What Is Custom 450 Steel? Origin & Definition
Custom 450 — formally designated UNS S45000, classified as Type XM-25 under ASTM A564, and governed by AMS 5773E for bars and forgings — is a martensitic age-hardenable (precipitation-hardening) stainless steel originally developed by Carpenter Technology Corporation in the United States.
It belongs to the semi-austenitic and martensitic precipitation-hardening (PH) family: a class engineered to combine the corrosion resistance typical of austenitic stainless steel grades with the high mechanical strength achievable only through controlled heat treatment.
The alloy was conceived as a direct upgrade to AISI 410 stainless steel. By increasing nickel content to 6–7 wt.% and chromium to 14–16 wt.%, Carpenter achieved corrosion resistance equivalent to AISI 304 stainless steel, while retaining the ability to develop yield strengths exceeding 830 MPa through a simple single-step aging cycle at 575°C.
This combination of 304-level corrosion resistance, high strength, high toughness, and single-step processing makes Custom 450 one of the most specifiable alloys for critical forged components in power generation, nuclear energy, aerospace, and chemical processing industries.
Custom 450 closes the gap that no other single alloy easily addresses: where 410 SS offers strength but poor corrosion performance, and 304 SS offers corrosion resistance but low strength, Custom 450 delivers both simultaneously through its unique composition and precipitation-hardening response — with higher toughness than competing PH grades.
Alternative Designations for Custom 450
The same alloy is referenced under multiple designations across specification systems and international supply chains:
- UNSS45000
- ASTM A564Type XM-25
- AMS 5773EBars, Forgings & Rolled Rings
- StandardsASTM A564 / AMS 5773E compliant
- Trade NameCustom 450 / Alloy 450 (Carpenter)
Precipitation Hardening Mechanism
Niobium carbides (NbC) and copper-rich clusters nucleate within the martensitic matrix during aging at 575°C, blocking dislocation movement and dramatically increasing yield strength — without sacrificing ductility or fracture toughness.
304-Equivalent Corrosion Resistance
Elevated Ni (6–7%) and Cr (14–16%) create a stable passive chromium oxide film thermodynamically equivalent to that of AISI 304 SS, providing strong resistance to general, pitting, and crevice corrosion.
Single-Step Aging Advantage
Unlike multi-step age-hardening alloys, Custom 450 reaches full specified mechanical properties via one aging cycle — reducing heat treatment time, energy cost, distortion risk, and overall production complexity.
Chemical Composition of Custom 450 (UNS S45000)
Each element in Custom 450's composition fulfils a specific metallurgical function. The values below are per AMS 5773E specification — the primary governing document for Custom 450 forged products in aerospace and high-performance industrial applications.
| Element | Symbol | Specification (wt.%) | Metallurgical Function |
|---|---|---|---|
| Chromium | Cr | 14.00 – 16.00 | Primary passive film former; key driver of corrosion resistance |
| Nickel | Ni | 6.00 – 7.00 | Elevates corrosion resistance to 304-equivalent level; stabilises martensite |
| Copper | Cu | 1.25 – 1.75 | Cu-rich precipitates contribute to precipitation hardening during aging |
| Molybdenum | Mo | 0.50 – 1.00 | Enhances pitting and crevice corrosion resistance |
| Niobium (Columbium) | Nb | 0.30 – 0.50 (8×C min.) | Forms NbC precipitates — principal strengthening phase; prevents sensitisation |
| Carbon | C | 0.025 – 0.050 | Low carbon reduces sensitisation risk; Nb ties up residual carbon as NbC |
| Manganese | Mn | Max 1.00 | Deoxidiser; minor austenite stabiliser |
| Silicon | Si | Max 1.00 | Deoxidiser; minor strength contribution |
| Phosphorus | P | Max 0.025 | Strictly controlled — high P causes grain boundary embrittlement |
| Sulfur | S | Max 0.005 | Very low limit prevents MnS inclusions that degrade fracture toughness |
| Iron | Fe | Balance | Matrix element |
The AMS 5773E specification of Niobium at a minimum of 8× the carbon content (8×C minimum) is a deliberate and critical design choice. Niobium preferentially combines with all available carbon to form niobium carbide (NbC), preventing chromium from forming chromium carbides at grain boundaries — the process known as sensitisation that causes intergranular corrosion. Any Nb in excess of that needed to tie up carbon then precipitates as NbC during aging, contributing to strengthening. This makes Nb a dual-function element that simultaneously protects corrosion resistance and provides hardening — central to Custom 450's performance profile.
