what makes japanese chisel steel so much harder?

[Kees Heiden]

Well, I am absolutely sure about the Damascus steel. When they make that from high and low carbon steel, they end up with a medium carbon steel throughout. But there still are very definitive color differences between the layers, due to other elements in the steel that don't diffuse so easilly around. Wrought iron contains a lot of sulphur while white steel doesn't, for example, but I don't know if that explains the color difference.

There is a very interesting study about 18th century woodworking tools available online:
http://preserve.lehigh.edu/cgi/viewc...66&context=etd

They meassured the hardness along the length of several chisels. In the area where the steelbit starts they measured a gradual increase of the hardness over a length of 2.25 mm (average). I don't know how quickly the hardness increases over the thickness of the chisel, but there is one image (nr. 16) that clearly shows this transition zone.

BTW, I think that the making of blister steel takes so long because the carbon has difficulty to jump the gap between the steel and the charcoal.

[Mike Henderson]

Well, I am absolutely sure about the Damascus steel. When they make that from high and low carbon steel, they end up with a medium carbon steel throughout. But there still are very definitive color differences between the layers, due to other elements in the steel that don't diffuse so easily around. Wrought iron contains a lot of sulphur while white steel doesn't, for example, but I don't know if that explains the color difference.

There is a very interesting study about 18th century woodworking tools available online:
http://preserve.lehigh.edu/cgi/viewc...66&context=etd

They meassured the hardness along the length of several chisels. In the area where the steelbit starts they measured a gradual increase of the hardness over a length of 2.25 mm (average). I don't know how quickly the hardness increases over the thickness of the chisel, but there is one image (nr. 16) that clearly shows this transition zone.

BTW, I think that the making of blister steel takes so long because the carbon has difficulty to jump the gap between the steel and the charcoal.

Antique wrought iron was not excessively high in sulphur. Sulphur makes wrought iron "hot short" (or "red-short") meaning that the iron would get brittle when heated to forging temperature.

Our ancestors did not have knowledge of chemistry but they could see the result of different ores. The ores from Sweden were very low in sulphur and were sought after for production of iron and steel. Bessemer had trouble with his process because of the ores used. He developed the process with Swedish ores but after he sold licenses for the process to others, they tried to use it with English ores which were high in sulphur and the process would not produce decent steel.

I don't think the migration of carbon is affected to any great degree by the origin of the carbon. The carbon was in intimate contact with the iron in the blister steel furnaces. I've not heard of any reports of rapid migration of carbon within iron. In fact, if it would migrate quickly once it was in the metal, we would not see the high gradient of carbon within blister steel. Once the carbon was in the iron, if it had high migration, carbon would migrate through the ingots (which were quite thin). But that's not what we see.

And while sulphur makes iron hot-short, phosphorus makes iron cold-short. That is, brittle when cold.

Mike

[Reinis Kanders]

Brian,

What chisel is this? Seems like a handy one for the corners of the half blinds.

Thanks.

Kees,

I think the forge line is fairly thin, I can make it out on some chisels;

[Roger Davis IN]

The conjectural diagram above (with the stars) could not be more wrong. As the first diagram notes, Young's Modulus is equal to the slope of the linear part of the graph. Young's Modulus is about 29,000,000 psi for anything that will rust, period. A publication from the National Bureau of Standards in 1966, "Heat Treatment of Steel," notes explicitly:

"The modulus of elasticity of steel is the same as that of iron (about 29,000,000 psi). It is not affected by heat treatment or by the addition of alloying elements. Since stiffness, or the resistance to deformation under load, is a function of the modulus of elasticity, it follows that the stiffness of steel cannot be changed by heat treatment or by alloying elements, provided that the total stress is below the elastic limit of the steel in question. Either heat treatment or alloying elements can raise the elastic limit and thus apparently improve the stiffness in that higher allowable unit stresses may be imposed on the steel."

"Elastic limit" is the Yield Strength in the first of the diagrams above. Comparison of the 50 HRc curve and the 64 HRc curve would suggest that the softer steel has a Young's Modulus of about 14-15,000,000 psi. This is nonsense; if it rusts it's about 29 million. Note that this constancy also implies that the soft back of a laminated chisel has exactly the same resistance to bending as the hard steel as long as you don't exceed its yield strength, which is to say, bend it. The two constituents will move together quite happily since their response to bending and compressive stresses will be identical unless you go so far as to induce a permanent bend. Heat treating changes yield strength, impact strength (toughness) and hardness. Throw in grain size and you've about covered it.

[Allan Speers]

So, in the long and short, which steel is best to look for when shopping for Japanese Chisels?

