spring-materials

name	spring-materials
description	Spring material selection and properties — ASTM wire grades (A228 music wire, A227 hard drawn, A232 Cr-V, A401 Cr-Si, A313 stainless, A555 phosphor bronze, B197 beryllium copper), tensile strength vs. wire diameter, shear modulus G, elastic modulus E, temperature limits, corrosion resistance, magnetic permeability, fatigue data (Zimmerli), cost comparison, heat setting (stress relieving), and wire standards (EN 10270, ISO 6931).
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Spring Materials — Complete Skill

Spring Wire Selection Framework

Key Selection Criteria

1. Tensile/shear strength — determines allowable stress; sets spring rate feasibility for given geometry
2. Fatigue strength — Zimmerli endurance limit τ_e; determines cyclic life
3. Temperature limit — max operating temperature without significant loss of properties (relaxation)
4. Corrosion resistance — environment: aqueous, oxidizing, acidic, saltwater
5. Magnetic properties — non-magnetic required for some medical, electronics applications
6. Cost — music wire cheapest among high-performance; specialty alloys 5–50× more expensive
7. Wire diameter range — availability varies; small D_w (< 0.3 mm): music wire easiest to procure

Carbon Steel Spring Wire

ASTM A228 — Music Wire (Best Carbon Steel)

Production: cold drawn from high-carbon steel (0.85–1.0% C, 0.7% Mn); patented before drawing Strength vs. wire diameter D_w: S_u = A / D_w^b [MPa; D_w in mm] A = 2,211; b = 0.145 for D_w = 0.1–6.5 mm (Shigley empirical)

D_w [mm]	S_u [MPa]
0.5	2,270
1.0	2,170
2.0	2,000
3.0	1,860
4.0	1,760
6.0	1,620
8.0	1,500

Moduli: G = 81.7 GPa (shear); E = 206 GPa (elastic) Temperature limit: 120°C continuous (above: relaxation increases rapidly) Corrosion: poor (rust rapidly in humid conditions; plate or coat for protection) Fatigue (Zimmerli): τ_e = 310 MPa unpeened; 465 MPa shot-peened (D_w < 10 mm) Applications: valves, instruments, clocks, general high-cycle applications up to small/medium loads

ASTM A227 — Hard Drawn Wire (Economy Grade)

Production: cold drawn; not patented; lower quality control than A228 S_u: 10–15% lower than A228 for same D_w Fatigue: τ_e ≈ 241 MPa (lower than A228); inconsistent surface → lower fatigue Applications: static loads; non-critical; cost-driven applications; industrial springs with low cycle requirements Price: cheapest carbon steel spring wire

ASTM A229 — Oil-Tempered Wire (General Use)

Production: cold drawn then oil-quenched and tempered; 0.55–0.65% C S_u: comparable to A228 at large diameters (D_w > 5 mm); lower at small diameters G = 80.0 GPa; T_max = 180°C (higher than A228) Applications: automotive valve retainer springs, general industrial

Alloy Steel Spring Wire

ASTM A401 — Chrome-Silicon (High Performance)

Composition: 0.51–0.59% C; 0.60–0.80% Mn; 1.20–1.60% Si; 0.60–0.80% Cr Strength: S_u = 1,700–2,050 MPa (D_w = 2–12 mm); slightly lower than A228 at small D_w but better at large D_w G = 80.0 GPa; T_max = 245°C (significantly better than A228 → important for engine valve springs) Fatigue (Zimmerli): τ_e = 380 MPa unpeened; 540 MPa shot-peened Relaxation at 200°C: < 1% loss of load after 100 h (vs. 5–10% for A228) Applications: automotive valve springs, high-temperature diesel injectors, industrial at elevated T Price: 1.5–2× A228

ASTM A232 — Chrome-Vanadium (Impact Resistant)

Composition: 0.48–0.53% C; 0.80–1.10% Cr; 0.15% V minimum Strength: S_u = 1,550–1,950 MPa (D_w = 2–12 mm); comparable to A401 G = 80.0 GPa; T_max = 230°C Fatigue: τ_e = 380 MPa unpeened; 530 MPa peened Vanadium advantage: refines grain → better impact and toughness vs. chrome-silicon Applications: industrial springs with shock loads; valve springs; clutch springs Price: 1.5–2× A228 (similar to A401)

17-7 PH Stainless Steel (Precipitation Hardened)

Condition CH900: S_u = 1,650 MPa; very high strength for stainless G = 73 GPa; T_max = 300°C (intermittent); corrosion: excellent Fatigue: τ_e ≈ 380 MPa (better than austenitic stainless) Applications: aerospace springs, high-strength with moderate corrosion requirement Non-magnetic: semi-magnetic in CH900 condition (vs. A228 which is magnetic)

Stainless Steel Spring Wire

ASTM A313 — 302/304/316 (Austenitic)

