HTS Coatings — machining & grinding

Stellite 6

19% Cr, 0.7% C, 2.3% Si, 3% Fe, 13.5% Ni, 1.7% B, 7.5% W, 1% Mn, Co-balance

  • Flame
  • HVOF
  • Weld

Stellite 6 is the workhorse of cobalt-chromium hardfacing — a Co-Cr-W-C alloy where hard chromium and tungsten carbides sit in a tough cobalt matrix. That structure is why valve shops, refineries, and turbine rebuilders keep coming back to it: it resists galling against stainless, handles cavitation, and — unlike tungsten carbide — holds its hardness and oxidation resistance up through roughly 500°C and keeps performing in valve and steam service well beyond that. WC-Co is harder at room temperature, but it decarburizes and loses binder above ~500°C. Stellite 6 keeps working.

At HTS we run Stellite 6 across every process that makes sense for it: PTA and GTAW weld overlay when you need a thick, fused layer on a valve seat or pump shaft; HVOF when the part can't take weld heat and you need a dense, sub-1% porosity thermal-sprayed coating; and flame spray for budget restorations on lightly loaded rotating equipment. We'll machine or grind the deposit to print in-house.

Got a galled valve trim or an eroded pump sleeve? Send us a sketch — we'll scope the right Stellite 6 process for the job.

Technical data

Hardness
380-490 HV as-deposited; HVOF commonly 600-720 HV after optimization
Hardness (HRC)
36-45 HRC (PTA/weld and HVOF baseline); up to ~52 HRC on optimized HVOF
Bond strength
9,500 psi typical HVOF (~33 MPa); weld overlay metallurgically bonded (substrate-limited)
Max service temp
~930°F continuous hardness retention; useful wear/corrosion service to 1,000-1,200°F in valve trim
Max service temp
~500°C continuous; 540-650°C in valve/steam service depending on load
As-sprayed porosity
<1% HVOF (typ. 0.2-0.8%); 3-8% flame spray; weld overlay ~0%
Typical thickness
Flame spray 10-30; HVOF 5-20; PTA/GTAW weld 40-120 (1-3 mm)
Melting range
2282-2480°F
Density
8.44

Where it earns its keep

  • Outstanding galling resistance against stainless steel mating faces
  • Retains useful hardness and oxidation resistance to ~500-650°C where WC-Co decarburizes
  • Excellent cavitation-erosion resistance in valves and pumps
  • Corrosion-resistant in mildly oxidizing acids and wet H₂S service
  • Can be applied by flame spray, HVOF, PTA, GTAW, and MIG — one alloy family, many processes
  • Machinable with carbide tooling (unlike tungsten-carbide coatings, which require diamond grinding)

Where it doesn't

  • Lower cold-hardness than WC-Co (36-45 HRC vs. ~70 HRC) — not the right pick for heavy 3-body abrasion
  • Cobalt raw-material cost is volatile and materially higher than Ni- or Fe-base hardfacers
  • Weld deposits are crack-sensitive; preheat, interpass control, and slow cool are typically required
  • Not recommended for seawater immersion (stress-corrosion cracking risk)
  • On 22Cr duplex, PWHT and dilution control are critical to avoid sigma-phase embrittlement

Typical applications

  • Oil & gas ball valve balls and seats (high-cycle, erosive service)
  • Gate, globe, and check valve trim in refining and chemical process
  • Steam turbine erosion shields and control-valve trim
  • Pump sleeves, shafts, and mechanical seal faces
  • Extrusion screws and barrels for abrasive polymer compounds
  • Poppet valves and exhaust seats in engines and compressors
  • Forging and hot-work die inserts exposed to galling
  • Pulp & paper chipper knives, doctor blades, black-liquor service parts

Wear modes addressed

  • Metal-to-metal adhesive wear / galling
  • Cavitation erosion (valve and pump)
  • Particle erosion (produced fluids, steam, flashing liquids)
  • Low-stress abrasion
  • Oxidation and hot corrosion to ~500-650°C
  • Fretting at loaded contacts

Industries

  • Oil & gas (upstream, midstream, refining)
  • Valve manufacturing and OEM valve rebuild
  • Power generation (steam turbines, boiler-feed pumps)
  • Chemical and petrochemical process
  • Pulp & paper
  • Pharmaceutical and food process
  • Pump and compressor OEM/MRO
  • Marine and offshore topsides

Substrates

  • Carbon and low-alloy steels (1018, 4140, 4340)
  • Martensitic stainless (410, 420, F6NM)
  • Austenitic stainless (304, 316, 316L)
  • Duplex stainless — with care; avoid on 22Cr due to sigma-phase risk
  • Ni-base alloys (Inconel 625, 718) for valve trim
  • Tool and die steels (H13) for hot-work

Which process, when?

Flame spray is the low-cost choice for 10-30 mil protective layers on lightly loaded pump sleeves and shafts; bond is mechanical, porosity runs 3-8%, service temp is limited by the interface. HVOF is the modern default for thermal-sprayed Stellite 6: <1% porosity, ~9,500 psi bond, dense enough for cavitation and erosion service on valve balls, seats, and pump components where weld heat would distort the part. PTA and GTAW weld overlay is the answer when you need a fully fused, metallurgically bonded layer 40-120 mils thick — oil & gas ball valves, gate-valve seat rings, anything that will see thermal cycling, high contact stress, or requires repair-grade depth. Pick HVOF for thin-and-precise, weld overlay for thick-and-bonded, flame spray for budget restorations.

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.

Thinking about Stellite 6 for a part?

Send us the spec or a photo. We'll tell you whether this fits, or point you at a better material for the job.

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