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copper sulphate Tests in Stainless Steels

August 31, 2012

Q. I'm a mechanical engineer, I work with machining of dental implants and surgical instruments and I'm responsible for developing test materials in our products. I'd like to have a technical question about corrosion tests.

One of the tests is about corrosion in stainless steel class 5 (ASTM B899 - precipitation hardening). I need help on the test run of copper sulphate [on eBay or Amazon]on UNS S45500 and UNS S46500 stainless steels, i.e., whether it is applicable or not and why. I consulted several standards (ASTM A380 , ASTM A967, ASTM F1089, etc.), publications, some labs and nothing yet.

Need to test for corrosion our (company) finished products. The applicable standard for such tests is ASTM F1089 (Standard Test Method for Surgical Instruments). However, this standard was based on the procedures of ASTM A380 and ASTM A967.

One of the tests required in these standards is the test of copper sulphate. My question is whether this test is applicable to stainless steels UNS S45500 and S46500 (ASTM B899).

Why this question? Because this is a point that is not clear in the standards cited. For example, in section 17.1 of ASTM A967 is indicated that this test isn't applicable to the stainless steels "series 400", but enables the execution in hardened steels by precipitation.

If you can help me with this, I'll be very grateful.

Thanks,

Felipe Soares
- Sao Jose dos Campos/SP, Brazil

A. Felipe

The copper sulphate test is good on PH steels with 16% or more chromium. There is an advisory that the test not be used on parts for food processing, so you might consider the safety of parts tested.

An alternate would be a high humidity test or alternating water immersion test. A scientific incubator can work for the high humidity test.

Reference ASTM A967

Willie Alexander
- Colorado Springs, Colorado
September 4, 2012

September 5, 2012

Q. Dear Willie,

First, thanks for your reply.

Initially, I thought the same. But then I realized that this statement "more than 16% chromium content" refers only to ferritic stainless steels. This is due to intergranular corrosion. Outside of this rule could cause a "false positive."

In this case, I was thinking the following:

If stainless steels UNS S45500 and S46500 belong to that "400 series", Ok, no need to run these copper sulphate tests.

Otherwise, it would be recommendable to perform tests of copper sulphate in them.

Another interesting fact is that these stainless steels contains titanium in its compositions. Based on the knowledge, the addition of titanium in austenitic stainless steel alloys improves in the aspect of intergranular corrosion.

But I think these facts are not enough to solve this issue. Why?

Because the ASTM A380 and ASTM A967 have not followed the evolution of ASTM F899. So, it would be very important to alert the ASTM committees about it.

However, I'm sure there are explanations for all this and we'll find out. I really believe that.

Best regards,

Felipe Soares
- Sao Jose dos Campos/SP - Brazil

A. Felipe,
I think I'll just echo Willie on this. Both 455 and 465 are 400 series grades with under 16% chromium content. There is not enough chromium in grades like this to ensure that an iron free surface is possible. Which is to say that even with the best passivation possible, you may or may not get a "fail" condition with the copper sulphate test, and therefore a "fail" doesn't mean anything. (Although a "pass" is still a "pass", so if you can achieve that, it's perfectly fine to hang your hat on the copper sulphate test.)

Unfortunately, there is not much communication that takes place between the ASTM A committee that handles ASTM A380 and ASTM A967 and the F committees that handle ASTM F1089 and ASTM F86, etc.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

September 19, 2012

Dear Ray,

First, thanks for reply.

Q. So, unless I try to take advantage of a "pass", it doesn't matter perform this test or not. OK?!

Surely that committees need to communicate better so that not occur these inconsistencies.

Best regards,

Felipe Soares
- Sao Jose dos Campos/SP - Brazil
September 21, 2012

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