AISI 4340
Alloy Steel AISI 4340 Supplier in Tunisia
Introduction
AISI 4340 alloy steel is a nickel-chromium-molybdenum low-alloy steel known for its high strength, good hardenability, toughness, and fatigue resistance. It is widely used to manufacture mechanical components that must withstand heavy loads, repeated stresses, and demanding operating conditions.
The combination of nickel, chromium, and molybdenum allows AISI 4340 to achieve a useful balance of strength and toughness when correctly heat-treated. Its properties can be adjusted according to the product form, section size, and required material condition.
AISI 4340 is used in aerospace engineering, oil and gas, mining, power generation, heavy machinery, and general mechanical engineering. Emirerri Steel supports sourcing requirements for AISI 4340 according to project specifications, dimensions, product form, and quality requirements, subject to availability.
Key Properties
The principal characteristics of AISI 4340 alloy steel include:
High mechanical strength: Suitable for components exposed to substantial mechanical loads.
Good hardenability: Enables suitable mechanical properties to be developed through controlled heat treatment.
High toughness potential: Provides a useful balance between strength and resistance to fracture when correctly processed.
Fatigue resistance: Suitable for selected components subjected to cyclic loading, depending on design and surface condition.
Wear resistance: Can be improved through appropriate heat treatment.
Versatility: Used for bars, forgings, and machined mechanical components, depending on the applicable specification and supplier capabilities.
Heat-treatment adaptability: Hardness, strength, and toughness can be adjusted to meet application requirements.
AISI 4340 is a low-alloy steel, not stainless steel. It should not be selected for corrosion resistance without evaluating the operating environment and any required protective measures.
AISI 4340 Chemical Composition
AISI 4340 contains nickel, chromium, and molybdenum as its principal alloying elements, together with carbon and other controlled elements.
| Chemical Element | Typical Composition (%) |
|---|---|
| Carbon (C) | 0.38–0.43 |
| Manganese (Mn) | 0.60–0.80 |
| Silicon (Si) | 0.15–0.35 |
| Nickel (Ni) | 1.65–2.00 |
| Chromium (Cr) | 0.70–0.90 |
| Molybdenum (Mo) | 0.20–0.30 |
| Phosphorus (P) | 0.035 max. |
| Sulfur (S) | 0.040 max. |
Note: These are commonly published composition ranges for AISI 4340. Exact limits depend on the applicable product specification and its edition. The material test certificate should be used to verify the supplied material.
AISI 4340 Mechanical Properties
The mechanical properties of AISI 4340 vary considerably with heat treatment, section size, manufacturing process, and material condition.
The properties commonly specified for AISI 4340 include:
Tensile strength
Yield strength
Elongation
Reduction of area
Hardness
Impact toughness, where required
Fatigue performance, depending on design and testing conditions
AISI 4340 can be supplied in different material conditions, including annealed and quenched-and-tempered conditions, depending on the product specification.
For high-strength applications, the required mechanical properties should be specified according to the applicable product standard, section size, and heat-treatment condition. Guaranteed values must be confirmed through the relevant inspection documents and material test certificate.
AISI 4340 Physical Properties
The physical properties of AISI 4340 are relevant to mechanical design, strength calculations, machining, and manufacturing operations.
| Physical Property | Approximate Value |
|---|---|
| Density | 7.85 g/cm³ |
| Modulus of elasticity | Approximately 205 GPa |
| Poisson’s ratio | Approximately 0.29 |
| Thermal conductivity at room temperature | Approximately 40–45 W/m·K |
| Mean coefficient of thermal expansion | Approximately 11–13 × 10⁻⁶/K |
| Specific heat capacity | Approximately 460–480 J/kg·K |
Note: These values are approximate and can vary with temperature, material condition, and reference source. Manufacturer data should be consulted for critical engineering calculations.
Grade Specification Comparison and Equivalents
AISI 4340 is a widely used designation for nickel-chromium-molybdenum alloy steel. Several international grades are commonly compared with it, but equivalent status must be verified before material substitution.
| Standard or Country | Comparable Grade |
|---|---|
| AISI / SAE (USA) | 4340 |
| EN (Europe) | 34CrNiMo6 |
| EN Material Number | 1.6582 |
| DIN (Germany) | 34CrNiMo6 |
| JIS (Japan) | SNCM439 — commonly compared; verify the applicable specification |
| GB (China) | 40CrNiMoA — possible comparison, subject to requirements |
These grades may differ in chemical composition limits, mechanical-property requirements, product dimensions, heat treatment, and inspection criteria. Their interchangeability should be established through a technical review of the relevant standards and certificates.
Additional Notes
When selecting AISI 4340 alloy steel, consider the following factors:
Product form: Bars, forgings, and other forms depending on the applicable standard and supplier capability.
Delivery condition: Annealed, heat-treated, or another specified condition.
Section size: Influences the properties achievable throughout the material after heat treatment.
Traceability: Product markings and material certificates should correspond to the supplied batch.
Quality control: Mechanical tests, dimensional inspection, and supplementary examinations should be specified as required.
Service conditions: Loading, fatigue, temperature, and corrosion exposure should be assessed before material selection.
