Tolerance on Mechanical (Tensile/Yield) Product of WCB test results

[msmedesign]

I have been performing mechanical test on speciments from the actual product to verify mechanical properties of WCB cast parts. About 50% percent of the test results were lower than ASTM A216 WCB requirements. (within 10%)

I tested the foundry samples for the same heats and found all of them within the ASTM requirements.`Samples from foundry have been in the same heattreated.

Cross section of the parts that they fail the tensile test does not show any indication of local casting void which may lower the mechanical properties.

Micro edge test performed on each parts and all of them are ok. ( meets heat treatment requirements)

Both elongation and reduction area is within ASTM A216 WCB requirements.

Please let me know if it is OK to have lower mechanical properties on the actual product testing. Is there any technical article which explains the reasons, or if any body had similiar experience.
Thanks

 

[metengr]

What type of mechanical tests are you conducting? If you are conducting standard tensile testing in accordance with ASTM E8 test method, have you reviewed ASTM A 703 and A 370 for comparison and determination of mechanical testing for cast products? At this point, if you are within 10% of the reported minimum values with your product line test results I would not be too concerned because this could be a margin of error related to your test method, and one would expect some variability in test results with castings. This is why one should follow standardized testing format to compare results - I would carefully review ASTM A 216,A 703 and A 370.

 

[msmedesign]

I am performing standard tensile test per A370
ASTM A703 stated product testing acceptance criteria shall be agreed between manufacturer and customer, but no tolerance is given.

 

[GRoberts]

My experience is mostly speaking from large castings, but it would not be unexpected to meet the requried mechanical properties in the center of a large section. If you are dealing with thick parts, it is a different ball game. What size of castings are you dealing with? What sort of section thicknesses? How does the thickness of the test coupon compare to that of the castings? The main thing in casting testing, is to get the right test block and test location within that block specified. If the requirements are met at the proper location of a properly sized test block, then your casting will be able to meet the properties you want in the areas you need.

 

[arunmrao]

Have you referred the sfsa electronic publication on the same topic.

http://www.sfsa.org.

You can find a good commentary on the results obtained from keel blocks,integral test bars, sectioned castings etc. I hope you may find it useful.

Point raised by Roberts is also well discussed in this publication. You can download for free.

 

[swall]

msmedesign--it has been my experience with castings, that results from test bars cut from castings will frequently be lower than those obtained from the separately cast foundry specimens. Many specs are written that reflect this, often listing separate mech properties for specimens machined from castings. You should discuss your results with the foundry and then determine what they can do to meet your required mechanical properties.

 

[msmedesign]

Dear Swall
I want to review as many as possible technical documentation about this subject so that I can come up with a reasonable solution (technically sound) for both the foundry and for me and for my customers. Otherwise foundry would tell me it is OK as it is , end-user will require to meet ASTM minimum mechanical values.
I will be downloading and review the file form

http://www.sfsa.org

web-site as arunmrao suggested.

Please let me know if there is any other technical document that MIGHT BE HELPFUL.