304H Spring Wire - Modulus of Elasticity in Spring Design

Product Introduction

TOPONE supplies 304H stainless steel spring wire in 0.15-12 mm diameters for springs that must hold a calculated force over time and temperature. Because the H grade carries a guaranteed 0.04 percent minimum carbon, its strength is stable at elevated temperature - and its elastic modulus, the property that sets spring stiffness, stays predictable. Tempers and surfaces are arranged per order.

Product Specifications

E and G: The Two Numbers Behind Spring Stiffness

Spring stiffness does not come from tensile strength. It comes from the modulus of elasticity. For compression and extension springs the governing value is the shear modulus G; for torsion bars and flat formed parts it is Young's modulus E. For austenitic stainless wire these sit near E = 193 GPa and G = 77 GPa, so a designer can predict the rate of a spring before a single coil is wound.

The Rate Formula in Practice

For a helical compression spring, the rate is:

k = G x d^4 / (8 x n x D^3)

where d is wire diameter, D is mean coil diameter and n is the number of active coils. The fourth power on d explains why a 0.1 mm diameter error changes the spring rate noticeably more than the same error in coil diameter - which is why diameter tolerance on the wire matters as much as the modulus value itself.

What Cold Work Does and Does Not Change

• Cold drawing raises tensile strength dramatically but changes the modulus only slightly.
• Modulus falls as temperature rises; 304H retains its strength advantage where 304 softens.
• Setting and creep, not the modulus, limit load loss in service at high temperature.
• Residual stresses from coiling are removed by low-temperature stress relief, without altering E.

Applications

• Calculated-rate compression and extension springs
• High-temperature valve and fastener springs
• Precision torsion and flat-form springs
• Spring pins and retaining rings

Product Advantages

• Tight diameter tolerance for predictable spring rate
• Guaranteed carbon minimum for stable elevated-temperature behaviour
• Consistent cast and helix for automatic coiling
• Certificates report the data designers need for calculation

Quality Control

Diameter is verified with laser micrometers along the coil, and tensile testing follows ASTM A370 / EN ISO 6892. Each batch ships with a 3.1 mill test certificate stating chemistry and mechanical values, so the modulus-based calculation can be trusted before winding starts.

Selection and Ordering Notes

1. Share the target spring rate and working temperature range.
2. Select the diameter and tolerance class together - rate depends on d^4.
3. Confirm temper (drawn classes per EN 10270-3) and surface finish.
4. Ask for stress relief recommendations for your coiling process.
5. State coil weight and packaging format.