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What Is Microalloyed Steel?

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  • Written By: Paul Scott
  • Edited By: E. E. Hubbard
  • Last Modified Date: 27 November 2016
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The term microalloyed steel refers to a group of steel products alloyed, or enhanced, by the addition of small amounts of various other elements. These alloying elements, which serve to improve the physical and working characteristics of the steel, include vanadium, molybdenum, and boron. Microalloyed steels fall, in terms of cost and performance, between carbon and low alloy varieties, and contain total alloy concentrations of between 0.05 and 0.15 percent. They offer many benefits, such as superior weldability, uniform hardness, and excellent resistance to metal fatigue and wear. Among the few disadvantages of microalloyed steel products are ductility and toughness values lower than quenched and tempered (Q&T) steel varieties.

Alloying is the practice of adding elements to a basic compound to enhance one or several of its physical characteristics or working properties. Steel is itself an alloy of iron featuring the addition of carbon during the smelting process to improve the hardness and durability of the raw iron. In turn, the steel alloy may be enhanced by the addition of other elements that serve to further enhance its qualities. Microalloyed steel is one such product that benefits from the addition of very small amounts of elements, such as vanadium, molybdenum, and boron. Other common steel microalloying elements include zirconium, titanium, and a range of rare-earth metals.

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Falling between plain carbon and low-alloy steel types in cost and working performance, microalloyed steel typically features total concentrations of additional alloy elements of around 0.05 and 0.15 percent by volume. These concentrations are low when compared to conventional alloys and produces an end product which features several distinct benefits. These include yield strengths in the range of 500 to 750 MPa (73,000 to 109,000 pounds per square inch) and good weldability. The alloy's resistance to metal fatigue and abrasive wear is also superior to comparable heat-treated steels.

The cold and hot working characteristics of microalloyed steel products are also superior to other steel varieties. Cold-worked microalloyed steels do not require as much working for any given process, while hot-worked products can be air-cooled successfully. The general machining characteristics of microalloy steel are also outstanding due of its very uniform hardness and the ferrite-pearlite microstructure of the material. In addition, the fact that no quenching and tempering is involved in the process means that microalloyed steel is not prone to quench-cracking failures. The only significant disadvantages to microalloyed steel are the relatively low ductility and overall toughness values exhibited by the products when compared to quenched and tempered alloys.

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