About the Knife Steel

Hello

Are you having fun with leather craft?

When I started leather craft, I usually touch three things the most.

1.Leather

2.Wood

3.Steel

So to the best of my knowledge, I would like to share information about those material.

if there's something wrong with this article, please feel free to correct me.

When you do leather craft, you use knife and awl a lot.

if you know your knife steel, you can sharpen them easily.

I will not go in to deep. just enough for the leather craft.

Knife steel is categorized into two.

Stainless Steel = SUS = inox steel = inox & Carbon Steel

you might know that stainless steel is a steel that does not rust, but actually stainless steel DOES get rust when exposed in harsh condition.

Harsh condition means, lots of sweat from hands or extreme humid weather.

  

  

For Carbon Steel, you need maintenance.

but you can sharpen Carbon steel sharper then Stainless steel.

so most of leather craft knife is more towards to the carbon steel.

(some stainless is also possible for razor sharpness)

If you want to cut leather, especially thick leather, you need to sharpen your knife extremely sharp. Sharp enough to shave.

and after you make sharp edge, your edge must maintain the edge.

that is called "edge retention"

If your knife has bad edge retention, it's bad knife.

you have to sharpen them after every each cut and that's very annoying. 

There are many knives out there for leather craft.

if the steel is hard and properly heat treated, you can assume that it has good edge retention.

Normally,

Hard steel is hard to sharpen, keeps a good edge,

Soft steel is easy to sharpen, loses a edge relatively easy.

I will stop here. just enough for the leather craft cutlerly.

The unit for hardness is HRC. it is Rockwell hardness.

Sharp tip press again the steel, and when the moment the tip dents the steel, the HRC

is determined.

If you look for specs into Survival or hunting knife, the manufacturer tells you what HRC

they are.

What HRC is "good" enough for knife?

In my humble opinion, above HRC 58 is good.

When HRC is about 65. it is very very hard steel.

almost, too hard that if you have thin blade and twist cut too much, it will break.

Most leather craft knives are not telling us HRC, how can we choose knives?

In that case, we can choose knife steel, instead of HRC.

because each type of knife steel is usually heat treated in certain range of HRC.

O1 steel for example, it is around 58~61 HRC.

Stainless Steel - Chrome 10.5% or more + others

SK steel  example : disposable blade

CPM154 , 154 CM, ATS 34 : Knipschield Knives (Minnesota, US)

CPM S(  )V Series

CPM S35VN :  Leather Wrangler Knives  (Texas, US)

Carbon Steel -  0.12 ~ 2 % of Carbon + Others and most company keeps them secret. 

Spring Steel : TINA 270, (Germany)

Japanese Knife steel

Steel below is manufactured by Japanese steel company "HITACHI-KINZOKU" (日立金屬)

Yasuki Hagane : Source of Iron material  

Yasuki Hagene →  reduce impurity → Yellow Steel, N.2  (Intermediate)

Yellow Steel, N.2  → reduce carbon slightly → Yellow Steel N.3 (Soft)

Yellow Steel, N.2 → reduce impurity more → White Steel N.2 (Intermediate)

White Steel N.2 → add carbon → White Steel, N.1 (Hard)

White Steel N.2 → reduce carbon slightly → White Steel N.3 (Soft)

White Steel N.2 → add Tungsten and Chrome → Blue Steel, N.2 (Intermediate)

Blue Steel, N.2 → add carbon → Blue Steel, N.1 (Hard)

Blue Steel, N.1 → HARDENING PROCESS → Super Blue Steel, N.2 (Hard)

Elements 

Carbon : Element for Strength and Hardness. High Carbon content means Hard Material.

therefore it needs good forging skills

Chrome : It increases the characteristics of wear resistance and ruse resistance.

Tungsten : It increases the hardness and increase sharpness

Molybdenum : it increases Toughness, Durability

Vanadium : it increases wear resistance and toughness and make steel crystal fine.

Super Blue Steel is most expensive.

Each steel has it's purpose, with white steel, you can get the sharpest edge.

Yellow Steel : Japanese Saw

White Steel : Japanese Plane, Chisel, Kitchen Knife

Blue Steel : Japanese Plane, Chisel, Kitchen Knife

for leather craft, Super Blue Steel and Blue steel is good.

Steels  don't show any of color. All steel has same color to human eye. 

It was a old way to recognize the steel by putting the color papers to the steel.  Hitachi no longer use this method  but the steels are still called the same way.

Yellow Steel = Yellow Paper Steel = Ki-gami

White Steel = White Paper Steel = Shiro-gami 

Blue Steel = Blue Paper Steel = Ao-gami

Super Blue Steel = Ao-gami-SUUPA

Super Blue Steel : Nobuyoshi Japanese Knife (Japan)