HTS Coatings — machining & grinding

Colmonoy 56

76.2% Ni, 0.5% C, 13% Cr, 2.5% B, 3.8% Si, 4% Fe

  • Weld
  • PTA

Colmonoy 56 is the softer, tougher one — the middle child of Wall Colmonoy's Ni-Cr-B-Si family, sitting at 50-55 HRC between Colmonoy 5 (45-50 HRC) and Colmonoy 6 (56-61 HRC). Nominal chemistry is Ni 75.5 / Cr 13.1 / Si 3.8 / Fe 4.4 / B 2.6 / C 0.60, density 8.18 g/cc, fusing at 1,885°F. Wall Colmonoy developed 56 for the plastic extrusion industry, and it is the standard for extrusion screws and a go-to for agricultural tillage, slurry valve trim, printing rolls, pump shafts, plunger pumps, boiler components, and moderate-abrasion screw conveyors.

The tradeoff is simple. Drop the carbon and chromium a notch, drop the carbide volume — which drops the hardness but buys back real ductility and impact tolerance. The deposit survives where a harder Colmonoy 6 or 88 would crack. The self-fluxing Ni-Si-B chemistry still delivers metallurgical bonding, and machining stays doable with carbide tooling. When to step up: abrasion is the primary driver. When to stay with 56: the part also sees impact, or the weld overlay has to survive service. HTS applies Colmonoy 56 via flame spray + fuse, PTA, GTAW, and SMAW. Got a worn extrusion screw or tillage part? Send a sketch — we'll tell you if 56 is the right call.

Technical data

Hardness
~500-560 HV equivalent (HRC 50-55 conversion, consistent with NiCrBSi hardfacings in the 450-600 HV band)
Hardness (HRC)
50-55 HRC as-deposited (Wall Colmonoy datasheet); positioned between Colmonoy 5 (45-50 HRC) and Colmonoy 6 (56-61 HRC) — the softer, tougher member of the family
Bond strength
Metallurgically bonded after fusing or welding (spray-and-fuse, PTA, GTAW) — substrate-limited, not coating-limited; self-fluxing Ni-Si-B chemistry pulls oxides during fuse and forms a true fusion interface
Max service temp
~1,000°F continuous (hot-hardness retention); onset of accelerated oxidation in Ni-Cr-B-Si research studies sits at ~1,830-2,010°F (1,000-1,100°C) on the 56 chemistry
Max service temp
~540°C continuous
As-sprayed porosity
Flame spray unfused 3-8%; after fuse cycle <1%; PTA/weld overlay ~0%
Typical thickness
Flame spray + fuse 15-40; PTA 40-120 (1-3 mm) — standard range for extrusion-screw flights; GTAW/SMAW weld overlay 60-250
Melting range
Fusing temperature ~1,885°F (1,029°C) per Wall Colmonoy datasheet — solidus/liquidus band sits a shade below and above this point
Density
8.18

Where it earns its keep

  • More ductile and tougher than Colmonoy 6 or 88 — lower carbon means less carbide volume, so deposits flex instead of cracking under moderate impact
  • Self-fluxing — boron and silicon scavenge oxides during the fuse cycle; bonds metallurgically to carbon steel, tool steel, stainless, and cobalt alloys with no separate flux
  • Machinable with carbide tooling after deposition — harder grades in the family (6 at 56-61 HRC, 88 at 59-64 HRC) typically need CBN or diamond grinding to finish
  • Balanced profile: genuine abrasion resistance plus real impact tolerance — the right pick when the duty cycle includes both
  • Materially cheaper per pound than Stellite 6 or Stellite 21 — no cobalt premium
  • Applies by every process HTS runs: spray-and-fuse, PTA, and GTAW/SMAW weld — one alloy, three deposition routes
  • Corrosion performance consistent with other Colmonoy-family nickel-base alloys — fit for mildly acidic and food-contact service where cobalt is unwanted

