But the problem with buying a baking steel from europe is that the postage is 100 dollars. I'm in Denmark and im too looking for a good stone/steel, since i just cracked 2 baking stones in 2 weeks

I've tried asking for A36, but no one has it and i have even been told that it's not recommended for using in cooking as it releases hazardous fumes.
Since everyone says that steel is superior heat conductor than stones and cast iron, i looked at the thermal conductivies of metals (Wikipedia).
Thermal conductivities:
Steel, carbon: 54
Cast iron: 55
Brass Cu63%: 125
Aluminium, pure: 204.3-250
Diamond (

): 3,320-41,000
So why is it that steel is preferred? Wouldn't it be way better to use for example Aluminium? Would also be nicer, since it weighs less.
How important is the thermal conductivity of the plate really?