Manufacturing spring steel needs to know its performance requirements and production process

The spring is used under impact, vibration or long-term cross stress, so spring steel is required to have high tensile strength, elastic limit, and high fatigue strength. In terms of technology, spring steel is required to have certain hardenability, not easy to decarburize, and good surface quality. Carbon spring steel is high-quality carbon structural steel with carbon content WC in the range of 0.6%-0.9%. Alloy spring steels are mainly silico-manganese steels, their carbon content is slightly lower, and their performance is mainly improved by increasing the silicon content Wsi; there are also alloy spring steels of , tungsten, and vanadium. In recent years, combined with China’s resources, and in accordance with the requirements of new technologies for the design of automobiles and tractors, new types of steel with boron, niobium, molybdenum and other elements added to silicon manganese steel have been developed to extend the service life of springs and improve the quality of springs.

 

Performance requirements

The spring is used under impact, vibration or long-term cross stress, so the spring steel is required to have high tensile strength, elastic limit, and high fatigue strength. In terms of technology, spring steel is required to have certain hardenability, not easy to decarburize, and good surface quality. Carbon spring steel is high-quality carbon structural steel with carbon content WC in the range of 0.6%-0.9%. Alloy spring steels are mainly silico-manganese steels, their carbon content is slightly lower, and their performance is mainly improved by increasing the silicon content Wsi; there are also alloy spring steels of 硌, tungsten, and vanadium. In recent years, combining the resources of our country, and in accordance with the requirements of new technologies in the design of automobiles and tractors, new steel grades with elements such as boron, niobium, and molybdenum added to the silicon-manganese steel have been developed to extend the service life of the spring and improve the quality of the spring.

 

Production Process

Generally, spring steel can be produced by electric furnace, open hearth furnace or oxygen converter; high quality spring steel with better quality or special properties can be refined by electric slag furnace or vacuum furnace. The specified content range of the main elements such as carbon, manganese, and silicon in spring steel is relatively narrow, and the chemical composition must be strictly controlled during smelting. When the silicon content is high, defects such as bubbles are easy to form, and white spots are likely to occur when the ingot is not cooled after forging and rolling. Therefore, the raw materials used 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 in the rolling process. When the surface of the steel 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, the stopping temperature during hot working should not be too low (≥850℃), and avoid staying too long in the temperature range (650~800℃) where graphitization is easier to form. After the spring is made, the shot blasting treatment can make the surface of the spring generate residual compressive stress, which can offset part of the working stress on the surface and inhibit the formation of surface cracks, which can significantly increase the fatigue limit of the spring.