NickE,
Bi-Sn has a eutectic at 46 at% Bi (~60 wt%) composition & 138.5C; the liquidus at 58 wt% Bi is ~10F higher.
Probably all common solder alloy systems have eutectics. 45Bi-23Pb-19In-5Cd-8Sn maybe melt at a quinternary eutectic, but my books don't go that far!
cbert,
Does "non-eutectic alloy" mean a composition a bit away from the eutectic in order to give a 10F melting range? I.e., either a hypo- or hypereutectic alloy with a liquidus at 230F & a solidus (or eutectic) at 220F. Preferable to say 'off-eutectic.'
Giving a melting range makes it redundant to say 'non-eutectic;' a eutectic defines a single temperature.
[If looking for a alloy system w/o any eutectic (like Cu-Ni), probably SOL.]
Search for "solder melting range" & low-temperature “fusible alloys,” then look at temperatures. e.g., Alloy 16 in the 'Table of Specialty Alloys and Solders,' of composition 44.7Bi-22.6Pb-16.1In-11.3Sn-5Cd, has a liquidus at 126F & solidus at 119F.
For application, first Ni-plate the steel tube to improve solderability (not Cu, it may build up in the liquid metal & change the melting range). Then apply by soldering (for a small quantity) or hot-dip (large quantity) technique. Maybe necessary to have a surface layer of flux atop the liquid metal bath owing to easy oxidizability of In. Can also find a non-In-containing alloy.
Good luck,
Ken