The "SUS304" Stainless Dish Racks Rusted Within Three Months
Stainless Steel 304 Grade Verification Guide - Why Stainless Products That Passed Inspection Get "It's Rusting" Complaints Within Months, 304, 201, 430 and 316 Compared, the Limits of the Magnet Test, Nickel Test Solution, Handheld XRF, Spectrometry and Salt Spray Tests Compared, Approximate Composition Criteria, Gaps in Mill Certificates and Factory Reports, Supplier Material Substitution Such as 304 Approval Samples Only, 201 Fittings and Low-Nickel 304, Surface Treatment and Iron Contamination, Spec Sheet Items, Stage-by-Stage Checks and a Checklist

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An online kitchenware seller imported 1,500 two-tier dish racks from a factory in Jieyang, Guangdong, a hub for stainless steel household goods in China. The product page said in large type: "SUS304 stainless, no worries about rust." The approval sample had a clean finish and a magnet didn't stick to it. The pre-shipment inspection found no problems with appearance, dimensions, assembly or packaging.

About three months into sales, photos started appearing in reviews: brown spots around the leg welds and the drip tray. At first the seller blamed customers for using steel wool or chlorine cleaners, but the same reviews kept coming. Five units from remaining stock measured on a handheld XRF analyzer showed 13.2-14.1% chromium, 0.9-1.2% nickel and 9.1-9.8% manganese. This was not 304 but a low-nickel grade commonly sold as "201" in the Chinese market. The approval sample kept aside measured 18.2% chromium and 8.1% nickel, which is genuine 304.

Stainless steel grade problems are tricky because you can't see the difference. New 304 and 201 look and weigh almost the same, and neither sticks well to a magnet. The difference only shows up as rust after months of exposure to moisture, detergents and salt. This article starts with how stainless grades differ, then covers verification methods and criteria, common supplier tricks, and how to build material checks into your spec sheet and inspection checklist.

A reply of "Yes, it's SUS304" or a magnet test is not enough. To prevent rust claims after sale, set the grade and standard, chromium, nickel and manganese ranges, and the material of each component in numbers in your spec sheet, then analyze the composition of each part on samples drawn from production lots.

1. Why Some "Stainless Steel" Rusts

Stainless steel resists rust because the chromium mixed into the iron forms a thin oxide film (the passive layer) on the surface. More chromium makes a sturdier film, and nickel stabilizes it while making the material softer and easier to form. Nickel is expensive and drives most of the price difference between grades, which is exactly why suppliers quietly swap materials.

The grades used most in household goods are 304, 316, 201 and 430. 304, the most widely used grade for kitchenware and tableware, has about 18% chromium and 8% nickel; adding 2-3% molybdenum to make it more resistant to salt and chlorine gives 316. 201 replaces expensive nickel with manganese, and much of what circulates as "201" in the Chinese market has only about 1% nickel and 13-14% chromium. 430 is a chromium grade with almost no nickel; it is magnetic and cheap.

When the label and reality diverge, it is usually for one of these five reasons.

• Grade substitution: The approval sample is made of 304 and production of 201 or 430. They are almost impossible to tell apart by appearance.
• Low-nickel 304 (低镍304, 非标304): A non-standard material with only 4-6% nickel is sold under the 304 name. The factory insists "it's 304."
• Different material only in fittings: The body is 304, but fittings such as screws, rivets, hinges, handles and welding wire are 201 or plain steel. Rust spreads from these parts first.
• Skipped surface treatment: If weld heat tint is not removed or pickling and passivation are skipped, even 304 rusts at the welds.
• Iron contamination: When stainless is worked with tools or abrasives previously used on ordinary steel, embedded iron particles rust and make the material itself look corroded.

For products that touch food, material is about more than rust. Food contact rules in many destination countries require separate metal migration tests, and materials that release a lot of nickel and manganese can fail them. Food contact imports in general are covered in Episode 64, and plating and corrosion tests in Episode 128. This article focuses on confirming that the labeled material was actually used.

2. Verification Methods - From Magnets to Spectrometry

If you just say "please check the material," the factory will likely hold a magnet to it or send a single mill certificate from its steel supplier. Each method reveals different things, so decide first what you will check with.

Non-Magnetic Doesn't Mean 304

The most common misconception is "if a magnet doesn't stick, it's 304; if it does, it's fake." 201 is austenitic like 304, so it barely sticks either. Conversely, genuine 304 becomes slightly magnetic in deep-drawn or bent areas and in parts drawn thin like wire. Use the magnet test only to screen out cheap grades like 430, never to separate 304 from 201.

