These are silver brazed onto steel shanks; the silver used is plated onto a thin copper sheet, the copper serves as a cushion for the carbide blank; the blank is placed in a step machined into the shank, everything having been thoroughly cleaned with a solvent, then generously fluxed with silver solder flux, the silver (shim) is placed on the shank, the blank on the shim, and the shank is heated with an oxy/fuel torch from the bottom to a low red, then some on top until the silver flows, then using a tool, such as a old screwdriver or awl, pressure is put against the top of the blank until the silver solidifies, then the tool should be put in a place to cool slowly until cold, then it can be ground.
Where I served my apprenticeship, we made up thousands of tools in this way for facing and beveling steel pipe, and also used them in our machine shop for heavy roughing jobs and interrupted cuts, they had 1" square shanks. First the torch was used for brazing, then later they bought an induction brazing machine, where a shaped water cooled coil partially encircled the tip of the tool leaving the area on top in the carbide blank exposed; set it up, push the button, and the machine would cycle the required time to heat the tool, cycle off, and (the operator) would manually push the blank in place; a few minutes in a day's work.