I know this is a controversial subject, but I'm trying to gather different opinons.

What would you consider to be the target hardness (I personally tend to think in Rockwell C), after quenching and tempering, for "optimum" spring steel armour? And why? Primarily I am discussing reproduction armour used in full contact re-enactment. Not necessarily what was achieveable or common in historic armour, as they faced many technical difficulties that might have precluded them from achieving their goals to a full extent.

And yes I realize that there is no perfect answer, and that it varies from maker to maker, and product to product. Just as in sword and knife making.

Thanks !

My answer would be "it depends on the piece". If the piece is indestructible (say knee cops made of 2 mm spring steel) it may be as hard as 50 HRC. Well, such piece will NEVER get any dents or other permanent deformation. Your leg will be broken long before your knee cops. However if your piece is expected to get some deformation (for example gauntlets, which should be as light as possible) I would not recommend anything harder than 40-45 HRC. A dented gauntlet still protects, unlike a broken one, you know. If the piece is too hard it may break instead of getting deformed. Or it may break when you try to straighten the deformation.

Another good thing to have is a differential hardness. For example you can make the whole piece harder and then temper stress points (holes and slots for rivets for example) to be softer but less prone to breaking.

Yet another thing to consider is the quality of steel and heat treatment. When doing it "authentic" way I would rather make my armor softer in order to compensate for errors in heat treatment process. However when using state-of-the-art tools and materials I would dare to make my armor harder.

A good example of spring steel armor are military helmets of the XX century (well, at least Swedish ones). These proved to be almost indestructible. They almost never get any dents when hit by blunt swords. However they do not break either. I have seen these helmets with huge dents made by 9 mm submachine gun bullets.