Interesting question and I'm afraid there is unlikely to be an answer here, which reviews the development and methodology of twist & crolle tubes
https://docs.google.com/document/d/1...Q/edit?tab=t.0
I believe the intent of combining iron and low carbon steel was for the elasticity of wrought iron with the strength of steel.
I've never seen a description of twist or crolle tubes using only steel.
I suspect after decarbonized/Bessemer steel was in general use in the 1870s, then Siemens-Martin (Open Hearth) steel in the 1880s it was much simpler/cheaper to bore out rolled rods.