Shaanxi Shangyou Stainless Steel Co., Ltd. supplies both Nickel Alloy 400 (UNS N04400) and Nickel Alloy K-500 (UNS N05500) in plate, sheet, round bar, wire, and forging forms. These nickel-copper alloys are among the earliest nickel-based alloys developed commercially and remain widely used in marine engineering, chemical processing, and oil and gas applications.

Alloy 400 is a single-phase solid-solution alloy containing approximately 63% nickel and 28-34% copper. It cannot be hardened by heat treatment and relies on cold working for moderate strength increases. It is the workhorse grade for valves, pumps, and piping in marine and chemical services.

Alloy K-500 has the same base nickel-copper composition as Alloy 400 but adds approximately 2.3-3.15% aluminum and 0.35-0.85% titanium. These elements form gamma-prime (Ni₃Al/Ti) precipitates during age hardening at 480-620°C, doubling the yield strength and tripling the hardness compared to the annealed condition. Both alloys are available with EN 10204 3.1 MTC, PMI testing, and full traceability.

Key Differences at a Glance

Chemical Composition Comparison

Strengthening Mechanisms: The Core Difference

Alloy 400 – Solid Solution Strengthened

Alloy 400 is a single-phase solid-solution alloy that cannot be hardened by heat treatment. It derives its strength from solid solution strengthening—copper atoms dissolved in the nickel matrix distort the crystal lattice, impeding dislocation movement. Strength increases only through cold working, with moderate gains at the expense of ductility. This simplicity is an operational advantage: the alloy is easy to form and fabricate with no requirements for additional heat treatments to re-balance the alloy.

Alloy K-500 – Precipitation Hardened

Alloy K-500 is precipitation-hardenable through additions of aluminum (2.3-3.15%) and titanium (0.35-0.85%). During age hardening at 480-620°C, these elements form gamma-prime (γ') precipitates (Ni₃Al/Ti) that act as powerful barriers to dislocation motion. This aging response enables K-500 to achieve tensile strengths above 1,000 MPa—roughly double that of Alloy 400—and yield strengths above 690 MPa. However, this strength comes at a cost: the alloy requires careful heat treatment, and overaging occurs above 480°C.

Property Deep Dive

Mechanical Strength

• Alloy 400 provides moderate strength for a solid-solution alloy: tensile strength ~483 MPa (70 ksi), yield strength ~172 MPa (25 ksi) in the annealed condition. Cold working can increase tensile strength up to 620-862 MPa (90-125 ksi).
• Alloy K-500 delivers exceptional precipitation-hardened strength: tensile strength >1,000 MPa (145 ksi), yield strength >690 MPa (100 ksi), roughly doubling the annealed yield strength.

Ductility and Toughness

• Alloy 400 exhibits excellent elongation (35-55%), making it very forgiving in forming operations and retaining ductility even at sub-zero temperatures.
• Alloy K-500 has lower elongation (20-30%) due to its precipitation-hardened microstructure but retains good toughness and ductility, remaining ductile and non-magnetic even at cryogenic temperatures.

Temperature Capability

Both alloys have comparable maximum service temperatures of approximately 480°C (900°F). Above this temperature, Alloy K-500 experiences overaging and strength loss, while Alloy 400 maintains its properties. Alloy 400 retains excellent mechanical properties at sub-zero temperatures.

Magnetic Properties

• Alloy 400 can be slightly magnetic depending on composition and prior work history, as its Curie temperature is close to room temperature (21-49°C).
• Alloy K-500 is virtually non-magnetic, making it suitable for gyroscopes, minesweeper components, and other applications requiring non-magnetic materials.

Corrosion Resistance

Both alloys have essentially identical corrosion resistance because the base nickel-copper matrix is the same. The age-hardening precipitates in K-500 do not significantly alter the alloy's electrochemical behavior.

