Colmonoy 6 is the original nickel-chrome-boron-silicon hardfacing alloy — the one the trade leans on when a part needs to shrug off abrasion and corrosion without the cobalt price tag. Wall Colmonoy's nominal chemistry is Ni 74 / Cr 14 / Si 4.2 / B 3 / Fe 4 / C 0.6. At 56-61 HRC (up to 720 HV after fuse) it sits between plain nickel and cobalt Stellite for pump sleeves, seals, plunger rods, valve trim, ag tillage, printing rolls, glass molds, oil-field rotors, and slurry parts.

When to pick Colmonoy 6 over Stellite 6: your wear mode is abrasion or erosion rather than galling or impact, and you'd rather not pay the cobalt premium. When to step up to Colmonoy 88 instead: fine-particle slurry erosion that needs 88's tungsten-boride network. When to fall back to Stellite 6: impact, shock loading, or sustained service above 1,000°F.

The self-fluxing part matters. Boron and silicon scavenge oxides during the fuse cycle, so flame-sprayed Colmonoy 6 finishes metallurgically bonded and sub-1% porosity with no separate flux. We run it via flame spray + fuse, HVOF, PTA, GTAW, and SMAW, then grind or machine to print.

Got an eroded sleeve or worn plunger? Send us a sketch — we'll tell you if Colmonoy 6 fits the job.

Technical data

Hardness: 620-720 HV typical as-fused (flame spray + fuse and PTA); HVOF + fuse has reached ~706 HV; refined/remelted microstructures reported up to 811-863 HV in research studies
Hardness (HRC): 56-61 HRC (Wall Colmonoy datasheet); 56-63 HRC across Colmonoy 6 / 6 PTA / 6 L product sheets
Bond strength: Metallurgically bonded after fusing (flame spray + fuse, PTA, GTAW) — substrate-limited, not coating-limited; as-sprayed (unfused) flame spray is mechanical bond and should be fused before service
Max service temp: ~1,000°F continuous (hardness retention); short excursions higher with oxidation penalty
Max service temp: ~600°C continuous
As-sprayed porosity: Flame spray unfused 3-8%; after fuse cycle <1%; HVOF + fuse ~1%; PTA/weld overlay ~0%
Typical thickness: Flame spray + fuse 15-40; HVOF + fuse 5-20; PTA 40-120 (1-3 mm); GTAW/SMAW weld overlay 60-250
Melting range: ~1,850-1,950°F (fusing temp ~1,890°F per Wall Colmonoy datasheet)
Density: 8.10

Where it earns its keep

Self-fluxing — boron and silicon scavenge oxides during the fuse cycle, so you get a metallurgically bonded, dense layer with no separate flux and no shielding gas on the fuse step
Genuinely balanced: good abrasion and corrosion resistance with moderate impact tolerance — a workhorse where Stellite is overkill and plain nickel is too soft
Retains useful hardness and oxidation resistance to ~600°C / 1,000°F — outperforms Ni-only overlays at temperature
Machinable with carbide tooling after PTA or weld deposition; grind-finishable on flame-sprayed coatings
Applies by every major process we run: flame spray + fuse, HVOF, GTAW, SMAW, and PTA
Materially cheaper per pound than Stellite 6 or Stellite 21 — cobalt premiums don't apply

Where it doesn't

Not the right pick for sustained service above ~1,000°F — chromium borides soften and oxidation accelerates
Impact-sensitive compared to cobalt-base Stellite 6; heavy shock loading or ballistic impingement will chip the deposit
Weld overlays are crack-sensitive — preheat (typical ~450°C / 840°F), interpass control, and slow cool are standard; thin single-pass deposits and controlled dilution reduce risk
Dilution from iron-base substrates (especially on GTAW/SMAW) drops hardness and corrosion resistance; PTA give the tightest dilution control
Flame-sprayed deposits must be fused before they see real service — as-sprayed is porous and mechanically bonded only

Which process, when?

Flame spray + fuse is the traditional, cost-effective route for 15-40 mil protective layers on pump sleeves, plungers, and printing rolls — the fuse cycle converts a porous mechanical layer into a dense, metallurgically bonded one. HVOF is used where a thinner, denser as-sprayed layer is needed before fusing, or where the part can't accept a fuse cycle. PTA welding is our go-to for thick, precisely-placed deposits with low dilution — ideal on valve trim, rotor heads, and wear bands. GTAW and SMAW rods are the field- and shop-friendly answer for repair and build-up, though preheat and slow cool matter.

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

Wall Colmonoy — Colmonoy® 6 Product Page
“Nickel-based hard-surfacing alloy; 56-63 HRC; rated excellent in resistance to abrasion, corrosion, and galling; good on impact; excellent red hardness and superior weldability; applied as hardfacing rod or Spraywelder thermal spray.”
MatWeb — Wall Colmonoy COLMONOY® 6 Datasheet
“Nominal composition: Ni 73.75%, Cr 14.3%, Si 4.25%, Fe 4.0%, B 3.0%, C 0.70%. Density 8.10 g/cc. Fusing/processing temperature 1030°C (1890°F). Rockwell C 56-61. Applied by oxyacetylene, DC electric arc, GTAW, and spray; used for shafts, sleeves, valve trim.”
Wall Colmonoy — Colmonoy Origins
“Colmonoy 6 was one of the first nickel-based hardfacing alloys; offers extreme abrasion resistance plus resistance to corrosion and high heat; 56-60 HRC; corrosion characteristics similar to Inconel; the Ni-Si-B trio is what makes it self-fluxing to carbon steel, tool steel, stainless, and cobalt alloys.”
ASM Alloy Digest Ni-78 — Colmonoy No. 6 Hard Facing Alloy
“Nickel-base hard-surfacing alloy containing chromium borides; recommended for parts requiring wear, corrosion, heat, and galling resistance; applied by oxyacetylene, DC arc, and GTAW.”
Certilas — NiCrBSi 6 TIG (Colmonoy 6) Filler Metal
“Nickel-based TIG filler for hardfacing and overlay; self-fluxing NiCrBSi chemistry; used on pump components, valve parts, glass-mould tooling, and other wear- and corrosion-exposed parts.”
HTS Coatings — Difference Between Stellite and Colmonoy
“Colmonoy (nickel-based) handles abrasive wear better — a fit for hard abrasive environments like material-handling screw conveyors, valve seats, and ball-valve components; Stellite (cobalt-based) is more ductile and handles impact better in welded applications.”
Welding in the World — Microstructural analysis of flame-sprayed and PTA-deposited NiCrBSi self-fluxing coatings
“Comparative study of Colmonoy-family NiCrBSi coatings deposited by flame spray (with post-fuse) and PTA; confirms dense, metallurgically bonded microstructures with hard chromium boride and nickel boride phases in a Ni-Cr-Si matrix.”
Materials Science and Technology — Effect of Dilution on GTAW Colmonoy 6 on 316LN
“GTAW Colmonoy 6 (AWS NiCr-C) deposits on austenitic stainless show significant substrate dilution; optimal preheat ~455°C to avoid cracking; dilution control governs hardness and corrosion performance of the overlay.”

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

Colmonoy 6

Technical data

Where it earns its keep

Where it doesn't

Typical applications

Wear modes addressed

Industries

Substrates

Which process, when?

Sources

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