What is the difference between Monel 400 and Monel K-500?

Monel 400 (UNS N04400) is a single-phase nickel-copper solid solution with 63 to 70 percent Ni and 28 to 34 percent Cu, supplied annealed at 25 ksi (170 MPa) yield minimum per ASTM B164. Monel K-500 (UNS N05500) keeps the Ni-Cu backbone but adds 2.30 to 3.15 percent aluminium and 0.35 to 0.85 percent titanium for Ni3(Al,Ti) gamma-prime precipitation hardening, supplied solution-treated and aged at 90 to 130 ksi (620 to 895 MPa) yield per ASTM B865. Corrosion resistance is similar; K-500 trades cost, machinability and weldability for roughly 4 times the yield.

Why is Monel K-500 stronger than Monel 400?

K-500 owes its strength to aluminium and titanium dissolved in the Ni-Cu matrix during a 980 degrees Celsius solution treatment, then precipitated as coherent Ni3(Al,Ti) gamma-prime particles during an 8 to 16 hour age at 593 degrees Celsius, furnace-cooled to 482 degrees Celsius. The precipitates pin dislocations and raise yield from the annealed 40 to 50 ksi range to 90 to 130 ksi. Monel 400 carries no aluminium and no titanium per ASTM B164 Table 1, so the precipitation route is closed; cold work is the only strengthening path and tops out near 85 ksi yield.

What is the price difference between Monel 400 and Monel K-500?

Monel K-500 bar typically sits 20 to 30 percent above Monel 400 bar by weight in the Indian market, driven by the aluminium and titanium additions, the longer melt route, and the mandatory solution-anneal plus age cycle. Premium widens on machined parts because K-500 hardens further during machining and demands lower feeds, slower speeds and more frequent tool changes than Monel 400. For flange bolting, HF piping and most wetted service where annealed 25 ksi yield is adequate, Monel 400 is the cheaper correct answer; K-500 is justified only where high yield is genuinely required.

When is Monel K-500 mandatory over Monel 400?

K-500 is mandatory when the design yield exceeds roughly 60 ksi (415 MPa) in a service that also needs the nickel-copper corrosion envelope. Typical landings: downhole tools and pump shafts in sour wells, propeller and impeller shafts in seawater, valve stems carrying high tightening loads, springs in marine and chemical service, and high-strength fasteners (ASTM F468 N05500) where Monel 400 Class 4 to 8 cold-worked grades cannot meet the load. For flange bolting at standard B16.5 tension, HF piping internals, brine handling and most plate-sheet-tube service, Monel 400 is the specified alloy.

Can Monel K-500 be welded like Monel 400?

K-500 welds, but the heat-affected zone overages and loses the gamma-prime hardening. Monel 400 welds in any thickness without post-weld heat treatment using ENiCu-7 / ERNiCu-7 fillers per AWS A5.11 and A5.14. K-500 needs the joint to be solution-treated at 980 degrees Celsius and re-aged at 593 degrees Celsius after welding to restore the aged yield, which is impractical for field welds. For welded fabrications, specify Monel 400. K-500 is for machined, threaded or hot-formed parts that ship in the aged condition.

Do both Monel 400 and K-500 qualify for NACE MR0175 sour service?

Yes, both nickel-copper grades qualify under NACE MR0175 / ISO 15156-3 for sour service at the 35 HRC hardness ceiling. Monel 400 (N04400) clears the cap easily in the annealed condition; K-500 (N05500) is age-hardened to roughly 27 to 35 HRC and must be controlled to stay at or below the 35 HRC limit. Both are listed in Annex A as acceptable CRA grades without prequalification testing for hydrogen sulphide partial pressure, chloride and pH within the standard envelope.

0091-22-66157017

info@torqbolt.com

Home

Monel 400 vs Inconel 600 — High-Temp & Chloride SCC Selection

Monel 400 (UNS N04400) and Inconel 600 (UNS N06600) are both nickel-base alloys but solve opposite problems. Inconel 600 is a Ni-Cr-Fe alloy designed for high-temperature oxidation resistance up to 1093°C and excellent resistance to chloride stress corrosion cracking. Monel 400 is a Ni-Cu binary for HF, reducing acids, and seawater service at ambient-to-moderate temperatures. The 540°C threshold is the cleanest selector: anything hotter goes to Inconel 600, anything cooler with HF or seawater goes to Monel.

