Frankly, I prefer to do braze welding rather than fusion welding. Braze welding is done at a much lower temperature so the distortion is far less and it is possible to join dissimilar metals using an active flux. The nickel silver bronze rod produces a joint that is tough and as strong as the mild steel tubing that is being joined.
Overheating the joint produces intermetallics and a weak, brittle joint so experienced weldors need to learn the new technique as it is not at all the same as they are familiar with. One disadvantage is that nickel silver bronze rod is expensive, particularly the ones containing a small percentage of silver but the silver promotes fluidity and is worthwhile. Finding this type of rod is not easy these days. It used to be commonly available from All-State, Eutectic, and others. The last 5 lbs I bought from Washington Alloys.
Braze welding forms a nice bead that distributes the joint stress over a wider area than TIG and its HAZ (heat affected zone) is not as dramatic if a gas torch is used. It is not as effective on 4130 according to an old Lockheed report that I found years ago.
