It is worth starting with the fact that any spring, spring and other similar elements are operated under conditions of severe and constant elastic deformation. In addition, most parts are also subjected to cyclic loads. For these reasons, high demands are made on spring steel in terms of elasticity, fluidity, endurance, ductility, and it is also important to have the necessary resistance to brittle fracture.
Composition
The composition of the steel, which is suitable for the production of springs and springs, includes from 0.5% to 0.75% carbon. Additional requirements for the content of alloying elements in the production of the following:
- silicon content in spring steel up to 2.8%;
- manganese content up to 1.2%;
- alloying with chromium reaches 1.2%;
- vanadium content up to 0.25%;
- alloying with tungsten up to 1.2%;
- nickel content up to 1.7%.
It is also important here to add that in the production of steel , the grain grinding process is carried out, which contributes to an increase in the resistance of the metal to small plastic deformations. This, in turn, increases the relaxation resistance of the spring steel product.
Application
Quite widespread use in vehicles found products from steel grades such as 552, 602, 703. But here you need to know that this material is prone to defects such as decarburization or graphitization. These disadvantages are dangerous in that they greatly reduce the elasticity characteristics, as well as the strength of the material. In order to avoid these defects and their negative effects on spring steel, the elements mentioned above are added to it.
The best indicators, unlike the siliceous variety of the alloy, are the 50HFA grade. This type of material has become most used for the manufacture of automotive springs. Also, this type of steel is very often used for the production of spring valves, since it is not susceptible to decarburization. But here it is worth adding that it has low hardenability.
Spring operation
It is important to understand here that the operation of any spring, spring or any other spring steel part is characterized only by the fact that only the elastic properties of the material are used. The total value of their elasticity is determined by the design features. The decisive indicator here will be the number of turns, their diameter, as well as the length of the product. Another important point that needs to be noted is plastic deformation. This is most often not allowed in springs, and therefore, the material used to produce the springs does not require a high impact strength or ductility index. The main requirement is a parameter of elasticity. The upper limit of this characteristic should be quite large. In order to achieve the required parameter, the steel is subjected to hardening under the influence of high temperatures, and then the material is tempered at a temperature of 300-400 degrees Celsius.
The properties
The main property of spring steel is fluidity (elasticity). The maximum value of this parameter is achieved only at the temperatures indicated above. However, if the material is released at such degrees, the temper brittleness of the final product will be in the first kind. As mentioned earlier, impact strength is not critical.
Another of the properties of steel relates to its composition. It is expressed in the fact that the carbon content in it is greater than in other alloys. Although, when compared with tool steel, it is still less.
For a conventional alloying process, manganese and silicon are used. For more critical springs or springs, chromium and vanadium are used as additives. These two elements give them increased elasticity. It can be added that in order to achieve the best performance properties, steel is often quenched in oil or water.
Types and grades of steel
Grades of spring steel are divided into many different groups. There are general materials. These include brands 65, 70, 75, U9A. From this product springs are made for machines with a small cross section. The special properties of these parts include their reduced relaxation resistance.
Silicon steels of grades 55C2, 60C, 60C2 are used to create elements such as springs and springs used in the automotive, automotive and tractor industries, as well as in the railway industry. It is important to add that these elements are prone to decarburization. This steel has no special properties.
Another type of steel is complex alloyed. This product is manufactured under the brands 50KHFA and 60C2KHFA. The use of this material is resorted to if it is necessary to create springs or springs for important parts. Resistance to temperature effects of this material is up to +300 degrees Celsius.
You can also distinguish steel for special purposes. These include such products of martensitic class 30X13, 40X13. They are used for the production of conventional springs or springs, but they have special properties. The characteristic of spring steel of this brand is that it has increased resistance to corrosion, increased heat resistance (up to 550 degrees Celsius), as well as pronounced magnetic properties.
GOST requirements
For spring steels, as well as for the other most diverse products, GOST was adopted. He sets all the rules regarding the material. For example, the following technical requirements are described there.
- The mass fraction of a substance such as copper should not exceed 0.2%. And the residual amount of nickel should not be higher than 0.25%.
- For a steel grade such as 602, there is a separate requirement, which states that the total mass fraction of sulfur and phosphorus should not be higher than 0.06%.
- Such steel grade as 51XFA according to GOST is intended only for the production of spring wire.
- The GOST of spring steel also prescribes that by the individual order of the consumer, the mass fraction contained in manganese steel can be reduced, despite the requirements that are indicated in the table contained in the same document. This is provided that the alloy was not doped with chromium and nickel.
Corrosion Resistant Steel
One of the special steel grades is characterized in that it has a high resistance to corrosion. In order to maximize the resistance of the material to a process that destroys it, both chromium and nickel are added to it in an amount of 13 to 27% and 9 to 12%, respectively. In other words, these products belong to the group of high alloy steels.
The main austenite-forming element in such a product is nickel. While manganese, for example, affects the formation of austenite less, the effect of its use is almost two times lower. If it is necessary to further expand the austenitic region, then substances such as carbon or nitrogen can be used.