What's the Difference Between Steel and Steel?

When you start getting into blacksmithing you will find that there's steel, and then there is steel. What I mean by that is there are hundreds of different kinds of steel, and they all have different characteristics. Listen to a group of blacksmiths talking and you will hear a lot of numbers that everyone except you know about.

"Well I made that blade from 10-75 but I was thinking about 10-95."

"Hey what did you make that hammer from?"

"... Steel? Iron?!..." I yell in my mind...

"Well I had some 41-40 laying around so I decided to use that for the hammer.."

"Ever work with 52-100?"

"Hell yeah but it's a pain in the butt to move!"

What is the deal with all that? Isn't steel steel?

Those numbers indicate different kinds of steel. Each kind of steel has a different ratio of iron to carbon. Some steels throw Manganese or Chromium into the mix; then there is stainless steel, mild steel, wrought iron... It can get dizzying.

So why are there so many different types of steel? It's because steel is an incredibly versatile material. Steel is simply a mixture of iron and carbon. Change the ratio of carbon to iron and the resulting steel will be different. Generally speaking the more carbon you add to the steel the harder the steel will be, but that hardness comes at the cost of flexibility. Add other elements into the mix and the steel will have some pretty incredible qualities. From the corrosion resistance of stainless steel to the ability to be harder when hot, like H13, steel is really the material our modern society is built upon.

Each type of steel has conditions under which it will perform best depending on what you are trying to do with it. For knife making you want a medium to high carbon steel like 1085, 1095, or W1 and W2. For axes and hammers you might want 4140 for it's ability to resist damage. Some steels are great for a certain task where others will be garbage. And this is why steel makes up the spines of skyscrapers, the blades of our kitchen cutlery, and the suspensions in our cars. Steel can be hard or flexible, can be hard at hot or cold temperatures depending on the alloy content, and can retain an edge able to cut despite abuse, or flex against damage without taking more than surface scratches.

Being as plentiful as it is, steel is not hard to find, especially once you start looking; but how do you tell what kind of steel you are holding?

Huh?

The best way is to source known steel from known sources. This means buying steel from metal suppliers. However scrap steel is cheap and plentiful. As an example, you can buy blade steel blanks for fairly cheap. The price fluctuates slightly but you can get known steel for just a few dollars on online supply stores like www.blacksmithdepot.com. However you can get steel for much cheaper in other places. At my local wrecking yard you can get an automobile Leaf spring package, for less than $20 providing you are willing to extract them from the vehicle yourself. Could springs are even cheaper at $6 per spring. At my local flea market I was able to get 25 old files for $20. So coming across scrap steel is often cheaper and easier to find, but how do you know what kind of steel you have, and why is knowing the type of steel important?

In order to properly harden and temper steel you need to know what kind you are dealing with because it changes what you choose to quench the steel in. Another time we will go into the specifics of quenching and heat treatment, but for now it will suffice to say that some steels like to be quenched quickly and some more slowly. If you do not quench your work correctly it can fail to harden, crack, or even shatter. This is because quenching turns the metal from being soft and pliable to being extremely hard and brittle. If the metal gets too hard too quickly it will crack or shatter. If it does not quench quickly enough it will fail to harden.

I have to stop myself from saying more because just reading briefly over what quenching is all about sends me down a deep rabbit hole of metallurgical knowledge that we do not need right now.

So what kinds of steels can be scavenged? And how do you tell what kind of steel you are dealing with? The only 100% sure way to know the identity of a mystery steel is to have it spectroscopically analyzed, however most of us do not have a spectroscope laying around and most of us don't have the money to send samples in from every piece of steel we find. There are some simple tests you can do to determine if a metal is hardenable, but ultimately the best way to test it is to cut a small piece off the steel and go through heat treatment. Put the piece in your forge and bring it up to critical temperature, then quench it; either in oil or water. After quenching you can file it or try and break it. If it bends it is not hardened. If it snaps it is hardened. Please wear protective equipment when trying to snap hardened steel.

Now let's talk about what you can find out there. This is not an exhaustive list, but here are some common steels you can find in scrap yards and flea markets.

Metal files - Files could be W1, W2, or 1095. Some newer files are not usable for forging, so the older the better.

Leaf and coil springs - Generally 5160, though definitely try hardening a small piece before you commit to a large chunk. Some springs that are very worn will have micro fractures that will cause problems.

Car axles - usually 4140 and make for great hammers and axes, but less than great knives.

Roller bearings - 52100, this steel is very hard to work because it gets harder at red heat,however if you have the energy or a friend who likes to swing a sledge, it can make amazing tools and hammers.

Lawn mower blades - I could not find much good info on these. Some say mild steel or some other low carbon steel. Others say 1080, which would make perfectly fine blade steel. Be sure to test your lawn mower blades for hardenability.

There are likely more types of steel you can scavenge, and many more you can buy from suppliers. From what I have read and heard, quenching in oil seems to be the safest route for a good hard blade that will not snap either in use or from the quench. There are a few resources I will refer you to for more and better information than my inexperienced ramblings.

First, this episode of the Forgecast:

Second, this video from Sam Towns:

Go out there and find some steel!