Hard-
Surfacing,
Building
Fusion
Welding
Carbon
Welding Non-Ferrous Metals
Heating
& Heat
Treating
Braze
Welding
Welding Cast Iron Welding Ferrous Metals
Brazing
&
Soldering
Equipment
Set-Up
Operation
Equipment
For
OXY-Acet
Structure
of
Steel
Mechanical
Properties
of Metals
Oxygen
&
Acetylene
OXY-Acet
Flame
Physical
Properties
of Metals
How Steels
Are
Classified
Expansion
&
Contraction
Prep
For
Welding
OXY-Acet
Welding
& Cutting
Safety
Practices
Manual
Cutting
Oxygen
Cutting By
Machine
Appendices
Testing
&
Inspecting
Continued on next page... HOW STEELS ARE CLASSIFIED Steels are classified in several different ways. The primary method of classification is by carbon content, or by content of alloying elements other than carbon (which is present in every steel); in short, by chemical composition. Let’s take a look at steels from that standpoint first. Classification by Composition Carbon Steels. When we refer to ”carbon” steel, we mean steel which contains iron, carbon, less than 1.65% manganese, less than 0.6% copper, and small amounts of silicon, sulphur, and phosphorus. The sulphur and phosphorus are considered impurities, and not more than 0.05% of either is allowed by specifications, except in the case of some grades designated as ”free-machining”. The amount of manganese may range from as little as .35% to as much as 1.65%. The family of carbon steels (it is a large family, with nearly 50 standard grades) is usually sub-divided into four sub- families: the low-carbon steels, which contain no more than 0.30% carbon; the medium-carbon steels, which range from 0.30 to 0.45% carbon*;  the high-carbon steels, from 0.45 to 0.75% carbon; and the very-high-carbon steels, which range up to 1.50% carbon. The low-carbon steels, often termed ”mild” steels, are more widely used than the grades with higher carbon content. They are quite ductile, can be machined or formed with relative ease, and can be welded by any process. As the carbon content increases, tensile strength and hardness increases, but ductility declines, and machining of the steel may become more difficult. The very-high-carbon steels are used principally for springs and for tools which are used to cut or form metals. High-carbon and very-high-carbon steels are seldom welded; when welding must be used, the metal must be heat-treated before, during, and after welding if sound welds are to be obtained, and the desired mechanical properties of the steel retained. Alloy Steels. Any steel which contains more than 1.65% manganese, or 0.60% copper, or a guaranteed minimum amount of any other metal, is termed an ”alloy” steel. The metals most frequently used for alloying purposes are nickel, chromium, molybdenum, vanadium, and manganese. *Some metallurgists refer to the medium-carbon range as ”0.25 to 0.50% ”. 1