The Strongest Steels Ranked: Choosing the Highest Strength Alloys for Tension
Six high-strength steels: 4140, 4340, 17-4 PH H900, H13, Maraging 300 and AerMet 100 compared for tensile toughness, stress-strain curves, UTS, and energy absorbed to fracture.
Updated: 7/5/2026
All six curves in 3-D, stacked in page order
What “tough in tension” means here
Strength is the load a steel carries; toughness is the energy it absorbs before it breaks. For a tensile member the measure is the modulus of toughness UT: the area under the full engineering stress-strain curve from zero strain to fracture:
UT = ∫0εf σ dε (stress in psi × strain in in/in → in·lbf per in³ of material)
That area is the energy absorbed in an overload, a jam, a hard landing. A very strong steel with a short curve can store less energy than a weaker one that stretches further; the toughest alloys pair high stress with long strain. All six of these highest strength alloys sit in the same hard-part window, roughly 39-55 HRc; the alloying route decides how much ductility survives there. The strongest steels by tensile rating are not automatically the toughest steels by absorbed energy.
Charpy impact energy (a notched impact test, ft·lb) and fracture toughness KIC (crack tolerance, ksi√in) measure related but different things, and neither follows from this number. Both appear in each property sheet: a steel can post a large smooth-bar area and still be notch-sensitive. H13 below is the example.
- Engineering stress-strain, imperial units (ksi vs in/in), identical axes on every plot so the areas compare directly.
- Curves are reconstructed from each alloy's typical room-temperature tensile report (0.2% yield, UTS, elongation) with a Ramberg-Osgood strain-hardening fit and a necking tail to the fracture ×.
- The shaded area under each curve is integrated numerically; that integral is the toughness value shown beside the graph, in in·lbf/in³.
- Values are typical, longitudinal, smooth-bar, not guaranteed minima.
1 · AISI 4140, quenched & tempered to 39-45 HRc
4140 is the workhorse chromium-molybdenum low-alloy steel: cheap, available everywhere, and deep-hardening. At 39-45 HRc (the common arbor, shaft and fixture window) it gives about 200 ksi tensile with useful ductility left over. Every other steel on this page is judged against it.
How it's made
Electric-arc melted and ladle-refined as standard bar stock (vacuum-arc remelt for critical work), supplied hot-rolled or forged. Harden by the standard quench-and-temper route: austenitize around 1,550 °F, oil quench, then temper at roughly 750-950 °F for this hardness window.
Typical use cases for this alloy
Machine shafts, arbors, fixtures, bolts, gears, tooling bodies: the default choice when a part needs strength without an exotic alloy bill.
| Carbon | 0.38-0.43 | Chromium | 0.80-1.10 |
| Manganese | 0.75-1.00 | Molybdenum | 0.15-0.25 |
| Silicon | 0.15-0.35 | Iron | balance |
| Density | 0.283 lb/in³ (MMPDS) |
| Young's modulus E | 29.0 × 10³ ksi (MMPDS) |
| Shear modulus G / Poisson ν | 11.0 × 10³ ksi / 0.32 (MMPDS) |
| Thermal expansion (70-400 °F) | 6.8 × 10⁻⁶ /°F |
| Thermal conductivity | ≈ 295 BTU·in/hr·ft²·°F |
| Hardness (this condition) | 39-45 HRc (curve at ~42) |
| Charpy V-notch (RT, typical) | ≈ 12-18 ft·lb |
| Fracture toughness KIC (literature) | ≈ 50-75 ksi√in |
| MMPDS min elongation / RA at 200 ksi | 10% / 43% |
| Modulus of resilience UR | ≈ 590 in·lbf/in³ |
2 · AISI 4340, quenched & tempered to 260-280 ksi
Where 4140 runs out of section size and strength, 4340 takes over: the nickel-chromium-molybdenum deep-hardening steel, and the classic landing-gear alloy of the jet age. MMPDS carries vacuum-remelted 4340 bar to a design ultimate of 260 ksi, the highest strength it publishes for a plain AISI grade, and this section runs it in that 260-280 ksi window (roughly 50-53 HRc).
How it's made
Aircraft-quality 4340 is consumable-electrode vacuum remelted (AMS 6414). Austenitize around 1,475-1,525 °F and quench in oil; the nickel buys hardenability, so bars through-harden to about 2.5 in in oil at this strength (MMPDS through-hardening table), versus roughly 1 in for 4140 at 200 ksi. Then temper low, about 400-450 °F, to land 260-280 ksi. The low temper is deliberate: MMPDS skips the 220 ksi level for 4340 entirely, because reaching it would mean tempering inside the 500-700 °F embrittlement range. At this strength the handbook caps service exposure near 350 °F.
