Pro Tip: How to Tell Steel By the Numbers

hot-roll-steelDid you know that carbon steels and alloy steels are designated by a four digit number and that each of those numbers signifies the alloying elements and carbon content?
The first digit indicates the main alloying element(s). The second digit indicates the secondary alloying element(s). The last two digits indicate the carbon percentage.
Let’s take a look at a few examples: Ex. – 1018

  •  The first digit indicates that it is plain carbon steel
  • The second digit indicates that there are no alloying elements
  • The last two digits indicates that the steel contains approximately 0.18 percent carbon

Let’s look at another example: Ex. – 4130

  •  The first two digits indicates a Chromium-molybdenum alloy steel
  • The last two digits indicates that the steel contains approximately 0.30 percent carbon

Here’s a reference table so you’ll always know your stuff  

10XXCarbon steelsPlain carbon, Mn 1.00% max
11XXCarbon steelsResulfurized free machining
12XXCarbon steelsResulfurized / rephosphorized free machining
15XXCarbon steelsPlain carbon, Mn 1.00-1.65%
13XXManganese steelMn 1.75%
23XXNickel steelsNi 3.50%
25XXNickel steelsNi 5.00%
31XXNickel-chromium steelsNi 1.25%, Cr 0.65-0.80%
32XXNickel-chromium steelsNi 1.75%, Cr 1.07%
33XXNickel-chromium steelsNi 3.50%, Cr 1.50-1.57%
34XXNickel-chromium steelsNi 3.00%, Cr 0.77%
40XXMolybdenum steelsMo 0.20-0.25%
44XXMolybdenum steelsMo 0.40-0.52%
41XXChromium-molybdenum steelsCr 0.50-0.95%, Mo 0.12-0.30%
43XXNickel-chromium-molybdenum steelsNi 1.82%, Cr 0.50-0.80%, Mo 0.25%
47XXNickel-chromium-molybdenum steelsNi 1.05%, Cr 0.45%, Mo 0.20-0.35%
46XXNickel-molybdenum steelsNi 0.85-1.82%, Mo 0.20-0.25%
48XXNickel-molybdenum steelsNi 3.50%, Mo 0.25%