Analyze spring performance requirements and production process
General spring steel can be produced by electric furnace, open hearth furnace or oxygen converter; high quality spring steel with good quality or special performance can be produced by electroslag furnace or vacuum furnace. The content of carbon, manganese, silicon and other major elements in spring steel is narrow, and the chemical composition must be strictly controlled during smelting. When the silicon content is high, defects such as air bubbles are easily formed, and white spots are easily generated when the steel ingot is cooled after forging. Therefore, raw materials for smelting must be dried to remove gas and inclusions as much as possible, and the molten steel must be prevented from overheating. Spring steel must pay special attention to decarburization and surface quality during rolling. Severe decarburization of the steel surface will significantly reduce the fatigue limit of the steel. For high-silicon spring steels such as 70Si3MnA, care should be taken to avoid graphitization. Therefore, during the hot-working, the stop-rolling temperature should not be too low (≥850°C), and the residence time in the easily-formable temperature range (650-800°C) can be avoided. After the spring is made, shot peening can produce residual compressive stress on the surface of the spring to offset part of the working stress on the surface layer and inhibit the formation of surface cracks, which can significantly increase the fatigue limit of the spring.
Springs are used under impact, vibration, or long-term stress, so spring steels are required to have high tensile strength, elastic limit, and high fatigue strength. In the process, the spring steel must have certain hardenability, it is not easy to decarburize, and the surface quality is good. The carbon spring steel is a high-quality carbon structural steel with a carbon content of WC in the range of 0.6%-0.9%. Alloy spring steels are mainly silicon-manganese steel grades. Their carbon content is slightly lower, mainly by increasing the silicon content Wsi to improve performance; in addition there are alloy spring steels of niobium, tungsten and vanadium. In recent years, combined with our country's resources, and based on the requirements of new technologies for the design of automobiles and tractors, we have developed new steel grades that incorporate boron, niobium, molybdenum, and other elements on the basis of silicon-manganese steel, extending the service life of springs and improving the quality of springs. .