Ah yep, I meant alloys that are reasonable to use for rail, including cost restrictions. I had heard that the TGV has welded rails rather than expansion gaps,

Ah yep, I meant alloys that are reasonable to use for rail, including cost restrictions. I had heard that the TGV has welded rails rather than expansion gaps, which necessitated a low-thermal-expansion alloy. But I don't anything about it beyond that.