Chemistry — UNS N04400 vs UNS N06600

Monel 400 = Ni 63+ / Cu 28-34 / Fe 2.5 max. Inconel 600 = Ni 72+ / Cr 14-17 / Fe 6-10 / C 0.15 max. Inconel's chromium content drives high-temp oxidation and SCC resistance; Monel's copper enables HF compatibility. Full Monel chemistry.

Mechanical & Thermal Properties

Property	Monel 400	Inconel 600
Tensile (min)	70 ksi / 485 MPa	80 ksi / 550 MPa
Yield (min)	28 ksi / 195 MPa	30 ksi / 240 MPa
Max continuous service temp	480 °C / 900 °F	1093 °C / 2000 °F
Thermal expansion 20-100°C	13.9 × 10⁻⁶/°C	13.3 × 10⁻⁶/°C

Corrosion Performance — High-Temp vs Reducing

Inconel 600 wins on: high-temperature oxidation (jet engines, furnace internals), chloride SCC (Inconel 600 is the de-facto standard for nuclear steam-generator tubing), caustic stress corrosion at elevated temp, dry chlorine gas at high temp.

Monel 400 wins on: hydrofluoric acid at any temp, reducing chloride environments, sulfuric acid <80%, hot ammonia, seawater (especially deaerated).

Cost & Availability

Inconel 600 typically 1.8-2.5x the cost of Monel 400. Both are stocked in major industrial markets. Quote either grade in 24h.

Applicable Standards

Monel 400: ASTM B127/B164/B165/F468
Inconel 600: ASTM B166 (rod), B167 (pipe), B168 (sheet/plate), B564 (forgings); ASME SB-166/167/168

Selection Guide

Above 540°C: Inconel 600. Below 480°C with HF or reducing acids: Monel 400. Pure-chloride SCC in nuclear-steam-generator service: Inconel 600 (this is its signature application). Sulfuric acid duty < 80%: Monel 400.

FAQs

Can Inconel 600 replace Monel 400 in HF service?

No. Inconel 600's chromium content causes accelerated corrosion in hydrofluoric acid. HF service is the one place chromium is a liability, not an asset. Monel 400's zero-chromium chemistry is what makes it HF-compatible.

Is Inconel 600 just a higher-temp Monel 400?

No — they're fundamentally different alloys. Inconel 600 is Ni-Cr-Fe (chromium-bearing) for oxidation and SCC resistance. Monel 400 is Ni-Cu (copper-bearing) for HF and reducing acids. Different metallurgy, different applications.

Which welds easier?

Both weld readily. Monel 400 uses ERNiCu-7 filler (Monel 60). Inconel 600 uses ERNiCr-3 (Inconel 82 / 182). Inconel needs slightly higher heat input and tighter interpass control to avoid HAZ cracking on thick sections.

For a furnace fixture seeing 800°C — which alloy?

Inconel 600. Monel 400's 480°C ceiling means continuous service at 800°C will cause rapid oxidation and grain-boundary attack. Inconel 600 is rated for continuous service to 1093°C in oxidizing atmosphere.

Xylan 1070 / 1014 / 1400 / 1424

Xylar 2 / 101

Geomet 321 / 500 / 720

SermaGard 1105 / 1280

Dacromet 320 / 500

TakeCoat 1000 Ceramic

Delta Tone/Seal

Magnigard

MolyKote

Sherardized

Zinc-Cobalt (ASTM B840)

Zinc-Nickel (ASTM B841)

ISO 9001 - 2015 Certified
PED 2014/68/EC
NACE MR0175/ISO 15156-2
NORSOK M-650
DFAR
MERKBLATT AD 2000 W2/W7/W10

Questions? Contact us.

Showcase of our Microsites.

Monel 400 vs Inconel 600 — High-Temp & Chloride SCC Selection

Chemistry — UNS N04400 vs UNS N06600

Mechanical & Thermal Properties

Corrosion Performance — High-Temp vs Reducing

Cost & Availability

Applicable Standards

Selection Guide

FAQs

Specifications

Surface Treatments

Certifications

About Us

Satisfaction Survey

Monel 400 vs Inconel 600 — High-Temp & Chloride SCC Selection

Chemistry — UNS N04400 vs UNS N06600

Mechanical & Thermal Properties

Corrosion Performance — High-Temp vs Reducing

Cost & Availability

Applicable Standards

Selection Guide

FAQs

Related

Specifications

Surface Treatments

Certifications

About Us

Satisfaction Survey