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Swords, Cutting and Military History

Razor Edged 3: Comparing metallurgy of special medieval swords

Razor Edged 3:  Comparing metallurgy of special medieval swords

photo by EMSL

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First, let’s recap the previous articles in this series (Razor Edge One and Two):

A blade’s sharpness is in part dictated by  the width of the blade itself, the geometric form of the blade, the angle of the edge bevel — which indirectly limits minimum edge width, by the nature of the polishing agent being used, and by the composition of the steel.  High carbon steels are capable of supporting denser and more complex micro-structures, which increase the hardness of steel.  Harder steels provide a much more durable edge  (remembering that anything less than 30 microns / 3/1000 inch is considered “sharp” by modern standards).  However, the harder a steel is, the more brittle.  Thus, the art of swordmaking has always been a trade-off between creating a flexible blade which cannot maintain a sharp edge, and an extremely sharp but fragile sword.

A graphic demonstration of this is taken from the chart in Craig Johnson’s article for MyArmory.com: Sword Blade Hardness: A look at the current research, which compares the range of carbon content of both modern steels and various medieval European swords to the range of hardness ratings found.  Note  the average blade-quality steel today is demonstrably of more consistent steel quality, carbon content and hardness than the vast majority of medieval weapons:

 

Carbon and Hardness Ratings of Swords

Figure A

 

On construction

One note before we go further:  due to the state of steel production and forging techniques available during Medieval times, it should be remembered that all three of these blade-types were created through variants of pattern-welding.  As such, it was entirely within the smith’s ability to create a blade core of a softer, less fragile steel, then attach, wrap or weld harder steel around it to create a blade with an hard and fine cutting edge, but with the ability to withstand impact without breaking;  today, many “battle-ready” sword manufacturers use monosteel and high-technology differential heat treating to create blade with the similar physical characteristics .  It’s not within the scope of this article to discuss the advantages / disadvantages of the mechanical nature of sword manufacture.

Rather, we’re  going to examine reports of scientific metallurgical analysis of examples of three types of blade.  Primarily, we’ll be comparing the carbon content, microstructures (pearlite, bainite, martensite) and hardness ratings of these antique weapons, with a view to understanding the average quality they exhibit, and to see if any of these blades exhibits exceptional qualities over the others.

 

Sword types examined

With this , we’ll have a look at metallurgical examinations of three famous swords types, famed as the “best of their day” if not actually better than swords produced today.   These will be the:

  • Ulfberht (Viking) sword;
  • Damascus steel blades;  and the
  • Japanaese nihonto, more commonly known today as the katana.

These three classes of weapon/weapon production have been selected solely because of popularity in both ancient and modern sword cultures.

Of course, there were other source of excellent quality weapons production in Europe during the Middle Ages and the Renaissance;  unfortunately, few smiths / smithies are known by name.  Rather, they tended to be noted by the city or region of production, such as Solingen swords (Germany), Milanese (Milan, Italy) Renaissance armour and weapons, etc.  Some specific names of famous smiths are known, whose forges mass producing good quality weapons, however, generally speaking these smiths were more famous for their high quality armour production than swords of legendary quality.

Note that most hardness testing done in the sources used the Vickers scale, for its accuracy;.  However, many people will be much for familiar with the Rockwell C measuring system.  In most places we will convert Rockwell C readings to VPH (Vickers Diamond Pyramid Hardness, or VPH for short).  To prevent confusion or misunderstanding, you can consult this Hardness Conversion Table to clarify/convert the readings into a system you are conversant with.

 

Viking Blades

It is immediately noticeable from Figure A chart that modern steels are much more standardized in carbon content and hardness than most medieval blades, matched only by the very best examples of Ulfbehrt blades, forged around the year 1000 CE.  All these blades have the name Ulfberht (or variations of) inscribed on the blade.

Ulfbehrt signature

These were pattern-welded swords, constructed of sections of steel welded into a bar, with three or more bars being welded together to create the sword body with a distinctive fold pattern due to the twisting of the bars; herring-bone, serpent and leaf are just a few of the patterns known.  Often a softer steel core would have harder steel welded around the edge to create the cutting edge of the blade.

 

Pattern weld leaf pattern

Leaf pattern welding

 

Modern production steels top out at .8% carbon and approximately 530 Vickers hardness rating.  The fact that some swords made a thousand years ago can match modern standards is a prime example of the exceptional smith.

