I have a difficult question. I am attempting to silver solder a 440C Stainless (AMS 5630) “doughnut” ring that is .5” long x .25” wall thickness onto a cast iron shaft. The .25” wall is not consistent and can grow to .45” on one side. The sstainless has been hardened to a Rc63-68 (knowing that I will lose some hardness out of the material). Both piece surfaces were sandblasted with a 1200 grit and have a .002” to .003” clearance fit. The shaft o.d. is .750"

I went to the local welding shop and they recommended a 4% sliver solder and a flux (flux is at my shop). I practiced on test pieces that were both steel (not the stainless) and results were very good. When heating up the test pieces and disassembling, they both retained a silver coating. When I try the stainless onto the steel, the solder does not seem to want to “stick”. It will flow into the joint, but it does not provide any metal bonding. The internet provides a million options. It appears as if the solder and flux that I have are not appropriate for the application.

I am getting the heat to it ~350 -375F. The solder appears to flow and go to the heat, but it just does not want to stick or make bond.

Suggestions for both a Solder and a flux please, part numbers, pricing, where to get the supplies....

Thank you and regards,