Monel 400 (UNS N04400) Supplier | Technical Guide: Corrosion Resistance & Engineering Properties
Date: 2024年11月18日 Categories: All Products、Monel Views: 2486
Excerpt:
Monel 400 (UNS N04400, W.Nr. 2.4360/2.4361) nickel-copper alloy technical guide from Hangbo Alloy (Shanghai Hangbo Alloy Group). Covers the 63% Ni / 28–34% Cu chemistry that distinguishes genuine Monel 400 from pure-nickel Nickel 201, ASTM B127/B164/B165 specification callouts, mechanical properties across tempers, hydrofluoric-acid and marine corrosion resistance, ERNiCu-7/ENiCu-7 welding practice, and a full import purchasing checklist — plus a 10-question technical FAQ.
Monel 400 (UNS N04400) — Nickel-Copper Alloy Plate, Rod, and Seamless Pipe | Hangbo Alloy
Alloy Import Pitfalls Series — Technical Bulletin for Buyers, Importers, and Plant Engineers
Reader Alert: A Specification Correction That Matters
If you are importing "Monel 400" and your mill certificate — or the product page you are reading — quotes a chemistry of 99.0% minimum nickel with 0.15% maximum carbon, stop the order. That chemistry is Nickel 201 (UNS N02201), a commercially pure nickel grade, not Monel 400. A genuine Monel 400 plate, rod, or seamless pipe is a nickel-copper solid-solution alloy carrying roughly 63% nickel and 28–34% copper, and it behaves nothing like pure nickel in hydrofluoric acid, seawater, and chloride service.
This page, supplied by Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com), is the corrected and complete engineering reference for Monel 400 (UNS N04400, W.Nr. 2.4360/2.4361). The mix-up you may have seen on other pages — pure-nickel data published under a Monel 400 heading — is precisely the class of grade-substitution error this Alloy Import Pitfalls series exists to prevent. Treat the tables below as the acceptance baseline for your next purchase order.
1. Alloy Identity and Metallurgy
Monel 400 is the original nickel-copper engineering alloy. Because nickel and copper are mutually soluble in all proportions, the alloy is single-phase — a face-centered cubic (FCC) solid solution (lattice parameter ≈ 3.534 Å) that cannot be hardened by heat treatment. All strengthening comes from cold work, which is why the alloy is purchased in controlled tempers rather than "as-quenched" conditions.
The metallurgical family relationship is important for importers: Monel K500 is the age-hardenable derivative (aluminum + titanium additions), while Monel R-405 is the free-machining sulfur-modified version. None of these may be substituted for one another without re-certification, and none of them is a pure-nickel grade.
| Property | Value | Notes |
|---|---|---|
| UNS designation | N04400 | W.Nr. 2.4360 (2.4361 for higher-strength tempers) |
| Density | 8.80 g/cm³ (0.318 lb/in³) | ~1% lighter than pure nickel |
| Melting range | 1300–1350 °C (2370–2460 °F) | Solidus–liquidus |
| Crystal structure | FCC, single phase | No age-hardening response |
| Magnetic behavior | Ferromagnetic | Curie temperature ≈ 21–49 °C (70–120 °F) |
| Electrical resistivity | ~51 µΩ·cm at RT | Higher than pure nickel |
| Product forms | Plate, sheet, strip, rod, bar, seamless pipe & tube, wire, forgings | See ASTM callouts below |
Because of its single-phase structure, Monel 400 retains useful toughness down to cryogenic temperatures and is a frequent choice for liquefied-gas and low-temperature marine hardware — attributes that disappear if a supplier quietly ships a two-phase or precipitation-hardened substitute.
2. Governing Specifications — Get the Callout Right
The single most common import error on this grade is citing the wrong ASTM product spec, or assuming one certificate covers every product form. Hangbo Alloy issues material to the following:
| Product Form | ASTM Specification | ASME Equivalent | Typical Sizes Supplied by Hangbo Alloy |
|---|---|---|---|
| Plate, sheet, and strip | ASTM B127 | ASME SB-127 | Plate 0.5–100 mm thick, up to 3000 mm wide |
| Rod, bar, and wire | ASTM B164 | ASME SB-164 | Round bar Ø 3–600 mm; flat bar; hex |
| Seamless pipe and tube | ASTM B165 | ASME SB-165 | Seamless pipe 1/8"–12" NB; tube per B165 |
| Condenser / heat-exchanger tube | ASTM B163 | ASME SB-163 | Straight or U-bend, welded or seamless |
| Welded pipe and tube | ASTM B725 / B730 | ASME SB-725 / SB-730 | Optional where seamless is not required |
Related international callouts your inspector may encounter: BS 3072 NA13 / BS 3073 NA13 / BS 3074 NA13 (UK), DIN 17750/17751/17752/17753 (Germany, W.Nr. 2.4360), VdTÜV 263, QQ-N-281, and SAE AMS 4544/4574 for aerospace procurement. When you write a purchase order to Hangbo Alloy, state both the UNS grade and the ASTM product specification — "Monel 400 per ASTM B164" — so there is no ambiguity about whether you are buying bar or plate chemistry, and never accept a certificate that lists only a trade name.
