Alloy Steel

Alloy steel  is alloyed with a variety of elements  in total amounts from  1.0%  to  50%  to  improve  the  mechanical properties. Alloy stainless steels are broken down into two groups:  low-alloy steels  and  high-alloy steels.  The difference between this two is  somewhat arbitrary:  Smith and Hashemi  define the difference at 4.0%,  while  Degarmo etal., define it at 8.0%.^[1][2] Most commonly, the phrase "alloy steel" refers to low-alloy steels.

Strictly speaking,  every steel is an alloy,   but not all  steels are  called "alloy steels".   The simplest steels are iron (Fe)  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  added  deliberately   in  addition  to  the  carbon.   Common  alloyants include  manganese  (the most common one),  chromium,  nickel,  vanadium, molybdenum,  silicon, and  boron.  Less common alloyants include cobalt,aluminum, niobium, copper, cerium, titanium,tin, tungsten,  zinc, lead, and zirconium.

The following is a range of improved properties in alloy steels  (as compared to carbon steels):  strength, toughness,  hardness, corrosion resistance,  wear resistance, hardenability, and  hot hardness. To achieve some of these improved properties the metal may require heat treating.

Some of these find uses in exotic  and  highly-demanding applications,  such as in the turbine blades of jet engines, in spacecraft,  and in nuclear reactors.  Because of the ferromagnetic properties of iron, some steel alloys find important applications where their responses to magnetism are very important, including in electric motors and in transformers.