Mold 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 |
| 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 |
| 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- | |
| 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 |
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.
