Ferrous and non-ferrous metals and their properties Flashcards
FERROUS METALS
These are the metals containing iron. Metals are rarely used in their pure state but are combined with other metals to form an ALLOY. In the case of iron, carbon is the most important addi- tion. Although it is only present in small amounts it causes big changes in the property of the metal.
What are the Ferrous Metals
Ferrous metals:
-Cast Iron
-Grey Cast Iron
-Plain Carbon Steels
-Mild Steel
-Medium Carbon Steel
-HIgh Carbon Steel
-Stainless Steel
-Silver Steel
-Tinplate
-Alloy Steels
CAST IRON
In this form the iron has been melted and poured into a mould, usually made of sand, in which it is allowed to solidify. This is a simple, convenient and relatively cheap pro- cess to manufacture components of a complicated shape. Cast iron is an alloy of iron and carbon with small amounts of manganese, silicon, sulphur and phosphorus. It contains about 3% of carbon.
GREY CAST IRON,
is the type in common use; it is cheap and easy to cast and machine. As a typical example a motor car cylinder block contains 93.32% of iron, 3.3% of carbon, 1.9% silicon, 0.8% manganese, 0.14% of sul- phur and 0.18% each of phosphorus, molybdenum and chromium. The car- bon content of approximately 3.3% consists of about 0.7% of combined carbon and about 2.6% of free carbon.
PLAIN CARBON STEELS
The main dif- ference between cast iron and steel is the carbon content. Plain carbon steel has never more than 1.5% carbon whereas cast iron, as has been stated above, has about 3%.
MILD STEEL
containing about 0.15% to 0.3% carbon combined with the iron is ductile and malleable. It is easy to weld, machine, forge or press into a new shape. It may be worked hot or cold. Because of its low carbon content it cannot be hardened by heating and quenching, but can be case-hardened, a process which will be described later. It is supplied in bar form with hexagon, round, square or flat sections in a ‘black’ or ‘bright’ form and in sheets of varying thicknesses.
MEDIUM CARBON STEEL
with a carbon content of 0.35% to 0.5% is much stron- ger than mild steel. Its hardness and strength can be increased by quenching the metal from a red heat. It can be tempered, rendering it suitable for many general engineering purposes where the stresses imposed are greater than could be withstood by mild steel.
HIGH CARBON STEEL
with a carbon content of 0.55% to 1.5% is used for most tools after being hardened and tempered. Chisels, files, drills and reamers are made from this steel
STAINLESS STEEL
is principally an alloy of iron, nickel and chromium. It has a high resistance to corrosion but in some forms it is difficult to machine. However, by introducing a free machin- ing agent into the alloy this drawback can be overcome.
TINPLATE
Sheets of mild steel are coated with tin to provide the metal used for the familiar food containers and for many other purposes. It is a useful material for the model engineer, being easily worked and soldered and can be obtained without cost from dis- carded biscuit tins etc.
ALLOY STEELS.
In order to improve the properties of steel and to suit the metal to special applications, other sub-
stances beside carbon are added to the steel. NICKEL improves the ductility and toughness of the metal. CHROMIUM and MOLYBDENUM increase its hard- ness while VANADIUM improves the elasticity, strength and fatigue resistance of the steel. All steel contains MANGANESE but sometimes more is added to improve the steel’s mechani- cal properties.
What are the Non-Ferrous Metals
-Aluminum
-Copper
-Lead
-Tin
-Brass
-Bronze
ALUMINIUM
is the lightest of the com- monly used metals. It is too soft to use in its pure state but alloyed with copper, magnesium and manganese it is widely used for many components. It is a good conductor of electricity but is impos- sible to solder by the usual methods.
COPPER
is soft, ductile and of low ten- sile strength. It is an excellent conduc- tor of electricity and is easy to solder or braze. It is the base of the brass and bronze alloys. Copper hardens with age and also work-hardens, that is it becomes hard when it is bent or stretched. It can easily be returned to its soft, ductile state by annealing. This is done by heating to a red colour and then allowing it to cool.
LEAD
is soft, ductile and of very low tensile strength. It is often added to other metals to make them free cutting. It is typically used for lead acid battery plates and in soft solder.
