Summary
Summary Heat treatment of metals
- Institution
- AQA
Overview and detailed exploration of heat treatment of metals. Reviews different types of treatments such as annealing, quenching, and normalising.
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Design technology – Heat treatment of metals.What is heat treatment? – Heating and/or rapidly cooling metals to
change their properties.
- To change the properties of metals, they are heated and cooled in
many ways, improving strength, malleability, ductility, brittleness, and
many other properties.
Forms of heat treatment
Quenching – Rapidly reducing the heat of a metal, using a
liquid or air. The metal is heated to an exceedingly elevated
temperature, above its recrystallisation point. When the metal’s
crystalline structures are deformed, it leads to a much lighter,
harder, and stronger version of metals. It leads to the crystalline
structure changing to austenite (non-magnetic phase of iron).
Water quenching is the most aggressive and provides the
fastest cooling rate. This leads to the material becoming
extremely hard but poses risks to cracks or distortion. Oil
quenching is slower; however, it poses less risk to cracks. It is
often used for alloy steels, such as stainless steel. Gas/air
quenching is the slowest form of quenching as it cools metals in
inert gases, such as nitrogen and noble gases. This method
gives high toughness but is less hard than the other methods.
Overall, quenching is mainly used for hardening and toughening
certain metals, to carry out specific functions in a job.
Hardening – The metal is heated to a specific temperature.
Once it has reached this desired temperature, it is quenched in
either oil or water (which are both faster than doing it in air or
gas). Doing this ensures that the crystalline structure of the
metal does not change. It will eventually leave you with a hard,
yet brittle metal.
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