Hi Derek,
As I wrote in my response to Luke (@#3 above) I'm trying to get an idea of the characteristics of other chisels for my purposes. I'm not trying to create a definitive all encompassing survey of chisels generally.
Regards,
Rob
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I think I understand what you are saying -- but as a maker why would you bother?
If you are set up and experienced with making chisels that are struck and therefore need to be at least a little bit ductile, why would you change steels and processes -- to make a less ductile chisel -- for what is essentially a small volume product.
Rob - my understanding is that some high carbon Japanese steels such as Shirogami 1 and Tamahagane will go 65+ HRC, for example Iwasaki's razors went up to 67 HRC, but as Ian points out most blades, and in particular those that will be struck, would be too brittle in that range, so blacksmiths remain in their comfort zone where they do most of their work. Sadly so, as a well made fishtail in Shirogami 1 or Tamahagane at HRC 67 would be a beautiful tool to use.
The two sets of Japanese chisels I've tested both have steel/iron hooped handles for hammer use. I do have another set of dog-leg chisels with the longer push style handles but haven't tested them yet.
During my experiments with saw steel I was able to over-harden 1095 to the point that it shattered under the indenter of the hardness tester. IIRC I was austentizing at ~1650-1675 oF / 30 min and quenching into NaNO2/NaNO3/H2O at ~400 oF. Quite spectacular little explosions with the resulting fracture patterns looking just like broken glass. Some of the pieces appeared to show hardnesses above HRC 70 before they let go because the indicator would sometimes settle for just a moment before failure. Might have made good razors but I doubt that they'd have held up in any application where real force was applied.
I've added additional data to the New Age MRBR-DI tester results in the form of measurements of the HRC 46.1 standard block. Please note, the reported HRC values are RAW values, i.e. uncorrected for slope and offset. When I report HRC values for my measurements of tools I always correct the reported values.
Attachment 427265Attachment 427264
These are the results, using the same blocks as for the New Age tester, for the Ames 2-S superficial hardness tester. These results are converted values from HRN45 measurements to HRC but they are not corrected for slope or offset.
Attachment 427263Attachment 427262
In a nutshell, the New Age results are + 0.41 HRC units and those for the Ames superficial hardness tester are + 0.25 HRC units at HRC 60. I'll do the Ames 4 and the HR-150A next.
As shown in this example, NIST transfer standards generally can have uncertainties of 0.2 HRC or less. Attachment 427282Attachment 427285Attachment 427281Attachment 427284Attachment 427287Attachment 427280Attachment 427283Attachment 427286Attachment 427279
Unfortunately Transfer Standards are ~$1350US each and you need three. I think + 0.5 HRC units accuracy (or a little less) for measurements of woodworking tools is more than adequate.
From the little I known, that is what I would expect with a high carbon/low impurities steel; it will take a high brittle hardness but at the expense of toughness & ductility. Common knowledge I'm sure among those following your thread, Rob.
I had one very old Tamahagne blade which was extremely hard (just a relative judgement on my part, not a measure) and it was in a class of its own. Took a superior edge, but so brittle that it developed some very fine cracks running back from the edge. Not an issue because the soft iron backing held it together.
If you are just hand pushing a blade, and not using a lever action, it may cope with that level of hardness, but drop it, and yes, it will shatter. I've experienced that a few times on less expensive blades that I have not been so careful with. Also with some of the cutting tools I've made myself.
Anyway, following your thread with interest.
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Thanks for your comment Neil, always good to have input on the project. Inspired by your reference to the Japanese tamahagane I found some references that have pretty well anatomized Japanese tamahagane/shingane blades and their processing. Attachment 427344Attachment 427346Attachment 427345
Remarkable accomplishment for the time but time marches on and modern technology can do better.
The soft part of the Japanese style chisels is often referred to as 'iron' but I haven't found an analysis such as for the above Inoue citation.
Typically the jigane is just old western cast iron. They love old anchor chains and the like that were cast well over 100yrs ago. When the bevel is sharpened it will often reveal the flow pattern from the original pour.
The softer, the better, to absorb any shocks that would crack the jigane.
It is the same reason why I like my woodturning lathes to be cast; they do a better job of absorbing any vibrations.
The old cast iron may also be better for fluxing the jigane to the higane.
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Not to nic-pic, but my understanding is that Japanese edge tool makers seek old WROUGHT iron. And the "flow pattern" is actually from the rolling and hammering process use to make the wrought iron.
I also understand that after about 1890, the process of making wrought iron changed enough to make the more recent iron less attractive to Japanese smiths.
Ian, I suspect the technological transition you're referring to is known as puddling. https://en.wikipedia.org/wiki/Puddling_(metallurgy)#