FYI The production of crucible Damascus steel

[Ann Feuerbach]

The Production of Crucible steel and the Damascus Pattern
There are two fundamental factors that will profoundly influence the final characteristics of the steel product: the crucible charge and the forging method. The materials and methods used to produce and forge the ingot will directly affect whether or not a pattern can be produced. Modern replication experiments, historical and ethnographic accounts demonstrate that there are many possible ingredients that can be used for the crucible charge to produce a crucible steel ingot. They have also determined particular factors which are necessary to produce a pattern.

Essentially crucible steel can be produced from an infinite number of possible crucible charge ingredients containing iron and carbon. The presence of minor and trace elements in the crucible charge, via the source of iron, carbon or additional substances added to the charge, will also affect the steel ingot. These elements can affect the forging of the ingot (e.g. in rendering it “hot short” due to phosphorus) in addition to the performance and appearance of the final product (see below).

The percentage of the carbon content of the crucible steel is significant for the creation of different types of patterns and the performance of the blade (see below). Hypoeutectoid (< 0.8% C) and hypereutectoid (> 0.8% C) steel can produce a pattern, but the microstructure and, therefore, the pattern will be noticeably different. Hypoeutectoid steel will produce a banded pattern (e.g. Sham pattern), however, the most characteristic Damascus steel patterns (e.g. Kara Khorasan pattern) is produced from hypereutectoid steel.

Hypoeutectoid ingots produce ferrite-pearlite banding. A factor in the production of the banding is the presence of elements, which during the solidification of the liquid ingot, remain in the interdendritic region (Samuels, 1980, 129). Pearlite will form in the interdendritic band, possibly influenced by the presence of manganese. According to Samuels (1980, 129) the dendrite itself is composed primarily of ferrite and very slow cooling will produce bigger bands.

Studies, primarily lead by Verhoeven (e.g. 2001) have found that the formation of the pattern in hypereutectoid steels is due to the alignment of globular/spherical cementite in the interdendritic zones. The cementite aligns because of the presence of impurity elements present in the interdendritic zone. Verhoeven et al. (1998) determined that elements such as vanadium and molybdenum, even in quantities as low as 0.003%, promote the alignment of cementite. Other elements, which also promote banding, are chromium, niobium, and manganese (Verhoeven et al., 1998, 63).

The effect of the cooling rate on the forging of the ingot and the resulting pattern has not been studied in any depth. Verhoeven and Jones (1987, 170) note that cementite at the prior austenite grain boundary form during slow cooling, whereas faster cooling rates promote Widmanstätten cementite. Richard Furrer (pers. com.) noted that during his replication experiments quickly cooled ingots were easier to forge than slowly cooled ingots. This is probably the result of the different cementite locations. Verhoeven (pers. com.) stated that the cooling rate of the ingot is not a necessary factor for the formation of the pattern. However, it seems reasonable to assume that the cooling rate affects the appearance of the pattern. This is because the faster the ingot cools, the smaller the dendrites are, and therefore, the closer the interdendritic zones. The closer the interdendritic zones, the closer the aligned globular/spheroidal cementite are, and therefore, the finer the final surface pattern. Therefore, a blade forged from a slowly cooled ingot would have a coarser pattern than a blade forged from a quickly cooled ingot, assuming that the blades require a similar amount of forging. In addition, Verhoeven and Jones (1987, 177) suggest that the grain boundary cementite grows coarser with each forging cycle, opposed to the Widmanstätten cementite, which becomes finer. It is the large cementite particles responsible for the thicker “thread” of the Damascus patterns. The extent of forging and consequently the extent of deformation of the dendrites would also affect the fineness and appearance of the pattern. The influence of the cooling rate was also noted by ethnographic accounts. Bronson (1986, 38) states that many ethnographic observers suggested that the Damascus pattern “is an effect of cooling the original crucible contents at an extremely slow rate”. However, Bronson (1986, 40) then continues with the supposition that this “is not well supported by the data on actual wootz making”. It seems that here he is assuming that wootz steel will make a pattern, although he reported that there are no firsthand sources that it yielded a Damascus structure. Therefore it seems likely that the fineness or coarseness of the final pattern would depend on the cooling rate of the liquid steel in addition to the amount of forging. A slowly cooled ingot could make a coarse pattern or, if forged for a long period, a fine pattern, but a quickly cooled ingot could never make a coarse patterned blade but only a fine patterned one.

