"Typically" the steel should break first.

Hello Chickwelder, to take your question just a bit further, you need to specify the filler rod classification that you are using and also the steel that you are welding. I say this because based on the type of electrode and steel, one may have a higher tensile or yield strength than the other. You should actually see the material stretch, if the weld metal is of a higher strength, the parent metal will stretch more and the weld will stand up from the surface of the bend coupon. If the parent material is of a higher strength the weld material will stretch more and the weld will sink down below the level of the parent material. In many instances the coupons will not break but will show the deformation that I described above. When coupons, welds, or parent materials break it is usually due to some form of incorrect welding procedure or trapped slag, or possibly insufficient voltage or amperage parameters that don't match a rod or wire manufacturers suggested values. Just a few more things for you to consider. Best regards, aevald

Also, it would depend on weld size. An under-sized weld would fail before the base metal. Fillet or groove testing would come into play. If you are testing Fillets and are looking for the weld to break and not the base metal, then a clean break from the center of the face to the root is what you would be looking for. This would demonstrate proper penetration at the root and fusion from the toes and along the leg lengths.