The Key Properties of Stainless Steel: What You Need to Know

Stainless steel is prized for its strength, durability, and corrosion resistance. This blog covers its key physical and chemical properties, including composition, resistance, and factors affecting performance. Understanding these properties will show why stainless steel is so versatile and reliable.

What is Stainless Steel?

Stainless steel, or inox, CRES, and rustless steel, is an alloy made of 70-80% iron, at least 10.5% chromium, and other elements like carbon. Chromium protects it against rust and corrosion, and it is easier to clean than aluminum and copper. With its high strength, highly recyclable, durability, and luster, stainless steel is used in construction, automotive, medical instruments, and kitchenware. Common types include austenitic, ferritic, martensitic, and duplex.

What Are the Physical Properties of Stainless Steel? 

Stainless steel’s excellent physical properties make it perfect for various uses. These properties include strength, thermal conductivity, magnetism, density, electrical conductivity, melting point, elasticity, impact resistance, and fatigue strength.

Thermal Conductivity

Stainless steel has lower thermal conductivity compared to other metals like copper and aluminum. This makes it less efficient at conducting heat but provides controlled heat transfer. This property is useful for kitchen appliances and cookware where even heating is desired, as well as in applications where heat insulation is important.

Magnetic Property

The magnetism of stainless steel varies by type. Austenitic stainless steels (300 series) are generally non-magnetic due to their crystal structure, while ferritic and martensitic stainless steels (400 series) are magnetic. This property is significant in applications such as magnetic separation, electrical appliances, and industrial processes where magnetic response is required.

Density

With a density of about 7.8 grams per cubic centimeter, stainless steel is relatively heavy. This density of SS Steel enhances its strength and durability, making it ideal for construction, automotive, and aerospace applications. The density also impacts the material’s performance in high-stress environments.

Electrical Conductivity

Stainless steel has low electrical conductivity, making it a poor conductor of electricity. This property is beneficial for applications requiring electrical resistance, such as heating elements, resistors, and components that require minimal electrical interference. It helps maintain safety and efficiency for electrical and electronic devices.

Melting Point

Stainless steel melts point at 1,400 to 1,530 degrees Celsius (2,552 to 2,786 degrees Fahrenheit). Its high melting point allows it to be used in environments like furnaces, heat exchangers, and jet engines. The ability to withstand extreme temperatures without deforming or losing strength makes it ideal for critical applications.

Elasticity and Plasticity

Stainless steel exhibits both elasticity and plasticity, meaning it can be stretched or compressed and then return to its original shape (elasticity), as well as permanently deformed without breaking (plasticity). These properties are crucial for manufacturing processes like bending, rolling, and forging, enabling the production of complex shapes and structures.

Impact Resistance

Stainless steel resists impact and shock, absorbing energy without fracturing. This property is important for safety-critical applications in the automotive, aerospace, and construction industries, where materials must withstand sudden impacts and vibrations. Its toughness ensures long-lasting performance and dependability in harsh conditions.

Fatigue Strength

Stainless steel has excellent fatigue strength, withstanding repeated stress cycles without failure. This makes it suitable for components subjected to cyclic loading, such as springs, fasteners, and structural elements in buildings and bridges. Its ability to resist fatigue cracking enhances the safety and durability of structures and mechanical systems.

These properties make stainless steel suitable for numerous industrial and consumer applications, from kitchenware to aerospace components. 

What Are the Chemical Properties of Stainless Steel? 

Stainless steel’s chemical properties make it perfect for various uses. These properties include its chemical composition, corrosion resistance, oxidation resistance, acid and alkali resistance, pitting and crevice corrosion resistance, intergranular corrosion resistance, stress corrosion cracking resistance, and surface passivation.

Chemical Composition

Stainless steel consists primarily of iron, at least 10.5% chromium, and elements like nickel, molybdenum, and carbon. Chromium is the key element that provides stainless steel with its corrosion resistance by forming a thin oxide layer on the surface. The composition varies by grade, with added elements like nickel for better corrosion resistance and toughness or molybdenum for increased strength and pitting resistance.

Corrosion Resistance

Stainless steel’s excellent corrosion resistance is due to chromium, which forms a protective oxide layer to prevent rust. This property makes stainless steel perfect for harsh environments like marine applications, chemical plants, and medical instruments, where rust and corrosion resistance are crucial. Its hygienic properties also help keep it clean in humid, corrosive conditions, preventing bacteria growth, making it perfect for sanitary applications.

