Production technology of spring steel

Spring steel is a kind of steel specially used for manufacturing springs and elastic elements due to its elasticity in quenched and tempered state. The elasticity of steel depends on its elastic deformation capacity, that is, within the specified range, the elastic deformation capacity enables it to withstand a certain load, and there is no permanent deformation after the load is removed
Spring steel should have excellent comprehensive properties, such as mechanical properties (especially elastic limit, strength limit, yield ratio), elastic reduction performance (i.e. anti elastic degradation performance, also known as anti relaxation performance), fatigue performance, hardenability, physical and chemical properties (heat resistance, low temperature resistance, oxidation resistance, corrosion resistance, etc.) to meet the above performance requirements, Spring steel has excellent metallurgical quality (high purity and uniformity), good surface quality (strict control of surface defects and decarburization), accurate shape and size
1. Classification
(1) Carbon spring steel
The carbon content of carbon spring steel is generally in the range of 0.62% – 0.90%. According to its manganese content, it can be divided into general manganese content (0.50% – 0.80%), such as 65, 70, 85 and higher manganese content (0.90-1.20%)
(2) Alloy spring steel
Alloy spring steel is a kind of steel which can improve the mechanical properties, hardenability and other properties of the steel by adding one or several alloy elements on the basis of carbon steel to meet the requirements of manufacturing various gas springs
The basic composition series of alloy spring steel include silicon manganese spring steel, silicon chromium spring steel, chromium manganese spring steel, chromium vanadium spring steel, tungsten chromium vanadium spring steel, etc. on the basis of these series, some brands have added molybdenum, vanadium or boron alloy elements in order to improve their performance in some aspects
According to the working conditions of spring, it can be divided into static load bearing spring steel, impact load bearing spring steel, high (low) temperature resistant spring steel and corrosion-resistant spring steel
2. Production process
Generally, spring steel can be produced in electric furnace, open hearth furnace or oxygen converter; high quality spring steel with good quality or special performance can be refined by electroslag furnace or vacuum furnace. The specified content range of main elements such as carbon, manganese and silicon in spring steel is narrow, so chemical composition must be strictly controlled during smelting. When silicon content is high, it is easy to form bubbles and other defects, Therefore, the raw materials for smelting must be dry, gas and inclusions should be removed as far as possible, and the molten steel should be avoided from overheating
It is necessary to pay special attention to decarburization and surface quality in the rolling process of spring steel. When the surface decarburization is serious, the fatigue limit of steel will be significantly reduced. For high silicon spring steel such as 70si3mna, attention should be paid to avoid graphitization. Therefore, the stop rolling temperature should not be too low (≥ 850 ℃) during hot working, so as to avoid staying too long in the temperature range (650-800 ℃) where graphitization is easy to form
After the spring is made, shot peening can produce residual compressive stress on the surface layer of the spring to offset part of the working stress on the surface layer and inhibit the formation of surface cracks, which can significantly improve the fatigue limit of the spring