6" snatch block with hook

[metric_taper]

bilby layer

That's a new word to me, a search changed the spelling to Beilby layer. Lots of odd research on the effects of surface treatments, polishing, passivation, that affect the atomic surface structure, and seen with x-ray diffraction.
But I understand your use as to the welding resulting in a air hardened surface layer that would be an PITA to cut through with just about any cutting tool.
I've always found using form tools to be noisy from the cutting force vibration of the tooling.