In ferrous alloys we have iron crystals that define metallic materials with infinite mechanical properties. Inside these crystals, either in their atomic networks, or in their holes or interstices, atoms of other elements can sneak in. When it comes to carbon atoms, we talk about steels.
Steels are by far the most momentous ferrous alloys. There are sweet, medium, or high carbon. We also have stainless steels, which in turn are classified into three classes: austenite, ferrite and martensite, each with its own crystalline structures and compositions.
Characteristics of ferrous alloys
Each of the ferrous alloys has its own distinctive characteristics. However, as the elemental base is the same, iron, the vast majority share some characteristics in common. Among them we can mention the following:
-They are more resistant to corrosion. Due to the fact that iron is accompanied by other elements, they are capable of forming a surface that protects it from oxidation and from external conditions of humidity or salinity.
-Its colorations are grayish or silver.
-They have carbon percentages that range from 0.2% to 2%. However, some alloys, such as gray or white cast iron, harbor even more carbon (2.5-4%).
-In addition to carbon, phosphorus, silicon and boron are added, depending on their final applications.
-They contain appreciable amounts (10% or more) of chromium, manganese or nickel.
-They show better resistance and toughness compared to metallic iron.
-Many ferrous alloys exhibit magnetic properties.
As there are so many ferrous alloys, it is likely to find highly unique characteristics for some of them. For example, ferrocerium, an alloy between iron and cerium (Fe-Ce), exhibits pyrophoricity, which means that it is very prone to generating fiery sparks when subjected to high stresses or shocks.
As such there is no strong classification for all ferrous alloys. However, here they will be divided into three types based on the mix of their metallic or non-metallic elements.
Iron-carbon alloys are the heart of ferrous alloys, as they constitute various types of steels (mild, medium, high carbon, stainless). In addition to steels, these blends include gray and white cast irons, which are even richer in carbon, and have different mechanical properties than steels.
Iron-metal alloys are those that are obtained when iron is mixed with other metals. Among them we can mention: copper, nickel, niobium, vanadium, manganese, chromium, molybdenum, aluminum, magnesium, tungsten, titanium and uranium. Each of these alloys will have oscillating compositions expressed in percentages.
The vast number of metals with which iron is alloyed offers a picture of how diverse its metallurgy is. In addition to this, it should be mentioned that steels also have other metals as additives, which is why they turn out to be iron-metal-carbon alloys. It is placed last to carbon, since it is the element that is found in the smallest proportion.
Iron is not only alloyed with carbon. It can also form alloys with other non-metallic elements, such as silicon (Fe-Si), phosphorus (Fe-P), nitrogen (Fe-N), and boron (Fe-B). As with iron-metal alloys, these can be added to steels to give them specific properties or characteristics.
For example, Fe-B alloys are added to steels to increase their hardenability, thus hardening their interiors.
Examples of ferrous alloys
Examples of various ferrous alloys have been provided throughout the preceding sections. Some of them will be listed below, followed by a brief description.
As the name alone indicates, it is an alloy of iron and aluminum, Fe-Al. It can be visualized as a strengthened aluminum, or a softened iron, all depending on the proportions of Fe or Al. Ferroaluminum alloys have low melting points, and are used as a reducing agent in steels.
Iron-chromium alloy, Fe-Cr, whose chromium composition is usually greater than 50%. Therefore, this alloy is rich in chromium, which is why it is used as a source of this metal for the production of stainless steels.
Iron and manganese alloy, Fe-Mn, used in the steel industry to deoxidize them. It is obtained by heating the oxides of their respective metals, MnO 2 and Fe 2 O 3 , in the presence of coke as a reducing agent.
Iron and molybdenum alloy, Fe-Mo, used in the production of steels with high resistance to corrosion. Note how many of the iron-metal type ferrous alloys end up being sources of metal atoms for steel crystals.
Like ferromolybdenum, ferroniobium, Fe-Nb, has a high composition of niobium (greater than 50%) and is used in the production of steels with high resistance to corrosion.
An iron-silicon alloy, Fe-Si, which is prepared by mixing silica with coke and iron. It is used for the production of steels intended for electrical applications. It also serves as a reducing agent for the industrial production of silicon or metals from their ores, and is also used for the militarized production of hydrogen.
An alloy of iron and uranium, Fe-U, whose uranium composition ranges between 35 and 50%. Currently it does not have many uses, since its solids melt at low temperatures (below 1000 ºC), so they are reserved for few applications, such as in cutting tools.
Finally, the iron-phosphorus alloy, Fe-P, composed of iron phosphides, is used as an excellent phosphorus source for the production of stainless steel powder. When added to cast iron it increases its fluidity. And also, it is used as an aggregate to strengthen concretes and cements.