix, and develops a new generation of 2000MPa high-stress plate Spring steel. Through product sampling analysis, it can be seen that the yield strength of the developed material is over 1700MPa, the tensile strength is over 1950MPa, and the impact energy of the U-shaped specimen at -40°C is greater than 40J, showing an excellent combination of strength and toughness. Compared with the existing leaf spring products, the strength can be increased by more than 20% and the toughness can be increased by more than 80%. At the same time, the production cost of the parts has hardly increased. In the fatigue test of the bench, the leaf spring using the 2000MPa grade spring steel can maintain 250,000 times without breaking under the load of the highest stress level of 1300MPa, showing excellent fatigue service performance.
Typical tensile curve of 2000MPa class leaf spring
Nano-precipitated carbides in 2000MPa class leaf spring
The product will provide solutions for the improvement of driving comfort and weight reduction of commercial vehicles in the future.