The applicability of steel relies on its array of properties, including toughness, strength, ductility, durability, and weldability. High-stress environments, such as high temperatures and pressures, significantly affect the properties of steel, impeding its industrial applications. This article provides an overview of the mechanical properties of steel and the impact of high-stress environments on these properties.
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Composition and Properties of Steel
Steel is an alloy of carbon and iron, with the carbon content constituting two percent. Owing to its abundance and low cost of making, processing, and forming, steel has gained immense popularity as a raw material in industrial applications, from building materials to oil tankers.
The properties of steel depend on both its chemical composition and the manufacturing method. The following are the main properties of steel that play a vital role in their industrial applications, such as in construction.
Ductility: This is an important steel property that determines its capacity to be plastically deformed, leading to any fracture. This property primarily indicates the softness or malleability of a material. The composition and amount of alloying elements significantly influence the ductility of steels. For example, increased carbon content in steel can improve its strength and decrease its ductility.
Tensile Strength: This property refers to the ability of steel to resist tensile stress by breaking it. It is a commonly used property of steel to determine its capacity to function in an application. A commonly applied method for determining the tensile strength of an alloy is to place a test piece in the jaws of a tensile machine.
Corrosion Resistance: It measures a material’s resistance to oxidation or other chemical processes. Generally, metals exposed to humidity, rain, and water may lead to surface oxidation, making them susceptible to damage due to corrosion. Thus, the use of stainless steel, galvanized steel, or weathering steel can prevent corrosion.
The exposure of stainless steel to corrosive chemicals can lead to the formation of a very thin oxide layer that remains passive. The deterioration of this passive layer exposes specific areas to corrosion. However, galvanized steel is resistant to corrosion because the zinc coating on its surface binds to the iron.
Hardenability: The carbon component of the steel primarily determines the hardness of the material, known as hardenability. Steels with deep hardenability are termed high-hardenability steels, whereas those without deep hardenability are termed low-hardenability steels. Hardenability is affected by factors such as grain size, carbon content, and alloying elements.
Machinability: The main elements affecting the machinability of steel include their chemical composition, thermal treatment, and cold work. Thermal treatment of steel lowers its strength, hardness, and stress and regulates its microstructure, consequently enhancing its machinability. Common machine techniques to enhance the machinability of steel bars include spheroidize annealing, lamellar pearlitic annealing, and stress-relief annealing.
The chemical composition of the steel also plays a crucial role in enhancing its machinability. The elements that contribute to the machinability of steel include lead, sulfur, carbon, and phosphorus.
Moreover, cold work enhances the machinability of low-carbon steel by diminishing the ductility of the hot-rolled product. Steel coldworking, performed by pulling it through a die or rolling it, results in harder, brittle, and curled chips.
Durability: Steel is a highly durable alloy that can tolerate harsh environmental conditions. Owing to its composition of iron and carbon, it becomes very resistant to extreme environmental conditions such as frequent storms, high winds, and harsh weather. Hence, steel is an ideal material for stormy places because of its ability to withstand blowing sand and severe wind.
Steel Properties in High-Stress Environments
An article published in the Journal of Constructional Steel Research examined how different levels of tension on steel, caused by slow and steady pressure, affect corrosion growth and the strength of steel. Here, plastic-stressed, elastic-stressed, and non-stressed steel specimens were immersed in hydrochloric acid with acidity in the range of 0.00001–1 Molar.
The corrosion behavior of the steel samples was tested after 7, 14, and 28 days. The results showed that the plastic-stressed steel underwent a higher degradation of mechanical properties, and corrosion spread faster than in the elastic- and non-stressed specimens over time.
This study explained the relationship between tensile stress and corrosion and its effect on the strength of corroded steel.
Another article published in the International Journal of Pressure Vessels and Piping reported the creep behavior of T90 steel in a steam environment. The tests were conducted at 650 °C and stress was applied in the range of 100 MPa-160 MPa in air and steam environments. The results revealed that specimens in steam had a higher creep rate and reduced plasticity than those in air.
A recent study published in Construction and Building Materials investigated the corrosion rates of weathering steel and a control material (Q235 steel) in industrial and rural atmospheric environments. The corrosion rates of both steels were monitored using the weight-loss method.
The results revealed that in the industrial environment, the corrosion rate of weathering steel was 30 % lower than that of Q235 steel, whereas in the rural environment, the difference between the two corrosion rates decreased substantially over time and disappeared after 360 h.
This difference in corrosion rates was attributed to the composition of the corrosion products of weathering steel consisting of a higher content of goethite (α-FeOOH), copper oxide, and nickel compounds than that of Q235 steel, which led to a compact and denser rust layer and consequently better corrosion resistance.
Conclusion
Overall, determining the mechanical properties of steel in high-stress environments is crucial for determining its structural integrity and performance. The resilience, ductility, and strength of steel make it a desirable material for industrial applications that are subjected to extreme loads and harsh conditions.
Factors such as tensile strength, ductility, machinability, and corrosion resistance are vital considerations to ensure the ability of a material to withstand the demands of its environment without compromising safety.
Advancements in engineering techniques and metallurgical science offer tailored solutions to meet specific requirements, leading to the development of specialized steel alloys with enhanced performance in high-stress environments.
More from AZoM: Cold Work vs Hot Work in Steel: Understanding the Differences
References and Further Reading
Chang, H., Yan, W., Wang, M., Shang, C., Lu, Y., Yagi, K., & Ren, X. (2023). Effect of steam on the creep behavior of T92 steel at 650° C. International Journal of Pressure Vessels and Piping, 204, 104976. https://doi.org/10.1016/j.ijpvp.2023.104976
Le, L., Sofi, M., Lumantarna, E. (2021). The combined effect of stress and corrosion on mild steel. Journal of Constructional Steel Research, 185, 106805. https://doi.org/10.1016/j.jcsr.2021.106805
Han, C., Li, Z., Yang, X., & Wang, J. Corrosion Behavior and Mechanical Performance of Weathering Steel in Industrial and Rural Atmospheric Environments. Available at SSRN 4594108. https://doi.org/10.1016/j.conbuildmat.2023.134284
Steel material properties. Accessed on December 7, 2023.
Properties of Steel Material. Accessed on December 7, 2023.
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