Verhoeven and Pendray’s (1992, 210) experiments found that the as-cast ingot was “hot short” due to microsegregation of phosphorus and sulphur. Although few ancient steels contain sulphur, they often contain phosphorous. Since the ingots solidified from a liquid, they have areas particularly high in phosphorus appearing as the iron-carbon, phosphorous phase steadite rather than being evenly distributed, thus the ingots are “hot short”. Whether ancient blades were also “hot short” and if this decarburization procedure would have been needed if the crucibles cooled slowly in the furnace or is necessary for all crucible steel is uncertain, however, the crucible steel blades examined did contain areas with around 0.1% P. The findings by Verhoeven, that the crucible steel ingots were “hot short”, are important for three reasons:

1) It supports the fact that Moxon among others noted that “hot shortness” was a feature of crucible steel.
2) Being “hot short”, the blades required a different forging technique than used for other types of steel.
3) The low temperature forging would produce spheroidal cementite.

The phosphorous in the ingots caused the ingots to be “hot short” and therefore they had to be forged at low temperatures. Verhoeven (2001, 65) found that during forging at the necessary low temperatures, below the austenite transition temperature (see Figure 94), the cementite collects in the interdendritic regions, perhaps nucleating on the impurity elements, which are concentrated in the interdendritic regions. The austenite transition temperature (Acm) is the temperature at which ferrite and cementite begin to separate during slow cooling (Samuels, 1980, 43). The austenite transition temperature depends upon the elemental composition of the steel, particularly the carbon content. The transition temperature begins in the region of 730OC, around the eutectoid composition (0.8% C). The austenite transition temperature increases with the carbon content until the carbon content reaches around 2% (cast iron) where the temperature is over 1100OC (see Samuels, 1980, 43).

The time and temperature of the forging are major factors in the formation of the pattern. Verhoeven and Pendray’s replication experiments heated the blades to 50OC below the austenite transition temperature and then forged the blade while it slowly air-cooled to around 250OC below the austenite transition temperature (Verhoeven, 2001, 64-65). They record that initially the carbides are randomly distributed but after additional heating and forging at these temperatures the cementite began to align. The more cycles they performed, the more distinct the banding became.

In order for the pattern to be readily observed on the surface of the blade, the decarburized and oxidized layer had to be ground off, the blade had to be cleaned and polished before it was etched. Wilkinson records that wood-ashes and water were used in India, or chalk and water to remove any surface grease (1837, 191). Other materials used to clean the steel include dry lime with water and tobacco ash (Sachse, 1994, 83). To etch the blades, Wilkinson (1837,191) discusses the use of dilute nitric and sulphuric acids at Cutch. He also records that a better effect is produced when the blade is immersed in a bath of copper sulphate in water for ten to thirty minutes (Wilkinson, 1937, 190-191). Sachse (1994, 84) refers to the use of ferric sulphate and ferrous sulphate to etch the blades. The etching reacts preferentially to the iron and carbide regions and the effect depends on the type of etchant used and the amount of time it reacts with the metal. According to Verhoeven and Jones (1987, 155) the white component of hypereutectoid Damascus patterned blades is the cementite. On hypoeutectoid blades the ferrite is the white or lighter component. The darker “background” colour (see below) is often a form of pearlite which appears darker, or having a pearl–like appearance, hence the name. However, which phases appear lighter or darker also depends on the microstructure and the etchant used.

In summary, the formation of the pattern particularly in hypereutectoid blades is due to the interdependent relationship between the elements contained in the crucible steel ingot and the forging process. The presence of phosphorous in the crucible steel dictated the low forging temperature. In turn, the low temperature forging produced spheroidal cementite. The presence in the ingot of the trace elements such as vanadium, molybdenum, chromium, niobium, or manganese promote the alignment of the spheroidal cementite in the steel, thus producing the Damascus pattern when etched. The relationship between the elemental composition of the ingot and forging method associated with hypoeutectoid blades has not been studied in detail. However, the presence of elements such as manganese promotes the growth of pearlite in the interdendritic region, whereas the dendrite is composed of ferrite. Slow cooling of the ingot will produce bigger bands and these bands can be observed when the blade is etched.
Other info and bibliography can be found at http://moltenmuse.home.att.net

[Yannis]

Dear Ann

Incredible details! Thank you very much. Actually you gave me reading material for a week, because English is not my language and I will need a lot of dictionaries to decipher the terminology.

