Ultra-high strength fasteners can reduce weight and increase installation space by reducing their own size under the same clamping force, so that the function and volume of the connected parts can be optimized, so that the equipment can achieve the purpose of overall weight reduction and performance optimization.
    For example, the total weight of fasteners used in a modern aircraft can be 5-6% of the total weight of the aircraft, while a medium-sized aircraft can have 2-3 million fasteners of various types. In terms of aircraft weight reduction alone, there is a huge market demand for ultra-high strength fasteners.


 

    According to the public data, the highest fastener strength of the dominant enterprises abroad has reached 17.8. According to the international development situation, China's 973 project has developed grade 13.9-15.9 fastener materials and fasteners.
    On November 28, 2021, by the materials department of Shanghai university, led by professor Dong Han high-performance team, hebei iron and steel materials Long Fengshan casting industry co., LTD., seven fung seiko technology co., LTD., zhoushan 7412 factory, jiangsu institute of metallurgical technology, Shanghai university (zhejiang) high-end equipment foundation materials research institute and other six units after more than a year of work, Successfully developed the world's first 19.8 grade ultra-high strength fastener, which has become the world's highest strength fastener.
    The project successfully developed B17.8 and B19.8 steels for ultra-high strength fasteners by using high purity iron raw materials produced by Longfengshan Casting based on the theory of high performance of steel materials through the collaboration of the whole industry chain of "material production-fastener manufacturing-service evaluation", and formed the fastener manufacturing technology of grade 16.8 and 19.8.
    Through material and heat treatment process optimization, the tensile strength of 16.8 and 19.8 bolts at room temperature is 1600~1770MPa and 1900~2070MPa, respectively. Shear test results (according to GJB 3376-1998) show that the shear forces of 16.8 and 19.8 bolts reach 97KN and 115KN respectively. The results of tensile fatigue strength test at room temperature (according to GJB 3376-1998 and GJB715.30A-2002, load ratio =0.1) show that the developed fasteners meet the fatigue life requirements (average fatigue life is not less than 65000 times, single fatigue life is not less than 45,000 times). The results of delayed fracture resistance test (according to GJB 715.12-1990, the constant tensile stress in atmospheric environment was maintained for 96 hours) showed that the bolt did not break during the test time, and no cracks were found on the bolt surface and thread after unloading. The comprehensive performance of the newly developed ultra-high strength bolt meets the requirements of service.
    It is reported that foreign ultra-high strength fasteners have formed corresponding design specifications (such as VDA 235-2005), by contrast, China's related product technology and standards seriously lag behind, the need to develop relevant specifications. This project successfully developed grade 16.8 and 19.8 fasteners, which is a breakthrough in the international fastener and material climbing the peak strength. It will strongly promote the lightweight manufacturing of China's major equipment (for example, it can realize the goal of miniaturization of engines and improvement of power density), and promote China's steel production and fastener manufacturing to lead the world. The breakthrough in the development of ultra-high strength bolts indicates that the process of basic parts and materials in China is accelerating from following and running to leading.