Thread: should new chisel edges be square?

You don't realise what a big can of worms you have opened up here Steve.

Just going through Machinery's Handbook and giving you all a quick once over.

Hardness is determined by the carbon content.

Hardenability is determined by alloying elements. Hardenability is the ability to harden a piece of steel to a greater depth. The way Japanese Smiths make cutting tools it isn't really such an important feature. The way Western Forges make blades it is, mostly because the hard bit of the steel is much thicker.

Alloy refers to a metal made of various elements. Brass is a good example being largely copper with whatever else added to it. There are many Brass Alloys. Alloy Steel is Steel with elements such as chrome Nickel Molybdenum Manganese and so on added. 4140 is a good example or A2 for that matter.

I think you are going to have to read the book so that you can get a good grip on the structure of steel and its changes due to heating. It is complicated stuff at that level. Basically when a steel has more that 0.85% carbon it has an excess of cementite above that required to mix with the to
ferrite to form pearlite.

At the lower critical point which is in the range 1335 to 1355ºF the alternate bands of ferrite and cementite that make up the pearlite begin to merge with each other. This process continues until the pearlite is thoroughly dissolved forming Austenite.

Effects of cooling on carbon steel: As the cooling rate is increased the layers of pearlite formed by the transformation to austenite become finer adn finer until they can not be detected under a high power microscope, while the steel increases in hardness and tensile strength. As the cooling rate is increased still further to beyond the critical cooling rate a new structure is formed. The Austenite is transformed into Martensite, which is characterised by an angular needle like structure and high hardness.

Just my impression but Japanese Smiths doing their quenching in water are very likely gaining this Martensite structure.

Back when I was an apprentice and the best steel they would give us was 1040 and they called it tool steel we used to make tools out of it and harden them with an oxy torch. Heat it up cherry red drop it in a bucket of oil then go and polish it up back to the oxy set and give it a gentle heat until the polished surface started to show straw and blonde colours, next you get up to the blues so we let that happen in the middle of the punch and tried to drop it in the oil when the straw colour was just at the tip of the tool. That might be all you need to know about hardening.

Anyway heat treatment is a huge area it is a discussion that could go on for years and still not be at the end.

Studley

Studley,

You are correct in that this subject is complex. My knowledge comes from reading various sources (just as yours). Obviously, my sources are limited and don't delve very far into the complexities (meant as a quick synopsis for the lay person). Realistically, when reading something out of a book or magazine that attempts to describe (in this case) the methods used by Japanese blacksmiths to make tools, knives and swords (methods which take years to master and understand), obviously the articles can't even approach being complete (for instance, there is no mention of age hardening, at least the chemistry of it, which seems to result from the existence of retained austenite amongst, no doubt, many other things going on) and often tend to put a bias of superiority over other methods (which I admit to adopting).
So I'm learning much more than I knew thanks to you illuminating the subject (and I mean that sincerely).
What we really need is a more complete pairing up of what's going on chemically in the steel with the various stages it goes through on its way to a tool. Its probably all ready out there in the various posts of this thread leading up to here.
Anyway, I'm happy to close the can unless others want to keep it open.

What I believe is, even though today's Japanese blacksmiths use modern steel, there is something in the traditional method of forging tools that results in a definite difference in the finished product, not merely a different path to the same end.

Steve

p.s., my use of the term alloy, was used erroneously. You are right (again) in that other elements are added to the steel to create an alloy.

Also, blacksmiths of any age and nation prefer(ed) to keep there forges dark so that they can see the colour of the steel and know its temperature.

Age hardening is when there you harden to a Martensite condition but there is left over Austenite. Over time the Austenite converts itself to Martensite. This can produce growth in the steel.

The Japanese method is important to the stuff they produce, I feel sure. To learn more I might have a dig around to see what I can learn about forging.

I did sell one of my planes once on eBay (actually I still have a heap so if anyone wants one email me, my PM box is full) and the guy who bought it was BlackSmith. We he came around to pick it up which was neat as I didn't have to pack and ship it and we got to talk for a while about it. he was quiet clear we had a laugh about unbreakable samurai swords. Because of course anything can be broken if you hit it hard enough. He told me a bit too about the "layering" of Japanese blades and how it was nothing more than a way of removing impurities from the steel. Of course steel being steel you fold it back on itself red hot beat it out and it is once again one layer of steel. That said there is very likely some interesting stuff going on at the microscopic level.

