Steel ? / What is Damascus Steel ? / Wootz Steel / A modern steel
STEEL: AN ADVANCED MATERIAL OF THE ANCIENT WORLD
November, 18th 2000
Srinivasan and S. Ranganathan
Indian Institute of Science
will be able to find the address of the original text in my link
development of ancient Indian wootz steel is reviewed. Wootz is
the anglicized version of ukku in the languages of the
states of Karnataka, and Andhra Pradesh, a term denoting steel.
Literary accounts suggest that the steel from the southern part
of the Indian subcontinent was exported to Europe, China, the
Arab world and the Middle East.
an ancient material, wootz steel also fulfills the description
of an advanced material, since it is an ultra-high carbon steel
exhibiting properties such as superplasticity and high impact
hardness and held sway over a millennium in three continents-
a feat unlikely to be surpassed by advanced materials of the current
deserves a place in the annals of western science due to the stimulus
provided by the study of this material in the 18th and 19th centuries
to modern metallurgical advances, not only in the metallurgy of
iron and steel, but also to the development of physical metallurgy
in general and metallography in particular.
of the recent experiments in studying wootz by re-constructing
composition, microstructure and mechanical behaviour, along with
some recent archaeological evidence, are described.
High-carbon Steel, South India, Superplasticity, Crucibles, Analyses
has been reputed for its iron and steel since ancient times. Literary
accounts indicate that steel from southern India was rated as
some of the finest in the world and was traded over ancient Europe,
China, the Arab world and the Middle East. Studies on wootz indicate
that it was an ultra-high carbon steel with 1-2% carbon and was
believed to have been used to fashion the Damascus blades with
a watered steel pattern. Wootz steel also spurred developments
in modern metallographic studies and also qualifies as an advanced
material in modern terminology since such steels are shown to
exhibit super-plastic properties. This paper reviews some of these
History of wootz steel
are numerous early literary references to steel from India from
Mediterranean sources including one from the time of Alexander
(3rd c. BC) who was said to have been presented with 100 talents
of Indian steel, mentioned by Pant . Bronson
 has summarised several accounts of the reputation
of Indian iron and steel in Greek and Roman sources which suggest
the export of high quality iron and steel from ancient India.
Srinivasan , Biswas  and
Srinivasan and Griffiths  have pointed out
that the archaeological evidence from the region of Tamil Nadu
suggests that the Indian crucible steel process is likely to have
started before the Christian era from that region. Zaky 
pointed out that it was the Arabs who took ingots of wootz steel
to Damascus following which a thriving industry developed there
for making weapons and armour of this steel, the renown of which
has given the steel its name. In the 12th century the Arab Edrisi
mentioned that the Hindus excelled in the manufacture of iron
and that it was impossible to find anything to surpass the edge
from Indian steel, and he also mentioned that the Indians had
workshops where the most famous sabres in the world were forged,
while other Arab records mention the excellence of Hinduwani or
Indian steel as discussed by Egerton .
European travellers including Francis Buchanan 
and Voysey  from the 17th century onwards
observed the manufacture of steel in south India by a crucible
process at several locales including Mysore, Malabar and Golconda.
By the late 1600's shipments running into tens of thousands of
wootz ingots were traded from the Coromandel coast to Persia.
This indicates that the production of wootz steel was almost on
an industrial scale in what was still an activity predating the
Industrial Revolution in Europe.
the word wootz is a corruption of the word for steel ukku
in many south Indian languages. Indian wootz ingots are believed
to have been used to forge Oriental Damascus swords which were
reputed to cut even gauze kerchiefs and were found to be of a
very high carbon content of 1.5-2.0% and the best of these were
believed to have been made from Indian steel in Persia and Damascus
according to Smith . Some of the finest
swords and artefacts of Damascus steel seen in museums today are
from the Ottoman region i.e. Turkey.
