Choosing the wrong spring steel grade costs more than material price — it costs scrap, rework, and field failures. This guide helps you match your application requirements to the right grade before you place an order.
The Four Most Common Spring Steel Grades
For cold-rolled strip used in flat springs, clips and stamped elastic components, these four grades are common candidates. The governing standard and finished-part requirements determine suitability:
| Grade | Carbon reference | Key alloy | Hardness reference | Typical candidate uses |
|---|---|---|---|---|
| 65Mn | 0.62-0.70 | Mn 0.90-1.20 | 42-48 HRC | General flat springs, lock washers |
| 51CrV4 (SUP10) | 0.47-0.55 | Cr 0.90-1.20, V 0.10-0.25 | 44-50 HRC | Valve springs, high-fatigue components |
| SK5 | 0.80-0.90 | — | 58-62 HRC | Precision springs, measuring tapes |
| C75S (SAE1075) | 0.70-0.80 | — | 44-48 HRC | Clutch plates, textile needles |
The table is a general grade comparison, not a guaranteed property or interchangeability table. Verify the relevant standard, condition, heat treatment and finished-part acceptance criteria.
Selection Criteria: What Actually Matters
1. Fatigue Life Requirements
For fatigue-sensitive springs, 51CrV4 may be considered alongside carbon and manganese spring steels. Grade alone does not determine service life: surface condition, edge quality, inclusion control, geometry, stress, heat treatment and validation method can all govern fatigue performance.
2. Operating Temperature
Operating temperature can change strength, relaxation and oxidation behaviour. Do not select a grade from a single temperature threshold; define the exposure temperature, duration, stress and required property retention, then validate the grade and heat treatment.
3. Forming Complexity
If your spring requires tight bends or complex stamped geometry, start with annealed strip and heat-treat after forming. In annealed condition:
- 65Mn: ≤229 HB — good formability for moderate bends
- SK5: ≤212 HB (spheroidized) — excellent for stamping and tight radii
- 51CrV4: ≤248 HB — harder to form, but possible for simple bends
For flat springs that only need a simple curve, you can order pre-hardened strip and cut/stamp directly — saving you the heat treatment step.
4. Corrosion Resistance
None of these grades resist corrosion. If the spring operates in wet environments, you need post-plating (zinc, nickel), surface treatment (phosphating), or switch to stainless spring steel like SUS301.
5. Cost vs Performance
Material price depends on specification, dimensions, condition, quantity and market conditions. Compare total processing and validation requirements rather than assuming a fixed price premium or fatigue-life multiplier between grades.
Decision Flowchart
- Fatigue-sensitive duty? Compare candidate grades together with edge, surface, cleanliness and heat treatment.
- Elevated temperature? Define the full thermal duty and property-retention requirement.
- High target hardness? Confirm the grade, condition, toughness and finished geometry together.
- Complex forming? Review annealed condition, bend geometry and post-forming heat treatment.
- Corrosive environment? Compare coatings with an appropriate stainless spring grade.
- Cost-sensitive project? Compare total processing, testing and service requirements, not material price alone.
What to Tell Your Supplier
When requesting a quote for spring steel strip, specify:
- Grade with equivalent ("65Mn / 1065 / 1.1230")
- Delivery condition: annealed or hardened & tempered
- Target hardness if H&T (e.g., "44-48 HRC")
- Thickness and tolerance (e.g., "0.80mm ±0.03mm")
- Width and edge type (slit or round)
- Surface finish: bright, blue, polished
- End use — helps recommend the right condition
Common Mistakes
- Ignoring the forming route: Confirm whether the specified condition can withstand the actual bend and stamping geometry.
- Selecting from hardness alone: Toughness, fatigue, surface and heat treatment also matter.
- Ignoring edge condition: Define the burr and edge requirements appropriate to cyclic loading.
- Over-specifying tolerance: State the tolerance and measurement method the part genuinely requires.