AISI 4140 Alloy

[htfi13856]

I had a NAS1219-3-8 reworked, material called for Alloy steel, UNS G41400, By rework, i had them grinded down to a smaller length , Now I was told they failed inspection that my Rockwell was: C31-40. Is this possible?
Please help, any information or direction would be greatly appreciated.

 

[Sparweb]

I don't have my NAS look-up handy, and ASSIST isn't running at the moment, but assuming NAS1219 is a kind of threaded steel fastener:

Grinding heats the thing up. Were they blue when you were finished? The heat treatment won't survive the high temperatures that grinding generates. If you want to "modify" a bolt, do it on a lathe, or a mill. Even then, don't expect it to meet the rated strength (depending on what you do to it). The spread on hardness tests on NAS bolts is usually only a few numbers on the Rock-C scale, such as 35-39 for a 160-180 ksi bolt. These are usually specified on the NAS spec itself. RC 31 is way too low.


STF

 

[aviat]

I agree with SparWeb that it is not a good idea to grind the screws. It is better to cut the ends off. For a -3 there are hand cutters that would cut them to what ever length you required. However, that is not a recommended practice because it removes the end of the screw that has been cad. plated and exposes it to corrosion. Depending on the operating environment it could lead to problems removing screws in the future.

 

[htfi13856]

Thankyou for responding so quickly, I appreciate your input.
I do believe they were actually cut on a lathe,We had them shortened at an outside facility. After screw was cut down, we stripped the finish and replated per qq-p-416,tyII,cl3, everything passed, dimensionally and finish its just the hardness failed.
Is there anyway that you all may know of that i can get the hardness up to spec?
Or do we just scrap these and start over?
Any input would be helpful

 

[Sparweb]

At this point, I'm trying to guess why you didn't just order a shorter screw... I'm sure there's a good reason. If you shorten it too much then there's not enough thread engagement to be effective, even if you can solve the hardness problem.

How about hardness testing some un-modified ones? Maybe they started out that way...

The plating spec you reference doesn't match the NAS spec. Does QQ-P-416 create a black chromate finish?


STF

 

[RPstress]

I agree that they should be between RC 35 (maybe 36) and 40. The 31 is a little odd...it's not as soft as the normalized condition, but not really up to scratch strength-wise.

It would be wise to test some others for hardness. They're a bit small for machining into a little tensile test specimen. If they're down on strength, then you could have an issue with the supplier.

NB: minimum strength in NAS spec is the standard 160 ksi. The RC 31 should be about 140 ksi.

Hope you haven't wound up with "bogus" bolts...

-RP.

PS: if you did class 3 coating you could be a little thinner than the NAS spec specifies (class 2 is called for, which is minimum 3/10 of a thou; class 3 is minimum 2/10).