Stainless Spring Grades: 302 vs 316 vs 17-7PH
Short answer: 302/304 stainless is the default spring wire — good strength, good corrosion resistance, moderate cost, works to about 300°C. 316 adds molybdenum for salt and chemical resistance but is weaker as a spring and costs more; use it only when the environment genuinely demands it. 17-7PH is the high-performance choice — roughly twice the strength of 302 in the RH950 condition, excellent fatigue, service to about 370°C — at a significant price premium, worth it for aerospace, medical and high-reliability applications. If you are not sure, 302/304 is the right default and 17-7PH is what you move to when 302 fails.
Stainless springs are specified for one reason: corrosion resistance. But "stainless" covers a wide strength and cost spread, and choosing by price alone leaves performance on the table while choosing by name alone overpays. This guide compares the three grades that matter for custom springs — austenitic 302/304, molybdenum-bearing 316, and precipitation-hardening 17-7PH — in the numbers a designer needs.
The Grades in One View
| Property | 302/304 (austenitic) | 316 (austenitic) | 17-7PH (precipitation hardened) |
|---|---|---|---|
| Typical tensile (spring wire) | 1,500–2,100 MPa | 1,200–1,700 MPa | 1,700–2,200 MPa (RH950) |
| Max service temp | ~300°C | ~300°C | ~370°C (RH950) |
| Corrosion resistance | Good | Best (Mo for chlorides/salt) | Good to very good |
| Magnetic? | Slightly (cold worked) | Slightly | Magnetic in hardened state |
| Fatigue performance | Good | Good | Excellent |
| Relative wire cost | 1x (baseline) | ~1.5-1.8x | ~3-5x |
| Forming | Good | Good | Harder after hardening; form then age |
| Typical uses | General corrosion-resistant springs | Marine, medical, chemical | Aerospace, high-reliability, high-temp |
302/304: The Workhorse Default
Type 302/304 stainless spring wire is cold drawn to high strength and is what most "stainless steel springs" are made of. It handles the vast majority of corrosion-resistant spring needs — humid environments, mild chemicals, wash-down equipment, food machinery, outdoor products where plating would fail. It keeps useful spring properties to about 300°C and resists oxidation well. The magnetic note matters in some applications: cold-drawn 302 is slightly magnetic even though it is austenitic, which surprises engineers who assume "stainless = non-magnetic." If truly non-magnetic is required, 316 behaves similarly (slightly magnetic after cold work) and fully austenitic grades like 305 are less magnetic but weaker. For most springs, 302/304 is the specification — it delivers the corrosion resistance with the best strength-per-cost of the stainless family.
316: Pay for the Chloride, Accept the Strength Drop
316 exists for one reason: molybdenum makes it markedly more resistant to chlorides, salt water and many chemicals than 302/304. For marine hardware, coastal outdoor equipment, medical devices that see saline, and chemical processing, 316 is the responsible choice. The trade-off is real: 316 spring wire develops lower tensile strength than 302 (roughly 1,200-1,700 MPa versus 1,500-2,100 MPa), so a spring that must carry the same load in 316 needs thicker wire or more coils, partially offsetting the material premium. Specify 316 when the environment demands it; do not specify it "for safety" on ordinary indoor corrosion duty, because you pay twice — material cost and a weaker spring.
17-7PH: The High-Performance Stainless
17-7PH is a precipitation-hardening stainless that starts as a formable austenitic wire and is aged (typically RH950: refrigeration + 950°F age) to very high strength. In spring terms it delivers roughly 1.7-2.2 GPa tensile — in the same league as music wire and chrome-silicon — combined with stainless corrosion resistance and excellent fatigue life. Service temperature extends to about 370°C, beyond both austenitic grades. The cost is the constraint: wire costs several times 302, and forming is done in the soft condition followed by heat treatment, which complicates manufacturing. Use it where 302 springs fatigue-fail or where temperature and corrosion meet: aerospace actuators, surgical instruments, high-cycle safety devices. For everything else, 302/304 with good design carries the load at a fraction of the cost.
How the Choice Affects Your Spring Design
| If your need is... | Specify | Design impact |
|---|---|---|
| General corrosion resistance, indoor/outdoor humidity | 302/304 | Standard rates, standard cost |
| Salt water, marine, chlorides, aggressive chemicals | 316 | Larger wire/sections for same load |
| Highest strength + corrosion + fatigue | 17-7PH | Premium cost; form then age |
| Service above 300°C | 17-7PH (or Inconel/high-temp alloys beyond 370°C) | Verify relaxation at temperature |
| Non-magnetic requirement | 305 or custom austenitic | Weaker; confirm magnetic spec carefully |
Remember that corrosion resistance depends on surface condition: passivation after coiling restores the chromium oxide layer that grinding and handling disrupt. A passivated 302 spring outperforms an unpassivated 316 spring in many environments, and it costs almost nothing to add. Specify passivation on your spring drawing regardless of grade.
Frequently Asked Questions
Q: What is the best stainless steel for springs?
A: For most applications, 302/304 stainless spring wire is the best choice — strong (1,500-2,100 MPa), corrosion resistant, and economical. Move to 316 only for salt/chloride environments, and to 17-7PH when you need much higher strength or service above 300°C.
Q: Is 316 stainless stronger than 302 for springs?
A: No — 316 spring wire is typically weaker (about 1,200-1,700 MPa) than 302/304 spring wire (1,500-2,100 MPa) because the molybdenum addition reduces work-hardening response. A 316 spring needs larger wire to carry the same load as a 302 spring.
Q: What temperature can stainless springs handle?
A: Austenitic stainless springs (302, 316) serve usefully to about 300°C. 17-7PH extends to about 370°C. Above that, nickel alloys such as Inconel X-750 or Nimonic are needed. Always verify load relaxation at your actual service temperature.
Q: Are stainless steel springs magnetic?
A: Cold-drawn 302/304 and 316 spring wire are slightly magnetic despite being austenitic, because cold work transforms some structure. If a non-magnetic spring is a hard requirement, specify 305 or verify magnetic permeability with the spring maker before ordering.
Q: Do stainless springs need passivation?
A: Yes, passivation is strongly recommended after coiling and grinding. It removes free iron contamination and restores the protective chromium oxide layer, which is what actually gives stainless its corrosion resistance. It costs little and significantly improves service life in corrosive environments.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
