Spring Material Selection: A Decision Tree That Gets It Right the First Time

Material mistakes are the most expensive spring mistakes — they surface in the field, not in inspection. This decision tree prevents most of them.

Question 1: What touches the spring?

Dry indoor air → carbon steels stay in play. Humidity, water, cleaning agents → stainless 302/304. Salt, chlorides, chemicals → 316 or beyond. Body contact/implant → 316LVM or titanium.

Question 2: How hot?

• < 120°C: any material
• 120–245°C: chrome silicon, stainless
• 245–340°C: 17-7PH
• 340–550°C: Inconel X-750

Question 3: How many cycles?

• Static or < 10⁴ cycles: whatever passed Questions 1–2, cheapest first
• 10⁴–10⁶: music wire or Cr-Si with margin; consider shot peening
• > 10⁶: Cr-Si valve-spring grade or 17-7PH, shot peened, with fatigue design review

Question 4: Any special physics?

Conductivity → copper alloys. Non-magnetic → phosphor bronze, BeCu, titanium (details). Weight → titanium. None → stop upgrading; take the cheapest survivor.

The meta-rule

Upgrade one dimension at a time, and only the dimension that failed. "Stainless everywhere, just in case" doubles cost across a product for corrosion resistance most parts never use; "music wire everywhere" puts rust in your bathroom products. State environment, temperature, and cycles on every drawing — then the RFQ review can confirm the cheapest material that genuinely survives.