I think the real genius of the Japanese Smith was to laminate a hard piece to a soft piece. That way the hard steel gets the toughness of the soft steel and you gain qualities that were hundreds of years ahead of their time. Modern alloy steels can almost certainly match the hardness and toughness combo. Can they be sharpened to as fine an edge as a Japanese Blade? My experience with A2 is that it can be made pretty sharp but not much point going beyond a 1200 stone. Doesn't seem to give it much if any more. I do have a 4000 grit that I use on them a bit but while they get sharper it isn't much sharper so usually I save myself the effort. Japanese blades on the other hand it is good to go to 8000 grit and finer as you will be rewarded with an amazing sharp edge. These edges hold very well too.

Could Western steel be as good? Don't know. I have thought that even though H7 is a hot work steel used for dies and punches and so on that it would make a very good blade. The big hang up would be keeping it sharp. So lamination would be a really good answer to this. Laminate it on to a bit of 1010 or whatever (I think they would more likely go for 1040 because 1010 machines up like rubbish) and just use a thin bit of H7 on the front of it.

More bleatings

Studley

Originally Posted by Studley 2436

...Japanese blades on the other hand it is good to go to 8000 grit and finer as you will be rewarded with an amazing sharp edge. ...

Studley....it's nice to go above #8000 but there are limited options available. In synthetic waterstones Naniwa go to #12000 and Shapton have #16000 and #30000 and they start getting to be quite expensive, the last costing over $500 for the professional series.

The other option is to go with natural finishing waterstones above #4000 or #6000, but it's a tricky road to go down. I have noticed a few members of this forum have and use them. I have a few and I'm still finding my way with them. There are many pros and cons for going with this option. Is there enough interest from members to start a new 'elementary' discussion on natural Japanese waterstones?

Neil

Those are the stones I have Neil. They weren't shockingly highly priced as they are Japanese but man made stones. I do have to get another 1200 or thereabouts as I have worn mine out *LOL*

Studley

Well swords I know something about.
When you fold steel over on itself and weld the two "layers" together, you do in fact now have two layers of steel within one solid piece. In order to get the two layers to weld together, you need a flux and this causes a distinct division between the two (or four, eight, sixteen, etc., depending on how many times the steel is split and welded together again). The steel doesn't get melted, so things stay separate (chemically). You probably can't see this division when the steel is polished as the whole thing is still the same type of steel. In order to make the layers visible after polishing, more than one piece of steel (each different slightly than the other) is used, so that as the folding continues, the layers alternate. So long as the layers don't become so thin as to be invisible (seven folds would produce 128 layers, each thick enough to be discernable in the finished blade, whereas 20 folds would produce over a million layers, so much too thin to be visible to the naked eye. Also would not be necessary to fold that many times).
The number of folds depends on how much refining of the steel is required to remove impurities (slag and voids usually left over from smelting), to more evenly distribute the carbon content throughout the billet (essentially, ending up with a homogenous piece of steel without melting it all together. After smelting, the raw steel or "kera" will be steel, but will not have a uniform composition throughout) and, since some carbon is lost with each "heat", to arrive at the carbon content the smith requires (it needs to start out with a higher content to compensate for the loss). A direct benefit of the folding and forging is the creation of all the layers which enhances the strength of the blade (think plywood).
This steel (high carbon) will become the edge and sides of the blade. Within the centre of the blade is a piece of low carbon steel to provide the same function as the low carbon steel used in a laminated tool (toughness).
Hardening differs from that used in tools, in that you don't want the whole blade to have the same harness as the edge. Because the entire outside steel jacket is the same carbon content, it has to be heated to different temperatures (hotter at the edge and cooler at the sides and back. The center doesn't matter because it is low carbon and will not harden). This is accomplished using a clay coating applied prior to the hardening heat. The clay is thin at the blade edge and thick elsewhere. Naturally, when hot, the heat differential due to the clay is minimal (eventually, the whole blade gets to be about the same temp.). But with the last seconds in the fire, the smith ensures the edge is in the hottest part of the fire, so t will gain temp. on the rest of the blade. He judges the temp. by the colour, and when right, plunges the blade into a trough of water. Where the clay coating is thinnest (at the edge), the steel cools very rapidly and forms martensite. The rest of the blade cools more slowly due to the thickness of the clay (sheesh, I'm writing a whole book here) and does not cool rapidly enough to become martensite, but changes back to pearlite.
Now, a couple of interesting things happen here. As the back of the blade cools, it contracts and imparts a curve to the blade shape (hence the usual shape of a Japanese sword). This curving away from the edge is resisted by the cold, hard edge martensite which tries to remain strait (it actually curves in reverse when the blade is first plunged in the water as the edge cools and contracts faster than the back). The resulting tension within the blade creates a tremendous force which enhances (I know Studley, you're going to roll your eyes at this one) the ability of the edge to cut. Honest, that's what they say (and they've actually proved it using strain gauges).
There is, just like the study of steels in general, a lot more to it. I won't go on, so if anyone is really interested, I encourage you to read up on the subject.

