The investigation is just beginning 3

[Tmoose]

The investigation is just beginning. I only have 2 pictures for now, and almost no details.

One brand new M36 "bolt" out of a litter of 26 snapped at installation.

The thread runout detail may not be the best. That will be part of the investigation.

The material nominally is hot rolled 1045, about Grade 8.8, but with yield strength more like 50% of UTS, not 80%.

The full diameter body bolts I've broken by tightening to maximum Moosage generally show some some necking as I recall.

 

[berkshire]

Tmoose,
were the bolts made in a far eastern country by any chance ?
B.E.

You are judged not by what you know, but by what you can do.

 

[IRstuff]

Counterfeiting, while prevalent, is not exclusive to the far east.

Seems like a thorough investigation of materials, annealing, etc. is in order, particularly if another one does the same thing

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[metengr]

Hydrogen embrittlement

 

[Screwman1]

Looks awful intergranular, but the part looks plain, so maybe some sort of SCC or dirty steel. There is no way that you should be able to break an M36 without a torque multiplier unless you are Arnold S.

 

[Ron]

Agree with screwman...intergranular corrosion and/or inclusions

 

[Tmoose]

The parts were made in early 2016 a shop in South Carolina, from hunks of 180 BHN 1045 HR steel bar provided by a US company with a custom material cert that states among other things, melted and made in the USA.

After machining about a year ago, and sitting in our warehouse the parts moved around by truck up to Canada where they were being installed Tuesday.

I learned that 6 bolts were installed fine, but the 7th the nutted stump snapped and flew away at high velocity awhile being tightened, allegedly to 1900 lb-ft.

I'm hoping to get lots more info over the next day or 2, and even the broken parts.

Wouldn't intergranular corrosion require a sophisticated nasty atmosphere to affect an unstressed HR carbon steel part?

 

[MikeHalloran]

Isn't it a little cold in Canada this time of year?


Mike Halloran
Pembroke Pines, FL, USA

 

[3DDave]

This is why I prefer the use of pullers and then snugging the nut - less chance for fly-aways and much better tension control.

I'd look for hydrogen as well. We had some steel belleville washers that were embrittled and could be snapped like a potato chip with finger pressure.

I don't see much runout on the thread - maybe it's the angle the photo is taken, but if it is short, then that would have been a stress concentration that would push it over the edge.

Did they just stop advancing and cut a ring groove rather than spiraling out? Sometimes the body is relieved after the threads to make the stress transition smoother.

It also looks like a really sharp root, also a nasty stress concentrator. Maybe this was the first one and the cutter was duller for the rest.

I would not trust any of them without inspecting them.

 

[RolMec]

There's just nothing to be seen of the plastic properties (16% elongation at break) of the material as if per standard, this here is seemingly pure brittle fracture.
Additional questions
- Have these bolts been hardened or tempered?
- What was the lubricant when nuts were tightened?
- Is there a washer under the nut?
For metric threads, to smoothen the notch at the end of the thread by a defined thread runout there's DIN standard 76. However, the bolt would need to be checked for the smaller diameter in the runout's root. dg would be 30.7 mm, pls. refer att. pic.
Another direction for improvement might be the bolts material. The tightening torque being approx. adequate to a 8.8 quality M36 slightly oiled at assembly, then is the 1045 in the chosen state adequate to this? Perhaps you could contact a bolt manufacturer for advice?
Regards

Roland Heilmann
Lpz FRG

 

[metengr]

One brand new M36 "bolt" out of a litter of 26 snapped at installation.

Folks, read the original post this is a brand new bolt. It snapped on installation. Either improper heat treatment or hydrogen embrittlement. Corrosion????

 

[dik]

As Mike noted... any Charpy testing of the material done? The cross-section appears to have a bit of a flaw. If critical, then all should be replaced and/or tested.

Dik

 

[Tmoose]

The "bolt" is machined from a bar of this stuff.

Here are the material certs provided.

 

[BrianE22]

I see "cast" in the cert. I assume that means it is a casting. Is that typical for material this large and highly stressed?

 

[Screwman1]

I'm not seeing that elongation at all on the failed part. The cert shows 18+% elongation and a 30% RA and it isn't there on the failed part. What sort of temperature was the part at when it broke? Could it have been below the brittle transition temperature? I find the yield point quite low for a 105ksi UTS, I would have expected to see something closer to 80ksi instead of the 55ksi that is listed on the cert.

 

[Tmoose]

The steel supplier said 1045-C1Q2 is their internal code for Hot rolled 1045 bar.

I believe the "continually cast" refers to the billet that was then patty-caked/hot rolled to an 8-1 reduction ratio.

I think Pretty much All us puny earthlings' steel forgings start their lives as castings.

https://www.youtube.com/watch?v=9AMbKpeJRoU

 

[Tmoose]

" I find the yield point quite low for a 105ksi UTS, I would have expected to see something closer to 80ksi instead of the 55ksi that is listed on the cert."

I'm Not very far into this, but I'm finding hot rolled materials often have similar Yield/UTS ratios close to 50%.

Here is good old A36.

 

[metengr]

Send the failed piece out for met analysis to determine the root cause of failure.

 

[gtaw]

I had a number of high strength bolts snap while being tightenedg when the ambient temperature was around 10 degrees F. When the workers waited until the temperatures climbed up to around 30 degrees, no more broken bolts. The manufacturer sent a sales rep to witness a few bolts being installed in the early morning and just like the ticking of the clock, snap, snap, snap. Each one failed during installation. We waited until after coffee break when the temperature was not as cold and there were no more failures.

Best regards - Al

 

[EdStainless]

I am not familiar with the fastener specs. Was this supposed to be Q&T, I see no HT notes at all.
Cut threads (I guess from the very sharp pictures) or rolled?
Were they even stress relieved after forming?
Not bad looking steel.
I sure didn't see 18% elong in the failure pictures.
Something doesn't add up.

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