Cold Drawn Stainless Steel Wire for Springs: Tensile Strength Guide

Introduction

Cold Drawn Stainless Steel Wire for Springs is stainless wire strengthened by repeated drawing through progressively smaller dies until the required diameter, tensile strength and spring temper are achieved. It is used for compression springs, extension springs, torsion springs, clips, retaining rings, wire forms, electrical contacts and precision mechanical components. Grade 302 or 304 is the normal starting choice for general-purpose springs, 316 is preferred for marine and chloride exposure, and 17-7PH is selected when higher strength, fatigue resistance or elevated-temperature stability is required.

Key Takeaways: Spring-wire selection cannot be based on stainless steel grade alone. Wire diameter, tensile-strength range, cold reduction, surface finish, cast, helix, straightness, forming radius and post-coiling treatment all affect spring performance. Higher tensile strength can increase load capacity, but excessive hardness may reduce formability and raise the risk of cracking during coiling.

ASTM A313/A313M is commonly specified for austenitic and precipitation-hardening stainless steel round spring wire. ISO 6931-1, EN 10270-3 and JIS G 4314 may also be referenced depending on the market and spring design. Buyers should state the complete standard, grade, diameter, tensile class, surface condition, package form and inspection documentation rather than requesting only “hard stainless wire.”

How Cold Drawing Creates Spring Strength

Cold drawing reduces wire diameter without heating the material to a recrystallization temperature. As the wire passes through each die, plastic deformation increases dislocation density within the metal structure. This process, called strain hardening or work hardening, raises tensile strength, yield strength and hardness while reducing elongation.

The amount of cold reduction determines the final mechanical condition. Lightly drawn material remains comparatively formable, while heavily drawn spring-temper wire provides high strength and strong elastic recovery. The mill may use intermediate annealing when the total reduction is too large for one drawing sequence.

The final spring does not rely on tensile strength alone. Surface defects, residual stress, wire roundness, decarburization-free condition, diameter consistency and coiling quality influence fatigue life. A shallow longitudinal scratch can become a fatigue-crack initiation point in a dynamically loaded spring.

Typical Product Data

Specification Item	Typical Options	Buyer Check
Grades	301, 302, 304, 304N, 316, 316L, 321 and 17-7PH	Match corrosion resistance, strength and temperature capability to the application.
Diameter	Fine precision wire to heavy spring wire	Confirm actual tolerance, ovality and measuring method.
Condition	Spring temper, hard drawn, half hard or custom tensile range	Specify tensile strength rather than relying only on a temper name.
Surface	Bright drawn, clean, coated, soap drawn or polished	Check lubricant compatibility with coiling, cleaning and final use.
Supply Form	Coil, spool, reel, carrier or straightened cut length	State coil weight, spool dimensions, cast and helix limits.
Certificates	MTC, EN 10204 3.1, tensile report and dimensional report	Request batch-specific documentation before production.

Recommended Stainless Steel Grades

302 and 304 for General-Purpose Springs

Grades 302 and 304 are widely used for industrial springs, clips and wire forms. Their austenitic structure provides good corrosion resistance and a strong work-hardening response. Grade 302 is commonly associated with spring-wire production, while Grade 304 offers broad availability and familiar corrosion performance.

These grades are suitable for household appliances, hardware, electrical components, automotive assemblies and general industrial equipment. Cold drawing may make the wire partially magnetic even though annealed 302 and 304 are normally considered austenitic stainless steels.

301 for High Work-Hardening Response

Grade 301 develops high strength rapidly during cold deformation. It can be useful for spring components requiring high elastic response, thin sections or strong retention force. Its greater work-hardening rate can also increase springback and make tight-radius forming more difficult.

316 for Marine and Chloride Exposure

Grade 316 contains molybdenum, which improves resistance to pitting and crevice corrosion compared with 302 or 304. It is commonly selected for marine equipment, coastal installations, food-processing machinery, chemical systems and outdoor springs exposed to salt spray.

The improved corrosion resistance does not make 316 immune to every chloride environment. Tight crevices, stagnant seawater, deposits and high temperatures still require engineering review.

17-7PH for High Strength and Fatigue Performance

17-7PH, also known as Type 631 or UNS S17700, is a precipitation-hardening stainless steel. It can be formed in a comparatively workable condition and then heat treated to develop substantially higher strength. It is used for aerospace springs, retaining rings, precision clips, valve parts and components exposed to demanding cyclic loads.

The final properties depend on the supplied condition and subsequent precipitation-hardening cycle. Buyers should define the complete material and heat-treatment route rather than ordering only “17-7PH hard wire.”

Chemical Composition Reference

The following values are simplified industry-standard composition ranges or limits. Final acceptance must follow the ordered standard edition and the actual heat analysis.

