There’s something about steel.
There are so many different kinds of steel available with different properties that choosing the right steel for the job can be a bit daunting. Ask any smith and they all have slightly different opinions based on experience and sometimes just what they like to work with. I will try and break down what I consider important in selecting the steel for a knife.
First we need to understand a little bit about steel, so let’s start here. According to the American Iron & Steel Institute (AISI), there are four basic groups that steel can be categorized into based on each steel’s chemical composition:
- Carbon Steels:
Carbon steels account for 90% of total steel production. Carbon steels can be further categorized into three groups depending on their carbon content:
- Low Carbon Steels/Mild Steels contain up to 0.3% carbon
- Medium Carbon Steels contain 0.3 – 0.6% carbon
- High Carbon Steels contain more than 0.6% carbon
- Alloy Steels:
Alloy steels contain alloying elements (e.g. manganese, silicon, nickel, titanium, copper, chromium and aluminum) in varying proportions in order to manipulate the steel’s properties, such as its hardenability, corrosion resistance, strength, formability, weldability or ductility.
- Stainless Steels:
Stainless steels contain between 11-20% chromium and are valued for high corrosion resistance. These steels can be divided into three groups based on their crystalline structure:
Austenitic steels are non-magnetic and non heat-treatable, so these don’t work well for cutting applications. They usually contain 18% chromium, 8% nickel and less than 0.8% carbon.
Ferritic steels are magnetic and can not be hardened with heat treatment, but can be strengthened by cold working. These steels contain trace amounts of nickel, 12-17% chromium, less than 0.1% carbon, along with other alloying elements, such as molybdenum, aluminum or titanium.
Martensitic steels contain 11-17% chromium, less than 0.4% nickel and up to 1.2% carbon. These magnetic and heat-treatable steels are used in knives, cutting tools, as well as dental and surgical equipment.
- Tool Steels:
Tool steels contain Tungsten, Molybdenum, Cobalt and Vanadium in varying quantities to increase heat resistance and durability, making them ideal for cutting and drilling equipment.
So best steel for blades fall into High Carbon, Martensitic Stainless and Tool steels. This still leave a dizzying selection of various steel to choose from. Now lets break things down a bit more.
Steel can get very expensive and there is a limited selection of dealers to buy smaller quantities from. I personally like New Jersey SB for my steel supply, but feel free to look around at places like Jantz, USA Knife Maker and others. When you venture into the so called super steels like the powder based CPM S90v Stainless, be prepared for a bit of sticker shock. If you are just starting out I suggest trying some of the less expensive steel first, because you will most likely create a certain amount of scrap before you make something that you would want to show off. Seriously.
It’s very important to consider where the knife will be used when selecting the steel for any knife that you make. For example you probably don’t want to use a steel that is so tough that it is impossible to maintain the edge with a simple stone for a camp knife that you expect to be out in the field much of it’s working life. On the other hand you probably don’t want to use carbon steel for a diving knife that will spend its life in salt water.
No knife should be abused, but in an emergency you want a knife to go above and beyond while hopefully surviving to cut another day. For example, most stainless steels are more brittle than high carbon steels. This means that you might use high carbon steel for a machete, but go with stainless for a smaller everyday carry utility knife.
Heat treating is a complete science by itself with charts and recipes for how to achieve the properties that you want for each type of steel. Stainless steel comes with its own needs, for example stainless steel needs to be treated in an oxygen free environment to keep from burning off the carbon in the steel. A good option is to send your knives to a reputable company like Peters Heat Treating to do your heat treating for a reasonable fee, at least at first. This way you won’t need to invest in a kiln and other supplies to successfully heat treat stainless steel, or worry about warping the heck out of your blade. I have turned more then one piece of steel into an expensive wavy piece of scrap. If you want to do your own heat treating you will probably want to stick with carbon or some tool steels that can be treated in a home made forge, at least at first.
Choose wisely. Don’t just go with what sounds cool, it may not be the right fit for the job. For me part of the fun is the planning. I like to visualize how and where a knife design will be used and plan accordingly.