In the bladesmithing world, there are a lot of different types of steels being used, and they are referred to as numbers- the type of steel I commonly use is 5160 steel, from an old car spring. Other common steels used in bladesmithing are 1095, 10520, etc.
These numbers always have confused me, so I asked questions around a bladesmith’s forum, did some research, and I think I have the answer.
The first number refers to the type of alloy the steel is. The chart below shows which number refers to what alloy. For example, 5160 is a Chromium alloy, and 1095 is a plain Carbon steel.
The second number refers to what percentage (by weight) of that element is in the steel. For example, 5160 has approximately 1% Chromium. 5260 would have about 2% Chromium.
The last two numbers show what percentage of the steel is Carbon. The point is always two digits from the end of the number; 5160 would be .60% carbon.
In total, 5160 is around 1% Chromium, .60% Carbon, with the rest Iron. Often there are a few other trace elements added, such as Nickel, but the numbers refer to the majoring elements in the steel. If the steel is a plain Carbon alloy, like 1095, the second digit refers to a little more than just the carbon content (that’s the job of the last two digits) and that gets a little complicated, but if there’s just a zero there, it turns out nuetral.
So for some practice: 52100 has 2% Chromium, 1.00% Carbon. 2380 (I’m making this one up btw) would have 3% Nickel, and .80% Carbon. 4037 steel is actually a trick one, as the 0 indicates there is, well, 0% Molybdenum, and .37% Carbon.