Microalloyed steel
Microalloyed steel is a type of alloy steel that contains small amounts of alloying elements (0.05 to 0.15%), including niobium, vanadium, titanium, molybdenum, zirconium, boron, and rare-earth metals. They are used to refine the grain microstructure or facilitate precipitation hardening.[1]
In terms of performance and cost, microalloyed steels are between a carbon steel and a low alloy steel. Their yield strength is between 275 and 750 MPa (40 and 110 ksi) without heat treatment.[2] Weldability is good, and can even be improved by reducing carbon content while maintaining strength. Fatigue life and wear resistance are superior to similar heat-treated steels. The disadvantages are that ductility and toughness are not as good as quenched and tempered (Q&T) steels. They must also be heated hot enough for all of the alloys to be in solution; after forming, the material must be quickly cooled to 540 to 600 °C (1,004 to 1,112 °F).[3]
Cold-worked microalloyed steels do not require as much cold working to achieve the same strength as other carbon steel; this also leads to greater ductility. Hot-worked microalloyed steels can be used from the air-cooled state. If controlled cooling is used, the material can produce mechanical properties similar to Q&T steels. Machinability is better than Q&T steels because of their more uniform hardness and their ferrite-pearlite microstructure.[4]
Because microalloyed steels are not quenched and tempered, they are not susceptible to , nor do they need to be straightened or stress relieved. However, because of this, they are through-hardened and do not have a softer and tougher core like quench and tempered steels.[4]
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- Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4.
- Steels