Measure XRF on Clean Base Metal, Part by Part

A handheld XRF is the most useful tool at inspection, but readings shift with where you measure. Values are easily skewed on coatings, plating, greasy spots and weld beads, so measure on a wiped, flat area of base metal. Measuring one spot on the body misses fitting substitution, so measure separately made parts such as screws, rivets, hinges and handles one by one. If manganese exceeds 2% and nickel falls below 8%, it is most likely not 304.

3. Setting Composition Criteria

Ranges differ slightly between standards, but the approximate compositions commonly referenced in the industry are as follows. Set actual criteria based on the latest edition of your chosen standard (ASTM, GB, KS, etc.) and the advice of a testing lab.

In China, 304 is commonly designated "S30408" or "06Cr19Ni10." Writing only "SUS304" in your spec sheet lets a factory borrow the Japanese grade name while matching the composition loosely, so write the standard number and composition ranges together. When your product page uses phrases like "18/8 stainless" or "medical-grade stainless," confirm that the actual composition backs them up.

4. Why You Can't Take Mill Certificates and Factory Reports at Face Value

Ask for proof of material and the factory usually sends a mill certificate (材质证明书, 质保书) from the steel mill that made the sheet or tube. These documents have several gaps.

5. Common Supplier Tricks

Stainless grades look nearly identical, and the raw material price gap between 304 and 201 is large, so the temptation to swap is strong. Here are the patterns we have actually encountered in consultations.

The most common is the case in the opening story: only the approval sample is made of 304. Appearance, dimensions and assembly are identical, so an inspector cannot tell by eye. Keeping a few approval samples and measuring the same spots on them and on production samples with XRF catches most of these cases. Material substitution follows the same principle as in Episode 125 on plastic resins.

6. The Cost of Material Defects

Material defects don't show at shipment and only appear after months of use, but the damage spreads well beyond the product's price.

• Reviews and returns: Just one or two reviews with rust photos can stall sales. The longer the sales period, the more units are subject to return.
• False labeling: Labeling "SUS304" and selling 201 can be treated as misrepresenting the material.
• Food contact non-compliance: Products that touch food and exceed metal migration limits can face sales suspension or recall.
• Distrust in future orders: A supplier that swapped material once is likely to do it again in the next lot, which eventually adds the cost of switching factories.

See Episode 53 for product liability and recalls, and Episode 47 for using third-party inspection.

7. What to Put in the Spec Sheet

A single line saying "SUS304" gets interpreted differently by every factory. Attach the items below as a table to your spec sheet. See Episode 59 on writing spec sheets.

Asking for purchase invoices and coil label photos along with mill certificates may seem tedious, but this is where the real value lies. A mill certificate only shows that a 304 coil existed somewhere; a coil label and invoice with the same heat number let you trace whether that coil actually went into your production run. See Episode 119 for the procedure when component materials change.

8. How to Build Material Checks Into Your QC Checklist

Sample Stage

When you receive approval samples, set a few aside and have one analyzed by a third-party lab independently of the factory's documents. Don't measure the body alone; measure every component including fittings, and record which spot was measured with which value, along with photos. This record becomes the baseline for comparing production units.

Production Stage

During production, check the mill, grade and heat number on the labels of incoming coils and tubes and match them against the mill certificates. If the factory has a handheld XRF, require measurements at raw material and fitting intake and ask for photos of the readings. If the results are the same number every time and there are no photos, start by questioning whether the measurements were taken at all. See Episode 102 for production schedule tracking.

Pre-Shipment Inspection Stage

The inspector picks packed units personally and measures the body and each fitting with a handheld XRF. Without an XRF, screen first with nickel test solution and a magnet, then send samples to a lab. Check welds for heat tint and the surface for embedded iron particles, and send the remaining samples for salt spray testing. See Episode 100 for pre-shipment inspection.

9. Sample Wording to Send to the Factory

Putting the wording below in your purchase order or spec sheet takes material choice out of the factory's discretion and makes it easier to assign responsibility if rust claims arise.

"本产品主体及所有配件（含螺丝、铆钉、合页、把手及焊材）均须使用304不锈钢（GB/T 20878 06Cr19Ni10），禁止使用201、430、低镍或非标304等材料。手持光谱仪检测须满足Cr≥18%、Ni≥8%、Mn≤2%。焊接部位须去除焊接变色并做酸洗钝化处理，加工须使用不锈钢专用工具和磨料，防止铁污染。成品经中性盐雾测试24小时后，主体、焊接部位及配件不得出现锈迹。未经我方书面同意不得更换材料、材料供应商、板材厚度或生产工厂，如需更换须事先书面通知并重新检测。每批须提交注明炉号的材质证明书、原材料采购发票、卷材及管材标签照片，以及注明检测部位、结果和照片的光谱检测记录。检测样品由我方验货员随机抽取并可逐个配件检测。如有不合格，须加抽复测；复测仍不合格的批次暂停出货。"
(The body and all fittings of this product, including screws, rivets, hinges, handles and welding materials, must be made of 304 stainless steel (GB/T 20878 06Cr19Ni10); materials such as 201, 430, low-nickel or non-standard 304 may not be used. Handheld spectrometer results must show Cr 18% or more, Ni 8% or more and Mn 2% or less. Welds must have heat tint removed and be pickled and passivated, and processing must use tools and abrasives dedicated to stainless steel to prevent iron contamination. After 24 hours of neutral salt spray testing, the finished product must show no rust on the body, welds or fittings. Without our written consent, the material, material supplier, sheet thickness or production factory may not be changed; any change requires prior written notice and retesting. Each lot must be accompanied by mill certificates showing heat numbers, raw material purchase invoices, photos of coil and tube labels, and spectrometer records showing measuring spots, results and photos. Test samples are drawn at random by our inspector, who may measure each fitting. If any sample fails, additional samples must be drawn and retested; lots that still fail on retest will be held from shipment.)

