Distinguish Between 202 and 304 Grade Stainless Steel

I'd send a sample to a local testing lab. That'll cost you a coupla hundred bucks (US) but, if you need to reject a shipment (and maybe even seek past damages), you'll need an outside verification.

I agree, you'd be making a guess, at best. Most sheet SS is marked at the mill. So if your not getting what your paying for, you need an independent lab to confirm this. At which point you could threaten a law suite. See how fast you get the right stuff then.

thanks guys..you're both right..though we would like to conduct preliminary investigations first and then go on with the real deal in case we find significant results. that might save us some cash. we can go to my school as i think we ask them for help and that they have material testing equipment there that we can use for free. im just not sure if there's one for this case. we're actually materials engineering students doing internships in this company so maybe we can ask our school for help. any specific tests you got in mind?

Hi jbp422,

My first thought was to go to the chemistry dept. and see if they can use Atomic Absorption or Ion-Coupled Plasma spectrometry to test for the individual elements and their concentrations. Then you can pinpoint what the composition of the alloy is.

Best Regards,

Mike

I'd run through some of the physical/thermal/electrical properties and look for one that your school has equipment for. The other thing is that 202 is kind of a "wastebasket" nomenclature that covers a lot.

But, anyway, is there something happening that causes your boss to suspect the vendor is switching? That might be the thing to test.

I understand you're only interns, but there is a sort of rule in engineering that, if a thing is worth doing, it's always cheaper to do it right.

"But, anyway, is there something happening that causes your boss to suspect the vendor is switching? That might be the thing to test."

-nothing as of yet but he said a lot of companies do this today and that's why he asked us to research on it. ive been searching the web on this and i found little info. i might try testing it for corrosion and mechanical property. i also might try some compositional analysis although that may be more tedious and im not aware of any method to do it.

"I understand you're only interns, but there is a sort of rule in engineering that, if a thing is worth doing, it's always cheaper to do it right."

-yea i'll keep that in mind. thanks.

Hey, I am an engineer and have had to deal with this before. Check out Stork MMA. THese guys will do full chemical analysis for about 50 bucks. It will take a week or so. Another option is using an x-ray diffraction instrument and checking for manganese peaks (your university should have one, stand alone or in their SEM as an EDS or EDX unit). Buying a hand help model of this for work would be 30 or 40K. Yet another option would be to measure the resistivity, though this would require a special high resolution tester, or special made samples. Hope this helps.

Thinking about it a little more, I think you should be able to tell by the Mn levels, but I'm not enough of a chemist to know how to do that easily. Any help out there?

Depending on what you want to see ASM Handbooks recommend etching with either a Modified Murakami Etchant or a solution of HCl Acid, Selenic Acid and ethanol. The Murakami etchant should give you just the grain boundaries, and the acids/ethanol etchant will color carbides and gamma phase particles because of the selenium.

You could get an approximation using EDS/EDX. Better results would be obtained by some spectroscopy method. I'd suggest OES if there is enough material and ICP if the sample size is small. The difference in Mn content should be listed in the UNS requirements for the two alloys S30200 and S30400. The nominal compositions can be found at matweb.com if you search by UNS number, but the acceptable ranges should be listed in an UNS book.

You can never be sure, but I believe the 200 series has more ferrite in it and would be is more magnetic.

WARNING: This is from memory, which isn't reliable from time to time.

Also ask for the heat numbers of the material from the vendors. They use that for tracablity for ASME built products.

phoenix911

I don't think that these two could be sorted by spark testing.

milo

If you heat both above the normalizing temp and immediately quench, the SS 304 should have a higher Rockwell Hardness (~70HRB vs 60-65HRB).

And, of course, somebody has to be the crabby old engineer and ask, if it's so dang hard to tell them apart, why bother?

Dear Crabby ol' Engineer,

Cost and corrosion resistance.

Sincerely,

Ornery Young Engineer

Well, that's a way to tell them apart then: read the bid prices and stack the stuff out in the rain.

A very simple test is to dip into a mixture of 50% hydroclorick acid and 50% sulfuric acid

mixed with 200 % water, leave sample in solution for 24 hours then wash, dry and inspect finish with magnifieing glass or microscope and look for degrading on finish

A) which would be most degrading?

B) Source of 200% water please?

milo

S30400 is austenitic and non-magnetic. It has excellent ductility and impact resistance even at cryogenic temperatures. When cold worked, S30400 becomes slightly magnetic

S30400 bar is less expensive than S31600 bar because it does not contain molybdenum.

So,we could judge by the magnetic.

Hi,

We are using 304 and 430. We encountered mixed material before. The only way we sort it out is by magnet.

304 is not magnetic and 430 is magnetic. SO the finish goods was sorted by just using a magnet. It if stick, then its 430...

