Steel used in Tsunesaburo planes.

Selecting a steel for a kanna blade.

Tsunesaburo offers a wide variety of steels in their blades, allowing them to be well matched to the material being planed.

Japanese blades are well known to be made from a thin layer of very hard steel and a heavier main body of softer wrought iron or steel. The hard steels used in these blades may be separated into plain carbon steel or alloyed and special steel.

Possibly the most well known and revered carbon steel is ‘Tamahagane’ more commonly known as ‘sword steel’ and has an incredible reputation, backed up no doubt by the fearsome Samurai katana.

Tamahagane does require special treatment and also requires a significant investment in time, resources and skill to use correctly, making it quite unsuitable for general use. It is also very expensive, and while some tools are made with it, they are naturally very expensive and ‘out of reach’ of those crafts persons who simply desire a tool that works well and is affordable.
 
As a result, steels have been developed both in Japan and overseas better suited to everyday blades. Many of these steels have been used in Japan from the late 19th century, and many have earned a solid reputation in their own right. The changing needs of craftspeople has also bought about the use of High Speed Steel where maximum edge retention is required in abrasive and demanding materials.  
 

 Carbon steel  
Plain carbon steel (white steel) is largely free of impurities making it easy to sharpen, and will also take a very keen edge. In kanna, this steel is best suited to working with those woods that require the keenest edge but do not prematurely blunt the edge such as paulownia and cedar.

Capable of being made into a fine blade that is easy to sharpen yet still quite durable is achievable, however plain carbon steel is not as ultimately durable as a blade made from a more complex alloy steel.

 Special (alloy) steel  

Taking plain carbon steel and adding elements to it such as Chromium (Cr) or Tungsten (W) increases the durability of a blade to a point where a plain carbon steel blade cannot compare. The addition of various other elements also affects how the steel behaves before, during and after heat treatment.

These alloy steels such as Blue steel, Super blue steel and the Swedish steels are recommended for hard woods where improved edge life is of great benefit, and where the keenest edge is not quite so critical. The added alloying elements in these steels affect the grain size of the steel, preventing them from becoming quite as sharp as plain carbon steel. While the edge may not be quite as sharp, a usable level of sharpness is retained for much longer.

As might be expected, these steels are a little more difficult and time consuming to sharpen. The difference is not great, and the added time and effort spent sharpening is returned by fewer visits to the sharpening station.

In most situations, these alloy steels are the optimal choice for plane blades and feature prominently in Tsunesaburo planes.

High Speed Steel (HSS) (SKH51, HAP-40.)

These steel were developed for machining metal at such at a rate that the tooling would become very hot, which will cause plain carbon and the previously mentioned alloy steels to become soft. The added benefit is that these steels have greatly increased toughness and stay sharp for significantly longer when used in hand tools than any plain carbon or alloy steel.

Of course, sharpening is more difficult due to the extreme toughness of the steel, but due to the fact that these steels can endure high temperatures, a power grinder can be used for much of the work, and only a very small edge bevel is required.

Tsunesaburo offers two choices in HSS, the commonly seen SKH51 type steel, also known as M2 HSS and Hitachi HAP-40 Powder metal HSS (also referred to as M4 HSS), and both are bonded (not welded) to a softer steel backing, making the daunting task of sharpening these tough steels much easier. A unique treatment to the back of the blade also aids sharpening ease, making what would normally be a very difficult to sharpen blade relatively easy.
 
The HAP-40 powder metal HSS is unique in that the special process of making the steel from powder allows a much sharper edge than more commonly seen M2 HSS, and also permits the composition of the steel to be improved as the alloying elements can be increased beyond what M2 HSS is capable of supporting. The end result is a blade that is no more difficult to sharpen, but offers even more edge life and an increase in toughness and durability as well.
These High Speed Steels are recommended for the most demanding materials such as very hard woods, abrasive woods and even man made wood products such as plywood. 


Steel compositions.

(Numbers represent the percentage of the given element in each alloy. The balance is iron with small amounts of additional elements/impurities.)

Steel type

Steel name

C

Cr

W

Mo

V

Carbon steel

Super White

1.35~1.4





Carbon steel

Kawasaki Carbon

1.05~1.1





Carbon steel

Sandvik

1.25~1.28





Alloy steel

Blue steel #1(A)

1.3~1.4

0.28~0.3

2.0~2.2



Alloy steel

Blue steel #1 (B)

