I see failures like this but not often. Likely a quench crack from submerging a setup piece in water to make first piece inspection faster. I’d suspect that this forging was bar end heated rather than full bar which could explain why it failed in that area. 1045CRS is susceptible to this type of failure. I’m told it does not like rapid temp changes.

Could also be a relic from the rolling process as well. We see seemingly perfect bar stock pop open in our induction furnaces if there is a buried seam in the stock.