Somebody in the forum says that 202 is more magnetic, so maybe u can just try it out..

in my opinion the only way is to make a chemical analisys (PMI) both series 200 and 300 are non-magnetic.

S.

Corrosion Control & Corrosion Protection

Yeah, I know - seems like nobody has read my post #6.

Mike

The question is not between 304 and 316 its between 304 and 202.

WHat is quantifiable magnetic discriminant for 202 and 304?

Units please?

milo

Dear Milo , the 300 series and 200 series stainless steels belong to austenitic stainless steels.

there commonly are not magnetic in the 300 series and 200 series stainless .

That was my point, how would magnetic properties distinguish between these two grades as originally asked?

milo

Dear milo,

sorry,I have error message above speaking.

now I have understand your idea, we have not distinguish between these two grades by the magnetic.

by the way, I have never happen the issue as the author, we customarily requrie that the supplier offer the material testify.

I have a idea, if the spplier use the 202 substitute 304, we could consider that the 202 can or can't use the products, by Comparison, e.g. composition, mechanical property, Physical Properties, Machinability, Corrosion Resistance, Welding and Heat Treatment, Temperature Range, industry standard etc, maybe we could ensure the products quality and reduce cost.

Today is one of chinese feast.

Have a good day!

Do enjoy your feast DAy, Mr. Wei.

I enjoyed the food every day when I was in China for 10 days in 2003; I can only imagine how good it will be for you on the special occassion.

peace.

milo

Realy, you like Chinese food ? ha ha

If you have chance, I will welcome to Chengdu, the panda home,at the same time, you could eat the especial food in the Chengdu.

Best Wishes,

Henry

It is my hope that I will visit once again.

If it is possible, i will look you up. Tell me about the industries that are in Chengdu.

milo

Industry in Chengdu is less-developed,there are not many Famous Manufacturing Companies. but I work in the natural gas technologies.

I looking forward to visit Chengdu.

Henry

316 stainless is magnetic.

Dear Janissariers,

Please read the following depiction, you could find the answer

S31600 and its casting version, CF8M, are 18-8 stainless steels with molybdenum added to increase pitting and general corrosion resistance. Due to the higher chromium and nickel content, S31600 has better high temperature strength than S30400. S31600 is completely austenitic, whereas CF8M contains some ferrite. This accounts for the slightly magnetic properties of CF8M. S31600 is non-magnetic.

Best Wishes,

Henry Wei

Thank you.

I know stainless steel is non-magnetic and I know it is because of some added propertied are what makes 316 magnetic.

The point is that when you order 316 it will have some magnetic properties to it. That's just the nature of it.

Having been in sales of metals for over 20 years- the only sure test is a to send the material to a lab. 202 is a catch all spec. The statement regarding companies switching materials "nothing as of yet but he said a lot of companies do this today and that's why he asked us to research on it" is very incorrect if you are using a reputable metals company. Only secondary junk houses switch materials. Stainless should come with MTRS and be line marked with grade, HT # size etc. This procedure is part of the material spec. If your suppleir can not guarantee the material it should be replaced by them or they pay for the testing if there is a doubt. If they can not I would switch vendors.

I would start by asking for documentation on the materials, you can find out allot from a heat number and a MTR. A few phone calls with a MTR number/heat number should/may find out if it is legit. Is the material marked? I would tell my superior that we need to invest in a quality control manual and involve receiving as the final inspection station. if it passes the inspection and is marked correctly then and only then, pay for it. If it does not meet your pre set criteria, send it back. I administer an ASME repair program for my company and our criteria for purchasing and receiving is to the standards of the ASME codes. Does you P.O. to the company require them to follow your rules such as supply a MTR with a valid heat number marked on the material? If not then you need to change this it doesn't cost any more for this documentation. If the supplier is forging documents to cover up the substitution then you must SEND IT TO A LAB. You will need the lab reports when you confront the sorry company for a refund. The last thing is that if you do find the supplier is doing a substitute then no matter what they do to make it right never buy from them again! I would not be able to ever trust them in the future, they only get one strike when it is my companies reputation on the line. Forging documents is against the law, people can get hurt by this. If this is the case then I would not suspect but one of the chain of suppliers is involved so if you talk to a supplier up the chain then you may be able to find out where the switch was done at. You can do this investigating for free and it may solve the problem with out going to the lab and paying for a analyses.

pipewelder

I agree that chemical analysis is the only sure way to determine if you have 202 or 304. 202 has 7.5-10 Mn and 4-6 Ni whereas the 304 has 2 Mn and 8-10.5 Ni. See if your university has an SEM with EDAX on it. Using EDAX on an SEM should give you a close enough chemistry to tell the two material apart also.

