When designing a torsion, extension, or compression spring, selecting the appropriate spring wire materials might mean the difference between a cost-effective, successful project and a costly, failed project.

Several characteristics have a direct impact on your choice of the best material for spring projects, such as tensile strength, corrosion resistance, elastic deformation, electric conductivity, and operating temperature or environment.

This guide aims to familiarize you with the different types of common materials used for spring manufacturing, allowing you to make an informed decision during spring design or spring selection.

Types of Spring Finishes

There are several different types of spring coating, and metal surface finishes intended for various purposes: corrosion prevention, improved spring performance, improved wear resistance, and all of the above. Here are different spring finishes explained:

Electropolishing

The principle of electropolishing is similar to electroplating, but the polarity of the workpiece and deposited (in this case, pick-up) material is reversed. That means that the workpiece serves as an anode, and the pick-up metal serves as a cathode which completes the electrical circuit through the electrolyte.

The material is quickly removed from the elevated and rough surface of the workpiece material — basically de-plating of the spring in this case — resulting in a highly smooth and polished surface. If the initial surface roughness is lower than 0.18-0.20µm (micrometers), a mirror finish with a surface roughness of less than 0.05µm can be achieved through electropolishing.

Tumbling

A tumbling finish is achieved either through vibrations or rotation of the tumbling container, which contains plastic poly pellets of various grits. These grits correspond to one of four stages of tumbling: grinding, smoothing, polishing, and shining.

Parts (or in this case, springs) are loaded into a tumbling container, and topped with poly pellets, also called the media. During operation, the media comes in contact with the parts and polishes the base material through friction.

Shot Peening

Shot Peening is a cold working method in which a high-velocity stream of shots is directed at the metal surface under strictly controlled conditions. This creates compressive stresses in the exposed layers of metallic objects, which results in significantly reduced tensile stresses in the material, and an increase in its tensile strength.

Shot peening is often confused with sand-blast cleaning due to the similarity of the process and the fact that shot peening also cleans the surface being peened. However, the primary goal of shot peening is to improve the fatigue strength of the material. The peening media can be iron, steel, or glass shot and chopped steel or stainless steel wire.

Electroplating

Electroplating uses electrical current to deliver ions of plating material into the plating substrate (a spring). Both the part to be plated, attached to a cathode, and the plating material, attached to the anode, are placed into an electrolyte bath. The flow of current through the electrolyte drives the ions of the plating material into the plating substrate, covering the part with a thin coating of the plating material.

The most commonly plated material types are carbon steels and various alloy steels, with either noble metals or non-corrosive metals. Electroplating with noble metals provides good corrosion resistance as long as the plating layer remains intact. Non-corrosive metals, such as tin, nickel, and chromium, are often used for electroplating steels for corrosion resistance. However, this type of plating is rarely used for parts that are exposed to the elements, immersed in water, or exposed to some other electrolyte.

Instead, less noble materials are often used, such as zinc or cadmium, which acts as a sacrificial anode that will oxidize instead of the substrate.

Electroless Plating

With electroless plating, a nickel coating is applied to the substrate without the use of electricity. In this situation, the substrate functions as a catalyst to initiate a chemical process that causes nickel ions in the electrolyte solution to be reduced and deposited on the substrate (there is no anode). The nickel coating also works as a catalyst, ensuring that the reaction continues until the substrate is removed from the electrolyte bath.

As a result, a relatively thick coating can be produced, ranging from 20µm to 50µm in thickness. In addition, the electroless nickel plate, unlike electroplating, is fully uniform and will enter any gaps and crevices. Other metals can be used for plating as well, but nickel and nickel alloys are the most popular.

Chemical Coatings

Chemical treatments for metals are mostly used on steel in the form of phosphoric acid washes, which provide limited and short-term oxidation resistance. Paint coatings can be used to provide long-term corrosion protection. Lastly, black oxide is the most affordable method of forming a corrosion-resistant barrier on steel, stainless steel, or copper substrates. They're also fantastic at eliminating light reflections in specific applications.

Different Types of Spring Materials

Choosing the right spring type mainly depends on your spring application and whether you require compression springs, torsion springs, or some other spring type listed in our Types of Springs and Their Uses guide.

However, using general-purpose spring wire doesn't always yield the required results. This is why spring manufacturers employ different spring materials to achieve the desired properties, such as electrical conductivity, heat resistance, and minimum tensile strength.

Consider the environment affecting the spring's operation, the amount of deflection, the frequency of cycles, and the ratio of wire form or spring costs to the overall project cost before choosing the proper sort of spring wire material. Note that we're only referring to mechanical springs and mechanical spring accessories in this guide.

