Acid testing is one test that will separate 304 and 316 grades of stainless steel. Hydrochloric acid attacks 304 grade very rapidly and produces gas, but attacks 316 grade only very slowly.
The key difference between 304 and 316 stainless steel that makes them different is the addition of molybdenum, an alloy that drastically enhances corrosion resistance, especially for more saline or chloride-exposed environments. 316 stainless steel contains molybdenum, but 304 does not.
With its higher nickel composition range, 316 is considered the "most nonmagnetic" stainless steel. However, an item of 316 stainless steel which has significant welding or machining may be sufficiently magnetic to produce a noticeable attraction when brought near a magnet.
Nitric acid reaction can be done to distinguish grade 304 from non-stainless steel elements. Grade 304 will not affect by nitric acid whereas non-stainless steel material will show brown fumigation. A Moly-drop test can be performed to test the difference between 304/304L and 316/316L.
The austenitic stainless steel grade 304 is not magnetic but it may become a little magnetic in areas that have been cold working (bending, deforming, etc.).
If you want to do spot check of SS, just take a random piece from the raw material and do a spark test. Run a grinder on it, if the sparks are reddish orange, thin and don't fly much it's SS304. If the sparks are yellow, thick and fly lot further it is SS 202.
The identification of the grinding is to grind the stainless steel on the grinder and observe the spark. If the spark is streamlined and has more dense knots, it is a high manganese or manganese nitrogen steel with higher manganese content. If there is no knot, it is chrome steel or chrome-nickel stainless steel.
A ferritic stainless steel owes its magnetism to two factors: its high concentration of iron and its fundamental structure. Both 304 and 316 stainless steels are austenitic, when they cool, the iron remains in the form of austenite (gamma iron), a phase of iron which is nonmagnetic.
So the “magnet test” is to take a magnet to your stainless steel cookware, and if it sticks, it's “safe”—indicating no nickel present—but if it doesn't stick, then it's not safe, and contains nickel (which is an austenite steel).
From our experience 304SS small particles are more likely to be held in the flow than 316 SS particles due to its slightly more magnetic nature. See more information on Paramagnetism.
Many people believe that if the magnet sticks, then the fastener is not stainless steel. This is not the case. There are several different types of stainless steel that are used to manufacture commonly available fasteners, most notably "410" and "300" series. Type 410 stainless will be strongly magnetic.
304 stainless steel is highly resistant to atmospheric corrosion, water, and many chemicals. Along with its ease of fabrication, 304 stainless steel is a popular choice for metal castings for applications such as pump & valve components, food processing equipment, bearings, heat exchangers, and pressure vessels.
316 contains a minimum 2.0% molybdenum which makes it much more corrosion resistant than 304 however, as it is a more expensive element, generally makes 316 a more expensive grade of metal.
304 stainless steel does have one weakness—it is susceptible to corrosion from chloride solutions, or from saline environments like those near an ocean.
This is commonly done. Type 316L, in most cases, is at least as corrosion resistant as 304L although not in all cases. For example, in nitric acid, 316L may be less corrosion resistant than 304L. If both alloys are sufficiently corrosion-resistant, there is no concern for galvanic corrosion.
Grinder test can be employed to state the identification between the grade 304 and 202. Grade 304 will show thin reddish-orange sparks and sparks will fly for a long time due to the higher density of more nickel content. On the other hand, thick yellow sparks will appear for grade 202.
Stainless steel grades 410, 420 and 440 – martensitic stainless steels. This type of stainless steel is magnetic primarily because it contains large quantities of ferrite in its chemical composition, which is a compound of iron and other elements.
Stainless steel does contain some iron. However, it also contains other elements that make it more valuable than regular iron or steel, although not as valuable as other scrap metals such as copper. Stainless steel's scrap metal price fluctuates with the market, typically ranging anywhere from $0.40-1.30 per pound.
Acid testing is one test that will separate 304 and 316 grades of stainless steel. Hydrochloric acid attacks 304 grade very rapidly and produces gas, but attacks 316 grade only very slowly.
Alloy steels and carbon steels are assigned specific grades through a four-digit AISI/SAE numerical index system. The first two digits indicate whether the material is plain carbon steel or if it may contain alloying elements. The last two digits indicate what percentage of the steel is made up of carbon.
Copper sulphate solution test
A simple 5 percent copper sulphate solution, applied in the same way as the water drop test, should confirm the differences between non-stainless steels and stainless steels.