Composition: 302: 17–19% Cr; 8–10% Ni; 0.08% C max Strength (cold drawn): S_u = 1,100–1,700 MPa (D_w = 0.3–8 mm; varies with degree of cold work) G = 69.0 GPa (lower than carbon steel — important for spring rate calculation!) T_max = 260°C (316: higher creep resistance) Corrosion: excellent (saltwater, mild acids); 316 superior to 302/304 in chloride environments Non-magnetic: essentially non-magnetic (paramagnetic); permeability μ_r ≈ 1.0–1.3 Fatigue (Zimmerli): τ_e = 241 MPa unpeened; 310 MPa peened (LOWER than carbon steel) Applications: food processing, marine, medical, chemical → anywhere corrosion resistance critical Price: 2–4× A228

316L wire: lower carbon → better weld corrosion resistance; similar spring properties to 316 2205 Duplex stainless: higher strength than 316; better chloride pitting resistance; G = 75 GPa

Non-Ferrous Spring Wire

Phosphor Bronze (ASTM B197)

Composition: Cu-5% Sn-0.2% P; cold-drawn S_u = 700–1,100 MPa (D_w dependent; much lower than steel) G = 41.4 GPa (half of steel — springs are much more flexible for same geometry) T_max = 95°C; Corrosion: excellent (non-oxidizing acids, salt water) Non-magnetic: completely non-magnetic; electrical conductivity ≈ 15% IACS Applications: electrical contacts, wave springs, precision instruments, low-frequency vibration mounts Price: 3–5× A228

Beryllium Copper (ASTM B197 Grade 2)

Composition: Cu-2% Be-0.3% Co; age-hardened S_u = 1,200–1,400 MPa (age-hardened — highest strength non-ferrous spring material) G = 48.3 GPa; T_max = 120°C Corrosion: excellent; non-magnetic; electrical conductivity 20–30% IACS (highest strength conductor) Beryllium hazard: machining/handling fine Be dust is carcinogenic → safety controls required Applications: electrical connectors, medical devices, military (non-sparking), precision springs Price: 10–20× A228 (most expensive common spring material)

Inconel 718 (Ni Superalloy)

Composition: Ni-19% Cr-18.5% Fe-5.1% Nb-3% Mo; precipitation hardened S_u = 1,380 MPa; G = 76 GPa; T_max = 550°C (for springs) Corrosion: excellent in oxidizing and reducing environments Applications: gas turbine engine springs (high T), aerospace, chemical processing Price: 15–30× A228

Key Moduli Summary

Material	G [GPa]	E [GPa]	ρ [g/cm³]
Carbon steel (A228/A232/A401)	80–81.7	206	7.86
Stainless (302/316)	69	193	7.90
17-7 PH	73	197	7.80
Phosphor bronze	41.4	103	8.86
Beryllium copper	48.3	131	8.23
Inconel 718	76	200	8.19
Titanium 6-4 (wire)	41	114	4.43

Spring rate with G: k = G × D_w⁴ / (8 × D_m³ × n_a) [changing material changes G → changes spring rate by G ratio] Phosphor bronze vs. steel: k_bronze = k_steel × 41.4/81.7 = 0.507 × k_steel (50% lower rate for same geometry) Must adjust geometry (D_w, D_m, n_a) to achieve same rate with non-steel wire

Stress Relieving and Heat Setting

Stress relieving (low-temperature annealing): Purpose: relieve forming residual stresses; stabilize dimensions; reduce residual stress variability Temperature: 150–200°C for 20–30 min (carbon steel); 230–260°C (Cr-Si, Cr-V) Effect: free length stabilizes; initial set reduced; fatigue scatter reduced

Heat setting: Compress spring to length equivalent to solid height; heat to stress-relieve temperature while loaded Effect: pre-set spring → reduces in-service settling; more consistent free length

Standards and References

Standard	Scope
ASTM A228	Music spring wire
ASTM A227	Hard drawn spring wire
ASTM A401	Chrome-silicon spring wire
ASTM A232	Chrome-vanadium spring wire
ASTM A313	Stainless spring wire (302/304/316)
EN 10270	Steel wire for springs (European; parts 1–4 cover patented, oil-tempered, SS, alloy)
ISO 6931	Stainless steel spring wire

Output

Provide: application requirements (operating temperature [°C]; environment: dry/wet/corrosive/saltwater; magnetic requirements; cyclic life N [cycles]; load range F_min–F_max [N]; wire diameter range needed [mm]), material candidates (2–3 options with S_u [MPa]; G [GPa]; τ_e [MPa]; T_max [°C]; corrosion resistance; price factor), recommended material (primary + justification; cost vs. performance trade-off), spring rate adjustment (if switching from steel: k_new = k_target × G_new/G_steel → new geometry), stress check (τ_max vs. 0.45×S_u for static; τ_alt vs. τ_e for fatigue), heat treatment (stress relieve temperature [°C]; time [min]; heat setting: required?), material certification (ASTM grade; EN 10270 equivalent; chemical cert. and mechanical test requirements), and applicable standard (ASTM A228/A227/A232/A401/A313; EN 10270; ISO 6931).