Development of spring materials
With the development of spring application technology, higher requirements are put forward for spring materials. It mainly focuses on improving fatigue life and anti-relaxation performance under high stress; Secondly, according to different applications, it is required to have corrosion resistance, non-magnetic, conductivity, abrasion resistance, heat resistance, etc. For this reason, in addition to developing new types of spring materials, beneficial results have been obtained in strict control of chemical composition, reduction of non-metallic inclusions, improvement of surface quality and dimensional accuracy, etc.
(1) Development of Production Technology of Spring Steel
In order to improve the quality of spring steel, refining technology outside the furnace, continuous casting process, new rolling and online automatic detection and control equipment have been widely used in industrially developed countries.
In order to ensure the chemical composition of steel and reduce the content of gas and various non-metal inclusion, the large-capacity electric furnace or converter smelting is adopted, and the ex-furnace ladle refining is adopted, so as to reduce the oxygen content (mass fraction) to (0.0021~00010)%, and produce ultra-clean steel, thus greatly improving the design and working stress of the spring.
Continuous casting process has been widely used in spring steel production. Continuous casting can reduce segregation of steel, reduce secondary oxidation and improve surface decarbonization through electromagnetic stirring, low-temperature coupling and other technologies, so as to stabilize and uniform structure and performance.
Split-type full continuous rolling mill is adopted, which can improve the dimensional accuracy and surface quality, and at the same time, the microstructure of the steel along the length can be uniform. In order to ensure the surface quality of the product during the rolling process, online automatic detection and control are adopted. In order to adapt to the production of variable cross-section spring flat steel, a new process of austenitic rolling forming is developed, that is, the steel is heated to the austenitic zone and then quenched to the metastable austenitic zone for plastic processing and quenching. This process allows steel to increase strength without reducing plasticity. In addition, the performance of spring steel is improved by online heat treatment and surface hardening after rolling.
(2) Development of Alloy Steel
The main role of alloy elements is to improve mechanical properties, improve process properties and give some special properties. SiCr steel has been widely used for valve spring and suspension spring. Si is the best alloy element for stress relaxation resistance. Adding V and Mo to SiCr steel to form SiCV and SiCrMo steel can improve fatigue life and anti-relaxation performance. Most valves fail loosely. Meanwhile, the anti-loose performance of SiCr drawn steel wire under high temperature is better than that of piano steel wire and important carbon elastic yellow steel wire. With the rapid miniaturization of engine, the alloy with good anti-flutter performance, light mass and small elastic modulus has been widely used, and its strength can reach 2000MPa.
(3) Development of Low Carbon Austenitic Steel
Low-carbon austenitic steel 38SiMnB is a new type of high performance spring steel independently developed in China. Based on this, the 38SiMnVBE developed on this basis has more advantages, and has high strength toughness, high hardenability, high applicability and high performance ratio. The tensile strength σb=1030~2140MP, yield strength σ0.2=900-2010MP, elongation δ5,=12%~15%, and surface shrinkage Ψ =48%~55% after ultra-fine grain control rolling. High performance material for less variable panel springs
(4) Development of stainless steel
China is a country producing stainless steel. With the development of stainless steel production, a lot of varieties have been developed naturally. At present, more than 50 varieties have been developed, basically meeting the needs of domestic production and development. A brief description of some new varieties currently developed.
4.1 Preliminary formation of austenitic stainless steel system.
In order to eliminate grain boundary corrosion fatigue of stainless steel caused by carbon, low-carbon austenitic stainless steel 0Cr18Ni9 and 00Cr17Ni2Mo2 have been developed. In order to improve its special properties, such elements as Cu, Ti, Nb, Mn, Cr, Si and N.
4.2 Development of ammonia-containing stainless steel.
Results have been obtained in replacing carbon with nitrogen in stainless steel. N and C have many common properties in austenitic stainless steels. N-stable austenite is more effective than Ni and is comparable to C. The binding of N and Mn can replace the expensive Ni.
N is also one of the most effective solid solution strengthening elements in austenite. The affinity between N and Cr is smaller than that between C and Cr, and the precipitation of Cr2N is rarely seen in austenitic steel. Therefore, N can improve the strength of stainless steel without reducing the corrosion resistance
4.3 Development of ultra-strong ferrite stainless steel.
Ferritic stainless steel has good corrosion resistance and oxidation resistance, and its stress corrosion resistance is superior to austenitic stainless steel. Cheaper than austenitic stainless steel. However, poor weldability and large brittleness tendency exist, and production and use are limited. The weldability and brittleness of ferritic steel can be improved by reducing carbon and nitrogen content in steel, adding stabilizing elements such as Ti, Nb, Zr and Ta, and adding weld metal toughening elements such as Cu, Al and V.
