Page 33 - Curriculum Visions Dynamic Book

 Steel will take a cutting edge well and is the main material used for making chisels, saw blades, twist drills and many other tools. Because it is not as hard as some other forms
of steel, cutting tools require frequent sharpening.
cathodic protection: the technique of making
the object that is to be protected from corrosion into
the cathode of a cell. For example, a material, such as steel, is protected by coupling it with a more reactive metal, such as magnesium. Steel forms the cathode and magnesium the anode. Zinc protects steel in the same way.
Hardening mild steel
Mild steel is relatively soft and for many purposes it must be hardened. In steel the hardness depends on the amount of carbon present. Carbon becomes part of the structure of steel, making an alloy of iron and carbon atoms. The structure of the atoms can be layered, and the properties changed by heating the steel in molten sodium cyanide. This makes the steel absorb nitrogen and carbon atoms which, when the steel is cooled quickly, causes the surface to harden greatly. This is known as case hardening.
Steel can also be hardened by tempering.
This is the process of reheating the steel and then cooling it without bringing about any chemical change. This process also makes the steel tougher and less liable to crack.
 One of the major steel uses in
the 19th century was in railway lines: one-quarter of a million miles of track were laid at this time.
 Steel is used as the body panels of almost all vehicles. It is a strong material, especially when formed into complex shapes, and it is relatively inexpensive. It can be formed into shapes when cold.
33