4 Ways to Identify Stainless Steel Materials

Nitrate Test

This method is used to identify stainless steel from carbon steel or other non-ferrous metals.

Identification basis

• Stainless steel has corrosion resistance to concentrated nitric acid and dilute nitric acid, and there is no reaction after dropping nitric acid.
• Carbon steel turns brown when exposed to concentrated nitric acid, and causes strong corrosion when exposed to dilute nitric acid.
• Non-ferrous metals are immediately corroded by concentrated nitric acid.

Tips: High carbon stainless steel 420 and 440 are slightly corroded after dripping nitric acid.

Identify process and conclusion

• Stainless steel + nitric acid => no reaction.
• Carbon steel + concentrated nitric acid => turns brown.
• Carbon steel + dilute nitric acid => strong corrosion.
• Non-ferrous metals + concentrated nitric acid => immediately corroded.

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Copper Sulfate Drop Test

This method can distinguish stainless steel from ordinary carbon steel or iron.

Identification basis and conclusion

Remove grease and impurities from the metal surface, polish a small area with a soft cloth, and then drip copper sulfate solution on the metal surface.

• The stainless steel => does not produce copper precipitation or show copper color
• Ordinary carbon steel and iron => Forms a layer of metallic copper in seconds

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Magnetic Identification

This method can be used to identify the authenticity of austenitic stainless steel (such as 301, 304, 316, 316L, etc.).

Identification basis

• Carbon steel, ferritic stainless steel, and martensitic stainless steel are magnetic.

• Austenitic stainless steel is generally non-magnetic.

Tips: 304 stainless steel may be magnetic after cold working.

Identify process and conclusion

Test the magnetic properties of the metal, if it is magnetic, it means that the metal is not austenitic stainless steel.

Austenitic stainless steel includes:

Euronorm (EN) number	EN designation	AISI grade	C	Cr	Mo	Ni	melting point (°C)
1.431	X10CrNi18-8	301	0.1	17.5	NS	8	1420
1.4301	X5CrNi18-10	304	< 0.07	18.5	NS	9	1450
1.4307	X2CrNi18-9	304L	< 0.030	18.5	NS	9	1450
1.4305	X8CrNiS18-9 e	303	< 0.10	18	NS	9	1420
1.4541	X6CrNiTi18-10	321	< 0.08	18	NS	10.5	1425
1.4401	X5CrNiMo17-12-2	316	< 0.07	17.5	2.2	11.5	1400
1.4404	X2CrNiMo17-12-2	316L	< 0.030	17.5	2.25	11.5	1400
1.4571	X6CrNiMoTi17-12-2	316Ti	< 0.08	17.5	2.25	12	1400

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Chemical Elemental Analysis

The chemical element analysis method is to use a few grams of metal drill cuttings for chemical analysis to obtain the correct content of each chemical element in the stainless steel, which is a common method in various enterprises.

However, this method requires professional testing equipment, so it will not be described in detail.

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Wrong Identification Method

The following identification methods are from the Internet, which is wrong, or quite inaccurate.

“Non-magnetic is stainless steel, magnetic is iron”

This statement is obviously wrong. As stated above, only austenitic stainless steels are non-magnetic.

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“Grind the metal on the grinding wheel, and you can distinguish whether it is stainless steel by the sparks emitted.”

In fact, it is difficult to distinguish with the naked eye by this method. Because not only the sparks between stainless steel and other metals are different, but the sparks between different stainless steels are also very different.

For example:

• 302, 303, 316 stainless steel is a reddish short spark with several prongs.
• 308, 309, 310, 446 stainless steel is a few dark red short sparks with a few prongs.
• 410, 414, 416, 430, 431 stainless steel is a long white sparkle with several prongs.
• 420, 420F, 440A, 440B, 440C, 440F stainless steel are shimmer colored sparks or long white sparks with distinct sparkle.

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