The address you mention for more info is not working. I think the right one is http://home.att.net/~moltenmuse/index.htm

Is it possible to give us a timeline? When the production of traditional crucible steel (wootz) stopped in India, Persia or Uzbekistan? I suppose that this happened in late 200 years but do we have witness of a workshop, let’s say in 1850?

[Mare Rosu]

YANNIS:
English is my native language (with a little Southern draw ) and it will take me more than a week to completely understand (yeah right) Dr. Ann threads.
However it is just great stuff, and we of the forum should be happy to have her posting on wootz steel as well as other good stuff,
Gene

[Chris Evans]

Hi Ann,

As a metallurgist, allow me to express my congratulations for an excellent article.

Cheers
Chris

[Andrew]

Ann, thank you for this outstanding information.

I'm going to "sticky" this thread for a while.

[Ann Feuerbach]

Thanks all, glad you like it . I have also corrected the weblink, thank you Yannis. Believe it or not, I have alot more information (hence the forthcoming book, when I get time to finish it). Off the top of my head I think the last documented production in Southern India was 1902, and in Bukara, Uzbekistan 1850's.

[Ian]

Ann:

Thank you for your second major contribution today. Excellent.

Could I suggest to you and our Moderators that what you have written above, supplemented by a few well chosen illustrations and perhaps a short glossary of terms, would make an outstanding essay for our archives section.

Ian.

[Mare Rosu]

Ian
Good suggestion, how about it moderators?

I am also waiting for her book and and the movie that is sure to follow the book.
Gene

[Gt Obach]

Hi Ann

in regards to the sham pattern.. which by my definition is a pattern of straight and course waterings can be produced in hypereutectoid steel.... the way i've done this is through the technique of hammering the steel....

generally when you hammer steel, the face of the hammer has a crown or curvature..... and this dimples the steel causing it to flow outward...
- the hammer face has an effect on pattern
-- if you hammer with a flat faced french hammer... you distort the pattern very little...... and the waterings will be straighter

-- but if you use a small narrow face hammer with a curved crown...it'll give a very busy watering (this is all excluding cutting or drilling grooves for pattern effects)

i aggree with the waterings getting finer the more forge cycles.... since I hand hammer all my ingots by myself..... the few times I was lucky enough to have an apprentice, the pattern was coarse
- at the moment it takes 2days of forging with a 8 or 12lbs hammer to get the ingot to barstock
- as you can see on the net.... most other smiths use powerhammers and presses to make wootz.... so their patterns are usually coarse

- i suspect that in ancient times ...to produce a coarse pattern the master smith would have two apprenti, sledging down the ingot...... reducing the forge cycles dramatically

this is just my opinion

thank you for your post... it is wonderful !!!

Greg

here is a pic of a straight waterings... with the matrix oxide buffed out

[Ann Feuerbach]

Thanks Greg for the info on forging. It is something very important but I have no practical experience at, and need imput from those who do. I would like to know how many man hours it takes to forge a knife or sword from ingot to finished product, using traditional forging methods, also how long it takes to sharpen and clean. For ethno-archaeometallurgical studies this is significant.
A standardized nomeclature for patterns does need to be further developed, but is tricky. I have more details on this and only included a bit here. The characteristion of Sham as hypoeutectic is not my "opinion". It was based on previous peoples characterisation (I think Verhoeven, Sashe, and others) together with metallurgical analysis.

[Mare Rosu]

Dr. Ann
I have sent you a PM, on Al Pendray.
Gene

[Gt Obach]

Hi
i'm not sure my methods can be directly compared to the ancient smiths... cause I could find nothing about how they forged their ingots...

