C1aL10  Using Steel

Key Words

Alloy - metal made by mixing two or more metals when they are molten.

Brittle - breaks which hit hard.

Cast iron - iron from a blast furnace, cast in a mould.

Coke - coal which has been heated (but not burned) to remove gases and other impurities.

Hardness - how difficult it is to deform a material.

Properties - features of a material.

Soft - changes shape easily

Stainless steel - an alloy of iron, chromium, and nickel.

Steel - an alloy between carbon and iron.

Strength - the extent to which a material does not change shape easily.

Grade E

The steel industry produces a wide range of steels for different applications.  These steels have different properties, for example, hardness, rust resistance, and strength.

Cast iron is a hard material but brittle; pure iron is soft to the point of being almost useless.  (Mind you, it's not that soft - drop a lump of it on your foot and you will know about it!)

Steel is an alloy of iron and other elements.  Small amounts of carbon are added to alter the strength and the hardness of the steel.

Grade C

Steels with a carbon content of 0.4 % are called low carbon steels. The are easily bent into shape, for example making the body of a car.  The strength of the body comes from the shaping of the steel  into box-sections.

Medium carbon steels (0.8 %) are less easy to bend, but a harder and stronger.  These are often forged to make items like hammers.

High carbon steels (1.5 %) are strong and hard.  They are used to make cutting tools.  They do not bend at all easily, and may snap if you try to do so.

Metals can be added by dissolving them in the molten iron.  Stainless steel is made of 7 % iron, 20 % chromium, and 10 % nickel.  It resists rusting and other corrosions.   Other metals alloyed into steel are:

• Nickel - makes steel pipes very resistant to chemical attack;
• chromium - makes steel resistant to corrosion, so it's used in cutlery;
• molybdenum - makes steel tougher, so it's used in gun barrels;
• tungsten - makes the steel stronger, even at high temperatures, so it's used in high speed cutting tools.
• cobalt - makes the steel more magnetic;
• vanadium - makes it more springy, which is useful for spanners.
• manganese - makes the steel harder-wearing, used for railway turn-outs.

Grade A

Iron is changed into steel by blowing oxygen through the molten iron.  It reacts with the carbon to make carbon monoxide and carbon dioxide.  Then carefully controlled amounts of carbon and other metals are introduced.

The purification process also oxidises silicon and phosphorus.  However, both of these oxides are acidic.  So calcium carbonate is added:

phosphorus oxide + calcium carbonate ® calcium phosphate + carbon dioxide

P₄O₁₀ + 6CaCO₃  ® 2Ca₃(PO₄)₂ + 6CO₂

silicon dioxide + calcium carbonate  ® calcium silicate + carbon dioxide

SiO₂ + CaCO₃ ® CaSiO₃ + CO₂

These form a slag.