Any decent silver alloy and flux will do the job. I've just done some scraping tools, and have a few more to do. Use a diamond something to really clean the carbide where you want the alloy and make sure the fit is decent with the steel. Flux the heck out of it. When heating keep the flame off the flux and the joint. Heat both pieces pretty evenly until the alloy flows. Did I mention that pre-placing the alloy in the flux at the joint is highly desireable???
I've done lots of this over the decades and it's never failed for me. The tri-foil is only really necessary when brazing a big flat area like a big carbide on a big shank.
Hey, worst is you mess it up. Then melt it off, clean it up, and try again!!
Pete