You might wanna check.
because he's given different answers over time to that question.
Here below for example he says SpaceX
is going to 304L for starship, in parts at least, and for a while at least.
He's also said 4 months later that due to alloy tweeks traditional names might not fit exactly for the steel in the future...
That said- the question was really about if CT and Starship will use the
same steel... and that seems pretty unlikely. The conditions and stresses the two will be put under are quite different... so I'd expect a custom, but different, alloy for each as the primary steel used... (and yes, using more than 1 type for certain specific parts wouldn't be surprising either as Elon alludes to about starship in the first tweet for example).