Have you ever faced the situation of removing a broken-off bolt, such as Grade 8? I personally experienced this while restoring an old farming implement. MA Ford offers a line of solid carbide drills specifically designed for this task, as well as other challenging drilling operations. Dubbed 'Hi-Roc', the screw machine length drills come in most common fractional, wire, and metric sizes. Even though they are solid carbide, they are tough enough to handle the rigors of production environments, as well as salvage and reclaim operations too.
Another trick that I have used with broken bolts that are flush with the surface is a fist full of standard size nuts. Generally the same size as what you are trying to remove. While holding a nut at the end of the broken stud use a mig welder to put a few tacks inside the nut. Usually this process needs to be repeated a number of times for a success. You will need to be careful not to weld to the base material. This process works exceptionally well when steel fasteners are in aluminum blocks or heads on vehicles.