- Key Takeaways
- What Makes Steel Suitable for Spring Applications?
- What Properties Matter in Spring Steel?
- What Are the Common Spring Steel Grades?
- 5160 vs. 65Mn: Which Should You Choose?
- What Forms of Spring Steel Are Available?
- How Is Spring Steel Processed into Custom Parts?
- How Do You Choose the Right Spring Steel Grade?
- What Are the Common Uses of Spring Steel?
- FAQ
Spring steel is a group of steels engineered to withstand repeated elastic deformation without yielding. Its high yield strength and fatigue resistance come from its composition, alloying elements, and heat treatment. This guide covers common grades such as 5160 and 65Mn, the sheet and strip forms used for custom parts, the fabrication limits that matter when you cut and bend them, and typical industrial applications.
Key Takeaways
Spring steel is designed to withstand repeated elastic deformation without permanent set.
Yield strength, hardness, toughness, and fatigue resistance are the properties that decide grade selection.
5160 and 65Mn are two of the most common grades, with different alloying and different hardenability.
Spring steel sheet and strip are the forms used for custom laser cut and formed components.
Grade selection should account for loading, geometry, the fabrication process, and material availability.
Table of Contents
- 1. What Makes Steel Suitable for Spring Applications?
- 2. What Properties Matter in Spring Steel?
- 3. What Are the Common Spring Steel Grades?
- 4. 5160 vs. 65Mn: Which Should You Choose?
- 5. What Forms of Spring Steel Are Available?
- 6. How Is Spring Steel Processed into Custom Parts?
- 7. How Do You Choose the Right Spring Steel Grade?
- 8. What Are the Common Uses of Spring Steel?
- 9. FAQ
What Makes Steel Suitable for Spring Applications?
Spring steel is suited to spring applications because it can withstand relatively large elastic strains before yielding. Its advantage does not come from a different elastic modulus: Young’s modulus is broadly similar across most steels. What sets spring steels apart is a high yield strength, which lets a component flex under load and return to its original geometry once the load is removed.
Within the elastic limit, a spring stores strain energy and recovers its shape after unloading. Exceed the yield strength and the deformation is permanent. Composition and heat treatment together provide the strength, hardness, toughness, and fatigue resistance the part needs to survive repeated loading.
What Properties Matter in Spring Steel?
Strength, Hardness and Elastic Deformation
Yield strength is the property that matters most, because it determines how much stress the component can take before it deforms permanently. Tensile strength and hardness matter too, particularly where the part has to hold its shape and resist wear in service. Maximum hardness is not the goal, though: push hardness too high and toughness drops, which makes the part more likely to crack under shock or heavy cyclic load.
Fatigue Resistance and Heat Treatment
Fatigue resistance is critical because springs see repeated loading throughout their service life. The required combination of strength and toughness is normally achieved through austenitizing, quenching, and tempering, with the exact cycle set by the grade and the target properties. Shot peening can improve fatigue performance further by introducing compressive residual stresses at the surface.
This is why a grade name on its own tells you very little. The same 5160 bar, oil quenched and then tempered at different temperatures, gives you materials with almost nothing in common: tempered at 205 °C it reaches 2,220 MPa tensile at 625 HB; tempered at 650 °C it comes out at 895 MPa and 270 HB. A drawing that calls for 5160 without naming the tempering temperature has not specified the material.
| Tempering temperature | Tensile strength | Yield strength | Hardness |
|---|---|---|---|
| 205 °C | 2,220 MPa | 1,790 MPa | 625 HB |
| 315 °C | 2,000 MPa | 1,770 MPa | 555 HB |
| 425 °C | 1,605 MPa | 1,460 MPa | 460 HB |
| 540 °C | 1,165 MPa | 1,040 MPa | 340 HB |
| 650 °C | 895 MPa | 800 MPa | 270 HB |
SAE 5160, 13 mm round bar, oil quenched from 830 °C. Section size changes these figures and bar data does not transfer directly to sheet or strip. Hardness above roughly 450 HB is converted from Rockwell C (625 HB ≈ 60 HRC), not measured on a Brinell tester.
Carbon and Alloying Elements
Carbon drives strength and hardness and governs how the steel responds to heat treatment. Chromium, manganese, and silicon modify hardenability, strength, and toughness - how much depends on the grade and the final heat treated condition.
What Are the Common Spring Steel Grades?
5160 Spring Steel
SAE 5160 is a chromium alloy spring steel used where the part needs high strength, toughness, and resistance to repeated loading. Chromium improves hardenability, so a consistent hardened structure can be achieved through heavier sections. It is the standard choice for automotive leaf and coil springs and other components under demanding cyclic loads.
