Steel NDT 4

[LeonhardEuler]

I have a high strength hardened 4140 steel component that has been struck with a hammer during install and there is concern that the material may have been damaged. What would be the best type of NDT to do on this component to make sure the material isn't damaged. Would ultrasonic testing be sufficient?

 

[racookpe1978]

Is there any visible damage to the "object"?
Is the FUNCTION of the steel "object" impaired by any scratch, ding, dent, bent-over section, or chip?
What does the object do? (Is it a shaft or tool holder, or a table leg? A nail or a precision-adjust threaded rod for a telescope?) Can it still "do" the job it is intended to do?

A soft iron nail, for example, has been known to work effectively after being struck by a hammer. The hardened edge of a piece of tool steel has been known to be ruined by being dropped on a tile floor.

 

[WARose]

Ultrasonic is a pretty good place to start. In general, it can detect cracks and other types of damage.....it can also establish the yield strength of the material you are dealing with. I've heard it can also establish the residual stresses from such impacts.....but i personally have never asked them for that bit of info.

 

[dhengr]

WARose:
“Ultrasonic is a pretty good place to start. In general, it can detect cracks and other types of damage....” Should read… ‘and some other types of damage and discontinuities and mat’l. thickness.’ Stop. You better check around a bit to find out how they use UT to determine yield strength and residual stress, I’ve never heard of that. It would be interesting to know how they do that. If the OP’er. can’t define the problem and the damage any better than he has, who knows what testing methods would be determinative, a pregnancy test or a litmus test might be just as good.

 

[RickyTickyTavi]

A positive pregnancy test on a steel structure would be quite alarming and fascinating.

 

[WARose]

Stop. You better check around a bit to find out how they use UT to determine yield strength and residual stress, I’ve never heard of that.

The former I have had done.....the latter I have heard of (i.e. seen a few Journal articles on).....but never seen.

EDIT: @OP....if you have trouble finding ultrasonic tester that can do that. Another option is: there are some that can determine yield & residual from making tiny indentations in the material. One such company:

https://www.uskoreahotlink.com/products/testing-inspection/ndt-tensile-strength/#NDT-Residual-Stress

 

[Ron]

Being struck by a hammer would produce a very localized issue at or near the surface. For this, use magnetic particle or dye penetrant inspection to determine surface cracking...otherwise, the limited strain hardening resulting from a hammer strike is likely irrelevant unless you have significant repetitive stress and reversals.

 

[dhengr]

WARose:
Thank you for the heads-up and new info. I’m finding some of the same articles which you are citing and seeing. I’ll have to read a few of them because I have not heard of these approaches before. Thanks again for the enlightenment. Otherwise, as first, fairly simple tests for what little we know about the situation I would agree with Ron’s thinking and approach.

 

[oldrunner]

Lets see now. AISI 4140 has a ultimate strength 95 ksi and is known for it's toughness and impact resistance. So how heavy is the hammer and what is the acceleration/velocity guess for the impact load? Is the hammer head impact surface flat or rounded? Take the worst case and run an impact force against a small area and estimate the ksi and then compare the result against the yield strength. Then decide whether its worth the cost to investigate.

But we did do one of these investigations on some sort of impact event on the bearings and pins of a large crane. Took months: Did all kinds disassembly and tests and inspections and the result was no damage.

 

[LeonhardEuler]

The situation I have is a hinge on a cantilevered structure that shows no visible damage. I suppose the concern would be that there could be micro fractures developing in the material that could grow over time? From what I’ve read ultrasonic testing should be able to check for this

 

[LeonhardEuler]

There are 3 high strength hinges that support the whole structure

 

[Erik Panos Kostson]

High frequency ultrasonic surface waves known as Rayleigh waves are very sensitive to surface defects. This is because most of the energy is on the surface. Other ndt methods for surface defects are dye penetrant and eddy current's. There are others also , e.g., magnetic particle inspection, that is popular for surface breaking defects. Of course for defects to grow you need to have fatigue loading and stresses that will open and tens the cracks to grow.

 

[Ron]

LHE....ultrasonics will not detect microcracking...at least not with conventional ultrasonic crack detection....that should be done by metallurgical microscopy. While that can be done in place, it is not easy and not cheap, as it must be done by one experienced in this technique. This requires polishing and etching in-place and then microscopic examination of the grain structure. If you can show the grain, you can generally show microcracking.

 

[LeonhardEuler]

So let's assume the component was hit hard enough to cause some microcracking and it will see fatigue loads through its lifetime. I need to check the material to check if there is damage and the extent of the damage. I will be able to take the material off site and test it, but would rather not if possible. The material is painted with a zinc based paint. The best way to check for material damage not visible on the surface would be... metallurgical microscopy?

 

[WARose]

I'm not sure of the particulars if the situation (i.e. size, fatigue stress range, etc)......but if you are worried about micro cracks (as opposed to deep cracks) why not used a reduced allowable stress range (like a welded structure) to compensate? People fatigue load welded structures every day and they are loaded with micro cracks.

 

[LeonhardEuler]

I'm trying to figure out what type of damaged I should be worried about and how I should check for it. There's concern that the material might be damaged and I need to suggest what should be done to ensure it is safe, whether that be give an explanation why there is no concern, or suggest a method of NDT.

 

[FLCraneBuilder]

In my part of the world, Ultrasonic testing costs $85 an hour with 4 hour minimum
For $340, we could be discussing testing results instead of approaches.
Do the test & get back to us
we can then discuss if further considerations needed

 

[Tmoose]

"high strength hardened 4140 steel component" .

Did you folks design the part/component? Almost certainly the entire part is not stressed equally.

https://www.esrd.com/wp-content/uploads/AeroModel1.png

https://www.simscale.com/forum/uplo.../3ca397c2a907ef776ca0c56e8ebd2f7c888a33d8.png

And if there is more than one hinge, and the hinge(s) support a door with the pins vertical, the loading is likely NOT shared equally.

http://3.bp.blogspot.com/_DB1URW97jPw/TT-Y4Ygs2kI/AAAAAAAAAFo/-_SxtaK64_Q/s1600/hinge2_2414.jpg

Do you have some particulars of the steel in question? Including certs?

The mechanical properties of Q and T 4140 can cover a mighty wide range.

http://www.timkensteel.com/~/media/4140HW_Brochure_July2015_Update

10% or greater elongation is typical, so as other said, I'd expect denting, mushrooming, upsetting or bending if any damage was done by the hammering.

Prehardened 4140 ain't that fancy. And if much depth of machining is done on PH 4140, the less-hard core remains to do the work.

When you say hinge, I think of a 3 piece device. Two leaves and a pin.
Are all the pieces "high strength hardened 4140 steel .?
Depending where the hinge was struck, and why it needed to be struck for installation, I'm thinking there are a couple of general areas that would suffer, so the fist locations in need of NDT.
- The point of impact, PreZOOmAbLY on a leaf.
- The pin/leaf interface.
- The pin, the second presumptive hammering point, installed for assembly, and perhaps responsible for a mis-strike if a very tight fit..

 

[Ron]

FlCraneBuilder...that's conventional UT flaw detection....this requires a different approach and equipment. Would be more expensive.