MIL-H-6875

[metman]

I searched here under FAQ's, Forums, and Links with no results.

As I recall, this specification covers most categories of heat treatment for steel but I think it has been superceded by another spec e.g. AMS...?

I am advising a friend to Normalize a 4130 weldment for an experimental airplane and will recommend he specify it to be Normalized per MIL-H-6875 or the currently applicable spec if someone can tell me the current specification designation.

Thanks in advance for help

 

[redpicker]

Asking more for my own information than to question your intent, but why normalize a 4130 weldment? Wouldn't a sub-critical stress relief provide a more consistent properties (particularly with respect to toughness) and get away from the problems of decarb and reisdual transformation stresses from normalizing?

I don't deal with 4130 weldments, so I am really just looking for information.

rp

 

[metman]

Normalized microstructure will be more homogeneous (consistent) than a sub critical anneal (stress relief) for welded 4130. As for residual stress you are correct it will be more uniformly stress relieved as you stated because air cooling during normalizing is likely to produce some variation in residual stresses but not to a signifant degree.

One of the reasons to specify 6875 is for control of decarb.

I would expect toughness to be better for normalize than stress relief since again the structure will be more homogenous. Normalized 4130 is used extensively for aircraft parts and the properties are well established.

 

[kenvlach]

MIL-H-6875H HEAT TREATMENT OF STEEL was superseded 2 Feb 1999 by AMS-H-6875 Heat Treatment of Steel Raw Materials, plus heat treatments for 4 classes of finished steel parts: AMS 2759/1 thru 2759/4.

In some cases, unless using inert or protective atmosphere or vacuum, the spec. for raw materials requires removal of a surface layer of material.

 

[TVP]

Even though it is obsolete, you still can obtain MIL-H-6875 using the following link:

http://assist.daps.dla.mil/eAccess/index.cfm?ident_number=6191