Disparity and Development Trend of Spring Steel at Home and Abroad

China's spring steel was referenced to the former Soviet Union's spring steel grade in the 1950s. Its main body is Si-Mn series spring steel. Due to the low hardenability of Si-Mn spring steel, it cannot meet the industrial development. In the future, high hardenability Cr-Mn-based spring steels were added. At present, there are 15 kinds of spring steel used in production. The main differences with foreign countries are as follows: 1. Steelmaking process: single or single refining of electric furnace, 80% refining ratio, vacuum degassing; while foreign refining ratio is 100%, more vacuum degassing treatment is used 2. Continuous casting process: continuous casting ratio accounts for about 80%; and foreign 100% continuous casting 3. Rolling process: horizontal two types of fire-based materials, finished product rate of 84%, generally no inspection; and foreign continuous rolled finished product rate 95% Most of the finished products are inspected for flaw detection. 4. Purity: Normally no inclusions are checked and no oxygen content control is required. For non-metallic inclusions tested abroad, the oxygen content is required to be 20 mg/L or less. Rolling material size: round bar reaches GB/T 702-2004 II group precision, flat bar meets GB/T 1222-2007; while foreign round bar is equivalent to GB/T 702-2004I group accuracy, flat bar is narrower than national standard tolerance band 50% 6 Surface quality: There are many surface cracks and serious decarburization; foreign surfaces have no missing filling. Domestic enterprises should improve from the above six aspects and pay attention to the development trend of international spring steel. The development trend of spring steel at home and abroad is: 1. Spring steel develops in the direction of high strength. The following two approaches are mainly used: 1) Research and development of new steel types. On the one hand, by optimizing the content of alloy elements in the existing spring steel and adding micro-alloying elements, on the other hand, the experience of ultra-high-strength steels for aviation is used to reduce the carbon content and add V and Nb. 2) Research and development of new thermal processing and heat treatment processes. Under the condition that the existing steel types are basically unchanged, ultra-high strength can be achieved through the research and development of processes such as deformation heat treatment, induction heat treatment, and on-line heat treatment. 2. Spring steel develops in the direction of high resilience. The main factor that determines the allowable stress of the spring is the anti-relief force. Therefore, increasing the anti-reducing force of the spring has always been the focus of high-strength spring steel research and development. In order to increase the detonation resistance, the appropriate chemical composition should be selected, together with the appropriate thermal processing and heat treatment, in order to obtain the ideal microstructure, grain size, second phase point and hardness. Si is one of the most effective elements in the alloying element to increase resilience, and its role is second only to C. Therefore, early spring steels with excellent ballistic resistance (design stress 1 000 to 1 100 M Pa) generally have higher silicon contents, such as SU P7 and SU P12. However, the Si content of such steels as SU P7 and SA E9260 has reached the highest value, and it is difficult to increase the resilience by increasing the silicon content. Must find new ways. One of the important ways is to use precipitation strengthening and grain refining strengthening techniques, such as the addition of microalloying elements V and Nb. 3. The development of spring steel to high purity The domestic and foreign steel plants and automobile plants have put forward high requirements for the oxygen content of spring steel. For example, the Swedish SKF standard requires the oxygen content of spring steel to be less than 15 mg/L, and the maximum size of inclusions is less than 15μm. The spring steel production enterprises should start from the two aspects of smelting process and continuous casting process, and strengthen measures such as strengthening raw material management, reasonable ingredients, concentrating materials into the furnace, strengthening smelting operations, optimizing smelting processes, improving deoxidation and slagging systems, and strengthening furnace refining and refining measures. , Produce high purity spring steel.