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Vern Wimmer

Definitions and history of "Wootz" and such

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44 minutes ago, Jerrod Miller said:

This is why I personally have no real interest in wootz: it is not a very good (mechanically) material. 

Well, it is and it isn't.  It depends entirely on the smith who made it and forged it out.  The devil is in the details, and if you don't forge and heat treat it just right, you don't get that really flexible structure which makes it such a great material.  It can be a very tough and sharp and durable material which outperforms some other modern steels.... if it is done right.  Modern makers don't always know how to, or choose to, make their steel perform to the best that it can, and seeing the process isn't automated in a massive factory and the qualities come from subtle forging and heat treating, individual blades will outperform some other steels, and others will not.

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That is along the lines of "properly worked heat treated 1045 makes a better knife than poorly worked and heat treated 5160".  While that is true, an apples-to-apples comparison is "optimally processed wootz" vs. "optimally processed <good standard blade material>".  I can't think of any standard blade alloy that we commonly discuss that would not turn out better than wootz in any mechanical test set (like the ABS journeyman test, for example).  Metallurgically speaking (and I am a metallurgist), the structure of wootz just isn't ideal.  

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1 minute ago, Jerrod Miller said:

  Metallurgically speaking (and I am a metallurgist), the structure of wootz just isn't ideal.  

Aha! but there are so many structures of wootz ;) what structure do you think is not ideal? It is important to have a specific quality or structure to identify with your thought.

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11 minutes ago, Tim Mitchell said:

Well, it is and it isn't.  It depends entirely on the smith who made it and forged it out.  The devil is in the details, and if you don't forge and heat treat it just right, you don't get that really flexible structure which makes it such a great material.  It can be a very tough and sharp and durable material which outperforms some other modern steels.... if it is done right.  Modern makers don't always know how to, or choose to, make their steel perform to the best that it can, and seeing the process isn't automated in a massive factory and the qualities come from subtle forging and heat treating, individual blades will outperform some other steels, and others will not.

Well that brings us to kind of a critical question . I think most forum members would agree that a single individual is capable of making a knife that is equal to, if not better than, a factory knife of the same steel. (Assuming the individual has the skill and heat treating equipment) . To take it a bit further I would opine that there are few "mission specific", dedicated, special purpose , etc steel knives that a factory can/does make better than a skilled, equipped 'smith.

That being the case why should it not be possible with the making of steel?

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I am not saying that it isn't possible, frankly I know it is. But my point is to do with the repeat ability of producing wootz between makers.  It all isn't made the same so the quality is a very individual thing as are the blades produced from it. 

Edited by Tim Mitchell

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Any production line steel has a formula of how to treat it so that it turns out the best.  Wootz does not have that yet... that is the problem.

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19 minutes ago, Tim Mitchell said:

what structure do you think is not ideal?

Large quantities of carbide, especially large carbides and large dendritic structures (you know, the thing that makes wootz - wootz).  Carbide + tempered martensite (in wootz quatities and distributions) is far more brittle than homogeneous tempered martensite; let alone a differentially hardened or tempered blade.  Carbide + pearlite (again wootz-style) isn't as tough or edge-retaining (or technically even able to get as sharp, but still can get plenty sharp) as homogeneous tempered martensite.  Add in very fine carbide distributed in some modern steels and they just get better.  If you can see the carbides (or any dendrites) with the naked eye (after etching), they are too big (for blade applications).  

I would again like to mention that there are certainly times when wootz can be good enough.  I think that in general too much emphasis is put on "optimal" properties.  With modern steels, if we make a blade that has achieved 90% of what the steel is capable of, then it probably ranks in the top 1% of blades EVER produced in history.  A decent attempt at HT with 5160 will get a better blade than you can find at Walmart (I'm assuming, as I don't even bother looking at knives at Walmart, just going off the quality of everything else there).  Think of the ABS journeyman test.  Those parameters are insane; in a good, but "overachieving" way.  Who really ever puts a blade through THAT?  

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Thanks Jerrod for explaining your comment, I had a basic idea of what you were saying, but wanted you to really spell it out for the record. ;)

I agree with you for the most part and you are correct with the majority of wootz today. In most Wootz today the cementite is made from large globular carbide clusters and the dendritic structure is still largely intact.  This is not the best state to have a blade in, if you are wanting to achieve sharpness, toughness and flexibility. 

The dendrites themselves actually don't exist in the ingot, it is the outline of the former dendrites which existed in the solidifying ingot which remain.  The carbides of the Interdendritic regions are the weakness in the crucible steel ingot and blade, however some Wootz steel is converted through the process into a finer less brittle spherodized carbide structure and the "dendritic arms" have become homogenized back into the steel. This makes a blade that is much more like the modern high carbon steels. It is all in how the steel has been created that determines the final mechanical strengths or weaknesses.

