I don’t know but I have seen warnings about using aluminum or copper lines as they do not have the burst strength. I’d guess that adding nickel to the copper would make it stronger. I just saw some copper nickel lines when I googled brake lines after I bought the set I bought…
Not steel with copper and nickel. Have you seen the buildings with rusted exterior panels? That’s what you get with copper intentionally added to steel. The oxide is tight to the iron surface beneath. Other than that, copper is a tramp element and renders the steel unusable for anything but the lowest cost applications, like nails. I’d say it is a copper nickel alloy.
Along with 6 or 7 other alloying ingredients:
Here’s some good info on the copper Nickel brakes tubing. @jtsanders is correct, not a steel allow. Almost completely copper and nickel, in the ratio of 90% copper to 10% nickel. Minor amounts of other stuff.
“The copper-nickel alloy used for brake tubing typically contains 10% nickel, with iron and manganese additions of 1.4% and 0.8% respectively”
It looks from the link below to a good choice for a diy’er install, as it is claimed to be easier to work with. No sure what the price premium compared to mild steel is, or if there is a price premium.
https://www.copper.org/applications/automotive/brake-tube/brake.html