455 stainless steel (commonly sold as Custom 455, UNS S45500) is a martensitic, precipitation-hardening stainless alloy engineered to combine very high yield strength after simple age-hardening with good corrosion resistance in atmospheric and fresh-water environments. It is supplied in clean vacuum-melted forms, machines and finishes well in the annealed state, and is widely used where a close-tolerance dimension can be finished then subjected to a single-step aging treatment (H-temper) to achieve exceptional strength and hardness.
What is 455 stainless (nomenclature & overview)
Often marketed under the tradename Custom 455® by specialty alloy suppliers, “455 stainless” is a martensitic, precipitation-hardenable (age-hardening) stainless steel. Its design goal is to permit near-final machining in a relatively soft annealed condition followed by a simple one-step aging treatment that produces very high yield strength (commonly several times that of 304 stainless) while retaining useful ductility and toughness. The alloy is vacuum-melted and frequently appears in aerospace, medical, oil & gas and industrial components that require a rare mix of high strength, good corrosion resistance and dimensional stability after aging.
Chemical composition (typical ranges)
Below is a consolidated composition table derived from multiple manufacturer datasheets. Individual lots and specification sheets (AMS/ASTM) should be consulted for contract purchases.
| Element | Typical / Specified range (wt%) |
|---|---|
| Carbon (C) | ≤ 0.03 – 0.05 |
| Chromium (Cr) | 11.0 – 12.5 |
| Nickel (Ni) | 7.5 – 9.5 |
| Copper (Cu) | 1.5 – 2.5 |
| Titanium (Ti) | 0.8 – 1.4 |
| Niobium (Cb/Nb) / Tantalum (Ta) | 0.10 – 0.50 (Nb+Ta) |
| Molybdenum (Mo) | ≤ 0.5 |
| Silicon (Si) | ≤ 0.50 |
| Manganese (Mn) | ≤ 0.50 |
| Phosphorus (P) | ≤ 0.015–0.04 |
| Sulfur (S) | ≤ 0.015–0.03 |
| Iron (Fe) | Balance |
Notes: Ti and Nb are intentional microalloying elements that promote precipitation hardening and dimensional stability during aging. Copper aids in precipitation strengthening. These compositional choices make Custom 455 different from classic 17-4PH despite similar roles.
Key physical & mechanical properties (typical values after aging)
The following table summarizes representative mechanical data. Exact values depend on heat treatment (H-temp), section size and vendor.
| Condition | Tensile strength (UTS) | Yield strength (0.2% offset) | Elongation (A%) | Hardness (approx.) |
|---|---|---|---|---|
| Annealed (solution treated) | ~850–1,000 MPa | ~400–600 MPa | 10–20% | ~20–30 HRC equivalent |
| Aged H900 (typical peak) | 1,300–1,600 MPa | 1,100–1,400 MPa | 6–12% | ~45–50 HRC |
| Aged H1000 (higher temp) | 1,100–1,350 MPa | 900–1,200 MPa | 8–14% | ~40–45 HRC |
Interpretation: a single-step precipitation (age) at temperatures between roughly 900–1050°F (≈480–565°C) for about 4 hours followed by air cooling produces very high strength and hardness with acceptable toughness — this ease of processing is a core selling point of the alloy.
Heat treatment & strengthening — practical recipe
Practical workflow used in industry:
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Solution treatment / anneal — bring to solution temp (manufacturer datasheet names specific ranges), hold to homogenize, then air cool. Machine to near-final size while soft.
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Aging (precipitation hardening) — typical aging cycles: H900 (≈900°F / 482°C for 4 hours), H950, H1000, H1050 — higher aging temperatures trade some strength for toughness and improved ductility. Air cool to room temperature.
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Dimensional change — very small (order of 0.001 in/in), enabling tight-tolerance finish machining before aging.
Because of predictable, reproducible hardening, the alloy is attractive when tight finishing tolerances are required followed by a final hardening step. For large cross-sections and critical service, refer to seller datasheet for section-size compensation and optimized cycles.
Corrosion resistance & environmental behavior
455 stainless resists staining and general corrosion in normal atmospheric and fresh-water service. Salt-fog and chloride environments will show more sensitivity than high-nickel austenitics (e.g., 316L), but wheelhouse performance is better than simple 12% Cr ferritic grades and is competitive with some martensitic PH grades. Labs report good resistance to pitting in moderate chloride concentrations, and the alloy shows no general corrosion in freshwater tests cited by manufacturer literature. For aggressive chloride or crevice environments, select a higher-alloy austenitic or superaustentic grade.
Manufacturing, processing & metallurgical notes
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Melting practice: typically VIM + VAR or other double-vacuum melt routes for cleanliness and inclusion control. This improves toughness and fatigue performance in demanding applications.
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Forming: good cold formability in annealed state because the alloy work-hardens slowly. Martensitic-type microstructure in annealed condition still permits bending and drawing operations.
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Machining: easier to machine in annealed state; finish machining before age hardening reduces tool wear and allows tight tolerances.
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Welding: welding of precipitation-hardening martensitics requires precautions (preheat, post-weld heat treatment) to avoid undesirable microstructures and to regain strength locally. Consult supplier guidance for welding procedures.
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Fatigue & fracture: like many high-strength martensitics, fatigue strength is good when surface finish is controlled; microcleanliness and proper heat treatment strongly affect crack resistance.
