Chrome Carbide (Cr3C2-NiCr) Thermal Spray Coatings
Chrome carbide (Cr₃C₂-NiCr) is a thermal spray coating material applied by HVOF or plasma spray to resist erosion, oxidation and hot corrosion, typically reaching 800–1,000 HV0.3 in production and used to about 900 °C on boiler waterwall and superheater tubes, ID fan blades and exhaust valve seats.
The high-temperature carbide. Where tungsten carbide starts to oxidise at around 500 °C, chrome carbide in a nickel-chromium binder keeps working to roughly 900 °C — which is why it is the coating on boiler tubes, ID fan blades and exhaust valve seats.
The Material.
Chrome carbide coatings are chromium carbide particles, usually Cr₃C₂, in a nickel-chromium matrix. The standard supply is 75% Cr₃C₂ with 25% NiCr; an 80/20 grade trades a little toughness for more hardness. The NiCr binder is the reason the coating survives heat: nickel-chromium forms a protective chromia scale, so the matrix resists oxidation instead of burning away and releasing the carbide.
The trade-off against tungsten carbide is straightforward. At room temperature, WC-Co is harder and wears better. Above roughly 500 °C that reverses, because WC oxidises and the WC-Co coating degrades while chrome carbide is barely affected. Choosing between them is almost always a service-temperature decision rather than a hardness decision.
In power generation the dominant failure mode is fly-ash erosion on waterwall and superheater tubing, and erosion-corrosion on fan blades handling flue gas. Chrome carbide addresses both at once, because the same NiCr matrix that resists the oxidation also resists the hot corrosion.
Properties And Specification.
Typical values for a production thermal spray deposit. Confirm against coupons for your own substrate, geometry and duty cycle before releasing a drawing.
| Property | Typical Value |
|---|---|
| Common grades | Cr₃C₂-25(Ni20Cr) — the 75/25 standard — and Cr₃C₂-20(NiCr) |
| Coating hardness | 800–1,000 HV0.3 as sprayed by HVOF |
| Bond strength (ASTM C633) | Above 60 MPa (8,700 psi) |
| Porosity | 1–2% by HVOF; higher by plasma spray |
| Maximum service temperature | About 900 °C — the reason to choose it over tungsten carbide |
| Typical coating thickness | 150–500 µm |
| Oxidation resistance | Chromia-forming NiCr matrix; resists hot gas and flue gas corrosion |
| Surface finish | Diamond ground where a sealing or running fit is required |
Which Spray Process Applies It.
HVOF
The preferred route. Produces the densest chrome carbide deposit with the best bond strength and the lowest oxide content.
See the equipmentPlasma spray
Workable and widely used, particularly where a plasma cell is already installed. Expect higher porosity than HVOF, which matters less in hot erosion service than in sliding wear.
See the equipmentTube mill coating plants
For boiler waterwall panels and tube banks, the coating is applied by a dedicated tube coating plant that indexes the gun along the tube rather than by handheld spraying.
See the equipmentTypical Applications.
- Boiler waterwall, superheater and economiser tubes
- ID and FD fan blades, casings and liners
- Exhaust valve seats, stems and faces
- Steam turbine diaphragms and nozzle blocks
- Fluidised bed combustor internals
- Hot mill rolls and guides
- Gas turbine compressor components
- Furnace fans and hot gas ductwork
Why Choose This Material.
Keeps working above 500 °C
The single reason to specify it. Tungsten carbide degrades in that range; chrome carbide holds hardness and oxidation resistance up to roughly 900 °C.
Erosion and hot corrosion in one coating
Fly-ash erosion and flue-gas corrosion usually attack the same component together. The carbide handles the particles and the NiCr matrix handles the chemistry.
Proven in boiler tube service
It is the established coating for waterwall and superheater tube protection, where the alternative is weld overlay at far greater cost and heat input to the tube.
Where It Is The Wrong Choice.
- Lower room-temperature abrasion resistance than WC-Co — do not specify it for cold sliding wear where tungsten carbide would serve better.
- Softer than tungsten carbide, so it is not a hard chrome replacement for hydraulic rod service.
- Line-of-sight process, with the usual constraints on bores and shadowed geometry.
Specify The Equipment For This Coating.
We manufacture the spray guns, plants, powder feeders, flow meters and blasting equipment that deposit Chrome Carbide (Cr₃C₂-NiCr) — built in Pimpri-Chinchwad, Pune and supplied across India and the Middle East. Tell us the component and the duty and we will specify against it.
Frequently Asked Questions.
Direct answers on specifying Chrome Carbide (Cr₃C₂-NiCr) thermal spray coatings.
When should chrome carbide be used instead of tungsten carbide?
Whenever the surface runs hotter than roughly 500 °C in service. Tungsten carbide is harder and wears better at room temperature, but it oxidises and degrades above about 500 °C, while chrome carbide in a nickel-chromium binder holds its hardness and oxidation resistance to roughly 900 °C. Below that crossover, specify tungsten carbide; above it, chrome carbide is the only sensible carbide choice.
How hard is a chrome carbide coating?
A chrome carbide coating sprayed by HVOF typically measures 800 to 1,000 HV0.3, with porosity of 1 to 2% and bond strength above 60 MPa to ASTM C633. Plasma-sprayed chrome carbide is more porous, which matters less in hot erosion service than it would in sliding wear. These are typical production figures for shortlisting, not guaranteed values for a drawing.
Which components are coated with chrome carbide?
Boiler waterwall, superheater and economiser tubes, ID and FD fan blades, casings and liners, exhaust valve seats, stems and faces, and steam turbine diaphragms and nozzle blocks. Fluidised bed combustor internals, hot mill rolls and hot gas ductwork are also common. In power generation the driving failure modes are fly-ash erosion and flue-gas corrosion, and the NiCr matrix addresses the second while the carbide addresses the first.
How is chrome carbide applied to boiler tubes?
Boiler waterwall panels and tube banks are coated by a dedicated tube mill coating plant that indexes the spray gun mechanically along the tube, rather than by handheld spraying. That is what gives a consistent thickness over the large areas involved. Metaflux Spray Solutions manufactures HVOF coating plants and tube mill coating plants in Pimpri-Chinchwad, Pune.