AISI 4140 Chromoly Steel (UNS G41400): Heat Treatment Guide vs AISI 4340 Ultra-High-Strength Ni-Cr-Mo Alloy Steel
Side-by-side engineering comparison of AISI 4140 Chromoly Steel (UNS G41400): Heat Treatment Guide (ASTM A29/A322) and AISI 4340 Ultra-High-Strength Ni-Cr-Mo Alloy Steel (ASTM A29/A322 / AMS 6415). Compare mechanical properties, chemical composition, density, yield strength, international equivalents, and typical applications to select the right material for your project.
Quick Comparison
| Property | AISI 4140 Chromoly Steel | AISI 4340 Ultra-High-Stre |
|---|---|---|
| Standard | ASTM A29/A322 | ASTM A29/A322 / AMS 6415 |
| Category | Alloy Steel | Alloy Steel |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Yield Strength | 655 MPa (95 ksi) Q&T | 1,240 MPa (180 ksi) Q&T |
| Tensile Strength | 930 MPa (135 ksi) Q&T | 1,470 MPa (213 ksi) Q&T |
| Key Applications | AISI 4140 is a medium-carbon chromium-molybdenum alloy steel (0.38-0.43% C, 0.8-1.1% Cr, 0.15-0.25% Mo) offering an exce... | AISI 4340 is a nickel-chromium-molybdenum ultra-high-strength alloy steel (0.38-0.43% C, 1.65-2.0% Ni, 0.7-0.9% Cr, 0.2-... |
International Equivalents
| AISI 4140 Chromoly S Equivalents | AISI 4340 Ultra-High Equivalents |
|---|---|
| EN 42CrMo4 | EN 36CrNiMo4 |
| DIN 1.7225 | DIN 1.6511 |
| SCM440 | SNCM439 |
| 42CrMo4 | 40CrNiMoA |
| BS 708M40 | BS 817M40 |
How to Choose
| Choose AISI 4140 Chromoly Steel when... | 4140 is the workhorse Cr-Mo alloy steel—sufficient for most industrial shafts and bolts. |
| Choose AISI 4340 Ultra-High-Stre when... | 4340 adds 1.65-2.0% nickel, tripling through-hardening depth and dramatically improving toughness below -40°C. |
Frequently Compared Questions
What is the main difference between AISI 4140 Chromoly Steel (UNS and AISI 4340 Ultra-High-Strength ?
AISI 4140 Chromoly Steel (UNS G41400): Heat Treatment Guide (ASTM A29/A322) provides 655 MPa (95 ksi) Q&T yield strength at 7.85 g/cm³ density, while AISI 4340 Ultra-High-Strength Ni-Cr-Mo Alloy Steel (ASTM A29/A322 / AMS 6415) delivers 1,240 MPa (180 ksi) Q&T at 7.85 g/cm³. The choice depends on whether your application prioritizes section thickness under 60mm and lower cost or deep hardenability (100+mm) and low-temperature toughness.
Can AISI 4140 Chromoly Steel (UNS be substituted for AISI 4340 Ultra-High-Strength ?
In many applications, these materials can be cross-referenced, but direct substitution should always be verified against specific project specifications, especially for section thickness under 60mm and lower cost, deep hardenability (100+mm) and low-temperature toughness, and operating environment. Consult your engineer of record.