OAUSA Net - Edged Implements - November 15, 2018

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DaveK
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OAUSA Net - Edged Implements - November 15, 2018

#1

Post by DaveK » Sun Nov 11, 2018 12:29 pm

EDGED IMPLEMENTS

Part of your essential outdoor gear should be edged implements (such as knives), whether in your vehicle, in your emergency supplies, your bug out bag, or what you always carry on your person. Edged implements go beyond just knives, however, and include hatchets, axes, shovels, machetes, saws, multi-tools, and even such things as chain saws. Although the net will primarily focus on knives, we will cover others as well.

Our guest for this net will be Daniel Humphries, KI6NAI, who is an engineer with a great deal of knowledge on this subject. Post your questions or comments here and join us on the net.
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Re: OAUSA Net - Edged Implements - November 15, 2018

#2

Post by KI7NAI » Mon Nov 12, 2018 10:12 pm

Hardness and toughness

Hardness refers to a material's ability to resist deformation, in the knife industry (as well as any other metal working industry) hardness is measured using a rockwell hardness tester, a special tool that uses a diamond tool of a specific geometry that is forced into the metal with a specific force, the depth of the resulting indentation determines the hardness. For knife blades hardness is typically expressed in HRC or Rockwell C. Normally cutlery falls in the range of 50-65HRC depending on the material and the intended use.


Ductility is a material's ability to deform under stress, a ductile material will bend before breaking. In knife blades ductility isn't necessarily desirable, but it's often referred to when comparing steels because ductility relates to toughness. Toughness is a combination of ductility and strength, it is normally measured with a Charpy notch test where a sample of a specified geometry is impacted with a specific weight dropped from a specific height and the energy absorbed in the impact is recorded as the toughness. For blades this is normally 20-85 Ft Lb depending on the material and the intended use.

Hardness and toughness are a tradeoff, harder materials have lower toughness and tougher materials have lower hardness. Compare a glass bottle to a plastic bottle, the glass bottle is very hard but will easily crack if impacted, the plastic bottle is very soft, but will resist impacts.
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Ultimately hardness determines wear resistance, which is the ability to cut through abrasive things without dulling. Knife steels have been developed to maintain high toughness at high hardness.

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Re: OAUSA Net - Edged Implements - November 15, 2018

#3

Post by KI7NAI » Mon Nov 12, 2018 10:15 pm

In the last 2 decades Powder Metals have grown popular, with improvements in manufacturing processes the cost has dropped considerably and superior alloys have been developed. At this point anybody who is a knife enthusiast most likely owns one or several knives with a powder metal blade.

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The goal of powder metal is to provide a finer and more consistent grain structure. Because the metal is powdered and sintered the grain growth is limited by the physical boundary of the powder sphere. Highly alloyed steels can be produced with even distribution of small carbides, if the same alloy were produced with conventional manufacturing processes the carbide grains would grow together and become un-workable.
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Powder metal has tangibly superior characteristics compared to traditional steels, it can be heat treated harder for better wear resistance without sacrificing toughness. Theoretically the fine grain structure of powder metals allows for sharper edges as the small carbides are less likely to tear out during sharpening. In the real world, your mileage may vary.

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Re: OAUSA Net - Edged Implements - November 15, 2018

#4

Post by KI7NAI » Mon Nov 12, 2018 10:36 pm

Steel comparison

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.
Steel composition chart.png
Steel composition chart.png (12.79 KiB) Viewed 6 times
Steel composition chart II.png
Steel composition chart II.png (17.12 KiB) Viewed 4 times
Generally speaking the following assumptions can be made when comparing one steel to another
Carbon: The higher the carbon content the harder the steel can be heat treated
Chromium: Chromium increases toughness and wear resistance, as well as gives the steel stain resistant properties, steels with more than 13% chromium are considered stainless
Cobalt: Increases hardness and strength
Manganese: increases hardness, makes the steel more stable in quench, increases wear resistance and tensile strength
molybdenum: increases hardness and high temperature strength, improves machinability, improves corrosion resistance, is a carbide former
Nickel: increases ductility and toughness
Niobium: Is a grain refiner, carbide former, improves strength and toughness.
Nitrogen: Can replace carbon in steels, increases stain resistance
Phosphorous: Considered an impurity in steel, can cause brittleness
Silicon: Can increase toughness and hardness, helps to remove impurities from steel
Sulfur: Considered an impurity in steel, in small amounts can improve machinability
Tungsten: Forms carbides and promotes wear resistance
Vanadium: Helps control grain growth, increases toughness and strength



There are lots of blade steels to choose from, an incomplete list includes
1. A2
2. D2
3. O1
4. M4
5. W1
6. CPM 3v
7. 52100
8. 154CM
9. CPM 154
10. ATS-34
11. 420HC
12. 440C
13. CPM S30V
14. CPM S35VN
15. CPM S110V
16. CPM 20CV
17. CTS 204P
18. M390
19. Elmax
20. 12C27M
21. 13C26
22. 14C28N
23. 8Cr14MoV

I'll talk about my experiences with most of these. Please share your experiences with any of these steels or others I haven't listed.

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