Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Monel 400 Heat Treatment - Annealing & Stress Relief, UNS N04400
Monel 400 heat treatment (also Monel 400 annealing, Monel 400 stress relief, UNS N04400 heat treatment, NiCu30Fe heat treatment) covers two cycles: soft-anneal at 871 to 982 °C and stress-relief at 538 to 649 °C. Monel 400 is a single-phase nickel-copper solid solution and cannot be hardened by heat treatment: no precipitation, no quench-and-temper, no martensite. Strength is set in the mill by cold work. Monel® is a registered trademark of Special Metals Corporation; TorqBolt is not authorized by, affiliated with or endorsed by Special Metals. The PH sister grade is Monel K-500 (UNS N05500), which adds Al and Ti for a Ni3(Al,Ti) response N04400 cannot reproduce.
Monel 400 Annealing - Temperature, Time, Atmosphere, Quench
Soft-annealing is the primary heat treatment for Monel 400. It restores the recrystallised FCC nickel-copper matrix, drops hardness to roughly 60 HRB, lifts elongation above 40 percent. Specified by ASTM B164, B127, B165, B564 as the standard supply condition.
| Parameter | Soft Anneal | Mill Anneal |
|---|---|---|
| Temperature | 871 to 982 °C | 982 to 1093 °C |
| Hold | 3 to 5 min/mm | 5 to 10 min/mm |
| Atmosphere | Dry, sulphur-free, slightly reducing | Slightly reducing |
| Quench | Water (sheet, strip); air cool thick sections | Water or air |
| Hardness | 60 to 75 HRB | 65 to 80 HRB |
| Yield | 25 to 35 ksi | 28 to 40 ksi |
Atmosphere control is non-negotiable. Sulphur embrittles nickel matrices: sulphur fuel, oil residue or rich combustion forms low-melting nickel-sulphide grain-boundary films. Parts must be degreased before charge. Sulphur is capped at 0.024 percent in the alloy itself - see chemical composition. Atmospheres: dry hydrogen, dissociated ammonia, vacuum, argon.
Monel 400 Stress Relief - When and How
Stress-relief sits at 538 to 649 °C (1000 to 1200 F) for 1 to 3 hours, furnace cool or still air. Below the recrystallisation start: cold-work yield is retained, residual stress drops 60 to 80 percent. Atmosphere can be dry air. Uses: thick cold-formed plate, restrained weldments, cold-finished fastener stock for sour service per NACE MR0175. PWHT after welding is not mandatory per B164, B127, B564 or F468; the alloy is single-phase, so welding produces no hardened HAZ.
Why Monel 400 Cannot Be Precipitation-Hardened
Precipitation hardening needs a second phase that dissolves at high temperature and precipitates on aging - in nickel-base alloys, gamma-prime Ni3(Al,Ti). Monel 400 per ASTM B164 Table 1 carries no aluminium and no titanium. With no precipitate-forming elements, no aging response. Monel K-500 (UNS N05500) carries 2.30 to 3.15 Al, 0.35 to 0.85 Ti and reaches 90 to 130 ksi aged. Closed to N04400 by chemistry.
Cold Work and Work-Hardening Response
With no heat-treatment hardening, cold work is the only route to higher strength. A 30 percent reduction lifts yield from 28 ksi soft-annealed to about 85 ksi, hardness from 60 to 95 HRB. ASTM F468 sets fastener classes for N04400 from this response.
| Condition | Reduction | Yield (ksi) | Tensile (ksi) | HRB |
|---|---|---|---|---|
| Soft annealed | 0% | 25 to 35 | 70 to 85 | 60 to 75 |
| Cold drawn light | 10% | 50 to 60 | 85 to 95 | 85 to 90 |
| Cold drawn medium | 20% | 60 to 75 | 95 to 105 | 90 to 95 |
| Cold drawn heavy | 30% | 80 to 95 | 105 to 115 | 92 to 98 |
For sour service per NACE MR0175, hardness stays below HRC 35, capping cold work at 30 to 35 percent. Cold-finished bolts and stud bolts meet F468 classes through this route.
Monel 400 vs Monel K-500 - Heat Treatment Route
The grades share the Ni-Cu backbone but split on route. Chemistry drives the split; strength outcomes are an order of magnitude apart.
| Item | Monel 400 (N04400) | Monel K-500 (N05500) |
|---|---|---|
| Family | Solid-solution Ni-Cu | PH Ni-Cu-Al-Ti |
| Al / Ti | Not specified | 2.30 to 3.15 / 0.35 to 0.85 |
| Hardening | Cold work only | Cold work + Ni3(Al,Ti) age |
| Age cycle | None | 593 °C / 8 to 16 h, FC to 482 °C |
| Yield, supply | 25 to 50 ksi | 90 to 130 ksi |
| Bolt grade | F468 N04400 Cl 4 to 8 | F468 N05500 |
If a spec calls for heat-treated Ni-Cu bolting above 80 ksi yield, the grade is Monel K-500. ASTM lists no hardened temper for N04400.
Frequently Asked Questions
Can Monel 400 be hardened? Not by heat treatment. Single-phase Ni-Cu with no Al or Ti per ASTM B164 Table 1; no precipitation response. Cold work is the only route; 30 percent reduction lifts yield from 28 to about 85 ksi. The PH Monel grade is K-500.
What is the annealing temperature for Monel 400? 871 to 982 °C (1600 to 1800 F) per ASTM B164, B127, B165, B564. Hold 3 to 5 min/mm. Water quench sheet, strip, soft bar; air cool thick sections.
Does Monel 400 need PWHT after welding? No mandatory PWHT - the alloy is single-phase, so welding produces no hardened HAZ. A 538 to 649 °C stress-relief for 1 to 3 h is used only on heavy cold-worked or restrained weldments.
Request a Quote
For Monel 400 in soft-annealed, hot-finished or cold-drawn condition with EN 10204 type 3.1 or 3.2 MTC, send drawing and quantity to info@torqbolt.com or WhatsApp +91-22-66157017. Mumbai stock; export through JNPT. Related: chemical composition, mechanical properties, ASTM F468, UNS N04400, vs Monel K-500, bolts, stud bolts.
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