Brake disc has been widely used in the braking system of rail vehicles. Vermicular graphite cast iron is a new engineering material. Its strength, plasticity and toughness are higher than those of gray cast iron, and its damping and thermal conductivity are similar to that of gray cast iron; The casting performance is better than that of nodular cast iron, and has excellent heat fatigue resistance and thermal conductivity. As a potential engineering material, it is very suitable for the working conditions of brake disc.
With the increasing speed of the railway, the vermicular cast iron brake disc will experience rapid temperature rise and strong convection temperature drop in a short time during the braking process, that is, the vermicular cast iron brake disc will bear strong thermal load and thermal stress during the braking process, which is easy to produce thermal cracks, wear and other problems; Therefore, the requirements for friction and wear resistance, high temperature mechanical properties, thermal fatigue resistance and stable thermal strength of vermicular cast iron brake disc are higher, which requires accurate and strict control of the process, especially the melting quality of molten iron.
(1) Choice of metal charge for vermicular graphite cast iron brake disc: for the production of high-end vermicular graphite cast iron brake disc castings, there are many choices of metal charge, not the more expensive the better. Appropriate and long-term stable supply of metal charge is the key, including pig iron, scrap, Vermicular Agent and other ferroalloys.
(2) Vermicular graphite cast iron brake disc vermicular control: vermicular iron production control process range is very narrow, there can be no deviation, and the control is difficult. The vermicular rate in Vermicular Iron production is stably controlled above 70% for a long time. Practice has proved that the stability of sulfur content in molten iron is the premise of vermicular process; Stable reaction of molten iron is the key to creep process; The returned materials shall be shot blasted to ensure the cleanness of metal furnace materials; Spectral analysis in front of furnace is fast and accurate; The ability to accurately distinguish the creep rate by using triangular test block in front of the furnace and remedial measures.
(3) Composition design of vermicular cast iron brake disc: the carbon equivalent is controlled near the eutectic point, the liquid iron has good fluidity, strong feeding capacity and good casting performance of vermicular cast iron brake disc. Adding an appropriate amount of alloy elements can strengthen and refine pearlite, reduce white mouth, improve strength and thermal strength, improve hardness and wear resistance, reduce section sensitivity and improve uniformity. Monitor all harmful elements and anti spheroidizing elements. Once problems are found, respond quickly and take measures immediately to prevent batch scrapping.
Through long-term optimization of smelting process, the yield of vermicular cast iron brake disc castings of more than ten varieties of vermicular cast iron brake disc series of various shaft and wheel mounted series has been steadily controlled at more than 95%, and the smelting scrap rate is less than 1%. The quality is controllable and the product is stable.