Metco 42C is Oerlikon Metco's martensitic stainless thermal-spray powder — essentially AISI 431 (17% Cr, 2% Ni, 0.18% C, Fe balance) water-atomized at -106 +45 microns for combustion powder Thermospray and atmospheric plasma spray. It's the workhorse answer when a worn steel shaft, pump sleeve, or hydraulic ram needs to come back to size with modest wear and corrosion protection on top.

431 stainless carries the best corrosion resistance of any martensitic stainless — Oerlikon's DSMTS-0080.7 says so — while keeping a usable hardness (HR15N 65, roughly 40-48 HRC as-sprayed). It drops onto carbon-steel substrates with negligible thermal-expansion mismatch, sprays thick for heavy rebuild work, and grinds to a good finish on silicon-carbide wheels. Materially cheaper than Ni-base Colmonoy or Co-base Stellite because iron is iron.

Pick it for shaft and sleeve build-up, dimensional restoration, automotive refurbishment, and general corrosion-plus-mild-wear duty on steel below 540°C (1,000°F). Above that, the martensite tempers and the coating softens — use a Ni-Cr overlay instead. For severe abrasion step up to a WC-Co cermet; for aggressive acid or chloride service, move to an austenitic stainless or Hastelloy. Qualified to MTU MTS 1049 and Rolls-Royce OMAT 3/45A and 3/103 for regulated aerospace work. Got a worn shaft or sleeve? Send us a sketch — we'll tell you if 42C fits.

Technical data

Hardness: APS as-sprayed: 271 HV0.3 microhardness per Oerlikon DSMTS-0080.7 — the martensitic matrix plus oxide network gives a harder splat than bulk-alloy HV numbers suggest; combustion-powder (Thermospray) deposits run slightly softer
Hardness (HRC): Macrohardness HR15N 65 per DSMTS-0080.7 (APS, TriplexPro-210) — rough HRC equivalent 40-48 as-sprayed, which tracks published 42-48 HRC ranges reported by industrial thermal-spray shops for 431-type martensitic deposits; bulk 431 SS in the quench-and-temper condition reaches 32-47 HRC for reference
Bond strength: Typical grit-blasted steel adhesion 4,000-6,000 psi (28-42 MPa) as-sprayed by APS or combustion powder — consistent with industry-published ranges for plasma-sprayed iron-base alloys; HVOF deposits of the companion Diamalloy 1002 powder are tighter and denser and typically reach the upper end of that band
Max service temp: 1,000°F (540°C) continuous per DSMTS-0080.7 — above this the martensite tempers, hardness drops, and the coating softens; brief excursions tolerable but wear and fatigue life degrade
Max service temp: 540°C continuous — hard ceiling on this alloy's usable range
As-sprayed porosity: 1.5 vol % APS per DSMTS-0080.7; combustion powder (Thermospray) deposits run higher, typically 2-5%; HVOF-compatible companion Diamalloy 1002 deposits <2%
Typical thickness: 10-40 mils (0.010-0.040 in / 250-1,000 microns) typical by combustion powder or APS; the DSMTS explicitly notes these materials 'can be sprayed very thick, allowing the coating to be utilized for rebuild or salvage of undersized parts' — build-up to 60-80 mils is common on heavy shaft and sleeve restoration
Density: ~7.7-7.8 (typical of 431-class martensitic stainless)

Where it earns its keep

Martensitic 431-type chemistry: the best corrosion resistance of any martensitic stainless in powder form, per Oerlikon's own DSMTS language — approaches 304 for pitting and crevice resistance
Drops onto steel substrates with minimal dilution concern — it IS essentially the same family of iron alloys as the substrate, so thermal-expansion mismatch is negligible
Can be sprayed very thick for heavy rebuild work — DSMTS explicitly highlights 'salvage of undersized parts' as a design intent
Materially cheaper per pound than nickel-base alternatives (Colmonoy, Hastelloy, Inconel) or cobalt-base (Stellite) overlays — iron is cheap, and this coating is iron with 17% Cr
Grindable to an excellent finish with silicon-carbide wheels; small sections machinable with carbide tools per the datasheet
Qualified to aerospace specs (MTU MTS 1049, Rolls-Royce OMAT 3/45A and 3/103) — documentation trail exists for regulated work
Sprays by every mid-shop process: combustion powder Thermospray, APS, and (in Diamalloy 1002 companion form) HVOF

Where it doesn't

Not as corrosion-resistant as austenitic 300-series stainless — for aggressive acid or chloride service, step up to an austenitic powder (Metco 45VF, Diamalloy 1003) or a Hastelloy-grade powder
Hard ceiling at 540°C / 1,000°F — above this the martensitic structure tempers and the coating softens measurably; do not spec this for hot-section or exhaust-manifold work
Moderate wear only — for high-stress abrasion, hard-particle erosion, or heavy galling, step up to a tungsten-carbide cermet (WC-Co, WC-CoCr) or a self-fluxing Ni-Cr-B-Si (Colmonoy-family)
As-sprayed coatings are NOT fully dense — 1.5% porosity in APS, higher in combustion powder. Where corrosion is the duty, Oerlikon recommends sealing with Metcoseal AP, especially on non-stainless substrates
Impact and shock loading are not this coating's strong suit — fair impact, not exceptional. Heavy impact service belongs to cobalt-base Stellite
Not self-fluxing — unlike Colmonoy, this does not fuse to the substrate. The bond is mechanical/metallurgical-splat, not a diffusion bond

Which process, when?

