Soldering and Colouring Steel

Calgang, I have soldered sterling to mild steel using silver brazing
flux, brand: Comweld, but that may not mean anything where you are.
I ordered it through my hardware store. I have used H, M and E
solder quite successfully but it is horrible stuff to work with.
Even with adequate ventilation and enclosing safety goggles it makes
my eyes sting and water and that could just be me, but I normally
don’t have problems with other fluxes. Hope this helps.
Christel in West Oz

Calgang, it occurred to me that you might not know about brazing
rods. One can get bronze and brass in various formulations and sizes
to use in joining steel. It is generally sold by the pound at the same
welding supply store where oxygen tanks are taken to get refilled.
This material is not used like solder (making into balls, picking them
et cetera) but is used like a welding rod, heating the fluxed steel
(using various flux techniques as recommended by the seller) then
letting the rod drip into the joint. Excess metal is then ground off
and the joint cleaned to remove flux if any is present.

One could not use them to join steel to silver due to silver’s low
melting point, but it works well joining steel to copper and to
bronze. Once the technique is known it can be used with silver wire
solder fairly effectively.