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Mechanical Properties of Ferrous Metals
Ferrous metals are materials composed of iron or iron-containing alloys. They are extensively used in engineering applications, construction and other industrial and commercial areas due to advantages like good strength, high malleability and good durability with suitable treatments. This article discusses the mechanical properties of ferrous metals, with emphasis on I-ferrous or plain carbon steels.
The strength of a material is measured as the amount of load or stress to it can bear before it fractures or yields. This is one of the most important properties of ferrous metals which mainly depends on their micro-structures like grain size and refinement, grain shape, defects, phases, and elements involved in a steel alloy. The plain-carbon steel microstructures can either be spheroidized or pearled due to annealing. The grain size usually decreases with increasing temperatures thus making high temperature strengthening (also known as age hardening) more effective. Steels can also be hardened by cold working and precipitation hardening.
Malleability of ferrous metals is related to their ability to get deformed without cracking. This property mainly depends on the grain size, microstructure and the amount of strain caused by the deformation process. Plain-carbon steels can be hardened by cold working and precipitation hardening. Some of the alloys like cast irons can be heat treated to increase their malleability.
Another important property of ferrous metals is toughness. It covers the metal’s ability to resist damage due to sudden impacts, vibration and fatigue. Toughness of a material is determined by the yield strength and other factors such as the degree of work hardening. One important measure of toughness, called Charpy V-notch impact test, is a standardized test which measures the ductility and toughness of ferrous metals, usually steels.
The ductility of a metal is simply its ability to get stretched or drawn without fracturing. It mainly depends on the grain size, microstructure and the number of dislocations that the material can accommodate. The ductility of plain-carbon steels can be improved by cold working, austenitizing and quenching, and proper heat treatment. Steels can be tempered by various processes like carburizing, martempering, quenching and tempering.
Fatigue strength is the measure of the resistance to gradual failure due to cyclic loads. It can be determined from the S-N diagram, which shows the relationship between the life of the material under cyclic loading to the maximum stress range. The fatigue strength of steels largely depends on the grain size, degree of cold working, and the surface finish. It can be improved by shot-peening and thermochemical treatments.
Ferromagnetic property is mainly related to the ferritic content present in ferrous alloys. This property determines the susceptibility of the material to magnetization. The magnetic permeability of the material depends on the temperature and the level of strain. Unalloyed steels are weakly magnetic and can be used in applications like magnetic shielding.
The wear resistance of a metal is quite critical in certain applications; it depends on various parameters like hardness, strength, lubrication and surface finish. Wear of steels can be reduced by improving their hardness, using coatings and changing their surface finish. These can be further enhanced by applying certain treatments like annealing, carburizing and nitriding.
In summary, ferrous metals like carbon steels are essential materials in engineering and manufacturing due to their comparatively better mechanical properties. By optimizing their composition, grain size, and microstructure, these properties can be fine tuned for specific applications. Some treatment processes like carburizing, nitriding and quenching and tempering can be used to enhance their strength and wear resistance.
