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Another casting failure

Another casting failure

(OP)
Continuing from this thread: http://www.eng-tips.com/viewthread.cfm?qid=418786
Taking the sound advice & opening a new thread as it's a different part.

This casting failed over the holiday break.




Here are the shots of fracture surface:




All these ridges and facets, does this look like "rock candy" fracture? I'm thinking of asking for Al and Boron content tests.



Why is there this different layer on the outside?? Brittle fracture inside then ductile failure on this shinier layer??


Other side survived.

The casting will be in town from the site next week, trying to get my head around & see if there's any obvious hint what happened here.

Thanks for looking & your comments highly appreciated.

RE: Another casting failure

just an unofficial observation.
it appears to me that with out knowing the the drawing requirements, in other words the detail of the material type, the manufacturing requirements, and any process that involves such as heat treating, chemical processing, the specification of the material. and the non destructive testing requirements. it is a guess. there should be the starting points. what are the allowable defects, what are the allowable porosity requirements. what are the non destructive and destructive test results. basic under standing of the casting requirements. next should be stress and strain analysis. make sure the load requirements are adequate.
I can not help to notice strange oxide over the failed areas. I would expect it to be a clean bright surface. I admit I am not a casting specialist but these are common sense approach ideas.

RE: Another casting failure

.appears to be ductile overload failure. There appears to be cold deformation

RE: Another casting failure

The fracture morphology looks more to me like fracture began at the weld repair. The origin you identified could be a second origin but more likely it was an extension of the crack that started at the weld. Without knowing the base material of the casting, I want to ask if 309 is an acceptable material for such a repair. Does it have compatible thermal expansion/contraction properties with the casting material? Why did a repair have to be performed there in the first place? If a crack was present as the reason for the repair, are you sure it was completely removed at the time of repair?

RE: Another casting failure

309 stainless steel has been used for local weld repairs to castings and even wrought components over the years with the thinking that PWHT can be avoided because of the inherent ductility associated with the filler metal.

I do not agree with this approach because you have a locally hardened heat affected zone to contend with that can be susceptible to cracking during welding or in service.

RE: Another casting failure

(OP)
Material is cast steel (Avg 0.2% C, 1% Mn, 1.8% Ni, 1% Cr, 0.4% Mo) with yield strength of minimum 700 MPa.

Repair weld was done by the foundry without our knowledge, we found out only after it failed.
Foundry is supposed to tell us before doing any kind of repair. We are using this foundry for the first time & they seem to have some serious issues.
We usually do not use stainless wire for our weld repairs.

On a side note we have asked a third party to do detailed failure analysis, they will be starting work from next week. I'll update with their finding as soon as I get them.

Any hint what these big steps in fracture face indicate?


Thanks.

RE: Another casting failure

The steps are called ridges and are formed from multiple fracture planes.

RE: Another casting failure

Quote (metengr)

309 stainless steel has been used for local weld repairs to castings and even wrought components over the years with the thinking that PWHT can be avoided because of the inherent ductility associated with the filler metal.

I do not agree with this approach because you have a locally hardened heat affected zone to contend with that can be susceptible to cracking during welding or in service.

I agree with both statements. 309 and 312 filler are often (mis)used for repairs. While strong and ductile, it still leaves traces in the base materials that cannot be discarded.

http://www.fusionpoint.be
http://be.linkedin.com/in/fusionpoint

RE: Another casting failure

Sounds like these are being made just for you.
Are you requesting/requiring test coupons for each pour that will be subjected to mechanical testing?
Regardless, maybe cutting some test coupons from the failed ( and a few un-failed) pieces and testing them is in order.

ASTM A488 / A488M - 16 Standard Practice for Steel Castings, Welding, Qualifications of Procedures and Personnel

ASTM A27 / A27M - 13(2016) Standard Specification for Steel Castings, Carbon, for General Application

ASTM A781 / A781M - 16 Standard Specification for Castings, Steel and Alloy, Common Requirements, for General Industrial Use

RE: Another casting failure

emonje ... thoughts...

Based on the tool-bag in the background, this looks like a very large casting [several hundred #s], with very deep/thick sections.

Based on the chemical analysis this material looks mostly like carbon steel with modifiers for casting and heat-treatment [strength].

