AMS 6359 Alloy Steel: Composition, Properties, and Uses
In the world of advanced engineering and manufacturing, materials play a pivotal role in determining the performance and longevity of…
In the world of high-performance materials, few stand out like AISI E4340 alloy steel. Renowned for its exceptional strength, toughness, and versatility, this low-alloy steel is a cornerstone in industries ranging from aerospace to automotive. But what exactly makes AISI E4340 so special? To answer that, we’ll delve into its precise chemical composition, explore its remarkable mechanical properties, and understand the critical role heat treatment plays in enhancing its performance. Whether you’re an engineer seeking robust materials for demanding applications or a researcher interested in the nuances of advanced alloys, this comprehensive guide will provide valuable insights into the specifications, certifications, and real-world uses of AISI E4340 alloy steel. Join us as we uncover the secrets behind one of the most reliable and widely-used materials in modern engineering.
AISI E4340 alloy steel, also known as UNS G43406, is a medium-carbon, low-alloy steel noted for its exceptional strength, toughness, and versatility. It is primarily composed of nickel, chromium, and molybdenum, which contribute to its superior mechanical properties and ability to withstand high stress and impact conditions. This alloy is widely recognized for its excellent hardenability, making it an ideal choice for applications requiring high strength and durability.
The unique combination of properties offered by AISI E4340 makes it essential for various high-performance applications, where its high tensile strength and toughness allow it to withstand demanding environments. The steel’s ability to retain its mechanical properties after heat treatment further broadens its range of uses.
AISI E4340 alloy steel is widely used in the aerospace, automotive, and industrial sectors due to its high strength and toughness. In aerospace, it is used for critical components like landing gears, crankshafts, and connecting rods, which must endure extreme stress without compromising safety or performance. In the automotive industry, AISI E4340 is used for durable parts such as gearboxes, sprockets, and chucks. In industrial applications, it is used for machine tool arbors, axle shafts, and other components that benefit from its strength and wear resistance, making AISI E4340 a versatile and valuable material for manufacturers and engineers.
AISI E4340 alloy steel (UNS G43406) is known for its excellent mechanical properties and is made from a specific blend of elements. This medium-carbon, low-alloy steel primarily consists of carbon, manganese, phosphorus, sulfur, silicon, chromium, nickel, molybdenum, and iron.
Carbon, present at 0.38-0.43%, is essential for the steel’s hardness and strength, providing a good balance between strength and ductility.
Manganese (0.60-0.85%) improves hardenability, tensile strength, and overall toughness, while aiding in the deoxidation process during steelmaking.
Phosphorus is kept below 0.025% to prevent embrittlement and maintain ductility.
Sulfur is limited to 0.04% to improve machinability without causing brittleness.
Silicon (0.15-0.30%) acts as a deoxidizer and adds to the alloy’s strength and hardness. Chromium (0.70-0.90%) improves corrosion resistance, hardness, wear resistance, and hardenability.
Nickel (1.65-2.00%) increases toughness, strength, corrosion resistance, and maintains hardness at low temperatures.
Molybdenum (0.20-0.30%) boosts high-temperature strength, hardenability, and overall toughness.
Iron makes up the remainder of the alloy, providing the matrix that holds the other elements and their properties.
The chemical composition of AISI E4340 steel is consistent across various forms like bars, plates, and forgings. Minor variations due to manufacturing processes are within acceptable ranges, ensuring the steel’s properties remain consistent.
Knowing the exact chemical composition of AISI E4340 is vital for choosing the right heat treatment and achieving the desired mechanical properties for different applications.
AISI E4340 alloy steel is highly regarded for its exceptional mechanical properties, especially when properly heat-treated. These qualities make it ideal for demanding applications where strength and durability are crucial.
Tensile strength measures the maximum stress AISI E4340 steel can endure before breaking. After heat treatment, it typically ranges from 140,000 to 160,000 psi (965 to 1103 MPa). This high tensile strength is a key attribute, making the alloy suitable for high-stress applications.
Yield strength is the stress at which AISI E4340 steel starts to deform permanently. After heat treatment, it usually ranges from 130,000 to 140,000 psi (896 to 965 MPa). This property is essential for applications requiring materials to maintain their shape under high loads without permanent deformation.
Elongation shows how much the steel can stretch before breaking. In its annealed state, AISI E4340 usually has an elongation of around 12%, though this can vary with heat treatment. Elongation is important for applications needing a degree of flexibility and toughness.
Hardness measures resistance to deformation. After quenching and tempering, AISI E4340 can reach a Rockwell hardness of HRC 50-55, making it resistant to wear and abrasion. This high level of hardness is crucial for parts that need to withstand severe conditions.
Impact strength measures the steel’s ability to absorb energy and resist impact. When properly heat-treated, AISI E4340 has excellent impact resistance, making it ideal for critical aerospace and automotive parts that endure dynamic loads.
Heat treatment processes like normalizing, austenitizing, quenching, and tempering significantly influence AISI E4340’s properties.
