At present, China is the country with the longest high-speed rail operating mileage, the largest under construction, the most EMU operations, and the highest commercial operation speed in the world. As EMU enters the maintenance cycle, the maintenance market for rail transit fasteners is huge. However, with the large-scale and continuous improvement of the power and speed of various rail transit vehicles, higher requirements are put forward on the working conditions of rail transit fasteners. Fracture failure of auto fasteners is a huge hidden danger. Affect the safe operation of rail transit vehicles. Let's take a look at its material and structure.
The raw materials of railway fasteners are alloy steel or boron-containing steel, and the chemical composition should comply with relevant national standards; 10.9 and above bolts, screws and studs should be made of alloy steel and contain at least one of the following elements: Cr, Ni , The total content of Mo and V alloying elements is ≥1%. The raw materials specified in the table below are recommended, but not limited to this.
The forming process of rail transit fasteners : the heads of bolts and screws should be up forged and formed. After the bolts, screws and stud bolts are quenched, the metallographic structure of the iron core is at least 90% martensite. Pearlite or massive ferrite and net ferrite are not allowed. The surface of bolts, screws and stud bolts is not allowed to have a white phosphide accumulation layer, which can be measured by metallography. The removal of the phosphide accumulation layer should be carried out before the heat treatment. After the final heat treatment, the threads of bolts, screws and stud bolts are rolled into one step. The bolts (screws, studs) formed in the heat treatment process need to be formed on the supporting surface, shaft, shaft transition arc and thread blank diameter. Remove it before rolling the thread.