India till the 19th century swords and daggers of wootz steel
were made at centres including Lahore, Amritsar, Agra, Jaipur,
Gwalior, Tanjore, Mysore, Golconda etc. although none of these
centres survive today. Different types of Damascus sword patterns
have been identified, described in some depth by Pant ,
who also identified a new design from blades kept in the collection
of the Salar Jung Museum in Hyderabad.
may be mentioned however that the term Damascus steel can refer
to two different types of artefacts, one of which is the true
Damascus steel which is a high carbon alloy with a texture originating
from the etched crystalline structure, and the other is a composite
structure made by welding together iron and steel to give a visible
pattern on the surface. Although both were referred to as Damascus
steels, Smith  has clarified that the true
Damascus steels were not replicated in Europe until 1821.
Role of wootz steel in the development of modern metallurgy
legends associated with the excellent properties of the wootz
steel and the beautiful patterns on Damascus blades caught the
imagination of European scientists in the 17th-19th centuries
since the use of high-carbon iron alloys was not really known
previously in Europe and hence played an important role in the
development of modern metallurgy. British, French and Russian
metallography developed largely due to the quest to document this
structure. Similarly the textured Damascus steel was one of the
earliest materials to be examined by the microstructure. Smith
[10, 11] has fascinatingly
elucidated this early historiography of the interest in the study
of wootz steel and its significance to the growth of metallurgy.
align="justify"iron and steel had been used for thousands of years the role of
carbon in steel as the dominant element was found only in 1774
by the Swedish chemist Tobern Bergman, and was due to the efforts
of Europeans to unravel the mysteries of wootz. Tobern Bergman
was able to determine that the compositions of cast iron, steel
and wrought iron varied due to the composition of "plumbago"
i.e. graphite or carbon. As suggested by Smith 
the Swedish studies received an impetus following the setting
up of a factory to make gun barrels of welded Damascus steels,
and it was on observation of the black and white etching of the
steel and iron parts that a Swede metallurgist guessed that there
was carbon in steel, and interest in replicating true Damascus
the early 1800's, following the descriptions of crucible steel
making in south India by the European travellers, there was a
spurt in interest in Europe in investigating south Indian wootz
steel, from which the fabled Damascus blades were known to be
made, with the aim of reproducing it on an industrial scale. Mushet's
 studies in 1804 were one of the first to
correctly conclude that there was more carbon in wootz than in
steel from England, although this idea did not gain currency until
later. Michael Faraday , the inventor of
electricity and one of the greatest of the early experimenters
and material scientists, as pointed out by Peter Day ,
was also fascinated by wootz steel and enthusiastically studied
it. Along with the cutler Stodart, Faraday attempted to study
how to make Damascus steel and they incorrectly concluded that
aluminium oxide and silica additions contributed to the properties
of the steel and their studies were published in 1820 .
They also attempted to make steel by alloying nickel and noble
metals like platinum and silver and indeed Faraday's studies did
show that that the addition of noble metals hardens steel. Stodart
 reported that wootz steel had a very fine
this the interest in Damascus steel moved to France. Wadsworth
and Sherby  have pointed out that Faraday's
research made a big impact in France where steel research on weapons
thrived in the Napoleonic period. The struggle to characterize
the nature of wootz steel is well reflected in the efforts of
Breant  in the 1820's from the Paris mint
who conducted an astonishing number of about 300 experiments adding
a range of elements ranging from platinum, gold. silver, copper,
tin, zinc, lead, bismuth, manganese, arsenic, boron and even uranium,
before he finally also came to the conclusion that the properties
of Damascus steel were due to "carburetted" steel. Smith
 has indicated that the analysis of ingots
of wootz steel made in the 1800's showed them to have over 1.3%
carbon. The Russian Anasoff  also studied
the process of manufacturing wootz steel and succeeded in making
blades of Damascus steel by the early 1800's.
the early 1900's wootz steel continued to be studied as a special
material and its properties were better understood as discussed
further in the next section. Belaiew  reported
that blades of such steel to cut a gauze handkerchief in midair.
In 1912, Robert Hadfield  who studied crucible
steel from Sri Lanka recorded that Indian wootz steel was far
superior to that previously produced in Europe. Indeed in the
18th-19th century special steels were produced in Europe as crucible
steels, as discussed by Barraclough .
