SAE AISI 4135 Steel UNS G41350: Composition, Properties, and Uses
When it comes to the world of high-strength, versatile alloy steels, SAE AISI 4135 stands out as a remarkable choice…
When it comes to engineering materials that combine high strength, toughness, and versatility, SAE AISI 4340 alloy steel stands out as a top contender. Known by its UNS designation G43400, this low-alloy steel is renowned for its exceptional mechanical properties and wide range of applications. Whether you’re an engineer specifying materials for aerospace components, a manufacturer seeking robust automotive parts, or a researcher delving into advanced metallurgy, understanding the intricacies of SAE AISI 4340 alloy steel is crucial.
In this article, we will explore the detailed chemical composition of this alloy, shedding light on how each element contributes to its remarkable characteristics. We’ll delve into the mechanical properties that make it a preferred choice in high-stress environments, and examine the various heat treatment processes that can further enhance its performance. Additionally, we’ll highlight the diverse applications across industries such as aerospace, automotive, and machinery, demonstrating why SAE AISI 4340 remains a material of choice for demanding applications. Finally, we’ll look into its physical properties, providing a comprehensive understanding of how this alloy behaves under different conditions. Join us as we unravel the secrets behind the strength and versatility of SAE AISI 4340 alloy steel.
SAE-AISI 4340 alloy steel, also known as UNS G43400, is a high-strength, low-alloy steel commonly used in various industries. It is renowned for its exceptional toughness, high tensile strength, and excellent fatigue resistance, thanks to its well-balanced chemical composition that includes nickel, chromium, and molybdenum. These elements improve the steel’s ability to be hardened and help it maintain strength and toughness under severe conditions.
The versatility of SAE-AISI 4340 alloy steel comes from its ability to be heat-treated to achieve various mechanical properties. This makes it suitable for demanding applications in the aerospace and automotive industries, where components need to handle high stress and require great strength and reliability. It is also used in manufacturing machine tools, hydraulic parts, and other high-performance machinery.
SAE-AISI 4340 alloy steel is a versatile and reliable material that excels in applications requiring superior mechanical properties. Its balanced composition and heat treatment adaptability make it a top choice across multiple industries, ensuring performance and durability in demanding conditions.
SAE AISI 4340 alloy steel, known as UNS G43400, is composed of specific elements that enhance its strength and durability. Knowing its chemical composition helps predict its performance in different conditions and applications.
Each element in SAE AISI 4340 alloy steel contributes to its properties and suitability for various uses:
Carbon significantly increases hardness and tensile strength, allowing the steel to be hardened through heat treatment for high wear resistance.
Manganese improves toughness and hardness, acts as a deoxidizer, and enhances hardenability for uniform properties in thicker sections.
Silicon adds strength and elasticity and helps remove impurities during steelmaking.
Phosphorus and sulfur are kept low to avoid brittleness, though they can improve machinability.
Nickel enhances toughness, strength, and corrosion resistance, making the steel suitable for demanding environments.
Chromium increases hardness, tensile strength, wear, and corrosion resistance.
Molybdenum boosts strength, hardenability, and toughness, especially at high temperatures.
Iron is the primary component, providing the base structure for other elements.
Understanding the chemical composition of SAE AISI 4340 alloy steel helps engineers and material scientists predict its performance, ensuring its optimal use in aerospace, automotive, and other high-stress applications.
SAE AISI 4340 alloy steel is renowned for its remarkable strength and durability, making it a top choice for high-stress applications.
SAE AISI 4340 alloy steel exhibits impressive tensile and yield strength, making it ideal for high-stress applications. The ultimate tensile strength (UTS) measures the maximum stress the material can withstand while being stretched or pulled before breaking. Yield strength indicates the stress at which the material begins to deform plastically. For annealed steel, the UTS is 745 MPa (108 ksi) and the yield strength is 470 MPa (68 ksi). For normalized steel, the UTS is 1282 MPa (186 ksi) and the yield strength is 862 MPa (125 ksi). For quenched and tempered steel, the UTS is 1207 MPa (175 ksi) and the yield strength is 1145 MPa (166 ksi).
Elongation at break and reduction in area are measures of how much the material can stretch or shrink in cross-sectional area before breaking. For annealed steel, the elongation is 22.0% and the reduction in area is 50.0%. For normalized steel, the elongation is 12.2% and the reduction in area is 36.3%. For quenched and tempered steel, the elongation is 14.2% and the reduction in area is 45.9%.
Hardness measures the material’s resistance to deformation and wear. The hardness of SAE AISI 4340 alloy steel varies with its heat treatment state. The Brinell hardness is 217 HB for annealed steel, 363 HB for normalized steel, and 352 HB for quenched and tempered steel.
The modulus of elasticity (Young’s modulus) describes the material’s stiffness, while the shear modulus indicates its resistance to shear deformation. SAE AISI 4340 alloy steel has a modulus of elasticity of 190 GPa (27 x 10^6 psi) and a shear modulus of 73 GPa (11 x 10^6 psi).