4.4 Development of super austenitic steel.
Superaustenitic steels are austenitic steels with significantly higher Cr, Mo, and N contents than conventional stainless steels. The more well-known is the steel with 6% Mo (245SM0). This kind of steel has very good local corrosion resistance. It has good pitting corrosion resistance (PI ≥ 40) and good stress corrosion resistance under the conditions of seawater, air inflation, gap and low velocity scouring. It is an alternative material of Ni base alloy and titanium alloy.
4.5 Development of ultramartensitic stainless steel.
The traditional martensitic stainless steels 2Cr13, 3Cr13, 4Cr13 and 1Cr17Ni2 lack sufficient ductility, and are very sensitive to stress in the process of cold forging deformation, so it is difficult to form by cold working. In addition, the weldability of steel is poor, and the application scope is limited. In order to overcome the above shortcomings of martensitic steel, an effective way has been found recently, which is to develop a new series of alloy steel – ultramartensitic steel by reducing the content of C and Ti in the steel and increasing the content of Ni. This kind of steel has high tensile strength, good ductility and improved welding performance, so ultra-martensitic steel is also known as soft martensitic steel or weldable martensitic steel.
(5) Development of Spring Wire
With more than 100 years of development, the spring steel wire has undergone lead quenching, oil quenching and induction heating quenching. In addition, the process technology and equipment are constantly innovated and perfected, and the variety and quality are constantly updated. The induction heating quenching and tempering treatment process of spring steel wire for valve has been developed recently. The test proves that the plasticity, shear, anti-relaxation, fracture toughness, delayed fracture resistance and fatigue life of the steel wire are greatly improved compared with the oil quenching and tempering steel wire due to short induction heating time, fine fire structure of the trousers and almost film carbon layer on the surface of the aluminum wire.
Another kind of ultra-fine grain deformation heat treatment steel wire has been applied in the field. Ultrafine grain deformation treatment is a composite strengthening and toughening process combining ultra-fine structure and deformation heat treatment. It can not only improve the mechanical property of steel wire, but also improve the surface quality of steel wire. The surface quality of the material has a great influence on the lean working performance. In order to ensure the surface quality, the materials with special requirements shall be subject to the stripping process, and the surface layer shall be removed by 0,1mm. Eddy current inspection is adopted for defects with depth of 0.5mm. Electrolytic grinding can be used to reduce the surface roughness to Ra=(6.5~3,4) μM.
(6) Development of Stainless Steel Wire
In recent years, the production of stainless spring steel wire in foreign countries has developed rapidly. The varieties with increased domestic demand are 1Cr18Ni9 and 0Cr17Ni7Al.
The advanced steel wire production process features that the wire rod is first stripped to remove the defects caused by hot working on the surface. Except for the first solution treatment, acid cleaning is required, and the whole cold working process is kept bright.
With the development of the process, the production process of stainless steel wire is further simplified, and the quality control of some original metal products industry is simplified into the requirements for the quality of wire rod. Following the coarse wire drawing machine, the surface coating and residual lubricating film shall be removed by wiping with a cleaning ball and washing with water. Before bright heat treatment, electrolytic pickling, alkali neutralization, water washing and drying devices are equipped to completely remove the oil stain on the steel wire surface and improve the surface quality.
(7) Development of Shape Memory Alloys
At present, 50Ti and 50Ni are the most promising unidirectional shape memory alloys for springs. The spring made of shape memory alloy is flexible under the action of temperature. It is mainly used in the control system of constant temperature, constant load and constant deformation. As the actuator is pushed by the spring, the working stress of the spring changes greatly.
(8) Application of Ceramics
Ceramic has high elastic modulus and low breaking strength, which is applicable to the place with little deformation. At present, ceramics with heat resistance, wear resistance and good insulation are under development, and super plastic zinc alloy (SPZ) is applied, which has high strength at room temperature. In addition, there is also high strength silicon nitride, which can withstand high temperature up to 1000 ℃. However, ceramic springs are not suitable for operation under impact loads
(9) Application of FRP in Springs
Glass fibre reinforced plastic (GFRP) leaf springs have been widely used in countries such as the UK, the US and Japan, in addition to lateral suspensions, they can also be used for special light vehicles such as longitudinal suspensions for racing cars. Recently, the carbon fiber reinforced plastic (CFRP) suspension spring has been successfully developed, which is 20% lighter than the metal plate spring.
Overall, the material development of springs is very rapid. As a spring and Wire Bending manufacturer, we welcome customers to customize springs of various materials.