Investigations of superplasticity and other mechanical properties
of wootz steel
European scientists were successful in replicating and forging
wootz and Stodart who used it in his cutlery business found that
wootz steel had a superior cutting edge to any other, while Zschokke
in 1924 found that with heat treatment this steel had special
properties such as higher hardness, strength and ductility, mentioned
by Smith . By 1918 an important finding
concerning Damascus steel was made by Belaiew 
who was probably the first to attribute the malleability of Damascus
steel to the globulitic (i.e. spheroidised) nature of the forged
steel and to recognize that this occurs during forging at a temperature
of red heat (i.e. 700-800 0 C).
 in the 1960's was one of the first to point
out that Damascus steel was a hypereutectoid ferrocarbon alloy
with spheroidised carbides and carbon content between 1.2-1.8%.
Recent studies have indicated that ultra-high carbon steels exhibit
superplastic properties. As pointed out by Wadsworth and Sherby
, by 1975 Stanford University had found
that steels with 1-2.1% C i.e. ultrahigh carbon steels could be
both superplastic at warm temperatures and strong and ductile
at room temperatures. It was only subsequently that it came to
the authors notice that these steels were in fact similar in carbon
content to the Damascus steels.
is a phenomenon whereby an elongation of several hundred percent
can be observed in certain alloys in tension, with neck free elongations
and without fracture. By contrast most crystalline materials can
be stretched to no more than 50-100 per cent. Superplasticity
occurs at high temperatures and superplastic materials can be
formed into complex shapes. For superplastic materials the index
of strain rate sensitivity (m) is high, being around 0.5. At ideal
m=1 flow stress is proportional to strain rate and the material
behaves like a Newtonian viscous fluid such as hot glass. Superplasticity
occurs only above 0.3-0.4 Tm K where Tm is the melting point.
Another feature is that once super-plastic flow is initiated the
flow stress required to maintain it is very low. Superplastic
material essentially comprises of a two-phase material of spherical
grains of extremely fine grain size of not more than 5 microns
at the working temperature. Such ultrafine grained materials exhibit
grain boundary sliding yielding superplastic properties.
studies by Wadsworth and Sherby  and Sherby
 indicated that UHCS (i.e. ultra-high carbon
steels) with 1.8% C showed a strain-rate sensitivity exponent
nearing 0.5 at around 750° C suggesting that Damascus
steel could well have exhibited superplastic properties and a
patent was awarded for the manufacture of such UHCS.
explanation of the superplasticity of the steel is that the typical
microstructure of ultra-high carbon steel with the coarse network
of pro-eutectoid cementite forming along the grain boundaries
of prior austenite, can lead to a fine uniform distribution of
spheroidised cementite particles (0.1 m m diam.) in a fine grained
ferrite matrix. This spheroidisation of cementite is described
in Wadsworth and Sherby , Sherby 
and Ghose et al. . Such steels are also
found to have strength, hardness and wear resistance.
steels had to be forged, however, in a narrow range of 850-650°
C and not at the white heat of 1200° C to get the
desired fine grain structure and plasticity. In fact as pointed
out in an appraisal of Indian crucible steel making by Rao ,
and in a review of ancient iron and steel in India by Biswas ,
the early European blacksmiths failed to duplicate Damascus blades
because they were in the practice of forging only low carbon steels
at white heat, which have a higher melting point. Biswas 
mentions that the forging of wootz at high heat would have led
to the dissolution of the cementite phase in austenite so that
the steels were found to be brittle enough to crumble under the
attractive combinations of strength and ductility were found to
be achieved by Wadsworth and Sherby  and
Sherby  when the ultra-high carbon steels
were in spheroidised conditions with high yield strengths varying
from 800 Mpa to 1500 Mpa with increasing fineness of spheroidised
carbides, while the steel with coarsely spheroidised carbides
was especially ductile with up to 23% tensile elongation.
it is not yet known how fully the superplastic or superformable
properties of this steel were exploited by the ancient blacksmiths
of West Asia and India, accounts indicate that they were certainly
able to manipulate the alloy with a skill that could not be easily
replicated by the European experimenters of the 19th century.
