Steel alloys are the most common material among the metals processed in the manufacturing industry. According to Polish Norms, the first component should constitute the vast majority of the alloy, and the second no more than 2.11%. If the carbon content is higher, we are already talking about cast iron. In addition, there are other metals, elements and non-metallic inclusions in the composition of steel alloys that influence the heat treatment process to obtain the desired structure and mechanical properties. You will find out more information later in this article.
What is metal and what are its properties?
Metal is a material, most frequently of crystal structure with metallic bonds. Its main properties include:
Steps in producing steel alloys to obtain the relevant properties
Steel production consists of two clearly separated production processes:
The pig iron produced by the blast furnace process is not suitable for processing due to its high content of carbon (approx. 4%), sulphur (0.5%) and phosphorus (0.5%). The material thus produced is brittle and non-forgeable, and is a raw material for the next process – processing into steel or cast iron.
The pig iron is then reduced in undesirable components such as excessive carbon (C), silicon (SI), manganese (Mn), phosphorus (P) and sulphur (S) by means of an oxidation process using oxygen and/or air. This process, called the Bessemer process, ensures obtaining the desired steel grade after the addition of suitable alloying elements.
After the Bessemer process, the steel alloys are cast into ingots adapted to the requirements of further forming processes. The solidified steel is then transferred by pulling rollers, then straightening rollers, behind which a gas torch cuts a strip of material into equal so-called billets with round, square, rectangular or slab cross-section (e.g. 200x1500mm). Billets are the starting material for the production of bars, wires, sections, rails or sheets.
How the properties of metals are influenced by alloying elements
Manufacturing of steel sheets, sections and tubes
A typical steel mill usually consists of 3 basic departments:
- blast furnace
- rolling mill
The steel alloys produced in the steel mill is subjected to forming mainly by rolling. The rolled product is therefore the end product of the metallurgical process. In the rolling process, the workpiece is given its intended shape by deforming the metal between rotating hard rollers or discs. Rolling takes place on a set of equipment that is called a rolling mill unit. The unit is adapted to the grade and temperature of the material being processed and to the dimensions and shapes of the rolling products being manufactured. The rolled products manufactured can be divided into bars, wire rod, sections, sheets, strips, tubes, special products such as rails or train wheel rims.
The process for producing aluminium is very similar to that of steel described above.
Mechanical properties of steel alloys
The mechanical properties determine the serviceability of steel. Their values depend on the chemical composition of steel alloys and their treatment (heat treatment / forming, etc.). The basic mechanical properties of steel include:
Selecting steel by properties
Before starting construction or production, the right steel grade must be selected to match the environment in which the structure or machine will be used. It is worth noting that there are many grades of steel in use today with different properties, and proper identification is the key to success.
Steel grades – structural steel
It is used to build the most common typical structures, machine parts, but also to strengthen other steel alloys. There are many types of structural steel:
- general purpose – lower grade alloy used for construction and machine parts; it proves useful where no specific material parameters are required;
- higher quality structural – characterised by strictly defined quantities of carbon and manganese with fewer impurities; it is used to make sheet metal, pipes and parts for vehicles and machinery;
- low-alloy structural – contains up to 0.22% carbon, is valued for its strength and high resistance to corrosion; due to its resistance to difficult weather conditions it is used in the construction of bridges, railway carriages, masts;
- carburizing steel – has high ductility and surface hardness, suitable for the manufacture of high strength parts;
- nitriding steel – this one involves saturating the surface of the metal with nitrogen, and works particularly well as a gear material;
- for hardening and tempering – suitable for manufacturing of heavily loaded parts;
- spring steel – contains a large amount of silicon and is used to manufacture springs, leaf springs and torsion bars,
- free-cutting steel – used to manufacture screws, washers, nuts, etc.
- bearing steel – features a very precisely controlled composition and is produced under a strict technological regime.
Types of steel alloys and their applications – tool steel
The high carbon proportion and appropriate heat treatment ensure its highly desirable properties. Tool steel is used to manufacture various types of tools and responsible parts of measuring instruments.It is distinguished by high hardness and abrasion resistance. It is resistant to overheating and, moreover, does not deform even after prolonged use.
Tool steel can also be divided into more specific grades including:
- carbon tool steels
- alloy tool steels
- cold-work tool steel
- hot-work tool steels
- high speed steel
What types of special steel alloys are there?
Special steel alloys are designed for a specific application. Its grades contain a large number of fluxes, have very specific parameters and require complex heat treatment. Due to their high price, they are not widely used. The group of special steels includes, among others:
- stainless steel – with special physical and chemical properties, resistant to corrosion and high temperatures;
- acid-resistant steel – with a high chromium content, it is resistant to the destructive effects of acids that are less powerful than sulphuric acid;
- heat-resistant steel – resistant to the destructive effects of oxidising gases at high temperatures;
- magnetic steel – with a very low carbon content, it exhibits ferromagnetic properties;
- wear-resistant – a steel with high carbon and manganese content.
I hope that after reading this article you are equipped with a basic knowledge of metals and their properties. Of course, you may be tempted to go deeper into materials science, which we encourage you to do if necessary. Don’t forget that when choosing an Otinus machine, you’ll have the support of our experienced technicians, who will assist you in choosing the ideal solution for the material you intend to machine. Feel free to contact us or visit our machine showroom in Bydgoszcz, at 14b Karola Szajnochy street.