Spring steel is a category of steels characterized by high yield strength, which enables it to return to its original shape. This guide discusses the properties of spring steel, including its chemical composition, manufacturing processes, and practical applications.
What is Spring Steel?
Spring steel is not a single material, instead, it is a family of steels defined by their very high yield strength. This property enables the material to undergo substantial bending or twisting and return to its initial form without permanent distortion. This capacity for elastic deformation is the defining characteristic of a spring.
The primary function of a spring steel component is to absorb mechanical energy during deformation and release it as the component returns to its original position. While numerous grades exist, they are typically medium-to-high carbon steels with specific alloys or specialized grades of stainless steel. To achieve their final properties, all spring steels must undergo a precise heat treatment process.
Spring Steel Material Properties
The performance of spring steel is determined by its key mechanical and physical properties.
Mechanical Properties
| Property | AISI 1095 | AISI 5160 | 301 Stainless (Full Hard) |
| Yield Strength (MPa) | 700 – 1250 | 1150 – 1300 | ~1030 |
| Tensile Strength (MPa) | 950 – 1400 | 1250 – 1450 | ~1275 |
| Hardness (HRC) | 45 – 55 | 42 – 47 | ~41 |
| Elongation at Break (%) | 9 – 14% | 9 – 12% | ~9% |
Note: Values are approximate and can vary significantly based on the exact heat treatment and tempering process.
What these properties stand for:
Mechanical properties describe how a material responds to applied forces. For spring steel, these properties are controlled through alloying elements and heat treatment.
Yield Strength
This is the most critical property. Yield strength is the maximum stress a material can withstand before it begins to deform permanently (plastically). Spring steel is heat-treated to maximize this value, thereby expanding its elastic range to endure deformation without taking a permanent set.
Tensile Strength
Tensile strength, or Ultimate Tensile Strength (UTS), is the maximum stress a material can withstand while being stretched or pulled before necking begins and it starts to break. While yield strength defines the elastic limit, tensile strength indicates the material’s ultimate failure point. Spring steels possess high tensile strength, which contributes to their overall durability.
Hardness
Hardness is a material’s resistance to surface indentation, abrasion, and wear. It is achieved by forming a hard martensite structure during quenching. Measured on the Rockwell C scale (HRC), high hardness is crucial for applications requiring wear resistance and edge retention.
Toughness
Toughness is a material’s ability to absorb energy and resist fracturing from impacts. It represents the trade-off for hardness. The tempering process is specifically designed to increase toughness by reducing the brittleness of the fully hardened steel.
Fatigue Resistance
Fatigue resistance is the material’s ability to withstand repeated load cycles without the formation of micro-cracks that lead to failure. Alloying elements such as chromium (Cr) and vanadium (V) can improve fatigue life.
Ductility
Ductility is a measure of a material’s ability to deform under tensile stress before fracturing, often expressed as “elongation at break.” While spring steels are not considered highly ductile compared to mild steels, they must possess some ductility to prevent brittle failure.
Physical Properties
Physical properties are characteristics of the material, independent of applied forces.
| Property | Typical Value |
| Density | ~7.85 g/cm³ (0.284 lb/in³) |
| Melting Point | ~1425 – 1540 °C (2600 – 2800 °F) |
| Modulus of Elasticity | ~200 GPa (29,000 ksi) |
| Thermal Conductivity | ~45 – 52 W/m·K |
| Coefficient of Thermal Expansion | ~12 µm/(m·°C) |
What these properties stand for:
Melting Point
The temperature at which the steel transitions from solid to liquid. Note that spring steel properties are lost at much lower tempering temperatures.
Modulus of Elasticity (Young’s Modulus)
This measures the intrinsic stiffness of the material. It is consistent across almost all steels.
Thermal Conductivity
A measure of a material’s ability to transfer heat. This can be a factor in high-performance applications where heat buildup might affect the spring’s temper.
Thermal Expansion
The tendency of the material to change its shape in response to temperature changes. This must be considered in precision instruments.
Corrosion Resistance
This is a critical property that varies dramatically between different types of spring steel.
Carbon and Alloy Spring Steels: These steels have poor corrosion resistance. The high iron content makes them highly susceptible to rust (iron oxide) when exposed to moisture and oxygen. For this reason, they are almost always protected with a coating, such as oil, paint, powder coating, or zinc plating (galvanization).
Stainless Spring Steels: These grades are selected specifically for their excellent corrosion resistance. The high chromium content (typically >10.5%) forms a passive, self-healing oxide layer on the surface that protects the steel from rust. This makes them ideal for use in medical, food processing, or marine environments.
Magnetic Properties
With few exceptions, spring steels are magnetic.
Carbon and Alloy Spring Steels: Being iron-based (ferritic), these steels are strongly magnetic.
Stainless Spring Steels: Most stainless spring steels, including cold-worked 300-series grades and all precipitation-hardening grades like 17-7 PH, are also magnetic.