SAE AISI 4340 alloy steel is known for its excellent resistance to fatigue and creep, making it ideal for applications involving cyclic loading and high temperatures. Its fatigue strength ranges from 330 to 740 MPa (48 to 110 x 10^3 psi), and it maintains good strength at elevated temperatures.
These mechanical properties make SAE AISI 4340 alloy steel a reliable and durable choice for demanding environments, ensuring high performance across various applications.
SAE AISI 4340 alloy steel is extensively used in the aerospace industry because of its high strength, toughness, and excellent fatigue resistance, which are critical for components in both commercial and military aircraft. It’s commonly used for:
The automotive industry leverages the robust properties of SAE AISI 4340 alloy steel for components that require high strength and durability. It is commonly used for:
SAE AISI 4340 alloy steel is also utilized in the manufacture of machine tools, where high strength, toughness, and wear resistance are essential. Applications include:
4340 steel’s mechanical properties ensure reliable performance and long service life in hydraulic systems and heavy machinery, making it suitable for gears, pinions, shafts, and pistons. These applications benefit from the alloy’s strength and resistance to fatigue.
SAE AISI 4340 alloy steel is also widely used in general engineering applications. Its versatility and strength make it ideal for:
Overall, the unique properties of SAE AISI 4340 alloy steel make it invaluable across various demanding industries.
Annealing is a heat treatment process that softens SAE AISI 4340 alloy steel, relieves internal stresses, and enhances machinability.
Full Anneal
Full annealing involves heating the steel to 844°C (1550°F), then cooling it slowly in a furnace to 315°C (600°F), and finally air cooling. This results in a coarse pearlitic structure, improving machinability.
Standard Annealing
Standard annealing involves heating the steel to 830-860°C (1525-1575°F), holding it at this temperature based on thickness, then cooling it in a furnace to 610°C (1130°F) at a rate of 20°C (11°F) per hour, and air cooling to room temperature. This results in a fine pearlitic structure, enhancing toughness and ductility.
Normalizing refines the grain structure and improves the mechanical properties of SAE AISI 4340 alloy steel. It involves heating the steel to 845-900°C (1550-1650°F), holding it for a time based on thickness, then air cooling. This produces a uniform, finer grain structure, enhancing strength and toughness.
Hardening increases the hardness and strength of SAE AISI 4340 alloy steel. Heat the steel to 800-845°C (1475-1550°F) for 15 minutes per 25 mm (1 inch) of thickness, then quench in oil or fused salt below 65°C (150°F). This rapid cooling transforms the microstructure to martensite, significantly increasing hardness.
Tempering
Tempering reduces brittleness after hardening and achieves a balance of strength and toughness. Temper at 232°C (450°F) for high strength (260-280 ksi), or at 510°C (950°F) for moderate strength (125-200 ksi). Avoid tempering in the 220-260 ksi range to maintain impact resistance.
Stress Relieving
Stress relieving removes residual stresses from machining or other processes. For pre-hardened steel, heat to 500-550°C (932-1022°F). For other conditions, heat to 600-650°C (1112-1202°F). Hold until uniform, soak for 1 hour per 25 mm section, then cool in still air to minimize distortion and enhance stability.
SAE AISI 4340 alloy steel has a density of about 0.284 lb/in³ or 7.9 g/cm³. This relatively high density reflects the presence of alloying elements such as nickel, chromium, and molybdenum, which enhance the material’s strength and toughness.
Melting Point
The melting point of SAE AISI 4340 alloy steel is between 2580 and 2650 °F (1417 to 1454 °C), making it suitable for high-temperature applications.
Specific Heat Capacity
The specific heat capacity is 1.14 x 10^-1 BTU/lb-°F, important for understanding how the material absorbs and retains heat.
Thermal Conductivity
With a thermal conductivity of 309 BTU-in/hr-ft²-°F, SAE AISI 4340 alloy steel effectively dissipates heat, beneficial for applications with heat generation concerns.
Thermal Expansion
The coefficient of thermal expansion is 0.00000683 per °F, which helps predict how the material’s dimensions change with temperature variations.
Modulus of Elasticity
SAE AISI 4340 alloy steel has a modulus of elasticity between 27,800 and 29,000 ksi, indicating its stiffness and resistance to deformation under load.
Shear Modulus
The shear modulus ranges from 10.7 to 11.3 ksi, showing the material’s ability to resist shear deformation.
Poisson’s Ratio
With a Poisson’s ratio of 0.29, this steel expands in directions perpendicular to compression, informing its deformation characteristics under load.
Electrical Conductivity
The electrical conductivity is 6.95% IACS, typical for alloy steels and adequate for applications where high conductivity is not needed.
These properties make SAE AISI 4340 alloy steel a versatile material suitable for a wide range of high-performance applications in various industries. Understanding these properties helps engineers and designers make informed decisions about material selection and application design.
