The following are common methods for distinguishing between 304 and 202 stainless steel, which combine rapid testing with laboratory means and are accompanied by references:

1. Chemical composition comparison (core difference)

304 stainless steel

Composition characteristics: 304 stainless steel contains chromium (Cr) ≥18% and nickel (Ni) ≥8%, some may also contain molybdenum (Mo). This alloy is austenitic stainless steel with good corrosion resistance and toughness.

Application scenario: Due to its excellent corrosion resistance, 304 stainless steel is often used in food processing equipment, medical equipment, building decoration and chemical industry and other occasions requiring high strength and corrosion resistance.

202 Stainless steel

Composition characteristics: 202 stainless steel contains about 17% chromium, about 4% nickel, but the manganese (Mn) content is as high as 8%. It is a low nickel and high manganese austenitic stainless steel, compared with 304 stainless steel, its corrosion resistance and toughness is slightly inferior.

Application scenario: 202 Stainless steel is usually used in environments with low corrosion resistance requirements, such as interior decoration and home appliance housings.

Second, practical detection methods

1. Magnetic test

Operation steps: Contact the material surface with a magnet.

Result judgment:

304 stainless steel: It is usually weakly magnetic or non-magnetic, because its austenitic structure is more stable.

202 Stainless steel: May exhibit weak magnetism due to its higher manganese content affecting the microstructure of the material.

Note: This method is only a preliminary screening, can not completely determine the material type, need to be combined with other tests to make a comprehensive judgment.

2. Chemical reagent test

Special test liquid method:

Reagents used: commercially available stainless steel test solution containing copper sulfate or other specific elements.

Operation steps: First polish the surface of the material to remove the oxide layer, then drop the reagent and electricity (some reagents need to wait 5 seconds), and finally observe the color change.

Color change:

304 stainless steel: no discoloration or light pink in 15 minutes.

202 Stainless steel: Turns brick red in 30 seconds.

Basis: The difference in nickel content leads to different color development, which is one of the important bases to distinguish the two kinds of stainless steel.

3. Spectrum /XRF Analysis (the most authoritative)

Operation steps:

Sand the surface of the material to a flat state.

Use a handheld XRF spectrometer or laboratory equipment to detect element content.

Advantages: This method can accurately determine the content of Cr, Ni, Mn and other key elements, so as to directly determine the material type, is one of the most authoritative detection means.

4. Spark identification

Operation steps: Rub the material with a high-speed grinding wheel and observe the spark form.

Spark characteristics:

304 stainless steel: The spark is short, fewer forks and dark red, because the presence of nickel inhibits the generation of sparks.

202 Stainless steel: the spark is longer, more forks and bright, which is due to the high manganese content to promote the occurrence of oxidation reaction.

Application scenario: It is suitable for the scene of rapid coarse screening in the factory, but it requires experienced operators to make judgments.

5. Identification and certificate verification

Check the surface markings: 304 products normally produced will be marked with "SUS304", "304" or "18/8".

Request test report: check whether the product meets the chemical composition and mechanical properties data under GB/T 20878, GB 4806.9 and other standards to ensure the purchase of qualified products.

Third, auxiliary judgment methods

Price reference

Cost difference: Due to the difference in nickel content, the cost of 304 stainless steel is significantly higher than that of 202 stainless steel. Therefore, when encountering abnormally low prices in the market, you should be vigilant, which may be counterfeit and shoddy products.

Corrosion resistance test

Brine soaking: Soak the sample in 5% brine for 48 hours to see if rust develops. Under normal circumstances, 304 stainless steel will not rust, and 202 stainless steel may appear pitting phenomenon.

Salt spray test: A neutral salt spray test is used to assess the corrosion resistance of the material. In general, 304 stainless steel can reach more than 200 hours without rust, and 202 stainless steel is usually less than 100 hours will appear obvious signs of corrosion.

4. Precautions

Comprehensive verification

A single method may have errors, in order to ensure accuracy, it is recommended to combine at least two or more detection methods (such as magnetic + reagent) to make a comprehensive judgment.

Surface treatment interference

Plating or passivation treatment may affect the results of chemical reagent tests. Before conducting such tests, it is advisable to properly sand the surface of the sample to remove factors that may interfere with the test results.

Professional equipment preferred

For large purchases or controversial situations, it is recommended to entrust a third-party laboratory with professional equipment (such as a spectral analyzer) for more accurate analysis to avoid unnecessary losses due to misjudgment.

Through the comprehensive application of the above methods, two different types of 304 and 202 stainless steel can be effectively identified, so as to avoid product performance problems caused by material confusion.