Typical use cases for this alloy
Landing gear (generations of it), rotor and drive shafts, heavy arbors and fixtures, crankshafts, high-load bolts. AerMet 100 was developed to replace 4340-class landing-gear steel; the summary table shows the size of the gap.
| Carbon | 0.38-0.43 | Nickel | 1.65-2.00 |
| Manganese | 0.60-0.80 | Chromium | 0.70-0.90 |
| Silicon | 0.15-0.35 | Molybdenum | 0.20-0.30 |
| Iron | balance |
| Density | 0.283 lb/in³ |
| Young's modulus E | 29.0 × 10³ ksi |
| Shear modulus G / Poisson ν | 11.0 × 10³ ksi / 0.32 |
| Thermal expansion (70-400 °F) | ≈ 6.3 × 10⁻⁶ /°F |
| Design minima, S-basis (AMS 6414 bar) | Ftu 260 / Fty 217 ksi / e 10% |
| Design shear / compressive yield | Fsu 156 / Fcy 235 ksi |
| Max service exposure at this strength | ≈ 350 °F |
| Hardness (this condition) | ≈ 50-53 HRc |
| Charpy V-notch (RT, typical) | ≈ 12-15 ft·lb |
| Fracture toughness KIC (literature) | ≈ 50-60 ksi√in |
| Modulus of resilience UR | ≈ 912 in·lbf/in³ |
3 · 17-4 PH stainless, condition H900
17-4 PH (Custom 630, AMS 5643) is the most-used precipitation-hardening stainless steel: martensitic, chromium-nickel-copper, and hardened to its peak H900 condition by a single low-temperature age. It brings corrosion resistance to the ~200 ksi class: 4140-level strength in a stainless.
How it's made
Arc-melted and AOD-refined stainless practice (remelted grades for aerospace). Supplied solution-treated at 1,900 °F (“Condition A”): a relatively soft untempered martensite around 36 HRc that machines cleanly. Parts are cut nearly to size, then aged at 900 °F for 1 hour, air cool: that is the entire H900 treatment. Copper-rich precipitates form inside the martensite and lift it to ~44 HRc / 198 ksi with almost no distortion or scale, which is why finished-machined parts can be hardened as-is.
Typical use cases for this alloy
Pump and valve shafts, aerospace fittings and fasteners, chemical and food machinery, surgical tooling: anywhere strength and corrosion resistance must coexist.
| Carbon | ≤ 0.07 | Copper | 3.00-5.00 |
| Chromium | 15.0-17.5 | Nb + Ta | 0.15-0.45 |
| Nickel | 3.00-5.00 | Iron | balance |
| Density | 0.282 lb/in³ |
| Young's modulus E | 28.5 × 10³ ksi |
| Shear modulus G / Poisson ν | 11.2 × 10³ ksi / 0.272 |
| Thermal expansion (70-200 °F) | 6.0 × 10⁻⁶ /°F |
| Thermal conductivity (300 °F) | 124 BTU·in/hr/ft²/°F |
| Hardness | ≈ 44 HRc (420 HB) |
| Charpy V-notch (RT) | 16 ft·lb |
| Fracture toughness KIC (literature) | ≈ 45-55 ksi√in |
| Modulus of resilience UR | ≈ 588 in·lbf/in³ |
4 · H13 hot-work tool steel, 52-55 HRc
H13 is the chromium hot-work die steel. Its 5% chromium, molybdenum-vanadium chemistry holds strength at elevated temperature and resists thermal-fatigue cracking. At 52-55 HRc it reaches nearly 290 ksi tensile while keeping real smooth-bar ductility, unusual for a tool steel.
How it's made
Premium grades are electroslag- or vacuum-arc remelted (NADCA-quality die blocks demand it) for cleanliness and uniform carbides. Hardening: austenitize around 1,875 °F, gas quench in the vacuum furnace, then double or triple temper at 1,000-1,100 °F. Tempering in that range precipitates fine Mo/V alloy carbides (secondary hardening), so the steel stays hard despite the high temper, and holds 52-55 HRc in service heat that would soften 4140.
