Without the discovery of steel, its properties and processing methods of modern civilization would not exist. Since ancient times, certain types of steel have been known that were used to produce weapons and tools. With the development of metallurgy and metalworking technology, this material began to be used in almost any field of human activity.
Chemical classification
The alloy of iron with carbon, the content of the latter in which does not exceed 2%, was called steel. Its main types are classified primarily by carbon content:
- low carbon;
- medium carbon;
- high carbon.
In the first form of the named component contains not more than 0.25%. In medium-carbon types of steel, its content lies in the range 0.25-0.6%, and high-carbon ones differ in concentration above 0.6%.
Steel alloying
The initial raw materials for steelmaking already contain some impurities. Most of them are harmful, but there are those that improve the properties of the final product. Over time, it was found that some additives significantly change the basic physical and chemical properties of the described alloy. So, the alloying process was opened. And today, the types and properties of alloyed steel are a priority in the research of metal science laboratories and institutes.
According to the concentration of useful impurities, these steels are divided into three groups:
- low alloyed (impurities up to 2.5%);
- medium-alloyed (alloying elements from 2.5 to 10%);
- highly alloyed (dopants of more than 10%).
Intended classification
Depending on the production method, chemical composition and the number of alloying elements , the following types of steel are distinguished:
- constructional;
- instrumental;
- with special physical properties;
- with special chemical qualities.
The structural appearance is the most widespread, such alloys are used in the manufacture of most engineering products and in construction.
Instrumental ones are high-carbon, they are characterized by high hardness, but they also have fragility. They are used in the manufacture of various instruments - from surgical to metal cutting. Hence the name of this type of steel.
For special cases in production, alloys with specified physical characteristics are required: a low coefficient of linear expansion, a high ability to magnetize, etc. Such types of steel belong to the class with special physical properties.
Alloys with predetermined chemical qualities are among the latest in our list. Some of them are not susceptible to corrosion, others are heat-resistant, and there are materials with increased chemical resistance.
Classification by level of harmful impurities
The most common impurities that degrade the properties of steel are sulfur and phosphorus. In alloys of ordinary quality, a sulfur content of up to 0.06% and phosphorus up to 0.07% is allowed. Steels belonging to the group of high-quality ones contain no more than 0.035% of each of the harmful elements, and high-quality ones - no more than 0.025%. In particularly high-quality types of steel, the level of sulfur impurities is not more than 0.015%, and the phosphorus content is allowed up to 0.025%.
Steel Processing Methods
According to the degree of heating, the treatment is hot and cold. In the first case, the alloy is heated to the stage of formation of austenite, but below the melting temperature. In this case, the steel becomes soft and lends itself to a change in its shape. The cold type of steel processing is carried out under normal conditions.
According to the type of impact, two main types of processing are divided: pressure and cutting. The first type includes forging, rolling, drawing, stamping and pressing.
The second type of processing includes the following operations: turning, drilling, milling. But there is also cold stamping, as well as cold forging, which received a separate name - “hardening”.
Recent developments in the cold processing of steel based on the theory of fluidity of metals can significantly change the shape and size of the initial billet without heating and using volumetric pressure. Steel is loaded until it reaches a state of flow and becomes "convenient" for processing. This method is relevant for some alloys, which, when heated, change their physical, chemical or strength characteristics.