Induction Hardened Steel Surface Etch Pattern 2

[MOB1]

I have seen two applications where the induction hardened surface of an alloy steel part of round cross section has a distinct circumferential pattern when polished and etched with Nital.
One of these applications was a press brake roll which I observed some years ago. The etched surface showed bands of dark and light. The light bands were approximately 6mm wide and the darker etched bands approximately 2mm wide. Can anyone enlighten me as to the induction hardening process which produces this pattern?

 

[swall]

It is not clear to me as to whether you are describing the surface of the roll or a metallographic cross section. For what it's worth, the surface of cylindrical parts that have been induction hardened using a scanning process rather than single shot will exhibit striping or "barber pole" effect on the surface.

 

[inductionexpert]

The surface etched pattern is the hardened zone. A 6mm is a 3 kHz depth. When using induction we refer to kW's and kHz the kW is how much power & the kHz is how deep it heats.

Also can get good results using a sand/glass bead or steel shot if acid is not desired.

The bands you see on the surface are the barber pole which the previous responder refers to. This is caused by the scanning motion and rotation that occurs during progressive hardening. Kinda like a prequenched area, only a few .002" thick, usually cleans up with grinding.