[TowerTalk] 4130 Chrome-Moly Grades

[kb0fhp at comcast.net]

Depending on the specification:  Condition N is normalized and ready to be heat treated.  CDSR is stress-relieved.  More than likely the material is in a form similar to hot rolled, and not normalized for uniform microstructure.  It is heated to some nominal temperature to relieve any stresses from the manufacturing process.  The final commercial grade is an unknow, but I would suspect that it is simply as-received from the mill.  It would be in a microstructure similar to a hot rolled microstructure.  However, all these grades can be heat treated to fairly high strength and toughness - and would yield (excuse the pun) excellent results.  Another big difference between the grades is the amount of testing done - the AMS grades require more testing, but the alloy chemistry is essentially the same.  There may also be some difference in the inclusion content which would affect fatigue life and impact strength.  

As a metallurgist, I would feel comfortable with using any of the grades, especially if they were heat treated appropriately.  The best is probably the airframe grade, followed by the aircraft grade, and finally the commercial grade.  For the purpose of mast materials, the service is relatively low, with failure usually being overload instead of fatigue.  Any one of them would work....

Hope that helps

Scott, KB0FHP

-------------- Original message -------------- 
From: "Ron Hylton" <ad7l at hevanet.com> 

> Here in the Portland metro area, we have an excellent source of tubing from 
> a company called Tube Service. They offer several grades of 4130 alloy 
> Chrome-Moly tube, including: 
> 
> 4130 Airframe (Cond. N) Specs: Mil-T-6736, AMS 6360 
> 4130 Aircraft (CDSR) Specs: AMS-6371 
> 4130 Commercial Specs: ASTM A-519 
> 
> My question is, which grade is typically used for masts? 
> 
> 73, 
> Ron AD7L 
> Hillsboro, Oregon 
> 
> 
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