spring steel
Spring steel refers to the special alloy steel for the manufacture of various types of springs and other elastic components. According to the performance requirements, use conditions can be divided into ordinary alloy spring steel and special alloy spring steel.
According to the basic performance and use characteristics, spring steel belongs to mechanical structure steel; According to the quality grade, it is a special quality steel, that is, a steel that requires special strict control of quality and performance in the production process. According to Chinese custom, spring steel is a special steel, the production of spring steel when the technical requirements are relatively high, excellent technology directly determines the level of quality.
The spring is used under shock, vibration or long-term alternating stress, so the 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 degree of hardenability, not easy to decarbonize, and good surface quality. Carbon spring steel is a high-quality carbon structural steel with carbon content WC in the range of 0.6%-0.9%. Alloy spring steel is mainly silicon manganese steel, their carbon content is slightly lower, mainly by increasing the silicon content Wsi to improve the performance; In addition, chromium, tungsten, vanadium alloy spring steel. In recent years, combined with China’s resources, and according to the requirements of new technology in the design of automobiles and tractors, a new steel has been developed to add boron, niobium, molybdenum and other elements on the basis of silicon manganese steel, which extends the service life of the spring and improves the quality of the spring.
Spring steel has hot rolled steel, cold drawn steel, cold rolled steel. The smelting of spring steel is very important, and it must be ensured that there is excellent metallurgical quality, not only to ensure the accurate chemical composition, but also to have high purity, low sulfur, phosphorus, oxygen, nitrogen and other contents, and better steel uniformity and stability. The metallurgical quality of spring steel should reach the level of high quality steel and high quality steel.
The surface quality and dimensional accuracy of the spring steel have a great influence on the performance and life of the spring. Because the surface of the spring steel delivery state is no longer processed except for surface shot peening, it is the working surface of the finished spring, and various defects on the original surface are also left to the spring. Therefore, the spring steel surface requirements are extremely high, and the restrictions on decarbonization, cracking, folding, scarring, inclusion, delamination and so on are extremely strict. Various surface defects will cause early damage and shorten the life of the spring.
Taking the steel wire of circular section as an example, the strength and stiffness of the finished spring are directly proportional to the third power and fourth power of the steel wire diameter, respectively, and small changes in the steel wire diameter will lead to huge fluctuations in the performance of the spring, so the shape and dimensional tolerances of the steel should be strictly controlled. In this way, the processing deformation of spring steel (hot rolling, cold rolling, cold drawing, etc.) is very important and must be taken very seriously.
According to GB/T 13304 standard, spring steel is divided into non-alloy spring steel (carbon spring steel) and alloy spring steel according to its chemical composition.
The carbon content (mass fraction) of carbon spring steel is generally 0.62% to 0.90%. According to its manganese content, it is divided into general manganese content (mass fraction) (0.50%~0.80%) such as 65, 70, 85 and higher manganese content (mass fraction) (0.90~1.20%), such as 65Mn two categories.
Alloy spring steel is a steel that is based on carbon steel and improves the mechanical properties, hardenability and other properties of steel by adding one or several alloying elements appropriately to meet the required properties of various springs.
The basic components of alloy spring steel series are silicon manganese spring steel, chromium manganese spring steel, chromium vanadium spring steel, tungsten chromium vanadium spring steel and so on. On the basis of these series, some grades have added alloy elements such as molybdenum, vanadium or boron in order to improve some aspects of their performance.
In addition, some grades are selected as spring steel from other types of steel, such as high-quality carbon structural steel, carbon tool steel, high-speed tool steel, stainless steel.
Hot rolled (forged) steel includes hot rolled round steel, square steel, flat steel, steel plate, forged round steel, square steel
Cold drawn (rolled) steel includes steel wire, steel strip, cold drawn steel (cold drawn round steel).
Delivered in hot-rolled (forged) condition, the steel is hot-formed into springs, which are then quenched and tempered；
Delivered in annealed condition, the steel is cold-formed into springs, which are then quenched and tempered.
Salt bath isothermal quenching cold drawn steel wire (also known as Patenton cold drawn steel wire) steel wire made of spring only need to be tempered at low temperature to eliminate stress.
Oil quenching and tempering steel wire: After cold drawing to the required size, continuous heating, continuous oil quenching and lead tempering are carried out. After the steel wire is made into a spring, it is only necessary to carry out a low temperature fire to eliminate stress.
Delivery in cold drawn condition;
Delivered in annealed, normalized or tempered condition;
The steel wire made of spring delivered in the above two states needs to be quenched and tempered.
Cold-rolled delivery: After the spring is made, it needs to be tempered at low temperature to eliminate stress.
Quench and temper delivery: After the spring is made, it needs to be tempered at low temperature to eliminate stress.
Delivery in annealed condition: After the spring is made, quenching and tempering are required.
Delivered in annealed condition: The steel is cold-formed into springs, which are then quenched and tempered.
This spring (such as 65, 70 steel, etc.) has the advantages of lower cost, convenient source of raw materials, and the disadvantage is that the elastic limit is low, it is easy to lose elasticity after repeated deformation, and it can not work normally under the temperature environment below 130 degrees.
This spring steel (such as 65Mn), compared with carbon steel, its advantage is that the hardenability and strength are significantly better, but there are also obvious shortcomings such as cracks and hot brittleness after quenching. However, due to its cheap price, it is often used in the manufacture of springs of small mechanical size, such as clutch springs.
This spring steel (such as 60Si2Mn), because the composition contains silicon, so the elastic limit has been significantly improved, tempering stability has also been improved, so it can be tempered at higher temperatures, so as to obtain good mechanical properties. Silicon manganese spring steel is widely used in industrial manufacturing, commonly used in the manufacture of spiral springs for automobiles and tractors.
The purpose of adding vanadium to this steel (such as 50CrVA) is to refine the structure and improve the strength and toughness of the steel. This material has good fatigue and impact resistance, and can work stably at temperatures ranging from -40 degrees to 210 degrees, but the price is usually higher. It is generally used in applications with high requirements, such as the production of springs in aero-engine regulation systems.
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