DIFFERENT FORMS OF IRON BASED ON CARBON CONTENT

HERE ARE SOME BASIC BUT VERY IMPORTANT TERMS EASILY EXPLAINED FOR YOU RELATED TO PIG IRON,CAST IRON,WROUGHT IRON......etc

'Iron is an element, found in chemistry labs'

Pig iron:- It is iron as cast after smelting from ore. It is so called because it used to be a very simple casting made by scooping roundish depressions in a row along a runnel. Add red-hot iron, and the visual effect resembles piglets feeding from a sow. Pig iron has 5% carbon by weight or more.

Cast iron:- It is pig iron remelted (or even, these days, shipped directly to a foundry in molten form) and cast into something useful. It still has 5% or more carbon, and the carbon separates out into flakes. This reduces the tensile strength, but not the compressive strength, so it is used where compression is important. Machine tool bases are often cast iron.

Take out all but 0.25% of the carbon, add a little manganese and silicon, and you have mild steel. This is the steel that you see the most of. It works relatively easily, has good tensile and compressive strength, and is cheap. Car and appliance bodies are mild steel sheet. Coat the sheet with zinc to prevent corrosion, and use it for roofs and ducts. Most modern "wrought iron" railings are really mild steel, so you need to keep them painted. This is what most people are thinking of when the say just "steel" with no qualifiers.

Take out just about all the carbon and you have wrought iron, easy to shape on a forge and weather resistant - it rusts a lot more slowly than other steels. It is almost pure iron. Rarely seen these days.

carbon steel:-Leave in just the right amount of carbon, around 1%, and you have carbon steel. This is useful in springs, knives, and high-tensile wire rope. Its big feature is that you can change its properties from soft via springy to hard and brittle by simple heat treatment. Also sometimes called tool steel, though this tends to be used for more complex alloys.

To get stainless steel you remove the carbon and add a lot of chromium, at least 10.5%. It is capable of taking a moderately good edge, (not as good as a tool steel) but it will not rust, provided it is exposed to air so that it can form a protective oxide layer. Great for cutlery and cooking gear, but not so good for bolts, which rust out fast where you can't see them, because there is no free oxygen there.