Stainless steel
Due to the multiplicity of unique properties of stainless steel, it is a very strong candidate among different sorts of materials. Engineers, specialists and designers often undervalue or do not perceive these assets. A relatively high purchase price of stainless draws their attention in the first place. However, taking into account the durability of products made of this material, contrary to what one may first think, stainless steel as raw material often turns out to be the best and cheapest solution.
What does stainless steel mean ?
Stainless steel is basically steel with a lowered content of carbon, in which chromium is at least 10% of weight; therefore, steel shows rustproof properties. As a result of the reaction of oxygen with chromium, a permanent and invisible and corrosion-resistant thin (approx. 1/1000 mm thick) layer of chromium oxide is formed on the steel surface. It is of passive nature - does not react with other substances and has self-healing capabilities - is able to heal physical or chemical damages even in the presence of small amount of oxygen. Due to these features, the stainless steel knives can be repeatedly sharpened and ground without exposing them to rust. The increased amount of chromium or other substances, e.g. molybdenum or nickel can, be added to stainless steel, therefore, its unique properties get even better.
There are 60 types of stainless steel alloys, however, the major classification includes 5 groups:
- chromium steel - hardened with martensitic structure: due to martensitic structure of such a type of stainless steel, it is hardened at high temperatures, similarly to conventional steels;
- chromium steel - non-hardened with ferritic structure: contains not only chromium but also titanium or aluminium. This type of steel is usually used in building industry;
- chromium-nickel steel - non-hardened with austenic structure: due to the lower content of carbon than in other alloys, it can be used at low temperatures. This type of steel is usually used, among other things, in the production of beer barrels, in the freezers and chillers;
- chromium-nickel steel - showing the ability to be hardened at relatively low temperatures, with martensitic, semi- austenic or austenic structure, depending on the amount of nickel in its composition. Being able to be hardened at relatively low temperatures;
- chromium-nickel steel - non-hardened with ferritic-austenic structure in 1:1 ratio. Very durable, usually used in chemical industry. Showing the ability to be hardened at low temperatures to some extent.
Discovery
The inventor of stainless steel, Harry Brearley, was born in 1871 in Sheffield, England. His father was a steelworker. Due to the lack of funds for living, at the age of twelve, he was forced to abandon school and undertake work in a chemical laboratory, where he washed bottles and containers. For several years, in addition to his laboratory work, he studied at home and later in evening classes. Thus, Harry Brearley became an expert resolving problems connected with metallurgy. As a well-known expert in the field of metallurgy, in 1908, Brearley established the Brown Firth Laboratories, which were jointly financed by two principal steelmaking companies.
In 1912, Brearley began to research stronger steel, not eroding under the influence of high temperatures so fast as conventional steel. One of the experiments involved the addition of chromium, with the higher melting point, to a steel alloy. He performed many tests, adding chromium in the range of 6 to 15 weight %, in connection with various contents of carbon. Thus, on 13 August 1913, the first true stainless steel was produced. It contained 0,24 weight % of carbon and 12,8 weight % of chromium. However, the author was not yet fully aware of his success. It became clear during further experiments, when Brearley examined the molecular structure of steel, being treated with strongly corrosive acids, and it turned out then that new steel did not change its structure under the influence of these compounds. Within one year from Brearley’s invention, the Krupp company in Germany performed experiments with metal alloys, adding nickel. Thus, steel, easier to machine, more resistant to acids, was created. Just these two inventions gave rise to stainless steel. But only after the First World War the experiments began, adding various combinations of chromium and nickel to the alloys.
Most of the present types of steels were invented between 1913 and 1935 in England, Germany, France and America. After the Second World War the production of stainless steel became more effective; new types, more resistant to acids, with better strength-to-weight ratio, were created. The stainless steel values were more frequently noticed and had an ever-increasing number of applications.
Benefits of stainless steel
- Resistance to corrosion - alloys with a relatively small addition of chromium (10%) may be used as raw material in products intended for operation in moisture, direct contact with water. The alloys with an increased chromium content are resistant to most acids, alkalis, chlorine solutions and other compounds;
- Resistance to temperature and fire - steels with an increased content of chromium and addition of nickel do not change their structure and retain resistance even under the influence of high temperatures;
- Hygiene - because of the ease with which contamination can be removed and resistance to highly corrosive substances, stainless steel is an unrivalled material for use in specific spaces, i.e.: kitchens, production halls in the food processing industry etc.;
- Aesthetic look - clear, glossy surface ensures an attractive, modern and noble look. Aesthetics may completed by with the ground, sandblasted or spotted surface;
- Strength-to-weight ratio - due to the variety of stainless steel alloys, materials, very durable, both at high and low temperatures, can be easily selected. The strong structure allows the use of more gentle constructions in relation to conventional materials, which gives some savings;
- Ease of processing - due to modern technologies, stainless steel can be processed just as conventional steel;
- Longevity - thanks to its properties, stainless steel is much more durable than conventional materials. Therefore, despite high costs of purchase, within a long-term time-frame, products made of stainless steel are often the cheapest solution;
- Prestige - stainless steel is the high class, modern material, with the value disproportionate to conventional steels and plastics. It gives the products their own unique style, creates the impression of solid construction, high quality and professionalism;
- Value - purchase of stainless steel is more expensive but its resale is also more expensive. The prices of stainless steel scrap are much higher than the prices of black steel scrap;
- Environmental protection - there are no ma problems with disposal of stainless steel waste. Over 50% of sold steel come from waste re-melting.
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