A little bit about steel

Carbon steels:

First I'll explain the ASM classification system. This system uses a series of numbers to indicate alloy and carbon content. The first number indicates the main alloy(s). The second number indicates the amount of alloy. (High, medium, low.) The last two or three numbers indicate the carbon content. Let's use 5160 as an example. The 5 means it has chromium. The 1 means it doesn't have a lot of chrome. (.80 percent) The 60 means it has .60 percent carbon. 52100 has twice as much chrome as 5160 and 1.00 carbon.

Carbon steels are probably the steels most used by bladesmiths these days. They are inexpensive, easy to work with and can make a very good blade. Some of the steels that are called alloy steels are used also. Of the carbon and alloy steels I have worked with are: 1095, 1080, 1045, 5160, 52100, and 6150.

Tool Steel:

The tool steels use a different identification system. They use a letter and numbers. This was setup by the SAE (Society of Automotive Engineers). The letter sometimes indicates the quenching medium: A (Air hardening), O (oil hardening), W (Water hardening). Sometimes the intended use: D (Die steel). Sometimes no obvious connection. (M2-high speed steel.) Usually each letter has a series of similar steels. For instance, L6, a popular steel known for it's toughness, is one in a series of L1-L7. L stands for Low alloy. The H series, has from 1-22.

Some of the tool steels I've used are: O1, L6, M2, H13, and W1.

Damascus (pattern welded) Steel:

Damascus steel is a combination of two or more different steels, which are welded together in layers, then manipulated in various ways to create different patterns. The pattern is brought out by etching the steel. The combinations of steels and patterns are endless. It's a good idea to use steels that require very similar heat treating, otherwise you could have problems. But at the same time, the alloys need to be different enough that there will be contrast when you etch it. I would also add, it's best not to mix in things like mild steel. What that will do is suck the carbon out of the tool steel you layer it with, and you might have a hard time getting your steel hard.

Some good combinations, in terms of similar heat treating, contrast, and performance are:
O1 and L6
15N20 and either 1084, 1095, or W1/W2.

High speed steels and stainless steels are more difficult to make into Damascus, but it can be done, using special procedures.

High Speed Steel:

High speed steels (HSS) are very wear resistant, even up to high temperatures. (1000 degrees) They are also reasonably tough. They would make some awesome cutlery, but thereís some obstacles to over come. They are so wear resistant, you HAVE to finish all the grinding and polishing BEFORE heat treating, because afterwards, normal abrasives wonít touch it. These steels are a good candidate for using salt baths to heat treat. Even before heat treating, they are about as difficult to work with as most carbon steels are when hardened and tempered.

The HSS I have worked with: M2, CPM M4, CPM REX T15

Stainless Steel:

Most smiths shy away from stainless steels for several reasons. They are more difficult to forge, being somewhat stiff under the hammer, and having the tendency to crack if you don't forge at the right temperature. They are more expensive, and not as easy to find. They really require an oven or salt bath for heat treat, to get the most out of them, and most smiths like to use their forges for heat treating. And they are not as tough. (Generally speaking)

A steel has to have at least 13 percent free chromium to be considered stainless. (Free chromium means not tied up with carbon in the form of carbides.) There's lot's of popular stainless's out there these days, some are only popular because they're cheap and easy to work. The only one I have experience with is 440C, and didn't have any problems forging it.

PM Steels:

PM is short for Particle Metallurgy. Whereas most steels are made by (literally) throwing shovelfuls of different alloys together and melting it, PM steels are much more clean and precise. PM steels are made by mixing the alloys, melting it, spraying the molten steel in such a way that it forms tiny particles, all having the same composition. The resulting powder is hot pressed together until it's at full density.

This results in a very homogenous material with very fine grain. Some alloys are limited as to how much can be added to steel when done in the traditional way. PM technology enables greater amounts of these alloys to be used. Crucible is probably the most well known company that makes these types of steels. (In fact, I believe they invented the process.) Crucible's CPM stainless steels are much tougher than traditional stainless. The steels I use regularly are: O1, W2, L6, 440C, 1080, and 8670. I use O1 when I want good edge holding, L6 for larger hard use knives where toughness is important, W2 when I want a hamon, 440C if rust resistance is an issue, 1080 and 8670 for my damascus. Eventually, Iíll probably switch to O1 and L6 for my damascus mix, just to simplify things. I have a lot of CPM M4, but Iím not making knives from it currently.