Indeed the swords of Damascus steel were reported to have high
strength and ductility. Nevertheless, whereas the links between
the patterns on the traditional Damascus blades and the crystalline
structure of ultra-high carbon steels have been better established,
the mechanical properties of the traditional Damascus blades and
the degree of exploitation of the unique properties of the steel
are less well understood.
 and Verhoeven et al. [28,
29] have attempted to "re-invent"
the Damascus steel and blades as it were with replication experiments
based on historical studies of Damascus blades and composition
of wootz ingots. Verhoeven et al.  used
two methods by which the ingots were made, one of which consisted
of melting iron charge in a small sealed clay graphite crucible
inside a gas-fired furnace with the ingot formed by furnace cooling.
These were made by rapidly heating the charge and holding it for
a period of 20-40 minutes between 1440° C-1480°
C followed by cooling at furnace cooling rates or faster. The
composition of the charge was chosen to match that of genuine
Damascus blades of about 1.6% C and 0.1% P. However the fairly
high level of phosphorus made the blades very hot short and difficult
to forge. To overcome this problem the ingots were held at 1200°
C in iron oxide to produce a protective rim of pure iron around
the ingot which was ductile so that the ingot could be forged.
Ingots were also made with the phosphorus levels reduced to the
point where the ingots were not hot short which eliminated the
need for the rim heat treatment. Verhoeven et al. 
also made ingots by a process of vacuum-induced melting whereby
the charge was melted by heating to around 1000°
C, backfilling with nitrogen gas, heating to about 1580°
C and then outgassing for around 5 minutes so that cooling rates
at arrest temperature were around 5-100 C/minute.
may be commented however, that although the structures of the
ingots so produced do simulate those of Damascus blades, the methods
used by Verhoeven et al.  are not strictly
experimental re-constructions of the traditional processes, but
rather laboratory simulations of the process, since the methods
used do not really replicate conditions related to traditional
or archaeological processes. For instance the charge is fired
in both the methods described above in a very short time and the
melt is cooled very rapidly under modern industrial conditions
which could not have been achieved traditionally, while the 19th
century descriptions of the wootz process suggest a very long
firing cycle for the charge. In fact the eye witness descriptions
of Voysey  and Buchanan 
lay emphasis on the fact that the prolonged heating of the charge
and its slow cooling were essential for obtaining the optimum
results in the wootz process.
the experimental simulations by Verhoeven et al. 
served to monitor in detail the thermal cycles and cooling curves
and composition so as to be able to arrive at a final product
which matched that of Damascus blades and to understand the mechanism
of formation of the pattern of aligned bands on the blades, which
is reported by them to be produced by a carbide banding mechanism
which was found to be assisted by the addition of P, S along with
V, Cr, and Ti. Moreover their experiments are amongst the few
comprensive studies on the general process of manufacture of the
Archaeological and analytical evidence
of the archaeological and analytical evidence for crucible steel
production is discussed covering the investigations of Rao ,
Rao et al. , Lowe [32,
33], Srinivasan  and Srinivasan
and Griffiths . These indicate that the crucible
processes for steel production were spread over large parts of
south India. Lowe's investigations have concentrated mainly on
surveying and studying numerous sites from the Hyderabad region
or the Deccani crucible steel process while pioneering investigations
by Rao et al.  have covered other parts
of south India such as the Mysore region and Salem district of
Tamil Nadu. Field and analytical investigations were made by Srinivasan
in 1990, whereby she was able to identify some hitherto unreported
sites of crucible steel production in South Arcot, Tamil Nadu
and from Gulbarga, Karnataka, reported in Srinivasan 
and Srinivasan and Griffiths .
 has pointed out that whereas the process
documented by Lowe [32, 33],
the Hyderabadi or Deccani process, involved the co-fusion of cast
iron with wrought iron, the crucibles from sites reported by Srinivasan
from Tamil Nadu and Karnataka pertained to the carburisation of
wrought iron in crucibles by packing it with carbonaceous material.
