AISI 4340 ALLOY STEEL | EN24 | 34CRNIMO6 | SNCM439
AISI 4340 steel is a low alloy steel which contains Cr-Ni-Mo as strengthening alloy elements as per ASTM A29.As a heat treatable steel,AISI 4340 has a very good balance of strength, toughness and wear-resistance,and can attain high strength while retaining good fatigue strength which makes it ideal for all highly stressed parts in the most severe conditions.
AISI 4340 is generally supplied with quenched and tempered condition with a tensile strength of 930 – 1080 MPa,hardness 28 to 34HRC. Pre hardened and tempered 4340 can be further surface hardened by flame or induction hardening and by nitriding.Flame or Induction hardening can achieve a typical surface hardness up to HRC 58,and nitride with a typical surface hardness up to HRC 60.
AISI 4340 steel Chemical Composition
| Grade | C | Si | Mn | P | S | Cr | Ni | Mo |
| 4340 | 0.38-0.43 | 0.15-0.35 | 0.6-0.8 | ≤0.035 | ≤0.04 | 0.7-0.9 | 1.65-2.00 | 0.2-0.3 |
AISI 4340 steel Related Specifications
| Germany | UK | China | Japan |
| 40NiCrMo6/1.6565 | EN24/817M40 | 40CrNiMoA | SNCM439/SNCM8 |
AISI 4340 steel Heat Treatment & Mechanical Property
- Forging:1150℃-1200℃,cool in sand or furnace cool.
- Normalizing:850℃-880℃,Cool in air
- Annealing:830℃-850℃,Cool in furnace
- Hardening:830℃-865℃,oil quench
- Tempering:450°C – 660°C, cool in still air
AISI 4340 Steel Mechanical Property with Quenched and Tempered Condition
| Size - inch | 1" | 3 3/4" | 7" | 10" |
| Tensile Strength, N/mm² | 1117 | 1075 | 1000 | 995 |
| Yield Strength, N/mm² | 1000 | 976 | 766 | 858 |
| Elongation (%) | 16 | 19 | 17 | 18 |
| Reduction of Area (%) | 50 | 55 | 47 | 45 |
| Hardness,HB | 331 | 321 | 302 | 302 |
AISI 4340 Quality Certification
A material test report(Inspection Certificate EN 10204 3.1) will be provided, documenting the following:
1.Chemical analysis
2.Mechanical properties
3.Surface hardness
4.Non Metallic Inclusion
5.Heat Treatment Process
6.Grain size
7.Forging ratio
8.Ultrasonic test report
AISI 4340 Steel Supply Form & Size &Surface Finish&Tolerance
| Form of Supply | Size(mm) | Length(mm) |
| Round bar | Φ6-Φ1,000 | 3,000-10,000 |
| Square bar | 100x100-600x600 | 3,000-6,000 |
| Plate/Sheet | Thickness :20-400 Width:80-1,000 | 2,000-6,000 |
| Flat bar/Blcoks | Thickness :120-800 Width:120-1,500 | 2,000-6,000 |
| Surface Finish | Black-Forged | Black-Rolled | Turned | Grinding | Polished | Peeled | Cold Drawn |
| Tolerance | (0，+5mm) | (0，+1mm) | (0，+3mm) | Best h9 | Best h11 | Best H11 | Best H11 |
Heat treatment:Quenched and Tempered (+QT), Normalizing (+N), Annealing (+A)
