Alloy steel is steel that is Alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low-Alloy steels and high-Alloy steels. Most commonly, the phrase “Alloy steel” refers to low-Alloy steels.
Every steel is truly an Alloy, but not all steels are called “Alloy steels”. Even the simplest steels are iron (Fe) (about 99%) Alloyed with carbon (C) (about 0.1% to 1%, depending on type). However, the term “Alloy steel” is the standard term referring to steels with other Alloying elements in addition to the carbon.