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Welded SUS430 part failed in salt spray test [Hong Kong] 

July 15, 2008

We made a t=0.5mm SUS430 rectangular tray, laser welded at the four corners. The box was passivated with a commercial product named MQ500 from Japan.

The box could only withstand about 8 hrs of neutral salt spray test. On the contrary, the original 430 sheet metal could withstand up to 120 hrs.

How could I passivate this box to withstand this test?

Lorin Tam
- Hong Kong

Lorin,
First I've heard of MQ500. What does it contain? Nitric acid? Citric acid? What concentration? How long did you have your tray in the bath and at what temperature?

For general passivation formulas and procedures, look to the specification ASTM A-967. Let us know if we can help.

Ray Kremer Stellar Solutions, Inc. Algonquin, IL, USA

MQ500 was suggested by my customer. However, the label on the packing revealed that it was for USU 3 series. The failure should be expected.

We tried citric acid 10% at 65C for 20 min. Still failed in the salt spray test but have a 100% improvement in time, from 12 hr to 25hr.

Could I have a recommendation?

Thanks.

Lorin Tam
- Hong Kong