Introduction
Micro-alloyed steel reinforcement (MAS) is a new generation of steel based on micro-alloying technology. It is characterized by higher strength, higher plasticity, excellent elongation and guaranteed weldability. The main strengthening mechanism of MAS is the precipitation of fine particle carbide and nitride in the steel.
Features and Strengthening Mechanisms
The main feature of micro-alloyed steel is the addition of small quantities of titanium and nitrogen during the steelmaking process. This titanium-nitrogen combination is known as masite. The production of masite is controlled by the quantity of titanium and nitrogen used and it is responsible for the superior mechanical and physical properties of the steel. The main strengthening mechanisms of MAS include:
1. Grain Refinement
The addition of titanium and nitrogen leads to the precipitation of micro-alloying particles, which are less than 10 μm in diameter, which are multiple orders of magnitude smaller than the grains themselves. This micro-alloying particles act as pinning points for the grain boundaries, preventing the grains from slipping or deforming during deformation. This effect results in a significant improvement of the yield strength of the reinforced steel.
2. Carbon Replacing Alloying
The micro-alloyed particles such as titanium nitride (TiN) and titanium carbide (TiC) are fully dissolved in austenitic steel. This process results in the replacement of alloying elements such as carbon and nitrogen in the steel matrix by the alloying particles themselves. As a result, the carbon content of the steel is reduced and its strength is increased.
3. Nitrogen Replacing Carbon
The addition of nitrogen during steelmaking also leads to the formation of nitride particles of titanium, zirconium, vanadium and chromium. These nitrides are also able to replace carbon and nitrogen in the steel matrix and further increase the strength of the steel.
4. Precipitation Hardening
The micro-alloyed particles present in the steel act as nucleation points for the precipitation of fine carbides and/or nitrides. This effect is known as precipitation hardening and is responsible for the increase in yield strength of the MAS.
Conclusion
The main strengthening mechanisms of MAS include grain refinement, carbon and nitrogen replacing alloying, and precipitation hardening. These mechanisms are responsible for the superior mechanical characteristics of the steel, such as improved strength, ductility and weldability. MAS is used in many different fields, such as construction, oil and gas, and transportation.
