The OnlineMetals Guide to Steel
Steel is a term used for iron to which between 0.02 to 1.7% carbon has been added. The old definition of steel used to be something like "it rusts and it sinks in water." This material comprises the most diverse group of alloys and applications in the metals world. If there is something that needs to be made, there probably is a steel alloy that it can be made of. Steel does, of course, have poor corrosion resistance, but its relatively low cost and ease of painting make it a common choice.
The numbering system for steel is actually one of the few things in the metals industry that seems to make sense. You can determine the alloying ingredients by the first two digits of the alloy number, and the carbon content by the last two digits. For instance, 1018 is simply iron with a carbon content of 0.18%. Generally speaking, as the carbon content goes up, strength increases, but machinability and weldability decrease.
OnlineMetals.com currently stocks six grades of steel in various shapes and sizes:
1018 Mild Steel
Alloy 1018 is the most commonly available of the cold-rolled steels. It is generally available in round rod, square bar, and rectangle bar. It has a good combination of all of the typical traits of steel - strength, some ductility, and comparative ease of machining. Chemically, it is very similar to A36 Hot Rolled steel, but the cold rolling process creates a better surface finish and better properties.
A36 Mild Steel
ASTM A36 steel is the most commonly available of the hot-rolled steels. It is generally available in round rod, square bar, rectangle bar, as well as steel shapes such as I-Beams, H-beams, angles, and channels. The hot roll process means that the surface on this steel will be somewhat rough. Note that its yield strength is also significantly less than 1018 - this means that it will bend much more quickly than will 1018. Finally, machining this material is noticeably more difficult than 1018 steel, but the cost is usually significantly lower.
1144 (Stressproof-equivalent) steel
This material is actually pretty cool, at least for steel. It is a higher-strength alloy than 1018 or A36, but in addition has improved ductility as well. The chief feature of 1144 steel, however, is that it has very low distortion or warpage after machining due to a combination of its chemistry, method of manufacture, and heat treatment. Finally, 1144 is relatively easy to machine, with a machinability rating of 83% of AISI 1212 steel.
12L14 free machining steel
This alloy has lead added to the mix in order to enhance its machinability. In fact, it is rated with a machinability of 160% of AISI 1212 steel. The addition of lead does, however, reduce the strength of this alloy, although it is generally stronger than 1018.
A653 Galvanized Steel
Galvanized steel is simply hot rolled steel to which a zinc coating has been applied for protection against corrosion.
This alloy is generally used for "commercial quality" cold rolled steel sheet. It is known for its very good formability and comparatively high strength. It has a very good surface finish that is far superior to hot rolled A36.
A513 (alloy 1020-1026) Steel
This alloy is generally used for DOM tubing. Its higher carbon content means higher strength, but lower weldability and machinability.
8620 Alloy Steel
This material is characterized by a hard outer surface, combined with a ductile interior for higher strength.
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