Outdoor Adventure USA

Edged Implements

Edged implements are the oldest tools known to mankind, yet in the 21st century we still find edged implements valuable.

In this net we will discuss:

• Metallurgy
• Sharpening
• Considerations choosing a knife

I start this net with a discussion on metallurgy as the blade material ultimately determines the worth of a tool. The two factors that are most important when discussing blades are toughness and hardness. These factors can be influenced by alloying or heat treating steels to achieve various benefits for specific applications.


This image shows a hatchet blade that is very ductile, notice the cutting edge dented or rolled over when impacted.


This image shows a knife blade that is very brittle, the blade cracked and chipped where it was impacted, or abusively used for prying.

Hardness determines wear resistance, which is the ability to cut through abrasive things without dulling. In the past it was difficult to find a material that would be tough and hard, traditional high carbon steels have an inverse relationship with ductility when heat treated to high hardness, meaning a compromise had to be made. Modern knife steels have been developed to maintain high toughness at high hardness.

Heat treating brings out the magic in steel. Steels with a carbon content higher than about .3% can be hardened through heat treating. Try this out at home with a piece of music wire, heat the wire to red hot then quickly submerge it in water. The wire will be as brittle as glass, try the same thing with a paperclip and it will stay ductile. The reason is because a paperclip is low carbon, its molecular structure doesn't change enough during heating to become hardened.
The iron carbon phase diagram shows how the percentage of carbon affects the formation of austenite, the area in green is of most interest. Heat treating takes place between 1400-1600 degrees F, at these temperatures the molecular structure of the steel changes where the carbon dissolves into the steel, much like salt dissolves into hot water, by quenching the steel from an elevated the molecular structure gets trapped in the steel and provides desirable properties.

Alloys such as tungsten, vanadium and chromium encourage formation of carbides. These carbides are microstructures with beneficial hardness and wear resistance.

In carbide structure, two carbon atoms are attached to each other with the three covalent bonds. From these three covalent bonds, two bonds are pi-bonds. These pi-bonds are formed by the lateral overlapping of the p-orbitals. Another bond is the sigma bond, which is formed by the head-on overlapping of the s-orbitals. The hybridization exhibited by the carbon in the carbide structure is sp. Each carbon carries one lone pair on it.

More carbide is not always a good thing, large carbide grains make sharpening difficult and edge stability may become compromised.

The current "best" steel in the knife industry is CPM Magnacut by Crucible steel. I'll refer to this datasheet throughout the net:
https://www.alphaknifesupply.com/Pictur ... Cut-DS.pdf

CPM MagnaCut is a unique powder metallurgy stainless tool steel
with a design which eliminates chromium carbide in the heat
treated microstructure. An excellent combination of toughness and
wear resistance is achieved by having only small, high hardness,
vanadium and niobium carbides, giving CPM MagnaCut
properties similar to non-stainless steel CPM 4V.

The bright white dots in these two images represent carbides. Chromium carbides tend to be larger (microscopically speaking) while very hard and wear resistant, large carbides can result in chipping at the edge as entire carbide grains rip out of the blade under stress.

Normally the grain in metal is not visible without magnification, but zinc readily forms large grains, if you've seen a galvanized fence post or street lamp you've probably noticed the spangled appearance, the splotchy shapes are grains in the metal coating. The molecules cluster together in specific orientations until an impurity disrupts the organization of molecules, then they will spontaneously cluster in another orientation until an impurity upsets the organization again. The grain boundaries are an area of weakness and unpredictability. By making the grain boundaries as small as possible the metal becomes more stable.

CPM Magnacut is considered the "best" because it blends carbides, hardness and toughness. Lacking chromium carbides, CPM Magnacut has a small penalty in edge retention but improved toughness when compared to 20CV or S90V (the previous "best" steels) The improved toughness results in better overall performance similar to 4V but with better corrosion resistance.

Metallurgy is a very complicated topic, comparing one steel to another can be very confusing. Reputable knife manufacturers will provide some guidelines for comparing one steel to another. Spyderco has a fairly comprehensive comparison tool on their website: https://www.spyderco.com/edge-u-cation/steel-chart/ this tool allows you to compare the percentages of certain elements within the alloy.





I consider these every day carry steels, good knives can be found with these steels for <$100.

• CPM 154, 154CM, ATS-34 VG10- Essentially the same steels, good corrosion resistance, good edge retention, fairly easy to sharpen.
• 12C27m, 13C26, 14C28N - These Sandvik steels were developed specifically for use as razor blades, they have excellent edge retention and are easy to sharpen, 14C28N has nitrogen added for corrosion resistance. These steels are used by Victorinox (swiss army knife) Mora and Kershaw.
• 440C - This was considered the best blade steel in the 70's and 80's, it's still pretty good, very stain resistant, good edge retention, can be difficult to sharpen.
• 420HC - Low cost, stainless, good corrosion resistance, easy to sharpen, doesn't stay sharp as long as more expensive steels.
• 8Cr14MoV - This is the "best" Chinese blade steel, it has good corrosion resistance, is easy to sharpen and holds an edge well, when it holds an edge well. Quality is hit or miss, I've had some import knives that stay sharp as long as knives that cost 3-4X as much, others dull if you look at them funny.

