in rigging a shackle is horseshoe shaped piece of steel that has a bolt going across the open end. it is (typically) rated for a specific load. occasionally the bolt will be deformed (over loading) or seize in it's threading for some reason (or the head broken off)
heavy duty bolt cutters are often used in rigging for a variety of things, one of which can be cutting wire rope of diameters larger than cable shears will manage easily.
so, you -can- cut some really burly chunks of steel with bolt cutters, but it requires a bit of effort.