Edited by Tim Mitchell

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18 hours ago, Tim Mitchell said:

finer less brittle spherodized carbide structure

Less brittle is very relative, and still way more so than tempered martensite.  

18 hours ago, Tim Mitchell said:

the "dendritic arms" have become homogenized back into the steel

If you can see a pattern when etched, it is not homogenized.  If it were to be homogenized you would have no pattern and you would indeed have something analogous to a modern steel.  Good for "best quality", but "boring" to look at.  

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The secondary arms of the dendrites are dissolved during an extended roast of an ingot.  This leaves the primary trunks, but they are also in a more dissolved state. This makes the steel matrix stronger than it was previously.  The brittleness of the steel matrix is a factor of the size of the carbides and the density of the clusters.  Not all blades have dense large clusters of carbides and in a properly forged blade, you have a laminar structure of steel sheets with no visible carbides and of steel sheets containing carbides in scattered loose clusters of spherodized carbides, not the blocks of cementite that you would have seen in most modern wootz.  When properly quenched and tempered, you get a blade with a nice perlite structure in the spine and body of the blade and at the very edge you get a hard tempered martinsite region.

My personal opinion is that a wootz blade with a good open watered pattern will be just as good as a blade made from something like W1 with a tempered martinsite structure.  Eventually we need to do some comparative testing of the different mechanical properties of a good section of wootz to show scientifically how it compares with other steels.  Until then it is purely subjective.

Naturally the carbon content of the steel is a factor, so we can't easily compare a 1.5% carbon wootz blade with say a really good 1095 blade.  The less the carbon the tougher the blade... And we also have to compare structure with structure, it isn't fair to compare a bainite structure with a martinsite structure and say that the weakness is in the steel :) 

Wootz can have no pattern, there is actually a name for a Pulad blade which showed no pattern from ancient times in Persia.  It is not the pattern which makes steel wootz or pulad, it is the type of steel, and it is hard to make generalisations about a quite diverse product.

 

 

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I have no problem with modern steel out performing "wootz" in standard mechanical tests. The value for me is in the knowledge and experience gained  during the attempts to duplicate what was done many years ago using very simple means. Most people do it for a while and it just becomes too tedious or fraught with too many obstacles. I very much empathize and share the frustration. So much has been learned by probing this material it just does not stop...or I just cannot stop. I will explain my inability to stop later in wootz posting thread.  

I have severely abused some wootz at 1.8 % C ..it was plenty strong, not brittle at all ( shaped to a tight U 1 " radius) and cold forged. If the material were only pretty and had very low mechanical strength I might have lost interest as well.

 

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Well said Jan. :) Wootz is one of those things that keeps on pulling you back.  I have a 1.6% C wootz knife which I have had for years and heavily used for all kinds of things, it has held up better than any of my stainless blades which have been my EDC for years, an SOG folder and a Ken Onion Leek. My wootz blades will beat them hands down for edge holding ability and toughness.

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So, not all wootz is created equal, and why should we ever have assumed it was? Not all 1095 is created equal and not all W-2 is created equal. I know of at least one notable smith who remembers 1095 and W-2 from way back in time and has become so disgusted with what modern steel manufacturers call 1095 and W-2 that he has begun making his own using the recipes he got when he worked in a steel mill as a youngster. 

It seems that there is much more to making good crucible steel than stuffing a bunch of materials in a crucible and getting it hot enough to melt iron and letting it cool. I think Jan has hit the nail on the head with why anyone would pursue making this material and Tim has also made an extremely valid point about repeatability. Using archaic methods, the QC is somewhat limited (compared to mass production methods). So does the same smith (modern day) following the same basic recipe and forging process still wind up with different ingot qualities? Not that one is "better" than the other, but each having different characteristics. 

I do have another question about the carbon content in those two blades mentioned above. How did you determine the % carbon content?

Edited by Joshua States

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Joshua,    I sent mine out for testing at what was then called Stork Labs, Huntington Beach CA...They have changed their name but are still in business. The actual C content was  1.87 % .

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Eh well, it seems that good quality crucible steel is achieved quite easily, even using archaic methods and material input such as I have in the recent past. Some due to one threory or another take on the watered banding and others do not. Some smiths claim it is all due to methodology while others claim it is trace elements and forging methodology, and other say it doesnt matter, it just does what it wants to do.

Chemically the only difference from one watered puck to the next could be a few hundredths of 1% of various elements.
 

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The quality in the steel in respect to the conversation is somewhat based on forging methods. Changing the structure of the steel is all in the forging methods. Even a puck that is capable of taking on the watered banding could be forged incorrectly and not display the banding and would be considered inferior in this regard.

