Is that screw a true Acme? You know the Europeans have a thread they call trapezoidal, how far it varies from our Acme I don't know. But I have an FPU vise, and had it apart, my poor memory was of a 60 degree thread, but I'd be happier if it were Acme or trapezoidal. (PS I looked, it is a trapezoidal style thread)
I assume they know how to make a good vise in Poland, especially Bison. So I assume these are ductile iron castings, not what we normally think of as cast iron. Still, that dovetail flange did break, and it should not have as ductile iron. I wonder what brazing does to the metallurgy of ductile iron, I think it is up around 60K tensile strength.