In principle, I'd suggest sea freight ought be cheaper, as it's...

In principle, I'd suggest sea freight ought be cheaper, as it's far slower and ships can carry far more than a 6000 tonne (gross) Australian 1800 metre long intermodal or steel train.

The national standard gauge network for carting steel is not perfect: the Melbourne-Sydney-Brisbane lines have many curves and some gradients slowing trains, and some of the trackage is shared with passenger (intercity and interurban) and numerous other freight trains, such as intermodals carrying containers only, plus grain, cotton, cement and the occasional special passenger working for heritage groups.

However, generally the rail operators do a pretty good job: QUB won a contract from Pacific National for steel, but both now carry some, including from Port Kembla (Qube) to Brisbane and Melbourne, and up to Newcastle (Pacific National, to/from Whyalla SA. A lot of steel is also carried by rail across the Nullarbor to Perth WA.