Typical use cases for this alloy
Die-casting dies, extrusion tooling, forging dies, hot shear blades, plus high-strength arbors, toolholders and wear parts that need hardness with a margin of ductility.
| Carbon | 0.32-0.45 | Molybdenum | 1.10-1.75 |
| Silicon | 0.80-1.20 | Vanadium | 0.80-1.20 |
| Chromium | 4.75-5.50 | Iron | balance |
| Density | 0.280 lb/in³ |
| Young's modulus E | ≈ 30 × 10³ ksi (published 27.5-31) |
| Poisson ν | 0.30 |
| Thermal expansion (70-400 °F) | 6.1 × 10⁻⁶ /°F |
| Thermal conductivity (RT) | ≈ 165-200 BTU·in/hr·ft²·°F (sources vary) |
| Hardness (this condition) | 52-55 HRc (curve at ~53) |
| Charpy V-notch (RT, premium grade) | ≈ 6-10 ft·lb |
| Fracture toughness KIC (literature) | ≈ 25-35 ksi√in |
| Modulus of resilience UR | ≈ 920 in·lbf/in³ |
⚠ This area is a smooth-bar result. At 52-55 HRc, H13's Charpy energy (~6-10 ft·lb) and KIC (~25-35 ksi√in) are the lowest on this page: it is notch-sensitive. A sharp corner, tool mark or crack releases the stored energy suddenly. Use generous radii, or step down in hardness, for tension service.
What the measured curves add: in the hardened (as-quenched, before tempering) state, H13's true-stress curve climbs to about 2,400 MPa (348 ksi) near 0.10 true strain, and its measured work-hardening rate starts near 45,000 MPa (about 6,500 ksi) before falling steeply, the same strong early hardening the engineering fit above uses (exponent n ≈ 13). Annealed H13 peaks near 710 MPa (103 ksi) but stretches to 0.20 true strain: the ductility is in the steel; hardening trades it for strength.
5 · Maraging 300, aged (AMS 6514)
Maraging 300 (NiMark® 300 / VascoMax® 300) abandons carbon entirely. It is an 18% nickel iron alloy whose martensite is soft and ductile; the strength comes later, from intermetallic precipitates. The result is 290 ksi yield with the highest yield-to-tensile ratio on the page (0.99): it barely work-hardens, holding nearly full stress from first yield to fracture. That is the flat-topped curve below.
How it's made
Double vacuum melted, VIM (vacuum induction) then VAR (vacuum arc remelt), to control inclusions. Supplied solution-annealed at 1,500 °F / 30 min, air cooled: a nickel lath martensite at ~32 HRc that machines and forms easily. Finished parts are then aged at 900 °F for 3-6 hours, air cool: Ni₃(Mo,Ti) precipitates harden it to ~52 HRc with essentially zero distortion and no quench. Nearly carbon-free, it welds readily and needs no protective atmosphere during aging.
Typical use cases for this alloy
Landing gear and rocket cases, high-performance flywheels and drive components, die-casting inserts, fencing blades: parts that need ultra-high strength with minimal heat-treat distortion.
| Nickel | 18.5 | Titanium | 0.65 |
| Cobalt | 8.75 | Aluminum | 0.10 |
| Molybdenum | 4.90 | Carbon | ≤ 0.03 |
| Iron | balance |
| Density | 0.289 lb/in³ (sp. gr. 8.00) |
| Young's modulus E | 27.5 × 10³ ksi |
| Thermal expansion (75-900 °F) | 5.6 × 10⁻⁶ /°F |
| Hardness | 52 HRc aged (~32 HRc annealed) |
| Charpy V-notch (RT) | ≈ 20 ft·lb |
| Fracture toughness KIC | ≈ 70 ksi√in |
| Fatigue endurance limit | 125 ksi |
| Modulus of resilience UR | ≈ 1,529 in·lbf/in³ (highest here) |
6 · AerMet® 100, aged 900 °F (AMS 6532)
AerMet® 100 is a cobalt-nickel secondary-hardening martensitic steel: 280+ ksi tensile with fracture toughness over 100 ksi√in and 14% elongation, a combination no other production steel on this page approaches. Carpenter reports production heats averaging 246 ksi yield, 287 ksi tensile, 16% elongation and KIC near 120 ksi√in, so the typical curve below sits inside reported mill data.
How it's made
Double vacuum melted (VIM + VAR). The heat treatment has four required steps: solution treat 1,625 °F / 1 h; quench to 150 °F within 1-2 hours (air for sections under ~2 in, oil above; the cooling-rate window is specified, not optional); cold treat at −100 °F for 1 hour to finish the martensite transformation; then age at 900 °F for 5 hours to 53-54 HRc. Aging precipitates ultrafine M₂C carbides while thin films of stable austenite form between martensite laths: the carbides carry the strength, and the ductile austenite films blunt cracks and carry the toughness.
