I am trying to repair a door from a wood stove from the shop. The frame looks to be brass and the inside is mild steel. Cleaned everything up and planned to tig braze with silicon bronze filler. Ran a test piece on mild steel and ran fine. Tried on my project and it doesn't stick to what I thought was the brass.

Using my cst280 in lift tig mode at 100 amps tri-mix tungsten and dcen. I tried between 75 and 125 amps and all the same result. What am I doing wrong? I have some pictures attached.

There is a lot of rust on the steel but I cleaned it up along the brazed section and also ground down to fresh metal on the bronze.