65Mn Spring Steel
65Mn is a high carbon manganese spring steel. For custom sheet metal components that do not need the hardenability of 5160, it is a practical and cost effective choice. Komacut stocks 65Mn at its China facility only; the Mexico / North America facility does not currently carry this grade. GB/T 1222-2007 sets the minimum properties for the grade: yield strength of at least 785 MPa and tensile strength of at least 980 MPa. Our materials page additionally lists a hardness range of HB 190–340 for the material as supplied. GB/T 1222-2016 has since superseded the 2007 edition.
Other Spring Steel Grades
Beyond 5160 and 65Mn, a handful of grades cover most other requirements. Where corrosion resistance matters, the stainless spring grades take over - they trade some cost and formability for the ability to run in wet or washdown environments.
| Grade | Type | Typical hardness (stated condition) | Typical applications |
|---|---|---|---|
| AISI 1095 | High carbon spring steel | 48–51 HRC, blue tempered | Springs, steel tapes, clips, washers |
| AISI 1075 | Carbon spring steel | 44–47 HRC, blue tempered, thin gauge | Springs, shims, clips, washers, wear strips |
| 50CrV4 / 51CrV4 (1.8159) | Chromium vanadium spring steel | ≈ 42–50 HRC, working condition | Automotive suspension springs, leaf springs, coil springs |
| SAE 9254 | Silicon chromium spring steel | 335 HB (≈ 36 HRC), oil quenched and tempered at 425 °C | Automotive suspension and valve springs |
| Type 301 (UNS S30100) | Austenitic stainless, hardened by cold work | 41 HRC, full hard (1,276 MPa / 185 ksi tensile) | Constant force springs, clips, contacts where corrosion resistance is needed |
| 17-7 PH (UNS S17700) | Precipitation hardening stainless | ≈ 46 HRC min, condition CH900 (1,650 MPa / 240 ksi min tensile) | Aircraft springs, bellows, diaphragms, corrosion resistant springs |
5160 vs. 65Mn: Which Should You Choose?
The two grades are not interchangeable, and the figures below only mean something alongside the condition they were measured in. Spring steel properties swing enormously with tempering temperature, so a comparison that ignores heat treatment is worthless.
| Property | 5160 | 65Mn |
|---|---|---|
| Carbon | 0.56–0.64% | 0.62–0.70% |
| Defining alloying element | Chromium, 0.70–0.90% (manganese is also present at 0.75–1.00%) | Manganese, 0.90–1.20% |
| Tensile strength | 1,165 MPa oil quenched, tempered at 540 °C (rises to 2,220 MPa at a 205 °C temper) | ≥ 980 MPa to GB/T 1222-2007 |
| Yield strength | 1,040 MPa oil quenched, tempered at 540 °C (1,790 MPa at a 205 °C temper) | ≥ 785 MPa to GB/T 1222-2007 |
| Hardness | 340 HB (≈ 37 HRC) at a 540 °C temper; up to 625 HB at a 205 °C temper, where elongation falls to 4% | HRC 42–48 as stocked, supplied hardened and tempered (confirmed with the China facility) |
| Hardenability | Higher. Chromium supports a consistent hardened structure through heavier sections | Moderate. Manganese improves hardenability, best suited to thinner sections |
| Typical applications | Automotive leaf and coil springs, heavy duty suspension components, wear strips | Sheet metal spring components, small flat springs, clips, saw blades |
| Supplied condition | Depends on the mill and the order - state what you need | Hardened and tempered, HRC 42–48. Komacut does not heat treat it in house |
| Stock thickness | Bar and plate, mill dependent | 1.0, 1.5, 3.0 and 6.0 mm sheet, ±0.1 mm on thickness |
| What to specify | State the tempering temperature and the required final properties, not just the grade | It arrives hard. Design the part to be cut, not formed, unless you have confirmed the bend |
Engineering Recommendation
For automotive suspension springs, heavy duty leaf springs, or anything under severe cyclic loading, specify 5160. The chromium content gives it the hardenability and the strength-toughness balance those parts need.
For custom sheet metal parts, small flat springs, saw blades, and cost sensitive applications under moderate cyclic loading, 65Mn does the job at lower cost. If the part will be exposed to moisture or a washdown environment, look at a stainless spring grade instead - coating a carbon spring steel is a compromise, not a fix. One caveat on sourcing: Komacut lists SS301 in the annealed condition (HB 76–187), not spring temper, so specify the temper explicitly if you need spring properties from a stainless grade.
What Forms of Spring Steel Are Available?
