Questionable 80-55-06 Ductile Iron Certifications 1

[farmer2]

Dwg spec is 80-55-06. Received cert with castings as follows:
Tensile: 119,400 psi
Yield: 84,900 psi
Elongation: 6%
Chemicals: 3.63 C, 2.56 Si, .64 Mn, .01 P, .02 S, .02 Cr, .06 Ni, .11 Mo, .55 Cu, .04 Mg.
Hardness: 207 Brinell

Is it believable that tensile and yield are that high, and that elongation is still 6%? Are tensile and yield too high as typical ranges?

This is the same foundry that sent bogus 65-45-12 certs about one month ago on another casting about which I posted.

Thanks,

 

[arunmrao]

farmer2,
This appears to be yet another case of false certification. There are no alloying elements like Ni, Mo, Cu in sufficient quantities to achieve such high mechanical properties. Also 6% elongation is a dream figure at those strength levels.

My suggestion would be to destroy a casting and prepare a tensile specimen for testing. This will enable you to know the deviations before you decide to scrap the castings.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[dbooker630]

The 207 Brinell is typical for D5506 iron but the tensile and yield do seem rather high. Did the foundry quench and temper this material or is it as-cast?

 

[farmer2]

We talked to the metallurgist at the foundry about the high tensile, yield and elongation. He claims the high values are attainable by varying the Mo and Cu and the "way the castings shake out" whatever that means? Also, said the 80-55-06 are minimums so they meet the spec.

Of course, if we test these and they pass load tests, then production shows up closer to the minimums, there could be a strength problem, yet the foundry could say they met our minimums. They are going to send us an extra test bar from this heat for test by our local test lab. Would it be better to cut a sample out of one of the castings, as you suggested, arunmrao?

 

[swall]

I would do both. Depending how your spec is written, tensile test results from a bar cut from a casting may or may not be used as a basis for acceptance. But it would be good information to have.

 

[arunmrao]

For disputed results, separate test bars are never accepted. It has to be an integral coupon or a witness stamped test coupon. In the absence of the two,samples drawn from actual castings are used to recheck. My first step would be to do a micro and chemical test of a sample taken from the casting.

Also check the chemistry of the new test bar offered and the casting sample,this will let the cat out of the bag.(if it is there!!).

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[farmer2]

Here are the results from a test lab on a specimen cut from an actual casting:

Tensile: 74,500 psi v. 119,420 (cert)
Yield: 58,000 psi v. 84,927
Elongation: 2.9% v. 6.0
Hardness: 222 BHN v. 2.7

The chemicals also showed some large differences:

P .016 v. .01 (cert)
S .058 v. .02
Ni .08 v. .06
Mg .05 v .04
C 3.71 v 3.62
Si 2.25 v 2.56
Mn .64 Same
Cr .03 v .02
Mo .12 v .11
Cu .55 v .53

They offered a duplicate test bar, which was not sent, but I see no need to test one if sent.

The tensile and yield are not far off the spec for 80-55-06 but the elongation is way off. Does anyone see a reason for this? How close would you expect the test results from a test bar and a specimen from the casting to agree? The test specimen was .354" dia. Elongation was in 1.4".

Thanks,

 

[farmer2]

Correction to previous post:

Hardness: 222 BHN v. 207 (not 2.7)

I am thinking we should not use these castings or this foundry. Any differing opinions?

 

[farmer2]

Is the 6% elongation an absolute minimum and should we not use castings that tested to 2.9% elongation? Does anything in the chemicals explain the low elongation?

The issue of false certs is a big problem, but that aside, would these castings be acceptable? The tensile strength tested 7% below minimum but that alone would not be a problem.