You will need different flux for the high-temp material. I like the
black stuff.

http://www.jwharris.com/welref/faq/flux_chart/

Scroll down to Stay-Silv.

Ask for the the black stuff because most beginners initially
overheat the work and kill the flux. It also seems to work well on
stainless.


A year or so ago, I ordered some silver solder from MMC and
black flux because it was recommended in this group. Frankly
I tried the black flux and I don't it much so this
time I ordered white flux. The while flux was recommend by the
welding company selling the harris silver solder too.

I suspect I got some learning to do!

chuck