Spring Steel Sheet
Spring steel sheet is a flat rolled form used for custom components that need high strength and elastic recovery. Depending on grade and supplied condition, it can be cut and formed into flat springs, clips, retaining components, clamps, and brackets. Thickness should be chosen alongside the required mechanical properties, not as a separate decision - a thinner section in a harder condition and a thicker section in a softer one can deliver the same spring rate with very different formability.
Spring Steel Strip
Spring steel strip is a narrow flat form used where the component needs controlled flexibility and consistent elastic recovery. Typical parts are flat springs, clips, electrical contacts, retaining components, and stamped or bent parts. Strip suits narrow geometries that flex repeatedly without taking a set.
How Is Spring Steel Processed into Custom Parts?
Laser Cutting
Laser cutting produces complex profiles from spring steel sheet and strip without dedicated stamping dies, which is what makes low and medium volumes viable. Cutting parameters have to suit the grade, thickness, and supplied condition so heat input stays controlled and edge quality holds up.
Komacut cuts sheet metal from 0.5 mm up to 20 mm, on standard sheet sizes of 1.2 × 2.4 m or 1.5 × 3.0 m. Standard laser cutting tolerance is ±0.45 mm on linear dimensions and ±0.12 mm on hole diameters; high precision tightens that to ±0.20 mm and ±0.08 mm. Minimum internal corner radius is R0.2. On a flat spring or clip that corner radius matters more than it sounds: sharp internal corners concentrate stress and are where fatigue cracks start.
CNC Sheet Metal Bending
Springback is the thing that catches people out. Higher strength material recovers elastically after bending, so the tool has to overbend to land on the specified angle. How much depends on material strength, thickness, bend radius, tooling, and target angle - there is no single compensation figure that works across grades.
Bend radius is the other constraint. Komacut’s design for manufacturing rules require an inside bend radius at least equal to material thickness (R ≥ T), with bend-to-hole distance of 2T + R for holes up to 25.4 mm and 2.5T + R for larger holes or slots. Hole-to-edge spacing must be at least 2T and hole-to-hole at least 5T. Those are minimums for sheet metal generally; harder spring tempers need more.
One thing worth planning around: once a part has a bend, the bend tolerance sets what you can hold, not the cutting tolerance. Standard bending is ±1.0° on angle and ±0.45 mm on dimensions across the bend, tightening to ±0.5° and ±0.20 mm on high precision. A flat spring cut to ±0.20 mm and then formed will carry the bending tolerance on any dimension that crosses the bend line.
Material condition changes the picture completely. Annealed spring steel is more formable than hardened and tempered strip, but there is no universal bend radius. The achievable radius depends on the grade, thickness, temper, grain direction, tooling, and flange geometry. Published bend-radius values should therefore be treated as supplier- and process-specific guidance, not limits that transfer automatically between materials or manufacturers.
This matters more for 65Mn at Komacut than the generic advice suggests, because the stock is already hard. At HRC 42–48 the material is at full spring temper, and the R ≥ T rule that governs mild steel does not carry over - fully hardened spring steel cracks at radii that annealed material shrugs off, and it springs back much further. If your part needs a formed flange rather than a flat profile, check with us whether the bend is achievable in this material at all before you commit to the geometry. A design that assumes annealed strip and gets hardened strip will not bend to the drawing.
The alternative most engineers reach for - bend it soft, harden it afterwards - is not available here either, because Komacut buys the material in its final condition rather than heat treating in house. For flat laser cut profiles this is an advantage: you get consistent, certified spring temper with no post processing and no distortion from a heat treat cycle. For formed parts it is a real constraint, and it is better to know about it at the design stage than after the first article.
Komacut bends up to 2,400 mm long, 600 mm wide, and 10 mm thick. Standard bending tolerance is ±1.0° on angles and ±0.45 mm on dimensions; high precision is ±0.5° and ±0.20 mm.
Confirmed with the China facility: Komacut stocks 65Mn in 1.0, 1.5, 3.0 and 6.0 mm sheet, held to ±0.1 mm on thickness, and buys it already hardened and tempered to HRC 42–48. There is no heat treatment step in house, so the material you order is the material you get - you cannot ask for it soft, form it, and have it hardened afterwards.
Surface Finishing
Carbon and low alloy spring steels rust. Any part going into a humid or corrosive environment needs protection - oiling, phosphating, black oxide, zinc plating, or powder coating, depending on the service conditions. See Surface Finishing for the full list. For 65Mn specifically, Komacut offers powder coating and e-coating - zinc plating, anodising and passivation are not available on this grade. Coating thickness eats into dimensional tolerance, so account for it on parts with tight fits, and check that the finish will not interfere with the spring function or with electrical contact where that matters.
