Yep, crane chain is very hard to cut. I've said before I worked for an overhead crane company back in my salad days, and MOST of the hoists we sold were chain hoists (the thing going the lifting is the hoist, which rides on a trolly, which in turn is often on a bridge, which rode on the rails, and the whole thing is a crane) We used to get the chain delivered in cardboard 55 gal drums. The prefered method of cutting it was a big disk grinder (7 or 9" if I remember right), but we'd use the dinky 4.5" grinders in a pinch. Bolt cutters wouldn't touch it. If we couldn't use a grinder, a cutting torch worked wonders