I am astonished that this thick-section material could be safely/consistently heat treated to yield strength of minimum 700 MPa [Fty 102-KSI min].

I suggest Your lab do a full mag particle inspection of each piece. I would NOT be surprised to see surface crazing/cracks all-around the land around the saddle where the fracture faces are located.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

RE: Another casting failure

(OP)
"Sounds like these are being made just for you.
Are you requesting/requiring test coupons for each pour that will be subjected to mechanical testing?
Regardless, maybe cutting some test coupons from the failed ( and a few un-failed) pieces and testing them is in order."

These castings are our own design, material is also of our in-house specs.
We do require the foundry to do mechanical tests on test coupons from each pour & their test results are showing things within specs..
We have also asked for thermal history & waiting for them.

Third party will do tests (including mechanical) on failed part starting from Monday.

Thanks.

RE: Another casting failure

(OP)
"Based on the tool-bag in the background, this looks like a very large casting [several hundred #s], with very deep/thick sections. "

Yes it's a quite thick casting. I should have included some dimensions, my apologies.

The section that broke is 100 mm thick.

RE: Another casting failure

emonje ...

Was the casting statically loaded, or unloaded, during this time?

IF this casting and alloy are proprietary to Your company, can we assume that they were fully/jointly 'characterized' [several castings statistically sampled] before use, for mechanical and physical properties, such as: X-Y-Z orientations for Ftu, Fty, Fcu, Fcy, Fsu Fbru, Fbry, e, E, KIc, Charpy impact, as cast/HT'ed, as-welded, within service temperature ranges [example for MIL acft: -65F to +160F]. Also, were the [dimensional] expansion/contraction rates characterized [X-Y-Z orientations] within the designated service temp range, etc?

Any idea RE lowest temperature that the failed casting reached 'during the holidays'?? Carbon steel fracture/impact toughness typically decreases rapidly with decreasing temperatures... especially with certain impurities and/or miss-processing and/or geometries and/or constraints.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

RE: Another casting failure

Where was the casting made ??? Which foundry is responsible ?

MJCronin
Sr. Process Engineer

RE: Another casting failure

Was the pin that passed through the two aligned holes bent after the failure?

The location of the failure would seemed to indicate the casting yielded, possibly bending the pin. Just curious.

It is difficult to tell for sure, but is it possible there were two welded repairs, the tack weld to the right in the photo and a weld to the left? The left edge of the lug looks similar to the tack weld on the right side.

The weld interface between the type 309 weld deposit and the casting would constitute what is called the mushy zone where there is partial melting and alloying between the filler metal and the original base metal. The chrome and nickel from the 309 filler metal would increase the hardness of the mushy zone due to the increase in the carbon equivalency. Even without an increase in Ce, the HAZ would form a metallurgical notch. Such a notch without an increase in hardness could still be a cause of crack initiation.

It would seem that it would be better if they had made the repair with a low hydrogen high strength low alloy electrode (8018-B2L) or a low hydrogen welding process using a high strength low alloy steel filler metal. That would mitigate the increase in Ce in the mushy zone and the associated higher hardness assuming the contractor used appropriate preheat before welding. Small repairs, without the benefit of preheat on a thick casting, could still experience high hardness if the weld cooled quickly. Did they repair the casting using 309 filler metal with the mistaken belief that preheat would not be required?

Best regards - Al

RE: Another casting failure

(OP)
WKTaylor (Aeronautics)
6 Jan 17 17:51
"... Any idea RE lowest temperature that the failed casting reached 'during the holidays'?? Carbon steel fracture/impact toughness typically decreases rapidly with decreasing temperatures... especially with certain impurities and/or miss-processing and/or geometries and/or constraints. "

The part was in use when it failed, we don't know yet exactly which part of the cycle it failed. It gets loaded gradually then picked up & then the load dumped.

Operating temperature rarely goes below 20 degrees Centigrade, & always well above 0.

RE: Another casting failure

(OP)
"MJCronin (Mechanical)
8 Jan 17 14:29
Where was the casting made ??? Which foundry is responsible"

This is the first time we got castings made by this foundry.

