selective carburization of 8620 1

[SpartanBill]

We received a drawing from a customer which calls for a part made from 8620 to be hardened and tempered to 190 ksi and case hardened in a specific area to 60 HRC. At first glance the notes seem redundant and I’m not sure 8620 can be heat treated to 190 ksi. While researching this I came across a Matweb datasheet which gives the core properties of carburized and tempered 8620 as 192 ksi with a case hardness of 63 HRC.

So, when a part is selectively carburized will the areas which have been masked to prevent carburization have similar core strength as the carburized section?

I have little experience in this area so any helpful information is much appreciated.

 

[tbuelna]

SpartanBill-

Any core material beyond the carburized case (ie. masked areas) will have a hardness determined mostly by the tempering process. I've attached some pages from the Jorgenesen Steel handbook that describe a typical carburize, quench & temper process for 8620, and the case/core properties that should result from it. Jorgensen recommends an oil quench from 1700degF and a 450degF temper for optimum core toughness. This should produce a core strength of 181 ksi and a case hardness of Rc58. If desired, a case hardness of Rc63 can be achieved by tempering at 300degF instead of 450degF. Although there is no mention of it in Jorgensen, the core hardness should also be somewhat higher by tempering at 300degF. As a guess, I say that tempering your 8620 parts somewhere between 300degF and 350degF should produce a core hardness of at least Rc41 (191 ksi).

Hope that helps.
Terry

 

[SpartanBill]

After comparing that to data for a similar mock carburizing process I have recommended the notes be rewritten to just the case hardening process.

Thanks for your help.