Corrosion Resistance
AISI 4340 does not offer the corrosion resistance of stainless steel. Its chromium content primarily contributes to hardenability and metallurgical performance; it does not make the grade stainless.
In the presence of moisture, seawater, chemicals, or aggressive industrial atmospheres, AISI 4340 can corrode unless appropriate protection is provided.
Possible protection measures include:
Applying a protective coating suitable for the operating environment.
Using temporary corrosion-inhibiting oils during storage and transportation.
Applying an appropriate surface treatment where compatible with the application.
Storing the material under conditions that limit moisture exposure.
For marine or highly corrosive applications, material selection should be reviewed carefully. Stainless steel or a corrosion-resistant alloy may be more suitable depending on the service requirements.
Heat Resistance
AISI 4340 can be used in mechanical components exposed to changing temperatures, but it is not specifically designed as a creep-resistant steel for prolonged high-temperature service.
Extended exposure to elevated temperatures can change hardness and the mechanical properties established by heat treatment. Actual performance depends on temperature, exposure duration, applied stress, and material condition.
For high-temperature applications, allowable operating conditions should be established using applicable engineering data and design requirements. Equipment operating under pressure or at sustained elevated temperatures may require a grade specifically qualified for those conditions.
Heat Treatment
Heat treatment is essential for obtaining the required mechanical properties from AISI 4340.
Annealing
Annealing can produce a material condition suitable for machining or subsequent manufacturing operations. The process depends on the product form and required final properties.
Normalizing
Normalizing may help refine and homogenize the steel’s microstructure, depending on the initial material condition and manufacturing process.
Quenching
Quenching involves heating the steel according to a defined procedure and cooling it under controlled conditions. It can increase hardness and strength but may also introduce internal stresses.
Tempering
Tempering is commonly performed after quenching to adjust hardness and improve toughness. The selected tempering cycle depends on the required final mechanical properties.
Heating temperatures, holding times, and cooling conditions must be determined according to the product form, section size, applicable procedure, and specification. The resulting properties should be verified through the required inspections and tests.
Welding
Welding AISI 4340 requires careful technical evaluation. Its hardenability and alloy composition can increase the risk of cracking and the formation of hard regions in the heat-affected zone.
Depending on component geometry, thickness, material condition, and welding procedure, precautions may include:
Evaluating weldability before fabrication.
Applying suitable preheating.
Controlling interpass temperature.
Selecting compatible filler material.
Managing cooling rates.
Applying post-weld heat treatment when required.
Performing non-destructive testing according to project specifications.
For critical components, welding should follow a qualified welding procedure and be carried out by competent personnel. Welding conditions should be reviewed and approved before production.
Fabrication
AISI 4340 is used to manufacture mechanical components that require high strength and toughness. Fabrication methods must be selected according to the material condition and product dimensions.
Machining
Turning, milling, drilling, and grinding parameters should be selected according to material hardness, tooling, and the required surface finish. Annealed material is generally easier to machine than highly hardened material.
Forging
Forging must be performed within an appropriate temperature range for the grade and process. Cooling after forging and any subsequent heat treatment must be controlled to achieve the specified properties.
Cutting and Forming
Cutting and forming methods depend on geometry, thickness, material condition, and dimensional tolerances. The selected processes should minimize defects and preserve the required material characteristics.
Inspection After Fabrication
Depending on project requirements, inspection may include:
Dimensional verification.
Visual and surface examination.
Hardness testing.
Mechanical testing.
Non-destructive testing, where specified.
Verification of traceability and conformity documents.
Applications
AISI 4340 alloy steel is used in industries requiring high mechanical strength, toughness, and fatigue performance.
Aerospace and Mechanical Engineering
High-strength shafts and axles.
Gears and transmission components.
Mechanical parts subjected to heavy loads.
Forged and machined components manufactured to project requirements.
Oil and Gas Industry
Mechanical components for drilling equipment.
Industrial equipment parts exposed to high stresses.
Selected components designed for specific operating conditions.
Mining and Heavy Equipment
Mechanical parts for heavy machinery.
Power-transmission components.
Components subjected to repeated mechanical loading.
Forged parts for demanding industrial equipment.
Power Generation and General Industry
Shafts and rotating components.
High-strength mechanical parts.
Industrial machinery components.
Equipment elements designed for specific loads and service conditions.
The suitability of AISI 4340 must be confirmed based on operating loads, temperature, environmental exposure, component geometry, heat treatment, and applicable standards.
Emirerri Steel – AISI 4340 Alloy Steel Supplier
Emirerri Steel supports industrial customers with sourcing requirements for alloy-steel materials used in demanding mechanical applications. We review AISI 4340 enquiries according to required dimensions, product form, applicable specifications, material condition, and quality documentation.
We support project requirements across the oil and gas, petrochemical, mining, power generation, mechanical engineering, and industrial equipment sectors in Tunisia and North Africa.
To request a quotation, please provide the required grade, product form, dimensions, quantity, applicable standard, heat-treatment condition, and certification requirements. Availability and delivery schedules are confirmed at the quotation stage.
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