Those unfamiliar with this class of weapons will find the NOVA documentary, Secrets of the Viking Sword very informative:

 

 

A detailed metallurgical survey of Ulfberht-type swords conducted in 2008-2009 ( A metallurgical study of some Viking swords ) revealed that the steel in these swords as actually “hypereutectoid steel of carbon content at least 1%”.  This is a very high level of carbon, creating a very hard but brittle steel;  researchers showed the blade was created at this high level of carbon and hardness, then tempered down to lower, more useful levels of hardness.

This report surveyed several dozen blades either absolutely as identified as being Ulfberht swords; had a signature which claimed to be from an Ulfberht smith; or had signatures which could have been interpreted as Ulfberht (various spellings).  The report lists the carbon content of each blade, along with core hardness ratings and a range of hardness readings from the edge;  in almost all cases, core blade hardness averages between 130 and 190 on the Vickers scale, with edge hardness averaging around 300-350 VPH.  One or two exceptional specimens have a recorded edge hardnesses of 575 VPH.   Photographs in the report include:  the blades, steel microstructure, and various images of the “Uflberht” signature (seen below).  Unfortunately, readings for the core area were not available for all weapons, as testing for core hardness and micro-structure would have required cutting into the sword, which was not allowed.  Thus only blades which had the core already exposed could be examined.

After the analysis of these weapons, the researchers came up with a fascinating conclusion.  While the smith’s forging technique was superb and highly adapted to the nature of the steel, it was the steel itself that was important, and it was likely imported from the Baltic Sea area, with some suggestions it may have originally been smelted in India :

“The original maker of the Ulfberht swords was evidently a craftsman (or perhaps a craftsman/merchant) who had access to a source of high-carbon steel. This may well have been ingots of crucible steel imported from the Middle East via the River Volga. In which case, his location was probably in the Baltic area, where this trade route terminated, and where most of these swords have been found (see map). Such a high-carbon steel would have needed to have been forged, counter-intuitively, at a lower temperature than customary. If forged at the correct temperature and for the correct time, the swords produced would have been both hard and tough, and would have been highly valued….

…The product (referring to the raw steel) was made around Herat and exported via North India to Persia & other Muslim lands. The Persians traded in crucible steel, but was any of this exported to Europe? This seems to be the first evidence that this might have been the case. Indeed, there was a well-established trade route from the Baltic to Persia via the Volga, exploited by the Vikings in the 10th centuries, during the period of their manufacture. So there are said to be more Samanid (815-1005) silver coins from their Afghan mines in Sweden than there are in Persia. After the fall of the Samanids, and the rise of the various Russian principalities, the use of this trade route by the Vikings declined. It is notable that, at this time, the manufacture of these «Ulf-berht» swords apparently ceases, presumably because the raw material is no longer available.”

 

Damascus Blades

There have been few exacting studies done on the metallurgical qualities of true Damascus blades;  I say “true”, as the actual forging process used in medieval times more than 300 years ago.  While there has been considerable work and testing done on different way to produce modern versions of wootz steel and weapons with Damascene qualities, the original methods of production are unknown.   Damascene steel weapons are most recognized by their distinctive “watered steel” pattern, often accompanied by distinct differences in colour in each banding.

 

Damascus steel - Muhammad Ladder pattern

Damascus steel – Muhammad Ladder pattern

 

It is believed each block of wootz steel stock came with its own set of impurities,  giving each raw block its own characteristic shade or colour pattern.  Damascus smiths would weld blocks together and forge-fold them to form the body of the blade.  This process would produce a blade with a distinctive pattern, and with the bands having different shades and colouration due to, and determined by, the impurities in each block.  Certainly today duplicate wootz steel blocks are purposely manufactured with such impurities, precisely to allow smiths to create beautifully patterned weapons.

