What Is Spring Steel – Spring Steel Grades, Strength, Hardness, Forming & Machining


Spring steel is a type of general use steel and commonly used as spring materials, now we’ll go over grades, strength, hardness, forming and machining of spring steel.

What Is Spring Steel?

Spring steel refers to a wide range of steels, generally including low-alloy manganese, medium-carbon steel, or high-carbon steel with very high yield strength. This steel is widely used in the manufacture of springs, which require the ability to absorb and release energy repeatedly without deforming or weakening over time. Spring steel can withstand intense twisting and bending, its high yield strength is obtained through hardening by heat treatment and work hardening.


How is spring steel formed?

Spring steel can be formed through a variety of processes, including hot and cold rolling, annealing, and heat treatment. The specific process used will depend on the grade of spring steel and the desired mechanical properties of the final product. In general, the process starts with melting and refining the raw materials to create the correct composition of the steel. Then, the steel is cast into large blocks or billets and allowed to cool. The billets can be further processed through hot or cold rolling to reduce their thickness and refine their grain structure. Cold rolling is often preferred for higher-quality spring steel as it allows finer control of the thickness and dimensional tolerances of the steel. After rolling, the steel may be annealed to relieve internal stresses and improve its ductility. The steel is heated to a specific temperature for a set amount of time and then allowed to cool slowly in a controlled environment. This process can improve the toughness and flexibility of the steel. Finally, the spring steel may undergo heat treatment to achieve the desired mechanical properties. This involves heating the steel to a critical temperature and then rapidly cooling it (quenching) to create a hard, brittle structure. The steel may then be tempered through a reheating process, which reduces its hardness and increases its toughness. The specific heat treatment process used will depend on the grade of spring steel and the desired properties of the final product.

Grades of Spring Steel

– AISI 1074 and 1075:These are high-carbon spring steels with a carbon content ranging from 0.70% to 0.75%. They are often tempered to produce a combination of high tensile strength and good ductility.

– AISI 9260: This is a silicon-manganese steel with a carbon content of 0.56% to 0.64%. It is commonly used for leaf and coil springs due to its good strength and fatigue resistance.

– AISI 6150: Also known as chrome vanadium steel, this alloy has a higher silicon content along with chromium and vanadium. It is often used for parts subject to high stress and where resistance to fatigue is important.

– AISI 5160: This is a spring steel with a carbon content of 0.56% to 0.64% along with small amounts of manganese and silicon. It is well-suited for leaf and coil springs due to its toughness and durability.

Strength of Spring Steel

What is the strongest spring steel? The strength of spring steel depends on its properties and the specific application for which it is used. Generally, higher-carbon spring steels tend to be stronger and offer better fatigue resistance than lower-carbon steels. One of the strongest and most widely used spring steels is AISI 1095. This steel has a carbon content of around 0.95%, which gives it excellent strength and resilience. AISI 1095 is often used to make high-stress springs and other parts that require high strength and durability. Another very strong spring steel is AISI 6150, also known as chrome vanadium steel. This alloy steel contains chromium and vanadium in addition to carbon, which gives it a combination of high strength, toughness, and fatigue resistance. AISI 6150 is often used to make springs and other parts that require high strength, such as truck springs and other heavy-duty applications.


Other strong spring steel grades include AISI 5160, which contains manganese and silicon in addition to carbon, and AISI 4340, which is nickel-chromium-molybdenum alloy steel with very high strength and toughness. The specific type of spring steel that is the strongest will depend on the specific requirements of the application, and factors such as the level of stress, the number of cycles, and the environment in which the part will be used.

Hardness of Spring Steel

As a general rule, spring steels are designed to have high hardness and strength to withstand the stresses of repeated loading and unloading without deforming or breaking. The hardness of spring steel is typically measured using the Rockwell hardness scale, which measures the depth of penetration of a diamond or tungsten carbide indent into the material.


Spring steel typically has a Rockwell hardness (HRC) range of 44-57, depending on the specific grade and heat treatment. For example, AISI 1095 spring steel typically has a Rockwell hardness of around 55-57 after quenching and tempering, while AISI 5160 spring steel typically has a Rockwell hardness of around 52-56 after heat treatment.

Can You Machine Spring Steel?

Yes, spring steel can be machined, but spring steel can be more difficult to machine than low-carbon steel due to its hardness. Machining spring steel typically requires the use of a hard, sharp cutting tool and low cutting speeds to prevent excessive heat buildup that can damage the tool and/or the workpiece. Workpieces made from spring steel can also be prone to hardening during machining, which can make them more difficult to machine as the process continues. To maximize the machinability of spring steel, it can be annealed or pre-hardened before machining. Annealing spring steel can be done by heating it to a certain temperature and cooling it slowly to soften the material. This can make it easier to machine, but it may reduce the material’s springiness and strength. Pre-hardened spring steel has already undergone a heat treatment process to achieve a certain hardness, which can make it easier to machine while retaining some of its desirable properties.