High Carbon Steels

High carbon steels have incredibly high tensile strength and can be tempered to great hardness, making carbon steel springs particularly effective in applications where strength is needed. However, there are some drawbacks, like susceptibility to rust and corrosion.

Music Wire

Music wires (cold drawn), also known as ASTM A228, are made of high carbon spring steel with uniform properties and high tensile strength. They're great for high-stress applications with repetitive loading. They usually have an excellent surface finish and are regarded as the toughest springs made of carbon steel. High-temperature spring wires are often used in heating elements found in foundries, heat treating, and other manufacturing processes, which require exhibiting extremely hot internal temperature applications.

Hard Drawn MB

Hard-drawn spring steel wire, often referred to as HDMB ASTM A227, has a minimal carbon content of 0.5%, making this type of spring steel suitable for frequent stress repetitions. However, they're not really suited for extremely low or high temperatures, not impact loading or shock loads.

Oil-Tempered MB

Oil-tempered ASTM A229 spring materials are some of the strongest and most durable high-carbon spring steels. They're great for large wire diameters that provide capabilities to support heavy-duty equipment and machinery, but they're also great for small-scale torsion springs.

Stainless Steels

Stainless steels are mostly used for general-purpose, cold-drawn spring wire materials that are heat and corrosion resistant and magnetic in spring temper. Corrosion resistance is generally better in alloys with 10% or more chromium than in regular alloys and plain steels. Precipitation and austenitic hardening are often used in the stainless steel spring production.

Stainless Steel 302

Owing to its high tensile strength and uniform characteristics, 302 stainless steel (ASTM A313) is one of the most popular stainless steel for spring production. Its mechanical properties are gained by cold drawing, and it can't be hardened by heat treatment.

Due to the cold-working, the material becomes mildly magnetic, but it's otherwise non-magnetic when fully annealed. It's fantastic for sub-zero temperatures and temperatures up to 550°F or 287.7°C, with high levels of corrosion resistance.

Stainless Steel 304

This material is quite similar to 302, except it bends better and has a lower tensile strength by around 5%. It has a slightly lower carbon content which makes it easier to draw.

Stainless Steel 316

316 stainless steel is chemically similar to Type 302. However, it contains 4% more nickel (12% total) than 302 and an additional 2% of molybdenum, which significantly increases its corrosion resistance. However, its tensile strength is approx. 10%-15% lower than 302 Stainless Steel, and it's mostly used to produce aircraft springs.

Stainless Steel 17-7 PH

This alloy, which also contains minor amounts of aluminum and titanium, is created in a moderately hard state before being precipitation hardened at low temperatures for several hours to achieve tensile strengths that are approximately equivalent to music wire. However, due to its high manufacturing cost, this material is not easily available in all sizes and has restricted applications.

Alloy Steels

Alloy spring steels are used in high-stress, shock, and impact loading applications. They're not as sensitive to temperature as high-carbon steels are and are available in pre-tempered or annealed forms.

Oil-Tempered Chrome Vanadium

Oil-tempered chrome vanadium is mostly used in applications that require higher stress, fatigue strength, and endurance than what high-carbon steels can provide. However, this type of steel performs admirably under shock and impact loading, and it's widely used in aircraft engine valve springs and for springs exposed to temperatures up to 450°F or 232.2°C.

Oil-Tempered Chrome Silicon

This particular alloy is used to create custom springs that are subject to exceptional strains and shock loading. In addition, they boast exceptional longevity and can be heat-treated to achieve hardness levels higher than those of other spring steels, which allows for greater tensile strength.

Composite Spring Materials

The automotive industry has shown great interest in composite materials for use in leaf springs — more specifically, replacing the steel leaf springs with composite ones. However, highly-engineered composites have been used to produce springs for quite some time now, as they're lightweight and offer exceptional performance in demanding industries such as electronics, aerospace, and medical.

Materials such as Ultem® offer operation at elevated temperatures, neutral magnetic properties, relatively low weight, low thermal conductivity, dielectric properties, and sustainability — they're recyclable.

Copper Alloys

Due to their outstanding electrical characteristics as well as their corrosion resistance, copper-base alloys are useful spring materials. Even though these materials are more expensive than high-carbon and alloy steels, they are often employed in electrical components and at temperatures below zero.

