Questions about a broken vise
Most vices have a handle scaled to match the force they can apply. Never do them up with extra leverage in other words. 

I've broken an old but good quality vice before, but by pulling against it with leverage rather than using its own handle. 

If it's new and you used it as designed, take it back. I did when I snapped a G-clamp using its own handle and got a refund on that and the identical one I bought at the same time and wouldn't trust.