Key Corrosion Characteristics (Both Alloys):

• Seawater: Excellent resistance at all velocities, including high-velocity impingement and cavitation
• Hydrofluoric acid: Standard material for HF alkylation unit piping and equipment; resistance demonstrated in all concentrations up to the boiling point
• Reducing acids: Sulfuric acid (concentrations above 80%), deaerated hydrochloric acid
• Alkalis: Caustic soda and potash at all concentrations and temperatures up to boiling
• Chloride SCC: Excellent resistance in most fresh and industrial waters

Selection Considerations:

• Neither alloy resists oxidizing acids (nitric acid, sulfuric acid with oxidizing contaminants) or aerated sulfuric acid above 80°C
• In hydrofluoric acid (HF) applications, Alloy 400 exhibits slightly better SCC resistance in HF vapors compared to Alloy K-500
• Alloy K-500 may experience SCC more rapidly in moist HF vapors, especially when cupric fluoride deposits are present, though stress-relieved rather than age-hardened K-500 partially mitigates this risk
• Both are susceptible to SCC in HF, with subtle application-specific differences
• Both are NACE MR0175 / ISO 15156 compliant for sour-service applications

Product Form Availability

Applications Guide

Choose Alloy 400 When:

Choose Alloy K-500 When:

Welding and Fabrication Considerations

Selection Summary: Which Alloy to Choose?

Choose Alloy 400 when:

• Moderate strength is sufficient for the application
• Corrosion resistance is the primary concern (seawater, HF, acids)
• Piping systems or heat exchangers are required
• Maximum weldability and fabricability are needed
• Cost sensitivity is a factor

Choose Alloy K-500 when:

• High strength (above 1,000 MPa tensile) is required
• Both high strength and corrosion resistance are needed simultaneously
• The application involves high-stress rotating components (shafts, impellers)
• Springs, fasteners, or valve stems are required
• Non-magnetic properties are critical

Request a Quote

For a detailed quotation or material selection assistance, please provide:

Alloy Grade Under Consideration · Required Standard · Product Form · Dimensions · Quantity · Service Conditions (Temperature, Medium, Pressure) · Application · Destination Port

For corrosive service, also provide:

Chemical Medium · Concentration · Temperature · Oxidizing or Reducing Conditions

Procurement Actions

• Request Alloy 400 Quote
• Request Alloy K-500 Quote
• Request Alloy Selection Support
• Upload Drawing or MTO

Frequently Asked Questions

1. What is the main difference between Alloy 400 and Alloy K-500?

Alloy 400 is a solid-solution nickel-copper alloy that cannot be heat-treated for higher strength. Alloy K-500 adds aluminum and titanium for precipitation hardening, achieving approximately double the strength while maintaining similar corrosion resistance.

2. What are the UNS and Werkstoff numbers for these alloys?

Alloy 400 is UNS N04400 and Werkstoff 2.4360/2.4361. Alloy K-500 is UNS N05500 and Werkstoff 2.4375.

3. Which standards apply to these alloys?

Alloy 400: ASTM B127 (plate), ASTM B164 (bar), ASTM B165 (pipe). Alloy K-500: ASTM B865 (bar/plate), AMS 4676.

4. Does Alloy K-500 require heat treatment?

Yes. Alloy K-500 requires age hardening at approximately 540°C for 8-10 hours to achieve its high strength. Overaging occurs above 480°C service temperature.

5. Which alloy has better corrosion resistance?

Both alloys have essentially identical corrosion resistance because the base nickel-copper matrix is the same. The age-hardening precipitates in K-500 do not significantly alter the alloy's electrochemical behavior.

6. Which alloy is better for seawater applications?

Both are excellent. Alloy 400 is the standard choice for general seawater piping and valves. Alloy K-500 is preferred for high-strength components like pump shafts and impellers requiring superior fatigue resistance.

7. Which alloy is better for hydrofluoric acid service?

Both are highly resistant. However, Alloy 400 exhibits slightly better stress-corrosion cracking resistance in HF vapors compared to Alloy K-500. Alloy K-500 may be more susceptible to SCC in moist HF vapors, especially when age-hardened.

8. Is Alloy K-500 available as pipe?

No. Alloy K-500 is rarely used for pipe; it is primarily a bar, forging, and wire product. Alloy 400 is the standard choice for piping systems.

9. Are these alloys magnetic?

Alloy 400 can be slightly magnetic as its Curie temperature is close to room temperature (21-49°C). Alloy K-500 is virtually non-magnetic.

10. What information is required for material selection?

Please provide the application, operating temperature, chemical medium (if corrosive), required strength, and product form needed. Our team can provide expert guidance based on your specific service conditions.