Combustion Powder Thermospray (CPS, oxy-fuel flame with powder injection) is the bread-and-butter Metco 42C process — it lays down thick, grindable deposits for heavy shaft and sleeve rebuilds at an honest price. Porosity runs 2-5% and bond is the usual grit-blast-and-splat mechanical/metallurgical bond; it's the right call when the part is coming back from worn-out and needs to be built back up to a grindable blank. Atmospheric Plasma Spray (APS) tightens the deposit meaningfully — 1.5% porosity and higher deposit efficiency per Oerlikon's TriplexPro-210 data — and is our pick for pump sleeves, precision shaft journals, and parts that need to hit tight dimensional tolerance after grind. HVOF isn't the primary process for Metco 42C itself (the particle size is too coarse); for HVOF work in this family, reach for the companion Diamalloy 1002 (similar to 420 SS, finer particle, optimized for HVOF) which produces denser, harder deposits (520-560 HV0.3) with less oxidation. Pick CPS for heavy build-up, APS for precision restoration work, Diamalloy 1002 HVOF when density and wear resistance trump cost.

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.

Oerlikon Metco DSMTS-0080.7 — Martensitic Stainless Steel Powders (Metco 42C, Diamalloy 1002)
“Metco 42C is a martensitic, high chromium stainless steel powder, similar to type 431 stainless steel; produces coatings that combine fair wear resistance and impact strength with the best corrosion resistance of any martensitic stainless steel. Nominal chemistry: Fe balance, 17 Cr, 2 Ni, 0.18 C. Particle size -106 +45 micron, water atomized, irregular morphology. APS coating properties: HR15N 65, HV0.3 271, porosity 1.5 vol %, deposit efficiency ~71%. Service temperature ≤ 540°C (1000°F). Qualified to MTU MTS 1049, Rolls-Royce OMAT 3/45A, Rolls-Royce OMAT 3/103.”
Oerlikon myMetco — Metco 42C Thermal Spray Powder Product Page
“Martensitic, high-chromium stainless steel powder similar to type 431; used for hard bearing surfaces (bearing journals, fuel pump rotors, sleeves), resistance to abrasive grains at low temperature (cylinder liners, pistons, pump plungers, hydraulic rams, crankshaft bearings), and resistance to hard surfaces and fretting; available in 5 lb and 20 lb stock quantities globally.”
AZoM — Stainless Steel Grade 431 (UNS S43100) Properties
“AISI 431 composition Fe/<0.2C/15-18Cr/1.25-3Ni/<1Mn/<1Si. Tensile strength 1,230-1,510 MPa (178-219 ksi). Fracture toughness 33-57 MPa·m^1/2. Rated excellent (5/5) for seawater and fresh water corrosion resistance; wear resistance 4/5. Density 7.7-7.9 g/cc.”
Abrams Industries — 431 Stainless Steel (1.4057 / X17CrNi16-2) Data Sheet
“Working hardness 32-47 HRC (~300-447 BHN). Good corrosion resistance in mild to moderate corrosive environments; susceptible to pitting in chloride-rich environments. Tempering range 600-650°C. Typical uses: compressor parts, fasteners, pump components, aircraft landing gear, automotive engine parts.”
Oerlikon Metco — Thermal Spray Materials Guide (2015)
“Martensitic stainless steel powders (Metco 42C, Diamalloy 1002) recommended for corrosion- and wear-resistant coatings, salvage and build-up of worn steel components, applied by combustion powder, atmospheric plasma spray, or HVOF; service below 540°C.”
Kermetico — Stainless Steel Thermal Spray Coating Materials
“Fe-based thermal-spray stainless coatings: flame spray produces porous coatings requiring 500+ micron (0.020 in) thickness for corrosion mitigation; HVOF coatings are adequate at 150 microns (0.006 in); HVAF metal coatings form an impermeable barrier at 100 microns (0.004 in).”
ASTM C633 — Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings
“Standard governing tensile-pull adhesion testing of thermal-spray coatings; industry-published bond-strength ranges for plasma-sprayed iron-base alloys on grit-blasted steel substrate typically fall in the 5-25 MPa range, with best-case HVOF and optimized plasma depositions reaching 40-70 MPa.”
Oerlikon Metco DSM-0257.0 — Martensitic Stainless Steel Powders (Diamalloy 1002 companion datasheet)
“Diamalloy 1002 (martensitic, similar to 420 SS) companion powder to Metco 42C; HVOF deposits reach 520-560 HV0.3 with <2% porosity; used where denser, harder wear surface is needed than combustion-powder Metco 42C provides.”

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.

Metco 42C

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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