304 or 201 stainless steel: how to tell what your pet bowl is made of

The difference between 304 and 201 stainless steel is roughly five percent nickel, and nickel is the expensive part. That is the entire commercial logic behind the 200 series, and it is why a cheap steel bowl is cheap. What makes this worth an article is that you cannot tell the two apart by looking at them, the magnet test that circulates online does not distinguish them, and most product listings will not tell you. Including, as it happens, ours. We will come back to that.

What the numbers mean

The three-digit grades are a composition standard, not a quality rating. 304 is an austenitic chromium-nickel steel. The 200 series are austenitic chromium-manganese steels, developed in the 1930s and expanded during the Second World War when nickel was scarce in the United States, which keep the austenitic structure by substituting manganese and nitrogen, sometimes with copper, for a large part of the nickel.

The Australian Stainless Steel Development Association publishes the registered compositions in its article on 200 series steels, in weight percent:

The worldstainless federation's technical paper on austenitic CrMn grades gives the same bands for 201 and 202 along with carbon of 0.15 max and sulphur of 0.030 max.

Below the registered grades sit proprietary low-nickel steels that are not in the ASTM or SAE three-digit system at all. ASSDA lists two commonly seen ones, J1 at 14.5 to 15.5 percent chromium with 4.0 to 4.2 percent nickel, and J4 at 15.0 to 16.0 percent chromium with 0.8 to 1.2 percent nickel. These are a long way from 304 and have no international standard.

Why chromium is the number to watch

Chromium is what makes stainless steel stainless. It forms the passive oxide layer that reforms when the surface is scratched, which is the whole mechanism. Nickel stabilises the austenitic structure and contributes to corrosion resistance, particularly to how quickly corrosion spreads once it starts.

The problem with cutting nickel is that it forces you to cut chromium too. ASSDA explains it directly: reducing nickel requires reducing the ferrite-forming elements, chromium among them, to keep the austenite balance. So a low-nickel grade is usually also a lower-chromium grade. ASSDA describes the drop from 18 percent or more in 304 down to 15 or 16 percent in J1 and J4 as a significant reduction, especially in the very low-nickel versions, and states that newer CrMn grades are generally less corrosion resistant than comparable CrNi grades.

The worldstainless paper is more granular and, for a bowl, more interesting. Testing a European CrMn grade designed to get as close to 304 as possible, it reports pitting resistance better than classic 201 but slightly below 304L, crevice initiation resistance close to 304L, and a slight overall decrease in resistance to localised corrosion compared with 304. In 1,000 hour salt-fog stress corrosion tests, that CrMn grade cracked where 304 did not.

And one line in that paper is worth the price of admission for anyone buying tableware: hand-washed tableware is cited as an application where 200 series corrosion resistance proved adequate, but dishwasher conditions are described as more corrosive. If you wash a bowl by hand, a lower grade may well last. If you run it through a dishwasher with detergent and heat twice a week for a decade, which is exactly what we recommend elsewhere in how often to wash a dog bowl, the grade starts to matter.

The magnet test does not work

The test you will find repeated everywhere is that 304 is non-magnetic and cheaper steel is magnetic, so stick a fridge magnet on the bowl.

The 200 series grades are austenitic. ASSDA states plainly that CrMn grades are non-magnetic, so they can look like 304 or 316 at first glance, and that magnetism has no relationship to corrosion resistance. The worldstainless paper makes the same point: non-magnetic 200 series grades can be mistaken for austenitic chromium-nickel grades.

A magnet will tell you that a bowl is not a 400 series ferritic steel. It will not tell you whether it is 304 or 201 or J4. It is a test that sorts the wrong categories, and it gives people false confidence.

There is one honest caveat in the other direction: a drawn or heavily cold-worked part made from 304 can become slightly magnetic at the formed areas, because cold work transforms some austenite. So a bowl showing a faint magnetic response at the rim is not evidence of a cheap grade either. The test fails in both directions.

What does work

ASSDA names the methods: X-ray fluorescence, which reads the elemental composition directly, and chemical drop test kits that detect manganese, which separates CrMn from CrNi, or molybdenum, which separates 304 from 316. They refer readers to their own technical FAQ for the procedure.

Neither is a kitchen test. XRF means a handheld analyser costing thousands. Drop test kits are cheaper but are a laboratory consumable, not something most households will buy to check a feeding bowl.

Which leaves you with the only test available to a shopper: ask the seller, and judge the answer. The useful questions are specific.

• What grade is the steel, by number?
• Is that on the product page in writing, or only in a reply to a question?
• Will you provide a mill certificate or a material test report?

A seller who states a grade in writing on the page has made a claim you can hold them to. A seller who says "food grade stainless" has said nothing, because that phrase is not a grade. A seller who says "high quality 304" without a document has said one useful word and one decorative one.

Our own bowl, which fails this test

We are not going to write this article and then quietly skip the part that applies to us.

Our bowl is a double stainless feeding bowl on a tilted base. The steel grade is not confirmed as 304. Our supplier has not provided a material test report we are willing to stand behind, and we are not going to print a number on a product page that we cannot evidence. Our product page says so, and it will keep saying so until we have a certificate in hand.

That is a real limitation and you should weigh it. If confirmed 304 is a requirement for you, buy from someone who documents it, and ask them for the certificate rather than the adjective. We would rather lose the sale than make up the number, partly because that is the only position consistent with everything else we publish, and partly because the whole point of how to choose a dog bowl is that the specifications nobody prints are the ones that decide the product.

The short version

Grade is a composition, not a compliment. 304 runs 18 to 20 percent chromium with 8 to 10.5 percent nickel. 201 runs 16 to 18 percent chromium with 3.5 to 5.5 percent nickel and more manganese. Below those sit unstandardised low-nickel grades with chromium around 15 percent. Lower chromium generally means less corrosion resistance, and dishwashers are harder on steel than hand washing. A magnet cannot tell these grades apart. Only a document or an analyser can, so the practical move is to ask for the document and treat its absence as information.