M3 DIN933 Fastener

QS Fastener: M3 DIN933 Fastener

Name: M3 DIN933 Fastener
Standard: DIN933
Material: SS304
Size: M3
Lenght: 12
Surface: Natural color

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M3 DIN933 Fastener is crafted from food-grade SS304 stainless steel, featuring 12 mm full thread and a natural finish with zero coating—completely non-polluting. It meets the high-torque DIN933 hex-head standard while delivering mirror-grade corrosion resistance, providing a safe, stable and maintenance-free connection solution for medical, food and precision-electronics assemblies.

M3 DIN933 Fastener Manufacturing Process and Quality Control
1 Manufacturing & Inspection
1.1 Cold forging: on a 250 t servo multi-station cold-header, M12×40 hex-head blanks are formed; the same line is equally suitable for small-lot mass production of the M3 DIN933 Fastener. The raw wire is Ø11.8 mm 304 (A2-70) austenitic stainless steel with 520 MPa tensile strength and ≥ 40 % elongation. A six-die six-blow process with 72 % deformation is used, giving a die life ≥ 500 000 pieces.

1.2 Shank reduction: an 800 kN servo reducer shrinks the shank from Ø11.8 → Ø10.0 mm, work-hardening the strength by 120 MPa while keeping the core grain size at 6–7; for the M3 DIN933 Fastener the reduction is scaled to Ø2.9 mm.

1.3 Thread rolling: on a 30 m/min high-speed thread-roller with TiAlN-coated rolls, 60° flank angle, M12×1.75-6g, surface roughness Ra ≤ 1.6 µm, effective thread length 34 mm. By contrast, the M3 DIN933 Fastener can be rolled at 50 m/min while still achieving Ra ≤ 1.2 µm.

1.4 Solution treatment: continuous mesh-belt furnace at 1050 °C ± 10 °C, 25 min dwell, then 0.4 MPa high-pressure water quench to < 50 °C, fully redissolving Cr23C6 and limiting inter-granular corrosion tendency to ≤ 0.4 mm/month (ASTM A262 Pr.E). The same parameters apply to the M3 DIN933 Fastener with dwell shortened to 6 min.

1.5 Pickling & passivation: HNO3 20 % + HF 3 %, 50 °C, 8–10 min; followed by 25 % HNO3 passivation 30 min, surface free iron < 0.1 µg/cm², 1000 h salt-spray without rust; the miniature surface of the M3 DIN933 Fastener allows more uniform passivation, controlling free iron < 0.05 µg/cm².

1.6 Eddy-current crack detection: through-type 8-channel eddy-current tester, 2 MHz frequency, crack sensitivity 0.05 mm × 0.1 mm, 100 % online rejection. The small-size M3 DIN933 Fastener switches to a 5 MHz high-frequency probe, raising sensitivity to 0.02 mm × 0.05 mm.

1.7 Spectral re-check: each lot is OES-spectrometer-tested at 10 points; elemental tolerances Cr 18.0–20.0 %, Ni 8.0–10.5 %, C ≤ 0.08 %, P ≤ 0.045 %, ensuring the corrosion grade of the M3 DIN933 Fastener.

1.8 Dimensional CPK: KEYENCE IM-8000 vision system samples 32 pcs/lot; critical dimensions (head thickness 7.5 mm ± 0.15, major diameter 11.8 mm ± 0.15, shank length 40 mm ± 0.3) achieve CPK ≥ 1.33 and Ppk ≥ 1.67. When gauging the M3 DIN933 Fastener, head thickness becomes 2.0 mm ± 0.08, yet CPK remains ≥ 1.33.

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