High end "super steel"

• CPM Magnacut - the best because it balances toughness and hardness and has superior corrosion resistance.
• CPM S30V - was considered the best high end steel about 10 years ago, powdered metal, good edge retention, difficult to sharpen, depending on heat treat and geometry can be prone to edge chipping.
• CPM S35VN - An incremental improvement over S30V, less prone to edge chipping, stainless, good edge retention. My current favorite knife has a S35VN blade.
• CPM S110V - One of the toughest and most wear resistant steels available according to the data sheets, I have found that S110V is very difficult to sharpen, the one knife I owned with an S110V blade didn't stay sharp very long. A good heat treat is needed for this steel to perform well.
• CPM 20CV, CTS 204P, M390 - Currently considered the best stainless blade steels, all three steels have essentially the same composition, but from 3 different manufacturers. In my experience Bohler Uddeholm has a superior powdered metal process and makes a slightly better blade steel, but all 3 steels hold an edge longer than any other steel I've used, they are all difficult to sharpen.
• Elmax - This steel is somwhere between S35VN and M390, it has really good edge retention but is easier to sharpen than M390.

Specialty steels

• CPM 3v, CPM 4v - Ultra high toughness, ideal for machetes and other large chopping blades, not stain resistant.
• H1 - stain proof for salt water applications

Excessively hard, wear resistant steels can be very difficult to sharpen with common honing stones. Most of the powder metals will require diamond hones to sharpen

Because of the difficulty sharpening high hardness steels great care should be taken to sharpen the blade with precise angles so you're only removing the minimal amount of material necessary. There are a number of sharpening systems, most of them are not inexpensive, Wicked edge, Edge Pro, Lansky, and others make sharpening systems for home sharpening with a very short learning curve.

Lansky

Wicked Edge

Edge Pro


A DIY version can be made inexpensively, this version uses automotive finishing sandpapers as an abrasive.

Crock sticks are a simple sharpening system using ceramic rods that are set at a specific angle, with a little practice these sharpening systems can provide very sharp edges


Crocksticks


The Spyderco Sharpmaker is another take on the crock sticks, it's a little more versatile for sharpening serrated blades, fish hooks and other unusual geometry.

Spyderco Sharpmaker


Natural stones and waterstones have been used for centuries, they are still very useful for sharpening most steels, but require considerably more skill. Stones are almost always used in a progression from coarse to fine regardless of the sharpening system used. Large bench stones, especially high quality Japanese waterstones can cost hundreds of dollars, much smaller stones are often used with sharpening systems, although the initial investment is high to pay for the sharpening mechanism, in the long run the cost savings of smaller stones or alternative abrasives makes the cost more comparable.

Freehand sharpening

Sharpening freehand is a skill every knife enthusiast should strive to learn. I have found using a the sharpie trick has helped me to build muscle memory to sharpen more efficiently.
https://www.youtube.com/watch?v=mvl-Y5bZwtw


Regardless of the sharpening method used the progression from dull to sharp should always include forming a wire edge or burr, once the burr is formed the two bevels have completely intersected and the burr can be polished away. Certain steels are easier to form a wire edge on, some steels will develop a very pronounced burr, coarse grained, high hardness steels may need magnification to see the burr form.

The work sharp electric sharpener is supposed to be user friendly

Work Sharp

A paper wheel is another option


Paper Wheel

Grinding wheels and other powered sharpeners require a lot of skill to use, it's easy to destroy a blade either by removing too much material or by overheating the blade when using powered equipment. Hand sharpening is recommended for anybody who isn't a professional.

The two most common blade geometries are flat ground (or variations of a flat grind) and hollow ground. How the blade geometry is formed plays an important role in how much the blade cost and the materials used.

Flat grinding is used for most high end blades with powdered metal steels.
https://youtu.be/LSZ9F0MNi5o

Hollow grinding is a faster process that grinds both sides of the blade simultaneously. It's not very easy to see what's going on in this video but I'll discus in detail how the machine works during the net.
https://youtu.be/8S6p-IR6vy4


Flat ground blades are very strong, there is a lot of material supporting the edge, as the blade cuts into the material it is gradually wedged apart. A hollow ground blade creates a very thin cutting edge, these blades can perform very well, but the hollow grind can very abruptly wedge into a material when making deep cuts.

Scandi grinds found on Mora knives is a variation of a flat grind, the full flat grind found on many spyderco knives is another variation of a flat grind. Chris Reeves uses a proprietary process to form a very shallow hollow grind, it's nearly a flat grind with a very slight concavity that cuts very well. Many of the traditional slip joint folders were originally manufactured with a flat grind, as factories grew and demand increased some of the more recent models have moved to hollow ground blades, especially brands like Schrade, Old Timer, Uncle Henry, that have gone out of business and the names and trademarks were bought by Chinese factories.

My favorite grind depends on the usage, for an everyday carry knife I like a hollow ground blade, I find they cut through thin materials like packing tape, envelopes and cardboard easily. For camping or other outdoor activities where I might be cutting into something with considerable force I like a flat ground blade. I'm not a huge fan of serrated blades because of the difficulty sharpening the serrations, that said when the serrations are sharp, they do cut extraordinarily well.

handle materials

steel

Kershaw Leek with steel handle

titanium


Lionsteel SR1 with Titanium Handle


aluminum


Swiss Army Classic with Aluminum Handle

G10


Spyderco Tenacious with G10 handle


carbon fiber


Zero Tolerance 0770 with carbon fiber handle


Micarta

Esse Izula with aftermarket Micarta handle

FRN


Benchmade Griptillian with FRN handle


wood


Buck 110 with wood handle


bone

Case Peanut with bone handle

Lock mechanisms
Liner Lock


Liner Lock

Frame Lock

Frame Lock

Lock Back

Lock Back

Axis Lock


Axis Lock


Pushbutton Lock

Pushbutton Lock