The question of whether nickel is stronger than steel is complex, depending heavily on the specific grade of material and the definition of “strength.” Strength in materials science encompasses several distinct properties, and the performance of both nickel and steel changes dramatically when they are alloyed with other elements. Ultimately, the material chosen for an application is selected not just for its strength, but for how it performs under specific conditions like high temperature or corrosive environments.
Defining Mechanical Properties
Materials scientists use several precise metrics to determine a material’s capacity to withstand external forces.
Yield strength is the amount of stress a material can endure before it begins to permanently deform. Designing structural components requires keeping stresses below this value to ensure the material returns to its original shape once a load is removed.
Tensile strength represents the maximum stress a material can handle before it ultimately breaks or fractures. This is often referred to as Ultimate Tensile Strength (UTS) and indicates the total load-bearing capacity before failure.
Hardness is a measure of a material’s resistance to localized surface deformation, such as indentation or scratching. Finally, toughness describes a material’s ability to absorb energy before fracturing, requiring a balance of both high strength and high ductility, or the ability to deform plastically.
Pure Nickel Versus Common Steel Grades
When comparing the elemental forms, pure nickel is considerably softer and less structurally robust than common structural steel. Pure nickel is highly ductile and malleable, meaning it can be easily shaped, but its yield strength is relatively low, often around 140 megapascals (MPa) in its annealed state. This makes it unsuitable for most high-load structural applications.
Conversely, even basic, low-carbon structural steel, such as a common AISI 1018 grade, is significantly stronger than pure nickel. These inexpensive steels achieve higher mechanical properties through the addition of carbon, which acts as a hardening agent. A standard carbon steel typically exhibits a yield strength in the range of 250–350 MPa, making it structurally superior.
Pure nickel is most often used for applications that require its excellent resistance to corrosion or for its electrical properties, not for its inherent mechanical strength. In a direct comparison, standard structural steel is the stronger material in terms of fundamental tensile and yield strength at room temperature.
The Role of Alloying: Nickel-Based Superalloys Versus Advanced Steels
The comparison becomes far more complex when considering the specialized alloys of each material. Steel strength is maximized by adding elements like manganese, chromium, and molybdenum, and through specific heat treatments, resulting in advanced materials like tool steels and high-strength low-alloy (HSLA) steels. These advanced steels can achieve exceptional tensile strengths, with certain grades of maraging steel reaching up to 2,400 MPa. For bulk structural strength at ambient temperatures, advanced steels often remain the most effective and cost-efficient choice.
Nickel’s strength is dramatically increased when it forms nickel-based superalloys, which are engineered to maintain their performance in extreme environments. Alloys such as Inconel and Hastelloy contain high amounts of nickel, along with chromium, molybdenum, and other elements, which form strengthening precipitates within the material structure. These precipitates allow nickel superalloys to retain a high percentage of their strength even at temperatures above 600°C, where steel’s strength rapidly degrades.
While the strongest advanced steels may have higher ultimate tensile strength at room temperature, nickel-based superalloys often surpass them in creep resistance at high temperatures. Creep is the tendency of a solid material to slowly and permanently deform under mechanical stress when exposed to high heat for an extended time. Nickel superalloys are specifically designed to resist this deformation, making them the material of choice for high-stress, high-heat applications like turbine blades in jet engines.
Beyond Mechanical Strength: Thermal and Chemical Resistance
Even when nickel alloys are not the strongest at room temperature, their unique non-mechanical properties often make them the only viable choice for certain industries. Nickel is inherently stable and less reactive with oxygen compared to iron, which contributes to superior performance in extreme heat. This thermal stability means nickel alloys resist strength loss and oxidation at temperatures well above 500°C, a point where most steel grades begin to lose significant load-bearing capacity.
Nickel alloys also offer exceptional corrosion resistance, particularly against aggressive chemicals and chloride-rich environments like seawater. The high nickel content, often combined with molybdenum and chromium, makes these materials highly resistant to pitting, crevice corrosion, and stress corrosion cracking that can plague even stainless steels. This superior chemical resilience is why nickel alloys are indispensable in chemical processing, marine engineering, and the oil and gas industry.