Ferrous metals and their alloys    

Ferrous metals and alloys are based upon the metal iron which is their main constituent. They get their name from the Latin word for iron which is ferrum. Iron is a soft grey metal rarely found in the pure state outside the laboratory.

The engineer usually finds it alloyed, or associated, with the non-metal carbon.  The associa­tion of iron with carbon greatly modifies the behaviour of the iron, making it harder, stronger, and of greater use to the engineer. Slight varia­tions in the amount of carbon present can make very great differences in the properties of the metal. Table 1.5 shows how the addition of varying amounts of carbon to the metal iron can produce a wide range of ferrous metals.

the effect of the carbon content upon the proper­ties of plain carbon steels up to a maximum of 1.2% carbon. The maxi­mum amount of carbon which will combine with iron to form iron-­carbide at room temperature is 1.7 % but, in actual practice, there is little or no advantage in increasing the amount of carbon present above 1.2% and there is always a possibility that as the amount of carbon approaches the maximum some carbon may precipitate out destroy­ing the properties of the steel.

  Plain carbon steels: Plain carbon steels are defined as alloys of iron and carbon in which the iron and carbon are combined at all times. Only the range of fer­rous metals with their carbon contents lying between the theoretical limits of 0.1% and 1.7% satisfy this definition. In practice an upper limit of 1.2% carbon is rarely exceeded.

 Dead mild steel: In dead mild steel the carbon content is deliberately kept as low as possible so that the steel will have a high ductility. This enables it to be pressed into complicated shapes, such as motor car body panels, even whilst it is cold. It is slightly weaker than mild steel and is not usually machined since its softness would cause it to tear and leave a poor finish.

 Mild steel:  This is a widely used material which is relatively cheap and freely available. It is soft and ductile and can be forged, pressed and drawn in the hot or cold condition. It is easily machined using high-speed steel cutting tools. Typical applications are listed.