SAE/AISI 4340 (UNS G43400) steel is an ultra-high strength low-alloy steel containing chromium and molybdenum. AISI 4340 Alloy Steel has good strength and toughness and exhibits excellent corrosion resistance in a wide range of environments. This guide will cover the various properties of UNS G43400, its uses, heat treatment options, machining & welding capabilities, and much more. Let’s get started!
AISI 4340 Composition
| Element | Content (%) |
|---|---|
| Iron, Fe | 95.195 – 96.33 |
| Nickel, Ni | 1.65 – 2.00 |
| Chromium, Cr | 0.700 – 0.900 |
| Manganese, Mn | 0.600 – 0.800 |
| Carbon, C | 0.370 – 0.430 |
| Molybdenum, Mo | 0.200 – 0.300 |
| Silicon, Si | 0.150 – 0.300 |
| Sulfur, S | 0.0400 |
| Phosphorous, P | 0.0350 |
AISI 4340 Physical Properties
| Properties | Metric | Imperial |
|---|---|---|
| Density | 7.85 g/cm3 | 0.284 lb/in³ |
| Melting point | 1427°C | 2600°F |
AISI 4340 Mechanical Properties
| Properties | Metric | Imperial |
|---|---|---|
| Tensile strength | 745 MPa | 108000 psi |
| Yield strength | 470 MPa | 68200 psi |
| Bulk modulus (typical for steel) | 140 GPa | 20300 ksi |
| Shear modulus (typical for steel) | 80 GPa | 11600 ksi |
| Elastic modulus | 190-210 GPa | 27557-30458 ksi |
| Poisson’s ratio | 0.27-0.30 | 0.27-0.30 |
| Elongation at break | 22% | 22% |
| Reduction of area | 50% | 50% |
| Hardness, Brinell | 217 | 217 |
| Hardness, Knoop (converted from Brinell hardness) | 240 | 240 |
| Hardness, Rockwell B (converted from Brinell hardness) | 95 | 95 |
| Hardness, Rockwell C (converted from Brinell hardness. Value below normal HRC range, for comparison purposes only) | 17 | 17 |
| Hardness, Vickers (converted from Brinell hardness) | 228 | 228 |
| Machinability (annealed and cold drawn. Based on 100 machinability for AISI 1212 steel.) | 50 | 50 |
AISI 4340 Thermal Properties
| Properties | Metric | Imperial |
|---|---|---|
| Thermal expansion co-efficient (20°C/68°F, specimen oil hardened, 600°C (1110°F) temper | 12.3 µm/m°C | 6.83 µin/in°F |
| Thermal conductivity (typical steel) | 44.5 W/mK | 309 BTU in/hr.ft².°F |
AISI 4340 Equivalent
| AMS 6359 | AMS 6454 | ASTM A331 (4340) | ASTM A711 | SAE J1397 (4340) |
| AMS 6409 | ASTM A29 (4340) | ASTM A506 (4340) | ASTM A752 (4340) | SAE J404 (4340) |
| AMS 6414 | ASTM A320 (L43) | ASTM A519 (4340) | ASTM A829 | SAE J412 (4340) |
| AMS 6415 | ASTM A322 (4340) | ASTM A646 (4340-7) | MIL S-5000 |
AISI 4340 Uses
SAE/AISI 4340 steel is used for various applications, including manufacturing aircraft parts such as gears, shafts, bolts, etc., engine components such as crankshafts and valves, and fasteners like screws and nuts. It is also commonly used for tools such as drill collars in the oil industry.
Corrosion Resistance
SAE/AISI 4340 steel offers excellent corrosion resistance in a wide range of environments. In fact, it can withstand temperatures ranging from -100F to +450F without any significant degradation or loss of corrosion resistance. This makes it an ideal choice for applications where corrosion resistance is essential.
Heat Resistance
In addition to its corrosion resistance properties, SAE/AISI 4340 steel also offers excellent heat resistance. It has been tested at temperatures up to 1000°F with no adverse effects on its mechanical properties or microstructure. This makes it suitable for high-temperature applications such as automotive exhaust systems or industrial furnaces where heat resistance is essential.
Heat Treatment
SAE/AISI 4340 steel can be easily heat treated using both conventional hardening methods, such as quenching and tempering (Q&T), or by using cryogenic treatments, such as liquid nitrogen cooling (LNC). Depending on the desired application and end-use requirements, the proper type of heat treatment should be selected. For example, Q&T treatments are typically used for applications that require improved wear resistance, while LNC treatments are often used for improved fatigue strength or increased dimensional stability during machining operations.
Machining
SAE/AISI 4340 steel is an excellent choice for machining operations due to its high strength-to-weight ratio and superior wear resistance properties. It can be machined using conventional cutting tools with good results; however, its high hardness may require specialized tooling or cutting fluids to achieve the best results possible when machining this material.
Welding
SAE/AISI43 40steel can be welded using all conventional welding methods with good results; however, due to its high hardness, it may require pre-heating prior to welding in order to minimize cracking or distortion during cooling after welding operations have been completed. Additionally, post-weld stress relief may also be required depending on the application and end-user requirements in order to ensure optimal performance from the finished weldment once fabrication has been completed.
Conclusion:
From aircraft components to automotive exhaust systems—and everything in between—SAE/AISI43 40steel offers superior performance across a wide range of industries thanks to its combination of exceptional strength-to-weight ratio coupled with excellent corrosion and heat resistance properties. The material also offers good machinability and weldability, making it suitable for just about any application you can think of, requiring superior performance under challenging conditions. If your project requires superior performance under extreme conditions, then look no further than SAE/AISI43 40steel!
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