HTS Coatings — machining & grinding

400 Series Stainless Steel

0.3% C, 1% Ni, 1% Mn, 12–14% Cr, Fe-balance

  • Flame
  • Arc
  • Plasma
  • HVOF

400 Series Stainless Steel is the workhorse coating for the bread-and-butter rebuild jobs — worn pump shafts, scored hydraulic cylinders, grooved line shafts, fatigued turbine blades. Chemistry is simple: 12-14% Cr, 1% Ni, 1% Mn, 0.3% C, iron balance — the martensitic family that includes wrought 420, 410, and 431. The 12% chromium floor handles atmospheric and freshwater corrosion; the 0.3% carbon puts the as-sprayed deposit in the 40-45 HRC band and the quench-hardenable chemistry opens the door to 48-56 HRC after heat treat if the part can take it.

At HTS we apply 400-series most often by twin-wire arc spray — fast deposition on cylindrical work, 1/4"-plus build capability for badly worn shafts, bond strength near 10,000 psi on grit-blasted steel. For smaller precision parts and turbine blade repair we shift to plasma or HVOF with a Diamalloy-1002-class powder, trading throughput for density (<2% porosity), higher hardness (520-560 HV0.3), and smoother finish. Service ceiling is 540°C — above that the martensite over-tempers and a nickel-chrome or MCrAlY stack takes over.

Got a pump shaft scored below tolerance, or a hydraulic cylinder the chrome plater won't quote? Send us the part and the fits — we'll tell you whether 420 is the right rebuild, or whether you're in tungsten-carbide territory.

Technical data

Hardness
HVOF deposits 520-560 HV0.3 (Diamalloy 1002, ~type 420); APS deposits 271-536 HV0.3 depending on powder cut; arc-sprayed wire typically 350-450 HV as-sprayed
Hardness (HRC)
40-45 HRC as-sprayed (twin-wire arc, PMET 720-class wire); heat-treatable to 48-56 HRC after quench-and-temper (wrought 420 reference); HVOF Diamalloy 1002 equivalent reaches HR15N 84
Bond strength
Twin-wire arc approaches 10,000 psi (~69 MPa) on grit-blasted carbon steel; HVOF exceeds 11,600 psi (80 MPa); flame-spray wire/powder typically 5,000-8,000 psi (35-55 MPa); 410SS reference coating coupons measured 259-349 MPa in-plane strength
Max service temp
≤1000°F (540°C) continuous per Oerlikon Metco martensitic SS datasheet DSMTS-0080 — above this the matrix over-tempers and hardness drops
Max service temp
≤540°C continuous service; short excursions tolerated but hardness loss is the limiting factor, not oxidation
As-sprayed porosity
HVOF <2% (best-case Diamalloy 1002 coatings <0.3% with optimized twin-arc); APS 1.5-5%; twin-wire arc 3-8%; combustion flame 4-10% — porosity accepts oil and sealers, which is why arc-sprayed 420 holds lubrication on journal surfaces
Typical thickness
5-60 mils production range per HTS arc-spray envelope (0.005"-0.250"); twin-wire arc builds 1/4"+ for dimensional restoration; flame-spray wire practical to 80-100 mils; HVOF 5-20 mils for precision wear surfaces
Density
~7.70 (matches wrought 420 reference)

Where it earns its keep

  • Hits the 40-50 HRC hardness band as-sprayed — hard enough to live against journal bearings, soft enough to grind or turn without exotic tooling
  • Handles corrosion AND wear in the same deposit — the 12% Cr floor gives mild atmospheric and aqueous resistance where carbon-steel weld build-up rusts
  • Thick build capability — twin-wire arc routinely deposits 1/4" or more in a single setup, restoring badly worn shafts and cylinders that chrome plating can't practically fix
  • Strong chrome-plate alternative — no hex-chrome waste stream, no rinse tanks, no long-cycle plating bath; applied in hours rather than days
  • Grindable to bearing-fit finishes (16 Ra and below) with standard carbide tooling at low speed — no diamond wheels required the way WC-Co demands
  • Fast, economical application on large cylindrical work — twin-wire arc is the production workhorse for 20-foot shafts and 100-inch-diameter rolls

