Heat Number on CofC - Stainless steel tube

[Graham1967]

Hi,

I have recently come across a problem with stainless steel tube that failed tensile testing, but the supplied mill certs stated it was within spec.

I was looking at a cofc from a different metal supplier, for the same material, but were actually from the same mill. Although 2 years apart the heat number of the mill certs were the same, but had a different batch number.

When I checked the chemical composition of the two mill certs they were exactly the same, but showed significant differences between the mechanical tests.

Questions are,

Can the same heat number be in different batches of material?

If a material is of the same chemical composition is it possible to get different mechanical test results?

Do mills keep back material for such instances where the validation of the results can be checked at a later date?

Thanks

Graham

 

[Sidney Vianna]

Chances are you have a counterfeit material with a counterfeit certificate. If you got the material from a distributor, you might want to reach out to the mill themselves and verify the two certificates. Certainly you can have material with the same chemical composition and different mechanical properties. That's achieved via refining the metallurgical properties of the steel through a series of processes. For stainless steel, the possibility of heat treating is not as much as carbon steel, but it still can be done, depending on the grade of the stainless steel.

There is a reason why counterfeit detection and avoidance is becoming an issue of quality management system standards in higher risk industries.

 

[CCaantley]

We just ran into a huge issue with a falsified material cert. A product we produce requires 304L stainless (less that .03% carbon) which the cert said, but after several failures at our customer, a chemical analysis was performed and it was found to be 304 stainless at .06% carbon. Huge headache, physically and financially.