AISI 4340 Steel / 36CrNiMo4 / 1.6511 / EN24 / 817M40 / SNCM439
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AISI 4340 Steel / 36CrNiMo4 / 1.6511 / EN24 / 817M40 / SNCM439
AISI 4340 steel is a medium carbon, low alloy steel known for its toughness and strength in relatively large sections. AISI 4340 is also one kind of nickel chromium molybdenum steels. 4340 alloy steel is generally supplied hardened and tempered in the tensile range of 930 – 1080 Mpa.
AISI 4340 Steel Specification and Relevant Standards
| Country | USA | Britain | Britain | Japan |
| Standard | ASTM A29 | EN 10250 | BS 970 | JIS G4103 |
| Grades | 4340 | 36CrNiMo4/ 1.6511 | EN24/817M40 | SNCM 439/SNCM8 |
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 |
AISI Alloy 4340 Steel Mechanical Properties
| Mechannical Properties (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
| 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 |
Forging of 4340 Alloy Steel
Preheat the steel 4340 first, heat up to 1150°C – 1200°C maximum for forging, hold until temperature is uniform throughout the section.
Do not forge below 850 °C. 4340 has good forging characteristics but care must be taken when cooling as the steel shows susceptibility to cracking. Following forging operation the work piece should be cooled as slowly as possible. And cooling in in sand or dry lime is recommended etc.
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