Inox or stainless is an iron alloy containing at least 10.5% chromium, and its main property is durability and corrosion resistance, which is why it is used in construction, surgery, auto industry etc.
The emergence of stainless steel alloy
Today’s world of construction, car industry, mechanical engineering and many other branches can hardly be imagined without inox or stainless steel. Inox was created in 1821 when French Berthier added 1.5% chromium to steel, in order to make cutlery. During the 20th century, the approach to the development of steel production technology was systematical; and a number of new ways and techniques have that have greatly contributed to and enhanced the production of the same have been discovered.
The importance of this material is reflected in the fact that during 2011, a total of 1 490.06 million tonnes of steel was produced in the world, and this figure is increasing over the years. The leading stainless steel manufacturer is China, followed by Japan, the United States and India. The special importance of stainless steel is that it can be completely recycled and the proportion of recycled stainless steel is up to 80%.
Chemical composition of inox
As it has already been said, in the production of stainless steel, a certain percentage of chromium or nickel is added to the mentioned. These materials make steel resistant to corrosion. Chromium, whose share can rise up to 20% is added to the iron and carbon. In addition to chromium, nickel is added to the mixture as well. However, different standards in stainless steel production require different proportions of chemical elements. For example, the steel of the standard X13 NiCr Si 35-16 contains up to 37% nickel and 17% chromium while other elements such as nitrogen come in a proportion of a 0.11% maximum. However, the most important metal in the chemical composition is chrome, which creates an oxidized layer on the steel surface, that protects it against corrosion and external influences.
The process of stainless steel production begins with loading the recycled material by large cranes or magnets into containers that are then transported to the high furnaces. In high furnaces, with the addition of nickel, or chromium, recycled steel is left to melt. There are different stoves that can be used in this process, and among the best is an electric furnace which produces the best and the fines steel as well. However, prior to the melting, the steel should be grinded or cleaned from impurities to make the quality as good as possible.
The production process is continued in the refining furnace after melting. Since molten steel itself contains many other chemical elements, these elements need to be removed, which is achieved by the refining process, after which the molten steel flows from the refining furnace and is formed into pieces of about 64 meters long. These pieces are further rolled to finally obtain a rolled steel strip that then goes to further purification, or where a protective layer is formed through the contact of chromium and atmosphere. After that, the steel is shaped or cut according to customer’s requirements, and later pipes, fences, and other things can be made of it.
Apart from the fact that steel can be produced by recycling an old steel, it can also be produced by the purification of crude iron, which is a process that in some segments differs from the production process done with recycled steel.
The process of steel production, as well as of other metals, happens in high furnaces. The electric furnace serves for the melting of the steel and is made on the basis of the electrical arc or induction. The electric arc-based blades function in a way that a high temperature is being created between the electrode and the metal by means of electric energy, and that’s how the steel melts. There are several basic reasons why an electric furnace is used, and the main reasons are an easy achievement of high temperature, an easier control of the chemical composition, no combustion product, and much less coating on the stove itself is being consumed.
Types of stainless steels
There are different types of stainless steels or inox, which can be divided into:
- Ferritic stainless steels – This kind of stainless steel contains 13 to 17% of chromium. This kind of steel is highly resistant to acids, is very soft, possesses the properties of the magnet but there is a problem of poor weldability
- Austenitic inox – the chromium content in this type of steel ranges from 15 to 20%. Its main characteristics are self-magnetism, bigger deformation in welding, plasticity and good properties at low temperatures
- Austenitic ferrite inox– chromium content ranges from 22 to 24%. This kind of steel is often used in mining, ie petroleum, petrochemical and chemical industry
- Martensitic inox – inox which has an increased carbon content, and is mainly used in the production of tools
- Soft martensitic inox – these steels are high-strength. They are used to make parts that are in an environment where unclean air is well present
Stainless steel processing techniques
Inox as one of the most common metals in today’s industry has various processing techniques. However, to make the positions made of stainless steel, processable, it is necessary to cut them. One of the most economical cutting techniques is laser cutting. In addition to laser cutting, inox can be cutted with the following techniques:
- Plasma cutting
- Water jet cutting
- Autogenous cutting
- Cutting steel by using cutting plates
However, of all the above mentioned cutting metal processing techniques, laser inox cutting represents a technique in which the ratio of the cutting quality, the speed and the economy of the cutting is the best.