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Analysis Report on Stainless Steel Button Materials and Needle Detection Performance

I. Core Principle Overview

The ability of stainless steel buttons to pass needle detection machines essentially depends on the matching relationship between material properties and detection sensitivity.

Needle detectors identify foreign objects by sensing the ferromagnetism and electrical conductivity of metals.

The alloy composition (especially Ni, Cr, Mn content) directly affects austenite stability, which further determines magnetic and conductive properties.

Important Note:

There is no unified industry standard for “needle detection grade”. It is generally a colloquial term based on the sensitivity scale of needle detectors.

Higher grade means higher sensitivity, capable of detecting smaller metal foreign objects or materials with weaker metallic characteristics.

II. Comparative Analysis of Main Stainless Steel Grades

1. Grade 201 Stainless Steel (also known as 218#)

Material Properties: Low-nickel, high-manganese austenitic stainless steel

Standard Composition: Ni 1.0%, Mn 16.0%, Cr 16.0%

Measured Spectrum: Ni 1.67%, Mn 16.13%, Cr 12.37%, Fe 68.56%

Process Feature: Manganese largely replaces nickel to reduce cost

Metal Properties: Slightly magnetic, relatively high conductivity

Needle Detection Performance:

Easily detected by low‑medium sensitivity machines;

Generally passes only Grade 2–4 needle detection.

Salt Spray Test:

1.0% NaCl – 12 hours; 5.0% NaCl – 12 hours.

Applications:

Decorative parts, shallow drawing parts;

Children’s wear, handbags, raincoats, stationery buttons with low overseas requirements;

Products with low needle detection standards.

Remark:

Actual composition differs greatly from standard (e.g., low nickel). This material is sometimes called 218# in factories.

2. Grade 202 Stainless Steel (also called Grade 8 Material)

Material Properties: Upgraded and optimized version of 201

Standard Composition: Ni 1.0%, Mn 18.0%, Cr 17.0%

Measured Spectrum: Ni 1.57%, Mn 19.05%, Cr 12.46%, Fe 65.39%, Cu 0.818%, Zn 0.105%, V 0.151%

Optimization: Adjusted Mn/Ni ratio to improve austenite stability

Metal Properties: Lower ferromagnetism, lower conductivity

Needle Detection Performance:

Weak signal to needle detectors; passes Grade 4–6 medium sensitivity.

Salt Spray Test:

1.0% NaCl – 12 hours; 5.0% NaCl – 12 hours.

Applications:

Shallow stamped parts, tableware, children’s wear with moderate corrosion resistance and needle detection requirements.

3. Grade 848 Stainless Steel (also known as 204#, 208# / YKK Grade)

Material Properties: High‑grade heat‑resistant stainless steel

Estimated Standard Composition: Ni 4.0%, Mn 14.0%, Cr 15%

Measured Spectrum: Ni 4.71%, Mn 15.01%, Cr 16.50%, Fe 61.93%, Cu 0.966%, Zn 0.124%, Mo 0.011%, V 0.367%

Process Advantage: EAF + AOD secondary refining, low impurities, high purity

Metal Properties: Extremely stable austenite, nearly non‑magnetic, low conductivity

Needle Detection Performance:

Extremely difficult to detect; passes Grade 8 high‑sensitivity needle detection.

Salt Spray Test:

5.0% NaCl – 48 hours.

Applications:

Food contact, precision instruments, medical products, high‑end children’s wear with strict needle detection requirements.

Top brands including YKK use this material for prong snaps and ring snaps.

III. Key Findings & Industry Status

Composition Deviation: Actual market material composition differs significantly from national/nominal standards, especially nickel content is generally lower than labeled.

Confusing Naming: Same material may have different codes (e.g., 201# vs 218#). “848#” is an industry nickname, not a standard grade.

Process Impact: Smelting process (e.g., secondary refining) greatly affects purity and needle detection performance.

Custom Material Advantage: Professional button manufacturers’ customized materials are optimized for drawability and plating, better suited for button production.

IV. Summary & Recommendations

Needle detection performance shows a clear material grade gradient:

Low-end: 201# (218#) → Grade 2–4， 5% Salt Water-12H

Mid-end: 202# → Grade 4–6， 5% Salt Water-12H

High-end: 848# (204#, 208#) → Grade 8， 5% Salt Water-48H