In order to obtain better material properties, a small amount of one or more other metals with smaller or larger atoms are added during the melting process of a metal. This makes it more difficult to shift the ions and, together with other alloying elements, an alloy is obtained that is, for example, stronger, harder and less flexible than the pure metal.
Steel consists of iron and carbon. To make it more resistant to corrosion (rusting), chromium is added. This makes the material too brittle again and nickel is added, creating stainless steel. Due to corrosion by salts and/or chlorides, this stainless steel can eventually corrode. Molybdenum is added to prevent this. The presence of carbon also causes corrosion problems. Titanium is added for this.
A certain type of stainless steel, also called stainless steel, stainless steel or inox, ultimately consists of, for example, iron and chromium, nickel and/or manganese, molybdenum, vanadium and titanium.
Steel is defined as an alloy containing at least 50% iron (Fe) and to which alloying elements have been added to obtain the desired properties in the final state. The influence of various alloying elements on the properties of stainless steel are shown in the overview below.
Increases hardness and mechanical properties. In austenitic and ferritic stainless steels, a high carbon content is undesirable due to the risk of carbide precipitation. The carbon % is therefore limited to max. 0,08%
Increases oxidation resistance. Minimum 12% chromium required to obtain a passive surface layer, which gives good resistance to general corrosion. Chromium together with carbon ensures good hardening.
Increases corrosion and heat resistance together with chromium. Makes the material less brittle. It increases the oxidation temperature and the impact strength at low temperatures.
Austenitic stainless steel is obtained when the nickel content is more than 8% and the chromium content is more than 12%. This material has high strength and impact strength at both high and low temperatures.
Stabilizes the carbon deposits and reduces the chance of intercrystalline corrosion. Titanium is a stronger carbide former than chromium so that titanium carbides will be formed preferentially.
Titanium carbides form in a matrix (homogeneous precipitation) in contrast to chromium carbides, which deposit on the crystal boundaries and cause chromium-poor areas around the crystal boundaries. This increases the chance of intercrystalline corrosion.
Increases resistance to pitting and crevice corrosion.
Improves deformation properties at high temperatures.
Increases strength and fracture toughness. Improves hardening properties.
It is a strong austenite former and is used as a replacement for nickel in the AISI 200 series.
In stainless steel it is considered an undesirable element (contamination). In low alloyed steels it improves machinability, strength and corrosion resistance.
It is present as an admixture in the nickel used in steelmaking.
It is present as a guiding element. It can be used to obtain precipitation hardening.
Niobium has the same effect on the precipitation of carbides in stainless steel as titanium. However, it is a more powerful carbide former than titanium.
Improves the machinability of stainless steel.
Used in steelmaking as a deoxidizer, so there is always a small amount present in stainless steel. Silicon increases the hardness of the ferritic phase in steel.
In austenitic stainless steels it increases the stability of the austenite. It increases the mechanical properties considerably. It has a favourable effect on the resistance to pitting attack.
Chemically, tantalum is similar to niobium.
Like phosphorus, it is considered a pollutant element. From a corrosion point of view, the sulphur content should be as low as possible. However, a certain sulphur content is necessary to guarantee weldability. However, the susceptibility to hot cracks increases when welding and deforming at high temperatures. By adding manganese, which forms manganese sulphide with sulphur, the susceptibility to hot cracks is reduced.
