Metallurgy includes the processing of minerals from their ores (separation from ores), smelting, refining and production of ingots, improving properties and preparing alloys, and the technology of working on metals and shaping them. The science of metallurgy is divided into two categories: physical metallurgy and mechanical metallurgy. Metallurgical engineering is divided into two categories: ferrous or ferrous metallurgy and non-ferrous or non-ferrous metallurgy. More than 95% of the world's metal production is the result of ferrous metallurgy.
Metallurgy or metalology?!
Metallurgy is a combination of two Greek words metal meaning "phase" and ourgein meaning "working". Here, it is necessary to pay attention to the fact that even many experts write and pronounce the name of this field as "metallurgy", which is incorrect according to the root of the word. Probably the origin of this error is a false analogy that some people make in their minds. Because biology, physiology, radiology and hundreds of other scientific fields end in "logy", they think that this scientific field should be the same as metallurgy.
History of metallurgy
Although metallurgy as a science should be considered a relatively new knowledge because it has not been a hundred years since metals have been studied in a practical way; While our fathers used metallurgy as a technique to produce the tools they needed centuries ago.
The history of metallurgy shows that the science of metallurgy has a history of about 6500 years. where metals such as gold, silver and copper were discovered as the first metals.
Extraction
The science of metal extraction deals with the separation and in other words the extraction of valuable metals from minerals, wastes and wastes and their purification until reaching pure metals. Extractive metallurgy processes are carried out in three ways: hydrometallurgy, pyrometallurgy and electrometallurgy.
Alloying
Nowadays, metals are usually produced and used as alloys. Alloys are obtained from a combination of two or more engineering materials because with alloying we can obtain properties that are not possible using pure metals. For example, we can increase the strength of the material several times or reduce the corrosion resistance in the desired areas.
Production
Casting
Casting can be defined as the process of turning metal into a piece of desired shape. This is achieved by melting metal and pouring it into a mold with the desired shape. Despite the fact that casting is the oldest method for shaping metals, it is considered one of the main production methods in today's industry, because about 50% of the total weight of machine parts are produced in this way.
Metalworking processes
Metal forming processes are another category of manufacturing methods. Metal forming is a metalworking method for making metal objects and parts by mechanical deformation. Usually, the work piece changes its shape without removing or adding a new material and its weight remains constant.
Today, hundreds of metalworking methods have been developed, each of which has been developed for specific applications. But these methods can be classified into 5 main groups:
rolling
extrusion
Attraction
forge
Sheet forming
In rolling, extrusion, stretching and forging processes, a lot of strain is applied to the work piece. In this case, if the piece is subjected to heat and heated to a high temperature (below the melting point), the grains undergo recrystallization and become grains without strain. Under such conditions, we can put the piece under shaping again, which is called hot working. But if the forming process takes place at a temperature below the recrystallization temperature, this process is called cold working.
Powder metallurgy
Powder metallurgy is another method of producing parts that includes other engineering materials such as ceramics and polymers in addition to metals. Among the forming methods, powder metallurgy is a relatively new method. In this method of pouring powder into a mold and combining it with a binder, a piece known as a raw piece is obtained. By placing this piece under a high temperature below the melting point, a process known as sintering occurs. In this process, the bonding agent evaporates and the particles stick together and the final part is formed.
Depending on the type of process and the type of raw material, different methods can be considered for powder metallurgy. The most important methods developed based on the type of raw material are:
Powder Injection Molding (PIM)
Metal Injection Molding (MIM)
Ceramic Injection Molding (CIM)
Welding
Welding is the process of connecting metal parts to each other by heating the contact area until it melts with a paste. (Although today, with new welding methods, ceramics and polymers can also be welded). In this case, the atoms of the welded parts penetrate each other and create a strong connection.
Today, various welding methods have been developed, which can be divided into 4 general categories:
Pressure welding
fusion welding
Yellow welding
Soldering
Machining
Machining is a method of shaping materials by turning and cutting. This work is done by cutting and turning tools and machines. In shearing, scissors are used with a cutting tool to break the metal. In turning, lathes, milling machines, drills, turning plates, grinding and drilling are used to achieve products. Usually these parts are products of casting, forging or rolling processes.
Additive Manufacturing
Sintering or melting of amorphous metal powder in a three-dimensional space to create a piece with the final shape. (Read more about additive manufacturing)
Post Processing
After producing parts, in order to achieve mechanical, chemical or better appearance, we subject them to an operation called post-processing. This operation aims to reduce the internal stresses of the parts, increase their hardness and strength, reduce the surface roughness, and in general includes all the operations that turn the parts into usable products. In this section, we mention some of the most important of these processes:
heat treatment
Heat treatment is done to change the physical and mechanical properties of metals. Change in properties such as strength, density, hardness, toughness and corrosion resistance. The most famous heat treatments that are used today are Annealing, Precipitation Hardening, Quenching and Tempering.
Surface treatment
In many production methods, the part is not ready for consumption directly after production. Surface engineering operations are performed for three purposes.
Beautification (such as shot blasting or painting)
Increasing surface mechanical properties (such as shot peening or surface hardening)
Increasing corrosion resistance (such as anodizing, painting)
Test & Analysis
An important part of the activities of metallurgists is the analysis and testing of metal products. Metal analysis methods can be divided into the following three categories:
Elemental analysis: with the aim of detecting the type and amount of elements in the sample (such as quantum analysis)
Phase analysis: with the aim of detecting the type and amount of phases in the sample (such as XRD)
Microstructural analysis: with the aim of examining the microscopic microstructure of the sample (such as metallography)
In order to ensure that the required properties are obtained, metal products are subjected to tests after production, which are divided as follows.
Mechanical tests (hardness, pressure, tension, impact, fatigue, etc.)
Chemical-corrosion tests (polarization, impedance, etc.)