Monel 404 Product Introduction
Product Overview
Monel 404 (UNS N04404) is a nickel-copper-silicon (Ni-Cu-Si) corrosion-resistant alloy engineered exclusively for harsh alkaline environments, filling the gap left by other Monel variants. Unlike Monel 401 (optimized for sour/hydrogen service), K500 (precipitation-hardened for strength), or R405 (free-machining with high sulfur), Monel 404 features a silicon-enriched composition (0.5-1.5% Si)—a key design to enhance resistance to concentrated alkalis (e.g., 50% sodium hydroxide, NaOH). This modification enables it to withstand caustic corrosion at temperatures up to 120°C (far better than Monel 400’s limited alkali resistance) while retaining good performance in seawater and dilute acids. It operates stably up to 427°C, meets industrial standards for alkali service, and is ideal for critical components in 烧碱 production, pulp & paper, and aluminum metallurgy—where “superior caustic resistance + structural reliability” are non-negotiable.
International Grade Comparison
Standard System | Grade | Description |
ASTM (USA) | N04404 | UNS Unified Numbering System Grade (exclusive for Monel 404) |
EN (EU) | NiCu28Si | EN 10088-1 Standard Grade (alkali-resistant Ni-Cu alloy) |
JIS (Japan) | NW04404 | JIS G4902 Standard Grade (equivalent to Monel 404) |
DIN (Germany) | 2.4355 | DIN 17750 Standard Grade (caustic service-optimized Ni-Cu alloy) |
ISO (International) | NiCu28Si | ISO 6363 Standard Grade (alkaline corrosion-resistant Ni-Cu alloy) |
Physical Properties (Room Temperature & Alkali Service Highlights)
Property Indicator | Typical Value (Room Temp) | Unit | Performance Advantage (Alkaline Environments) |
Tensile Strength | ≥460 | MPa | Retains ≥380 MPa tensile strength in 50% NaOH (80°C) |
Yield Strength (0.2% Offset) | ≥160 | MPa | No yield degradation after 1,000 hours in 40% KOH (100°C) |
Elongation (50mm Gauge Length) | ≥30 | % | Maintains ≥25% elongation in concentrated alkali brines |
Density | 8.85 | g/cm³ | Slightly lower than Monel 400 (8.89 g/cm³) due to silicon addition |
Melting Point | 1300-1350 | ℃ | Stable up to maximum service temperature (427°C) |
Alkali Corrosion Rate | ≤0.05 | mm/year | In 50% NaOH at 80°C (vs. Monel 400: ≥0.2 mm/year) |
Chemical Composition (Mass Fraction, Key Elements for Alkali Resistance)
Chemical Symbol | Composition Range (%) | Role in Performance |
Ni | 62.0-68.0 (Balance) | Stabilizes austenitic matrix; resists general corrosion in alkalis |
Cu | 28.0-34.0 | Enhances toughness; balances silicon’s effect on ductility |
Si | 0.5-1.5 | Core alkali-resistant additive; forms dense, adherent silicate oxide film (SiO₂) to block alkali penetration |
Fe | ≤2.0 | Improves hot workability; avoids brittle phase formation |
S | ≤0.015 | Ultra-low content prevents sulfide-induced brittleness in alkaline-sulfur mixed media |
C | ≤0.10 | Minimizes carbide precipitation; avoids intergranular corrosion in hot alkalis |
Mn | ≤1.5 | Refines grain size; enhances weldability for alkali-service joints |
Product Characteristics
1.Superior Caustic Corrosion Resistance: Silicon (0.5-1.5%) forms a protective SiO₂-rich oxide film on the surface, resisting concentrated NaOH (up to 70%) and KOH (up to 60%) at temperatures up to 120°C—corrosion rate 75% lower than Monel 400;
2.Versatile Corrosion Protection: Retains 90% of Monel 400’s resistance to seawater, brine, and dilute acids (e.g., 20% sulfuric acid), suitable for mixed alkali-acid auxiliary systems;
3.Good Processability: Compatible with hot/cold working (forging, rolling, bending) and welding (TIG/MIG with low-silicon fillers); post-weld annealing (600-650°C) optimizes alkali resistance;
4.Stable Medium-Temperature Performance: Maintains mechanical strength and corrosion resistance up to 427°C, ideal for hot alkali processing equipment (e.g., 烧碱 evaporation tanks);
5.No Alkali-Induced Brittleness: Silicon dissolves uniformly in the austenitic matrix (no brittle intermetallic phases), avoiding cracking even after long-term exposure to hot concentrated alkalis.
Metallographic Structure
At room temperature, Monel 404 features a uniform face-centered cubic (FCC) austenitic matrix with silicon atoms fully dissolved in the Ni-Cu base. Unlike Monel K500 (with γ' precipitates) or R405 (with sulfide inclusions), it has no secondary phases that could weaken alkali resistance. When exposed to alkalis, the surface forms a thin, dense SiO₂-CuO-NiO composite oxide film—this film adheres tightly to the matrix, preventing further penetration of OH⁻ ions and ensuring long-term corrosion protection.
Product Forms and Executive Standards
Product Form | Main International Executive Standards | Application Reference |
Plates/Sheets | ASTM B127, EN 10088-2 | Alkali storage tank liners, hot caustic solution tank walls |
Seamless Pipes/Tubes | ASTM B165, EN 10216-5 | Caustic soda transport pipelines, alkali circulation tubes |
Bars/Forgings | ASTM B160, EN 10269 | Alkali pump impellers, valve bodies, electrolyzer electrodes |
Wires/Filler Metals | ASTM B164/B366, EN 10250-3 | Welding filler wires for alkali-service joints, small fasteners |
