![]() ![]() These alloys cannot be hardened through heat treatment. This chemical composition allows them to maintain an austenitic structure from cryogenic temperatures up to the melting point of the alloy. Chromium content ranges from 16.00 to 28.00% and nickel content ranges from 3.50 to 32.00%. In austenitic grades, carbon is usually kept to low levels (C < 0.08%). 1.1.3 Austenitic Stainless Steels: Fe-Cr-Ni-(Mo) alloys Ferritic grades are magnetic and chosen when toughness is not a primary need but corrosion resistance, particularly to chloride stress corrosion cracking (SCC), is important. These grades cannot be hardened through heat treatment. While some ferritic grades contain molybdenum (up to 4.00%), only chromium is present as the main metallic alloying element. In ferritic grades, carbon is kept to low levels (C<0.08%) and the chromium content can range from 10.50 to 30.00%. 1.1.2 Ferritic Stainless Steel: Fe-Cr-(Mo) alloys The common uses are knife blades, surgical instruments, shafts, etc. These grades can be hardened through heat treatment to offer strength and hardness. They have relatively high carbon content from 0.15 to 1.20% compared to other stainless steels and molybdenum can also be used. These alloys have a chromium content that ranges from 11.50 to 18.00%. 1.1.1 Martensitic Stainless Steels: Fe-Cr-C-(Ni-Mo) alloys Stainless steels can be divided into five categories: martensitic, ferritic, austenitic, austenitic-ferritic so-called duplex, and precipitation hardening (PH). Stainless Steel is a generic term for a large family of corrosion resistant alloys containing at least 10.50% chromium (according to the European standard EN10088) and may contain other alloying elements. ![]() The most important characteristics common to all chromium-containing alloys, among them stainless steels, is that they contain sufficient chromium to make them corrosion resistant, oxidation resistant and/ or heat resistant.Īll of these alloys contain chromium (Cr), manganese (Mn), silicon (Si), carbon (C), nitrogen (Ni), sulphur (S), and phosphorus (P), and may contain: nickel (Ni), molybdenum (Mo), titanium (Ti), niobium (Nb), zirconium (Zr), copper (Cu), tungsten (W), vanadium (V), selenium (Se), and some other minor elements. Each one was developed for a particular need, and each has its own set of properties and characteristics. There are more than a hundred chromium-containing metallic alloys. In the case of chromium added to iron (Fe-Cr alloys), there is another advantage, which consists of a tremendous increase in the corrosion resistance of the new metallic alloy compared to pure iron. This is because the different atom sizes of other elements interrupts the orderly arrangement of atoms in the lattice and prevents them from sliding over each other as easily.Īlloying elements have the capability to block slip planes. Pure iron is too soft to be used for the purpose of structure, but the addition of small quantities of other elements (carbon, manganese or silicon for instance) greatly increases its mechanical strength. chromium with iron to form Fe-Cr alloys, can drastically alter some of its properties. The presence of a proportion of a second element associated with a metal to form an alloy, e.g. Most metals are not used in their pure form but have alloying elements added to modify their properties and this can be used for specific applications. Even if the added elements are non-metals, alloys still have metallic properties. The metallic bond is therefore strong and uniform. This is very different from ionic or covalent bonds, where electrons are shared by one or two atoms. Because these valence electrons are shared by all the atoms, they are not considered to be associated with any atom in particular. cations being surrounded by a cloud of electrons (valence electrons). Such bonds are formed between metal atoms allowing their outermost electrons to be shared by all the surrounding atoms, resulting in positive ions i.e. The strength of metals is that their atoms are held together by strong bonding forces.
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