Oxidation Resistance

Stainless steel exhibits high resistance to oxidation, even at elevated temperatures. Chromium forms a stable oxide layer that prevents further oxidation. This property is especially useful in high-temperature applications like exhaust systems, heat exchangers, and industrial furnaces exposed to oxidative environments.

Acid and Alkali Resistance

Stainless steel resists many acids and alkalis, making it ideal for chemical processing and food industry uses. The level of resistance depends on the grade of stainless steel and the concentration of the acid or alkali.

For example, 316 stainless steel, which contains molybdenum, offers enhanced resistance to chlorides and acidic environments compared to 304 stainless steel.

Pitting and Crevice Corrosion Resistance

Stainless steel, especially grades containing molybdenum like 316, is resistant to pitting and crevice corrosion. These localized forms of corrosion occur in confined spaces and are often caused by chlorides. The resistance to these types of corrosion is essential for applications in marine environments, chemical processing, and other industries where exposure to chloride-rich environments is common.

Intergranular Corrosion Resistance

Intergranular corrosion happens at the grain boundaries of stainless steel exposed to high temperatures. Stabilized grades such as 321 and 347, which contain titanium or niobium, are designed to resist intergranular corrosion. This property is critical for maintaining the structural integrity of stainless steel in welding and high-temperature applications.

Stress Corrosion Cracking Resistance

Stainless steel resists stress corrosion cracking (SCC), which is caused by tensile stress and a corrosive environment. Austenitic stainless steels like 304 and 316 are generally resistant to SCC, making them suitable for use in environments where chloride-induced SCC is a concern, such as in chemical plants and oil and gas industries.

Surface Passivation

Surface passivation is the process by which stainless steel’s protective oxide layer is enhanced. This is usually done with nitric or citric acid baths that remove contaminants and promote a passive layer. Passivation enhances stainless steel’s corrosion resistance and is essential for manufacturing medical device and semiconductor equipment components.

These chemical properties ensure that stainless steel remains a versatile and durable material, capable of withstanding a variety of harsh chemical environments and maintaining its integrity over long periods.

What Are The Mechanical Properties of Stainless Steel

Tensile Strength of Stainless Steel

Tensile strength refers to the maximum stress a material can withstand before breaking. Different types of stainless steel have varying tensile strengths, influenced by processes like heat treatment and cold working. Thicker materials may also exhibit higher strength. For example, the common grade 304 has a tensile strength of about 210 MPa (30,000 psi) in the annealed condition. Cold working can increase its strength to 1,050 MPa (153,000 psi) in the full hard state.

Yield Strength of Stainless Steel

Yield strength is the point where a material begins to deform plastically under tensile or compressive loads, typically lower than tensile strength. Methods like cold working, grain refinement, solid solution strengthening, strain hardening, and precipitation strengthening can improve yield strength. However, excessive processing should be avoided. Annealed 304 stainless steel has a lower yield strength, around 200 to 250 MPa, while cold-worked 304 can reach 250 to 300 MPa.

Ductility of Stainless Steel

Ductility is the ability of a material to deform without breaking under stress. Austenitic stainless steel exhibits excellent ductility and toughness, typically around 40%-60%, allowing it to be drawn into wires and sheets. Martensitic stainless steel has lower ductility, usually between 20% and 40%. While carbon steel is more ductile than stainless steel, annealing or increasing nickel can enhance the austenitic structure and improve ductility. This property makes stainless steel widely used in automotive, construction, and aerospace industries.

Fatigue Strength of Stainless Steel

Fatigue strength is the maximum stress a material can withstand after repeated cyclic loads. It varies with loading types; for instance, uniaxial tension and bending affect fatigue performance differently. Duplex stainless steels show the best fatigue strength, ranging from 400 to 600 MPa, while precipitation-hardened stainless steels exceed 600 MPa. Additionally, heat treatment processes like quenching and tempering can significantly enhance the fatigue performance of other stainless steels.

Hardness of Stainless Steel

Hardness is the ability of a material to resist deformation and wear, typically measured by Brinell (HB), Rockwell (HRC), or Vickers (HV) scales. Martensitic stainless steel has the highest hardness (HRC 40-60), while austenitic stainless steel has the lowest (HRC 15-30). Processes like quenching, tempering, and annealing, as well as alloying elements like chromium, nickel, carbon, and molybdenum, can increase the hardness of stainless steel.

