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topic 31430

Hy-Tuf Steel Machinability & Hardenability

A discussion started in 2004 but continuing through 2018


Q. Machining Hy-Tuf in the Normalized & Tempered state (311BHN )has issues … the material is 'gummy' and has a tendency to build on the edge of cutting tool inserts, producing surface-finish issues and broken inserts. Is there a cutting tool geometry, or intermediate heat treatment process that can improve the machinability of this material?

Pete Owen
Mfgr Engineer (Aerospace) - Oakville, Ontario, Canada


A. Hy-Tuf (SAE AMS6418 [link by ed. to spec at TechStreet] or AMS6425 [link by ed. to spec at TechStreet]) has optimum machinability in the Normalized & Tempered condition, although your hardness is a little high-- a maximum of 285 HB is recommended. This is obtained by tempering at 1200 °F (650 °C).

You didn't provide any information on the current setup, insert types, etc., so all I can provide is some general information. Coated inserts will provide better lubricity and reduce the formation of built-up edge. TiN is a one such coating. Have you investigated multilayer coated tools such as the GC4000 series from Sandvik? No matter what, you really should discuss this issue with your tool supplier.

Toby Padfield
Automotive module supplier - Michigan

July 18, 2018

Q. A question has raised regarding the service life of a carburised down the hole drill bit manufactured from this material.
It has historically been quenched and tempered and occasionally carburised and tempered at 540 °C.
This appears to give reasonable service life.
How would the material respond to 'air-quenching' after carburising?
Would the dual phase structure still be achieved which is the inherent part of its designed durability?

gary weppner
heat treater - perth, western australia

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