Since by this definition: "Steel is an alloy consisting mostly of Iron with a Carbon content between 0.2% and 2.04% by weight." It would seem the only qualification for an armour to be identified as "Steel" would be if the overall carbon content met that criteria of percentage of carbon by weight.
According to this article which I found at The Oakeshott Institute web site entitled, "Some Aspects of the Metallurgy and Production of European Armor", by Craig Johnson, (first published in the Armored Proceedings Symposium Notes, 1999.)
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| One of the main issues to arise from the metallurgical examination of period pieces is that steel was used for the construction of armor to a much greater extent than was previously thought. Many scholars up to a couple of decades ago were of the belief that the majority of armour was made from iron and not steel. The fact that steel was the material of choice for the majority of armor greatly affects the work process to make and maintain the armor. Iron was used for armor and weapons but it does not seem to have been the choice for even common objects and was reserved for the lowest quality munitions grade items. When the modern researcher comes across a piece of quality armor made of iron this can be seen as a red flag that the item may be a later reconstruction. |
The author of this article goes on to describe the process of carurizing wrought iron and decarburizing cast iron. To carbuerize wrought iron, which seems the easier of the two options, the piece (iron bar, plate or perhaps even a finished piece of armour) and pack it in an organic material in a sealed vessel and bake at high temperature (red heat) for a long period of time. He then points out that the first mention of this process in Europe was in the late 12th Century, and then supplies us with a description of the process from Giambattista della Porta, Natural Magick, Book XIII, Ch IV, 1558;
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"Take soft iron armour of small price, and put it into a pot, strewing upon it [soot, and organic powders to supply carbon], cover it, and make a good fire about it: then at the time fit, take the pot with iron pinchers; and striking the pot with a hammer, quench the whole herness red hot in water; for so it becomes hard ... But, lest the rings of a coat of male should be broken, and flie in pieces, there must be strength added to hardness. Workman call it a return. Take it out of the water, shake it up and down in vinegar, that it may be polished and the colour be made perspicuous: than make red hot a plate of iron and lay upon the same: when it shows an ash colour, cast it again into water, and that hardness abated, and it will yield to the stroke more easily: so of a base coat of male, you shall have one that will resist all blows." |
Since an Armourer makes his living selling "garments" to wear for protection in battle, those who produced harder, better protecting armours would garner the lion's share of business, and if a particular armourer was able to do this consistently then one can bet this was not by accident, that a process or processes were known to them which would improve the hardness and toughness of the armour they made. According to the author of this article, that process controllable by the armourer was heat treating.
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| To harden steel, one needs to bring it above a critical temperature (usually a bright orange heat) for a certain amount of time and then cool it sufficiently fast, or quench it, to lock the crystalline structure in a form not usually created by a slower cooling process. Pure or wrought iron, a Ferrite crystalline structure, will not harden when quenched, and the majority of armor tested up to now have some form of heat treatment done to them. This indicates that the armorers tried to maximize their materials' qualities and it was the inconsistency of material and difficulty in controlling the process that separated the so-so from the masterful in creating hardened armors. |
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| There are a couple of different methods one can use to attempt a quench. The full quench is where the steel is quickly cooled, creating a transformation to a 'Martensite structure' as fully as possible. This results in the steel being as hard as it can be and usually requires a quench in water for the materials it to achieve this state. This Martensite structure is a solid solution of carbon in iron which possess a distorted crystalline structure, this needs to be tempered to relieve stress and reduce some of the hardness by allowing some carbon to come out of the solution as iron carbide. A piece fully hardened could be tempered by heating to about 150°C to 260°C (300°F-500°F), to reduce brittleness and avoid cracking and breaks under use, by "relaxing" the martensite structure. The slack quench uses a slower quenching medium than water, such as brine, oil, boiling water, or some combination of materials which slows the cooling and results in a combined structure of Martensite and other constituents such as Bainite and Pearlite. Materials treated in this way will be harder than an air cooled item but not in need of a temper for performance as armor or a tool. This is the method used by the majority of armor makers. Interrupted, or timed quench is also a technique that was sometimes used. The item would be withdrawn from the quench medium before being fully cooled and the internal heat left in the item would temper the piece to some degree. The interrupted and delayed quenches are also called "slack quenching" today. |
The author then points out that the processes involved in the production of the raw material and the hardening by the armourer were experiential processes, the mastery of which would have bordered on the magical since the real, scientific processes the metals were undergoing were not understood in the same way we "understand"them today. The results therefore would have been hit or miss and, as the author points out, ran the gamut of achievable results. The stats I found most interesting here were the relative hardnesses achieved by actual period pieces shown in the quote below;
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The results of heat treating ran the full spectrum of achievable results. Many munitions armors were iron or unhardened steel, while even some of the early examples of plate armor pieces were achieving 75-430 VPH (less than 6-44 Rc). The Pembridge helm (bef. 1375) testing at 430 VPH on the surface and the Küssnach Coat of Plates(c. 1352) Item No. LM 13367 in the Swiss National Museum, Zürich averaging 390 VPH (about 40 Rc). The Braybrook Helm (bef. 1405)Royal Armories No. AL.30 with less than .1% carbon and left without heat treating, averages 108 VPH.2 Later in the 15th and 16th C. armorers achieved more consistent results, such as the Helmshmied family of armorers in Augsburg who between c.1480 and 1551 averaged 240-441 VPH (20.3-44 Rc) on 17 items of their work sampled.4 Lorenz Helmschmied created one of the most consistent and well hardened pieces yet tested in an Armet (c. 1492), No. 66 Churburg which averaged 525 VPH (abt. 50 Rc). |
In my opinion a hardness of 20-44 Rockwell (which is what I interpret that Rc to mean) is a very respectable result.
My questions and assumptions then are these;
1)If the carbon content of period armours was inconsistent, then am I wrong in assuming that any sheet of steel I get from a source like Lowes or Home Depot will have a better and more consistent distribution of carbon in it?
2)Am I wrong to assume that the overall content of carbon will also be, on average, higher than the average period piece?
3)Would modern steel used for reinforcing structures, like rebar, or plate steel be a better quality steel than that found in period pieces even though these types of steel are only required to meet "performance" standards and not "Materials" standards? The reason I ask this is that I have access to large quantities of this material for free and don't see any reason I need to spend alot of money on material at this stage of my new hobby.
To close, here is the link to the article from which I quoted; http://oakeshott.com/metal.html
Thanks in advance for any advice or other input/ sources which can be given.