Grade	Cr, %	Ni, %	Other Key Element	Selection Effect
301	16.0-18.0	6.0-8.0	Lower nickel than 304	Strong work-hardening response and high cold-drawn strength.
302	17.0-19.0	8.0-10.0	Controlled carbon	Traditional general-purpose stainless spring-wire grade.
304	18.0-20.0	8.0-10.5	Low controlled carbon	Balanced corrosion resistance, forming and availability.
316	16.0-18.0	10.0-14.0	Mo 2.0-3.0%	Improved localized-corrosion resistance in chloride service.
17-7PH	16.0-18.0	6.5-7.75	Al 0.75-1.50%	Supports precipitation hardening and high spring strength.

Understanding Tensile Strength

Spring-wire tensile strength is strongly dependent on diameter. Fine wire can normally reach higher tensile strength than heavy wire because smaller sections receive greater effective cold reduction and contain a lower probability of critical defects. A single tensile value should therefore not be applied to every diameter.

Wire Condition	Typical Tensile Direction	Recommended Application
Soft / Annealed	Low strength with high elongation	Complex forming and components that will be strengthened later.
Half Hard	Moderate strength and retained formability	Clips, wire forms and lightly loaded springs.
Spring Temper	High tensile strength with reduced elongation	Compression, extension and torsion springs.
Precipitation-Hardened 17-7PH	Very high strength after the specified aging cycle	Aerospace, valve, precision and fatigue-sensitive springs.

For many cold-drawn austenitic spring wires, practical tensile levels may extend from approximately 1,000 MPa to above 2,000 MPa depending on grade, diameter and standard class. These figures are not universal acceptance limits. The exact range must be taken from the ordered standard or agreed mill specification for the relevant diameter.

Why the Highest Tensile Strength Is Not Always Best

A very high tensile wire may provide greater spring force, but it can also produce more springback, higher tooling wear and a greater risk of cracking around small mandrels. Spring index, which is the mean coil diameter divided by wire diameter, must be considered together with tensile strength.

For a tightly coiled spring, the buyer may need a lower tensile class or a material with better ductility. For a large-diameter coil under high load, a higher tensile class may be appropriate. Prototype coiling is recommended when the design operates near the forming limit.

Standards and Grade References

Reference	Typical Scope	Procurement Note
ASTM A313/A313M	Austenitic and age-hardenable stainless steel round spring wire	State grade, diameter, tensile requirement and supplied condition.
ISO 6931-1	Stainless steels for spring manufacture in wire form	Confirm grade designation and tensile class.
EN 10270-3	Stainless spring steel wire for mechanical springs	Check project acceptance and current referenced edition.
JIS G 4314	Stainless steel wire for springs	Common designations include SUS304-WPA and SUS304-WPB.
EN 10204	Inspection-document types including 3.1 certificates	Specify the document type in the purchase order.

Grade and Application Comparison

Grade	Strength Potential	Corrosion Direction	Best-Use Recommendation
301	High after cold drawing	General atmospheric service	High-strength clips, retaining rings and precision wire forms.
302	High and widely established for springs	Good general corrosion resistance	Compression, extension and torsion springs.
304	High after controlled cold reduction	Good indoor and outdoor resistance	Appliances, hardware, electrical and automotive springs.
316	Moderate to high depending on diameter	Improved chloride resistance	Marine, chemical, food and coastal equipment.
17-7PH	Very high after precipitation hardening	Good, but application-dependent	Aerospace, precision, valve and fatigue-sensitive springs.

Industrial Applications

Application	Recommended Grade Direction	Critical Selection Factor
General Compression Springs	302 or 304	Spring index, tensile class, load and cycle life.
Marine Equipment	316	Salt exposure, crevice conditions and cleaning frequency.
Food and Beverage Machinery	304 or 316	Cleanability, chemical exposure and surface condition.
Automotive Clips and Springs	301, 302 or 304	Fatigue, vibration, temperature and forming repeatability.
Aerospace and Precision Instruments	17-7PH or project-approved alloy	High strength, relaxation resistance and heat-treatment control.
Medical and Laboratory Devices	316L, 316LVM or specified medical grade	Cleanliness, melting route, surface quality and regulatory requirements.

Spring Manufacturing and Post-Coiling Treatment

Coiling and Forming

Cold-drawn stainless spring wire produces substantial springback during coiling. Tool settings should be developed using wire from the intended grade, diameter and tensile range. Substituting a higher-strength batch without adjusting the tooling may change coil diameter, free length and pitch.

The wire surface should be smooth and compatible with the spring machine. Drawing compounds may improve feeding, but residue can interfere with welding, plating or cleanliness requirements. The purchase order should define whether the wire is supplied dry, soap coated, lightly lubricated or specially cleaned.

Stress Relief

Cold-formed austenitic stainless springs are often stress relieved after coiling to reduce residual stress, stabilize dimensions and improve elastic behavior. The appropriate temperature and holding time depend on grade, wire diameter, spring geometry and required properties.