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1 hour ago, Daniel Cauble said:

The quality in the steel in respect to the conversation is somewhat based on forging methods. Changing the structure of the steel is all in the forging methods. Even a puck that is capable of taking on the watered banding could be forged incorrectly and not display the banding and would be considered inferior in this regard.

So, (to use a cliche') that begs the question "without the watered banding is it inferior ?"

Or to turn it around. "Does the banding impart desireable qualities and is its presence in a puck a measure of the presence of desired elements and at that point it has served its purpose ?

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I hear more about vividness of the pattern due to the amount of carbon. Not so much from the trace elements. Some believe these trace elements simply make the watering pattern possible, and dont necessarily impart any metallurgical advantage, especially at the trace levels as suggested.

 

As described, bolder patterns are somewhat directly related to the carbon content.

The tricky thing about this steel is the various experiences smiths have had with it. As said before, in the opinion of some well respected smiths, typically any crucible steel in the UHC range can form banding based on the forging schedule.

Some of the steps Al has taken to make his was to bring out certain characteristics in his pattern, and not so much to get the pattern to form itself. That may be where some of the confusion is.

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If you arent worried about dendrites, you could very well use this steel like other steels and say forge weld it to something else and make a modern pattern weld. Why? Because then you could make pattern weld with well over 1% carbon something like kitchen knives, which is what I plan on doing eventually.

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6 hours ago, Joshua States said:

So does the same smith (modern day) following the same basic recipe and forging process still wind up with different ingot qualities? Not that one is "better" than the other, but each having different characteristics. 

I do have another question about the carbon content in those two blades mentioned above. How did you determine the % carbon content?

Within reason the answer is yes. If you forge out a similar ingot with the same basic forging profile, you will usually get the same type of result.  Every blade is that little bit different, but they will be similar in mechanical properties and appearance.  Sometimes you just get that curve ball and we don't know why that happens, but most of the time the answer is yes. This is why I encourage the use of forging diagrams, so that a smith can reproduce and improve on the quality and appearance of the previous blade or ingot.

4 hours ago, Vern Wimmer said:

So, (to use a cliche') that begs the question "without the watered banding is it inferior ?"

Or to turn it around. "Does the banding impart desireable qualities and is its presence in a puck a measure of the presence of desired elements and at that point it has served its purpose ?

Some would say that it does, and in my opinion it is not so much the pattern that contributes the qualities, but it is what causes that pattern to appear which makes the open watered patterns slightly better.  It is to do with the microstructure of the pattern and how that effects the quality of the final steel blade in flexibility, edge holding ability and toughness.  So the bands.... not so much, but what makes the high quality bold open watered bands, definitely helps to make a better blade.

As far as carbon content, not many smiths can get a carbon test done.  Most just calculate the precise final percentage from the known carbon content of their ingredients.  There is another way which I have been thinking about, kind of a poor man's carbon test. 

It involves burying an insulated thermocouple inside a lump of your ingot or forged bar, and then raising the temperature of the furnace at a steady rate.  where the critical points are in the steel you will get a little plateau in your temperature plot.  These will show you where Acm is for this steel and consequently will give you a relatively accurate calculation of your carbon content when you compare it with the carbon iron phase diagram... If anyone does this before I do... please post how you went and show the plot!

 

Edited by Tim Mitchell

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4 hours ago, Tim Mitchell said:

Most just calculate the precise final percentage from the known carbon content of their ingredients. 

I could use an explanation of how that goes. It cannot be as simple as adding 20 grams of charcoal to a kilo of iron in the crucible.

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If they use a closed crucible.

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Joshua,   

    let's assume you are using cast iron at 3.4% C and low carbon wrought iron  ..if used at 50/50 your C content will approach 1.7% C

 

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Some smiths add graphite, some calculate as Jan mentioned and some use charcoal in layers with their iron which regulates the carbon content roughly itself.

If you have a closed crucible you have a more accurate final carbon level as you will lose less out the top as gas.  There is usually a bit of addition of carbon to the melt from any graphite in the crucible, but if you line it with a refractory wash that is also no longer a problem.  Through calculation, especially if you use cast iron and purer iron with known carbon contents, you can get the melt accurate to plus or minus one point of a percent of carbon with no real trouble. 

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Joshua,  Adding carbon to iron is a different story..for me a bit of a crap shoot. I once added 4X the amount of carbon needed to make 1% carbon steel and got cast iron. I once added 2X the amount of carbon and got a nice steel. If you read historical accounts, some mention that 10% of the wight of the iron  was added as organic material,  so organic material turns into carbon at about 22% of it's weight 22% of 10% is about 2% so I copied them....in that case I used no glass/ alloys....that iron has been forged out quenched and broken into pieces and is waiting for me to get back into the Hamon thread.

 

Edited by Jan Ysselstein

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