Spring Steel Selection: Types, Properties, and Applications

Springs store and release mechanical energy through elastic deformation. The material must withstand repeated stress cycles without taking permanent set—a demanding requirement that limits material options and requires careful selection based on operating conditions.

What Makes Steel “Spring Steel”

Any steel can technically function as a spring, but practical spring steels share several critical characteristics that separate them from ordinary structural materials.

High yield strength is the most fundamental requirement. The material must return to its original shape after loading, and higher yield strength means higher allowable stress without permanent deformation. A spring that takes a set is a failed spring.

High fatigue strength matters because springs typically experience millions of load cycles over their service life. The material must resist crack initiation and propagation under cyclic stress, which is a different failure mode than static overload.

Despite high strength, adequate ductility is necessary because the material must tolerate some plastic deformation without fracturing. This is especially important for shock loading where instantaneous stresses can exceed the design envelope.

Finally, consistent properties ensure predictable spring behavior. Variation in material properties causes inconsistent spring rates, which can be catastrophic in precision applications. This is why spring steels are produced to tight specifications with careful quality control.

Carbon Spring Steels

1074 / 1075 (ASTM A682)

The workhorse spring steel for flat springs and stamped springs, 1074/1075 dominates general-purpose applications because it delivers excellent spring properties at low cost.

Property	Value
Carbon	0.70-0.80%
Manganese	0.50-0.80%
Typical Hardness	44-48 HRC
Tensile Strength	225-280 ksi
Max Thickness (through-harden)	0.125”

This grade finds its way into clock springs, flat springs, retaining clips, lock springs, and electrical contacts. Its popularity stems from easy hardening by oil quenching and ready availability in strip form with various tempers. The limitation is hardenability—thicker sections won’t through-harden, restricting use to thin cross-sections. Like all carbon steels, it requires corrosion protection in most environments.

1095 (ASTM A682)

When maximum hardness in a carbon steel is required, 1095 is the answer. Its higher carbon content pushes hardness to levels unachievable with lower-carbon grades.

Property	Value
Carbon	0.90-1.03%
Manganese	0.30-0.50%
Typical Hardness	50-60 HRC
Tensile Strength	280-330 ksi
Max Thickness (through-harden)	0.090”

Applications include thin springs requiring the highest strength, scrapers, knives, and high-stress flat springs where the section is thin enough to harden properly. The grade achieves the highest hardness of plain carbon steels, delivering maximum strength for a given thickness.

However, 1095 demands respect in heat treatment. Very poor hardenability means water or brine quenching for thin sections only—oil quenching won’t develop full hardness. The material is more brittle than lower-carbon grades and sensitive to decarburization during heat treatment, requiring careful atmosphere control.

Music Wire (ASTM A228)

For helical springs, music wire is the default choice. This pre-hardened round wire comes ready for spring forming with no additional heat treatment needed.

Property	Value
Carbon	0.80-0.95%
Typical Tensile	230-400 ksi (varies with diameter)
Diameter Range	0.004” - 0.250”

Music wire dominates precision helical springs, extension springs, and torsion springs because it offers the highest strength and best fatigue properties of any common spring wire. The material is cold-drawn to develop its properties, so springs only require stress relief after forming rather than full heat treatment.

The limitations are maximum diameter (larger sections aren’t available) and temperature—properties degrade above 250°F, making it unsuitable for elevated-temperature service. Corrosion protection is required for any exposed application.

Alloy Spring Steels

5160 (Chrome-Vanadium Spring Steel)

When sections are too thick for carbon steel to through-harden, 5160 is the standard choice. The chromium addition transforms hardenability, allowing oil quenching of sections that would remain soft in 1074 or 1095.

Property	Value
Carbon	0.56-0.64%
Chromium	0.70-0.90%
Manganese	0.75-1.00%
Typical Hardness	40-48 HRC
Tensile Strength	180-230 ksi
Max Thickness (through-harden)	0.500”

Automotive leaf springs, coil springs, torsion bars, and agricultural equipment springs all commonly use 5160. The grade offers excellent fatigue properties and is more forgiving in heat treatment than plain carbon steels—the process window is wider and the consequences of small variations are less severe.