3. Chemistry: The Composition You Must Verify on the MTC
The composition limits below are the contractual gate. Hangbo Alloy recommends checking the mill test certificate (MTC/EN 10204 3.1) element-by-element against these ranges before goods leave port — and independently re-testing the copper figure on arrival, because a "nickel 63 min, copper balance" confusion is how pure-nickel stock historically slips into Monel orders.
| Element | Specified Range (wt %) | Typical Check Value | Import Watch-Point |
|---|---|---|---|
| Nickel (+ Cobalt) | 63.0 min | ~65 | Cobalt counts toward Ni; verify Co is declared |
| Copper | 28.0 – 34.0 | ~31 | Critical element — pure-Ni substitute shows Cu < 1% |
| Iron | 2.5 max | ~1.5 | Elevated Fe degrades HF performance slightly |
| Manganese | 2.0 max | ~0.9 | Deoxidizer |
| Carbon | 0.30 max | ~0.12 | NOT 0.15-max-as-201 confusion; 400 allows far more C |
| Silicon | 0.50 max | ~0.15 | |
| Sulfur | 0.024 max | ~0.005 |
Note what is absent: no specified aluminum or titanium minimum. When a "Monel 400" certificate shows deliberate Al/Ti residuals, the heat may actually be destined for K500-type processing — a red flag for grade integrity. And when a certificate shows >99% nickel with carbon ≤0.02%, you are holding Nickel 201 and the order is nonconforming.
4. Mechanical Properties — Yield, Tensile, and Hardness Baselines
Monel 400 is sold in several tempers, each with a distinct mechanical envelope. ASTM B164 and B127 define minimums; the table below lists typical ranges published for annealed and hot-finished product, which Hangbo Alloy uses for pre-shipment verification and machinability planning.
| Temper / Condition | Tensile Strength | Yield Strength (0.2% offset) | Elongation | Hardness |
|---|---|---|---|---|
| Annealed rod & bar (typical) | 517–620 MPa (75–90 ksi) | 172–345 MPa (25–50 ksi) | 60–35% | 110–149 HB; 60–80 HRB |
| Hot-finished (typical) | 552–758 MPa (80–110 ksi) | 240–550 MPa (35–80 ksi) | 50–20% | 135–240 HB |
| Annealed plate (typical) | 483–586 MPa (70–85 ksi) | 170–310 MPa (25–45 ksi) | 50–35% | — |
| Cold-drawn, stress-relieved | Per ASTM B164 grade & diameter | Highest yield available without heat treatment | Reduced | Increased with cold work |
ASTM minimum guidance (representative): hot-finished or annealed rod commonly carries ~550 MPa (80 ksi) tensile minimum with 35% elongation in 50 mm, while plate per B127 typically requires 483–586 MPa tensile depending on thickness. Always quote the exact ASTM table for your diameter/thickness — minimums scale with section size, and Hangbo Alloy certifies the specific value applicable to your dimension.
For fabricators, the annealing response matters: open annealing at 1600–1800 °F (870–980 °C) for 2–10 minutes fully softens cold-worked material, while box annealing at 1400–1500 °F (760–815 °C) for 1–3 hours is the production route. Stress equalizing of cold-worked parts (≈575 °F / 300 °C, ~3 h) raises yield strength without meaningful ductility loss. Do not accept "mill annealed" claims without a hardness and grain-size record.
5. Hydrofluoric Acid Service — Where Monel 400 Justifies Its Reputation
The defining corrosion credential of Monel 400 is its behavior in hydrofluoric acid (HF). Special Metals' engineering evaluation describes the alloy's resistance to HF in all concentrations up to the boiling point, and notes it is arguably the most resistant of all commonly used engineering alloys in this medium. The mechanism is the formation of a protective surface film in both aerated and deaerated HF; the alloy performs across dilute through anhydrous concentrations where stainless steels, and even many nickel-chromium alloys, fail rapidly.
| Service Condition (illustrative) | Material Response | Engineering Comment |
|---|---|---|
| HF, all concentrations up to boiling point | Monel 400: low, stable corrosion rates | First choice for acid, stripper, and alkylation sections |
| Anhydrous HF (alkylation units) | Monel 400 widely used | Avoid oxidizing contaminants, which accelerate attack |
| Aerated dilute HF | Rates rise with aeration and temperature | Design margin needed; consult Hangbo Alloy |
| HF vapor at elevated temperature | Good but temperature-dependent | Keep oxidizing impurities (air, Fe³⁺, Cu²⁺) out of process |
The import pitfall: this HF superiority belongs to the nickel-copper alloy, not to Nickel 200/201 and not to Monel K500 in every condition. Pure nickel has its own excellent HF record in specific alkylation circuits — the Special Metals corrosion literature tabulates Nickel 200 plant tests in HF alkylation service — but the two alloys are not interchangeable in design. If your heat exchanger or valve spec says "Monel 400 for HF," a certificate for 201 will fail metallurgical review even if the dimensional inspection passes.