Where it doesn't

  • 540°C service ceiling — above 1000°F the martensitic matrix over-tempers and hardness falls; specify NiCrAlY or MCrAlY bond-coat-and-topcoat stacks for hot-section duty
  • Corrosion-resistant but NOT corrosion-proof — 12% Cr handles atmosphere and fresh water, NOT chlorides, strong acids, or sour H2S service (pick 316L, Hastelloy C-276, or Inconel 625 for those)
  • Arc-spray deposits run 3-8% open porosity — sealers (epoxy or phenolic) are recommended on hydraulic cylinder bores and pump wear surfaces exposed to pressurized fluid
  • Oxide stringers in twin-wire arc deposits reduce corrosion resistance vs wrought 420 — for corrosion-first duty step up to HVOF or sealed HVAF deposits
  • Hardness band sits below tungsten-carbide territory — if the duty is hard-particle abrasion or gouging at 60+ HRC equivalent, step up to WC-CoCr or Stellite 6/12
  • Post-spray heat treatment is possible but rarely done on sprayed deposits — wrought 420 hits 48-56 HRC after quench-and-temper; sprayed 420 is usually accepted in its as-sprayed 40-45 HRC state

Typical applications

  • Shaft build-up and dimensional restoration on worn pump shafts, motor shafts, and line shafts where corrosion and wear both matter
  • Hydraulic cylinder rods and hydraulic rams — chrome-plate alternative with similar hardness and better build thickness
  • Steam and low-pressure turbine blades — droplet-erosion protection and repair on stages that run cool enough (<540°C) to keep the martensitic matrix
  • Crankshaft journals, bearing journals, and wear-ring mating surfaces on stationary machinery
  • Cylinder liners, pump plungers, and piston rods in reciprocating machinery
  • Valve stems, seat surfaces, and mechanical seal faces where soft-dense 316L is too soft and a carbide is overkill
  • Press-fit bearing seats, machine bedways, and feed-roll surfaces resisting fretting
  • Wire-drawing capstans, pulleys, and sheaves where hard-surface wear meets mild corrosion
  • Salvage and rebuild of mis-machined or worn grindable steel parts before re-dimensioning
  • Hydroelectric valve trim, exhaust fans, and hydro-turbine components for mild-duty particle erosion

Wear modes addressed

  • Adhesive wear and galling on shaft journals and sliding fits
  • Abrasive wear from hard-particle contact at low-to-moderate temperature
  • Fretting wear at press-fits, bearing seats, and vibrating mating surfaces
  • Water-droplet and low-angle particle erosion on turbine blades and valve trim
  • Mild aqueous and atmospheric corrosion (the 12% Cr floor is the corrosion-resistance argument)
  • Cavitation on pump and hydro-turbine components (secondary — tungsten carbide does this better)

Industries

  • Pulp and paper (press rolls, dryer rolls, pump shafts, valve trim)
  • Hydropower and water / wastewater (turbine blades, valve trim, pump components)
  • Steel and aluminum processing (work rolls, levelers, tension rolls, run-out table parts)
  • Oil and gas (pump shafts, mud pump liners, valve bodies in mild-sour service)
  • Power generation (low-pressure turbine blade stages, feedwater pump shafts)
  • General manufacturing and machine rebuild (shafts, crankshafts, hydraulic rods, gearbox components)
  • Food processing and pharmaceutical (corrosion-resistant wear surfaces on mixers and conveyors)
  • Marine and offshore (deck machinery shafts, winch drums, mild-seawater service)

Substrates

  • Carbon and low-alloy steels (1045, 4140, 4340, A36) — the primary arc-spray substrate for shaft and cylinder work
  • Cast irons (gray, ductile) on engine and pump components
  • Austenitic stainless steels (304, 316, 316L) where a harder wear face is needed over a corrosion-resistant core
  • Tool steels and bearing steels (52100, D2) for localized repair
  • Existing 420 / 410 / 416 martensitic stainless shafts returning to OEM diameter after wear

Which process, when?

Twin-wire arc spray (TWAS) is the production workhorse for 400-series stainless on shafts, rolls, and cylinders. Fast deposition rate, 3-8% porosity, bond strength approaching 10,000 psi, and 1/4"+ build capability make it the right call for dimensional restoration work — pump shafts, crankshafts, hydraulic rods, paper-mill rolls. Combustion flame-spray wire (oxy-fuel wire pistol) covers the same duty at slightly tighter porosity (4-10%) and lower deposition rate; useful on smaller parts and field repairs where a pistol-and-bottles setup is easier to rig than a full arc-spray cell. Atmospheric plasma spray (APS) with Metco 42C or Diamalloy 1002 powder delivers denser deposits (1.5-5% porosity) with higher hardness (HR15N 65-79) — picked when a harder, denser 420-class surface is needed on smaller precision parts and turbine blade repair. HVOF (Diamalloy 1002) is the high-end answer: <2% porosity, >11,600 psi bond, 520-560 HV0.3 hardness, smoother and less oxidized than any of the above. Pick arc-spray for throughput on big cylindrical work, flame for small parts and mobile repair, plasma for hardness-plus-density on precision jobs, HVOF when porosity is the failure mode.

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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