How Do You Choose the Right Spring Steel Grade?
Start with the load and the strength it demands, then work through geometry, thickness, the fabrication process, heat treatment, and availability.
1. Required Mechanical Performance
Define the yield strength, tensile strength, hardness, toughness, and fatigue performance the part has to hit - and the condition those figures apply to.
2. Loading Condition
Establish whether the load is static, dynamic, impact, or reversing. Cyclic stress magnitude and component geometry drive fatigue life more than the grade name does.
3. Component Geometry and Material Thickness
Thicker sections demand more hardenability. Thin sheet and strip bring their own forming and heat treatment constraints. Check the bend radius against the R ≥ T minimum before the geometry is locked.
4. Manufacturing Process
Match the supplied condition to the process. Annealed material where the part needs substantial forming; hardened and tempered where it needs little forming after cutting.
5. Heat Treatment Requirements
Confirm the quenching and tempering the grade needs is actually available, and specify the tempering temperature rather than a hardness alone.
6. Material Availability
Availability decides more grade selections than engineers expect. Komacut stocks 65Mn in 1.0, 1.5, 3.0 and 6.0 mm sheet at the China facility, hardened and tempered to HRC 42–48; it is not currently offered at the Mexico / North America facility. If your design needs 2 mm or 4 mm, that is a conversation before you draw it. For current options, see Komacut’s sheet metal materials. For broader guidance on picking a carbon steel grade, see our Guide to Carbon Steel Material Selection.
What Are the Common Uses of Spring Steel?
In automotive assemblies, spring steel shows up as retaining clips, clamps, leaf and coil springs, and other components living under repeated load and vibration. Valve springs are the demanding case: controlled elastic behaviour and fatigue resistance over hundreds of millions of cycles.
In industrial and mechanical equipment, it is used for flat springs, Belleville washers, retaining rings, circlips, snap rings, and similar fastening and retention parts. These rely on the material flexing during assembly and then holding a predictable spring force for the life of the machine.
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FAQ
What is spring steel?
Spring steel is a high carbon or low alloy steel selected for its ability to flex under load and recover its original shape. Its combination of strength, hardness, toughness, and fatigue resistance suits it to components under repeated loading.
Is spring steel magnetic?
Most carbon and low alloy spring steels - including 5160, 65Mn, 1075, and 1095 - are magnetic. Austenitic stainless spring steels such as annealed Type 301 are generally non-magnetic, though cold working raises magnetic response through partial martensitic transformation.
A magnet gives a quick indication but cannot identify a specific grade. Use a material certificate, grade marking, or chemical analysis for verification.
What is the difference between spring steel and stainless steel?
Spring steel is selected for strength, elastic recovery, and fatigue resistance. Stainless steel is selected for corrosion resistance. The categories overlap: 301 and 17-7 PH are stainless grades used as spring materials.
Choose carbon or alloy spring steel when strength and cost lead. Choose stainless spring steel when the part will see moisture, chemicals, or washdown.
Can spring steel be welded?
Yes, but it needs careful process control. Carbon and low alloy grades such as 5160, 65Mn, 1075, and 1095 form hard, brittle microstructures in the heat affected zone and become crack sensitive.
Welding hardened and tempered spring steel also alters the heat treated condition locally and degrades spring performance. Preheating, low hydrogen practice, controlled heat input, and post weld treatment may all be required. For fatigue critical or load bearing springs, avoid welding unless a qualified procedure exists for that material and application.
Is 5160 a spring steel?
Yes. SAE 5160 is a chromium alloy spring steel used for automotive leaf and coil springs. Its chromium content improves hardenability and supports the strength and toughness demanding spring applications require.
What is 65Mn spring steel used for?
65Mn is used for springs, clips, retaining components, saw blades, and other parts needing strength and elastic recovery. Komacut stocks it at the China facility only, in 1.0, 1.5, 3.0 and 6.0 mm sheet, supplied hardened and tempered to HRC 42–48.
Is spring steel available as sheet and strip?
Yes. Both forms are available depending on grade, supplier, and required condition. They are the usual starting point for flat springs, clips, retaining components, and stamped parts.
Can spring steel be laser cut and bent?
Yes. Spring steel sheet and strip laser cut well. Bending depends on grade, hardness, thickness, and bend geometry - springback has to be compensated, and fully hardened material may not be formable at all without cracking. Where the material is supplied at spring temper, as Komacut supplies 65Mn, confirm the bend before designing it in.