ALLOY STEEL : PROPERTIES AND USES
by Aditya Pandit
Posted on March 14, 2017 at 5:20 PM
Alloy steel is a steel which has had small amounts of one or more elements (other than carbon) such as such as manganese, silicon, nickel, titanium, copper, chromium and aluminium in addition. This creates an alloy which has specific properties that are not found in carbon steel. Alloy steels are workhorses of many industries because of their low cost, extensive availability, ease of processing, and mechanical properties. So what are these properties?
Each different alloying element has its own effect on the properties of steel. Some of the properties that can be improved by alloying include:
- Stabilizing austenite: Elements like nickel, manganese, cobalt, and copper increases the temperatures between which austenite exists.
- Stabilizing ferrite: Molybdenum, vanadium, aluminium, and silicon may have the effect of lowering carbon's solubility.
- Carbide forming: Minor metals, including chromium, tungsten, titanium, niobium, tantalum and zirconium, form carbides that - in steel - increase hardness and strength. Such alloy steels are used to make high-speed steel or hot work tool steel.
- Graphitizing: Silicon, nickel, and cobalt can decrease the stability of carbides in the steel, promoting breakdown and the formation of free graphite.
- Decrease of eutectoid concentration: Molybdenum, tungsten, silicon, chromium, and nickel all can help to lower the eutectoid concentration of carbon.
- Increase corrosion resistance: Aluminium, silicon and chromium form protective oxide layers on the surface, thereby protecting the metal from further deterioration in harsh environments.
Major Steel Alloying Agents:
Following is a list of commonly used alloying elements and their effect on steel (standard content in brackets):
- Aluminium (0.95-1.30%): A deoxidizer. Can limit the growth of austenite grains.
- Boron (0.001-0.003%): A hardening agent that improves deformability and machinability. It is added to fully killed steel and only needs to be added in small quantities to have a hardening affect.
- Chromium (0.5-18%): A key component in stainless steels. At over 12% content, iy significantly improves corrosion resistance. It also improves hardenability, strength, response to heat treatment and wear and tear resistance.
- Copper (0.1-0.4%): Often found as a residual agent in steels, copper can also be added to produce hardening properties and increase corrosion resistance.
- Lead: Although virtually insoluble in liquid or solid steel, lead is added to carbon steels via mechanical dispersion during pouring, to improve machinability.
- Manganese (0.25-13%): Manganese increases strength at high temperatures by eliminating the formation of iron sulfides. It also improves hardenability, ductility and wear resistance.
- Nickel (2-20%): Another element critical to stainless steels, nickel is added at over 8 percent content to high chromium stainless steel. It increases strength, impact strength and toughness, while also improving resistance to oxidization and corrosion.
Pipes made of alloy steel have exceptional performance properties. They are generally developed for energy-related applications involving oil and gas drilling and are subjected to stresses in machine parts.
The common material used to produce the load carrying components in precision ball bearings, roller bearings, and tapered roller bearings is chrome steel. These components are the bearings inner and outer rings, balls. Using controlled processing and heat-treating methods the finished bearing components have high strength to resist cracking and a hard surface to resist subsurface rolling contact fatigue.
With the proper combinations, the following are some other things that could be manufactured are:
- Coins, medals, electrical hardware, tools, heavy gears
- U.S. coins
- Boats, aircraft, railroad cars and machinery
- Corrosion-resistant containers
- Heating elements in toasters, electric heaters, etc.
- Electrical springs, boat propellers
- Jewellery and Art Objects
- Type for printing
- Silverware, pots and pans
Alloy Steel hence forms a major a chunk of the materials used in manufacturing industries all around the globe in multiple sectors.
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