Why is stainless steel used for springs?

Stainless Steel Springs and Their Surprising Benefits

Although certain materials have been regarded as a spring material, not all are specially designed alloys for spring use. An ideal spring material will have properties of high strength, high elastic limit, and low modulus. Because springs are inherently resilient structures, they are designed to experience large deflections, requiring an extensive elastic range. Other characteristics, such as corrosion resistance, fatigue strength, formability, electrical conductivity, magnetic permeability, availability, and cost, are also considered in light of cost/benefit. Because they require so many diverse characteristics, stainless steel springs are emerging as the most popular.

Although not clearly delineated through national specifications, surface quality also has a major impact on fatigue strength. For fatigue applications, it is best to utilize materials with high surface integrity, particularly in the high cycle region.

In recent years, stainless steel springs have gained an impressive popularity, due to its special characteristics. One of the most common reasons for selecting steel springs for industrial use is its corrosion resistance. Stainless steel springs resist chemicals and rust, making them the ideal choice for industrial and processing industries.

Stainless Steel – The Wonder Material

Scientists around the world consider stainless steel to be an astounding material perfect for many different types of applications. Harry Brearly was one of the first to notice that gun barrels didn’t rust when they were left out in the rain. Upon taking the barrels to a lab, it was discovered that they contained 13% chromium, which attributed its anti-corrosive property. This exciting news marks the discovery of stainless steel as a wonder material, and was published in the New York Time’s 1915 publication. Stainless steel has been the optimal choice for a variety of industries and applications ever since.

The Making of Stainless Steel Springs

Springs are found in almost every industry around the world. Stainless steel is one of the most favored spring materials because of its high yield strength, resistance to rust, and durability. Steel springs are typically crafted from wire that has been tempered and hardened to best suit the needs of the type of spring it will become.

Steel springs begin as a large metal bar, which weighs several hundred pounds. As the metal bar is heated for malleability, steel is drawn out through a series of dies, gradually decreasing until they reach a size that is suitable diameter for the manufacturing of springs.

There are two different types of steel used in spring manufacture. Carbon steel, which is well known for its quality and uniformity, often becomes music wire. However, steels crafted from carbon are susceptible to rusting. For this reason, stainless steel is generally recommended in industrial industries, or any areas that have the possibility of coming in contact with water.

Here are the most common types of stainless steel springs, which can be crafted to meet the needs of any diameter or length:

• When at rest, extension springs crafted from stainless steel are tightly coiled. When extended, they exert the highest levels of mechanical energy.
• Compression springs are the opposite of extension springs. These stainless steel springs are at rest when they are fully extended, and contain the highest amount of stored energy when they are compressed.
• Torsion springs crafted from stainless steel are also tightly coiled like extensions springs. However, their force is created by torque or twisting.

Types of Steel Springs and their Applications

Stainless steel, including 10% chromium, offers an excellent source of corrosion resistance in harsh environments. In recent years, many new variants have improved its temperature resistance. Stainless steel is generally classified into four types – austenitic, precipitation hardening, martensitic, and ferritic. Typically, precipitation hardening and austenitic steels are considered to be the most ideal materials for spring use.

Here are some of the popular precipitation hardening steels and austenitic materials used in spring construction.

300 Series Stainless Steel:

This austenitic stainless steel variant is alloyed with 17-25% chromium and 10-20% nickel. The nickel that is present improves its ductility and durability, in addition to contributing to its excellent corrosion resistance. Because of its anti-corrosive property, this type of stainless steel is often used in marine construction. Bridges, harbours, and ports require a solid foundation so that they can withstand the impact of heavy loads of containers and vehicles. For the construction of such structures, a piling company needs to be contacted which often uses steel and concrete combinations for inserting piles into the sandy ground. These piles are considered strong enough to support any superstructure built above them. Hence, different variants of steel are usually used to give strength to any building. The 300 series is generally hardened by means of cold working. It is not hardenable through heat treatment.

Stainless Steel Type 302:

Stainless steel 302 is ductile and austenitic, in addition to being strong. This stainless steel type is another heat resisting steel variants that is strengthened through cold working. Type 302 springs have a silver graycolor, and are used in cryogenic, pressure-containing, sanitary applications.

Stainless Steel Type 304:

This non-magnetic alloy can withstand extremely high temperatures. Stainless steel type 304 offers one of the strongest known resistance against corrosive acids. Thus, springs type 304 are used throughout a variety of applications that come in contact with corrosive acids. Additionally, steel type 304 holds low measurements of carbon, which helps in avoiding carbide precipitation. The springs that are manufactured from this variants are largely used in chemical, cryogenic, dairy, pharmaceutical, and food industries.

Stainless Steel Type 316:

This stainless steel alloy holds a carbon content lower than that of stainless steel type 302. This is especially useful in welding applications that require lower carbide precipitation. This stainless steel variant works to provide an extra resistance to corrosion due to its higher molybdenum content. Type 316 stainless steel springs are most suitable for industries that demand highest levels of hygiene such as pharmaceuticals and food, in addition to sub-zero temperatures and even marine environments found in piping of oil and gas industries. This variant is distinguishable in appearance due to its silver gray color.

