Chemical Composition and Metallurgical Properties of Ultrafine Grained Steels
Introduction
Steel is a widely used material in a variety of industries and applications. With advancing technologies, steel is being manufactured with increasing sophistication. To keep up with the expanding range of applications of steel, practitioners are now forming steels with ultrafine grain structures. Such ultrafine grained steels, also known as Ultra High Strength Steels (UHSS) not only improve the mechanical properties of the steel but also provide better corrosion resistance. In this article, we will discuss the chemical composition and metallurgical characteristics of ultrafine grained steels.
Chemical Composition
The chemical composition of ultrafine grained steels is in general the same as that of regular steels. However, ultrafine grained steels may have higher concentrations of certain alloying elements. Carbon and manganese are present in all as ratios of iron. Alloying elements, notably nickel and chromium, are often added to improve the mechanical properties of ultrafine grained steels, particularly their strength and toughness.
Metallurgical Properties
Ultrafine grained steels have excellent mechanical properties due to their fine grain structure. The fine grain structure is obtained through a process known as recrystallization. Recrystallization involves the setting of an elevated temperature, applied pressure and deformation which reduces the size of grains and forms new ones leading to a refined, homogeneous grain structure. The refined grain structure results in better mechanical properties of the steel, resulting in higher strength and toughness, better corrosion resistance, greater wear resistance and improved fatigue performance.
Ultrafine grained steels can be divided into two categories: annealed steels and hardened steels. Annealed steels are steel that has been heated, then cooled in order to reduce the strength and improve workability. Hardened steels are those that have been subjected to a heat treatment process in order to increase the strength and wear resistance.
Conclusion
Ultrafine grained steels are materials with excellent mechanical properties due to their microstructural characteristics. Such steels are characterized by their homogenous grain structure, resulting from a heat treatment process, which gives them improved strength, wear resistance and corrosion resistance. The chemical composition of such steels is in general similar to that of regular steels, however they may have higher concentrations of alloying elements, notably nickel and chromium, to increase their mechanical properties.
