Thread: Chisel Hardness Study, the first step.

Before you head too far down that path... Do you have any way to have some arc-spark analysis done to determine the actual carbon and alloy content of "winners"... My prediction is that none of the "winners" have a carbon content less that 1%.... All of them above 1.15% would not surprise me at all..

In my mind at least - there's probably not a lot of value in trying to start off from a place where the deck is stacked against you....

I'd imagine the threshold is lower than that, something more like 0.9%, but that's just a guess. The cleaner the steel is, the higher the hardness can be at a lower carbon level.

I've made extremely good irons out of good quality 01 stock, actually better than any I've bought, and I only have crude heat treatment equipment. Some of my nicest chisels in the balance of holding up and sharpening (ashley iles) are probably around 1%.

it's possible for O1 stock to sneak out with carbon significantly higher than 1%, but I doubt it's common for Starrett and Precision's products to be too far off the mark (I can't tell the difference between irons that I've made with either, but all of my made irons are better than Hock's O1 stanley plane irons. I'm assuming that the difference isn't process (theirs should be better than mine), but base stock.

At any rate, the quality of the blade on 1095 knives that I've gotten from tidioute (which are relatively hard, despite their spec quote - they're harder than that) leads me to believe that it would be perfectly fine for chisels (no clue where you get really true to spec 1095, as the acceptable range is huge, isn't it?).

Originally Posted by truckjohn

Before you head too far down that path... Do you have any way to have some arc-spark analysis done to determine the actual carbon and alloy content of "winners"... My prediction is that none of the "winners" have a carbon content less that 1%.... All of them above 1.15% would not surprise me at all..

In my mind at least - there's probably not a lot of value in trying to start off from a place where the deck is stacked against you....

No, not at a decent price. I could go over to the local U and contract with the EM lab but they're too expensive at ~$1300/ for something like this. Likewise I know a place to get ICP done but the pricing is also too high for my taste. Most of the metals I've bought come with some kind of cert.

Later on I plan to add this kind of capability but I've got some fish to fry before I can.

While that is no doubt true - at least know where that takes you... For example - the standard DIN/ISO spec calls out

That the chisel must demonstrate cutting performance equal or better than a chisel made of this material:

These alloy limits:
C - 0.9% - 1.25%
Si - 0.15%-0.25%
Mn - 0.25%-0.40%
P - 0.035% max
S - 0.035% max
And a hardness range of Rc 58-61...

So... In my mind at least - that's probably a reasonable yard stick for a place to start off... Assuming good quality W1 or 1095... Made Q&T correctly to about Rc 60 - would meet the minimum alloy and hardness requirement would probably serve as a fine "known" yardstick candidate... And I have a feeling that a chisel made just like this and carefully heat treated would likely beat most commercial offerings.... Even better if quality O1 or Silver Steel was used that started off with carbon of 1% (min) and low impurities..

Back when I was experimenting with 1095 saw steel hardening I was able to get some readings in the high 60's and low 70's before the test coupons exploded, particularly when I quenched in molten salt at about 400 ^oF.

Having read about the tungsten steels I also want to look into them. My understanding is that Terry Gordon uses them for his "HSS" plane blades.

Tungsten HSS makes nice chisels and plane blades. I think it's fairly expensive, but it makes nice blades that sharpen well on a much wider range than M2.

The Cru Wear product looks interesting Special Purpose Tool Steels - Niagara Specialty Metals.

Originally Posted by truckjohn

Interesting that the Japanese have been doing it for over 400 years (as were the Europeans and British prior to about 1850)... And even Stanley was doing this around WWII... Surprising to me that a couple of those fellows didn't visit one of those Japanese festivals where the blacksmiths forge tools out in public the old way and then made friends with a Japanese blacksmith over a couple bottles of sake and just learned from them... I mean to my untrained non-blacksmith eyes - it looks pretty straight forward for those guys...

I'm not pretending that I have anything approaching a trained blacksmith's eye, but I recall being told more than once that a good blacksmith is heavily reliant on their eyes being able to discern very slight changes in colour and I've watched smiths move steel around in the forge selecting the billet that is just the right colour for the next process.
So perhaps not as straight forward as it seems.

Certainly it takes both skill and technique...
But - lots of smiths have mastered the technique... It's not like a magic impossible thing where 1 guy in the world does it with a 30% success rate... Or some specialized thing where you need $20MM worth of specialized custom robotics, inert atmosphere and vacuum furnaces, custom proprietary fluxes, and 30 years of experience to pull it off in the one single plant in the entire world they do it...

We stand on the shoulders of giants.

Originally Posted by rob streeper

Back when I was experimenting with 1095 saw steel hardening I was able to get some readings in the high 60's and low 70's before the test coupons exploded, particularly when I quenched in molten salt at about 400 ^oF.

