HTS Coatings — machining & grinding

Stellite 12

29% Cr, 8.5% W, 1.8% C, Fe, Ni, Mo, Mn, Si, Co-balance

  • Flame
  • HVOF
  • Spray & Fuse
  • Weld

Stellite 12 is the Goldilocks cobalt-chrome-tungsten hardfacer — the one you reach for when Stellite 6 is too soft for the abrasion and Stellite 1 cracks under the impact. Bump the carbon and tungsten up from Stellite 6, back them down from Stellite 1, and you land at 45-51 HRC with a carbide-rich microstructure that shrugs off low-angle erosion and severe sliding wear while still taking moderate impact and thermal cycling. The extra tungsten also pushes useful service temperature to roughly 700°C — a meaningful step up from Stellite 6's ~500-650°C envelope, which matters for hot-work dies, steam-turbine parts, and glass-mold tooling.

At HTS we run Stellite 12 across every deposition process that fits the job: PTA, GTAW, and SMAW weld overlay for thick, fully fused layers on extrusion screws, hot-work die inserts, and screw-conveyor flights; HVOF when the part can't take weld heat but needs a dense, sub-1% porosity coating on valve trim or glass plungers; spray & fuse as the middle path for paper-mill rolls; and flame spray for budget restorations. We'll preheat it right, control dilution, and grind or machine to print in-house.

Got an eroded die insert, a galled extrusion screw, or a valve seat that's chewing through Stellite 6 too fast? Send us a sketch — we'll scope it.

Technical data

Hardness
420-500 HV as-deposited (PTA/weld); 435-590 HV range per Kennametal spec; optimized HVOF deposits trend to the upper end
Hardness (HRC)
44-51 HRC (PTA and HVOF); Kennametal nominal 45-50 HRC for weld metal
Bond strength
~4,800 psi (33 MPa) HVOF on steel substrates; weld overlay metallurgically bonded (substrate-limited)
Max service temp
~1,290°F continuous; useful wear/oxidation service to ~1,300°F in valve and steam applications
Max service temp
~700°C continuous; higher hot-hardness than Stellite 6 thanks to added tungsten
As-sprayed porosity
<1% HVOF (typ. 0.2-0.8%); 3-8% flame spray; spray-fuse ~1-2% after fuse cycle; weld overlay ~0%
Typical thickness
Flame spray 10-30; HVOF 5-20; spray & fuse 20-60; PTA/GTAW/SMAW weld 40-120 (1-3 mm)
Melting range
2240-2335°F
Density
8.53

Where it earns its keep

  • The Goldilocks Stellite — more carbide than 6 (better abrasion), more ductility than 1 (better impact and thermal shock tolerance)
  • Service temperature to ~700°C, meaningfully higher than Stellite 6 thanks to added tungsten
  • Better corrosion resistance than Stellite 6 in oxidizing environments (higher Cr)
  • Weld-overlay friendly across PTA, GTAW, SMAW, and oxyacetylene with proper preheat
  • Runs well self-mated or against Stellite 6 / Stellite 1 mating faces in valve and pump service
  • Handles low-angle erosion and severe sliding wear where 6 is too soft to last

Where it doesn't

  • Cobalt raw-material cost is volatile and materially higher than Ni- or Fe-base hardfacers
  • Higher carbide fraction than Stellite 6 means it's still crack-sensitive — preheat, interpass control, and slow cool are required; excessive preheat can actually exacerbate craze cracking
  • When abrasion is the dominant mode and impact is light, Stellite 1 (55-60 HRC) is the better pick
  • When impact is heavy and mating face is stainless, Stellite 6 is more forgiving
  • More difficult to machine than Stellite 6 — carbide tooling required, often grind-to-finish
  • Not recommended for seawater immersion (stress-corrosion cracking risk, same as other cobalt alloys)

Typical applications

  • Hot-work die inserts where Stellite 6 galls and Stellite 1 cracks
  • Extrusion screws and barrels for abrasive polymer compounds
  • Valve trim in refining and chemical process (middle-severity service)
  • Steam-turbine erosion shields and control-valve components
  • Glass-manufacturing plungers, rolls, and narrow-neck mold tooling
  • Paper-mill doctor blades, chipper knives, and wear parts
  • Screw-conveyor flights handling abrasive bulk solids
  • Engine exhaust valve hardfacing and pinch rollers in metal processing
  • Industrial cutting knives for paper, plastics, and synthetic fibers
  • Pump vanes, bearing bushes, and rotor blade edges

Wear modes addressed

  • Low-angle particle erosion (Stellite 12's carbide-rich microstructure excels here)
  • Severe sliding / metal-to-metal wear under moderate impact
  • Two- and three-body abrasion against hard particulate
  • Cavitation erosion in valve and pump service
  • Oxidation and hot corrosion to ~700°C
  • Adhesive wear / galling against stainless mating faces

Industries

  • Oil & gas (refining, process valve trim)
  • Power generation (steam turbines, boiler-feed components)
  • Glass manufacturing (molds, plungers, shear blades)
  • Pulp & paper (chipper knives, doctor blades, roll surfaces)
  • Plastics and polymer extrusion
  • Automotive and diesel engine (exhaust valve hardfacing)
  • Chemical and petrochemical process
  • Pump and compressor OEM/MRO
  • Bulk materials handling (screw conveyors, augers)

Substrates

  • Carbon and low-alloy steels (1018, 4140, 4340)
  • Tool and die steels (H13, H11) for hot-work inserts
  • Martensitic stainless (410, 420, F6NM)
  • Austenitic stainless (304, 316, 316L)
  • Ni-base alloys (Inconel 625, 718) for high-temp valve trim
  • Cast irons — with careful preheat and dilution control

Which process, when?

Flame spray handles 10-30 mil restoration layers on lightly loaded rolls and shafts where budget matters more than density; bond is mechanical and porosity runs 3-8%. HVOF is the modern thermal-spray default for Stellite 12: sub-1% porosity, ~33 MPa bond, dense enough for valve trim, glass plungers, and extrusion components where weld distortion isn't acceptable. Spray & fuse gets you a metallurgically bonded layer without full weld heat — a middle path for glass molds and paper-mill rolls. PTA, GTAW, and SMAW weld overlay is the answer when you need a thick, fully fused layer (40-120 mils) for hot-work die inserts, extrusion screws, and screw-conveyor flights that will see thermal cycling and heavy contact stress. Pick HVOF for thin-and-precise, spray-fuse for bonded-but-not-welded, weld overlay for thick-and-repairable.

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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