Ferrous Metals mostly contain Iron. They have small amounts of other metals or elements added, to give the required properties. Ferrous Metals are magnetic and give little resistance to corrosion.
Ferrous materials are produced in larger quantities than any other metallic material. Three factors account for it:
In ferrous materials the main alloying element is carbon (C).
|Material carbon(C) < 2.14%||eutectoid transformation||steels|
|Material carbon(C) > 2.14%||eutectic transformation||Cast irons|
One main drawback of ferrous alloys is their environmental degradation i.e. poor corrosion resistance. Other disadvantages include: relatively high density and comparatively low electrical and thermal conductivities.
Iron is not found in free state because of its high reactive nature.Iron is found in combined state in the form of oxide, carbonate and sulphide.
Pure iron is a soft, grayish-white metal. Although iron is a common element, pure iron is almost never found in nature. The only pure iron known to exist naturally comes from fallen meteorites.
Most iron is found in minerals formed by the combination of iron with other elements. Iron oxides are the most common. Those minerals near the surface of the earth that have the highest iron content are known as iron ores and are mined commercially.
|Iron ore type||Properties||Available places|
Iron ore is converted into various types of iron through several processes. The most common process is the use of a blast furnace to produce pig iron which is about 92-94% iron and 3-5% carbon with smaller amounts of other elements.
The raw materials used to produce pig iron in a blast furnace are
Pig iron has only limited uses, and most of this iron goes on to a steel mill where it is converted into various steel alloys by further reducing the carbon content and adding other elements such as manganese and nickel to give the steel specific properties.
In ferrous materials the main alloying element is carbon (C). Depending on the amount of carbon present, these alloys will have different properties, especially when the carbon content is either less/higher than 2.14%.
Thus the ferrous alloys with less than 2.14% C are termed as steels, and the ferrous alloys with higher than 2.14% C are termed as cast irons.
Alloying additions are necessary for many reasons including:
Arguably steels are well known and most used materials than any other materials.
Mechanical properties of steels are very sensitive to carbon content. Hence, it is practical to classify steels based on their carbon content.
Thus steels are basically three kinds based on carbon content
The other parameter available for classification of steels is amount of alloying additions, and based on this steels are two kinds:
These are arguably produced in the greatest quantities than other alloys.
These are stronger than low carbon steels. However these are of less ductile than low carbon steels.
Effects of alloys:
These are strongest and hardest of carbon steels, and of course their ductility is very limited.
Effect of an alloy:
A special group of ferrous alloys with noticeable amount of alloying additions are known as HSLA (high-strength low-alloy) steels.
Carbon is by far the most important constituent of steel. It combines readily with iron to form iron carbide (Fe3C),which is a compound known as cementite.
Next to carbon, manganese is the most important ingredient in steel.
Manganese does possess the property known as “penetration hardness” which means that in heat treatment of large sections, the hardness is not merely on the surfaces but penetrates to the core as well.
Only a very small amount, not exceeding 0.3% of silicon, is present in steel.
Silicon and manganese in large amount are used as alloying elements in the formation of silico-manganese steels. These steels have good impact resistance.
Sulphur is a very undesirable impurity.
Phosphorus, like sulphur, is an undesirable impurity.
Nickel is a white metal almost as bright as silver. In the pure state it is malleable, ductile, and weldable.
Chromium is a hard gray metal with a high melting point.
Corrosion-resisting steels contain large amounts of chromium.
Some chromium alloys are used where great wear resistance is required.
A small percentage has as much effect as much larger amounts of other alloying elements.
Uses in aircraft:
Vanadium is the most expensive of the alloying elements.
It is an intensive deoxidizing agent and improves the grain structure and fatigue strength.
|Chemical||It’s effect on steel|
By adding alloys, specials alloy steels can be produced to suit specific requirements by modifying the properties
The name comes from their high resistance to corrosion i.e. they are rustless (stain-less).
Stainless steels are mainly three kinds based on prominent constituent of the microstructure
For modern industrial production, in particular mass production, machining is one of the most important shaping and forming processes. High Speed Steels are high-performance special steels offering high hardness at temperatures up to 500°C and high wear resistance, thanks to alloying elements like tungsten, molybdenum, vanadium and chromium which are able to form carbides. To improve hot hardness, cobalt may also be added.
High Speed Steels can be produced either by conventional route or by powder metallurgy.
The characteristic properties of all high speed steels grades include.
These are high nickel based steels which have high red hot hardness. These are also called as super alloys
Based on the form of carbon present, cast irons are categorized as gray, white, nodular and malleable cast irons.
Effects of alloy:
How name came:
Alloying additions are of prime importance in producing these materials.
A relatively recent addition to the family of cast irons is compacted graphite iron (abbreviated CGI). In the gray, ductile, and malleable irons, carbon exists as graphite, which formation is promoted by the presence of silicon.
Compared to the other cast iron types, desirable characteristics of CGIs include the following:
Wrought iron is composed primarily of iron with 1 to 2% of added slag, the byproduct of iron ore smelting—generally a mix of silicon, sulfur, phosphorous, and aluminum oxides.
During manufacture, the iron is removed from heat and worked with a hammer while still hot to get it into its intended final form.
Cast iron is iron that has been melted, poured into a mold, and allowed to cool.
Wrought iron is iron that has been heated and then worked with tools. In fact, the term “wrought” derived from the past participle of the word “worked.”
|Nickel||Increases machinability of cast iron by improving carbon structure|
|Copper||Improves machinability,castability and toughness by promoting graphite formation|
|Chromium||Acts as carbon stabilizer thereby improves hardness, strength and corrosion resistance|
|Silicon||It acts as a softener in cast iron by promoting free graphite and decreases cementite|
|Sulphur||Promotes formation of cementite|
|Phosphorus||Improves castability of cast iron|
|Molybdenum||Improves machinability,toughness and fatigue strength|
|Manganese||Reduces effect of sulphur on cast iron there by reduces hardness and brittleness|
Q: What is red hardness?
Ans: Red-Hardness. (also called heat resistance), the ability of steel, upon heating to red heat, to retain the great hardness and durability obtained through heat treatment. A high level of red-hardness is characteristic of tool steel.