Laminated plate

[Baron Alcyoneus]

In the past, at least, due to evidence of delamination of plates in armor (the Galiot's suit in the Met is just one example), it was thought that some armor was made of laminated steel with softer iron on the inside, and harder steel on the outer layers.

Is that still believed to be the case?

[Mac]

Alcyoneus,

My understanding is that the test used on the Genhuillhac armor (Shore scleroscope) will show the outsides of domed objects to be harder than the insides. This is an artifact of the test method, which drops a diamond tiped hammer on the test piece and measures the rebound.

The delamination which is so characteristic of preindustrial iron and steel is caused by slag inclusions which were not expelled properly from the bloom. These inclusions become thin leaves of silica as the metal is hammered into plates or sheets. Where these siliceous lamellae break the surface of the plate is a place where rust can form at the boundary of the silica and the iron, within the thickness of the plate. Since rust takes up more volume than iron, the overlying iron will be forced up, and perhaps detach entirely from the plate.

The edges of plates are more prone to delamination than the surfaces, because the lamellae are exposed.

Mac

[Otto von Teich]

Wow, Thanks Mac, that makes perfect sense. I've wondered about that for a long while myself.

[Vermin]

" Since rust takes up more volume than iron, the overlying iron will be forced up, and perhaps detach entirely from the plate. "

Big time!!!!
I get artifacts from 1700's wrecks that haven't ever had the concretion taken off of them, and they were brought up in the late 70's to mid 80's.
Sometimes there isn't anything left in them, sometimes there is.
The giveaway is if there IS any viable iron in the concretion, the rust "expansion" will form cracks in the concretion from the pressure.

I tell students that come through that it's like a tree root under concrete, at first it's not noticeable.
But over time....

[Thomas Powers]

Starting with the bloom of smelted iron: you hammer it out into "muck bar"; then cut, stack, weld and draw out into "merchant bar"; then cut stack weld into "singly refined wrought iron"; then cut stack weld into "doubly refined wrought iron"; then cut stack weld into "triply refined wrought iron"

So just plain wrought iron is a laminated material and any weld can have problems!

Thomas