SAE/ASTM 4340 Steel | EN24 | 1.6581 | 36CrNiMo4 | SNCM439 | 40CrNiMoA alloy engineering structural steel
AISI 4340 is a medium carbon low-alloy steel known for its toughness and strength with larger cross-sections. AISI 4340 is also a type of nickel chromium molybdenum steel. 4340 alloy steel is typically hardened and tempered within the tensile range of 930-1080 MPa. Pre hardened and tempered 4340 can undergo further surface hardening through flame or induction hardening and nitriding. 4340 steel has good impact resistance and wear resistance under hardening conditions. The performance of AISI 4340 steel has good ductility under annealing conditions, allowing it to bend or form. Our 4340 alloy steel can also undergo fusion welding and resistance welding. ASTM 4340 material is typically used in cases where other alloy steels do not have the required strength for hardenability. For high stress parts, this is a good choice. AISI 4340 alloy steel can also be processed by all conventional methods.
Due to availability, ASTM 4340 grade steel is typically replaced by European standards 817M40/EN24 and 1.6511/36CrNiMo4 or Japanese standard SNCM439 steel. Below is the detailed data of 4340 steel.
1. AISI 4340 Alloy steel Supply Range
2. Specification and Relevant Standards of AISI 4340 Steel
| Country | USA | Britain | Britain | Japan |
| Standard | ASTM A29 | EN 10250 | BS 970 | JIS G4103 |
| Grades | 4340 | 36CrNiMo4/ 1.6511 | EN24/817M40 | SNCM 439/SNCM8 |
3. ASTM 4340 Steels And Equilvalents Chemical Composition
| Standard | Grade | C | Mn | P | S | Si | Ni | Cr | Mo |
| ASTM A29 | 4340 | 0.38-0.43 | 0.60-0.80 | 0.035 | 0.040 | 0.15-0.35 | 1.65-2.00 | 0.70-0.90 | 0.20-0.30 |
| EN 10250 | 36CrNiMo4/ 1.6511 | 0.32-0.40 | 0.50-0.80 | 0.035 | 0.035 | ≦0.40 | 0.90-1.20 | 0.90-1.2 | 0.15-0.30 |
| BS 970 | EN24/817M40 | 0.36-0.44 | 0.45-0.70 | 0.035 | 0.040 | 0.1-0.40 | 1.3-1.7 | 1.00-1.40 | 0.20-0.35 |
| JIS G4103 | SNCM 439/SNCM8 | 0.36-0.43 | 0.60-0.90 | 0.030 | 0.030 | 0.15-0.35 | 1.60-2.00 | 0.60-1.00 | 0.15-0.30 |
4. AISI Alloy 4340 Mechanical Properties
| Mechannical Properties of 4340 (Heat Treated Condition ) | Condition | Ruling section mm | Tensile Strength MPa | Yield Strength MPa | Elong. % | Izod Impact J | Brinell Hardness |
| T | 250 | 850-1000 | 635 | 13 | 40 | 248-302 | |
| T | 150 | 850-1000 | 665 | 13 | 54 | 248-302 | |
| U | 100 | 930-1080 | 740 | 12 | 47 | 269-331 | |
| V | 63 | 1000-1150 | 835 | 12 | 47 | 293-352 | |
| W | 30 | 1080-1230 | 925 | 11 | 41 | 311-375 | |
| X | 30 | 1150-1300 | 1005 | 10 | 34 | 341-401 | |
| Y | 30 | 1230-1380 | 1080 | 10 | 24 | 363-429 | |
| Z | 30 | 1555- | 1125 | 5 | 10 | 444- | |
Thermal Properties of ASTM 4340
| 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 |
5. 4340 Alloy Steel Forged
Firstly, preheat steel 4340 and heat it to a maximum of 1150 ° C-1200 ° C for forging, maintaining uniform temperature throughout the entire section.
Do not forge below 850 ° C. 4340 has good forging properties, but caution must be taken during cooling as the steel is prone to cracking. After forging operation, the workpiece should be cooled as slowly as possible. Suggest cooling in sand or dry lime, etc.
