Ti Grade 5 (Ti6Al4V) and AISI 4340 frequently come up against each other for the same part in aerospace and defence projects. One is a titanium alloy, the other an alloy steel — so the comparison is made not at the chemical level but at the level of an engineering choice.
Strength, or specific strength?
In absolute strength AISI 4340 is ahead: according to our datasheets, when hardened and tempered its tensile strength is 1793 MPa and its yield strength 1496 MPa. In Ti Grade 5 those values are ≥895 and ≥830 N/mm².
But the densities are very different. The density of Ti Grade 5 is ≥4.43 g/cm³ against roughly 7.85 g/cm³ for steel — that is, titanium is half the weight. When strength per unit weight (specific strength) is taken into account the two materials come very close, and in some design scenarios titanium moves ahead.
The real decisive difference is elsewhere: corrosion. AISI 4340 rusts; it requires plating, paint or cadmium/zinc protection. Ti Grade 5 can be used uncoated in seawater, salt-laden air and many chemicals. On the other hand the modulus of elasticity of titanium is far lower (114 kN/mm² against roughly 205 GPa for steel), so it deflects twice as much under the same load — a serious constraint if stiffness is critical.
Finally, cost and manufacturing: titanium is markedly expensive, its machining is slow and welding requires a shielding gas environment. 4340 can be machined and heat treated in any workshop.
Comparison in numbers
| PROPERTY | Ti Grade 5 (Ti6Al4V) | AISI 4340 |
|---|---|---|
| Material class | Titanium alloy | Alloy steel |
| Main elements | 5.50–6.75% Al · 3.50–4.50% V | 1.65–2.00% Ni · 0.70–0.90% Cr · 0.20–0.30% Mo |
| Carbon (C) | ≤ 0.08% | 0.38 – 0.43% |
| Tensile strength Rm | ≥ 895 N/mm² | 1793 MPa |
| Yield strength Rp0.2 | ≥ 830 N/mm² | 1496 MPa |
| Elongation | ≥ 10% | 10% |
| Hardness | ≥ 310 HB | — |
| Density | ≥ 4.43 g/cm³ | ~7.85 g/cm³ |
| Modulus of elasticity | 114 kN/mm² | ~205 GPa |
| Corrosion resistance | Resists seawater uncoated | Requires plating or paint |
| Thermal conductivity | ≥ 7.1 W/m·K | — |
| UNS | R56400 | G43406 |
| AMS | 4928 · 4911 | 6414 · 6415 · 6484 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
Ti Grade 5 is required — aircraft and space structures where weight converts directly into performance, marine and offshore equipment, corrosive environments where coating is not possible, medical and prosthetic applications, parts that must be non-magnetic.
AISI 4340 is required — parts demanding high absolute strength and stiffness such as landing gear and shaft assemblies, gear and spindle applications, anywhere weight is not critical and cost comes first. If the specification calls out AMS 6414 or AMS 6415, substituting titanium is not an option.
A practical rule: weight and corrosion → titanium; stiffness, absolute strength and cost → 4340.
Neighbouring materials
For the steps above 4340, see our AISI 4340 – 300M and 300M – AerMet 100 comparisons; on the titanium side, our Ti Grade 2 – Grade 5 article.
Technical datasheets
Ti Grade 5 — chemical composition, mechanical values, standard equivalents
AISI 4340 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.