Micro-alloyed non-quenched steels: Progress in Technology
Introduction
The 21st century has seen a massive push towards creating lightweight, high strength materials. Micro-alloyed non-quenched steels (MANQS) have been at the forefront of such efforts, providing an economical and safe solution for a number of applications. MANQS is an alloy of low carbon steel containing small additions of microalloying elements, namely niobium and/or titanium, to reduce the grain size and increase strength. In the past decade MANQS have been widely adopted in many industries due to its favorable properties which include higher strength-to-weight ratio, higher yield strength, lower deformation under load, good weldability and excellent toughness. This paper will discuss the progress made in MANQS technology since its introduction, with specific focus on the materials processing techniques used in the development of MANQS. Furthermore, the paper will provide an overview of the various applications of MANQS, with a discussion on the benefits of using MANQS in these applications.
History of MANQS Development
The development of MANQS began in the early 1950s with the introduction of vanadium as an alloying element for low carbon steels. Vanadium was added in trace quantities (0.2- 0.5%) to promote grain refinement, retard segregation, increase strength, and reduce cost. Later, niobium emerged as a viable alloying element for steels due to its superior grain refinement capabilities over vanadium and its creep resistance at high temperature. During the same period, titanium became popular as an alloying element due to its ability to increase toughness and weldability. As a result, the technology of MANQS developed in the 1960s and 1970s.
Processing Techniques
A number of processing techniques have been used to develop MANQS throughout the years. These techniques can be divided into three main categories based on their purpose—thermo-mechanical processing, diffusion treatments, and surface treatments.
Thermo-mechanical processing is the most common method used to develop MANQS. This method involves simultaneously controlling time, temperature and strain rate to reduce the grain size and increase strength. The stress-strain curve obtained from this process is divide into three distinct regions—a yield point region, a plateau region, and a hardening region. The yield point and hardening regions, if controlled properly, can enhance the strength and toughness of the material.
Diffusion treatments are also commonly used for MANQS development. In diffusion treatments, a diffusion layers forms on the surface of the material which hardens due to the interstitial atoms that accumulate over time. This technique also allows for changes to be made to the material properties as the interstitial atoms can modify the microstructure of the material and increase mechanical properties.
Finally, surface treatments can also be used to improve the strength and toughness of MANQS. These treatments often include shot peening, thermal spraying and laser cladding, among others. Shot peening is a process used to improve fatigue strength and corrosion resistance by inducing a compressive layer on the surface of the material. Thermal spraying is used to produce a wear-resistant layer on the surface of the material and also to improve corrosion resistance. Lastly, laser cladding is used to improve wear resistance and abrasion resistance.
Applications of MANQS
MANQS have been applied in a variety of industries due to their strength, toughness, and weldability. MANQS have been used in automotive applications such as suspension systems, engine components and transmission parts. MANQS have also been used in the construction industry for structural steel components and in the oil and gas industry for pipelines and offshore platforms. MANQS have also been used in aerospace applications such as engine components, landing gear, and airframe components.
Conclusion
To summarize, MANQS technology has advanced significantly since its introduction, providing an economical and safe solution for a number of applications. With its favorable strength-to-weight ratio, higher yield strength and excellent toughness, MANQS are now widely adopted in many industries due to their properties. This paper has discussed the progress made in MANQS technology since its introduction, with specific focus on the materials processing techniques used in the development of MANQS. Furthermore, an overview of the various applications of MANQS has been provided, along with a discussion on the benefits of using MANQS in such applications.