We never had any such issues in castings from our regular foundry. They were bit too busy so we decided to try this new one. On paper they looked good but now it seems we should stick to our proven supplier.

Unfortunately some legal mumbo jumbo stops me from disclosing names & locations of the foundries.

RE: Another casting failure

(OP)
"gtaw (Structural)
8 Jan 17 16:26
Was the pin that passed through the two aligned holes bent after the failure?
.................
Small repairs, without the benefit of preheat on a thick casting, could still experience high hardness if the weld cooled quickly. Did they repair the casting using 309 filler metal with the mistaken belief that preheat would not be required?"

The pin was not bent. We haven't measured it but it looked as straight as when it went in.

The foundry that did the repairs are being very sketchy about what they did & how & why.
We require the suppliers to let us know of any required repairs & we usually use combination of pre-heat, low Hydrogen wire & GMAW to do such weld repairs. This new foundry apparently went rogue with procedures.

RE: Another casting failure

From a similar event,
the outcome of the failure analysis was
Brittle fracture, due to
a) too coarse a microstructure (grain size being not to spec) --> manuf. error
b) de facto non-killed --> manuf. error
c) (hidden) welded spots (construction enterprise welded in some alignment bars and cut those off & ground away the stubs, however the metallurgical notches remained) were the starting points of the fracture.
The complex structure of the part will bring a multi-plane stress state, so adding to a metallurgical analysis a thorough check on load and load direction and perhaps a load / stress analysis might be adviseable.
Regards




Roland Heilmann
Lpz FRG

RE: Another casting failure

(OP)
An update, just got hands on some preliminary mechanical tests results:



Material is too brittle, for Charpy our specs ask for 40J at -40 degrees C. Also Tensile strength is some 200 MPa below our minimum requirements.
Chemical analysis meets specs, so may be they didn't tamper it to high enough temperature?

RE: Another casting failure

Was it heat treated at all?
Maybe you should try to HT some samples as see what you get.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Another casting failure

(OP)
It was supposed to be quenched & tempered, the foundry is being very sketchy with what they did. We are not going to use them anymore.

RE: Another casting failure

2
Looking at this from a foundry perspective. With a 700MPA yield I am assuming this is a 120ksi/100ksi (tensile/yeild). How thick is the part? It looks pretty beefy from the pictures. What specification did you order it to? The chemistry looks like a 4320, which is a good match for the section and mechanical requirements. Where did you take the mechanical samples from? Was there any evidence of porosity in the tensile and charpy specimens?

The reason I ask, material properties out of castings are not directly comparable to the test bar results. Test bars are over rigged to ensure no imperfections in the metal. If you ordered to a specification that allowed for standard 1 1/4 x 1 1/4 sized test bars to represent such a large casting that may not be appropriate. You will see a large difference between the part and test bar properties. If you ordered to a spec that required and equivalent round test coupon like API or ASTM A1001 the properties will be better represented but still can differ from the actual part depending on where you took your test coupon. The API and ASTM A1001 require the test coupon to be taken at (1/4)T (API) or (1/8)T and (3/8)T for A1001. You should not be taking the samples out of the direct center of the section thickness.

Any porosity in the sample coupons will give you low ductility and low impact values. That porosity may be completely acceptable per the specification. That is why we should be careful when comparing mechanical results out of parts.

Now 31 ft-lbs at -40° out of a 120ksi material is pretty stout for a 4320 material if you expect that out of a test coupon 4" or above. If, the mechanical coupons show no evidence of porosity at the fracture surface and the test coupon were taken near the 1/4T section, from the tensile results it looks like the quench was not adequate to completely through harden.

On the weld repair. 309 is not the proper electrode to weld repair this material. Any weld repair done should have underwent PWHT no matter what filler metal was used.

RE: Another casting failure

How cold does the part get in service, and was it at the time of failure ?

RE: Another casting failure

(OP)
Rarely gets below 10 degrees Celsius where it works. It was a hot day, above 20 degrees C when it failed.

RE: Another casting failure

40J at -40C is really high spec, this part must have been tempered wrong. Not sure if it met the hardness spec, cant see in the image? Possibly temper embrittled going by the low CVN values, SEM would identify any intergranular fracture on the surface to confirm.

Any microstructure results you have would help to understand further.

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