however with that in mind... a basic ingot starts out to be 6lbs and is cut in half before roasting (however I do make some ingots 3lbs also).... then after the roast it is forged down to 1/4 " by 13 or 16" long
- this can take from 1.5 days to 3 days (6-8 hrs a day)
- wootz is crazy in nature...sometimes it is extremely hard to forge/reduce at the beginning....being as hard as strike the surface of the anvil...
- once the steel is down to 1/4 inch size bar..... it works very easily... like a very plain carbon steel ....so it would take me an hour to two hours to forge out a bowie size knife (keep in mind, that I shaped the bar very quickly with an 8lbs hammer)
- now.. I place this in a bucket of wood ash to slow cool overnight
- put the blade into a jar of vinnegar for an hour.... this pickle will loosen the scale and it can now be scrubbed off with steel wool
- now I like to use coarse files and work my way up to fine files to shape the steel blade
- then use coarse stones up to fine.... followed by paper abrasives up to 600grit.... and these all must be done with oil (corn oil is my fav) ... the oil stops the abrasives from loading up and burnishing the steel surface... so it cuts clean
- this stock reduction... usually takes up to a day
- the knife is now heat treated... quenched, tempered for an hour and tempered again, and repolished at 600grit
- now it is degreased... with soap, rubbing alcohol, Tsp..... and let dry.... see if all the streaks are gone... (cause any grease will destroy an even etch!)
- now dip into the appropriate solution (etch) and watch it on the side of the clear vessal..... till the waterings are clear then pull out quick... wash immediately under cool water, then a quick dip in cool water and baking soda, now litely rub with a paper towel soaked in rubbing alcohol.... (be quick with the rinse and neutralize or else your waterings will take on a rusty brown)
-allow to air dry and litely oil it
- the heat treat and etch should also take a day......

now i'm not a speed demon at anything... lol... so I'm not sure how this stack up to other peoples methods

as for the sharpening... this takes me a minute on a 2by72 inch belt grinder.... and you always want to have a sharp edge before the etch

i'm sure I'll think of more later.... this is just a brief summary
- in the summer I will try to gear up and do some swords again... but first I have to get a real shamshir, tulwar, saif, or kilij etc to examine an begin the process of replicating it.. .. it's hard to make something from just pic's... lol

anyhow, gotta hop a flight to halifax....
take care
Greg

[Jens Nordlunde]

Gt Obach,

Thank you for your ‘manual’ on making a blade, it is very interesting. I don’t know about others, but I have always wondered how long time it took to make a blade. Th.H.Hendley would have known, as he lived in India at the end of 1800, the time when many of the weapons we collect were made, but he does not mention it for some reason or other.
In the book ‘Persian Steel’ by James Allan and Brian Gilmour. Oxford University Press, 2000, James Allan writes, in the chapter Arms and Armour/Centres of production that the production of arms and armour, under Timur was centralised, and that he had more than one thousand workmen making arms and armour ‘…and to this business they are kept at work throughout the whole of their time in the service to his Highness’. When I read this, I thought that this would have accumulated at a ‘mountain’ of arms and armour, and it did, but over the years; and one must not forget, that they did not only make the weapons, they also had to repair what had been broken. Due to this relatively show production process, and to avoid the enemies use of the weapons again; looting, when a battle had been won, was very important. Weapons from the south are found in armouries to the north and opposite, just like they ‘travelled’ from east to west, and from west to east.

Jens

[Ann Feuerbach]

Thanks Greg for the detailed information. Somewhere I have information about annealing to make the ingot easier to forge. I also have information on sword making in Istanbul during the Ottoman empire...I'll try to dig it out. It talks about all the different types of swords for sale and how many workshops.

[Gt Obach]

I've also got the "persian steel" book and it's a good read !

Ann: that would be fantastic to see ! I've searched quite abit to find some details on the roasting of ingots and especially the forging.. and only found a small amount

it seems there are tonnes of crucible steel recipes written but it is quite hard to find accounts on forging. Especially the types of hammers, tools, anvils,hammering techniques, etc are almost absent from record ??
- i'm sure it is there but i was only limited to what my univ library could get on loan

Greg

[Ann Feuerbach]

I have not found any information on things like hammers, forging techniques etc (apart from the mention of forging at red heat and the time of day). Smiths were not usually literate and no one really cared about their tools. In the archaeological record, craftsmen would have passed down their tools and/or took them with them so we have none. In many parts of Central Asia they did not bury the dead with goods, so we have none from their either. I will keep looking.

[Jens Nordlunde]

Hi Ann,

When and how will 'crucible' steel end up as cast steel?
At one point you wrote something about this subject, but I think it should be explained more in detail.

