How to Know If Stainless Steel Is 304

How to Know If Stainless Steel Is 304

Gangsteelsupplies high-quality stainless steel plate ASTM A240 TP304, ASTM A240 TP304L, and ASTM A240 TP316L for pressure vessels, heat exchangers, and industrial fabrication.
Because many stainless grades look similar, customers often ask: How can I tell if my stainless steel is 304?

1. Visual Appearance and Finish

304 stainless steelhas a bright, silver-white appearance with a slightly bluish tone.
Compared with carbon steel, it does not rust easily and shows excellent gloss after polishing.
However, looks alone are not enough — 304, 316, and 430 grades all appear very similar to the naked eye.

2. Magnet Test

A quick field test is to use a magnet:

• 304 stainless steelis mostly non-magnetic in the annealed condition.
• It may show slight magnetism after cold working or bending.
• In contrast, 430 stainless steel is strongly magnetic, while 316 stainless steel is usually non-magnetic.

⚠️ Note: Magnetism can vary, so this test is only a rough indicator, not a confirmation.

3. Chemical Spot Test

You can apply a nickel test solution or molybdenum test kit:

• 304 contains 8–10.5% nickel and no molybdenum.
• If the test shows no Mo but strong Ni content, it’s likely Type 304.
• If molybdenum is present, it could be Type 316, such as ASTM A240 TP316L.

These quick chemical kits are commonly used in workshops and warehouses.

4. Material Certification and Marking

Authentic 304 stainless steel from Gangsteel always includes mill test certificates (MTC) confirming:

• Standard: ASTM A240 / ASME SA240
• Grade: TP304, TP304L, or TP304H
• Heat number, batch number, and chemical composition
  You can find this information stamped directly on the stainless steel plate ASTM A240 TP304 or printed on its packaging.

5. Laboratory Analysis

For absolute verification, a spectrometer (PMI test) or X-ray fluorescence (XRF) analyzer is used.
Typical composition of ASTM A240 TP304:

• C ≤ 0.08%
• Cr: 18.0–20.0%
• Ni: 8.0–10.5%
• Mn ≤ 2.0%, Si ≤ 1.0%, P ≤ 0.045%, S ≤ 0.03%

If your sample matches these ranges, it is confirmed as Type 304 stainless steel.

6. Difference Between 304 and 316

While both grades have similar appearance and mechanical strength, the main difference lies in molybdenum (Mo):

• 304→ No Mo element
• 316→ Contains 2–3% Mo for better resistance to chlorides and acids

Therefore, 316 (see ASTM A240 TP316L) is preferred for marine and chemical environments, while 304 remains the most economical choice for general use.

7. Typical Applications of 304 Stainless Steel

Gangsteel’s stainless steel plate ASTM A240 TP304 is widely used in:

• Food processing equipment
• Storage tanks and pressure vessels
• Heat exchangers and boilers
• Building decorative panels
• Automotive exhaust components

8. Conclusion

To identify 304 stainless steel, check magnetism, perform simple chemical tests, and confirm the chemical composition using certified data.
When you purchase from Gangsteel, all ASTM A240 TP304 and TP304L plates come with full test certificates, traceable heat numbers, and reliable quality assurance.

For more information, visit the product page for stainless steel plate ASTM A240 TP304 or contact Gangsteel’s technical team for verification support.