PROPERTIES OF METALS

A. READING

Key terms and concepts.

To say how much different metals and alloys are suitable for manufacturing machine parts, it is necessary to know what properties they possess and how much these properties meet requirements made to finished products. Quality of metal works in most cases is determined by their phisical, chemical, mechanical and technological properties. These properties affect manufacture and application of metals.

Phisical properties include colour, specific gravity (density), the melting point, electrical conductivity, thermal conductivity, specific heat, heat expansion, magnetism.

Chemical properties are corrosion resistance, heat resistance, high temperature strength, solubility.

Mechanical properties include strength, hardness, toughness, plasticity, brittleness.

Technological properties are foundry characteristics, malleability, weldability, ability to be machined.

Knowledge of chemical properties enables to make a right selection of proper metals for different products, especially for those, which work in the condition of high temperature, of attacking by acids, basics, etc.

Most important of these properties is corrosion resistance or susceptibility to atmospheric or chemical destruction. The rusting of iron is the commonest example.

Knowledge of technological properties is of great importance under selecting one or another method of treatment.

Most important of these properties are malleability or ability to be deformed permanently under compression without rupture; foundry characteristics or ability to be cast into varied and intricate shapes.

Knowledge of mechanical properties is also of great importance, because it enables to estimate behaviour of metal subjected to the influence of external forces (called “loads”) which are brought about by the course of using (or treatment) machines or parts of machines.

Most important of these properties are strength or ability to support weight without bending or breakage; toughness or ability to bend rather than break under a sudden blow.

Knowledge of phisical properties enables to select the proper metal when some special properties are required, for example: light weight (parts of airplanes), power to conduct electric current (electrical engineering products), ability to be magnetized (transformers electromagnets), etc. So most important of these properties are specific gravity or the weight of the metal compared to the weight of an equal volume of water; electrical conductivity or ability to resist to the passage of the current.

The selection of the proper metal or alloy for a given use is an important part of the practice of metallurgy.