Typical use cases for this alloy
Carrier landing gear (its original application), armor, actuators, ordnance, jet-engine and drive shafts, high-load fasteners, with service up to about 800 °F. Not corrosion resistant: parts run coated or sealed.
| Carbon | 0.23 | Chromium | 3.10 |
| Cobalt | 13.40 | Molybdenum | 1.20 |
| Nickel | 11.10 | Iron | balance |
| Density | 0.285 lb/in³ |
| Young's modulus E | 28.2 × 10³ ksi |
| Thermal expansion (to 600 °F, HT) | 6.08 × 10⁻⁶ /°F |
| Hardness | 53-54 HRc |
| Charpy V-notch (RT, typical) | ≈ 30-35 ft·lb |
| Fracture toughness KIC | 100 ksi√in min (typ. ≈ 115-125) |
| Fatigue strength | > 100 ksi at 10⁷ cycles |
| Max service temperature | ≈ 800 °F |
| Modulus of resilience UR | ≈ 1,108 in·lbf/in³ |
7 · Summary: the strongest steels, ranked
| Alloy | UTS ksi | Toughness UT in·lbf/in³ (area under curve) |
|---|---|---|
| AerMet® 100 · AMS 6532 🏆 | 294 | 37,100 |
| H13 · 52-55 HRc | 290 | 28,900 |
| Maraging 300 · aged | 294 | 28,800 |
| 17-4 PH · H900 | 198 | 27,600 |
| AISI 4340 · 260-280 ksi | 275 | 26,000 |
| AISI 4140 · 39-45 HRc | 200 | 22,400 |
Strength alone does not set the order: AerMet 100 and Maraging 300 both pull 294 ksi, yet AerMet absorbs 29% more energy. When choosing among the highest strength alloys for tension, the area under the curve is the tiebreaker; it separates the toughest steels from the merely strong.
Method & assumptions
- Curves are typical room-temperature, longitudinal, smooth-bar engineering stress-strain, reconstructed from each alloy's published 0.2% yield, UTS, elongation and reduction-of-area using a Ramberg-Osgood hardening fit up to uniform strain and a falling engineering-stress tail from necking to fracture. They are representations of typical behavior, not certified test records, and not guaranteed minima.
- Toughness UT is the trapezoid-rule integral of exactly the curve plotted; recomputed live on this page, so the shaded area and the number can never disagree. Units: 1 ksi × (in/in) = 1,000 in·lbf/in³.
- 17-4 H900, Maraging 300 and AerMet 100 use Carpenter Technology / SSA datasheet values (links below); 4140 and H13 use standard ASM tempering-curve data at the stated hardness. 4340 uses the MMPDS-01 design table for vacuum-remelted bar (Ftu 260 / Fty 217 / e 10%, S-basis) with a typical curve drawn above those minima; the low-alloy family constants E 29.0 × 10³ ksi, G 11.0 × 10³ ksi, ν 0.32 and 0.283 lb/in³ applied to 4140 and 4340 come from the same tables.
- Modulus of resilience UR = σy²/2E is the elastic (recoverable) slice of the same area, the “spring” budget before permanent set.
- Values marked ≈ are literature bands, not single certified measurements; published sources genuinely disagree at that level (H13's room-temperature modulus and conductivity are the widest examples). Datasheet and MMPDS numbers are quoted exactly as published.
References & further reading
- 17-4 PH (H900): SSA · 17-4 AMS 5643 (UNS S17400) and Carpenter Technology · Custom 630 (17-4): composition, H900 aging practice, and the typical H900 tensile set used here.
- Maraging 300: SSA · Maraging 300 AMS 6514 and Carpenter Technology · NiMark® 300 (M300): VIM/VAR practice, solution + age cycle, and the aged bar properties used here.
- AerMet® 100: SSA · AerMet 100 AMS 6532 and Carpenter Technology · AerMet 100: the full solution/quench/cold-treat/age schedule, aging-vs-hardness table, and property minima quoted here.
- AISI 4340 and low-alloy family constants: MMPDS-01, Metallic Materials Properties Development and Standardization (DOT/FAA/AR-MMPDS-01, January 2003, via NTIS): design mechanical properties for vacuum-remelted 4340 bar at the 260 ksi level, through-hardening diameters, temperature exposure limits, elongation and reduction-of-area minima, and the E / G / ν / density values used here for both 4340 and 4140.
- H13 true stress-strain and work-hardening data: Effects of Cooling Rate on the Mechanical Properties and Precipitation Behavior of Carbides in H13 Steel during Quenching Process (figure via ResearchGate, accessed 5 Jul 2026): the as-annealed vs as-quenched true-stress curves redrawn in section 4.
- AISI 4140 and H13: typical quenched-and-tempered tensile data from ASM Handbook Vol. 1 / ASM Heat Treater's Guide tempering tables at the stated hardness; AISI composition ranges.
Disclaimer
Recommendations on application design and material selection are based on available technical data and are offered as suggestions only. Each user should make their own tests to determine the suitability for their own particular use. Standards Applied LLC offers no express or implied warranties concerning the form, fit, or function of a product in any application. Material properties shown are typical values for comparison, not specification minima; design to the governing specification (AMS, ASTM, MMPDS) and certified test reports.
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