Introduction
Alloy steels are designated by AISI four-digit numbers. They comprise different kinds of steels having composition exceeding the limitations of B, C, Mn, Mo, Ni, Si, Cr, and Va set for carbon steels.
4340 Loha alloy steel is a heat treatable and low alloy steel containing chromium, nickel and molybdenum. It has high toughness and strength in the heat treated condition.
Chemical Composition
The following table shows the chemical composition of Loha 4340 alloy steel.
| 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 |
Physical Properties
The physical properties of Loha 4340 alloy steel are given in the following table.
| Properties | Metric | Imperial |
|---|---|---|
| Density | 7.85 g/cm3 | 0.284 lb/in³ |
| Melting point | 1427°C | 2600°F |
Mechanical Properties
The mechanical properties of annealed Loha 4340 alloy steel are displayed in the following table.
| 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 |
Thermal Properties
The following table outlines the thermal properties of Loha 4340 alloy steel.
| 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 |
Other Designations
Other designations that are equivalent to Loha 4340 alloy steel include the following:
| AISI 4340 | 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 | |
| AMS 6359 |
Fabrication and Heat Treatment
Machinability
Loha 4340 alloy steel can be machined using all conventional techniques. Machining process can be performed in the annealed or normalized and tempered conditions.
Forming
Loha 4340 alloy steel has good ductility and formability in the annealed condition. It can be bent or formed by pressing or spinning in the annealed state.
Welding
Loha 4340 alloy steel can be welded using fusion or resistance welding methods. Preheat and post heat weld procedures are followed while welding this steel by established methods.
Heat Treatment
Loha 4340 alloy steel is heat treated at 830°C (1525°F) followed by quenching in oil.
Forging
Loha 4340 alloy steel is forged at 427 to 1233°C (1800 to 2250°F).
Cold Working
Loha 4340 alloy steel can be cold worked using all conventional methods in the annealed condition. It has high ductility.
Annealing
Loha 4340 alloy steel is annealed at 844°C (1550°F) followed by cooling the furnace.
Tempering
Loha 4340 alloy steel should be in the heat treated or normalized and heat treated condition before tempering. Tempering temperatures depend upon the desired strength level.
Hardening
Loha 4340 alloy steel can be hardened by cold working or heat treatment.
Applications
Loha 4340 alloy steel is mainly used in power transmission gears and shafts, aircraft landing gear, and other structural parts.