You probably cranked too hard. But don't feel too bad. These modern vises are pretty poor quality. They're not built to last, which is why you often can pay as much for an old vise as a brand new one.

Two years ago, I bought a cheap Irwin face vise. It worked fine up and generally felt like a well-made vise up until about three months ago, when the threads in the cast iron stripped out. I was in the middle of a new bench build, so it wasn't a huge deal, but it did make building the new bench more difficult since I was without a vise for about a month. Not granted, I put that vise through a lot in those two years, and when it worked, it worked great. And I didn't pay much for it, so I wasn't expecting it to last forever. But I was expecting more than two years.

I think they do alright with the steel parts, but the cast iron parts just aren't made with the same quality as in the old days. Either way, all of my new vises (leg, wagon, and Moxon) are designed so that the screws can be easily replaced, because I bought the cheap Lee Valley and Woodriver screws for them, so I'm planning on them failing one day. I could have gone for Benchcrafted hardware, but I did the math and I can replace all of my current vise hardware 5 times over and still save money. Though, if I only get another two years out of them, I'll probably go ahead and make the upgrade.