Anvils should never have sharp corners. They are bad for forging as they cut up work make sharp inside corners which forgings should not have. This can also create cold shuts. Sharp anvil corners also tend to chip off. From the factory anvils have a minimal chamfer on the edges which should be
dressed by the purchaser to a nice radius. On old anvils chipped edges can be dressed from the side and rounded to finish. Welding up edges to make them sharper is a cosmetic fix that should be avoided. - guru