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Sword Blade Hardness: A look at the current research
An article by Craig Johnson 
There is no perfect blade design. The blade of every well-made sword is unique, comprised of a balance of objectives and components. These attributes, in proper proportion, produce a blade with a certain harmony; whether that harmony is appreciated is a matter of personal taste, within the additional defining context of its historical period. Recognizing this shifting universe of maker, available material, purpose and additional preferences is crucial for the serious student, collector, or maker of swords. One aspect of Medieval sword composition that is often touted by modern enthusiasts, but is little understood, is the hardness of the blade itself. Many will use conjecture and outright guessing when discussing the hardness of original swords. It is important to look at the materials available to the artisans of the era, the blades produced, and the resulting accomplishments given these materials. Blade Composition I would like to briefly address the composition of the blade, while recognizing that this is a complex topic; in general, there would be a long list of microstructures, elements, photomicrography and constructional drawings for any given sample.
The homogenous steels used by modern producers are probably the largest leap from the original materials considering all of the aspects of what makes up a reproduction sword. There is some variation in our modern steels used by makers today, but this is a far smaller variation than seen in the Medieval blades. As with any industry standard, it is usually expressed in a range rather than a specific number. Here are some examples for common modern sword steels:
In the period swords we are looking at, there are indications of a carbon content range noted on six of the blades. They show carbon in levels from .1 or less (in all) up to .8 with four of the six being .6 or less. This indicates that even in the highest quality period blades of this group the carbon content ranges over a much larger area than modern steels. Blade Hardness In the current marketplace there is much that is said about the hardness of blades. In fact there is customer resistance to production of swords that are not hitting certain benchmarks on specific hardness scales. Why is this? It may well be a desire by our modern minds to latch onto a definitive qualifier. We want to say, "This is better than that because of X". The inherent problem we create with this approach is that steel does not work that way; it is a balance or harmony of competing functions. Flexibility, edge holding ability, tensile strength, material composition, material manipulation—these are all considerations the craftsman can manipulate and all will have a bearing on what the end result may be.
There are three main testing options for the "hardness" of steel that are referenced in the discussion of swords: the Brinell scale, developed in Great Britain and used mainly in Europe; the Vickers Scale, developed in Great Britain and most often seen in the literature of testing historical blades; and the Rockwell scale C (actually ranging from A to V, but C is the range we deal with here) developed in the United States. Each of these methodologies tests the surface of a material by indentation with a known hardness indenter of a particular shape and then in varying ways measuring the mark that is left and converting this to a number on that particular scale. Here is a brief description of the methods without formulas: Brinell This is an average of the diameter of an impression made in the test medium. When it is fully listed, the number should look like this: 481 HB 10/500/30. This is translated as a Brinell Hardness of 481 using a 10mm ball with 500-kilogram load for 30 seconds. This test is usually viewed as having the highest degree of general accuracy. Vickers This process involves measure of the surface area of a pyramidal indentation into the test medium under a given load and duration, providing a quotient that can then be translated into the Vickers number. This is usually accomplished with a conversion table. The number will be represented as 513 HV/10, which indicates a Vickers Hardness of 513 with a 10Kgf force. The strength of this system is the use of one scale, from top to bottom of the hardness range, and one indenter type throughout. Rockwell C The Rockwell test is a measure of the depth of penetration when set to equilibrium with the testing machine under a minor and major load. The result is read directly from the machine. This test is the quickest test to perform, but is also the most susceptible to error and machine differences. The Rockwell scale system is a bit arbitrary, as the A-V scales relate to each other, and it is not exactly translatable to the other systems. There is a general understanding that Rockwell numbers will vary +/- 2 points either way as an acceptable industry standard—i.e., 50Rc can be 48 to 52 and pass general industrial inspection. Of the three, the Rockwell scale C is the range that best covers the hardened steel we will be discussing. Defining Hardness