IMO:

Top quality white for paring.

Blue for mortising.

Your choice for bench chisels, depending on your preference for sharpness or durability.

[Kees Heiden]

Thanks for the explanation Roger. Glad you joined in and share your knowledge. Like I wrote, this is all new for me, and no wonder I get things mixed up.

When I put a length of hardened steel in a vise and try to push it over, bending it, that wil take a lot of force to reach a small deflection. If I do the same with a piece of spring steel, it is easier to bend it a larger distance. At least that was my train of thought. Can you explain where I went wrong?

[Roger Davis IN]

Put a hardened bar and an annealed (dead soft) bar of the same stuff and the same size and shape in your vise. Hang the same weight on each, and they will droop exactly the same amount, UP TO A POINT! At some point as you increase the load, you will see the soft bar bend farther than the hard one, and when you unload them, the soft bar will not return to its original shape. The hard one will come back to its original shape with the same load because its yield strength was increased by heat treatment. At some higher load, it, too, will fail to return to its original shape. The load which causes permanent deformation (and breaks the linearity of the stress-strain relationship) is the yield strength (elastic limit) of that bar, and can be converted to a universally applicable stress value by knowing the geometry of the bar and how the load was applied (complicated beyond this forum). If you were to test these bars for impact strength, you would find that the harder one can absorb less energy before snapping than the soft one can; this is the tradeoff between hardness and toughness one always faces with heat treatment. Note that all the data points for both bars would lie along the same line as long as you are below the yield point of the softer one. They have the same Young's Modulus (as above), and that is the slope of the linear stress-strain relationship. The harder bar would simply go farther up the same line before deviating at its (higher) yield point. Note the use of "apparently" in the last sentence of the passage I quoted. That is the key.

I've been planning to set up a demo of this for my blacksmithing club, as I have heard a lot of nonsense bandied about regarding the effect of heat treating on stiffness there.

[Roger Davis IN]

Kees:

Note that the increase in yield strength between the annealed bar and the hardened one can be really large, like a factor of 5 or 6 in some cases.

[Kees Heiden]

Thanks for explaning. It's always good to know when you are wrong about something.

But now I am unsure how all this relates to laminated chisels. Is the total toughness of the laminated bar increased beyond the toughness of the hardened steel part?

[Brian Holcombe]

Brian,

What chisel is this? Seems like a handy one for the corners of the half blinds.

Thanks.

Reinis, That one is by Kikuhiromaru, it's hooped for striking as well. Very handy for half blinds.

[Roger Davis IN]

Kees:

I think that's clearly a true statement. I haven't really given a lot of thought to the effects of lamination.

[Kees Heiden]

I probably learned more from this thread then anyone else. I'll shut up for now (sleeping time) and again, many thanks Roger for your information. I wish your blacksmith club was a lot closer.

[Stanley Covington]

Antique wrought iron was not excessively high in sulphur. Sulphur makes wrought iron "hot short" (or "red-short") meaning that the iron would get brittle when heated to forging temperature.

Our ancestors did not have knowledge of chemistry but they could see the result of different ores. The ores from Sweden were very low in sulphur and were sought after for production of iron and steel. Bessemer had trouble with his process because of the ores used. He developed the process with Swedish ores but after he sold licenses for the process to others, they tried to use it with English ores which were high in sulphur and the process would not produce decent steel.

I don't think the migration of carbon is affected to any great degree by the origin of the carbon. The carbon was in intimate contact with the iron in the blister steel furnaces. I've not heard of any reports of rapid migration of carbon within iron. In fact, if it would migrate quickly once it was in the metal, we would not see the high gradient of carbon within blister steel. Once the carbon was in the iron, if it had high migration, carbon would migrate through the ingots (which were quite thin). But that's not what we see.

And while sulphur makes iron hot-short, phosphorus makes iron cold-short. That is, brittle when cold.

Mike

Great information, Mike.

Swedish iron ore is still listed as the purest commercially available in the world. Least sulfer, least phosphorus, less silica. I have it on good authority that Hitachi Metal's better products begin with it. And there are tool steels produced in Sweden today that are equal to (and some say better than) Hitachi's products. Harder to work with though, my blacksmith friends tell me.

Stan

[Stanley Covington]

Brian,

What chisel is this? Seems like a handy one for the corners of the half blinds.

Thanks.

Its called a "bachi" chisel from the tool used to pluck the strings on shamisen.

[Brian Holcombe]

Yessir!

I recieved some Konobu tsuki's and the weld line looks more like that of Yokoyama plane blade than most chisels I've come across. I'll post up a close up later on tonight.