Normalizing heats the steel above its critical range and cools it in air, refining the grain structure and improving strength and toughness. This process enhances the uniformity of the microstructure.
Austenitizing heats the steel to 830°C-860°C (1526°F-1580°F), preparing it for quenching and tempering to enhance hardness and strength. This step is crucial for achieving the desired mechanical properties.
Quenching rapidly cools the austenitized steel in oil or water, increasing hardness and strength but also brittleness, which requires further heat treatment. This process transforms the austenite into martensite, a very hard microstructure.
Tempering reheats the quenched steel to 200°C-650°C (392°F-1202°F), reducing brittleness while maintaining strength and hardness. The specific tempering temperature determines the final balance of hardness, strength, and toughness.
AISI E4340 retains high tensile and yield strengths at room temperature, exhibits good toughness and ductility at elevated temperatures, and maintains strength and hardness in cold environments. This versatility makes it reliable under various conditions, ensuring consistent performance across different applications.
Heat treatment is crucial for enhancing the mechanical properties of AISI E4340 alloy steel, such as strength, toughness, and hardness. The following processes are commonly used:
Annealing involves heating the steel to 1525°F (830°C), then cooling it to 1350°F (730°C), followed by furnace cooling to 1130°F (610°C) at a controlled rate of 11°F (20°C) per hour, and finally air cooling to room temperature. This process relieves internal stresses and softens the steel, improving machinability.
Normalizing involves heating the steel to 1500°F (815°C) ± 50°F (10°C) and letting it cool in air. This process refines the grain structure, enhancing strength and toughness.
To harden AISI E4340, heat it to 1500-1550°F (815-845°C), then quench it in oil. This rapid cooling transforms the structure, significantly increasing hardness and strength but also making the steel brittle.
Tempering follows hardening to reduce brittleness while maintaining strength. Reheat the steel to a temperature between 392°F and 1202°F (200°C and 650°C) based on the desired properties. For a strength level of 260-280 ksi, temper at 450°F (232°C). For 125-200 ksi, temper at 950°F (510°C). Avoid tempering for 220-260 ksi to prevent loss of impact resistance.
Stress relieving reduces residual stresses in pre-hardened steel. For thin sections, heat to 932-1022°F (500-550°C) and cool in still air. For thicker sections, heat to 1112-1202°F (600-650°C), soak for one hour per 25 mm of thickness, then cool in still air.
To achieve optimal strength and hardness, maintain precise temperature control, avoid overheating, use the recommended quenching medium, and select the correct tempering temperature based on the desired balance of strength and toughness. By following these heat treatment processes and tips, AISI E4340 alloy steel can be tailored to meet specific mechanical property requirements, making it suitable for a wide range of demanding applications.
AISI E4340 alloy steel is widely used in the aerospace industry due to its high strength, toughness, and resistance to stress and fatigue. These properties make it ideal for critical components that must endure extreme conditions while maintaining structural integrity and performance.
AISI E4340 alloy steel is commonly used for aircraft landing gear because it can handle significant impact forces during landing and take-off, ensuring safety and reliability.
Crankshafts and connecting rods in aircraft engines are made from AISI E4340 because they need to withstand high stresses and rotational forces, ensuring long-term durability and performance.
The high strength and toughness of AISI E4340 make it ideal for landing gear struts, which support the aircraft’s weight and absorb shock during landing.
In the automotive industry, AISI E4340 alloy steel is used for components that require high strength, wear resistance, and the ability to withstand repeated stress.
Transmission gears made from AISI E4340 can endure high pressures and repeated stress, ensuring reliable performance and longevity.
Power transmission gears benefit from AISI E4340’s strength and wear resistance, making them reliable in machinery and equipment.
Shafts and axles in automotive applications are made from AISI E4340 because of its high tensile strength and resistance to torsional stress, ensuring they can handle rigorous demands.
AISI E4340 alloy steel is also used in various industrial applications where high strength and toughness are essential.
Machine tool arbors, which hold cutting tools, require materials that maintain strength and stability under stress. AISI E4340 provides the necessary hardness and toughness.
Couplings, sprockets, and chucks benefit from AISI E4340’s wear resistance and toughness, ensuring reliable performance in mechanical systems and machinery.
Molds and dies made from AISI E4340 retain hardness after heat treatment, ensuring precision and longevity in manufacturing processes.
Examples of parts made from AISI E4340 include crankshafts, landing gear struts, valves, connecting rods, axle shafts, and machine tool arbors. These parts need high strength and durability, making AISI E4340 an excellent choice.
AISI E4340 alloy steel is regulated by several industry standards to ensure its quality and performance. These standards define the chemical composition, mechanical properties, and heat treatment processes required for the steel.
Relevant ASTM specifications include:
Relevant AMS specifications include:
Relevant MIL specifications include:
AISI E4340 alloy steel must undergo rigorous testing and certification to ensure compliance with standards.