Stainless Steel Type 301:

Type 301 is hardened through cold working, and is not hardenable through heat treatment. It can achieve high tensile strength and ductility through cold working. This stainless steel type is not magnetic in the annealed condition, but does become magnetic following the cold formation.

Stainless Steel 17-7:

17-7 stainless steel springs are favorable in the fact that they can withstand even higher temperatures than type 302 or 316. This steel is alloyed with aluminium, nickel, and chromium. The max temperature limit in this stainless steel spring is 343 C (650 F).

Stainless steel spring application can be found across a myriad of industries. Their manufacture and production provide safe support for business in all types of verticals, including oil and gas piping, industrial machinery, electronic components, defense and aerospace mechanisms, and much more.

Selecting the correct material for the design of a spring is one of the first and most important considerations in its application. Stainless steel used for springs, for example, has many advantages and favorable properties—above all, corrosion resistance—which makes the material ideal for many applications. A variety of stainless steel grades and types are available for designers in applications, but there are other materials used in spring manufacturing, ranging from carbon spring steels to nickel-based spring alloys. Ultimately, the defining factor for material relates to the properties necessary for the spring to function as required, say, in a particular environment, temperature or load.

Copper and High-Carbon Spring Materials

Used for music wire and oil tempered spring wire, high-carbon spring steels are the most common spring material. In part because the material is inexpensive, but also because it is easily worked and readily available. However, the material has a limited operating temperature range and is not well-suited for shock or impact loading as alloy spring steels are. Alloy spring steel is made for high stress and impact loads and can operate in both higher and lower temperatures.

Though a more expensive spring material, copper-based spring alloys offer excellent electrical properties, good resistance to corrosion, and operate in sub-zero temperatures. Nickel-based spring alloys are also used in sub-zero temperature applications, as well as elevated temperatures. Combined with the material’s corrosion resistance and non-magnetic properties, nickel-based spring alloys are often designed for such applications as indicating instruments and gyroscopes.

Benefits of Stainless Steel for Springs

Yet, stainless steel holds many desirable properties that make it ideal for many spring applications. As an iron-based alloy, what sets stainless steel apart from other spring materials is its high corrosion resistance. Stainless steel consists of a minimum 10.5% chromium, which forms a tough, invisible, corrosion-resisting chromium oxide film that adheres to the steel surface, making it approximately 200 times more resistant to corrosion than steels without chromium. Other elemental alloys like nickel, magnesium, molybdenum, and nitrogen are often added to increase versatility.

In addition to its corrosion-resistant properties, stainless steel is well-known for its tensile strength, durability, biocompatibility, and low maintenance. It offers high and low-temperature resistance increased formability and easy fabrication. It is long-lasting, environmentally friendly, and recyclable. Once it is put into service, it does not need to be treated, coated or painted.

Stainless Steel Grades

Stainless steel is available in many different grades—300 or 400 series, for example—that are further subdivided into several metallurgical types—austenitic, ferritic, martensitic, and duplex. Determining the grade or type of stainless steel to use for spring design and fabrication will depend on the properties desired of the application. The most common grades of stainless steel spring wires are 302, 304, 316, and 17/7, all of which offer varying degrees of corrosion resistance, tensile strength and heat resistance.

Popular Applications

Medical Industry

Because of its versatility and many favorable properties as a material, stainless steel is ideally suited for applications in numerous industries. Stainless steel’s biocompatibility and hygienic characteristics provide the necessary properties for use as a spring material in medical applications. Stainless steel grades austenitic 304 and 316 are considered surgical or medical-grade stainless steel and are used as components in a variety of medical products, equipment, and pharmaceuticals.

Food Processing & Handling

Stainless steel’s easy cleaning makes it the first choice for applications requiring strict hygienic conditions. For similar reasons as the medical industry, stainless steel is commonly used in food-grade applications. Because grade 316 stainless steel springs resist moisture and rust, they are recommended for use as components where needed in food processing and handling equipment.

Power & Energy

The energy industry depends on stainless steel’s corrosion, chemical, and heat resistant properties. Stainless steel spring components are used in applications on oil and gas platforms, pipelines, and renewable energy sources like wind turbines. Emerging energy technologies like solar, hydro, and geothermal also utilize stainless steel spring components.

Transportation

The transportation sector is greatly impacted by stainless steel springs. The automotive, aerospace, rail, and marine industries all rely on stainless steel parts and components. Springs are, after all, the foundation of any vehicle’s suspension system, whether car, plane or on rail, but are also used for smaller parts such as hose clamps and seat belt springs. Rust and corrosion-resistant spring components are vital to marine applications. Marine-grade stainless steel springs are necessary where exposure to damages of saltwater, mist, fog is expected. The material’s standard passivation adds additional strength and resistance against the elements.

Durable Goods

Finally, stainless steel springs are also used as components in durable goods and appliances. From household kitchens and laundry rooms to commercial kitchens and dry cleaners, the many different appliances—dishwashers, refrigerators, freezers, ovens, microwave ovens, toasters, washing machines, dryers and so forth, consist of stainless steel spring components.

At James Spring & Wire, we strive to meet each one of our customers’ expectations by providing quality precision springs, on-time, and within budget. Check out our products for more information on all the types of springs we offer and as always, feel free to contact us with any questions or concerns.