Please find below reply I received from the technical manager at the mill.
It is not entire good English but I guess it is understandable.
I have forwarded your other questions as well but perhaps this reply give a bit more clarification.
- Traditional cleaning up: is performed in a bell oven with gas heating is followed by a cooling in oil tanks or water where the bars are immersed. Then follows tempering through reheating in Bell-shaped gas furnace and cooling in air
- Remediation in an induction furnace: the furnace is a tunnel of electromagnetic inductors, and advancing the bars (one behind the other) in the tunnel are heated by electromagnetic effect. Following cooling by water spray. Finally it runs the tempering consists of induction heating in a tunnel oven (as before) and cooling in air.
The reclamation in the induction furnace is the most uitilizzata (for measurements up to approx 160 mm) as much less expensive than the traditional.
The circular cracks on the head (typical of this kind of remediation process) are generated due to the effect of the edge, in fact, here the material cools much more abruptly generating precisely these circular cracks that cause the detachment of a ring materiale.
we say again that the material is absolutely free from cracks that can disturb utilisation of work of this.