Legendarily, Damascus blades were said to be unbelievably sharp, to hold an edge practically forever (one reported test was to cut a iron bar without notching the edge), yet to be extremely flexible under stress.   Since a full metallurgical analysis would require cutting into — and effectively ruining — a rare antique, there have been few researchers able to fully examine the qualities of wootz blades.  Fortunately, a collector donated several antique blades to one university research group,  these samples supplemented with several blades the researchers acquired personally.  This allowed researchers to conduct a modern metallurgical analysis of these antique weapons ( The Key Role of Impurities in Ancient Damascus Steel Blades )

Their research showed that one of the qualities of wootz steel was an extremely high carbon rating ( averaging approximately 1.5% carbon).  This high a carbon level should have made the steel extremely hard and brittle, yet hardness readings taken from transverse (core) sections from four of the blades with high carbon readings give Rockwell C ratings of 29, 32 and 37 (294, 319 and 368 VPH) and consist mainly of perlite microstructures, including at the blade edge;  by no means the hardest of the steel structures created in forging or tempering.  Metallurgical researchers believe that Damascus blades were “air quenched” (cooled) rather than quenched in liquid;  slow cooling increases the formation of perlite structures. Modern reproduction Damascus steel products rate between 50 and 60 on the Rockwell C scale (513 – 697 VPH).

The relatively recent discovery of nano-steel wires formations within one 18th century blade ( Legendary Swords’ Sharpness, Strength From Nanotubes, Study Says ) suggests that at least one smith, or lineage of smiths, had stumbled upon a forging technique which would indeed produce blades of exceptional sharpness and durability, and as such may have formed the basis for the Damascus steel legend.  The nanowires would have allowed the accretion of harder microstructures in laminate layers along the length of the blade, which may explain the puzzle of  why a blade type would have such extreme carbon rating, display mainly softer perlite microstructures, yet maintain an extremely sharp edge.

It is commonly accepted that the original source of the wootz steel ingots was India; source identified by chemical analysis, though a precise location of mining / production  has not been identified.

 

Japanese blades

Famed in story, myth and movie, the Japanese blade (nihonto) — whose modern incarnation is the katana — is well known if imperfectly understood.  You’ll note I use the term “nihonto”, which literally translates as “Japanese sword”.  This is to refer to the general category of Japanese blades, rather than a specific style, such as the katana.  While the most obvious physical characteristics of the nihonto have not changed for many centuries (single-edged, moderately curved, hand-and-a-half to two-handed hilt / tsuka), there were dramatic changes in purpose and manner of use over this period, changing from primary use on foot, to mounted combat, and back again.  From fighting against lightly armoured opponents, then heavily armoured samurai, to unarmoured fencing.  Changes in forging, and changes in access to imported ores and pre-processed steels of various natures and qualities also changed the nature and quality of the blades produced.

Classic nihonto forms from various Japanese time periods

Click to see full size image. Source: http://www.arscives.com/historysteel/japaneseintroduction.htm

 

Researchers and collectors generally believe that the blade-making art in Japan reached its height between the 11th and 16th centuries, with blades made by specific smiths, or lineages of smiths.  As these smiths died out, so did the secrets of forging exceptional swords.   A high-grade introduction to the nihonto and it’s forging can be found in NOVA’s Secrets of the Samurai Sword

 

 

Much like those who studied the Viking and Damascus blades, Japanese researchers had difficulty in getting access to an antique sword for use in destructive testing ( Study of Microstructures on Cross Section of Japanese Sword ).  They eventually received a sword defined as  “2nd generation of Muramasa”, which is to say the blade was approximately 600 years old,  made by one of the first generations of smiths trained in the Muramasa tradition of forging / smithing.    The construction of the blade included a softer steel core, the attachment of slightly harder steel side pieces and an extremely hard cutting edge.

Their research showed that blade’s overall carbon content was .78%, a higher carbon percentage than many European blades.   Micro-structures found were primarily martensite on the cutting edge, with dense collections of softer perlite on the side areas, and an even less dense distribution of perlite in the central core.  The density of these structures are visibly apparent under an electron microscope.

 

Microstructures of Muramasa blade

 

When tested for hardness, the core was found to have Vickers ratings of close to 200, the side pieces slightly higher, and the cutting edge skyrocketing to a high of 720.  They were able to take multiple readings, and show the steel hardness dropped off rapidly as they tested points further away from the final edge thickness, suggesting the smith had a fine control over tempering  (see diagram below).  Note that the report mentions that previous researchers had tested for hardness along length of the edge, and found hardness ratings from 700-820 VPH.

 

Nihonto hardness ratings

 

Comparisons

An equal scientific comparison of the composition, structure and hardness of all three types of blades is impossible, given that each research team operated under different methods of investigation, followed different procedures and equipment, and had different limitations on the use of destructive testing for all samples.

