> what is called wrought iron (i.e the material not the process of wroughting), isn't really wrought iron but mild steel. It's very difficult to buy REAL wrought iron
I haven't seen any in a decade, since they tore down the 1880 iron bridge in town. That was fascinating to study up close, because wrought iron is very unlike modern steel. Oh, there may be a few wrought-iron ornamental fences around the oldest churches in town, but rust never sleeps and most old iron fences decay and get replaced with bent-up steel, aluminum, or (gag) plastic fencing. There's maybe one fence I know with the tell-tale pastry-flake of wrought iron.
Bessemer and other steels completely displaced wrought-iron. I'm surprised anybody still makes it, though I suppose it is a big world and a lot of places where the old craft is not completely forsaken.
I probably have some details wrong, but.....
Throw red dirt in a hot fire. After a while you have a red-hot lump of slag in the bottom. There are bits of iron in the slag. Start hammering. This welds the iron-bits together and squeezes out slag. Sticking with the hammer, you work it like flaky pastry: hammer out thin, fold, hammer out thin, repeat hundreds of times. You wind up with layers of iron with thin sheets of slag between. If your arm gets tired, build a rolling mill and roll the slagball into rods, you get tendrils of iron with slag inclusions. Strong wrought iron is always strong in one or two directions, weak in the other 2 or 1 direction(s). Not unlike wood, which is 1,000PSI one way and 100PSI the other way (you can split a log that you could never break).
What I think this means in transformer terms is: wrought iron has very high resistivity for paths that pass through slag, even though the majority of the mass has fair conductivity both electric and magnetic. So in an AC transformer, if you lay the "grain" of the wrought iron the right way, eddy-current circles are small, eddy-current losses are small. Switch to steel, and no matter what you do with the carbon, a solid block of steel acts like a shorted-turn with resistance not a lot higher than your copper winding. Idle core losses are very high. The fix is to use thin steel with insulation (varnish or even controlled rust) between them, to limit the size of eddy-circles. Now we ask why we burned-out all the slag to steel, hammered thin, and put "slag" back between layers of iron, when wrought iron works this way naturally. Of course the demand for strong-all-ways steel and its mass production drove wrought iron out of production, and the precision sheet-rolling and varnish gives a more predictable product than wrought iron.
Hmmmmm...mmmm.... now I'm wondering if the shift from 25Hz to 60Hz power might have followed the shift from WI to sheet-steel. Of course the main reason was the Electric Light and its flicker, but maybe WI was adequate at 25Hz and new Steel allowed a shift to 60Hz and smaller cores.
> get one of the nickle iron alloys rather than pure iron anyway.
You can certainly make door-bells and solenoids with mild steel. Its hundreds of times better than air. I've always wanted to wind a transformer with soft steel wire core. But almost any serious transformer application will be better with one of the "electrical steels", the trade term for steel that has been alloyed, rolled, and tempered for transformer/motor uses rather than for bridges or shelf-bracket uses. And power-iron has a different balance of features than audio-input iron: power-iron has to work at very high flux with low loss but distortion is unimportant; input iron wants high permeability at low flux, and distortion is critical. Much power-iron (including large audio outputs) is just steel with silicon to increase its resistance, and careful rolling and annealing to bring out the magnetic property. Small-signal tranny irons are witches-brews of odd metals and artful processing.