Phosphor Bronze

Phosphor bronze ASTM B159 is the most popular alloy in the copper-based alloys category, as it combines tensile strength, hardness, electrical conductivity, and corrosion resistance with an incredibly low production cost. Admittedly, it's more expensive than brass, but it can take 50% greater strains, and it's capable of withstanding temperatures of 212°F or 100°C and sub-zero conditions. It's mostly used for flat springs in finger switches due to its low arcing qualities.

Beryllium Copper

Beryllium copper ASTM B197 is the most expensive alloy in the copper-based alloys category, as it's shaped by costly heat-treating processes, which include heat-forming at approx. 600°F or 315.5°C, and precipitation hardened for two to three hours. It's mostly used to conduct electrical current in switches and electrical components.

Spring Brass

Spring Brass ASTM B134 is the least expensive of the copper-based alloys. It's a hard-drawn material with poor spring properties and very low tensile strength, as it can't be hardened by heat treatment and performs very poorly at temperatures over 150°F or 65°C. However, it performs exceptionally well at sub-zero temperatures, and it's mostly used in flat stampings and acute bands.

Nickel-Based Alloys

Nickel-based alloys are corrosion-resistant, non-magnetic alloys that perform well in both high and low temperatures, making them ideal for gyroscopes, chronoscopes, and indicating instruments. Due to their high electrical resistance, these alloys should not be used as electrical current conductors.

Monel 400

Monel 400 range (400, 401, 404, and 405) contains a minimum of 63% nickel and anywhere between 28% to 34% copper and is the least expensive of the nickel-based alloys. It also has the lowest tensile strength of the group, but it's very important due to its resistance to a range of acidic and alkaline environments, which makes it suitable for applications in marine engineering, chemical, and hydro-carbon processing, heat exchangers, valves, and pumps.

Monel K-500

Monel K-500 features almost the same chemical composition as the Monel 400, as it also contains 63% of nickel, 27% to 33% of copper, and the same basic trace elements. However, it also has 2.3% to 3.15% aluminum and 0.35% to 0.85% titanium, which provide it with greater tensile strength and hardness. Its properties make it suitable for shafts and centrifugal pumps in marine applications.

Inconel 600

Inconel materials are a family of austenitic nickel-chromium-based superalloys, and they're capable of withstanding extreme conditions while subjected to high mechanical loads. Type 600 is one of the most popular non-magnetic nickel-based alloys due to its corrosion resistance and the ability to withstand temperatures up to 700°F or 371°C. It's also more costly than stainless steel but more affordable than beryllium copper.

Inconel 718

Inconel 718 contains less nickel than type 600 but approximately 4% to 7% more chromium and more trace elements in its chemical composition. Its chemical makeup allows type 718 to maintain high tensile strength in extreme temperatures at both ends of the scale, ranging from cryogenic temperatures up to 1300°F or 704°C. It's a corrosion-resistant, well-balanced material that's often used in the aviation and aerospace industries.

Inconel X750

X750 is very similar to type 718, as it's a precipitation-hardened alloy created in a soft or partially hard state and then hardened for four hours at 1200°F or 649°C. It's a non-magnetic alloy that can maintain elasticity up to 850°F or 454.4°C and stress levels of up to 55,000lbs per square inch.

Elgiloy

Elgiloy is considered a nickel-based alloy with a constant modulus of elasticity across a wide temperature range. It's commonly known as 8J alloy, Durapower, and Cobenium; this material is precipitation-hardened for eight hours at 900°F or 482°C. It operates well in sub-zero temperatures, including temperatures below 0°F or -17.7, and up to 1000°F or 537°C as long as torsional loads are kept below 75,000lbs per square inch. High-quality springs for watchmaking are made of this type of material.

NiSpan C

This popular constant-modulus alloy is typically made in a 50% cold-worked state and precipitation-hardened at 900°F for eight hours, though heating to 1250°F or 676°C for three hours produces a hardness of 40 to 44 Rockwell C, allowing safe torsional loads of 60,000 to 80,000 pounds per square inch. The alloy is ferromagnetic up to 400°F or 204°C, at which point it becomes non-magnetic.

Hastelloy (C276)

Hastelloy spring material is a nickel-chrome-moly alloy with good corrosion resistance and good resistance against pitting and stress corrosion cracking. It's also resistant to various chloride solutions. It's considered the most versatile corrosion-resistant alloy available.

Summary

The selection of spring material during spring design and selection most depends on the material's mechanical properties, typical uses, most common applications, frequency of load cycles, and the overall cost-effectiveness. If you want to learn more about different types of springs, visit us at Reid Supply and check out our Types of Springs and Their Uses guide.

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