Alloy steels are those having special physical or chemical properties which come about as a result of the addition of small amounts of metallic elements as nickel, molybdenum, chromium, vanadium, tungsten, manganese and silicon. Each of these elements give certain qualities to the steel to which they have been added.
Stainless steels are common examples of alloy steels. Their outstanding characteristic is their ability to resist corrosion. This group of steels contains measured amounts of nickel and chromium. One type of stainless steel also contains from 7 to 20 percent of nickel. Low carbon steels and most cast irons are relatively inexpensive while some alloy steels and many of the non-ferrous metals may be quite expensive.
When alloying elements other than carbon, such as chromium, manganese, molybdenum, nickel, tungsten, and vanadium are used to make steel harder, tougher, and stronger, the resulting metals are called alloy steels.
Chromium is added when toughness, hardness, and wear resistance are desired. It is the basis of stainless steel. Chromium steel is used extensively for automobile and aircraft parts.
Manganese purifies steel and adds strength and toughness. Manganese steel is used for parts that must withstand shock and hard wear.
Molybdenum is the alloying element added when steel must remain tough at high temperatures.
Nickel imparts toughness and strength to steel. Nickel steel does not rust easily. It also enables the metal to withstand shock. Much armor plate is nickel steel.
Tungsten, added in the proper amount, makes steel that is self-hardening. Tools made from tungsten steel need no special hardening treatment and will withstand heat. It is used extensively for making cutting tools.
Vanadium, as an alloying element, makes steel that has a fine grain structure and is very tough. Vanadium steel is used when a tough, strong, but not brittle, metal is needed.