Mechanical Properties of Custom 450 at Room Temperature
All values below represent minimum requirements per AMS 5773E for forged bars and rings in the solution-treated and single-aged condition, tested at room temperature (23 ± 5°C) in the longitudinal direction.
Custom 450 (UNS S45000) Mechanical Properties Summary — AMS 5773E
| Property | Symbol | Requirement (AMS 5773E) |
|---|---|---|
| Ultimate Tensile Strength | Rm | 965 – 1,210 MPa |
| 0.2% Proof Strength (Yield) | Rp0.2 | Min 830 MPa |
| Elongation | A | Min 16% |
| Reduction of Area | Z | Min 50% |
| Brinell Hardness | HB | 302 – 363 HB |
| Charpy V-Notch Impact | KV | Min 68 J |
Property Comparison (Normalised)
Relative to class maximum — AMS 5773E values
Custom 450's minimum Charpy V-notch impact of 68 J is more than 2.5× that of 17-4 PH stainless steel (27 J minimum). This superior toughness is essential for components subject to dynamic loading, thermal cycling, or operation in pressurised environments — nuclear pressure vessel containment rings, gas turbine guide rings, and high-pressure boiler nozzles all depend on this toughness level to prevent brittle fracture in service.
Custom 450 can be machined efficiently in the annealed condition, with final geometry achieved before aging. This eliminates the dimensional distortion risk inherent in heat-treating already-finished components, significantly reducing scrap rates and machining costs for complex precision forgings used in aerospace and nuclear applications.
Custom 450 Heat Treatment Procedure per AMS 5773E
One of Custom 450's most commercially important advantages is reaching full AMS 5773E mechanical properties via a straightforward two-stage thermal cycle. The process below applies to all forged bars, open die forgings, and seamless rolled rings in Custom 450 / XM-25 / UNS S45000.
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Step 1 — Solution Treatment (Austenitising)
Heat to 1040°C ± 15°C. Hold for a minimum of 45 minutes to a maximum of 2.5 hours. Temperature is measured and controlled at the centre of the heaviest section using load thermocouples. Cool by forced air blast or water quench. This step dissolves all precipitates, homogenises the alloy into a single-phase austenite structure, and the rapid cooling transforms it to martensite — the foundation for subsequent precipitation hardening.
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Step 2 — Straightening (Post-Solution, Pre-Aging)
Cold straightening may be performed after solution treatment and before aging if dimensional correction is required. This step is critical to achieve geometric accuracy in long forged bars and structural sections before their final properties are locked in by the aging treatment. Straightening after aging is not recommended as it may introduce residual stresses into the final component.
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Step 3 — Aging Treatment (Single-Step Precipitation Hardening)
Heat to 575°C ± 5°C. Hold for a minimum of 4.0 hours. Air cool to room temperature. During this stage, niobium carbide (NbC) precipitates and copper-rich clusters nucleate and grow within the martensitic matrix, blocking dislocation movement and driving the alloy to its AMS 5773E-specified strength and hardness levels. The tight temperature tolerance of ±5°C (tighter than most PH alloy specifications) ensures consistent, batch-to-batch repeatability of mechanical properties.
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Step 4 — Stress Relief Anneal (Optional)
If residual stress relief is required after forming or welding without significantly reducing mechanical properties, a stress relief anneal may be performed at a temperature no less than 10°C below the maximum aging temperature, and no lower than 540°C. This preserves the precipitate microstructure while allowing partial relaxation of internal stresses introduced by cold working or welding operations.
High-integrity Custom 450 forgings for nuclear and aerospace applications require a dual-melt process per AMS 5773E: primary melt via Basic Electric Arc Furnace (EAF) followed by secondary melt via either Electro-Slag Remelting (ESR) or Vacuum-Arc Remelting (VAR). The secondary melt removes macro-segregation and non-metallic inclusions to meet ASTM E45 Method D cleanliness (maximum inclusion rating: 2 thin / 1½ heavy), and produces a prior austenitic grain size of ASTM No. 5 or finer. These dual-melt parameters are non-negotiable for nuclear and aerospace applications and are verified by full material traceability documentation.