Below are answers to some frequently asked questions:
The chemical composition of SAE AISI 4340 alloy steel (UNS G43400) consists primarily of iron (Fe), which makes up approximately 95.1% to 96.3% of the alloy. Key alloying elements include carbon (C) at 0.38% to 0.43%, nickel (Ni) at 1.65% to 2.00%, chromium (Cr) at 0.7% to 0.9%, manganese (Mn) at 0.6% to 0.9%, and molybdenum (Mo) at 0.2% to 0.3%. Additionally, it contains silicon (Si) at 0.15% to 0.35%, with minor elements like phosphorus (P) not exceeding 0.035% and sulfur (S) not exceeding 0.040%. This precise blend of elements contributes to the steel’s high tensile strength, toughness, fatigue resistance, and deep hardenability.
SAE AISI 4340 alloy steel is known for its exceptional mechanical properties, which are significantly influenced by its composition and heat treatment. The tensile strength can range from 860 to 1980 MPa, while the yield strength varies from 740 to 1860 MPa, depending on the heat treatment applied. It exhibits good ductility with an elongation at break ranging from 11% to 23%. The Rockwell hardness of this steel can range from 24 to 53 HRC, and it has a plane strain fracture toughness between 53 to 110 MPa√m. 4340 steel is renowned for its high fatigue and creep resistance, making it ideal for applications involving cyclic loading and high temperatures. The machinability of 4340 steel in its annealed state is rated at 50-57%, using AISI 1212 as a reference, and its modulus of elasticity is about 205 GPa. The mechanical properties can be tailored through various heat treatment processes, such as annealing, normalizing, and hardening followed by tempering, with oil quenching commonly used for hardening thin sections. These attributes make it a versatile material for applications in heavy shafting, fasteners, aircraft, automotive, and hydraulic systems.
SAE AISI 4340 alloy steel is commonly used in various applications due to its high strength, toughness, and fatigue resistance. In the aerospace industry, it is utilized for components such as aircraft landing gear, engine mounts, and other structural parts. In the automotive sector, it is employed in transmissions, gears, shafts, and other critical components that require durability and high strength. The steel is also used in power transmission gears and shafts, machine tools, hydraulic parts, and heavy-duty structural components like crankshafts. Additionally, it is favored in tooling and general engineering applications where high strength and resistance to fatigue and creep are essential.
SAE AISI 4340 alloy steel undergoes several heat treatment processes to enhance its mechanical properties. These processes include:
Annealing: This involves heating the steel to 1525°F (830°C), cooling it to 1350°F (730°C), followed by furnace cooling to 1130°F (610°C) at a rate of 11°F (20°C) per hour, and finally air cooling to room temperature. Annealing relieves internal stresses, making the steel more machinable and formable.
Normalizing: Conducted at around 1500°F (815°C) +/- 50°F (10°C), normalizing refines the grain structure and improves mechanical properties.
Hardening: The steel is heated to 1500-1550°F (815-845°C) and then oil quenched to achieve high hardness.
Tempering: After hardening, tempering is performed to reduce brittleness and achieve a balance of hardness and toughness. Tempering temperatures vary depending on the desired tensile strength: 450°F (232°C) for 260-280 KSI, and 950°F (510°C) for 125-200 KSI. It’s recommended to avoid tempering within 220-260 KSI to prevent impact resistance degradation.
Stress Relieving: This process is done at 1000-1200°F (538-649°C) to alleviate stresses introduced by welding or other procedures.
By carefully controlling these heat treatment steps, SAE AISI 4340 steel is optimized for applications requiring high strength and durability.
SAE AISI 4340 alloy steel (UNS G43400) exhibits several important physical properties that make it suitable for various high-strength and high-stress applications. The density of this alloy steel is 7.87 g/cm³. It has a melting point of approximately 1408°C. The specific heat capacity is 582 J/(kg·K) at 0-100°C. The linear expansion coefficient is 12.8 × 10^-6/K at 0-100°C. Poisson’s ratio for this steel is 0.295, and the elastic modulus is 213,000 MPa (or 213 GPa). The shear modulus is 82,300 MPa. Thermal conductivity is measured at 36.01 W/(m·K) at 150°C, and the electrical resistivity is 36.2 × 10^-8 Ω·m at 150°C. These properties contribute to the alloy’s effectiveness in applications requiring high strength, toughness, and resistance to fatigue and creep.
SAE AISI 4340 alloy steel is commonly used in several industries due to its exceptional strength, toughness, and hardenability. In the aerospace industry, it is utilized for aircraft landing gear and other critical components. In the automotive sector, it is employed for gears, shafts, and structural parts requiring high tensile strength. The oil and gas industry uses it for drilling equipment and other high-stress applications. It is also significant in power transmission and machine building for heavy-duty components like axles and gears. Additionally, it finds applications in general engineering, forging, forming, and hydraulic systems where high-strength and wear resistance are essential.
