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Coating on pilger mill mandrels

Dear,

I work in a company that produces seamless tubes by a pilger mill process. We have some problems in the inner surface quality when we produce high nickel tubes as Inconel 600. The surface appears with tears or orange peel.
Following some recommendations we coat the mandrels with AlTiN and the results were the same, no improvement. Also we found deep marks on the surface mandrel in the rolling direction. It's not easy for me to understood which kind of particle could mark this very hard coating. The mandrel is made of ASP 30 steel with 66 HRC.
Could someone give me some idea about these problems, tubes surface quality and coatings.
Thank you very much

Diego Del
Engineer - Bs As, Argentina
October 6, 2010

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Nickel alloys are extremely tough and very difficult to machine more so to form.
Your situation relates to localized pressures, local generation of heat, temperature rise, friction-welding?
Perhaps the coating you mention is not thick enough. Have you investigated other substrate materials with less affinity to stick weld like tungsten carbide and other coatings such as whisker reinforced ceramics or perhaps DLC?
G. Marrufo-Mexico

Guillermo Marrufo
Monterrey, NL, Mexico
December 11, 2010