Once iron ore has been extracted from pig iron, an additional process is carried out on the iron ore. This additional process is carried out so as to remove certain impurities and gases from the iron ore. Impurities removed range from excessive carbon (C), silicon (Si), phosphorus (P), sulfur (S), and gases like oxygen (O), nitrogen (N).
Once this process has been completed the final product is “steel”. Note however that in the steels group, there are variations based on the chemical composition. The main groups being, carbon steel, alloy steel, tool steel and special-purpose steel.
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Carbon steel and alloy steel
Carbon steel is a steel that consists mainly of two elements iron (Fe) and carbon (C). It is used in applications such as couplers for trains.
Alloy steel is a steel that has had a variety of elements alloyed into it to purposely change the chemical characteristic to enhance certain properties. Ice axes and pliers are examples of alloy steels.
Tool steel
Within the tool steel group there are three sub-groups. These are known as carbon tool steel, alloy tool steel and high-speed tool steel. One of the main requirements of tool steels is to have both hardness and toughness.
To achieve the correct hardness and toughness it is necessary to heat-treat the materials. In order to make the heat-treating process more effective tool steels tend to have a slightly higher carbon (C) content.
Carbon tool steel contains more carbon (more than 0.6%) than carbon steel. Carbon tool steel has poor heat resistance and at temperatures that exceed 200°C the effects of hardening reduce and the overall hardness can not be maintained.
Its main application is nippers blade etc.
This is a steel that is manufactured by alloying a variety of other elements to carbon tool steels. The reason for alloying other materials is to increase its material characteristics. The result of which compensates for the disadvantage of carbon tool steel in regards to the poor heat resistance properties, shock resistance, and prevents deformation under high heat treatment processes.
Alloy tool steel as a cutting tool offers better hardness and higher wear resistance at higher cutting edge temperatures. The elements that are generally alloyed are chromium (Cr), tungsten (W) and vanadium (V).
Basically there are 2 main types of high-speed steels, tungsten (W) based high-speed steels and molybdenum (Mo) based high-speed steels. However there also exists cobalt (Co) based high-speed steels that offer increased hardness.
Tungsten-based high-speed steels are often used for tool holders, due to its high heat hardness. Molybdenum-based high-speed steels are often used for drills due to the high its high shock resistance properties.
Special-purpose steel
Today, special steels have been developed to support different uses for workpieces in modern industry. These steels are commonly referd to as special-purpose steel.
One of the main characteristics of stainless steel is that is less prone to rusting or staining than iron is. Stainless steel’s tend to be sticky and soft, however they are subject and prone to work hardening. They are generally divided into three types, 13 chrome stainless steel, 18 chrome stainless steel and 18-8 stainless steel.
Due to the many various kinds of stainless steels, there is a need for them to be sub-divided. By changing the composition the characteristics can be changed to suit various applications. For example the characteristics that can be changed are (1) to enhance hardening, (2) to improve carburizing or nitriding, (3) enable solution treatment to be carried out, (4) to improve free machining property, (5) enhances resistance to corrosion and heat, and (6) to improve the weldability.
This is a steel with increased hardness that has been achieved by a heat treatment process or a surface treatment process. Generally the hardness is above 45HRC.
Heat-resistant alloy or corrosion-resistant alloy is a term given to an alloy with sufficient mechanical strength at high temperatures and with high resistance to oxidation and corrosion.
The main components of most heat-resistant alloys are iron (Fe), nickel (Ni) and cobalt (Co). Within this group there are two types, one being if the Fe content is 50% or more then it is termed a heat-resistant steel, the other if the Fe content is less than 50% then it is termed a heat resistant alloy. This category are generally referred to as Super-alloys. For example Inconel (Ni base superalloy).
Spring steel
Spring steel is steel used for springs. There are two kinds of spring forming methods, hot forming* and cold forming*. Spring forms include coiled spring, leaf spring, volute spring, spiral spring and disc spring.
Bearing steel
Bearings are generally in the form of a ball-and-roller bearing (ball bearing, roller bearing). Bearings need to be hard and have high wear-resistance properties. In addition, bearings need to be inexpensive as they are a basic mechanical part used in nearly all application. And as such expensive elements are not added to bearing steels.
Magnetic steel
Magnetic material encompasses materials for permanent magnets and iron core material for electromagnets.
There are two kinds of permanent magnets, casting magnets and sintering magnets. Casting magnets are made by casting and sintering magnets are made by sintering.
Workpiece classification and applications
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