General spring steel can be produced by electric furnace, open hearth or oxygen converter; high-quality spring steel with good quality or special properties can be made by electroslag furnace or vacuum furnace. The specified content range of carbon, manganese, silicon and other main elements in spring steel is narrow, and the chemical composition must be strictly controlled during smelting. When the silicon content is high, it is easy to form defects such as bubbles, and white spots are easy to occur when the ingot is not cooled properly after forging and rolling. Therefore, the raw materials for smelting must be dried to remove gas and inclusions as much as possible, and to avoid overheating of molten steel.
Spring steel must pay special attention to decarburization and surface quality during rolling. When the steel surface is severely decarburized, it will significantly reduce the fatigue limit of the steel. For high silicon spring steel such as 70Si3MnA, care should be taken to avoid graphitization. Therefore, during hot working, the rolling stop temperature should not be too low (≥850°C) to avoid staying too long in the temperature range (650-800°C) where graphitization is easier to form.
Springs are used under impact, vibration or long-term alternating stress, so spring steel is required to have high tensile strength, elastic limit and high fatigue strength. In the process, the spring steel is required to have a certain hardenability, not easy to decarburize, and good surface quality. Carbon spring steel is 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 steels, their carbon content is slightly lower, and their performance is mainly improved by increasing the silicon content Wsi; in addition, there are alloy spring steels of tungsten, tungsten and vanadium. In recent years, combined with our country's resources and according to the requirements of new technologies for automobile and tractor design, new steel grades with boron, niobium, molybdenum and other elements added to silicon-manganese steel have been developed, which prolongs the service life of the spring and improves the quality of the spring.
