Alloy 455,Custom 455 Rod,UNS S45500

Alloy 455,Custom 455 Wire,UNS S45500

Introduction to Alloy 455 (Custom 455 Wire, UNS S45500)

Alloy 455, commercially referred to as Custom 455 and designated under UNS S45500, is a precipitation-hardening martensitic stainless steel engineered to deliver an exceptional balance of high mechanical strength, superior corrosion resistance, and excellent formability. Unlike conventional martensitic stainless steels (e.g., 410, 420), it achieves enhanced strength via controlled precipitation of copper-rich phases (instead of solely relying on martensitic transformation) and maintains corrosion resistance comparable to austenitic grades (e.g., 304) in mild to moderate aggressive environments. This alloy operates reliably across a temperature range of -50°C/-58°F to 315°C/600°F, making it ideal for applications requiring both structural integrity and resistance to atmospheric, marine, or chemical exposure. Custom 455 wire, a specialized form of this alloy, is widely used in industries such as precision engineering, medical devices, aerospace, and marine hardware—excelling in components like miniature springs, surgical instruments, and high-strength fasteners that demand tight dimensional tolerance and long-term durability.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS S45500 adheres to strict industry standards including ASTM A895 (for precipitation-hardening stainless steel bars) and ASTM A693 (for precipitation-hardening stainless steel wire), ensuring consistent precipitation-hardening behavior, corrosion resistance, and mechanical performance. The typical composition is as follows:

Element

Content Range (wt%)

Function

Iron (Fe)

Balance

Serves as the alloy matrix, providing the base for martensitic transformation and mechanical stability; interacts with other elements to form strengthening phases.

Chromium (Cr)

11.0 - 13.0

Forms a dense chromium oxide (Cr₂O₃) protective layer, delivering resistance to atmospheric corrosion, mild acids, and salt spray; critical for preventing pitting in marine environments.

Nickel (Ni)

4.5 - 5.5

Stabilizes the austenitic phase during heating, enabling controlled martensitic transformation during cooling; enhances toughness and reduces brittleness, especially at low temperatures.

Copper (Cu)

1.5 - 2.5

Key element for precipitation hardening—forms fine, coherent copper-rich precipitates (ε-Cu) during aging, significantly boosting tensile and yield strength without compromising ductility.

Titanium (Ti)

0.3 - 0.8

Refines grain structure during solidification and heat treatment; prevents excessive grain growth, enhancing fatigue resistance and ensuring uniform mechanical properties across the wire.

Molybdenum (Mo)

0.3 - 0.8

Enhances localized corrosion resistance (e.g., crevice corrosion in chloride-containing media) and supplements strength by solid-solution strengthening the martensitic matrix.

Carbon (C)

≤ 0.05

Minimized to avoid carbide precipitation at grain boundaries, which can reduce corrosion resistance and cause intergranular cracking; controlled to maintain martensitic phase stability.

Manganese (Mn)

≤ 1.0

Aids in deoxidation during melting and improves cold workability for fine wire drawing; limited to avoid compromising corrosion resistance.

Silicon (Si)

≤ 1.0

Reduces oxide formation during hot processing and improves molten alloy fluidity; controlled to avoid excessive inclusions that degrade fatigue life.

Phosphorus (P)

≤ 0.03

Strictly limited to prevent grain boundary embrittlement, especially in welded joints or components exposed to cyclic loading.

Sulfur (S)

≤ 0.03

Minimized to prevent hot cracking during wire drawing and welding; reduces the risk of pitting corrosion in sulfur-rich environments.

2. Physical Properties

Custom 455 wire exhibits distinct physical properties before and after precipitation hardening, with post-aging performance optimized for high strength and corrosion resistance. Key properties (measured at room temperature unless specified otherwise) are:

Property

Value (Solution Annealed)

Value (Aged)

Test Condition

Density

7.78 g/cm³

7.78 g/cm³

Room temperature (25°C)

Melting Point Range

1425 - 1475°C

1425 - 1475°C

-

Thermal Expansion Coefficient

11.2 × 10⁻⁶/°C

11.2 × 10⁻⁶/°C

20 - 100°C; 13.5 × 10⁻⁶/°C (20 - 300°C)

Thermal Conductivity

15.1 W/(m·K)

15.1 W/(m·K)

100°C; 20.3 W/(m·K) (300°C)

Electrical Resistivity

0.65 × 10⁻⁶ Ω·m

0.68 × 10⁻⁶ Ω·m

Room temperature (25°C)

Modulus of Elasticity

193 GPa

195 GPa

Room temperature (tensile)

Poisson’s Ratio

0.29

0.29

Room temperature

Curie Temperature

≈ 280°C

≈ 280°C

Above this temperature, loses ferromagnetism; relevant for high-temperature magnetic applications.

