Structural Changes during Steel Processing

It is impossible to overestimate the role of metals and alloys in the development of human civilization. Entire historical periods are named in accordance with alloys and metals that played significant roles in technological progress. The history of mankind is closely bound with the history of the investigation of metals and alloys. It is obvious that we currently use both inorganic and organic materials in order to manufacture a great variety of goods for our customer needs. However, metals and alloys stand at forefront of a long list of known and invented materials. Technological progress is the main moving force capable of creating any new material with a specified set of properties.

Iron and steel take the primary position among construction materials due to their properties which can be varied in a wide range by employing a different carbon content or alloying procedure, or by changing the processing methods or their regimes. It is a well-known fact that steels are currently classified into carbon steels and alloyed steels depending on their chemical composition. Carbon is an obligatory element in all kinds of steel that plays a significant role to form certain properties. The carbon content designates the microstructure of steels and is the main factor to consider when choosing the method or regime for further processing. Low-carbon steels with less than 0.03% C are very ductile with low strength properties. Consequently, this kind of steel is used to manufacture pipes, wires, and several kinds of fasteners. Medium carbon steels (between 0.31% and 0.60% C) exhibit higher levels of strength, which is necessary for metal products that are manufactured by most kinds of deformational processing methods. In addition, heat treatment is used in order to enhance the values of the ductile and/or strength properties. With a carbon content more than 0.6% to 2%, high-carbon steels have high strength but low ductility. Thus, this kind of steel is used for tool manufacturing. The range of alloyed steels is very wide. Different alloying elements are used for steels to influence their microstructures and properties. Specific areas of application demand using alloying elements for steels such as molybdenum, chromium, nickel, vanadium, titanium, vanadium, etc. Every alloying element and their combination for one type of steel play a peculiar role in the microstructure and properties’ formation. Another aspect that can be used to classify steel is the kind of microstructure. Usually, this is important for stainless steels that have microstructures such as ferritic, martensitic, austenitic, etc. In fact, the presented examples show the significance of steels, as they are used for a wide range of metal products. It is necessary to keep in mind that every approach to classification is proper depending on the aim of the investigation with respect to iron and steels.

Plenty of studies are devoted to the exploration of the peculiarities of the structures and properties of metals and alloys under different kinds of processing. Different efforts are applied to improve the properties of metals and alloys in accordance with the exploitation conditions and external impacts. There exists a great variety of methods in this direction. The papers published in this Special Issue, “Structural Changes during Steel Processing”, show this tendency very clearly. The results presented by different scientific groups prove the interconnection between the microstructure and properties in steels. The research into this interconnection plays an important role with respect to choosing the necessary types and modes of metals and alloys’ further processing.

The effect of (NbTi)C particles on the microstructure and hardness of chilled cast iron alloyed with chromium and nickel is studied by Hongwei Zhu et al. [1]. Precise methods of metallography to investigate the form of the precipitated particles were used. Since this kind of cast iron is an excellent hot-rolled material with a good combination of surface roughness, heat-cracking resistance, and heat wear resistance, the obtained results can be used to find the best level of equilibrium between the microstructure and properties in order to find new areas of application for high-chromium and nickel-indefinite-chilled cast iron.

Several papers in this Special Issue were devoted to investigating steels with different chemical compositions. Currently, steel remains the most commonly used construction material, which is why the attention of engineers is attracted to its microstructure and properties. The use of modern scientific methods and equipment enables the study of microstructures on different levels of a material’s nature. Therefore, the evolution of the structure and properties of 2507 duplex stainless-steel at the micro-nano level is described by Faqi Zhan et al. [2]. Since the microstructure of duplex steel contains both austenite and ferrite it possesses a good combination of high strength and ductility. The study of the phase transformation of duplex steel with this kind of chemical composition can be used to design the technological process of its rolling in order to achieve the necessary relationship between its strength and ductile properties. Low density steels are an interesting object for investigation because of their promising use as a potential lightweight material for automobiles. High-carbon steel (1% C) alloyed with manganese (27%) and aluminum (10%) was chosen for investigation. The deformation behavior of this kind of steel depends on the existence of k-carbides, as described in [3]. The size of k-carbides is measured at the nanoscale; thus, they play a significant role in the formation of the mechanical properties of processed low-density steel.

The role of silicon content in the cold workability of high-grade non-oriented silicon steel is shown in [4]. This kind of steel is usually used in electrical transformers; therefore, the choice of regimes for its processing is an important aspect for further manufacturing. The simultaneous optimization of the Si content and normalization of the temperature was useful for decreasing the difficulty with respect to the cold workability and improving the cold-rolling yield. The validity of the obtained results was proven by a texture formation study.

When discussing the application of steels it is necessary to consider the wide variety of possible temperatures and exploitation conditions. This very aspect was studied by Diqiang et al. [5]. The high-strength steel EH36 is a very promising kind of steel for exploitation under low temperatures; thus, the role of using different alloying elements in this steel is the aspect under investigation for many scientific groups. In [5], the research results showed that the addition of yttrium-based rare earth to EH36 offshore-engineering steel refines the inclusions, resulting in the increase in the cryogenic temperature impact properties of this steel.

The papers presented in this Special Issue, “Structural Changes during Steel Processing”, showed that the process of the investigation of steels is continuous. This kind of material stores plenty of secrets with respect to the different levels of its structure. The aim of engineers and investigators is to try to find the proper instruments to study steels and to explain the peculiarities of their microstructure and properties’ formation. Such investigations will become the next brick in the wall of knowledge regarding this simultaneously known and unknown material.