Analytical investigations made by Rao et al ,
Lowe [32, 33], Srinivasan
, Craddock  and Srinivasan
and Griffiths  on crucibles from production
sites are briefly summarized.
details of the furnace described and sketched by Buchanan 
indicate that crucibles were packed in rows of about fifteen inside
a sunken pit filled with ash to constitute the furnace which was
operated by bellows of the buffalo hide, fixed into a perforated
wall which separated them from the furnace probably to minimize
fire hazards. The fire was stoked from a circular pit which was
connected to the bottom of the ash pit. The crucibles themselves
were conical and could contain up to 14 oz. of iron, along with
stems and leaves. The wootz steel process in general refers to
a closed crucible process and Lowe  has
remarked that the processing of plant and mineral materials in
closed crucibles is often described in Indian alchemical Sanskrit
texts of the 7th-13th c. AD.
by Craddock  indicated the wootz ingot itself
had a dendritic cast structure. Lowe [32, 33]
has investigated particularly well the refractory nature of the
crucibles of the crucibles which indicate that they were robust
enough refractories to withstand the long firing cycles of up
to 24 hours for the process. The formation of mullite and cryistobalite
was detected in the crucible fragments studied by Lowe [32,
33] suggesting they had been well fired to high
temperatures of over 1300-1400° C, while Rao et al 
also observed the formation of mullite and cryistobalite in crucibles.
the microstructures investigated by Lowe 
of the metal remnants within the particular Deccani crucibles
studied by her from Konasamudram could only be related to a failed
process of crucible steel production at that particular site or
context since they related more to white cast iron, a brittle
and not very malleable material formed by over-carburisation,
rather than ultra-high carbon steel. In fact based on these findings
Lowe  has preferred to cautiously aver that
it was a white cast iron ingot that was produced by the Indian
crucible process. Craddock  has also opined
that the product of the Indian crucible steel process was probably
a general homogenous steel rather than specifically a high-carbon
the other hand investigations by Srinivasan 
and Srinivasan and Griffiths  indicated the
presence of solidified metal droplets in the crucibles with a
typical micro-structure and micro-hardness corresponding to a
good quality hypereutectoid steel with the formation of hexagonal
grains of prior austenite with fine lamellar pearlite within the
grains, with the precipitation of pro-eutectoid cementite along
the grain boundaries of prior austenite: which is in fact the
classic structure of ultra-high carbon steels of about 1.5% C
which were made under laboratory conditions by Wadsworth and Sherby
 and Verhoeven et al. .
The findings reported in Srinivasan  and Srinivasan
and Griffiths  are hence significant in that
they prove beyond doubt that high-carbon steels were indeed made
by crucible processes in south India. Studies by Srinivasan and
Griffiths  also indicated that temperatures
of over 1400° C had indeed been reached inside
the crucibles to melt the wrought iron and carburise it to get
a molten high-carbon steel with the typical hypereutectoid structure
above review indicates that the reputation of wootz steel as an
exceptional and novel material is one that has endured from early
history right into the present day, with the story of the endeavours
to study it in recent history being nearly as intriguing as the
story of its past. The archaeological findings indicate that crucible
steel does have an ancient history in the Indian subcontinent
where it took roots as suggested by literary references, while
the analytical investigations indicate that a high-grade ultra-high
carbon steel was indeed produced by crucible processes in south
India. Recent investigations on the properties of the ultra-high
carbon wootz steel such as superplasticity justify it being called
an advanced material of the ancient world with not merely a past
but also perhaps a future.
authors would like to acknowledge the Indian National Academy
of Engineering. Srinivasan would like to acknowledge the support
of British Council, New Delhi for a British Chevening Scholarship
for doctoral research, and the interest of Dr. D. Griffiths, Institute
of Archaeology, University College London, Dr. J. A. Charles,
Cambridge University, late Dr. C. V. Seshadri, founder-President,
Congress of Traditional Science and Technology, and Hutti Gold
Mines Ltd. for assistance with fieldwork and the support of the
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