Re: [CAD_CAM_EDM_DRO] Re: Metal selection 101

What kind of color(s) does this alternate hardening process of yours
provide?

If none, do you have a different easy to use method for hardening that will
impart the colors?

Smoke

>Smoke wrote:
>
>> I think the best method for hardening the 8620 is color case hardening.
>> the process is simple, leave a nice looking HARD surface and a soft inner
>> core.
>
>Not quite true. Color case hardening quenches into water directly from the

carburizing mixture and is guaranteed to lead to

>microcracking. Indeed this method has been used successfully for years but

in today's enviroument with too many attorneys I think

>better methods (as below) are more defensible. i.e.
>Carburize, cool. reheat and quench or do the double reheat mentioned in my

previous post.

>According to : "Met Trans", Vol 4, p 1195-1200.
>
>per previous post:
> low number of stress cycles high number of stress

cycles

> 1. 200 ksi 155 ksi

quench from 1550

> 2. 250 180

cool, reheat, quench from 1550

> 3. 325 260

cool, reheat, quench from 1550, reheat quench

>from1450.
>
>> treatment #3 had about half the retained austenite of treatments 1 & 2.

This is where the dry ice treatment has a chance to

>> really do some good in driving down retained austenite. :-)
>
>BTW - surface hardness was somewhere between Rc 60 and 65 for all three

treatments.

>
>I doubt whether carburizing in charcoal/calcium phosphate or gas

carburizing makes much difference.

>
>I hope this makes it a bit clearer than my orginal post.
>
>Dave
>
>>
>> This is ideal for firearms receivers as the soft core helps prevent
>> shattering of the receiver(in your face) if an overloaded cartridge

happens

>> to be fired in it.
>>
>> Smoke
>
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