Custom 450 vs. Other Stainless Steels
The comparison below helps design engineers and procurement specialists understand where Custom 450 (UNS S45000) sits relative to the most commonly specified stainless steel grades, and identify when it is the technically correct material to specify.
| Property | Custom 450 (UNS S45000) | 17-4 PH (UNS S17400) | 304 SS (UNS S30400) | 410 SS (UNS S41000) |
|---|---|---|---|---|
| Steel Class | Martensitic PH | Martensitic PH | Austenitic | Martensitic |
| UTS (Aged) | 965–1,210 MPa | 930–1,310 MPa | 515–700 MPa | 480–760 MPa |
| Yield Strength (Aged) | Min 830 MPa | Min 725 MPa | 205–310 MPa | 275–415 MPa |
| Charpy Impact | Min 68 J ✓✓ | Min 27 J | >100 J | 20–40 J |
| Corrosion Resistance | ≡ 304 SS ✓✓ | Between 410 & 304 | Excellent (reference) | Moderate |
| Ni Content | 6.00–7.00% | 3.00–5.00% | 8.00–10.50% | Minimal |
| Weldability | Good | Good | Excellent | Fair |
| Heat Treatment | 1-step aging | 1-step aging | Anneal only | Quench + Temper |
| Primary Standard | ASTM A564 XM-25 / AMS 5773E | AMS 5643 | ASTM A276 | ASTM A276 |
| Best Use | Nuclear, Power Gen, Aerospace | High-strength aerospace | General corrosion | General strength |
Custom 450 vs. 17-4 PH: Key Differences
Both are martensitic precipitation-hardening stainless steels using a single aging step — but the performance differences are substantial. Custom 450 achieves a Charpy impact minimum of 68 J, compared to only 27 J for 17-4 PH — more than 2.5× higher toughness. For fracture-critical applications in nuclear pressure vessels, this difference is decisive in material selection.
Custom 450 also delivers corrosion resistance equivalent to 304 SS due to its higher nickel content (6–7% vs. 3–5% in 17-4 PH). For aqueous environments, acid exposure, or nuclear environments, Custom 450 provides measurably superior protection against pitting and crevice corrosion. The trade-off: 17-4 PH can achieve slightly higher peak tensile strength in H900 condition where toughness is secondary.
Custom 450 vs. 304 SS: Strength Without Sacrifice
The most significant substitution Custom 450 enables is replacing 304 SS in load-bearing or high-pressure applications. Where 304 SS yields at only 205–310 MPa, Custom 450 offers a guaranteed minimum yield of 830 MPa — approximately 3× higher — while maintaining equivalent corrosion performance. Engineers can reduce wall thickness and weight, carry higher loads, or extend service life.
For forged structural components in power generation and nuclear applications, this 3× strength differential is the primary technical justification for specifying Custom 450 over standard 304 SS austenitic stainless steel.
Where Custom 450 Is Used: Industry Applications
Custom 450 (XM-25 / UNS S45000 / Alloy 450) forged steel is specified wherever a component must simultaneously resist corrosion, withstand high mechanical loads, and survive demanding thermal or radiation environments. Its unique combination of 304-equivalent corrosion resistance and 830+ MPa yield strength makes it the correct specification across six critical industries.
Nuclear Energy
- Pressure vessel flanges and closure heads
- Seamless rolled containment and support rings
- Reactor coolant pump shafts and impellers
- Steam generator support components
- Requires ASTM E45 Method D + ASTM No. 4 grain size + full traceability
Aerospace
- Airframe structural connectors and brackets
- High-strength fasteners and bolts (AMS 5773E)
- Hollow forged bars for actuator housings
- Landing gear components requiring high toughness
- Engine mount hardware under cyclic vibration loading
Power Generation
- Gas and steam turbine guide rings and seal rings
- Turbine discs, blisks, and compressor impellers
- Boiler tube sheets and nozzle forgings
- High-pressure fastener assemblies (studs, bolts)
Chemical Processing
- Pump casings, impellers, and wear rings
- Valve bodies, bonnets, and stems for corrosive media
- Agitator shafts and mixing equipment
- Demonstrated 1.5× longer service life vs. standard SS
Pulp & Paper
- Rolls for bleach plant and press sections
- Digester hardware in hot alkaline liquors
- Treatment equipment and screens
- Pump impellers in bleaching circuits
General Industrial
- Precision machine shafts and spindles
- High-strength structural forgings per custom drawings
- Tooling, dies, and wear-resistant components
- Scientific instrument structural frames
Custom 450 Forged Steel: Shapes, Sizes & Lead Times
Custom 450 is most commonly supplied as forged products because the forging process refines grain structure, eliminates internal porosity and segregation, and aligns grain flow with the component's load-bearing geometry — producing substantially superior mechanical properties compared to cast or machined-from-bar alternatives.
