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In North America, the AISI/SAE steel grade nomenclature system is widely used.
In this system, 4 numeric digits (XXXX) describe the base grade.
The first two digits tell you whether the steel is a carbon or alloy
grade.
If the first digit is any number other than a "1″, that steel is an alloy steel. We'll discuss alloy steels in a later post.
If the first digit is a " 1 ", the steel is a carbon grade. 10XX is the template for the plain carbon steels. We'll explain those last two digits at the end of our post. (Exception:
if the second digit is a "3″- then its one of the alloy manganese
13XX grades- grades we don't encounter very often these days.)
If the second digit is a "1″, the steel is a resulfurized carbon steel.
11XX. Guess how many "extra" elements were added to the grade? If you
guessed 1- thats right. Sulfur is the one element added to
promote machinability in the 11XX grades of steel.
If the second digit is a "2″, the steel is called a rephosphorized and resulfurized steel.
Both sulfur and phosphorus,-2 elements- are added to make these free
machining steels. 1215 and 12 L14 are the grades we mostly see today.
(As many of you know, that "L" as an infix tells us that there is a
lead addition in the 12L14 steel.)
If the second digit is a "5″ the grade is a high manganese carbon steel. Grades 1524, and 1541 come to mind as the principal 15XX grades seen by our industry.
A "B" infix tells us that the steel has been treated with boron.
This makes it especially adept at being heat treated. 15B21 is used to
make fasteners that are heat treated.
So, now that you know what the first 2 digits mean in a US grade designation for steel, what about the last two?
Diamonds are just a special form of 'carbon'. Same as in steel.
The last 2 digits in the grade are the mean or average carbon content of the steel. In weight percent.
So grade 1018, is a plain carbon steel, 0.18% average carbon content.
1144 is a resulfurized 0.44% average carbon content steel for higher strength and machining.
And 1215, well- 1215 is a resulfurized, rephosphorized 0.09 max weight % carbon steel for machining. 0.09% max!
Don't you just love exceptions?
Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which originally appeared here.
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Re: Basics of the North American Steel Grade System