Stress relief does not convert 302, 304 or 316 into heat-hardened steel. Their primary strength comes from cold working. Precipitation-hardening grades such as 17-7PH require a specific transformation and aging route to develop their intended final properties.

Passivation and Surface Cleaning

After coiling and heat treatment, springs may require degreasing, descaling, passivation or electropolishing. These processes remove contamination and improve surface cleanliness. Passivation cannot repair deep scratches, laps or mechanical damage already present in the wire.

Limitations and Failure Risks

Excessive tensile strength: Wire that is too hard for the spring index can crack during coiling or produce excessive springback.

Surface defects: Seams, laps, scratches and die marks can initiate fatigue cracks under repeated loading.

Stress relaxation: Springs held under load at elevated temperature can gradually lose force. The alloy and heat treatment must match the operating temperature.

Incorrect corrosion grade: Grade 304 may corrode prematurely in severe marine or chemical exposure. Grade 316 improves resistance but is not immune to stagnant chloride crevices.

Magnetic response: Cold-worked austenitic wire can become magnetic. Applications requiring tightly controlled magnetic permeability need an agreed test method and acceptance limit.

Batch variation: Small differences in tensile strength, cast or lubricant can affect automatic coiling. Production lots should remain controlled for critical spring programs.

Inspection, Certification and Traceability

Heat and batch traceability should link every coil or spool to the original melt, drawing lot and inspection record. Package labels should identify the grade, diameter, tensile range, heat number, lot number, net weight and purchase-order reference.

An EN 10204 3.1 MTC may document the material grade, standard, heat number, chemical composition, tensile results and production identity. For spring wire, the tensile report should clearly identify wire diameter because the required strength normally changes with size.

Dimensional inspection should include diameter, ovality and, where specified, cast and helix. Surface inspection may be performed visually or with enhanced methods appropriate to the wire size. Torsion, wrapping, bend, tensile or hardness tests may be required by the material standard or customer specification.

PMI can support grade verification, particularly when distinguishing molybdenum-bearing 316 from 302 or 304. It does not verify tensile condition or complete heat chemistry. UT is not normally useful for small spring wire. Surface quality, dimensional measurement, tensile testing and forming tests provide more relevant quality evidence.

Spring Wire RFQ Checklist

✅ State the grade, UNS designation and applicable ASTM, ISO, EN or JIS standard.

✅ Provide wire diameter, tolerance and ovality requirement.

✅ Specify the tensile-strength range for the actual diameter.

✅ Identify spring type, coil diameter, forming radius and expected cycle life.

✅ Define bright, coated, lubricated, cleaned or polished surface.

✅ State coil, spool or reel dimensions, unit weight, cast and helix.

✅ Request MTC, EN 10204 3.1, tensile report and dimensional inspection.

✅ Define moisture-resistant export packaging, quantity and destination port.

FAQ

Which stainless steel grade is best for spring wire?

Grade 302 or 304 is suitable for most general-purpose springs. Grade 316 is preferred for marine and chloride exposure, while 17-7PH is selected for higher strength, fatigue resistance or elevated-temperature performance.

What tensile strength should stainless spring wire have?

The required tensile strength depends on grade, wire diameter, spring geometry and governing standard. Fine spring wire generally has a higher specified tensile range than heavy wire. The purchase order should state the applicable diameter-based range rather than one universal value.

Why does cold-drawn stainless wire become magnetic?

Cold working can transform part of the austenitic structure into deformation-induced martensite. This can make 301, 302 or 304 spring wire noticeably magnetic even though the same material may be nearly nonmagnetic in the annealed condition.

Should stainless steel springs be heat treated after coiling?

Cold-drawn austenitic springs are commonly stress relieved after coiling to stabilize dimensions and reduce residual stress. Precipitation-hardening 17-7PH springs require a grade-specific heat-treatment cycle to develop their final strength.

Related Stainless Steel Wire Products

Product	Typical Procurement Use
Stainless Steel Spring Wire Range	Spring-temper stainless wire in multiple grades, diameters and tensile conditions.
302 Stainless Steel Spring Wire	General-purpose spring wire for compression, extension, torsion and wire-form applications.
316 Stainless Steel Spring Wire	Molybdenum-bearing spring wire for marine, chemical and chloride-containing environments.
1.4568 / 17-7PH Spring Wire	Precipitation-hardening wire for high-strength and fatigue-sensitive spring components.
316L Stainless Steel Wire Applications	Material-selection guidance for soft, hard and spring-condition 316L wire.

Conclusion

Cold-drawn stainless steel wire provides the strength, elastic recovery and corrosion resistance required for industrial springs and precision wire forms. Grades 302 and 304 cover most general applications, 316 improves performance in chloride environments, and 17-7PH provides a higher-strength option for demanding cyclic loads. Reliable performance depends on controlling diameter, tensile range, surface quality, cast, helix and post-coiling treatment as one complete specification.