As modern industry began to need a more refined scale, the other systems were developed. The Brinell and Vickers measurements arrive at their numbers by measuring the resistance to displacement, while the Rockwell scale is more a measurement of resistance to penetration. This is why there is not an exact correlation between the scales, and why the Vickers and Brinell systems can be correlated roughly to some measure of tensile strength while the Rockwell numbers do not. I would also like to comment on another methodology that is used by some knife makers and has been the subject of some discussion in the sword field as well: the use of hardness files. This is done with a set of files graduated in hardness. The file test is most useful in making general comparisons rather than generating a specific number. They are also only testing the actual surface material on a given spot. The drawback to file testing is the actual hardness of the file and the inconsistency of the load applied to the test stroke. The file sets themselves usually have a five point range in which they are effective, i.e., a typical set of files would be calibrated to 30, 40, 45, 50, 55, 65. Thus an experienced tester with a trained consistent hand would probably be approximating a hardness number in a 3 to 4 point range. The variables present in such a process create difficulties for limited testing on a few samples with files and should be viewed cautiously in discussions of test result specifics. As described above, the hardness of a sword blade is a test of its surface resistance to abrasion and indicative of its edge-holding ability. There are some correlations to tensile strength, but the flexibility and other factors of a blades totality are not closely linked to these specific numbers. Period Blade Hardness With the knowledge of what the hardness tests indicate of a blade, we can now turn to look at some of the surviving swords from the period. Looking at the tests that have been done, we can see where they indicate the Medieval sword manufacturers were setting their goals, and what the medieval customer was purchasing.
Several different researchers have tested the blades that I will be referencing here over the last twenty years; I have tried to use those examples with multiple spots tested per blade. This allows a better view of what made up a period blade, as pieces tested in just one spot will be unreliable as indicators of the nature of that blade. Furthermore, the items all appear to be working weapons of their period. The number of swords tested is not statistically significant when compared to the number of swords made over the historical period. Thus we must use these as anecdotal examples that may indicate the range of what was done. As more information is gathered we can refine the picture, but at this time it is the hard evidence we have to work from, much better than the oft-repeated "true" stories that no one can source or document. The most definitive characteristic that we can see from the hardness testing that has been done on original swords is the fact that the hardness varies dramatically throughout a piece, not just surface to core or edge to mid blade, but literally in the span of the material the hardness will fluctuate through quite a range. As an example, an 11th to 13th century sword in the Hofjagd und Rustkammer shows a range of hardness from 119 to 520 VPH.4 The average of the piece is 217VPH. The sword was additionally tested with four samples removed from the blade. These pieces were tested across the thickness of the blade and the microhardnesses ranged from 258VPH to 329VPH, with an average of 300 VPH. When we would describe this sword using the Rockwell system, we are looking at a piece that ranges from less than 20Rc to 50Rc, with the average still below 20Rc. This graph details the range of hardness found in several period blades compared to what modern replicas generally are listed at by their manufacturers. Keep in mind that the range on the period blades includes all points tested on the sword; thus the upper and lower numbers may be just one point on the blade and not correlated to edge or core areas. A dot has been applied to the ranges on the period swords to indicate where the testers listed an average edge hardness for that blade.
