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ARMOUR MAKING MATERIALS

There are many materials available for making armour including leather, bronze and steel. However for the purposes of replicating late medieval war harness iron and particularly steel (iron containing some carbon) is of most importance. There are however several grades (strengths) of steel such that a comparison is necessary.

• Low Carbon (‘mild’) steel has such a low carbon content that its mechanical performance is hardly better than pure iron. Hardness for ‘mild’ steel (where carbon content is in the region of 0.1%) can be as low as 100 VPH (Vickers Pyramid Hardness test) Compare this with bronze which can exhibit hardness in the region of 200 VPH when cold worked (work hardened). This illustrates just how very soft ‘mild’ steel can be such that when using it to make armour it is necessary to use thick, and therefore heavy, gauges for sufficient durability. Also surface finish lasts poorly (scratches quickly develop after polishing) because of its relative softness. Most significantly, armour made from ‘mild’ steel is easily dented and twisted out of shape and will therefore damage easily and wear out faster than one made from a more durable material. Anything other than very careful use when worn will result in the armour requiring specialist repair and constant up-keep if one wishes to keep it looking good. ‘Mild’ steel cannot be hardened and tempered because there is insufficient carbon present within it to transform austenite to martensite on quenching.
  
• Medium carbon steel(carbon content = 0.5% to 0.8%) contains sufficient carbon so that its mechanical strength can be greatly increased when heat treatment processes are applied to it. For example, a forged piece of armour (i.e. hammered when red hot) which is then air cooled will exhibit hardness in the region of 250 VPH and perhaps even higher depending on the amount of forging applied to the piece before it is allowed to cool slowly in air.

However if the piece is hardened and tempered after forging and shaping (this is carried out with a specialist oven and to a specific procedure) then a dramatic change takes place within the steels microstructure. If quenched rapidly in cold water when red hot then the austenite microstructure transforms into a new microstructure called martensite. This is a very hard substance that exhibits the disadvantage of being very brittle so it is therefore necessary to heat the steel again, after quenching, at a lower temperature than the quench temperature. Thus the martensitic microstructure is tempered, reducing hardness a bit but more importantly dramatically increasing its toughness (a materials ability to resist localised impact loading). This is very good for armour and is the process used by the German armourers working in Augsburg and Innsbruck in the late 15th century. This is the best quality, toughest steel one can employ and it is only when the above procedure is applied to the steel that it becomes proper ‘spring steel’ – just like the steel that makes the coil springs in your car suspension.

Hardened and tempered medium carbon steel should exhibit hardness in the region of 600 VPH or more depending on the carbon and other alloying element content and the exact hardening and tempering process used. Testing has revealed that armour components thus treated are – to all intents and purposes – practically indestructible being resistant to permanent deformation (they just spring back into shape no matter how much you twist and bend them) and resisting denting from all but the hardest and most violent blows from a lance or beaked hammer.
 
Advantages of making armour from medium carbon steel are that it is possible to reduce the armour mass (from between 20% and 50% depending on the armour piece) yet still maintaining a much greater strength and toughness advantage over mild steel. The armour is therefore far more durable (despite being thinner and therefore lighter) which means less damage in use and, in addition, has a far more lasting surface finish due to the materials greater hardness.

Why does it cost more to make armour from medium carbon steel as opposed to one made from mild steel?

CHOOSING THE RIGHT STEEL FOR YOUR ARMOUR

LOW CARBON ‘MILD’ STEEL
If the customer requires it then Englyshe Plate Armourie can supply armour made from mild steel. However it is considered to be such a poor quality alternative to the medium carbon steels that the small cost saving is just not worth it. This is particularly true when you consider that for most people the purchase of a harness of armour is a life time investment and one that should see many years of use.

MEDIUM CARBON STEELS (0.5% to 0.8% C)
If you require armour for serious use (on foot or on horseback) then Englyshe Plate Armourie recommend the use of medium carbon steels. These steels can be heat treated in two basic ways (see explanation above).

1.         Heat treated and air cooled
As already explained the steel is forged (hammered red hot) and then allowed to air cool slowly. No additional heating or quenching processes are applied to the steel so costs are reduced. The result is armour that is significantly lighter, tougher and more durable than mild steel.

2.         Hardened and tempered.
After forging, the medium carbon steel is hardened and tempered using specialist equipment and procedures. The finest quality armours crafted in Germany (Augsburg and Innsbruck) in the late 15th century would have been hardened and tempered as described above.

The result of hardening and tempering is that the steel far exceeds the strength and durability of the mild steel and the air cooled medium carbon steel. The obvious advantages allow the armourer to use plate of a significantly thinner gauge (less mass!) while maintaining a much greater toughness and durability. The price of this extra strength for less mass is a proportionally greater cost to craft the armour.