6. AISI steel material 4340 grade heat treatment
stress relief
For pre hardened steel, stress relief is achieved by heating steel 4340 to between 500 and 550 ° C. Heat to 600 ° C-650 ° C, maintain uniform temperature throughout the entire section, soak every 25mm section for 1 hour, and then cool in still air.
annealing
Complete annealing can be carried out at 844 ° C (1550 F), followed by controlled (furnace) cooling at a rate not exceeding 10 ° C (50 F) per hour until 315 ° C (600 F). Air cooling can be performed within the temperature range of 315 ° C to 600 ° F.
tempering
AISI 4340 alloy steel should be in a heat treated or normalized and heat-treated state before tempering. The tempering temperature depends on the required strength level. For strength levels within the range of 260-280ksi tempered at 232 ° C (450 F). Suitable for strength in the range of 125-200 ksi at a tempering temperature of 510 ° C (950 ° F). If the strength of 4340 steel is in the range of 220-260ksi, do not temper it, as tempering will cause a decrease in impact resistance at this strength level.
Due to tempering brittleness, tempering should be avoided as much as possible within the range of 250 ° C-450 ° C.
Flame quenching or induction quenching
As mentioned above, pre hardened and tempered 4340 bars or plates can be further surface hardened through flame or induction hardening methods, resulting in a surface hardness exceeding Rc 50. AISI 4340 steel parts should be heated to the austenite temperature range (830 ° C-860 ° C) and the required surface depth as soon as possible, and then immediately quenched with oil or water according to the required hardness, workpiece size/shape, and quenching arrangement.
After quenching to hand temperature, tempering at 150 ° C-200 ° C will reduce stress and have the least impact on its hardness.
All decarburized surface materials must be removed first to ensure optimal results.
nitridation
Hardened and tempered 4340 alloy steel can also be nitrided to achieve a surface hardness of up to Rc 60. Heat to 500 ° C-530 ° C and maintain for sufficient time (10 to 60 hours) to form the depth of the shell. After nitriding, it should be slowly cooled (without quenching) to reduce deformation problems. Therefore, materials with nitride grade 4340 can be processed to near the final size, leaving only a small grinding allowance. The tensile strength of the 4340 steel core is usually not affected because the nitriding temperature range is usually lower than the original tempering temperature used.
The achievable surface hardness is 600 to 650HV.
7. Processability of AISI 4340 bar
It is best to use alloy steel 4340 for processing in annealed, normalized, and tempered states. It can be easily processed through all traditional methods such as sawing, turning, drilling, etc. However, under high strength conditions of 200ksi or higher, the machinability is only 25% to 10% of the alloy under annealing conditions.
8. The 4340 alloy steel material Welding
It is not recommended to weld 4340 in the hardened and tempered state (usually provided). If possible, it should be avoided as much as possible due to the risk of quenching cracking, as mechanical properties can change within the welding heat affected zone.
If welding is necessary, preheat to 200 to 300 ° C and maintain this temperature during welding. After welding stress release at 550 to 650 ° C, before hardening and tempering.
If welding is indeed required under hardening and tempering conditions, the workpiece should be stress relieved as much as possible at a temperature 15 ° C lower than the original tempering temperature after cooling to hand temperature.
9. Application of 4340 alloy material steel
AISI 4340 is used in most industrial sectors for applications that require higher tensile/yield strength than 4140 steel.
Some typical applications, such as:
Aircraft landing gear
Cars,
Oil and gas drilling,
Forging,
Warm forming and cold forming,
Mechanical manufacturing,
Transmission systems, such as power transmission gears and shafts.
General engineering industries and structural applications, such as heavy-duty shafts, gears, axles, spindles, couplings, dowels, chucks, molds, etc.
SAE SPecial is the alloy steel AISI 4340 supplier for your different application . And we also supply 4140 steel, 4130 steels as well. Contact and show your requests anytime. the feedback will be send to you in short time.
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