Porosity on 347SS investment casting 1

[alphavince]

Was wondering if any anyone has experienced porosity/microshinkage with SS347 investment castings. These defects are visible in FPI and concentrated
in pockets, cores, holes etc. Any help would be greatly appreciated.

 

[metengr]

Yes. Acceptance criteria should be used to disposition surface defects, which depends on end use. Did you take an RT (x ray ) of a casting to evaluate soundness?

 

[alphavince]

Thank you for the reply. Yes x-ray was
Performed and casting meets grade. Is there anyway to
Minimize or eliminate these defects

 

[metengr]

Check melt degassing practice, pouring temperature, cooling and cleanliness of the mold.

 

[arunmrao]

Agree with metengr's observations. Check your charge, ladle, and design of the moulds with respect to gating and feeding.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[alphavince]

Thank You, agree with you comments. We degas, verify our pouring temps for every mold. These defects are only visible on inner cores. Outer surfaces of part are very nice.

 

[EdStainless]

Look at core practices, are cores coated? dried? how long are they allowed to sit before use?

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P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

alphavince...

What specification are Your castings being produced to?

ASMH 1309 for Type 347 [UNS S34700] and Type 348 [UNS S34800] CRES lists the casting version for these two alloys as CF-8C [UNS J92710]???

The only specs that I could find for CF-8C [= CF8C] are as follows

AMS5364 Steel, Corrosion and Heat-Resistant, Investment Castings 19.5Cr - 10.5Ni - 0.65Cb (CF-8C) Solution Heat Treated - UNS J92710

ASTM A351 Standard Specification for Castings, Austenitic, for Pressure-Containing Parts

ASTM A488 Standard Practice for Steel Castings, Welding, Qualifications of Procedures and Personnel

ASTM A703 Standard Specification for Steel Castings, General Requirements, for Pressure-Containing Parts

ASTM A743 Standard Specification for Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General Application

ASTM A744 Standard Specification for Castings, Iron-Chromium-Nickel, Corrosion Resistant, for Severe Service

ASTM A781 Standard Specification for Castings, Steel and Alloy, Common Requirements, for General Industrial Use

ASTM A985 Standard Specification for Steel Investment Castings General Requirements, for Pressure-Containing Parts


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]

 

[alphavince]

We are using the AMS specs. As for the core idea, we do not use cores on these parts - we shell the cores.

 

[WKTaylor]

alphavince...

AMS2175 Class/Grade ????

Per AMS2175
3.1.1 Determination of Classes and Grades
The cognizant engineering organization shall establish the class and grade(s) for each casting design in accordance with
1.3). If the grade of casting is not specified on the drawing or other contractual document, Grade C shall apply, except for
Class 4 castings, where Grade D shall apply. Sections of a casting may be of varying grades depending on the applied
stresses to that portion of the casting. Particular attention should be given to areas that contain, or will eventually contain,
stress risers after machining (such as sharp internal corners, holes, or notches).

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]

 

[alphavince]

Class 3, Grade C

 

[EdStainless]

Sounds like you either need better degassing and/or venting.
You aren't letting out-gassing from the cores to escape.
And poor melt degassing makes you more sensitive to this.

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P.E. Metallurgy, Plymouth Tube

 

[alphavince]

I don't think its a gas issue as we characterized the indications as micro-shrinkage through micrographs

 

[EdStainless]

Are your cores too strong and not collapsing as the metal solidifies?

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P.E. Metallurgy, Plymouth Tube

 

[alphavince]

The cores are only .250" in diameter, so they are solid shell once they finish our dipping process.

 

[WKTaylor]

alphavince...

I took a hard look at AMS2175 for Class 3C. Based on Your description I am NOT convinced Your castings meet 3C quality requirements. However, IF they do, then You may have 'gotten what You paid for'. IF Your finish-machined part meets drawing requirements and NDI's OK, then 'it is what it is'... even IF the appearance is not 'ideal'. IF your finish-machined parts can't pass final drawing requirements, then a higher quality requirement [more stringent casting quality controls] might be in order.

Is the caster's shop in a high humidity environment? Make sure Your cores and molds are baked dry and [as mentioned] that the melt is thoroughly degassed before pouring.

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]

 

[1gibson]

RE: humidity, did someone bring a swamp cooler into the foundry?

 

[tbuelna]

Took a look at AMS 2175. Section 8.8.17 discusses types of shrinkage conditions. Table 4 provides penetrant inspection acceptance criteria for microshrinkage discontinuity limits in Grade C castings, including several exceptions listed in the footnotes. Worth taking a closer look to see if your castings might meet the acceptance criteria.

Microshrinkage is often due to local solidification conditions. Changes to the cross section transitions or geometry of the casting, changes to the local shell thickness of the mold, or any other change that will provide a more uniform solidification rate in the local area would be helpful.