As a preliminary screening test you could look at running a tensile test on the material in question and compare it with a known 304 sample. Things to look for are elongation and the shape of the stress-strain curve. If you look at the handbooks, 304 SS has an elongation of ~55% or more, whereas the 202 SS has an elongation of ~40% (assumes annealed at 70F). Comparing the plastic portion of the stress-strain curve for 304 SS and 202 SS, the 202 SS plastic range curve should have a steeper slope than the 304 SS because it workhardens more rapidly.

Finally, there may be some color metallographic and etching techniques that could be use to distinguish between the two alloys because of the differences in Mn content. I would suggest checking some of the handbooks on etchants.

Good Luck.

The difference is that 202 Stainless has a lower nickel content to it so it maintains a more stable price on the market.

There's not much difference between the two. In fact 200 series stainless is stronger then the 300 series.

202 forms and handles almost identically to that of 304.

Some stainless in the 200 series is also USDA approved. Much of your stainless steel pots and pans and appliance skins are 200 series SS.

200 series is almost as corrosion resistant as that of the 300 series as well.

The problem is that 200 series stainless steel isn't offered everywhere and is hard to get on the west coast of the United States. There is also an issue with being able to get it in as many shapes and sizes as we can the 300 series.

Primarily the vendor is selling you something that is almost identical in handling and having most of the other properties of the 304 stainless steel and trying to deal in a material that is more stable in price. Because stainless steel prices fluctuate as readily as gas prices.

Might try asking for a mill cert from your supplier, and checking the master coil numbers from received material. We have experienced a similar situation, and this was all that was needed to identify in-house material and reject and return noncomforming material at the vendor's expense. If they drag their feet, you can ask for the material cert from the mill using the master coil number. If that doesn't work, then you might procede to the next step, which would be outside lab verification.

Someone mentioned cryogenic differences which are true. If you have anything that can do a Charpy Impact, or at least mimic the test, then the failure mechanism should be different. SS 304 will only fail ductilly because of its FCC structure, while SS 202 will fail both ductilly and brittley because it has a mixed atomic structure.

Do you have anyone on staff with some experience in fractrography who would be able to tell the difference between the two failed surfaces?

I think if you go from a 202 to a 207 SS the handling will be very similar to 304.

I tried to get 207 in my area but was having a hard time making that happen simply because no one wanted to move any unless the purchase was a minimum 25,000 lbs.

I had done some research on the difference and they supposedly handle the same with the 207 being structurally stronger.

try this publications maybe can give you some good advise.

Qualitative Sorting Test for Stainless Steels

These tests are intended for rapid, inexpensive and usually non-destructive and on-site sorting of grades of stainless steel. They are particularly useful for sorting products when, for example, bars of grades 304 and 303 have been accidentally stored together, or grade 304 and 316 sheet offcuts mixed

" A manganese spot test is available with specific relevance in sorting "200-series" Cr-Mn-(Ni) austenitic stainless steels from the more usual Cr-Ni "300-series" grades such as 304. The 200-series steels are non-magnetic and otherwise indistinguishable from the 300-series, but do have some reduced properties and have considerably less value as scrap."

http://metals.lincdigital.com.au/files/ASM_Tech_Notes/TN1-0506-qualitative%20sorting%20tests.pdf

hope this help u

S.

Corrosion Control & Corrosion Protection

Hello,

I have a factory in China that manufactures kitchen appliances so we often come across 201,202,304 & 430 grades of stainless steels.

304 is the most ideal grade for kitchen appliance due to good corrosion properties after working and nice finishing. But it is less used now due to the high price of nickel.

Options being deployed now include 201 & 202. From our experience (this is not scientific), the 200 series are not good forming as 304. 202 can perorm better than 201 in drawing. 201 often fractures when thin sheet are drawn in steep corners. When cold worked in tight shapes, the 200 series sometimes exhibit small magnetic charateristics. From our own salt spray test, the 200 series have good resistance almost as good as 304. In our trade, the surface finish have a grain brushed on with a sanding belt and 304 will have a silky, gloss feel. The 200 series will have a whitish, dry flaky look. Under a microscope, your will see fracture cuts. 201 stainless steel will wear off cutting, drawing and stamping faster. I will get my laser cutter later this month and I will see if 300 and 200 series cut the same.

if you don't want to do a spectroscopy, then you can use this.

http://www.koslow.com/1399.html

Any questions please email me ed@artinox.com.cn

how to sort out ss304 & ss202 finished item by simple (chemical test ) & fast method ?

If you still suspect the material i can test one sample for free with my niton xrf analyzer. minimum sample size 1" x 1". I am in southern california. the sample could fit in an envelope and I would e-mail you with the results.