Help with ASTM Specification for Decarburization on 8620H Forgings

[Maui]

What ASTM specification covers allowable decarburization limits on 8620H forgings for use in gearing applications? I don't have access to the necessary reference materials to look it up, and was hoping that someone here would be able to identify it. Thanks.

Maui

http://www.EngineeringMetallurgy.com

 

[dbooker630]

At our facility we follow SAE J419. Type 1 free ferrite is to be avoided, otherwise the decarb cannot affect subsequent heat treatment.

 

[Maui]

dbooker, thanks for your reply. But it looks like that is a method for measuring decarb, not a standard that establishes how deep it is allowed to be on an 8620H forging. I know that there is a spec somewhere that establishes these limits, I just don't have the ability to look it up where I am at the moment. Does anybody happen to know the relevant ASTM spec?

Maui

http://www.EngineeringMetallurgy.com

 

[dbooker630]

Yes, SAE J419 covers measurement methods, the parameters I note are from our own internal specs. I did a search of ASTM standards in the IHS database using 'decarburization' 'forgings' and 'steel' as key words, and found A290 and A291 specific to gear forgings, A837 for alloy steel forgings, A711 for general forging stock, A788 for steel forgings that are carburized. I could not find any decarb limits called out. If you have any other keywords to suggest, feel free.

 

[TVP]

Arthur,

I have reviewed every ASTM standard related to steel forgings, but cannot find anything on decarburization limits. ASTM A837 Standard Specification for Steel Forgings, Alloy, for Carburizing Applications shows grade 8620, but there is no mention of decarburization or limits. ASTM A788 Standard Specification for Steel Forgings, General Requirements is the general spec for steel forgings, and there is no mention of decarb here either. Two other forging specs for gear applications, A290 and A291, similarly do not reference decarburization limits. The only one I could find that even mentions decarb is A579 Standard Specification for Superstrength Alloy Steel Forgings, but only as a Supplemental requirement, and even then the purchaser still has to specify the limits. Perhaps you are thinking of an SAE AMS or other standard.

 

[metengr]

Perhaps the AGMA (American Gear Manufacturing Association) has a relevant standard for incoming forging stock. I looked at three AGMA standards and could not find decarb limits, only hardness criteria.

 

[redpicker]

I have never seen any material specification that detailed decarburization limits. I have seen them in product specifications, but not in material specifications.

I suspect the reason is because the assumption is made that the surface of a forging will have to be machined if a decarburization-free surface is required, and since the machining allowance is greater than the decarb depth, it is not an issue. In these cases, specifying a decarburization limit on the forgings would be seen as a wasteful and unnecessary requirement. In most forgings I have dealt with, folds and laps in the forged surface are of a much greater concern than decarburization.

I have seen product specifications that require "chemical milling" of all forged surfaces, presumably to remove all decarb from surfaces that were not practical to machine. I found this to be unusual, however, and in general, surfaces that must be free of decarb are machined after forging (and final heat treatment, unless HT is performed in a controlled atmosphere).

rp

 

[CoryPad]

AGMA 923 Metallurgical Specifications of Steel Gearing identifies decarburization limits for final gears, but not forgings.

ASTM F2282 Standard Specification for Quality Assurance Requirements for Carbon and Alloy Steel Wire, Rods, and Bars for Mechanical Fasteners is a material standard that provides limits for decarburization for a starting material prior to forging.