Upvote:1
I'm not a metallurgist, that's your field. I'm looking at your question from a historic and economic angle:
Was the quality of Roman armour really worse than the armour of knights of the XII-XIV centuries?
Of course. There is a full millennium between the Roman Empire and the XIV century. Even if technology developed very slowly during the dark ages (early medieval period), progress was there. Every generation added a little to it. Some generations more than others. 40 generations adds a lot.
Armour became progressively cheaper, lighter and stronger. Look at an early medieval hauberk: it was very expensive to make (many months), worn only by well-to-do military. The sleeves were short, the hauberk reached slightly over the groin area.
It doesn't differ much, if at all, from any Roman armour. Also notice the fairly large shield. Roman shields (republic, early & mid-empire) were even larger. Those relatively large shields were needed to make up for what the armour didn't protect.
As technology progressed, we see more armour worn by more common people. Also, armour would protect more of the body. The hauberk of a Frankish knight wouldn't look overtly strange on an English or a Burgundian footsoldier. (Yes, it would, but the armour worn by Burgundian or English footsoldiers was at least as good if not better as that worn by Frankish knights.)
A knight would of course get the best he could afford, which was a good deal more, being custom designed full plate armour, if he was really rich.
I don't doubt Romans could cast plates, but not cheap, light and strong enough. A Roman cuirass is fairly heavy and seriously more expensive compared with a late medieval cuirass. I've seen Roman gladiators equipped with full plate armour, almost like a late medieval knight. (Sorry, no links.) The type was very rare, but it was possible. Or better phrased: not completely impossible.
I mentioned the shield. I noticed - but can't proof - shields tend to get smaller when the technology of the armour allowed for it. A late XIV century knight would wear a shield more for decorative than practical purpose. An early knight wore a large kite shield. I don't think that was purely coincidental. However, plenty of warriors wore a small shield, so it's just something I noticed.
The Romans themselves developed Lorica Segementata, but dropped it at the end of the second century. The reason was probably very high maintenance and repair costs. The different metals reacted to each other, and it rusted, as we nowadays would say: "in the catalogue". Roman soldiers spend a good deal of their time polishing and fixing their lorica segmentata. Reminds me of my army days when we spend many hours polishing our white canvas belts absolutely white. Was a great way to avoid PT!