Material Selection and Surface Treatment Comparison for Precision Small Screws

Material Selection and Surface Treatment Comparison for Precision Small Screws

Material grade and surface finish are the two most consequential decisions in precision small screw specification, governing service life, corrosion resistance, and total cost. This article systematically compares mainstream options to guide procurement engineers with quantitative data.

Material Performance Comparison

SUS304 stainless (A2-70) is the workhorse—tensile strength ≥700 MPa, good corrosion resistance, ideal for indoor electronics. SUS316 (A4-70) adds molybdenum for superior chloride resistance in coastal or humid environments, at roughly 30% cost premium. Carbon steel 10B21, case-hardened to HRC 32–38, offers high strength at 60% of stainless cost but requires a protective coating. Titanium alloy (TC4/Gr.5) combines 4.5 g/cm³ density with exceptional strength-to-weight and non-magnetic properties for aerospace and premium wearables, though it costs 5–8× more than stainless.

Surface Treatment Comparison

Electroplated nickel (3–5 μm) delivers a bright finish, good solderability, and 24–48 h salt spray at low cost—the consumer electronics default. Zinc plating (5–8 μm) with trivalent passivation reaches 72–120 h salt spray but faces wastewater constraints. Dacromet (8–12 μm) exceeds 500 h salt spray with zero hydrogen embrittlement risk, suited to automotive and outdoor applications, but its zinc-aluminum flake coating is unsuitable for conductive contacts. Passivation, exclusive to stainless, removes free iron to boost corrosion resistance without dimensional change, though gains are modest.

Selection Recommendations

Indoor electronics—SUS304 with nickel or passivation; outdoor/automotive—carbon steel with Dacromet or SUS316; high-end lightweight—titanium with anodizing. Note that high-strength carbon steel (≥grade 10.9) must undergo hydrogen baking (190–230 °C, ≥4 h) after plating to prevent delayed fracture caused by hydrogen embrittlement.