Determining whether a piece of stainless steel is of the 304 grade can be challenging without specialized testing equipment. However, there are some general characteristics and methods you can use to make an educated guess:

1. Visual Appearance: Stainless steel grade 304 often has a distinctive silvery-gray color with a smooth and polished surface. It’s relatively easy to spot compared to other grades, but keep in mind that surface treatments and finishes can alter the appearance.
2. Magnetism: Stainless steel grade 304 is generally non-magnetic, meaning it doesn’t attract a magnet. If a piece of stainless steel is strongly attracted to a magnet, it’s likely not 304. However, it’s worth noting that slight magnetism might still be present due to work-hardening or other factors.
3. Corrosion Resistance: Stainless steel 304 is highly corrosion-resistant, particularly in non-severe environments. If the material shows signs of rust or corrosion, it’s probably not 304.
4. Weight: Stainless steel 304 is denser than many other metals and alloys, so it will generally feel heavier compared to similar-sized pieces of other materials.
5. Chemical Testing: Chemical tests can help confirm the presence of certain elements in the stainless steel composition. However, these tests are usually performed in a laboratory setting and require specialized equipment and expertise.
6. Spark Testing: While not foolproof, spark testing can provide some insight into the type of stainless steel. Different stainless steel grades can produce different spark patterns when touched with a grinding wheel. However, this method requires experience to interpret accurately.
7. Professional Testing: If you need to be certain about the grade of stainless steel, especially in critical applications, it’s advisable to seek the services of a professional materials testing laboratory. They can perform more advanced tests like X-ray fluorescence (XRF) analysis or spectroscopy to accurately identify the alloy composition.
8. Certifications and Documentation: If you have access to documentation or certifications from the manufacturer or supplier, that information should clearly state the grade of the stainless steel.

Keep in mind that these methods have limitations and might not guarantee accurate identification of stainless steel grade 304. When in doubt, it’s best to consult with professionals who specialize in materials testing and analysis.

It is often referred to as “rust-resistant” or “corrosion-resistant,” but not “rust-proof.”

There are scenarios where 304 stainless steel can still experience rusting:

1. Exposure to Chlorides: Chlorides (like salt) can break down the passive layer and cause pitting or crevice corrosion. This is why 304 stainless steel is not recommended for use in highly chlorinated environments, such as near the ocean or in swimming pools.
2. Harsh Environments: In extremely corrosive or acidic environments, the passive layer may not be as effective, and the stainless steel could still experience corrosion.
3. Mechanical Damage: Scratches, abrasions, or other forms of mechanical damage to the surface can compromise the passive layer and lead to localized corrosion.
4. High Temperatures: 304 stainless steel’s corrosion resistance decreases at high temperatures, and it can be more susceptible to corrosion in such conditions.
5. Stagnant Conditions: In stagnant or low-flow conditions, debris or contaminants can accumulate on the surface, leading to localized corrosion.

In most everyday applications and normal environments, 304 stainless steel provides excellent corrosion resistance and will not rust or corrode easily. However, if you’re using it in particularly harsh conditions or environments, it’s important to consider the potential for corrosion and take appropriate measures to protect the material or choose a more suitable grade of stainless steel.