Jiangsu Liangyi Co., Limited is a professional Custom 450 (XM-25 / UNS S45000 / Alloy 450) forging manufacturer in Jiangyin, Jiangsu, China, with over 25 years of specialised experience since 1997. Products are manufactured to ASTM A564, AMS 5773E, ISO 9001:2015 standards. Annual capacity: 120,000 tonnes. Component weights: 30 kg to 30,000 kg per piece.
View All Custom 450 Forgings →Available Product Forms
- ◆Round bars, square bars, flat bars, rectangular bars, and rods
- ◆Seamless rolled forged rings (all diameters)
- ◆Hubs, housings, shells, sleeves, bushings, hollow bars
- ◆Discs, blocks, and steel plate forgings
- ◆Pipes, tubes, casings, and housings
- ◆Fully custom open die forgings per client drawings
Frequently Asked Questions About Custom 450 Steel
The most frequently asked questions from engineers, procurement specialists, and buyers about Custom 450 (XM-25 / UNS S45000 / Alloy 450) stainless steel.
Custom 450 (XM-25 / UNS S45000 / Alloy 450) is a martensitic age-hardenable precipitation-hardening stainless steel. Per AMS 5773E: tensile strength 965–1,210 MPa; yield strength minimum 830 MPa; Charpy impact minimum 68 J; hardness 302–363 HB; corrosion resistance equivalent to AISI 304 SS — all achieved through a single aging step at 575°C. It is the preferred material for critical nuclear, aerospace, and power generation forgings requiring both high strength and reliable corrosion resistance.
Both are martensitic PH stainless steels. Key differences: Custom 450 (UNS S45000) has higher nickel (6–7%) giving 304-equivalent corrosion resistance, while 17-4 PH (UNS S17400) has lower nickel (3–5%) and lower corrosion resistance. Custom 450 achieves a minimum Charpy impact of 68 J versus only 27 J for 17-4 PH — making Custom 450 the correct choice for fracture-critical nuclear and power generation components. 17-4 PH can reach higher peak tensile strength (up to 1,310 MPa in H900) where toughness is secondary.
They are the same alloy under different designation systems. Custom 450 and Alloy 450 are Carpenter Technology trade names. XM-25 is the ASTM type designation within ASTM A564. UNS S45000 is the Unified Numbering System identifier. AMS 5773E is the aerospace specification for bars and forgings. All refer to the identical martensitic precipitation-hardening stainless steel composition.
Per AMS 5773E: (1) Solution treatment at 1040°C ±15°C, hold 45 min to 2.5 hours, forced air or water quench; (2) Aging treatment at 575°C ±5°C, hold minimum 4.0 hours, air cool. Optional: cold straightening between steps 1–2; stress relief anneal post-aging at ≥540°C. Temperature is controlled at metal centre using load thermocouples and documented with time-temperature curve records.
Yes. Custom 450 has good weldability using standard stainless steel welding practices. For restoration of full mechanical properties, post-weld solution treatment and re-aging per AMS 5773E is recommended. For forged structural components (turbine rings, pressure vessel flanges) where Custom 450 is most commonly used, field welding is rarely required.
Yes. Custom 450 is a martensitic stainless steel and is ferromagnetic in both the solution-treated and aged conditions. Unlike austenitic grades (304, 316) which are essentially non-magnetic when annealed, Custom 450 responds to magnets. This is important for applications with magnetic permeability requirements.
Jiangsu Liangyi Co., Limited manufactures Custom 450 (XM-25 / UNS S45000 / Alloy 450) forged steel in Jiangyin, China, since 1997 (25+ years). Products: open die forgings and seamless rolled rings, 30 kg to 30,000 kg per piece, to ASTM A564, AMS 5773E, ISO 9001:2015. Standard lead time 2–4 weeks, worldwide shipping. Full material traceability and inspection reports included. Visit: jnmtforgedparts.com/custom-450-forged-steel.html