Hi Guys,
About two years ago, a friend of mine who tried to help me clean a turkey that I shot complained that I had not sharp knife in my tool box. Since then I have been researching and playing various knives. I thought I would like to write down that I have learnt about knife steel so far, doing so helps me streamline my thoughts and I hope it also helps others who may be looking or just researching about knives.
What Attributes Makes a Good Knife Steel?
Let's start with this simplest question. In my view there are 5 attribute that matter to a Knife Steel:
(in no particular order)
1, Sharpness. Sharpness potential basically just depends on two things: steel hardness and grain. The harder the steel, the sharper it can get. the hardness of steel depends on heat treatment and composition. In terms of composition, generally speaking the higher the carbon content in the steel the harder the steel. Some element tend to increase hardness of steel, and some tend to reduce. Elements that tend to increase hardness include vanadium and manganese. Most cheap stainless steel have about 0.15% to 0.3% carbon, in contrast most high carbon steel and high end stainless steel tend to have 1% carbon (for example VG10, Cowry Y, and S35VN), and they usually can get over 60 HRC in hardness. Super high end steel such as Cowry X and ZDP-189 have as much as 3% carbon and hardness of HRC 66-70.
Any steel that is over 63 HRC will produce top tier edge. Between 60 to 63 you will get very sharp edge too. below 60, generally speaking the top tier sharpness cannot be obtained. However this level of sharpness is not really necessary for any practical application. VG10 steel at 60 HRC will hold excellent edge that is good enough for any practical application. I have used a Hattori FH Sujihiki in VG10, easily shaving sharp.
As for the grain, from what I have seen so far is that Powder Metal tend to produce sharper edge than conventional steel. Pure carbon steel tend to produce sharper edge than steel with more alloy elements or stainless steel, for example Hitachi White 1 is considered slightly sharper than Blue 1.
2, Edge Holding. Generally speaking, pure carbon steel will hold sharp edge longer than simple stainless steel (carbon steel + chromium), but added manganese, cobalt, vanadium, etc will improve edge holding. for example, Blue 1 is considered to have better edge holding than White 1.
3, Toughness. The tougher the steel, the better it will withstand abuse, the less likely it will bend or chip or break. Pure carbon steel is less tough than carbon steel with a bit of added element such as tungsten and vanadium. Chromium will decrease toughness. This is why non-stainless steel knifes (little or no chromium) are tougher than stainless steel (minimum 10.5% chromium) - and why real swords are only made using high carbon steel, never stainless. ZDP-189 has 20% Chromium so while it is very hard, it also chips easily compared to some other super high end steel. For the same steel, the knife maker can choose through different level of heat treatment, higher hardness (which will result in better sharpness) or more toughness ( less likely to chip and manufacture failure). Spyderco has a lot of knives made in Japan using Japanese steel, yet they do not harden their knives to the same level as japanese private smiths tend to. I suspect this choice is to reduce production failures and thus keep the prices low.
4, Easiness to Sharpen. Apart from the steel's hardness (the harder the steel, the harder it is to sharpen), basically the purer the steel ( i.e. only carbon and iron), the easier the sharpening. The degree which added elements affects sharpening vary. Chromium for example, affects sharpening less than vanadium. Vanadium heavy steel are generally considered hard to sharpen. I have a S35VN (vanadium heavy) knife, it is harder to sharpen than all other knives I have used. Hard to sharpen will cause you several different problems. First, if you are good at sharpening, it will simply mean you spend more time doing the same thing. Secondly, if you are not good at sharpening, it could mean you will never get the knife sharp. Thirdly, some sharpening stone just do not work if the steel is too hard to sharpen, you may have to buy diamond rods.
5, Rust/Stain Resistance. Generally speaking, the more chromium, the more rest/stain resistant; the more carbon, the more rust/stain prone. Many cheap stainless steel have very little carbon, their stain resistance is very good. ZDP-189 has 20% chromium which is almost twice as high than cheap stainless steel, but it is not as stain resistant because it has 3% carbon, which is about 10 times higher than cheap stainless steel. There are some semi-stainless steel on the market with less than 10% chromium, they try to strike a balance between rust resistance and toughness.
6, Price. Strictly speaking this is not an attribute of a steel, but it matters because we have to balance price into our purchase. Generally speaking, the more complex the composition, the more expensive. Country of original also matters, Japanese and USA powder metal steel tend to be the most expensive - Cowry X and S110V are among the most expensive knife steels. I said generally because brand, manufacturing process, design, handle material also affect the price of a knife quite a lot. Within the same brand and model, cheaper steel tend to result in cheaper knife. But you may well see a Spyderco with ZDP-189 being cheaper than a more fancy brand with S35VN.
What Steel Should I Buy?
Based on the above discussion, I would say choice of steel depends on your intended usage and budget.
If you are looking for a survival knife, which you will use for chopping, even against hard materials such as wood and maybe softer metal, you should consider non-stainless steel. Cheap options are Chinese 1040, going up to 1090 or T10. more excotic options are Japanese Hitachi White 1, 2, Blue 1, 2, and Blue Super. Just remember that they will rust very fast. My Blue Super knife rusts within a hour if left wet.
If you are looking for a hunting knife which you will only use to cut up animal, and will not abuse, you can consider stainless. In fact stainless may be preferable because you do not have to wife it dry all the time. Sharpness and easy to sharpen is important for a hunting knife. Most cheap stainless steel cannot give you super sharp edge.
Below I will rate out of 10 (higher the better), each of the 6 attributes of the steels that I either own, or have used extensively.
VG10 (HRC sub 60 Spyderco) - Sharp 7, Edge 5, Tough 5, Sharpen 7, Stain 10, Price 6.
VG10 (HRC 60+ Hattori) - Sharp 9, Edge 5, Tough 5, Sharpen 7, Stain 10, Price 4.
ZDP-189 (HRC 64 Spyderco) - Sharp 9, Edge 9, Tough 7, Sharpen 5, Stain 7.5, Price 3.
ZDP-189 (HRC 67 Sukenari) - Sharp 9.5, Edge 9, Tough 6.5, Sharpen 5, Stain 7.5, Price 2.
S35VN (HRC 60+ Spyderco)- Sharp 6, Edge 5, Tough 6, Sharpen 2, Stain 10, Price 5.
Blue Super - Sharp 8.5, Edge 6.5, Tough 8, Sharpen 9, Stain 1, Price 6.
CarboNext (Japanese Semi-Stainless) - Sharp 7, Edge 5, Tough 6, Sharpen 6, Stain 6, Price 8.
old English 440C - Sharp 5, Edge 4, Tough 5, Sharpen 5, Stain 10, Price ???.
Chinese 1060 - Sharp 7, Edge 6, Tough 9, Sharpen 8, Stain 1, Price 10.
Zwelling Henkel unnamed "ice-hardened" - Sharp 4, Edge 5, Tough 5, Sharpen 3, Stain 10, Price 5.