The included swords ranged from the 9th to the 16th century. While recognizing that this is not a large enough group to be statistically significant, I separated them into groups by their period, as it is difficult to compare industrial technology from such a wide span of time. Two additional swords were tested, from the 17th and 18th centuries respectively; these were not included in my considerations, though it maybe interesting to note that their average hardness (the only number given for them) were 441VPH (~45Rc) and 472VPH (~47Rc). 1, 4, 7, 14, 15 9th to 13th Century Group This subgroup consisted of 13 swords. The range of hardness in the group ran from 93VPH (no Rc equivalent) to 650VPH (~58Rc), and these blades all demonstrated a range of hardness in different areas of each blade. There were indications of several different construction methods, including core-wrapping, pattern-welding, piled and edge application. Heat-treat evidence showed that majority of blades were slack quenched with differing degrees of success, and there was evidence indicating a quench and temper process in a few of the blades. There were two blades that showed no evidence of heat-treat at all. 14th to 16th Century Group This group numbered seven blades and ranged in hardness from 136VPH (>20Rc) to 650VPH (~58Rc). These blades showed piled, billet, core-wrapped and carburised iron construction. This group showed evidence of slack quench and quench/temper operations being performed. The importance of selecting several points on a blade to test can be exhibited in this example from Some Early Medieval Swords in The Wallace Collection and Elsewhere by David Edge and Dr. Alan R Williams, which details the variance one can expect in a medieval sword.4  The diagram above details the hardness found along the edge and the middle of a possibly 12th century sword (A 457) in The Wallace Collection, London (Sword B in graph 1). The sword was tested at 5 cm intervals along a cutting edge and the middle with the results averaging 211 VPH in the middle and 279 VPH along the edge.4 The edge of a blade is where hardness is usually the most desired and the area of greatest comment. If we take those blades that specifically tested areas of the edges and look at the range of hardness, we find a sample of nine items where this is listed. The highest number detailed for specific points on each edge ranged from 200VPH (>20Rc) to 540VPH (~52Rc). Seven of the samples are below 460VPH (~46Rc), with the remaining two testing at 520VPH (~50Rc) and 540VPH (~52Rc). The investigators listed the average hardness of the edges in seven of the samples. The two swords listed above averaged 217VH (>20Rc) and 476VPH (~47Rc) respectively. The other five swords had one at 279VPH (~27Rc) and the remaining four averaging between 133VPH and 217VPH (all >20Rc). This range of hardness appears to be due to two factors: first, the material the blades are constructed from, with variable carbon content present in different sections of the blade; second, the heat-treat process attempted on the blade, such as slack quenching compared to full quench and temper. As the variations in carbon content of any given sample of material limits the achievable hardness possible in the quenching process, this is a limiting boundary and is connected to the success of any heat-treatment. One must also keep in mind that the quenching processes varied from blade to blade. Such elements of this process—including initial heat temperature, quench medium, quench time, cooling rate and whether the sample was tempered or not—play important roles. The following graph illustrates the comparison of some period samples to some steels used for today's replica blades. The carbon content and hardness are shown. The modern pieces are given a standard heat-treat with 50 Rc as the target.
Another important factor that would have significant impact on hardness was the construction of the blade. The blades in this group show piled, billet, core-wrapped, pattern-welding, carburised iron and edge application construction (See appendix). With the variance in material and methodology for blade manufacture, it was a distinct challenge to the period smith to produce a blade that would have had as tight a window of hardness range as modern steels are able to produce. In some cases the construction of the blade indicates this type of hardness range was not a goal of the smith. Thus one must ask whether that challenge was something they were even interested in achieving as a result and we will need a great deal more research to answer with any confidence. Conclusion The knowledge base concerning medieval swords has been expanding quickly over the last several decades, and we have learned a great deal about the pieces as working tools. The development of this research has been crucial to opening our eyes to the reality of what makes a sword. The examples we have reviewed here illustrate that the hardness of a sword, an attribute dear to the modern maker and consumer, was not always an attribute that the period makers where emphasizing. The two examples with no heat-treat are indicative that a choice was being made on how hard a sword needed to be. It also enlightens the modern sword user to the fact that a piece with less than the perceived ideal for hardness and composition was considered a functional blade by the medieval craftsman and one that would be acceptable to at least a sector of their market.
