Steel
Steelisironmixed with carbon and sometimes othermetals.It is harder and stronger than iron.Ironwith more than 1.7%percentcarbon byweightis namedcast iron.Steel is different fromwrought iron,which has little or no carbon.
Making steel
[change|change source]Steel has a long history. People inIndiaandSri Lankawere making small amounts of steel more than 2,500yearsago. It was very expensive and was often used to makeswordsandknives.In theMiddle Ages,steel could be made only in small amounts since the processes took a long time.
In the time since, there have been many changes to the way steel is made. In about the year 1610 steel started to be made inEngland,and the way it was made got better and cheaper over the next 100 years. Cheap steel helped start theIndustrial RevolutioninEnglandand inEurope.The first industrialConverter (metallurgy)for making cheap steel was theBessemer converter,followed by Siemens-Martin open-hearth process.
Today the most common way of making steel is the basic-oxygen process. The converter is a largeturnip-shaped vessel. Liquid raw iron called "pig iron"is poured in and somescrapmetal is added in to balance the heat.Oxygenis then blown into the iron. The oxygen burns off the extra carbon and other impurities. Then enough carbon is added to make the carbon contents as wanted. The liquid steel is then poured. It can be eithercastinto molds or rolled into sheets, slabs, beams and other so-called "long products", such asrailway tracks. Some special steels are made inelectric arcfurnaces.
Steel is most often made bymachinesin huge buildings calledsteel mills.It is a very cheap metal and is used to make many things. Steel is used in making buildings and bridges, and all kinds of machines. Almost allshipsand cars are today made from steel. When a steel object is old, or it is broken beyond repair, it is calledscrap.It can be melted down and re-shaped into a new object. Steel isrecyclablematerial; that is, the same steel can be used and re-used.
Iron and steel chemistry
[change|change source]Steel is ametalalloywhich includesironand often somecarbon.
Everymaterialis made up ofatomswhich are very small parts. Someatomshold together quite well, which is what makes somesolidmaterialshard. Something made of pure iron is softer than steel because the atoms can slip over one another. If other atoms likecarbonare added, they are different from iron atoms and stop the iron atoms from sliding apart so easily. This makes the metal stronger and harder.
Changing the amount of carbon (or other atoms) added to steel will change those things that are interesting and useful about the metal. These are called thepropertiesof the steel. Some properties are:
- Hardness
- How easily it bends
- Ductility:can it be made into thin wires?
- Is itmagnetic?Can amagnetpick it up?
- Will itrust(orcorrode)?
Steel with more carbon is harder and stronger than pure iron, but it also breaks more easily (brittle).
Types of steel
[change|change source]There are thousands of steel types, each made of different amounts of different chemical elements.
All steels have some elements that have a bad effect, such as phosphorus (P) and sulphur (S). Steel makers take out as much P and S as possible.
Plain carbon steelsare made only of iron, carbon, and undesired elements. They fall into three general groups. Plain carbon steel with 0.05 to 0.2% carbon does not harden byheat treating.Weldingit is simple, so it is used for shipbuilding, boilers, pipes, fence wire and other purposes where low cost is important. Plain steels are used for springs, gears, and engine parts. Plain carbon steel with 0.45 to 0.8% carbon is used for very hard items such as shears and machine tools.
Alloy steelsare plaincarbon steelwith metals such asBoron(B),manganese(Mn),chromium(Cr),nickel(Ni),molybdenum(Mo),tungsten(W), andcobalt(Co) added. These give other properties than plain carbon steel. Alloy steels are made for specialized purposes. For example, chromium can be added to makestainless steel,which does not rust easily, or boron can be added to make very hard steel that is also not brittle.
Uses of steel
[change|change source]There are a huge number of things that people make from steel. It is one of the most common and useful metals. A lot of items made from iron in the past are now made of steel. Some of them are:
- Tools
- Machines
- Motorsandengines
- Wires
- Railsfortrains
- Buildings
- Bridges
- Bars for making reinforcedconcrete
- Hulls ofshipsand largeboats
- Carandtrainbodies
- Major appliances
- Cutleryandknives
Other websites
[change|change source]
- steel-Citizendium