The first way metal is classified is as ferrous or non-ferrous. This has to do with the amount of iron content in it. Material with more than 5% iron content is a ferrous metal, such as steel. A non-ferrous metal, like aluminum, has little or no iron in it.

Ferrous Metals

Mild Steel

A common low carbon steel, mild steel is an iron alloy containing manganese, carbon or other alloying elements. Mild steel is stronger and harder than iron, yet it is softer than tool steel. The carbon content affects the properties of steel. Higher carbon content makes the steel harder. Mild steel is common in two forms, cold rolled or hot rolled. Just like the name indicates, the material has been process either hot or cold giving different characteristics. Cold rolled is smooth and shiny, usually with a light coating of oil to prevent corrosion. Since it has been processes cold, it has been work hardened. Hot rolled steel is black/blueish in colour and usually has a scaly appearance.

Tool Steel

An alloyed steel with a high content of carbon is called tool steel. As the name implies, tool steel is used for making tools. It is hard enough to cut standard steel and iron. The metal must be able to withstand high temperatures, high load and abrasive conditions. Because of the many applications of tools, tool steels vary in their composition.

Stainless Steel

Stainless steel contains chromium and nickel as principal alloys. Stainless steel is the only non-magnetic ferrous metal. It has high tensile strength, ductility and hardness, as well as being highly resistant to corrosion and oxidation.

Available in many different grades and finishes, some of the common grades are: 304 for general use, 316 is a marine grade (better corrosive resistance) and 430 which is the only magnetic grade, used commonly on cooler doors.

Finishes range from 1-8 (dull-mirror) with a #4 being the most common. A #4 finish has a grained appearance used as kitchen counter tops. 2B is another common finish with a cold rolled, grey appearance. A #8 finish is a polished, mirror finish used in applications like public bathroom mirrors.

Iron

Soft, malleable metals can be made by alloying pig iron and nickel. The resulting metal is known as nodular iron. Wrought iron and ingot iron are two other soft, easily worked and relatively weak metals.

Cast Iron

Cast iron is re-smelted pig iron and includes all of the iron and carbon alloys with more than 2% carbon and almost always, some silicon. High carbon and silicon contents give cast iron a low melting temperature and high fluidity in its liquid stage. It is easy to pour cast iron into complex molds.

When the carbon and silicon content is in the range of 3% to 4%, the material is known as grey cast iron. Lower carbon and silicon content and rapid cooling of the casting make hard, brittle, white cast iron. White cast iron can be converted with heat treatment to a malleable iron that has properties similar to mild or low carbon steel. Cast iron is used for engine blocks, heads and housing assemblies.

Pig Iron

Pig iron is the basic metal obtained from iron ore.

Most ferrous metals begin as pig iron. It has a very high carbon content and is cast into bars called pigs.

Non-Ferrous Metals

Aluminum and copper are two common examples of non-ferrous metals. Non-ferrous metals are usually non-sparking and non-magnetic. They also have a common characteristic, in that the oxides that form on non-ferrous metal tend to protect the metal, not destroy it. Meaning they may not be damaged by water (oxidation), but they will stain if allowed to sit in wet for any length of time. Always dry sheets before storing.

Aluminum

Aluminum is light weight and resistant to corrosion. It has low electrical resistance, high heat conductivity and good ductility combined with considerable strength. Used extensively in the aeronautical industry, aluminum is also used for industrial tanks, truck and bus frames and equipment body parts. The principle ore it is made from is called bauxite, it weighs approximately 60% of same thickness of steel.

There are seven types of aluminum which have a series number to indicate the main alloys added. If a series number is followed by an “H” that means it is not heat treatable and has been strain hardened. A number following the “H” such as “H1” indicates the degree of strain hardening. A series number followed by a “T” indicates its temper has been modified but that it is heat treatable. That is, it may be annealed.

Brass

Brass is an alloy of copper and zinc. Brass is stronger than copper and is corrosive resistant, making it an ideal metal for ships’ fittings, locks and condenser tubes. Standard brass, which contains 30-34% zinc, is used extensively for valves and fittings.

Bronze

An alloy of copper and tin commonly used in castings.

Copper

Copper is fairly resistant to corrosion, has good tensile strength and is an excellent conductor of electricity. Copper is highly resistant to many chemicals and to corrosion from air and sea water. It should not be used in contact with oxidizing acids. Copper is very malleable and ductile. As it is drawn or cold worked, it will increase in tensile strength and become less and less ductile or work hardened. It may be annealed after. Copper is used for water supply lines, electrical wiring and soft tubing.

Lead

Lead is a very dense, heavy metal. It has a low melting point of 327°C (620°F), making it easy to use in liquid form. Lead can be rolled into sheets, cast or bent into shapes and extruded into pipes. However, due to its plastic nature, it is structurally weak. One of lead’s most important assets is its corrosion resistance owing to a protective film of oxides formed on its surface. Lead is often used as a coating on other metals to protect them from corrosion. Lead is also used in the construction of batteries and in solder. It is very toxic, so caution should be taken when handling lead.

Monel

An alloy of copper and nickel that has a high corrosive resistance.

Coated Metal

Another way that metal is classified is as coated or solid. A sheet metal worker will use both solid (uncoated) and coated. The coating in most cases is for corrosion protection, but can be for other purposes as well. Welding of coated sheets always should be considered carefully.

Alclad

Some aluminum sheets are not very corrosive resistant because of their alloying, like 2024 for example. These sheets are commonly coated in pure aluminum, called Alclad. Aircraft and aluminum RV’s use these sheets. Usually covered on a clear plastic for protection, Alclad aluminum goes through much more involved processing, making it much more expensive.

Galvanization

Galvanized sheet metal is when the metal has been coated in zinc. This is the most common coating used in sheet metal. This can be done in 2 different processes: hot dipping or electroplating. Sheets that have a “spackled” and smooth appearance have been hot dipped and are commonly used for ductwork. Sheets that have been electroplated have a chalky, dull-grey appearance. Also known as satin coat, paint bond, or wipecoat, these sheets are used when painting is required. The coating not only acts as corrosion resistance, but because of the finish, it will accept paint easily with no scuffing or priming.

Pre-painted

Pre-painted material is commonly used in architectural sheet metal. They come in an almost endless array of different colour and finishes, even wood grain. Vinyl coating may also be included in this category.

Tinplate and Terneplate

Tinplate is a sheet of steel coated in pure tin. It was commonly used in the past. Now, tinplate is used in tin cans and other food products for its corrosive resistance and sanitary qualities. Terneplate is a coating of tin and lead alloyed together.

Media Attributions

• “Specularite (high-grade iron ore)” by James St. John is licensed under a CC BY 2.0 licence.
• “Pig Iron” by Alfred T. Palmer is in the public domain.
• “Movable Lead Type” by Willi Heidelbach is CC0 public domain.
• “Tinplate Bath” an caption by Science Museum, London is licensed under a CC BY 4.0 licence.