Creep Resistance of Stainless Steel

Creep resistance is a material’s ability to resist deformation under high temperature and constant load, a slow deformation process. Higher temperatures and loads increase the creep rate. Austenitic stainless steel has the best high-temperature creep resistance, followed by martensitic, with ferritic being the weakest. Factors like melting methods, deoxidation, solidification techniques, heat treatment, and processing also affect creep resistance.

Elongation of Stainless Steel

Elongation is the ratio of the material’s extended length to its original length before fracture, indicating ductility. Austenitic stainless steel has the highest elongation (40%-60%), while martensitic and ferritic have lower values (20%-30%). High carbon content and cold working reduce plasticity, while proper heat treatment, like annealing, increases elongation. Stainless steels with high elongation are ideal for complex shapes and precision manufacturing, such as in automotive and aerospace industries.

Elastic Modulus of Stainless Steel

Elastic modulus, or Young’s modulus, measures a material’s ability to resist elastic deformation. It depends on temperature and stress conditions. Ferritic stainless steel has the highest modulus (about 200 GPa), while austenitic has the lowest (about 193 GPa). At high temperatures, austenitic stainless steel’s modulus drops faster, while ferritic and martensitic decrease more slowly. Alloying elements have minimal impact on elastic modulus.

What Are the Factors Affecting Stainless Steel Properties? 

The properties of stainless steel are influenced by its alloy composition, heat treatment, and work hardening processes.

Alloy Composition

The composition of stainless steel alloys significantly affects their properties. The primary elements include iron, chromium, nickel, and molybdenum, each contributing to different characteristics:

• Chromium: Provides corrosion resistance by forming a passive oxide layer.

• Nickel: Adds toughness and ductility, and improves corrosion resistance, especially in acidic environments.

• Molybdenum: Boosts strength and resists pitting and crevice corrosion.

• Carbon: Affects hardness and strength but can reduce corrosion resistance if present in high amounts.

Different grades of stainless steel feature diverse compositions tailored to specific applications, balancing elements to achieve desired properties such as strength, ductility, and corrosion resistance.

Heat Treatment

Heat treatment processes, including annealing, quenching, and tempering, are used to alter the microstructure of stainless steel, thereby enhancing its mechanical and physical properties:

• Annealing: Involves heating the steel to a specific temperature and then slowly cooling it to remove internal stresses and increase ductility and toughness.

• Quenching: Rapidly cooling the steel after heating to harden it, improving wear resistance and strength.

• Tempering: Heating quenched steel to a lower temperature and then allowing it to cool slowly, increasing toughness and reducing brittleness.

These heat treatment techniques can be applied to different stainless steel grades to achieve the desired balance of hardness, strength, and ductility for various industrial applications.

Work Hardening

Work hardening, or strain hardening, involves deforming stainless steel at room temperature to boost its strength and hardness. This process is typically achieved through methods such as rolling, drawing, and bending:

• Rolling: Compressing the steel between rollers to reduce thickness and increase tensile strength.

• Drawing: Pulling the steel through a die to decrease its cross-sectional area and enhance strength.

• Bending: Deforming the steel by applying force improves its hardness and yield strength.

Work hardening is particularly useful in applications requiring enhanced mechanical properties without altering the steel’s composition through heat treatment. It’s used to make springs, fasteners, and other high-stress, wear-resistant components.

Will Stainless Steel Eventually Rust?

Stainless steel is highly resistant to rust due to its chromium content, but under extreme conditions, such as prolonged exposure to harsh environments or if the protective oxide layer is damaged, it can eventually rust.

Further Reading
Will Stainless Steel Rust and How Can You Solve It?

Is Stainless Steel Stronger Than Steel?

Stainless steel typically surpasses regular steel in strength and durability, offering better resistance to corrosion and wear. However, the exact strength depends on the specific alloy and treatment.

How Long Can Stainless Steel Last?

Stainless steel can last for decades, even up to 100 years, depending on the environment and maintenance. Its longevity makes it a popular choice for both industrial and household applications.

Conclusion

Stainless steel’s unique combination of properties makes it suitable for many applications. Its performance is influenced by alloy composition, heat treatment, and work hardening. Understanding these factors underscores stainless steel’s versatility and reliability in both industrial and everyday use.

SteelPRO Group offers a wide range of stainless steels with excellent properties, and we can customize them to enhance specific characteristics. For more information on stainless steel, visit our blog page.

Contact our experts now for the best quote!