10. Three Real Cases

These are anonymized versions of patterns we often see in consultations. Amounts and figures are examples.

Case 1 - Stainless Steel Dish Racks

This is the case from the opening. The seller took the analysis results to the factory, but the spec sheet only said "SUS304" with dimensions, with no composition ranges, per-component materials or test method, so the factory produced a mill certificate and said, "Our material supplier told us it was 304." The heat number on that certificate belonged to a shipment for another customer. The factory eventually refunded part of the amount, but returns, review handling and product page revisions still left a loss of about KRW 18 million. From the next order on, the seller has put the standard number and composition ranges in the spec sheet and runs XRF on each part for every lot.

Case 2 - Camping Stainless Steel Mugs

A camping gear brand imported 4,000 stainless steel mugs, and the mug bodies measured as genuine 304. Two months into sales, though, returns came in saying "rust is spreading around where the handle attaches." Measuring only the rivets that held the handles showed 201 with around 1% nickel, and some were nickel-plated steel. The factory held its ground: "If the body is 304, it's a 304 product." The brand now lists the material of each component in a table in the spec sheet and measures rivets and handles with XRF at inspection.

Case 3 - Bathroom Towel Bars

A bathroom accessory supplier had analyzed 2,000 towel bars in advance and confirmed they were 304, yet still received weld rust claims a few months after installation. The returned units showed that the rainbow heat tint at the welds had only been polished over, and that the same grinding belts used for ordinary steel products had embedded iron particles in the surface. The material was right, but skipping surface treatment led to rust. The supplier has since added pickling, passivation and dedicated abrasives to the spec sheet and made salt spray testing a shipping condition.

11. Common Mistakes

• Writing only "SUS304" without a standard number or composition ranges
• Judging a part to be 304 because a magnet doesn't stick
• Measuring only the body and not checking fittings such as screws, rivets, hinges and handles
• Accepting a steel mill's certificate as proof of your product's material
• Checking the material but not weld heat tint removal or passivation
• Not keeping approval samples, leaving no baseline to compare production against

12. Stainless Steel Material Control Checklist

Specification Stage

• The grade and standard number (GB, ASTM, etc.) are set
• Chromium, nickel and manganese ranges and measurement tolerance are written down
• The material of the body and each fitting is set in a table
• Thickness, unit weight and surface treatment (heat tint removal, passivation) conditions are written down
• Salt spray and food contact migration test conditions are set

Sample and Production Stage

• A few approval samples are kept aside as reference samples
• Approval samples were analyzed part by part at a third-party lab
• Mill certificate heat numbers were matched against coil labels and purchase invoices
• XRF records per lot were received with measuring spots and photos

Pre-Shipment Inspection Stage

• The body and each fitting of random samples were measured with XRF
• Readings were compared with the same spots on the approval sample
• Welds were checked for heat tint and the surface for iron contamination
• Remaining samples were sent for salt spray testing

Final Thoughts - Verify With Composition Numbers, Not a Magnet

When new, stainless products shine the same whether they are 304 or 201. The difference only shows up as rust after a few months beside a customer's kitchen sink. Writing the standard number, composition ranges and per-component materials into your spec sheet and measuring each lot with a handheld XRF doesn't cost much. Put a few hundred thousand won in testing next to tens of millions of won in returns and review damage, and it's clear which is cheaper.

There is something you can do right now. Ask the factory currently in production to send the mill certificates and heat numbers for the raw material it is using, coil label photos, and a list of materials for each fitting. If the reply is a single line saying "It's 304," put together a material control sheet and send it before your next order.

StartMade supports you on the ground with spec sheets that set grade and composition criteria, third-party composition analysis of approval samples, raw material tracing in production, and pre-shipment inspections with a handheld XRF in hand. If you have already received rust claims, we can start with part-by-part analysis of remaining stock; if you are preparing a new product, we can start with grade selection and setting criteria.