Application of Nitrogen on Microalloyed Steels
Abstract
Nitrogen, a non-metallic element, is an important additive to steels and the inclusion of nitrogen in steels can affect the steel’s physical, chemical, and mechanical properties. Microalloyed steels, which are low alloy steels, form a separate family of steels due to their relatively low cost, availability and better machinability and weldability than other steels. The addition of nitrogen to microalloyed steels can further improve the performance of these steels. This paper attempts to provide an overview of the different forms and levels of nitrogen addition, along with the main characteristics and applications of nitrogen-bonded steels.
Keywords: Steels, Nitrogen, Microalloyed Steels, Performance
1. Introduction
Steel is one of the most important engineering materials which finds wide applications in different areas of engineering due to its superior strength, ductility, and toughness. A variety of steels are available in the market based on the alloying elements used and the production process adopted. The addition of nitrogen to steels has gained importance historically due to its power to increase the strength of steels without affecting the elongation. From production point of view, nitrogen is considered an environmentally friendly element which does not escape from steelmaking process and is recycled throughout the process. Microalloyed steels (sometimes known as low alloy steels) form a separate family of steels with improved properties due to a combination of alloying elements. These steels have many advantages over conventional steel grades, such as better cost, better machinability, better weldability, better strength-to-weight ratio, and superior formability.
Nitrogen is an important additive to these microalloyed steels and its addition can further improve the performance of these steels. There is a lot of research taking place to study the effects of nitrogen in steels and its applications in different grades of steels. The aim of this paper is to provide an overview of the effects of nitrogen addition and its applications in microalloyed steels.
2. Nitrogen Content and Forms
Nitrogen is a non-metallic element which is mainly available in two forms: soluble and insoluble. The solubility of nitrogen in solid steel increases with the increase of temperature(Kurz et al, 1991). Dissolved nitrogen can be present two forms, either in solid solution or in combination with other elements to form nitride, nitro (nitrogen-oxygen) or nitrocarbide precipitates. In addition, it can also appear in non-metallic elements, such as sulphide and oxide inclusions.
The amount of nitrogen present in steels is varied depending on the process of production. Nitrogen content in steels produced by open-hearth furnaces, electric-arc furnaces and induction furnaces can range from 0.001 % to 0.03 %. The amount of nitrogen added to steels is determined by its solubility and has to be adjusted according to the conditions of treatment. Reportedly, the highest levels of nitrogen added to steels is 0.08 % and up to 0.1 % (Kemppainen et al., 2003).
3. Effects of Nitrogen on Steel Properties
The addition of nitrogen to steels can significantly improve the strength of steels without adversely affecting the ductility. The hardness and strength of steels increase with increasing nitrogen concentration, while the ductility of steels remains unchanged or slightly decrease with increasing nitrogen concentration. The addition of nitrogen to steels can also affect the corrosion resistance of steels as nitrogen is known to reduce the activity of various acids.
In addition, the addition of nitrogen to steels is known to improve fatigue strength and wear resistance of steels which is desirable for certain applications. The surface roughness of a steel part is also influenced by the nitrogen content of the steel.
4. Applications
The increased strength and improved wear resistance of steels due to nitrogen addition have made them suitable for several applications in the auto and aerospace industry. The applications of nitrogen-added microalloyed steels include automotive parts, such as axles, bearings, and drive shafts. Nitrogen addition has been found to improve the fatigue performance of these parts significantly and make them suitable for use in automobile engines and transmissions.
In the aerospace industry, nitrogen added steels have been used in the manufacture of various aircraft components such as landing gear, wing components and fuselages. With the increased strength of steels due to nitrogen addition, the use of smaller and lighter components is possible.
5. Conclusion
The addition of nitrogen to steels has been found to have beneficial effects on their mechanical and physical properties. Nitrogen-added microalloyed steels have been used for many different applications in the auto and aerospace industry due to the improved strength and wear resistance of the steels. These steels are relatively cheaper and more available than other steels and make them attractive for many applications. It is believed that with further studies and research, more applications and uses of nitrogen-added steels will be seen.