The trade-off is higher cost than carbon steels and the requirement for proper heat treatment to develop properties. The material has no shortcuts; you must invest in the heat treatment process.

6150 (Chrome-Vanadium)

Similar to 5160, this grade adds vanadium for grain refinement, which translates to improved fatigue resistance and toughness.

Property	Value
Carbon	0.48-0.53%
Chromium	0.80-1.10%
Vanadium	0.15% min
Typical Hardness	40-46 HRC
Tensile Strength	180-220 ksi
Max Thickness (through-harden)	0.500”

Heavy-duty automotive springs, agricultural equipment springs, and high-stress applications requiring toughness benefit from 6150. The vanadium creates a finer grain structure that resists fatigue crack propagation, making it excellent for applications with shock loading.

Premium cost and less common stocking compared to 5160 are the practical limitations. For applications that don’t specifically need the improved toughness, 5160 is usually more economical.

9254 (Silicon-Manganese)

This high-silicon grade targets valve springs and premium applications where standard chrome-vanadium grades fall short.

Property	Value
Carbon	0.51-0.59%
Silicon	1.20-1.60%
Manganese	0.60-0.80%
Chromium	0.60-0.80%
Typical Hardness	46-50 HRC

Valve springs, high-performance suspension springs, and racing applications specify 9254 because silicon increases the elastic limit and fatigue strength beyond what chrome-vanadium grades achieve. The material also maintains properties at elevated temperatures better than most alternatives.

The expense and demanding heat treatment requirements—careful control is needed to avoid decarburization—limit use to applications that genuinely need the superior properties.

Stainless Spring Steels

17-7PH (ASTM A693)

When corrosion resistance and high strength must coexist, 17-7PH is the premium choice. This precipitation-hardening stainless achieves strength levels approaching carbon steel springs.

Property	Value
Chromium	16-18%
Nickel	6.5-7.75%
Aluminum	0.75-1.50%
Condition	CH900 (precipitation hardened)
Tensile Strength	200-235 ksi

Marine springs, chemical processing equipment, and food processing equipment all rely on 17-7PH when both corrosion resistance and high strength are non-negotiable. The alloy can be formed in the solution-treated condition when it’s relatively soft, then hardened afterward.

The complex heat treatment sequence—solution treat, cold work, then precipitation harden—and the high material cost limit use to applications that genuinely require the combination of properties. Supplier options for some forms can also be limited.

302/304 Stainless (ASTM A313)

For applications where moderate strength suffices, austenitic stainless springs offer good corrosion resistance at reasonable cost.

Property	Value
Chromium	17-19%
Nickel	8-10%
Condition	Spring temper (cold worked)
Tensile Strength	125-185 ksi

Springs in corrosive environments where 17-7PH strength isn’t required, food service equipment, and industrial washdown environments commonly use 302/304. The grades are readily available in wire and strip form with spring temper already developed.

The important limitation is that these are not heat-treatable for hardness. Properties come from cold work during drawing or rolling, so you can’t heat treat to harden after forming—only stress relieve. Lower strength than carbon or 17-7PH and stress relaxation at elevated temperatures are inherent limitations.

420 Stainless (Hardened)

Martensitic stainless fills the gap between austenitic stainless and carbon steel, offering heat treatability with moderate corrosion resistance.

Property	Value
Chromium	12-14%
Carbon	0.15% min
Typical Hardness	48-52 HRC
Tensile Strength	180-220 ksi

Springs requiring moderate corrosion resistance with higher hardness than 302/304 can achieve specify 420. It heat treats like carbon steel springs, making the process familiar to heat treaters.

Corrosion resistance is inferior to austenitic grades—420 is not stainless in the same sense as 304. Post-hardening tempering is required, adding a process step.