Tensile Strength

≥ 620 MPa

≥ 1100 MPa

Room temperature; ≥ 850 MPa (300°C, aged)

Yield Strength (0.2% Offset)

≥ 380 MPa

≥ 950 MPa

Room temperature; ≥ 750 MPa (300°C, aged)

Elongation

≥ 20%

≥ 8%

Room temperature

Hardness

≤ 240 HB

33 - 38 HRC

Room temperature

Impact Toughness (Charpy V-Notch)

≥ 50 J

≥ 25 J

Room temperature; ≥ 15 J (-50°C, aged)

Corrosion Resistance

Passes 1000-hour salt spray test (ASTM B117)

Passes 1000-hour salt spray test (ASTM B117)

5% NaCl solution, 35°C

3. Production Process of Custom 455 Wire

The manufacturing of Custom 455 wire requires precise control of chemistry (especially copper and titanium) and heat treatment to balance precipitation hardening, corrosion resistance, and dimensional accuracy. Key steps include:

3.1 Raw Material Melting & Casting

Melting: High-purity raw materials (iron, chromium, nickel, copper, etc.) are melted via electric arc furnace (EAF) followed by argon oxygen decarburization (AOD). This process reduces carbon content to ≤0.05 wt%, eliminates gaseous impurities (O₂ < 30 ppm, N₂ < 50 ppm), and ensures uniform distribution of copper and titanium—critical for consistent precipitate formation.

Casting: Molten alloy is cast into ingots (500 - 2000 kg) or blooms, which undergo homogenization annealing at 1050 - 1100°C for 6 - 8 hours. This step eliminates chemical segregation (especially of copper and chromium) and dissolves coarse intermetallic phases, preparing the material for hot working.

3.2 Hot Working & Wire Rod Production

Hot Rolling: Ingots/blooms are hot-rolled at 950 - 1050°C into wire rods (diameter: 8 - 20 mm). Hot rolling is performed above the martensitic transformation temperature (Ms ≈ 350°C) to maintain austenitic phase, ensuring ductility; rods are air-cooled to room temperature to induce martensitic transformation, forming a hard yet workable matrix.

Descaling: Hot-rolled rods undergo shot blasting (to remove loose oxide scale) followed by acid pickling (nitric-hydrofluoric acid solution) to eliminate residual chromium oxide layers. This step prevents surface defects during cold drawing and ensures clean alloy surfaces for corrosion resistance.

3.3 Cold Drawing (Wire Formation)

Multi-Pass Cold Drawing: Wire rods are cold-drawn through diamond dies in 5 - 9 passes to achieve the desired diameter (typically 0.1 mm - 8 mm). Each pass reduces diameter by 15 - 20%, with intermediate solution annealing (920 - 980°C for 30 - 45 minutes, water-quenched) between passes. This annealing step relieves work hardening, restores austenitic phase (enabling further drawing), and dissolves any unintended copper precipitates—ensuring uniform mechanical properties.

Dimensional Control: Tension, die alignment, and drawing speed are precisely regulated to maintain tight diameter tolerance (±0.01 mm for precision wire) and roundness (≤0.005 mm). For medical or aerospace applications, laser diameter monitoring and ultrasonic testing are used to detect dimensional variations or internal flaws that could affect performance.

3.4 Precipitation Hardening (Strength Optimization)

Precipitation hardening is the core step to activate copper-rich precipitates and achieve target strength. The process follows a standardized three-stage cycle (per ASTM A693):

Solution Annealing: Heating the wire to 920 - 980°C for 1 - 2 hours, followed by rapid water quenching. This step converts the martensitic matrix back to austenite, dissolves all copper precipitates, and ensures a uniform microstructure.

Austempering (Optional): For applications requiring enhanced toughness, the wire is quenched to 300 - 350°C and held for 1 - 2 hours (austempering), then air-cooled. This step refines martensitic lath structure, reducing brittleness.

Final Aging: Heating the wire to 450 - 500°C for 2 - 4 hours, then air cooling. This step promotes nucleation and growth of fine ε-Cu precipitates (5 - 15 nm) within the martensitic matrix, maximizing strength while preserving sufficient ductility and corrosion resistance.

Note: For ultra-fine wire (diameter < 0.5 mm), aging time is reduced to 1 - 2 hours to avoid excessive hardening, which could compromise flexibility for applications like miniature springs.

3.5 Surface Finishing & Quality Inspection

Surface Treatment:

Pickling: Post-aging pickling in nitric acid to remove oxide scales and enhance the protective chromium oxide layer—critical for marine or chemical applications.

Passivation: Optional nitric acid passivation to further strengthen the oxide layer, reducing the risk of pitting corrosion in chloride-rich environments (e.g., seawater, bodily fluids).

