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STAINLESS STEEL
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HOW CAN I TEST FOR DIFFERENT GRADES OF STAINLESS STEEL?
The reason I want to know is that my company manufacture machines used in the food industry and we have recieved a customer complaint regarding stainless steel rusting. We specify 304 grade but we would like if possible to know if there is an easy way to check the grade of steel supplied to ensure that our supplier is suppling us as specified.
PAT CURTISDIGI EUROPE - HAVERHILL, SUFFOLK, ENGLAND
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Yes but like all things it depends on how much you want to spend. You can buy spot testing kits £1000-£2000 which will let you do a test for alloy composition on a qualitiative present/not present status. This may give a guide. 304 having few trace elements will be difficult.
If you want to get up into the £20,000 mark you can start looking at something called an arc spark spectrometer that is quantitative and will let you positively identify the alloy grade. Only other method is to audit your suppliers.
Ciaron Murphy- Great Britain
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A basic test to understand if you have a 304 stainless or a non-corrosion resistant steel is with a magnet. 304 stainless is not magnetic while corrodible steels are, in general, magnetic.
John Hetherington- Canada
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I think the first response may be a bit over the top for your immediate needs. If you want to know if you have an obvious problem first check that the material is an austenitic stainless.
Two simple tests would be a magnet to check if the material is austenitic (304 is) (note:occ Austenitics have slight magnetic props but it should be essentially non magnetic).
Secondly I always keep a bottle of copper sulphate solution handy this 'spot test' will easily show if the material is 'stainless'; if it isnt a copper deposit should show after a few seconds. If you need more information contact a local test house who will perform an analysis for your for ~£50 - £100.
Nick Clark- England
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Was the stainless properly passivated after fabrication ? any 300 grade stainless will pick up iron from tooling or fabricating equipment that must be removed with a mild acid pickle. Is the stainless rusting at a weld inter-face? If so ,the welding process will deplete the corrosion resistance in the heat affected zone. Please ensure that when welding 300 series stainless,use a 310 stainless rod. The next time 304 is purchased. It may be advisable to order 304-L if welding is required. Also be aware that 304/301 grades will overlap in chem. NI,being much higher in the 304 grades.I would cut a small corner of the material and have it checked on a spectrometer, the cheapest way to go. On many projects we test a sample of the sheet or bar as a condition of purchase. Hope this helps.
John Musat- Clarkston, Michigan, USA