Heat Treatment Fundamentals

Spring steel achieves its properties through proper heat treatment. Understanding the process helps you specify appropriate requirements and troubleshoot problems.

Hardening

The hardening process heats steel above its transformation temperature—typically 1450-1550°F depending on grade—and quenches rapidly enough to form martensite. This microstructure is hard and brittle, providing the foundation for spring properties.

Temperature accuracy matters, with ±25°F being typical tolerance. Time at temperature must be sufficient to ensure full transformation throughout the section. Quench severity must match the steel’s hardenability—carbon steels need fast quenches while alloy steels tolerate slower cooling.

Tempering

After hardening, the steel is reheated to a lower temperature—typically 400-900°F—to restore ductility while retaining adequate hardness. The tempering temperature directly controls the final hardness and ductility balance.

Temper Temperature	Resulting Hardness	Characteristics
350-400°F	58-62 HRC	Maximum hardness, low ductility
450-500°F	52-56 HRC	High strength, moderate ductility
550-600°F	48-52 HRC	Balanced properties
650-750°F	44-48 HRC	Good toughness, lower strength

For springs, temper to achieve the target hardness based on required strength and fatigue life requirements. Higher hardness provides more strength but less tolerance for impact loading.

Pre-Tempered Material

Some spring materials come pre-hardened and tempered, eliminating the need for full heat treatment after fabrication. Music wire is cold-drawn to develop properties. Spring temper stainless strip and pre-tempered 1074/1075 strip arrive ready for forming. These materials only require stress relief after forming—typically 500-600°F for 30-60 minutes—to relieve residual stresses from the forming operation.

Selection Criteria

Load and Stress

Match material strength to operating stress levels to ensure the spring can handle the load without permanent deformation.

Application Stress	Suitable Materials
Light (< 80 ksi)	302 stainless, blue temper carbon
Moderate (80-120 ksi)	1074/1075, 17-7PH
High (120-180 ksi)	Music wire, 5160, 6150
Very high (> 180 ksi)	High-tensile music wire, valve spring quality

Fatigue Life

For cyclic applications, fatigue strength—not static strength—determines service life. The more cycles required, the more carefully you must select material and surface treatments.

Life Requirement	Material Selection
10,000 cycles	Most spring steels adequate
100,000 cycles	Music wire, alloy steels preferred
1,000,000 cycles	Shot-peened music wire, 6150
10,000,000+ cycles	Premium materials, surface treatments

Environment

The operating environment dictates corrosion resistance requirements, which may override other selection criteria.

Environment	Recommended Material
Indoor, dry	Carbon steels with oil/paint
Indoor, humid	Zinc plate or stainless
Outdoor	Stainless or galvanized
Marine	17-7PH or 316 stainless
Elevated temp (over 250°F)	Inconel X-750 or alloy steel

Section Thickness

Hardenability limits the maximum section that can be through-hardened. Exceeding these limits means the core remains soft even when the surface hardens.

Material	Maximum Through-Harden Thickness
1074/1075	0.125”
1095	0.090”
5160/6150	0.500”
Stainless	Varies by type

For thicker sections, you must use alloy steels or accept surface hardening only.

Procurement Specifications

When ordering spring steel, specify the material grade (AISI designation), the governing specification (ASTM, AMS, or proprietary), the condition or temper (annealed, pre-tempered, etc.), the form (strip, wire, bar), dimensions and tolerances, edge condition for strip (slit, deburred, round edge), surface finish requirements, and certification requirements. Complete specifications prevent receiving material that meets some requirements but not all.

Working With NextGen Components

We supply spring steels in various forms including 1074/1075 strip in annealed and pre-tempered conditions, music wire per ASTM A228, 5160 and 6150 bar stock, and stainless spring strip in 302 and 17-7PH.

Custom slitting, heat treatment, and testing are available for production requirements. Contact us with your spring application details for material recommendations and pricing.