Manufacturers must provide a certified test report verifying the chemical composition of AISI E4340, ensuring it falls within specified ranges for elements like carbon, manganese, phosphorus, sulfur, silicon, chromium, nickel, and molybdenum.
Certified test reports must confirm mechanical properties such as tensile strength, yield strength, elongation, and hardness, typically conducted on samples that have undergone specified heat treatment processes.
Heat treatment processes must be certified to ensure they have been performed according to specified temperatures and durations, ensuring AISI E4340 achieves desired mechanical properties.
Third-party inspections may be required to validate compliance with relevant standards, adding an extra layer of quality assurance.
AISI E4340 alloy steel is also recognized under various international standards, ensuring its global applicability and acceptance. Some of these standards include:
By adhering to these standards and obtaining the necessary certifications, manufacturers and users of AISI E4340 alloy steel can ensure its high quality and suitability for demanding applications across various industries.
AISI E4340 alloy steel comes in various forms to meet a wide range of industrial needs. The most common forms include:
AISI E4340 alloy steel can be sourced from various suppliers, each offering different forms and specifications to suit specific applications. Some notable suppliers include:
When sourcing AISI E4340 alloy steel, ensure the material meets required standards. Look for suppliers that provide certified test reports, heat treatment documentation, and third-party inspections to verify material properties and compliance.
AISI E4340 alloy steel is recognized under various international standards, making it accessible globally. It is produced and supplied by manufacturers in North America, Europe, and Asia, making it accessible for international projects.
Below are answers to some frequently asked questions:
The chemical composition of AISI E4340 alloy steel (UNS G43406) is as follows:
This composition provides AISI E4340 with its distinctive balance of strength, toughness, and wear resistance, making it suitable for demanding applications in various industries.
AISI E4340 alloy steel exhibits impressive mechanical properties after heat treatment. When annealed, it has a tensile strength of approximately 745 MPa (108,000 psi), a yield strength of around 470 MPa (68,200 psi), an elongation at break of 22%, and a Brinell hardness of 217. Through normalizing and hardening, the mechanical properties are significantly enhanced. After hardening (heating to 1500-1550 °F and quenching in oil), the tensile strength ranges from 930 to 1230 MPa (135,000 to 178,000 psi), yield strength from 635 to 925 MPa (92,000 to 134,000 psi), elongation between 11-13%, and Brinell hardness from 248 to 375. Tempering further refines these properties, with specific tempering temperatures achieving varying strength levels. For instance, tempering at 232°C (450°F) can yield strengths of 1790 – 1930 MPa, while tempering at 510°C (950°F) results in strengths of 862 – 1379 MPa. Surface hardening processes can also be applied to achieve a case hardness exceeding Rc 50.
To achieve maximum strength in AISI E4340 alloy steel, follow these heat treatment steps:
By following these steps, you will achieve the desired high strength and mechanical properties for AISI E4340 alloy steel.
AISI E4340 alloy steel is commonly used in applications that require high strength, toughness, and resistance to wear and stress. This makes it ideal for a variety of industries. In the aerospace sector, it is frequently used for structural components like aircraft landing gear due to its durability and ability to withstand high stress. In the automotive industry, it is used for transmission gears, crankshafts, connecting rods, and axle shafts, which all require high strength and durability. The alloy is also used in the manufacture of mechanical parts such as shafts, nuts, bolts, and pins, as well as industrial equipment like sprockets, chucks, molds, and couplings. Additionally, AISI E4340 is employed in the defense sector for producing gun parts that need to endure high pressures and repeated stress. Its versatility and robust properties make it a preferred material in these demanding applications.
AISI E4340 alloy steel meets several important specifications and certifications, which ensure its quality and suitability for various high-stress applications. These include AMS 6359 for sheet, strip, and plate; AMS 6409 and AMS 6484 for bars and forgings, normalized and tempered; AMS 6414 for vacuum-melted bars and forgings; AMS 6415 for bars and forgings; and ASTM A322 and ASTM A331 for general alloy steel bars. Additionally, it adheres to the MIL-S-8844 Cl1 military specification, Boeing’s BMS-7-28 and BPS-299-947-055/BPS-299-949-055 standards, European equivalents EN 10250 (36CrNiMo4/1.6511) and BS 970 (EN24/817M40), and Japanese equivalent JIS G4103 (SNCM439/SNCM8).
You can buy AISI E4340 alloy steel in various forms from several reputable suppliers. Benedict-Miller offers sheet, plate, and round bar (both cold finished and hot rolled) and provides metal cutting and finishing services. California Metal & Supply supplies 4340 alloy in sheet, plate, bar, and forged bar forms and has a stocking program for long-term contracts. Aero-Vac provides round bar, flat bar, rectangular bar, forged bar, forged block, machine ready blanks, machined block, and forgings, meeting various industry specifications. Service Steel Aerospace offers round bar, flat bar, square bar, block, and billet, available in both air-melted and electroslag remelted (ESR) materials. You can contact these suppliers directly for quotes and more detailed information on their offerings.
