Changing Metal Properties With Heat Treatment

Throughout history people have been creating things from different metals. Presumably the discovery of metal was an accident and probably caused inadvertently when a campfire burnt away some low melting point metal bearing ore and left the bewildered ancient with a crude metal lump.

Most likely the first such metal would have been tin as this has the lowest melting point by far of all other common metals. At two hundred and thirty two degrees centigrade the core of the fire would not have to be particularly hot to extract tin unlike iron which needs one thousand five hundred and thirty degrees to melt.

The melting point of metals vary a great amount and as the discovery of tin extraction became more and more understood and easier to achieve, the ancients of Mesopotamia and at the same time China, began looking for other metals. Tin was a useful metal but far too soft to create anything much more than plates, pots and ornaments. The next big step was the discovery of copper with tin deposits and this alloy we know of as bronze.

With a melting point of just under one thousand degrees centigrade, bronze could be fashioned into a much stronger finished product. For the first time metal swords and other weapons could be made as well as intricate jewellery mounted with precious stones.

Today bronze is still a valued alloy. With the addition of less than one per cent phosphor, the alloy can be easy to cast with an exceptionally smooth finish. This tough alloy known as phosphor bronze has a very low coefficient of friction making it ideal and nearly always the preferred metal of ships propellers. It has the additional property of not sparking which makes it ideal for electrical contacts. Screws made of phosphor bronze are used whenever there is the threat of electrical shorting and water.

Any metal can be heated to change its properties and every metal has some unique uses. Heat treatment of steel along with quick but not harsh cooling can toughen the original product. During heating magnetic alignments can be changed and this will also change the properties of the original.

Heat treatment is used to add subsidiary metals creating alloys for very specific uses. There are many types of aluminium die casting alloys for specific purposes and NASA and European as well as Russian space agencies all use the same particular Aluminium alloy for their space craft.

Over thousands of years men have been making things out of pure metals and alloys. The values of all metals can change with the discovery of new uses. For example, when catalytic converters were first discovered in the late 1980s the catalyst used in the exhaust system to convert carbon monoxide into harmless air and water was a mix of palladium and rhodium. Prices of these two metals shot up in value and later when more cars were being produced globally with diesel engines, palladium dropped heavily as Platinum took over.

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