Wikipedia quotes Bob Woodward's Fear : Trump in the White House, writing:
Former Australian Prime Minister Malcolm Turnbull successfully lobbied President Trump to get an exemption at the 2017 G20 Hamburg summit, arguing "[w]e do this steel that's specialty steel. We’re the only one that produces it in the world. You've got to let us out. You’ve got a $40 billion trade surplus with us. We’re military allies with you. We’re in every battle with you.
I'm interested in the specialty steel part of the quote. Especially the part "We’re the only one that produces it in the world." Is there a specialty steel that's only produced by Australia or is this made up?
Next generation ZINCALUME® steel’s patented Activate® technology introduces magnesium into the aluminium-zinc alloy coating, improving galvanic protection by activating the aluminium. The result is a tougher protective coating that's more resistant to scratches and scuffs encountered during construction.
Since BlueScope is the assignee of some steel production patents, for example US 8840968, others are prohibited from infringing.
There are many specialty steel variants, and no doubt at least some of them are patented by Australian firms and therefore cannot be sourced from other places.
Also, the exact composition of the raw materials (any source will leave its trace contaminants) can have an effect on the resulting alloy, and Australian steel mills are going to source their raw materials from other sources than those in other countries, especially they're going to have a larger proportion of raw materials from Australian sources.
So yes, it's quite likely that Australia produces some steel alloys that are unique to its steel mills.
And it's likely that at least some of those alloys are important to US industry in certain applications, else that US industry wouldn't be importing them which no doubt is more expensive than sourcing steel from say China or India, or from the US itself.
Of course you can't prove a negative. It's impossible to prove that none of those patents are being infringed somewhere, anywhere, and leading to another steel mill in say Vietnam producing an alloy that would have identical physical and chemical properties to the point it would be considered the same alloy.
Mind that an alloy is not just defined by its chemical composition but also by its physical characteristics, especially the crystal lattice of the steel (yes, metals have a crystal lattice as well), all of which help define things like tensile strength, brittleness, melting point, electrical and heat conductivity, resistance to corrosion, etc. etc. etc.
Not really ; mixing zinc and aluminum in steel coatings has been around over 40 years. Different compositions will have different physical and chemical/cathodic properties , anyone can claim theirs is the "best". Look in Woldmans' Alloy Index; of the many thousands of listed alloys,possibly half can be called some type of carbon steel - It doesn't take much to copyright an alloy name.