Axle is walking part of the key vehicle parts, and bears the weight of the vehicle load, when vehicle running and parking also inherit the impact force and braking force, under the conditions of high speed and heavy loading situation is more complex, is key to railway construction of the three parts (heavy rail, axle and wheel), one of the train axle belongs to very large axisymmetric ladder-like shaft parts, its largest diameter is 200 mm, length is 2200 mm or so.
With the operation of high-speed railway in China, the train speed is further improved. As one of the key parts of railway trains, high-speed axle is an important running part of railway trains, and its quality is directly related to the safety of high-speed railway operation. High-speed train axles should be provided with sufficient safety, reliability and long service life under specified conditions, which puts forward higher requirements for axle materials and related technologies. The axle of high speed train is subjected to various loads from the body and track. According to statistics, among these failure forms, the failure caused by crack accounts for more than 90% of the whole failed axle. The failure form of axle caused by crack finally presents as fatigue fracture, which is a process of crack generation and propagation leading to fracture, and its fatigue damage directly endangers transportation safety. Therefore, the axle steel, mainly to ensure its good strength (especially bending and torsion composite fatigue strength) and toughness. The main factors affecting the fatigue performance of steel are: cleanliness of steel, composition and structure of steel, surface state and size effect of steel, corrosion resistance of steel, etc.
All the railway developed countries in the world attach great importance to the research work of high-speed axle, and keep improving from the aspects of material, design, production, thermal treatment, application and maintenance. Due to different national conditions and technical views, the choice of axle materials are not the same. At present, high-speed axle steels at home and abroad can be roughly divided into three categories: high quality carbon structural steels, medium alloy structural steels, and high alloy structural steels.
(1) high quality carbon structural steel. Ordinary carbon steel (S38C) and surface medium frequency quenching and heat treatment process are adopted in Japan. Compared with the heat treatment process of alloy steel and quenching and tempering treatment adopted in Europe, the raw material cost of high-speed axle in Japan is low, but the heat treatment process is complex, and the control precision of heat treatment process parameters is required to be high.
(2) high alloy structural steel. Some European high-speed axle materials are made of 30NiCrMoV12 and other high alloy structural steel, which contains cro.6 (tl.00%, ni2.70?). 3. 30%, M 0.4 (T. 60%, v0.08? 0. 13%, this kind of steel has many advantages, such as good hardenability, oil quenching, small deformation, high hardness, high yield to strength ratio, good corrosion resistance and so on, but the cost is relatively high.