6. Marine Service: Monel 400 vs. Monel K500
Both Monel 400 and K500 serve the marine industry, but they are specified for different reasons, and substituting one for the other is a classic procurement error with real consequences in shafting and fastener applications.
| Attribute | Monel 400 (N04400) | Monel K500 (N05500) |
|---|---|---|
| Strengthening mechanism | Cold work only (single-phase FCC) | Cold work + age hardening (Al 2.3–3.15%, Ti 0.35–0.85% → γ′ Ni₃(Al,Ti)) |
| Typical yield strength, age-hardened bar | 170–550 MPa depending on temper | Up to ~790–1000 MPa (115–145 ksi) in fully aged, cold-worked condition |
| Ductility after full strengthening | High (35–60%) | Lower (~20–30%) |
| Seawater corrosion resistance | Excellent in flowing seawater; crevice/pitting risk under stagnant or fouled conditions | Similar general marine resistance; higher strength for shafts, pump rods, fasteners |
| Stress-corrosion behavior | Resistant in most marine and industrial waters | Resistant, but higher strength raises sensitivity in some aggressive media |
| Typical marine parts | Sheathing, piping, valves, pump trim, propeller shafts (low-load), seawater strainers | Propeller shafts, pump shafts, fasteners, drill collars, wear rings |
| Thermal treatment flexibility | Single-phase, no aging cycle required | Requires full solution + age (e.g., 1095 °C anneal + 480–590 °C age); wrong heat treatment = property failure |
Two field truths every importer should record:
- In flowing seawater, Monel 400 exhibits very low corrosion rates — the classic "clean, fast, wetted" marine environment suits it. Stagnant or fouled seawater, however, induces crevice and pitting corrosion, so the alloy must be designed with full-drain, high-velocity, or inhibited geometries. Do not promise "immune in any seawater" performance to your customer; promise controlled behavior with correct design.
- Monel K500 exists because 400 cannot deliver high strength in a marine fastener. If your drawing demands K500 yield properties, Monel 400 will fail. If your application demands maximum fabricability and weldability in seawater, K500's aging response (and its sensitivity to over-aging in heavy sections) is a liability. Hangbo Alloy carries both grades and will certify each against its own UNS chemistry.
7. Fabrication, Welding, and Heat-Treatment Notes for Importers
- Hot forming: Monel 400 hot-forms readily; working range roughly 1200–2150 °F (650–1175 °C) with heavy forging finishing above ~1300 °F. Never heat above 2150 °F, and avoid prolonged soaking at hot-working temperatures. In no case heat the alloy above ~2150 °F; permanent damage may result.
- Welding: SMAW with ENiCu-7-type electrodes (Monel Welding Electrode 190 class), GTAW/GMAW with ERNiCu-7 filler (Monel Filler Metal 60 class). All-weld-metal and transverse weld properties per the table below illustrate typical deposited weld performance used in procedure qualification.
- Machining: cold-drawn or cold-drawn stress-relieved stock machines best. Expect work-hardening behavior between mild steel and Type 304 stainless; use positive rake, rigid setups, and adequate coolant. The R-405 version exists specifically for free machining.
- Pickling / surface: adherent oxide forms on air cooling after heating; controlled reducing-atmosphere heating keeps surfaces bright. Specify surface finish (e.g., 2B, ground, peeled) on the PO — surface defects are a leading cause of arrival rejection.
| Typical Butt-Weld Properties, Monel 400 plate (SMAW, matching filler) | Tensile Strength | Yield Strength (0.2%) | Elongation |
|---|---|---|---|
| All-weld metal, room temperature | ~74–78 ksi (510–538 MPa) | ~46–49 ksi (317–338 MPa) | ~38–41% |
| Transverse across weld, room temperature | ~76–78 ksi (524–538 MPa) | ~48–52 ksi (331–358 MPa) | ~21–24% |
8. Purchasing Checklist — Alloy Import Pitfalls Edition
| Check | Why It Matters | Hangbo Alloy Practice |
|---|---|---|
| UNS + ASTM product spec on PO | Prevents "trade-name-only" ambiguity | Every PO is confirmed against N04400 + B127/B164/B165 |
| MTC chemistry vs. Section 3 table | Catches Nickel 200/201 substitution | 100% heat-lot traceability from melt to shipping |
| Copper content on certificate | Single best discriminator vs. pure nickel | Independent arrival testing available on request |
| Temper / condition stated | Mechanical acceptance depends on it | Cold-drawn vs. annealed vs. hot-finished declared per item |
| HF or marine designation on the spec | Ensures correct grade family (400 vs. K500 vs. 201) | Technical review of intended service before quoting |
| Heat-treatment record | Verifies anneal/age cycles | Furnace logs archived per heat number |
| Third-party inspection (SGS/BV/TÜV) | Protects importer at discharge | Supported; witness testing at our Shanghai mill |
Technical FAQ — Monel 400 (UNS N04400)