However, drawing from the information presented above, we can conduct a basic comparison of some qualities.  As defined at the beginning of this article, these are the metallurgical qualities which most influence edge sharpness and usefulness.

 

Steel carbon percentages

  • Ulfberht:    1.2% (maximum reading on one sample: approximate average of .75% across all blades)
  • Damascus: 1.5%
  • Nihonto:      .78%

All of these ratings equal or exceed,the carbon content of modern mono-steel used in the production of “battle-ready blades”.

 

Dominating edge microstructre of samples

  • Ulfberht:    Perlite, laminar (layered, strong) to unorganized (and therefore soft)
  • Damascus: Perlite, laminar.  Nanowire theory may apply, but this sample was not investigated for this quality.
  • Nihonto:     Martensite at apex of cutting edge, shift to Bainite as one moves away from that edge

Of these samples, the nihonto displays the densest formations of hard microstructures, suggesting it may have the capability to carry the sharpest possible cutting edge.  The Damascus blade and its laminar perlite formations come next, those being recognized as the next hardest form of structures of those examined.

The microstructure samples of the Ulfberht blades range widely in formation and density, and therefore quality.  Based on this example, the quality of the Damascus and nihonto blades are both exceptional for their time period, but not up to modern standards.

 

Edge hardness ratings

  • Ulfberht:    Average 300-350 VPH, max 575 at a single point.  Varies widely at different points on same blades, and blade-to-blade.
  • Damascus:  Unfortunately, the researchers did not specifically test edge hardness.  However, core hardness was found to be, on average, approximately 350 VPH.  It would be expected that edge hardness would be 200 or more points higher, which would place edge hardness at 550 VPH or more, at least equal to readings for modern steel.  The article mentions that the hardness readings made seemed to be consistent, leading to the suggestion that roughly equal consistency  edge hardness would be found along the blade.
  • Nihonto:   Variation of 700-820 VPH along cutting edge

 

As stated at the start of this article, it’s not my intention to say which blade is better than another, but to provide some scientific points of comparison.  There are simply too many variables in materials, construction, manufacture and use for any simple selection of “best” to be made.

We can say that, from a metallurgical perspective, all of these blades were far ahead of their time.  All, at their best, exhibit qualities far beyond the global average for smiths at that time, and indeed equal or exceed some modern standards.  They are all well worthy of their place in cutting legends.

 

Sources

A metallurgical study of some Viking swords – Gladius, Estudios sobre armas antiguas, arte militar y vida cultural en oriente y occidente XXIX (2009), pp. 121-184

 The Beauty of the Japanese Sword: History and Traditional Technology, The – Macau Museum of Art

Damascus Steel – Dissertation, Farzin Fatollahi-Fard

Damascus Steel, Crusades and other Myths – SwordForum.com discussion

Famous Makers and European Centers of Arms and Armor Production – New York Metropolitan Museum of Art

Japanese Sword Appraisal – Its significance for Archeo-metallurgical Research with International Archeology and Materials Science –  Dissertation

Key Role of Impurities in Ancient Damascus Steel Blades, The – Journal of the Minerals, Metals and Materials Journal 50 (9) (1998), pp. 58-64.

Legendary Swords’ Sharpness, Strength From Nanotubes, Study Says – National Geographic

Oakeshott’s Typology of the Medieval Sword – A Summary – Albion Swords

One problem and three solutions: The steel of European, Indo-Persian and Japanese swords compared:  Part 1 – The European Swords of the 17th and 18th centuries – Francisco A. B. Coutinho, Japanese Sword Society of the United States Newsletter, Vol 40 / #4 August 2008

One Problem and three solutions: The steel of European, Indo-Persian and Japanese swords compared:  Part 2 – Indo-Persian swords and wootz steel – Francisco A. B. Coutinho, Japanese Sword Society of the United States Newsletter, Vol 40 / #5  October  2008

One problem and three solutions: The steel of European, Indo-Persian and Japanese swords compared:  Part 3 – The hada of Japanese swords – Francisco. A. B. Coutinho, Japanese Sword Society of the United States Newsletter, Vol 40 / #6  December  2008

Study of Microstructures on Cross Section of Japanese Sword – ESOMAT 2009, 07018 (2009) DOI:10.1051/esomat/200907018

Sword Blade Hardness: A look at the current research – MyArmoury.com

Technical Report: Microstructural Characterization of a Knife with Damask Patterning

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