Polishing: For high-precision applications (e.g., medical instruments, aerospace sensors), the wire is polished to a smooth surface finish (Ra ≤ 0.1 μm) using electrochemical or mechanical polishing, minimizing friction and contamination risks.

Quality Control:

Chemical Analysis: Optical emission spectroscopy (OES) to verify copper (1.5-2.5 wt%) and titanium (0.3-0.8 wt%) content—critical for precipitation hardening.

Mechanical Testing: Tensile testing (pre- and post-aging) to confirm strength and elongation; hardness testing (HRC) to validate aging effectiveness; fatigue testing (10⁷ cycles) for cyclic-loading components like springs.

Corrosion Testing: Salt spray testing (ASTM B117), crevice corrosion testing (ASTM G48), and potentiodynamic polarization testing to validate resistance to harsh environments.

Non-Destructive Testing: Eddy current testing (for surface defects like cracks or pits) and magnetic particle testing (for subsurface flaws)—essential for safety-critical components.

Microstructural Analysis: Optical microscopy to confirm ε-Cu precipitate distribution and martensitic lath structure, ensuring consistency across production batches.

4. Product Applications

Custom 455 wire’s unique combination of high strength, corrosion resistance, and formability makes it indispensable in industries requiring precision and durability in mild to moderate aggressive environments:

4.1 Medical Devices

Surgical Instruments: Ultra-fine wire (0.05 - 0.2 mm) for laparoscopic tools, orthopedic drill bits, and dental scalers—biocompatible (ISO 10993), resists bodily fluid corrosion (e.g., saliva, blood), and provides sufficient strength for load-bearing applications.

Implantable Devices: Wire for orthopedic staples, cardiovascular stents, and pacemaker leads—maintains strength and corrosion resistance in long-term bodily contact, with low risk of galvanic corrosion.

Diagnostic Equipment: Wire for catheter sensors and endoscope components—flexible yet strong, enabling precise movement within the human body while withstanding sterilization (autoclaving at 134°C).

4.2 Precision Engineering & Electronics

Miniature Springs: Wire (0.1 - 1.0 mm) for watch springs, battery contacts, and microelectromechanical systems (MEMS)—high fatigue resistance (10⁹ cycles) and stable performance in temperature cycles (-50°C to 150°C).

Electrical Connectors: Wire for high-reliability connectors in aerospace and automotive electronics—resists atmospheric corrosion and maintains conductivity, even in humid or salty environments.

Optical Components: Wire for lens mounts and camera shutter mechanisms—tight dimensional tolerance (±0.005 mm) and low magnetic permeability, avoiding interference with optical systems.

4.3 Aerospace & Defense

Aerospace Fasteners: Wire for small-diameter rivets and bolts in aircraft interiors (e.g., cabin panels)—combines lightweight properties (density 7.78 g/cm³) with resistance to hydraulic fluid corrosion and temperature cycles (-50°C to 150°C).

Missile & UAV Components: Wire for guidance system springs and sensor housings—maintains strength and dimensional stability under vibration and G-forces, with resistance to fuel and lubricant corrosion.

Satellite Hardware: Wire for antenna springs and structural supports—resists space vacuum and atomic oxygen corrosion, ensuring long-term functionality in low Earth orbit.

4.4 Marine & Coastal Applications

Marine Hardware: Wire for small fasteners, hinges, and spring-loaded components in boats and offshore platforms—resists saltwater corrosion (ASTM B117 pass) and biofouling, reducing maintenance costs.

Coastal Electronics: Wire for sensor cables and corrosion-resistant enclosures—protects against salt spray and humidity, ensuring reliable performance in coastal monitoring systems.

4.5 Industrial Machinery

Valve & Pump Components: Wire for valve stems and pump diaphragms in chemical processing equipment—resists mild acids (e.g., acetic acid, dilute sulfuric acid) and maintains strength at 200 - 300°C.

Textile Machinery: Wire for precision needles and thread guides—high wear resistance (hardness 33-38 HRC) and corrosion resistance to textile dyes and cleaning agents.

Conclusion

Alloy 455 (Custom 455 Wire, UNS S45500) is a premier precipitation-hardening martensitic stainless steel wire, distinguished by its rare balance of high strength, corrosion resistance, and formability. Its ability to deliver reliable performance in mild to moderate aggressive environments—from bodily fluids to saltwater—makes it a critical material for medical, aerospace, and precision engineering industries. The precise control of its manufacturing process, especially copper/titanium content and precipitation hardening, ensures consistent performance across applications. For custom requirements—such as ultra-precision wire (down to 0.01 mm diameter), specialized surface finishes (e.g., electropolishing), or tailored aging cycles for specific strength-ductility balances—manufacturers offer customized solutions to meet the most demanding precision and durability challenges.

Packing of Standard Packing: 

Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 687 gallon liquid totes Special package is available on request.