Is this a home brew molten salt or a commercial product?

Also - what is the process for a molten salt quench? How long does it take - and do you leave it there for a while for an isothermal transformation, or just quench into low temp molten salt, wait a minute, then quench into brine/oil/water to finish cooling?

I want to try re-hardening an Aldi chisel to see how it behaves a bit harder.. 95% chance it's something like W1... And a faster quench is going to make it work better all the way around...

Originally Posted by truckjohn

Is this a home brew molten salt or a commercial product?

Also - what is the process for a molten salt quench? How long does it take - and do you leave it there for a while for an isothermal transformation, or just quench into low temp molten salt, wait a minute, then quench into brine/oil/water to finish cooling?

I want to try re-hardening an Aldi chisel to see how it behaves a bit harder.. 95% chance it's something like W1... And a faster quench is going to make it work better all the way around...

It was a NaNO₂/KNO₃/water system. I got the recipe from a paper on martempering that I have somewhere on the computer. Direct quench from the oven at around 1600 ^oF into the salt. Temperature of the salt was about 400 ^oF if I remember right. I posted about the experiments on WWF, I'll look up and post the link-back later.

I have been Thinking about chisels made via stock reduction vs modern hot forging.... And modern forging may in fact not be an advantage to edge life....

Paul at ASW had previously noted that his HSS plane irons cut "with" the rolled direction of the HSS plate held their edge considerably longer than those cut "across" the grain... Hmmm. Did he just stumble onto the anisotropic nature of rolled steel plate that most materials text books gloss over?

Something interesting I was looking at a bit..... Steel can be quite anisotropic - aka the properties "with the grain" are much different than the properties "across the grain".... Even the Youngs Modulus can change significantly with grain direction.... Yield strength (compression and tension) of crossgrain steel can be 40% or 50% that of long grain steel..

Of course - I had always been taught that it was Isotropic... Apparently, this is simply an assumption made in the books to make the math easier... As according to the scholarly articles - everybody knows material properties are not the same in all directions, and they have known that for a long time... And if you are designing parts in real life where actual strength matters - they encourage you you take this into consideration..

Annealing is shown to reduce this tendency by perhaps 15% - it doesn't eliminate this nature....

Where is this going? We are often taught that forged chisels are superior because of how the work effects the steel grain... And that *might* be true assuming the blanks are sufficiently large and die progressions are carefully designed so that the material flows "longways" and not "crossways" .... Aka the chisel is "drawn out" of the blank (aka starting with short/fat and ending with long/skinny)... But look at the most youtube videos and you notice that the round blanks used to make chisels are mostly forged wider and flatter - not longer and flatter... And this sort of thing may actually undo all the potential advantages of forging where we are concerned - edge life and resistance to chipping/rolling....

And there is a potential opportunity here for the small maker - cutting all the chisel blanks "with" the steel plate's rolling direction (or grinding them out of rolled bar stock) has a very high likelihood of improving everything we want without basically any downside other than stock waste - simply because of the anisotropic nature of steel...

As an aside - I have been puzzling over why Lee Valley's O1 chisels are reported by multiple sources to significantly outlast competitor's O1 chisels when theirs are cut out of plate and their competitors are mostly forged..... And also David's observation that his own plane irons made from high quality O1 plate outlast Hock irons (nominally made from the same alloy steel)... Does this answer the question (at least in part....)

and so this makes me want to try grinding a chisel out of round O1 or W1 bar stock.. Just to see what happens... If there is something to this - then this could pretty big....

The anisotropic nature of ferrous metals has been long known and is well documented since the 18th century. The effect of grain orientation was apparently first investigated systematically starting in the 1850's. The impetus for the earliest investigations were various disasters, particularly failure of iron cannon.

These three books provide excellent historical and technical details of the development of iron and steel technology.

early steel reference books.jpg

The books by Tweedale and Barraclough are commercial versions of their doctoral theses from the 80's. Tweedale writes somewhat peevishly of Barraclough as '...a trained metallurgist, not a professional historian...'.

Each of these books offers indispensable and complementary information to students of the subject. The Gordon book is a more general discussion of the American iron industry from colonial times up through the 19th century and provides a great deal of detail on the processes used for converting ore to iron and iron to steel. Tweedale discusses the relationship between Sheffield and the emerging iron and steel industry of America with a special emphasis on crucible steel and tool steels including a chapter on saw steel. Barraclough discusses the technology of steel making generally with a special focus on Sheffield and the other European pioneers of the field.

Of all of the texts I've looked at to date on the general subject of the development of the modern iron and steel industries these are the most informative.