Jens

[Ann Feuerbach]

Ah, yes. this is a particular problem in Russian, as I believe bulat means both cast steel and crucible steel. Primarily it is semantics: by definition cast steel is cast, ie: poured into a mold. In cast steel, usually premade steel is remelted in a crucible, rather than made in it.
Crucible steel is steel made in a crucible. Traditionally it is not cast (poured). However, what happens if the craftsmen put too much carbon into his crucible? The product can be cast iron. There is really no reason why a tradtional craftsmen could not have "cast" crucible steel or "cast iron". Just lack of evidence. Casting crucible steel would cause quick solidification, small dendrites and probably no pattern. But it could be done.

[tom hyle]

Fascinating and so much thanks to everyone!
Ann, "cast steel" is not steel which has been cast. It is a specific early industrial product (patented in England in 1749, I think) called "acero fino" ie. "fine steel" in Spainish (a freind has a Spainish language degree, and she said "fino" has all the same shadings of meaning in Spainish as does "fine" in English.) I've never made either. From my readings it seems to me that the big distinguishment of cast steel (also cast-steel, etc.) from "Eastern"/Tartaric crucible steel, or at least from blister steel, etc. was that it fully melted in the alloying process, while the European blister steel, sheer steel, etc. were alloyed at welding heat, some types in a crucible, which sort of "pudding"ed together, and had to then be hammered down to further join it and folded for homogeneity; don't know enough about Tartar steel to know how much this crosses over to it, or to what specific type of traditional European steel it most closely relates; shear steel I think.
Modern steel production is a full-melt process often and even usually involving (thankfully for my part, except when someone melts an old blade) recycled steel (different percents of different scrap items are allowed for different classes of industrial product), but its product is not "cast steel". Last I heard cast steel may still be produced in Sweden, but the last I heard was some sort of bad news involving this..... Wrought iron still comes out of Sweden, I read, too.
What of Japanese "blue steel"; anyone know what that is? High carbon, obviously; at a guess, real high, like cast steel.

[Ann Feuerbach]

Thanks Tom for the info on cast steel. All this terminology can be such a problem. What would you call ancient Chinese cast iron which has been decarborized while liquid to make it steel, and then it is cast? Is this not cast steel too? (hence my working definition). We really should go back to the term in the original language in which these processes were undertaken so we are certain what is meant. Steel production and nomenclature is such a grey area, where does one stop and the other begin?

[tom hyle]

Yeah, I agree; the problem is that W European overculture industry, as is its way, made its own efficient working definition of a phrase that has a seperable, and perhaps even older/foreign traditional or simply linguistic/logical meaning. Thus "cast steel" (you could quote it, "per se" it, "caststeel" or "cast-steel" or "acero fino", which I was questioning my friend is it fine grained or fine quality and she said you can't tell because "fino" exactly equals "fine".....) is a type of cast steel, if you will. Doubled shear steel (or any double/doubled steel) is steel that has been doubled; ie folded; triple steel AFAIK has no tightly defineable meaning, though it may imply many foldings or folding together of three different bars to form a billet; speculating. I think my brother has etched marked shear steel to a wootz-like crystally pattern. I also think he may have a spring-tempered wootz kard, though I don't remember that for sure. (If you think I'm fascinated with spring temper you don't know my brother! ) I'll attempt to question him or get him to read this.
There came to be something in the legalistic/industrial definition of "cast-steel" that included the crucible had to be below a certain size, and the ingredients were famously balanced by intuitive art as much as by any precise or scientific analysis, which was levelled as a criticism by the early large-batch full-melt industrial steel proponants, of course.

[tom hyle]

My intent, BTW, was not to "correct" Ann's usage, but to give her a piece of information that may help her understand some old writings, if nothing else, or may otherwise help her in her researches.

[B.I]

hi ann,
i hope all is going well with your studies. i recently came across the remnants of a wootz (i am assuming) blade from the 10th-12thC, probably afghanistan area. the possible date and region comes from the hilt, which is now long gone. however, whilst it has moved on to bigger and better things, i have a very rusty (crusty) remnant of a blade that can only be interesting to you, and no-one else.
let me know if you want it, and where to send it to.
i'm afraid you will just have to trust me on the dating, but it was definately (relatively definate) of this period.
any updates on publication?

[Chris Evans]

Hi Ann,


Your exposition rings sweet to the ears of this old metallurgist. Well done!

Cheers
Chris