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Stainless steel coil springs made from flat strip commonly use cold-worked 301. Grades 304 and 316 are alternatives when fabrication or corrosion requirements justify a different choice; 17-7PH is an option for designs requiring precipitation hardening. Material selection must include temper, dimensions, edges and operating conditions. This Myriad guide focuses on flat spiral and constant-force springs, where half hard material is a candidate to evaluate, not a universal specification.
Choosing a spring material involves more than naming a stainless steel grade. The same alloy can arrive annealed or heavily cold-worked, with different strength and forming behavior. A strip that passes a chemistry check can still be unsuitable for the required load, travel or production process.
The distinction matters when ordering 301 stainless steel coil: “coil” describes the supplied material package, not a finished spring. According to spring manufacturer Vulcan Spring, most of its flat steel springs use Type 301. That supports treating 301 as a practical starting point for this application, without assuming it is the best choice for every mechanism.
HV: 150~190. This is a stainless steel coil with lower hardness and tensile strength. It is an annealled stainless steel coils. It is used to produce mechanical equipment And parts, and because of its strong plasticity, it can be used to make machinery housing or furniture.
HV: 250~300. It is also called half-hard stainless steel coil. It has certain tensile properties. 1/2H stainless steel coil needs to be annealed. It is mainly Used in machining and parts industry.
HV: 310~360. It is the stainless steel coil that Myriad is best at. 3/4H stainless steel coil has good extensibility. After machining, it can be quickly hardened. It is mainly used to produce elastic products, such as clamps, springs, oil pipelines, etc.
HV: 370~580. Full Hard stainless steel coil has high tensile strength and hardness. It is mainly used to produce mechanical springs and some products that do not require secondary deep processing. It is also widely used in the production of knife.
Flat spiral, power and constant-force springs use strip shaped into a coiled form. Their material requirements differ from those of round-wire compression and extension springs. Before comparing grades, identify whether the mechanism must deliver rotational torque or a linear pulling force, and define the required output over its working range.
A flat spiral spring stores energy as its strip bends during rotation. Its torque depends on the design and angular position; a spiral shape alone does not make torque constant. A constant-force spring uses preformed strip that unrolls to provide approximately constant linear force over a specified working stroke. Vulcan distinguishes these from constant-torque spring assemblies, which deliver rotational output. Vulcan Spring: flat spring designs
For a buyer, this creates two separate specifications. The material specification describes the incoming strip. The finished-spring drawing describes force or torque, movement, mounting and acceptance criteria. Neither document replaces the other.
Product standards also depend on material form. ASTM A666 addresses annealed or cold-worked austenitic stainless flat products, including strip; ASTM A313 covers stainless spring wire. Do not copy a wire tensile-strength table into a strip purchase order simply because both products share a grade designation. ASTM A666 scope, ASTM A313 scope
Start by evaluating 301 for conventional flat-strip spring designs. Consider 304 or 316 when the application creates a reason to change the corrosion or fabrication balance. Consider 17-7PH when a qualified precipitation-hardening route offers an advantage. These are candidate materials, not interchangeable replacements for an existing spring drawing.
| Material | Reason to evaluate it | Decision that still needs validation |
|---|---|---|
| 301 stainless steel | Established cold-worked strip option for flat springs | Required strength, forming limits and fatigue life in the actual geometry |
| 304 stainless steel | General-purpose corrosion resistance with useful fabrication characteristics | Whether the available strip condition meets the spring’s stress and forming requirements |
| 316 stainless steel | Molybdenum-bearing alternative when localized corrosion is a concern | Environmental suitability and sufficient mechanical properties in the purchased condition |
| 17-7PH stainless steel | Precipitation-hardening option for strength and demanding service requirements | Delivery condition, forming sequence, heat treatment and final-property acceptance |
301 develops high strength through cold working. Ulbrich identifies full-hard and extra-full-hard conditions among the options used for spring strip, while emphasizing the balance between strength and remaining ductility. This makes the temper part of the material choice rather than a secondary purchasing detail.
Use the spring drawing to establish the required condition before requesting a quotation. A supplier’s general 301 coil listing does not establish that every thickness, width and tensile range is available together.
304 is a useful general-purpose stainless steel, but its corrosion and fabrication credentials do not independently qualify a strip for spring service. The Australian Stainless Steel Development Association describes 304 as a starting point for many stainless applications. For a spring, buyers must additionally specify the cold-worked condition and relevant mechanical requirements. ASSDA: 304 grade selection
316 contains molybdenum, which improves resistance to localized corrosion in many environments compared with molybdenum-free austenitic grades. Outokumpu includes 316 in its Supra range for more demanding corrosion conditions. However, neither a “marine” description nor the grade number guarantees suitability for seawater immersion, trapped deposits or a particular cleaning chemical. Outokumpu: Supra range
Avoid ranking 301, 304 and 316 by strength without identifying their conditions. Comparing full-hard 301 against annealed 316 would mix the effects of alloy selection and processing. Request mechanical data for the actual strip being considered.
17-7PH, UNS S17700, is a precipitation-hardening stainless steel available in strip form. Ulbrich identifies springs among its applications and explains that age hardening provides the strengthening mechanism. Its use requires coordination between the material supplier and the spring manufacturer over delivery condition and subsequent processing. Ulbrich: 17-7PH strip and processing
Specify the intended final condition and inspect the finished component after the agreed process. Do not transfer fatigue figures for 17-7PH wire springs to flat-strip springs: the ARMCO technical bulletin distinguishes its test forms and conditions. ARMCO: 17-7PH technical bulletin
Half hard stainless steel can suit some formed spring components when its strength and formability meet the drawing. It should not be the default for every constant-force or flat spiral spring. Select the condition from the working stress, required forming operations and acceptable permanent deformation, then verify the finished design.