Steve

Originally Posted by Sheets

The resulting tension within the blade creates a tremendous force which enhances (I know Studley, you're going to roll your eyes at this one) the ability of the edge to cut. Honest, that's what they say (and they've actually proved it using strain gauges).
There is, just like the study of steels in general, a lot more to it. I won't go on, so if anyone is really interested, I encourage you to read up on the subject.

Steve

Nah Steve tension introduced to steel by the hardening process is pretty standard knowledge. There are sometimes large forces contained in a piece of hardened steel.

The way the Japanese do their blades think kitchen knives is to have the bevel on the right and keep the blade flat (well it isn't flat there is a hollow as Steve describes) on the back. This is really good in the kitchen as you can slice things very thin. It gives you really good control, first rate stuff.

I do want to have a think about this idea of layers of steel. I am skeptical. I know for instance that Fitters have been "marrying" steel together for ages. Good way to do it put a steel pin in the chuck of a drill press and start the drill. Then press the pin into an undersized hole. Gets all bright and red hot press it in and hit the stop button before anything really lets go. No flux nothing melted but it is welded in there. It would be possible to see the difference between the join and the two metals but within the weld could the point of joining be seen? I don't know.

Another point is that for the so called million layer blade you end up with layers that are smaller than an atom. It would be really interesting to find a metalurgist and see what they had to say about all this.

Studley

Originally Posted by NeilS

Is there enough interest from members to start a new 'elementary' discussion on natural Japanese waterstones?

I use natural waterstones in most cases. Am getting more proficient.

Would be delighted to get involved with that discussion. (Not tonight: you guys are just up; I'm about to fall down.)

What d'you say?
Becky

Creating a millions layers, while possible, is not practicable (and certainly not common practice). For one thing, as the steel is heated each time, some is lost due to oxidation and the formation of scale (which just flakes off and falls away. It becomes an impurity, so you don't want any of it in your steel - so couldn't add it back in) and the carbon content is being reduced as well, so you either run out of sufficient steel to continue, or the carbon content goes too low, or both. Now I suppose you could combine say ten pieces of steel (all previously folded a number of times) and fold all that lot a few more times to reach your million layers (you'd only need 500,000 layers here, because the final fold occurs when the high carbon steel is wrapped around the low carbon core, doubling its own layer count and incorporating how ever many layers are in the core steel). But, the cost in time, labour, raw material and fuel (charcoal) involved makes it almost totally impractical and there is in any case, not likely any advantage (quite likely some disadvantages and the law of diminishing returns) over stopping the folding as soon as the steel has reached the state desired (in terms of purity and carbon content).
When you're trying to make a living, being efficient as well as skillful means you just can't afford to spend time and resources beyond what is reasonably necessary (unless you have customers willing to pay enough - but they need to know (believe) they are getting something worth more).

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Steve

Originally Posted by Sheets

This week's special - anti shuriken shirts - 5 pieces of gold (free with the purchase of a new sword)

Good to see you back in form, Steve. 'Bout time. Cripes, haven't seen a truly howl-worthy pun from you in ages.

Becky

Hey thanks. Last week's special was "Elevator Geta (sold out)". Not only will you cut an imposing figure, but very useful in the rain.

Steve

"When one has nothing to say, it is better to remain silent".
- Kwai Chang Caine

Get help. Now.

Really.

Originally Posted by yojimbo

...The ball peen's an interesting idea, though I'd worry about seeing as well, since the ball will, of necessity, occasionally obscure my view of the blade. I'll give it a try on a really shot old kanna I've got. No great loss if I screw up, and I may find it works great....

Becky, a narrow cross peen might be a better idea than ball peen.

Also, do you know what type of lacquer Tomonori-san sells for stone integrity? It's water based, which begs several questions about using it in water. But my main concern is whether it's urushi, since I recently read that urushi is a close relative of poison ivy/oak/sumac, to which I'm very allergic.

Pam

For stone cutting, use a stone cutter. I wouldn't think of applying my table/band/mitre saw blades to stone, they're too expensive and don't work. I used a stone cutter (circular saw with special blades and a water bath) saw when learning masonry in a survey course on bldg tech. These saws are pretty cheap, but someone advised hiring a stone cutter for this, I agree, good advice.

Or perhaps you want to learn the score and tap method like brick layers and stone fence builders? Using cold/stone chisels? I haven't a clue how to do this, but I've seen it done.

Pam