About the Author Craig Johnson is a craftsman who has been making swords and armour at Arms & Armor, Inc. in Minneapolis for about twenty years. A desire to study and learn about medieval and renaissance weapons and armour stems from a deep love of history and a misspent youth of watching Errol Flynn movies and the 70s version of The Three Musketeers. An interest in how these items were used also lead to a study of western martial arts. He also holds the position of Secretary to The Oakeshott Institute. Author's Note Research continues in this area and the author would be interested in hearing about any new publications dealing with sword blade composition and hardness not listed below. Acknowledgements The author wishes to thank Peter Johnsson for consultation, insight and critique. I would also like to thank Melissa, Mark, Ian, and Reece for their comments and critiques. Appendix European blade construction is a large topic and one that cannot be comprehensively addressed in this article. Here are quick descriptions of some terms mentioned: Piled: Layered construction Billet: Blade forged from one piece of material Core-wrapped: Blade core of one material with a sheath of different material wrapped around the core Pattern-welded: Material bound and twisted together to create a pattern in finished blade. Examples of core and veneered commonly seen Carburised iron: Core or section of blade made from iron and carburised to increase carbon content and hardness, examples seen both heat-treated and not heat-treated Edge application: Core of blade created from one of above methods and different material applied to edges usually with higher carbon content but not always Sources 1. Anstee, J. W. & Biek, L. (1961), A Study in Pattern Welding, Medieval Archaeology, 5: 71-93 pl. IV-XVI 2. Anteins, A.K., Structure and Manufacture Techniques of Pattern-Welded objects found in the Baltic States, Journal of Iron & Steel Institute,(1968), 563 3. Dunning, G. C. Evison, V. I. (1964), The Palace of Westminster Swords, Archaeologia, 98 123-158 pl. 275-XXXII-XL VI 4. Edge David & Williams, Dr. Alan R. Some Early Medieval Swords in The Wallace Collection and Elsewhere, Gladius XXIII, 2003 pp 191-210 5. Feuerbach A., Merkel, J. F., and Griffiths D. R. (1997), Co-Fussion production of Crucible Steel, Material Issues in Art and Archaeology, 5: 105-110. Washington: Materials Research Society 6. Lang, J. (1988) Study of the Metallography of some Roman Swords, Britannia, 19, 199-216 pl. 5-10 7. Lang, J. & Williams, Dr. Alan R., The Hardening of Iron Swords, Journal of Archaeological Science, 2., (1975), 199 8. LaSalvia, V. (1988) Archaeometallurgy of Lombard Swords, Florence 9. Mihok, L (1993) Metallographic Examination of Pattern Welded Swords from the Early Roman Period in Eastern Solvakia, Archaeomaterials, 7, 41-51 10. Pleiner, R. (1993), The Celtic Sword, Oxford 11. Williams, Dr. Alan R., Slag Inclusions in Armour Plate (1400-1640), Bloomery Ironmaking During 2000 Years. Seminar in Budalen, Norway, 1991 12. Verhoeven, J. D. & Pendray A. H. & Peterson, D. (1992) Studies of Damascus Steel Blades Materials Characterisation, 29, 335-341 and (1993) 30, 175 & 187 13. Williams, Dr. Alan R. & J. G. O'hara, The Technology of a 16th Century Staff Weapon, JAAS Vol. IX, No 5 14. Williams, Dr. Alan R., Methods of Manufacture of Swords in Medieval Europe: Illustrated by the Metallography of some Examples, Gladius XIII, 1977 15. Williams, Dr. Alan R., Seven Swords of the Renaissance from an Analytical Point of View, Gladius, 1978, p97 16. Williams, Dr. Alan R. & K. R. Maxwell-Hyslop, Ancient Steel from Egypt, Journal of Archeological Science, 1976, London Suggested Reading From the period: Agricola, Georgius, De Re Metallica. Herbert Clark and Lou Henry Hoover (editors and translation). Dover Publications, Inc., 1950, New York Biringuccio, Vannoccio, The Pirotechnia. Translated and edited by Cyril Stanley Smith and Martha Teach Gnudi. M.I.T. Press, 1966, Cambridge Listed by author: Tylecote, R. F. and Joan Day (editors): The Industrial Revolution in Metals, The Institute of Metals, 1991, London Metallurgy in Archaeology: A Prehistory of Metallurgy in the British Isles, 1962 Edward Arnold (Publishers) Ltd., London: The Prehistory of Metallurgy in the British Isles. The Institute of Metals, 1962, London The Early History of Metallurgy in Europe. Longman, 1987, London and New York Craddock, Paul T.: Scientific Studies in Early Mining and Extractive Metallurgy. British Museum Occasional Papers 20. 