Spring Steel Chemical Composition
Here are the chemical compositions of some common spring steel grades.
| Grade | C [%] | Si [%] | Mn [%] | P [%] max. | S [%] max. | Cr [%] max. / – | Mo [%] | Ni [%] max. | V [%] |
| C55S | 0.52 – 0.60 | 0.15 – 0.35 | 0.60 – 0.90 | 0.025 | 0.010 | 0.40 | 0.10 | 0.40 | – |
| C60S | 0.57 – 0.65 | 0.15 – 0.35 | 0.60 – 0.90 | 0.025 | 0.010 | 0.40 | 0.10 | 0.40 | – |
| 1070 | 0.65 – 0.73 | 0.15 – 0.35 | 0.60 – 0.90 | 0.025 | 0.010 | 0.40 | 0.10 | 0.40 | – |
| 1075 | 0.70 – 0.80 | 0.15 – 0.35 | 0.60 – 0.90 | 0.025 | 0.010 | 0.40 | 0.10 | 0.40 | – |
| 1095 | 0.95 – 1.05 | 0.15 – 0.35 | 0.30 – 0.60 | 0.025 | 0.010 | 0.40 | 0.10 | 0.40 | – |
| 6150 | 0.47 – 0.55 | 0.40 | 0.70 – 1.10 | 0.025 | 0.010 | 0.90 – 1.20 | 0.10 | 0.40 | 0.10 – 0.25 |
| 80CrV2 | 0.75 – 0.85 | 0.15 – 0.35 | 0.30 – 0.50 | 0.025 | 0.010 | 0.40 – 0.60 | 0.10 | 0.40 | 0.15 – 0.25 |
The Heat Treatment Process
A high-carbon steel billet is not considered spring steel until it undergoes a precise, two-step heat treatment process that transforms its internal crystal structure.
Quenching (Hardening). The steel is heated to 800-850°C to form austenite, then rapidly cooled (quenched) in oil or water. This transforms the austenite into martensite, an extremely hard but brittle crystal structure.
Tempering. To reduce brittleness, the hardened steel is reheated to a lower, precisely controlled temperature (typically 350-550°C). This process relieves internal stresses and increases toughness. This final step creates the high yield strength and resilience that define spring steel.
For a visual demonstration, see this video on the heat treatment process.
Common Spring Steel Types and Grades
Spring steels are categorized based on their chemical composition, which dictates their performance characteristics, cost, and ideal applications.
High-Carbon Spring Steels
These are the most widely used and cost-effective spring steels. Their properties are primarily derived from their high carbon content.
AISI 1075 & 1095: These grades are workhorses for flat springs, clips, and saw blades due to their ability to be hardened to a high degree.
Music Wire (ASTM A228): A high-carbon steel wire drawn to very high strength, prized for its high tensile strength and fatigue resistance in small springs like those found in instruments and mechanical controls.
Alloy Spring Steels
By adding elements like chromium, silicon, and vanadium, alloy spring steels offer superior performance in terms of toughness, fatigue resistance, and durability under harsh conditions.
AISI 5160 (Chromium): It offers good toughness, which makes it the industry standard for automotive leaf springs.
AISI 6150 (Chrome-Vanadium): It offers excellent toughness and fatigue life, used for high-quality tools and coil springs.
AISI 9260 / 60Si2Mn (Silicon-Manganese): The high silicon content significantly increases the yield strength, making it ideal for springs that experience high stress and shock loading.
55CrSi & 50CrVA: High-grade alloys with excellent fatigue and relaxation resistance, used for critical components like valve springs, brake springs, and torsion bars.
Stainless Spring Steels
When corrosion resistance is as important as mechanical performance, stainless spring steels are the solution.
300 Series (e.g., 302, 304, 316): These austenitic grades gain their spring temper through cold working. Grade 316 offers superior corrosion resistance in marine or chemical environments due to the addition of molybdenum.
17-7 PH (AISI 631): A precipitation-hardening stainless steel that can be formed in a soft state and then hardened to a high strength level through a low-temperature heat treatment. It’s used in aerospace, chemical, and processing industries.
High-Performance and Non-Ferrous Spring Alloys
For the most demanding environments involving extreme temperatures, high stresses, or severe corrosion, non-ferrous alloys are used.
Nickel-Based Alloys (e.g., Inconel 718, X-750): Offer excellent strength, fatigue resistance, and oxidation resistance at very high temperatures (up to 650-700°C), making them suitable for aerospace, nuclear, and turbine applications.
Cobalt-Based Alloys (e.g., Elgiloy): A cobalt-chromium-nickel alloy with a very high elastic limit, excellent corrosion resistance, and fatigue life. It is widely used in medical devices, watchmaking, and oil & gas exploration.
Copper-Based Alloys (e.g., Beryllium Bronze, Silicon Bronze): These alloys are non-magnetic and have good electrical conductivity combined with good spring properties. Beryllium Bronze (C1720) is particularly notable for its high strength, making it ideal for precision springs in electrical appliances and instruments.
Summary Table of Spring Steel Grades
| Grade Category | Common Grades | Key Characteristics | Typical Applications |
| High-Carbon | 1075, 1095 | Cost-effective, good hardness | Flat springs, clips, small high-stress springs |
| Alloy | 5160, 6150, 9260, 55CrSi | High toughness, fatigue resistance | Vehicle suspension, valve springs, torsion bars |
| Stainless | 302, 316, 17-7 PH | Corrosion resistance, good strength | Springs in corrosive environments, medical devices |
| High-Performance | Inconel 718, Elgiloy, Beryllium Bronze | Extreme temperature/corrosion resistance | Aerospace, medical, oil & gas, precision electronics |
Common Uses of Spring Steel
Spring steel is a versatile material that has been applied in an array of applications across industries.
Springs and Suspension
This is the most common application. Spring steel is used to manufacture coil springs, leaf springs, and torsion springs, which are essential components in automotive suspension systems, industrial machinery, and any device requiring controlled movement and shock absorption.
Tools and Blades
The material’s high hardness and excellent wear resistance make it ideal for cutting and scraping tools. This includes high-quality saw blades, scrapers, knives, and durable hand tools like wrenches and pliers that need to resist deformation under load.
Clips, Fasteners, and Shims
Spring steel’s ability to return to its original shape after being flexed makes it perfect for all types of clips, fasteners, retaining rings, and shims. These components rely on the steel’s tension to hold parts together securely.
Medical and Precision Instruments
In the medical field, spring steel is used to create surgical tools and orthodontic appliances like braces, where precise, consistent force is required. Its reliability also makes it suitable for components in watches and other precision instruments.
