How to tell the difference between 303 and 316 Stainless Steel Bar Stock?

[ScottK]

We've run into a situation where a supplier has sent us one in place of another. To my eye, they look the same and the material cert called it out as it was ordered. We discovered it was not what is seemed after it had already been put on the machine and the machining properties changed.

What do you folks feel is a good, easy test to tell the difference?

We are using a hydrochloric acid test, but I'd prefer something without a hazardous chemical.

Resistivity? Hardness?

thanks.

 

[Kevin H]

Hello Discordian, a quick grade check shows: 303 has 0/0.15 % C,1% max Si, 2% max Mn, 8.0/10.0 % Ni, 17.0/19.0% Cr, 1% max Mo (which is an optional element),0.06 % max P, and 0.15/0.35% S and is annealed to 262 max Brinell Hardness.
316 has 0.03% max C, 1% max Si, 2% max Mn, 10.0/14.0 % Ni, 16.0/18.5% Cr, 2.0/3.0% Mo, <0.045% P, <0.03 % S and is annealed to 217 max Brinell Hardness.

The best way to tell the 2 apart is run a chemical analysis. Based on the above information found on the internet from 2 different sources, the least expensive/quickest way would be to run a hardness check. If you run one and got near the 217 Brinell hardness max or over it, you could identify material as suspect and run additional tests to determine the grade. A third method would be to get a sample to run a Leco C/S test - based on C & S results (primarily S) you should be able to identify as suspect - S>0.03% and OK - S< or= to 0.03%

I would not expect them to be any different in appearance.

 

[roland_lu]

Machine the 2 samples

Non-chemical ways,

Maybe you can try to machine or cut them, the experienced machine operators can tell the differences, if you are sure they are either 303 or 316.

Another way is to run electric spark spectrum analysis, it is semi-quantative, you have to have the equipment.

Wayback in the university (almost 30 years ago), we were taught that experienced workers could tell the carbon difference by using the grinding wheel, and S and P have their special colors when burned. I tried then, and could not tell .

 

[Wes Bucey]

I confirm the only true test is chemical/spectrographic analysis. Hardness test may be compromised by too many variables. I would NOT waste time trying to do this in-house (if you have to ask how, you are not qualified to do it!)

Let's put this in perspective:

• If you are buying bar stock directly from a mill, you have a legitimate reason (based on machinability observance) to return a sample bar to mill and ask them to confirm the analysis. Every mill will do this free of charge for mill-quantity buyers.
• If you are buying from a reputable steel distributor who only buys stock directly from mills, they will do the same thing.
• If you are buying scavenged goods from certain kinds of resellers, you would be best served by taking a "coupon" (a 10-12 inch cutoff from a bar) to a metallurgy lab and ask them to perform an analysis. This will cost you some money (get verbal "ball park quotes" by phone first), but armed with the results, you can either proceed to manufacture parts or stop and seek financial redress from the distributor while you obtain correct bar stock from a different source (with which you will include a test analysis as part of the contract.)

 

[Jen Kirley]

I agree that if you want to do the test in-house, the chemical analysis is best. Otherwise, a spectrographic analysis because the two are too similar to risk spark tests and hardness.

The supplier should do the test without charge since you have reason to believe there was a mixup. I would phone them with the request at once--do not waste any more time or use up more stock if it might be the wrong stuff!

The mill should be consulted right away because the swapped stock might still be laying around, or worse, going off to another customer mistakenly.

 

[Randy]

The taste test always worked for me when I was in aviation maintenance

 

[ScottK]

This is both a mill problem and an internal problem.
The mill has mixed the two on occasion and our receiving dept has lost heat ID tags.
The problem was always caught in machining because as roland_lu says "the experienced machine operators can tell the differences". But, of course, we need to catch it before it gets to the machine because we run CNC machines with bar stock feeders, 3 machines to an operator.

At any rate these are issues I was hired to help fix.

From what you're all saying the best bet is to just stick with the chemical test (which is also what the mill recommends).

Thanks for your input.

 

[ScottK]

The taste test always worked for me when I was in aviation maintenance

Hmmm... I'm relatively new to steel machining...

could you document the training process for this so I can teach my incoming inspectors?

 

[Wesley Richardson]

Portable X-ray fluorescence equipment is available that you may consider. This equipment can be purchased. If the need is infrequent, you can get a laboratory to bring the equipment to your facility and do the sorting. It provides a semi-quantitative result. With a built-in library of alloys, it should be able to provide alloy identification. Most do not work for the lighter elements such as carbon.

The disadvantages of purchase include initial cost, maintenance, training, need for reference standards, may not be able to distinguish two very close alloys, and depending upon the State, you may need to file documentation with the State radiation board. The advantages include rapid turn-around and ability to identify a wide variety of alloys.

Wes R.