Intro to Steel
As a result of my fishing hobby I’ve found that having a good knife is very important. I didn’t put much thought into it and purchased a cheap Kershaw Tanto Brawler blade for ~$25. After a bunch of fishing however it started to rust due to me not taking good care of it – so I started reading a bit about metallurgy and got into the various types of steel and whatnot. This post is mostly going to be a collection of information I read about knife steel that I don’t want to forget / want to refer to later on.
To get iron, iron ore is melted along with some materials like limestone and coke. Coke is purified coal, the goal of which is to provide pure carbon. Since iron ore is basically iron oxide (also known as rust – the next section will talk about it) the goal of melting the iron ore is to turn the iron oxide back into pure iron. Heating up the iron oxide will separate the iron and oxygen, but the oxygen will go back to the iron when it cools. So to actually soak up the oxygen and take it away, we use coke to provide pure carbon. Oxygen bonds easily to carbon, and you’re left with iron and this carbon-oxygen mix (which shows up in the leftover slag).
OK so what’s steel? Steel is just iron + carbon! As you might imagine we can use coke to add carbon to steel as well.
How much carbon is in your steel affects how hard it is. High levels of carbon make steel very hard, so knife blades tend to be high-carbon steel.
As your steel increases in hardness it also increases in brittleness. Tempering is a process (…basically heat treating) which lets you reduce the hardness of a steel a little along with its brittleness.
Rust is simply when iron reacts with oxygen to form iron oxide. It’s a natural process because iron oxide is more chemically stable than standalone iron. Given enough time / moisture all iron will rust (water also can react with iron to create iron oxide).
Pure iron coming in contact with pure water / dry air is mostly OK. Salt water rusts things faster because the chlorides in salt react with iron. This is why saltwater fishing gear is more expensive; you have to treat the metal parts with rust-resistant coatings or use better more corrosion-resistant alloys.
Rusting increases the volume of the metal (iron oxide takes up more volume than just iron). So if you build iron structures you better be careful that rust doesn’t mess everything up (aside from being brittle, exerting large expansion forces).
Corrosion is just oxidizing of other metals that aren’t steel. Rust is corrosion of iron.
Metal can rust all the way through because each layer of rust becomes permeable to air and water, which allows the next layer of metal to rust. Thus rust spreads.
Once iron rusts the only way to unrust it is to go back to basics: melt it back down, add coke to take away the oxygen, and you’ll get pure iron once more. Obviously that means if you have a knife or a tool that started to rust…you have to destroy the tool. So you can’t, practically speaking, un-rust a knife. You can only destroy the knife and make a new one (though in practice you just throw it away and buy a new one).
A lot of knife-carriers oil their knives. Oil and water don’t mix so it seems the primary goal is to keep moisture out of the knife-steel.
On boats a lot of sailors used to use (maybe still use) Lanolin to coat metal pieces. This is somewhere between an oil and wax and serves the purpose of keeping moisture out. All metal will corrode and rust eventually though because it’s impossible to form a perfect seal.
Stainless steel generally refers to iron-chromium-carbon alloy, generally at least 13% chromium to be considered “stainless.” The chromium reacts with iron to form chromium oxide, which acts as a passivation layer that slows corrosion (by blocking out oxygen / water / chlorides that would otherwise oxidize the metal). It’s not possible to completely halt corrosion, but we make tons of materials and coatings and such to slow the process, stainless steel being one of them.
My rice cooker is made of stainless steel so as to prevent corrosion from constant exposure to hot steam (…air and water).
Knives have a few dimensions worth mentioning.
- Edge Retention: How often do I have to sharpen the knife? Hardness vs brittleness tradeoff is captured in this dimension.
- Corrosion Resistance: How careful do I have to be wiping down the blade? Can I use the blade in wet conditions?
- Ease of Sharpening: How long does it take to sharpen the knife? Do I have to do anything special?
Higher carbon generally translates to more edge retention / harder knives. Higher chromium content means corrosion resistance.
The kind of steel used confers benefits but the actual knife’s characteristics can still differ based on how the steel is tempered. Poorly tempered high-quality steel might perform the same as well-tempered low-quality steel.
Types of Knife Steel
The 10-series steel line does not belong to any specific company (it’s kind of a standard). This is a lower mid-range steel found in Wal-mart machetes, axes, fixed-blade survival knives, etc. It’s 1% carbon which is high, making it tough (won’t chip easily). And it can be honed to be very sharp and is easy to sharpen. However it corrodes and blunts easily.
Knives in the $25-50 price range can be found with these steels.
14C28N (C/N series)
A Swedish steel made by Sandvik, 14C28N is an upper mid-range steel that uses Nitrogen to increase corrosion resistance. Can be honed very very sharp and is common in knives for this price range.
440C (400 Series)
Another steel that does not belong to a specific company, 400-series steels are a standard. 440C is one of the most corrosion resistant upper mid-range steels. It sacrifices some toughness for it but may be one of the most popular steels, now common in mass-produced pocket knives. Easy to sharpen. Used to be considered high-end in years past.
8Cr13MoV (Cr/MoV Series)
A Chinese steel made by Ahonest, 8Cr13MoV is an upper mid-range steel that is less corrosion resistant than 14C28N and also worse at retaining its edge, but is easy to sharpen. Also common though some people seem adverse to chinese steels.
The Cr/MoV line is basically the chinese competitor to 400-series steel which tends to be American.
Made by Aichi Steel in Japan, the AUS series steels are basically equivalent to / compete with the American 400 series and the Chinese Cr/MoV series.
A popular tool steel / “semi-stainless” steel. Doesn’t belong to a company. Great edge retention / performance but low corrosion tolerance. Difficult to sharpen. Very popular for tools.
Japanese steel made by Myodo Metal. Extremely rust-resistant but doesn’t hold its edge well.
German steel made by Bohler. Slightly less rust-resistant than H1 but retains its edge better…also harder to sharpen because that’s generally the tradeoff you make.
American high-end steel made by Crucible Industries. Popular with American knife-makers e.g Benchmade. Fairly corrosion resistant, a harder steel that holds its edge well, and isn’t hard to sharpen but requires some better sharpening equipment.
It gets its added edge-holding through molybdenum.
Knives that use steels in this category generally go for $150-$250.
American high-end steel made by Crucible Industries. Leverages a technique called Crucible Particle Metallurgy to get finer carbide particles for tougher and more edge-retentive steel. Very corrosion resistant, retains its edge well, and isn’t harder to sharpen than steels like 154CM. Considered the gold standard for price/feature balance in 2018.
American high-end steel made by Crucible Industries. Incredibly difficult to sharpen and corrodes rather easily but retains its edge better than most other steels – will perform better when cutting than other steels but you really have to take care of it.
Knives that use steels in this category generally go for $250-$400+.
German super high-end “super steel” made by Bohler. This is currently the most popular super-premium steel. Very high hardness (60 Rockwell hardness), very corrosion resistant, and relatively easy to sharpen.
American super high-end steel made by Crucible Industries. The vanadium in this steel allows it to somehow have top edge retention, above-average corrosion resistance, and super ease-of-sharpening all at the same time. Found in the most expensive EDC knives.
American super high-end steel made by Crucible Industries. The next-gen S90V, just strictly better. Also strictly more expensive.