“Half hard” describes a material condition, not a stainless grade or a universal hardness number. Ulbrich explains that cold working changes stainless steel’s strength and ductility. For cold-worked austenitic strip, annealing generally softens the material; it is not a universal final step for preserving the purchased half-hard condition.
The following values illustrate why the condition matters. ASSDA’s published table lists these minimum properties for Type 301 flat products under A666:
| Published 301 condition | Minimum 0.2% proof strength | Minimum tensile strength |
|---|---|---|
| Half hard | 760 MPa | 1,035 MPa |
| Full hard | 965 MPa | 1,275 MPa |
These are published reference values, not allowable design stresses or Myriad supply guarantees. ASSDA instructs readers to consult the relevant product standard for definitive requirements. Confirm the applicable standard edition, thickness-dependent provisions, test direction and agreed acceptance values before ordering. ASSDA: mechanical properties
For a component with demanding bends or formed ends, a lower-strength condition may help fabrication. For a tightly packaged spring, it may leave insufficient resistance to permanent set. The practical decision is whether the material can be formed successfully and then meet the finished spring’s performance requirement.
Request tensile strength, proof strength and elongation where relevant to the specification. Hardness can be an agreed inspection parameter, but a hardness reading alone cannot establish fatigue life, the force curve or the suitability of a forming process.
Stainless Steel Belt: Characteristics, Advantages, and Applications
Dimensions, edge quality, spring geometry and service conditions must be considered alongside grade and temper. Treat material certificates as evidence about the incoming strip, then use finished-spring testing to verify the mechanism. Vulcan’s design guide explicitly links constant-force spring selection with dimensions, required force and desired cycle life. Vulcan Spring: design guide
Thickness and width: Put tolerances on the drawing and purchase order. When comparing quotations, confirm that suppliers are quoting the same measurement requirements. A nominal size without tolerances leaves an important part of the specification open.
Edges and surfaces: Define acceptable burrs, edge profiles, scratches and handling damage. Ask the spring manufacturer which edge condition the design requires, rather than assuming that every slit edge or every rounded edge will perform identically. Include the inspection method so supplier and buyer assess the same features.
Force, travel and mounting: Specify the working stroke or rotation, allowable output variation and end details. State whether the force or torque is measured during loading, unloading or both. The qualification fixture should reproduce the relevant mounting and contact conditions.
Fatigue and permanent set: Define the cycle, test frequency, environment and failure criterion. A target such as “long life” is not an acceptance requirement. Separately specify any permissible loss of force, torque or dimensional recovery after testing; a spring can become unacceptable before it breaks.
Temperature and exposure: Record operating temperature, dwell time, cleaning media and wet or dry conditions. Corrosion evaluation must consider temperature, chemical concentration and crevices rather than relying on an alloy nickname. Outokumpu’s corrosion guidance explains why environmental conditions govern stainless steel selection. Outokumpu: corrosion resistance
These checks create a measurable qualification plan. They do not establish a universal cycle-life or temperature rating for 301, 304, 316 or 17-7PH.
Build the request for quotation around the spring drawing, required material condition and inspection requirements. Grade selection should follow the operating conditions, while the final order should identify measurable strip requirements. The following examples are illustrative selection scenarios, not customer case studies or proven outcomes.
Scenario 1 — an indoor constant-force retractor: Begin by evaluating 301 spring strip with the spring designer. Confirm force across the required stroke, coil envelope and life-test conditions. Compare candidate tempers through forming and component trials before approving the material specification.
Scenario 2 — a formed flat spiral spring: If bends or attachment details are difficult to form, evaluate whether half hard stainless steel provides a workable balance. Check the resulting torque curve and permanent set. Easier forming is useful only if the finished spring still meets its operating requirements.
Scenario 3 — a mechanism exposed to cleaning chemicals: Record the chemical, concentration, temperature and contact time before considering 316. If temperature-related force retention is also a concern, investigate suitable material and processing options, including 17-7PH where appropriate. Neither substitution should bypass environmental and component validation.
A useful material inquiry includes:
For a 301 stainless steel coil inquiry, share the strip specification with Myriad for a material-supply review. Myriad’s documented grade scope includes 301, 304 and 316; availability of the requested size, condition and edge combination requires confirmation. The discussion of 17-7PH here is technical guidance, not a statement of Myriad supply capability.
Stainless steel coil springs perform as a combination of material, geometry and manufacturing process. Start with 301 for many flat-strip designs, evaluate alternatives for a stated reason, and approve the material against measured requirements. Keep incoming-strip acceptance and finished-spring qualification connected throughout purchasing.
301 is a common starting point for flat-strip springs. The appropriate choice depends on temper, geometry and exposure; 304, 316 and 17-7PH are alternatives to evaluate against specific requirements rather than automatic upgrades.
No. It is coiled raw material that must be processed into the required spring geometry. Specify its dimensions and mechanical condition separately from the finished spring’s force, torque and life requirements.
Only after the design and process have been checked. Published reference minima differ substantially: ASSDA lists 760 MPa proof strength for half-hard 301 and 965 MPa for full-hard 301, so replacement is not simply a purchasing substitution.
No. 316 may address a corrosion requirement, but its purchased condition must also meet the mechanical specification. An environmental advantage does not establish equal spring performance in unchanged geometry.
The answer depends on the alloy, delivery condition and manufacturing route. Cold-worked 301 and precipitation-hardening 17-7PH use different strengthening routes, so a heat-treatment instruction must identify the material and required final condition rather than apply a generic spring recipe.
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