1.2~1.3

0.3~0.5

1.5~2.0



Alloy steel

Forged Blue #1

1.25~1.28

0.3~0.5

1.5~2.0



Alloy steel

Special blade steel

1.33~1.35

0.72~0.75

5.5~5.7



Alloy steel

Swallow steel

1.28~1.3

1.4~1.43

6.45~6.5



Alloy steel

Super Blue steel

1.4~1.5

0.3~0.5

2.0~2.5

0.3~0.5

0.3~0.5

Alloy steel

Inukubi Reigo

1.15~1.17

1.32~1.35

5.0~5.06

0.18~0.21

0.38~0.4

Alloy steel

Togo Reigo

1.4~1.5

0.5~0.6

2.5~3.06

0.05~0.08

0.16~0.2

High Speed Steel

SKH-51 (M2)

0.85~0.9

3.8~4.5

6.0~7.0

4.8~5.8

1.8~2.3

Powder metal HSS

HAP40 (M4)

1.27~1.37

3.7~4.7

5.6~6.4

4.6~5.4

2.8~3.3

Carbon (C)

Allows iron to be hardened and improves strength. Affects the ability of the steel to be forge welded.

Chromium (Cr)

Adds corrosion and abrasion resistance, but also increases brittleness.

Tungsten (W)

Improves hardness and wear resistance.

Molybdenum (M)

Increases toughness, durability and hardenability.

Vanadium (V)

Reduces the grain size of the steel, adds toughness and abrasion resistance.


Suggestions for use.

Steel name

Soft wood

Moderate hardwood

Dense hardwood

Man made material

Super White

X

X

Kawasaki Carbon

*

X

X

Sandvik

X

X

Blue steel #1 (A)

*

*

X

Blue steel #1 (B)

*

*

X

Forged Blue #1

X

Special blade steel

X

Swallow steel

X

*

X

Super Blue steel

*

*

X

Inukubi Reigo

X

*

X

Togo Reigo

*

*

X

SKH-51 HSS

X

*

HAP40 HSS

*

Ideal

*

Recommended

Satisfactory

X

Not recommended


These suggested uses are a guideline only. Your experience may vary depending on the preparation of the blade and the material being planed.

Blade steel characteristics.

Steel name

Comments;

Super White steel

Produced in a vacuum furnace, and to a high degree of purity, this steel is has a ‘sticky’ feel, possesses high toughness and excellent hardness making a very durable blade. Improved by what is taken out rather than what is added to it. 

Kawasaki Carbon steel
(No longer produced)

Produced by Kawasaki steel works in the 1950’s, it shares some similarities with white steel in use, but allows greater sharpness. Easy to sharpen, especially suitable for soft woods. 

Swedish steel (Sandvik & Assab)

Produced from high purity ore, this steel also improved by what is left out. Allows an exceptionally keen edge with good durability and easy sharpening. Highly recommended for medium hardwoods. Easy to use.

Blue steel #1 (A)

The addition of tungsten and chromium add durability, toughness and edge life. The most popular steel in Japan for high quality plane blades, it is stable, reliable and predictable.

Blue steel #1 (B)

As for Blue steel #1 (A)

Forged Blue #1

Specially ordered steel by Tsunesaburo the 1st in the 1940’s and hammer worked to remove forging impurities. It has a sticky feel, and is very easy to sharpen. Especially suitable for very soft woods due to its ability to take an especially keen edge. 

Special blade steel

With the addition of tungsten as very small molecules in a significant quantity, this steel offers improved durability over blue steel and also allows a keen edge to be created. Light in use, suitable for moderate hardwoods, but not recommended for very softwoods.  

Swallow steel (Tsubame)

This special steel is especially suited to hardwoods, but is not recommended for softwoods due to its need for a less acute bevel angle. Maintains its edge for an exceptionally long time in hardwoods, has a sticky feel and is difficult to sharpen with its high tungsten content. 

Super blue steel

Yasuki steel works’ premium steel, high levels of carbon and tungsten add hardness and strength, molybdenum allows great sharpness. Recommended for all woods. A superior, modern manufacture steel. 

Inukubi Reigo

Similar to High Speed Steel, also used for lathe tooling. Very difficult to forge and sharpen, has exceptional durability. A unique steel specifically for blade aficionados. 

Togo Reigo

Manufactured during the early Showa (1925-1989) era by Andrews steel of the UK, now extremely rare. Suitable for all woods. Very tough, and due to expense and rarity, suggested for very top end users only. Performs like a blend of tamahagane (sword steel) and premium quality western steel. 

SKH-51 HSS

As used for drills and lathe tooling, has impressive impact toughness and is very durable. Suitable for all woods, laminated materials and abrasive materials. “Uradashifuyoh” blade back treatment allows easy sharpening. High speed grinding possible due to high heat tolerance (550°C/1000°F) before the temper is affected.

HAP40 HSS

Toughest, longest lasting plane blade steel available. Manufactured by sintering very fine powder (6 micron). This keeps the steel’s grain size smaller and allows additions to the alloy that cannot be made with traditional steel. Suitable for all materials, recommended for highly abrasive exotic woods.


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