1. What is the difference between Monel 400 and Nickel 201, and why would a Monel 400 order ever arrive as Nickel 201?
Monel 400 is a nickel-copper alloy (Ni 63% min, Cu 28–34%), while Nickel 201 is commercially pure nickel (Ni 99% min, C ≤ 0.02%). They are specified for different corrosion services — Monel 400 for hydrofluoric acid and seawater, Nickel 201/200 for caustic soda. Substitution usually results from warehouse mislabeling or certificate copy-paste errors; the copper content on the MTC is the fastest way to detect it. Hangbo Alloy segregates heats by UNS and verifies chemistry before release.
2. What is the maximum service temperature of Monel 400 in air?
Monel 400 is useful up to about 1000 °F (540 °C) in oxidizing atmospheres; higher temperatures may be tolerated in reducing environments where scaling is less severe. Above this range, oxidation and loss of mechanical properties accelerate — for sustained hot strength, select a chromium-bearing alloy instead.
3. Is Monel 400 resistant to hydrofluoric acid?
Yes. Monel 400 is considered among the most resistant of the common engineering alloys to hydrofluoric acid in all concentrations up to the boiling point, and is the standard metallurgy for HF alkylation and acid-handling equipment. Performance degrades if oxidizing species such as ferric or cupric ions are introduced.
4. Does Monel 400 resist seawater corrosion?
In flowing seawater, corrosion rates are very low. In stagnant or fouled seawater, crevice and pitting attack can occur, so designers must avoid dead zones and low-velocity pockets. Monel 400 also resists stress-corrosion cracking in most fresh and industrial waters.
5. Which ASTM specifications cover Monel 400 plate, bar, and pipe?
ASTM B127 covers plate, sheet, and strip; ASTM B164 covers rod, bar, and wire; ASTM B165 covers seamless pipe and tube. ASME equivalents are SB-127, SB-164, and SB-165. Hangbo Alloy certifies each product form against its own spec — a B164 bar certificate is not valid proof for B127 plate.
6. Can Monel 400 be hardened by heat treatment?
No. It is a single-phase solid-solution alloy; only cold working increases its strength. If you need age-hardenable strength, Monel K500 is the correct grade. Be suspicious of any "heat-treated Monel 400" claim implying precipitation hardening.
7. What is the difference between Monel 400 and Monel K500 for marine shafts?
K500 adds aluminum and titanium so it can be precipitation-hardened to roughly double the yield strength of Monel 400, which is why heavily loaded propeller shafts and pump shafts use K500. Monel 400 is preferred where maximum weldability, formability, and corrosion margin in complex fabrications matter more than strength.
8. Why does my mill certificate show cobalt counted with nickel?
Most specifications for Monel 400 state "Nickel + Cobalt 63.0% minimum" because cobalt accompanies nickel in the ore and behaves similarly. The combined figure must meet the minimum; cobalt itself typically remains low. Confirm the cobalt residual is declared so downstream magnetic or nuclear-property reviews have the data.
9. What filler metal is used to weld Monel 400 to itself and to steel?
For matching welds use ERNiCu-7 filler metal (GTAW/GMAW) or ENiCu-7 electrodes (SMAW). For dissimilar joints to carbon or stainless steel, nickel-based fillers such as ERNi-1-type or alloy 625-class products are frequently selected depending on service; Hangbo Alloy provides a welding-consumable recommendation with every fabrication package.
10. Does Hangbo Alloy supply Monel 400 with full traceability and third-party inspection?
Yes. Every Hangbo Alloy Monel 400 plate, bar, and pipe ships with an EN 10204 3.1 mill certificate, heat-lot traceability, and, on request, third-party witness testing at the mill (SGS, BV, TÜV, or your designated inspector). We also perform independent arrival testing for copper and nickel content to close the loop on grade integrity.
This page is part of the Alloy Import Pitfalls series by Hangbo Alloy (Shanghai Hangbo Alloy Group, nickel-alloy.com). Data presented are typical engineering values compiled from recognized industry sources and are provided for material selection guidance; the governing documents for any purchase are the applicable ASTM/ASME specifications and the certified mill test report. Contact Hangbo Alloy for current stock, mill certificates, and application engineering support.
