The development of spring application technology puts forward higher requirements for materials. It mainly improves fatigue life and anti relaxation performance under high stress; Secondly, it is required to have corrosion resistance, non-magnetic, electrical conductivity, wear resistance and heat resistance according to different processes. Therefore, in addition to developing new types of spring materials, beneficial results have also been achieved in strictly controlling chemical composition, reducing non-metallic inclusions, improving surface quality and dimensional accuracy.
1. Development of alloy steel: Si Cr steel has been widely used in valve springs and suspension springs. In order to improve fatigue life and relaxation resistance, V and mo were added to Si Cr steel. At the same time, Si CR drawing steel wire has been developed, and its anti relaxation performance is better than that of Qin 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 2000mPa.
2. Development of stainless steel wire
1) The strength of austenitic stainless steel wire is better than that of ferritic structure, and its corrosion resistance is also better than that of martensitic structure. Therefore, its application scope is expanding continuously.
2) Low temperature wire drawing or low temperature nitriding wire drawing can improve the strength of steel wire. The structure of martensite is unstable when it is heated, and the hidden needle martensite can be formed by drawing in low temperature liquid nitrogen, which can obtain high strength in hot state. This kind of steel wire has been widely used in the United States and Japan, but it can only handle steel wire less than 1mm at present.
3) The precision spring in electronic equipment requires non-magnetic, and this kind of steel wire cannot generate hidden needle like martensite during drawing. For this purpose, elements such as N, Mn and Ni are added. To meet this demand, the United States developed aus205 (0.15c-17cr-1ni-15mn-0.3n) and Yus (0.17c-21cr-5ni-10mn-0.3n). As the content of Mn increases, cryptoacicular martensite will not be formed during processing. After solid solution treatment, the strength can reach 2000mPa, and the fatigue property is high, which is better than SUS304.
3. Improve material purity for high-strength materials, strictly control the inclusion and improve the purity to ensure its performance. For example, the oxygen content of valve spring material has reached 20 × 10 ¯ 6 development.
4. Improve the surface quality the surface quality of the material has a great influence on the fatigue performance. In order to ensure the surface quality, the material with special requirements shall be peeled to 0.1mm. Eddy current flaw detection shall be adopted for defects with depth of 0.5mm. For the uneven surface produced during wire drawing, electrolytic grinding can be used to reduce the surface roughness to RA = 6.5-3.4 μ m。
5. Under special circumstances, the development of galvanized steel wire requires not only spring characteristics, but also additional properties such as corrosion resistance and conductivity, which are mostly solved by electroplating process.
The corrosion resistance of some stainless steel wires and Piano wires is equivalent to that of zinc plating. If another layer of ZnAl (5%) alloy is plated, the corrosion resistance can be increased by about 3 times.
For stainless steel wire or piano wire with resistance performance requirements, the wire diameter less than 0.4mm can be plated with copper, and the wire diameter greater than 0.4mm can be plated with copper inside and stainless steel outside. General piano steel wire plating 5 μ M U.M thick can improve its conductivity.
Generally speaking, the processes (such as shot peening and surface nitriding) that can make the material surface hardened to form residual stress can improve the fatigue strength. At present, electroless Ni plating is being studied. By heating (300-500 ℃), 7% of P can be precipitated as PNI, and the Vickers hardness can be increased to HV500. After shot peening, if Ni plating is heated below 300 ℃, the hardness can also be increased by 10%.
6. Development of shape memory alloy the unidirectional shape memory alloy with good performance of 50ti-50ni has a promising application in spring. The spring made of shape memory alloy can expand and contract under the action of temperature. It is mainly used in the control system of constant temperature, constant load and constant deformation. Since the actuator is pushed by the expansion and contraction of the spring, the working stress of the spring changes greatly.
7. Application of ceramics ceramics have high elastic modulus and low breaking strength, and are suitable for places with little change. At present, ceramics with good heat resistance, wear resistance and insulation are being developed; Superplastic zinc alloy (SPZ) is applied, which has high strength at normal temperature. In addition, there is high-strength silicon nitride, which can withstand high temperature, up to 1000 ℃. However, ceramic springs are not suitable for working under impact loads.
8. Application of fiber reinforced plastics in springs glass fiber reinforced plastics (GFRP) plate springs have been widely used in Britain, the United States and Japan. In addition to being used for horizontal suspension, they can also be used for vertical suspension of special light vehicles, such as racing cars. At present, carbon fiber reinforced plastic (CFRP) suspension spring has been successfully developed, which is 20% lighter than metal plate spring.