Typical applications
Because of the strength / corrosion / finishing balance, common uses include:
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Aircraft components, fasteners and landing-gear subcomponents (where AMS spec forms exist).
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Medical instruments, pins, and small implants that require high strength and corrosion resistance.
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Industrial shafts, small gears, and valve components.
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Oil & gas downhole or surface components where high strength and freshwater resistance are needed.
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High-performance springs and precision components finished before aging.
Equivalents and comparisons
| “455” name / ID | Typical equivalent or comparison |
|---|---|
| Custom 455® | Trade name used by several stockists & CarTech origin. UNS S45500. |
| UNS S45500 | Universal UNS designation used in spec literature. |
| AMS 5617 / ASTM A564 / ASTM F899 | Common specification packages for bars/wire/forgings in aerospace/medical formats. |
| Comparable grades | 17-4PH (similar family but different chem/PH response); Custom 465 (higher strength/corrosion but different cost/profile) |
Note: there is no direct single-numbered “drop-in” alloy that perfectly equals Custom 455 — compare strength, toughness, corrosion and processing when substituting (17-4PH is a typical close relative but differs in Ti/Cu/Nb balance and aging response).
Global price snapshot — 2025 (representative quotes & context)
Caveat: Specialty stainless like Custom 455 is sold through distributors and mills; prices vary by form (bar, wire, plate), lot size, finish, and region. The table below is a representative snapshot (sample distributor listings collected in 2025) to give ballpark supplier prices for small/retail purchases — bulk mill pricing will differ and require RFQ.
| Region / source (2025 sample) | Product form | Representative retail price (sample listing) |
|---|---|---|
| USA — OnlineMetals (retail cut-to-size bar) | 1/2" round bar, 12" | US$36.40 / ft (annealed) — sample listing. |
| USA — Distributor (Magellan, Michlin) | Round bar, small qty | Distributor quotes typically higher per-kg than commodity stainless (varies) — request RFQ. |
| Europe — specialist stockist | Bar / specialty forms | Usually priced in €/kg or €/piece; expect premium over 304/17-4PH due to vacuum melt & certifications. |
| China / Asia — production mills / foundries | Bar/wire (export) | Mills will quote per-ton basis; price often lower but depends on melt method and certification (VIM/VAR premium). |
| India / Middle East — stockists | Small-lot supply | Similar premium; logistics and certification add to landed cost. |
How to interpret: the OnlineMetals retail sample above provides concrete per-piece pricing useful for prototyping or small runs; for any production purchase ask suppliers for mill test certificates (MTC), melt route, and AMS/ASTM spec compliance. Prices move with nickel and alloy markets and with lead times — always request live RFQs specifying material condition, dimension, heat treatment and certification.
Specifications, quality & sourcing
Common specifications and procurement cues:
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UNS: S45500 — helpful in RFQs and certificates.
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AMS/ASTM: AMS 5617 (bars, wire, forgings), ASTM A564 variants, ASTM F899 references appear in datasheets — ensure the seller’s spec package matches application requirements (aerospace vs medical).
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Melt route: VIM + VAR (vacuum induction + vacuum arc remelt) is common for critical applications — specify if fatigue / fracture toughness matters.
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MTC: Always collect heat number, compositional analysis and hardness/tension test results as required.
Practical selection tips & failure modes
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If your part is machined to tight tolerance then age-hardened, Custom 455 is often ideal because of low dimensional change during aging.
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For high chloride or seawater exposures, consider superaustenitic or duplex grades; Custom 455 is good for many atmospheric and fresh-water services but not a seawater super-alloy.
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Watch for hydrogen embrittlement risk in some hydrogen-rich environments when material is in the high-strength aged state; design accordingly.
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For welded structures, expect local property changes; consult welding procedure specification (WPS) and post-weld heat treatments.
FAQs
Q1: Is 455 the same as 17-4PH?
A: No — both are precipitation-hardening martensitic stainless steels and can occupy similar roles, but their chemistries and aging responses differ. 17-4PH is a well-known standard grade; Custom 455 delivers a specific strength/corrosion/performance balance and is produced under different melt/chem control.
Q2: What is UNS S45500?
A: UNS S45500 is the universal numeric stainless designation for Custom 455; use it in procurement and MTC requests.
Q3: What heat treatment gives maximum strength?
A: Typical peak aging is H900 (≈900°F / 482°C for ~4 hours) producing very high hardness and yield — higher aging temps (H1000 etc.) trade some strength for toughness. Always confirm with supplier data.
Q4: Can I weld Custom 455?
A: Yes, but welding requires controlled procedures and may need local heat treatments to restore properties in the weld zone; follow supplier recommendations.
Q5: Where is it used?
A: Aerospace, medical instruments, shafts/valves, oil & gas components, and precision high-strength parts.
Q6: Is it corrosion-resistant like 316?
A: Not identical — 316 offers superior pitting resistance and chloride tolerance. Custom 455 resists staining and general corrosion well, and often outperforms basic 12% Cr ferritic grades, but for severe chloride exposure choose a superaustenitic or duplex alloy.
Q7: What certificates should I request?
A: Request Mill Test Certificate (MTC), chemistry for the heat, mechanical test results, melt route (VIM/VAR), and any spec conformance (AMS/ASTM) required by your application.
Q8: Is Custom 455 available in wire and bar?
A: Yes — stock forms include bar, wire, plate and forgings under AMS/ASTM spec packages; availability depends on the stockist.
