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 the process, the spring steel is required to have certain hardenability, not easy to decarburize, and good surface quality. 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 silico-manganese steel grades, 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 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 springs and improve spring quality .

Performance requirements

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 the process, the spring steel is required to have certain hardenability, not easy to decarburize, and good surface quality. 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 silico-manganese steel grades, 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 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 springs and improve spring quality .

Production process

General 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 produced by electroslag furnace or vacuum furnace. The specified content range of carbon, manganese, silicon and other major elements 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 steel 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 the molten steel must be prevented from overheating. Special attention must be paid to decarburization and surface quality of spring steel during rolling. 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 too long residence time in the temperature range (650～800℃) where graphitization is easier to form. After the spring is made, the shot peening treatment can make the surface of the spring generate residual compressive stress to 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.