Research on the properties of foreign heavy-duty trucks with small-piece variable cross-section leaf spring materials

With the development of the automobile industry, weight reduction and energy saving have become the current development direction of heavy vehicles. Heavy-duty vehicles adopt few-piece variable-section leaf springs to reduce the weight of the spring assembly by 30-50%. Foreign heavy-duty vehicles have widely used few-piece variable-section leaf springs. For example, the VOLVOS35 car uses a structure of 2 front springs and 3 rear springs.
In order to understand the application status of foreign heavy-duty vehicles with small-piece variable-section leaf springs, the material properties and shot peening performance of VOLVOS35 variable-section leaf springs for vehicles were studied.

Tensile specimens with a diameter of 10mm and U-notch impact specimens with a diameter of 55mm×10mm×10mm were prepared on the VOLVOS35 vehicle leaf spring. The tensile test is carried out at room temperature, and the impact test is carried out at room temperature and low temperature (-40°C) respectively. At the same time, the hardness test of the VOLVOS35 vehicle leaf spring was carried out, and its hardness was 420-432HB. Microstructure analysis found that the metallographic structure is fine tempered sorbite with a grain size of 8.

In view of the development needs of leaf spring performance, the steel for leaf spring should have: high tensile strength, elastic limit and fatigue strength; suitable hardenability, the core of the leaf spring should obtain more than 80% martensite structure after quenching; High purity and suitable grain size, in addition, also require suitable shot peening performance.

The analysis results of VOLVOS35 vehicle leaf spring show that the material of the leaf spring is European traditional 50CrV4 spring steel, which is equivalent to my country’s CrMnV steel. The main elements C, Mn, and Cr of VOLVOS35 steel for leaf spring are controlled to the upper limit of the composition requirements, and an appropriate amount of V, Al, etc. are added to maximize the use of C, Mn, Cr and microalloying elements to improve steel performance The role of. VOLVOS35 leaf spring steel optimizes the ratio of C, Mn, and Cr to make the end hardenability of the steel reach the upper limit of 50CrV4 spring steel, and the hardenable thickness of the leaf spring reaches 35mm. A proper amount of C and Al precipitate carbon in the steel. , Nitride, precipitation strengthening of VOLVOS35 steel plate spring, and refine the grain of the steel, so that the grain size reaches 8 levels. After tempering and heat treatment, the matrix α solid solution (troostite) has a higher dislocation density, and there are a large number of dispersed and evenly distributed carbonitrides in the matrix, which meets the high tensile strength and Good toughness and plasticity requirements.

In order to adapt to the development of the long life of automobile leaf springs, the steel for leaf springs is required to have high purity. While reducing the content of impurity elements and controlling the total amount of inclusions, the shape should also be controlled to make it a low melting point and easy to deform inclusion Things. The analysis results of the VOLVOS35 leaf spring show that its O2 content is 15×10-6, Ti content is 27×10-6, alumina content is low, and there is no titanium oxide inclusions, indicating that the steel has high purity and high The fatigue strength and life span.