Where it doesn't

  • Lower hardness than Colmonoy 6 (56-61 HRC) or Colmonoy 88 (59-64 HRC) — step up when abrasion is the primary wear driver and ductility is secondary
  • Not for heavy impact or ballistic impingement — still crack-sensitive on weld overlay despite being the softer Colmonoy; reserve shock-load duty for cobalt-base Stellite 6 or 21
  • Continuous service temperature limited to ~1,000°F (540°C) — chromium borides soften and oxidation accelerates above that
  • Weld deposits benefit from preheat (typical ~450°C / 840°F), interpass control, and slow cool — standard Colmonoy practice
  • Dilution control matters on GTAW and PTA — iron pickup drops hardness and erodes corrosion performance; PTA gives the tightest control
  • Flame-sprayed deposits must be fused before service — as-sprayed is porous and only mechanically bonded

Typical applications

  • Plastic extrusion and injection-molding screw flights (Wall Colmonoy's original 56 application — the standard for plastics and rubber)
  • Extrusion screw repair and re-flighting on worn single-screw and twin-screw barrels
  • Agricultural tillage parts — plowshares, sweeps, disc edges, cultivator shanks — where abrasion is moderate and impact toughness matters
  • Slurry valve trim (gates, plugs, seats, stems) in mining and minerals processing
  • Printing and paper-mill rolls exposed to moderate abrasion (doctor rolls, anilox rolls, wear sleeves)
  • Pump shafts, sleeves, and wear rings in petroleum and chemical process service
  • Plunger-pump plungers and piston rods where some impact toughness is needed alongside abrasion resistance
  • Boiler-tube waterwall wear shields and superheater components in moderate-temperature service
  • Screw conveyors and auger flights in moderate abrasion (cement, aggregate, grain, plastic pellet)
  • Forming and drawing dies; cement gate valves; centrifugal pump parts
  • Glass-mold components where ductility is needed more than peak hardness

Wear modes addressed

  • Low-stress abrasion (soil, slurry, pellets, particulate)
  • Moderate three-body abrasion with intermittent impact
  • Adhesive wear and galling in metal-to-metal contact
  • Mild corrosion in aqueous and mildly acidic process streams (Ni-Cr matrix)
  • Oxidation to ~540°C / 1,000°F continuous
  • Combined wear-plus-modest-impact duty where Colmonoy 6 would crack

Industries

  • Plastics and rubber processing (extrusion, injection molding, compounding) — the original 56 target market
  • Agriculture and ag-equipment OEM (tillage and soil-engaging tools)
  • Mining and minerals processing (slurry valves, chutes, augers)
  • Pulp, paper, and printing (moderate-abrasion rolls)
  • Oil & gas (pump internals, valve trim, plungers)
  • Chemical and petrochemical process
  • Power generation (boiler and balance-of-plant components)
  • Cement, aggregate, and bulk material handling
  • Glass container manufacturing (mold components)

Substrates

  • Carbon and low-alloy steel (1018, 1045, 4140, 4340) with standard preheat
  • Tool and die steel with controlled preheat and slow cool
  • Martensitic stainless (410, 420) with verified preheat
  • Austenitic stainless (304, 316) — watch dilution on GTAW deposits
  • Cast iron (ductile and gray) with careful thermal cycle
  • Nickel alloys (Monel, Inconel) for high-temp or corrosive service

Which process, when?

Flame spray + fuse is the traditional route for 15-40 mil protective layers on pump sleeves, plungers, and moderate-abrasion rolls — the fuse cycle converts a porous mechanical layer into a dense, metallurgically bonded one. PTA welding is the standard deposition method for extrusion-screw flights and valve trim, delivering thick (40-120 mil) fused overlays with tight dilution control on new and worn screws. GTAW and SMAW rods handle shop and field repair on pump shafts, plunger rods, and agricultural tillage — straightforward with standard Colmonoy preheat and slow-cool practice. Pick spray-and-fuse for broad uniform coverage, PTA for thick fused overlay on production screws, GTAW/SMAW for repair and build-up.

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.

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.

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