Testing for genuine 304 stainless steel: what magnets and reagents can tell you

Many people buying a stainless steel gate or railing bring a magnet and believe "if it sticks it is fake, if it does not it is 304." This is not entirely wrong but very easily leads to the wrong conclusion. This article helps you understand the limits of each test.

Testing with a magnet: what it can and cannot do

Austenitic stainless steel (such as 304 and 316) is in theory non-magnetic. 430 stainless steel, which is ferritic, clearly sticks to a magnet. So a magnet helps you rule out 430 when a seller claims it is 304.

However, there are three points to remember:

1. 201 stainless steel is also austenitic, and usually does not stick or sticks very weakly. This means a magnet can hardly tell 201 from 304.
2. Bent, stamped or welded areas of genuine 304 can be slightly magnetic due to cold working. A slight pull at a bend does not mean the product is fake.
3. Some sellers deliberately mix: the visible part is 304, but the hidden part is a different material.

Stainless steel test reagent

Dedicated reagent solutions are sold on the market to roughly distinguish stainless steel grades. The general method is to put one drop on a cleaned surface, wait a few tens of seconds and compare the color per the manufacturer's instructions. This is much faster and cheaper than machine measurement, but gives only approximate results.

Safety notes:

• Use only ready-made reagents, read the instructions carefully, and wear gloves and safety glasses.
• Do not mix strong acids at home. Acids can damage the surface and are dangerous.
• Test in a hidden spot, then wipe thoroughly clean to avoid leaving marks.

Composition analyzer (XRF)

The most accurate way is a handheld X-ray fluorescence (XRF) analyzer that reads the chromium, nickel and molybdenum content. Many inspection bodies and some larger workshops offer this service. For a high-value project, you can hire testing at a few representative points.

Indirect signs

• Material certificates (CO, CQ) accompanying the batch of stock: ask the workshop to show them and check the batch number.
• Actual thickness: measure tubes and box sections with calipers. Tube thinner than quoted is a sign to ask questions.
• Surface color: 304 is usually bright with a slight gray tint, while 201 may look yellower or darker, but lighting and polishing method distort this, so it is for reference only.
• Testing over time: 201 is prone to rust spots in damp environments after a few months, but by then it is hard to claim your rights.

The best prevention

Instead of testing after you buy, make things clear beforehand:

• State the material grade and thickness in the quote (for example: 304 tube, 42 mm diameter, 1.2 mm thick).
• Ask for a warranty document that states the material.
• Choose a workshop willing to let you see the stock and check on the spot.

A reputable workshop will not mind you checking. If you need to, bring a sample to the workshop for advice on a suitable way to test.