FYI The production of crucible Damascus steel

Ann Feuerbach · 23rd March 2005, 06:09 PM

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 · 23rd March 2005, 07:35 PM

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 · 23rd March 2005, 08:20 PM

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 · 24th March 2005, 12:43 AM

Hi Ann,

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

Cheers
Chris

Andrew · 24th March 2005, 12:52 AM

Ann, thank you for this outstanding information.

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

Ann Feuerbach · 24th March 2005, 01:33 AM

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 · 24th March 2005, 03:02 AM

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 · 24th March 2005, 01:19 PM

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

tom hyle · 12th April 2005, 05:18 AM

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 · 3rd October 2005, 03:30 PM

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 · 7th October 2005, 03:19 AM

Hi Ann,

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

Cheers
Chris

23rd March 2005, 06:09 PM	#1
Ann Feuerbach Member Join Date: Feb 2005 Posts: 133	FYI The production of crucible Damascus steel 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 Last edited by Ann Feuerbach; 24th March 2005 at 01:26 AM.

23rd March 2005, 08:20 PM	#3
Mare Rosu Deceased Join Date: Dec 2004 Location: USA, DEEP SOUTH, GEORGIA, Y'all hear? Posts: 121	WEEK? 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

24th March 2005, 01:19 PM	#8
Mare Rosu Deceased Join Date: Dec 2004 Location: USA, DEEP SOUTH, GEORGIA, Y'all hear? Posts: 121	Movie? 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

23rd March 2005, 07:35 PM	#2
Yannis Member Join Date: Dec 2004 Location: Athens Greece Posts: 479	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?

24th March 2005, 12:43 AM	#4
Chris Evans Member Join Date: Mar 2005 Location: Australia Posts: 678	Hi Ann, As a metallurgist, allow me to express my congratulations for an excellent article. Cheers Chris

24th March 2005, 12:52 AM	#5
Andrew Member Join Date: Nov 2004 Location: USA Posts: 1,725	Ann, thank you for this outstanding information. I'm going to "sticky" this thread for a while.

24th March 2005, 01:33 AM	#6
Ann Feuerbach Member Join Date: Feb 2005 Posts: 133	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.

24th March 2005, 03:02 AM	#7
Ian Vikingsword Staff Join Date: Dec 2004 Location: The Aussie Bush Posts: 4,200	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.

12th April 2005, 05:18 AM	#9
tom hyle Member Join Date: Dec 2004 Location: Houston, TX, USA Posts: 1,254	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.

3rd October 2005, 03:30 PM	#10
B.I Member Join Date: Jan 2005 Posts: 485	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?

7th October 2005, 03:19 AM	#11
Chris Evans Member Join Date: Mar 2005 Location: Australia Posts: 678	Hi Ann, Your exposition rings sweet to the ears of this old metallurgist. Well done! Cheers Chris