1987, London, The British Museum Agricola and the study of early metallurgy. Journal of the Historical Metallurgy Society 28(1):1-6. Institute of Materials, 1994, London Early Metal Mining and Production. Smithsonian Institution Press, 1995, Washington, D.C. Bergman. Torbern: A Chemical Essay on the Analysis of Iron. Translated by J.P. Hickey and C.S. Smith. In Sources for the History of the Science of Steel 1532-1786, edited by Cyril Stanley Smith, pp. 165-255. The Society for the History of Technology and The M.I.T. Press, 1968, Cambridge and London Espelund, Arne: An Attempt to Define Archaeo-Metallurgy. In Early Iron Production- Archaeology, Technology and Experiments, edited by Lars Chr. Nørbach, pp. 7-14. Technical Report Nr. 3. The Historical-Archaeological Experimental Centre, Lejre, 1997, Denmark The "Evenstad" Process- Description, Excavation, Experiment and Metallurgical Evaluation. In Early Iron Production- Archaeology, Technology and Experiments, edited by Lars Chr. Norbach, pp. 47-58. Technical Report Nr. 3. The Historical-Archaeological Experimental Centre, Lejre, 1997, Denmark Ironmaking in Trøndelag During the Roman and Pre-Roman Iron Age. An Archaeo-Metallurgical Evaluation. In Early Iron Production- Archaeology, Technology and Experiments, edited by Lars Chr. Nørbach, pp. 103-114. Technical Report Nr. 3. The Historical-Archaeological Experimental Centre, Lejre, 1997, Denmark Heskel, Dennis and Carl Clifford Lamberg-Karlovsky: An Alternative Sequence for the Development of Metallurgy: Tepe Yahya, Iran. In The Coming of the Age of Iron, edited by Theodore A. Wertime and James D. Muhly, pp. 229-266. Yale University Press, 1980, New Haven and London Hjarthner-Holder, Eva, Peter Kresten, and Lena Larsson: From Known to Unknown. Application of well-Known experimental Iron Production Results to Archaeological Materials. In Early Iron Production- Archaeology, Technology and Experiments, edited by Lars Chr. Norbach, pp. 15-26. Technical Report Nr. 3. The Historical-Archaeological Experimental Centre, Lejre, 1997, Denmark Joosten, Ineke, Ben Jansen, and Henk Kars: The Use of a Model to Describe Bloomery Production in the Netherlands. In Early Iron Production- Archaeology, Technology and Experiments, edited by Lars Chr. Norbach, pp. 37-46. Technical Report Nr. 3. The Historical-Archaeological Experimental Centre, Lejre, 1997, Denmark Joosten, Ineke, Matthijs van Nie, and Patrice de Rijk: Experiments with a Slag-Tapping Furnace at the Historical-Archaeological Experimental Centre, Lejre. In Early Iron Production- Archaeology, Technology and Experiments, edited by Lars Chr. Norbach, pp. 81-92. Technical Report Nr. 3. The Historical-Archaeological Experimental Centre, Lejre, 1997, Denmark Rostoker, William and Bennet Bronson: Pre-Industrial Iron: Its Technology and Ethnology. Archeomaterials Monograph No. 1, 1990, Philadelphia Rostoker, William and James Dvorak: Wrought Irons: Distinguishing Between Processes. Archeomaterials 4:153-166, 1990 Rozdzienski, Walenty: Officina Ferraria: a Polish poem of 1612 describing the noble craft of ironwork. Translated by Stefan Pluszczewski; edited by Waclaw Rozanski and Cyril Stanley Smith; introd. by Jerzy Piaskowski. Society for the History of Technology and M.I.T. Press,1976, Cambridge Sim, David: Beyond the Bloom: Bloom Refining and Iron Artifacts Production in the Roman World. Edited by Isabel Ridge. BAR International Series 725. Archaeopress,1998, Oxford |
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