Automobile spring material and its development
(1) Development of spring steel production process in order to improve the quality of spring steel, industrial developed countries have generally adopted the external refining technology, continuous casting process, new rolling and on-line automatic detection and control equipment.
In order to ensure the chemical composition of steel and reduce the content of gas and various non-metallic inclusions, large capacity electric furnace or converter smelting is adopted, and ladle refining is adopted outside the furnace to reduce the oxygen content (mass fraction) to (0.0021 ~ 0.0010)% to produce ultra pure steel, which greatly improves the design and working stress of the spring.
Continuous casting technology has been widely used in the production of spring steel. Continuous casting can reduce the segregation of steel, reduce secondary oxidation, improve surface decarburization, and make the structure and properties stable and uniform through electromagnetic stirring, low-temperature casting and other technologies.
By adopting the split type full continuous rolling mill, the dimensional accuracy and surface quality can be improved, and the microstructure of the steel along the length can be made uniform. In the rolling process, in order to ensure the surface quality of products, online automatic detection and control are adopted. In order to adapt to the production of variable cross-section spring flat steel, a new austenitic rolling forming process is developed, that is, the steel is heated to austenitic zone first, then quenched to metastable austenitic zone for plastic processing and quenching treatment. This process can improve the strength of the steel without reducing the plasticity. In addition, the properties of spring steel can be improved by on-line heat treatment and surface hardening treatment after rolling.
(2) The main role of alloying elements in the development of alloy steel is to improve mechanical properties, improve process properties and give some special properties. SiCr steel has been widely used in valve springs and suspension springs. Si is an alloy element with good stress relaxation resistance. Adding V and Mo to SiCr steel to form sicrv and sicrmo steel can improve fatigue life and relaxation resistance. At the same time, SiCr drawing steel wire has better anti relaxation performance than Qin steel wire and important carbon spring steel wire when working at high temperature. With the high-speed miniaturization of the engine, Ti alloy with good anti flutter performance, light weight and small elastic modulus has been widely used, and its strength can reach 2000 MPa.
(3) Development of low carbon austenitic steel the low carbon austenitic steel 38simnb is a new type of high-performance spring steel independently developed by China. The 38SiMnVBE developed on this basis has more advantages, such as high strength and toughness, high hardenability, high application and high performance ratio. After ultrafine grain controlled rolling, its tensile strength = (2030 ~ 2140) MPa, yield strength = (900 ~ 2010) MPa, elongation = (12 ~ 15)%, and area shrinkage = (48 ~ 55)%. It provides a high-performance material for a few variable section panel springs.
