Page 34 - Curriculum Visions Dynamic Book

Special steels
Steel is an extremely versatile material, whose properties can be tailored to a wide range of needs. For example, by changing the amount of carbon in the steel, the strength can be improved. In general the higher the carbon content, the tougher the steel. Thus, ordinary (mild) steel (described on page 32) contains 0.25% carbon; medium steels contain 0.5% carbon and high carbon steels (the toughest) contain from 0.6% to 2% carbon. Varying the chemical content in this way is quite different to heating the metal and then cooling it quickly (quenching), a process that hardens the steel (see the previous page).
The reason that not all steels have a high carbon content is that it makes the steel more brittle. This is why mild steel is often preferred for example, for pressing vehicle panels.
But medium steels are best for beams and other construction uses and high carbon steels are preferred for machine tools.
Adding other metals to a steel also causes
it to become harder. Manganese and silicon
are two of the most commonly used alloying metals. Tungsten is an important alloying metal when hardness needs to be maintained even at very high temperatures, such as at the tip of a high-speed drill cutting into metal. Chromium and nickel as alloying elements are used to improve corrosion resistance, giving stainless steels. Silicon steel can be magnetised. Cobalt has a similar effect, and is used to make permanent magnets. Finally, molybdenum and vanadium are also used as alloying metals for special steels.
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