A worn-out part does not always mean a scrapped part. Hard facing turns components headed for the scrap bin into assets that outperform the originals — and the gap between choosing the right alloy and the wrong one is the gap between a machine that runs for years and one that fails in weeks.
Quick Summary
- What this covers: The full hard-facing decision system — process fundamentals, all six major alloy families with hardness and resistance data, the role of dilution, plasma arc and laser cladding, chromium plating as a finishing complement, and a step-by-step selection framework.
- Why it matters: Surface failure, not bulk failure, ends the life of most industrial components. Hard facing lets you engineer the wear surface independently of the base metal — restoring worn parts at a fraction of replacement cost and building wear resistance into new parts from the start.
- The key insight: Hardness is the headline property, but it is never the whole story. Impact tolerance, hot hardness, abrasion mode, corrosion exposure, and machinability all trade against one another. Matching the failure mechanism to the alloy is the entire game.
- Who this is for: Maintenance engineers, welders, reliability teams, and design engineers responsible for components that wear — in mining, aggregate, agriculture, steel, cement, power, and general heavy industry.
Introduction: The Day the Crusher Stopped
Marcus Obi ran a mid-size aggregate operation. His primary jaw crusher — the workhorse responsible for breaking down 400 tons of raw limestone per shift — had been grinding slower for weeks. The manganese jaw plates were worn past their service limit. Replacement plates would consume a meaningful slice of his annual maintenance budget and take three weeks to ship.
His welder, Priya Nazari, walked the floor with him and pointed at the worn contact faces. "We don't replace these," she said. "We rebuild them."
What Priya proposed was hard facing — depositing a wear-resistant alloy directly onto the degraded surfaces to restore the plates to full service condition in days rather than weeks, at a fraction of replacement cost.
This is not a niche trick. Hard facing is one of the most powerful and most underused surface engineering methods in manufacturing. Whether you maintain mining equipment, rebuild agricultural implements, extend tool life, or design new components with built-in wear resistance, the leverage is enormous — if you select correctly.
This guide leaves nothing assumed. It walks through the process fundamentals, every major alloy family with its real hardness and resistance numbers, the application methods, the selection criteria, and the role of chromium plating as a complementary finish. By the end, you will be able to take any worn part and reason your way to the right surface.
Core Concepts: What Hard Facing Actually Is
Hard facing is a method of adding a coating, edge, or point of a metal or alloy capable of resisting abrasion, corrosion, heat, or impact to a metal component.
It applies equally to two situations:
- New parts — engineering a superior wear surface from the start.
- Old, worn parts — restoring, and often upgrading, degraded components.
The mental model is simple: you are giving a metal part an armor layer engineered specifically for the punishment it will take in service. The base metal handles structure; the deposited alloy handles the surface.
The Application Methods
Hard-facing materials are deposited by welding and spraying processes. The right method depends on part geometry, the alloy, the deposit quality required, and your production environment.
| Application Method | Process Type | Best For |
|---|---|---|
| Oxyacetylene gas welding | Manual welding | Precision deposits, small areas, repair work |
| Shielded-metal arc welding (SMAW) | Arc welding | General-purpose hard facing, field repairs |
| Submerged arc welding (SAW) | Arc welding | High-volume, flat-position deposits |
| Plasma arc welding (PAW) | Arc welding | Low dilution, high deposition rates |
| Inert-gas-shielded arc (GTAW/GMAW) | Arc welding (consumable & non-consumable electrode) | High-quality deposits, low oxidation losses |
| Thermal spraying | Spraying | Wire or powder coatings, rapid coverage |
| Laser cladding | Laser-based | Ultra-low dilution (below 2%), dense metallurgical bond |
Welding vs. Spraying: The Critical Distinction
Welding-based hard facing creates a metallurgical bond — the deposited alloy and the substrate fuse at the atomic level. This bond is extremely strong, but it introduces dilution: base metal mixes into the deposited layer and can reduce hardness and shift alloy properties away from their designed values.
Spraying creates a mechanical bond — the coating adheres by interlocking of sprayed particles. Porosity is generally higher, but the process covers large areas quickly with minimal heat input to the workpiece.
Laser cladding sits in its own category. It produces a dense, homogeneous, nonporous clad layer that is metallurgically bonded to the substrate, with dilution rates below 2% — against 5–15% for plasma arc and 20–25% for stick-electrode processes. The payoff is superior coating integrity with minimal alteration of the deposited alloy's intended properties.
The Dilution Problem
Dilution is the total volume of the surface layer contributed by melting of the substrate. It is the single most important variable governing the final hardness and performance of a hard-facing deposit.
<code>Dilution (%) = (Volume of base metal melted into deposit ÷ Total volume of deposit) × 100</code>
| Process | Typical Dilution |
|---|---|
| Laser cladding | below 2% |
| Plasma arc surfacing | 5–15% |
| Stick electrode (SMAW) | 20–25% |
The greater the dilution, the lower the hardness. This is precisely why arc-welded deposits consistently show wider hardness ranges than gas-welded deposits — more base-metal mixing means less predictable alloy properties in the deposited layer. Keep this in mind every time you read a hardness range below: the low end usually reflects high dilution, the high end low dilution.
How to Select a Hard-Facing Material
The first thing to consider when selecting a hard-facing material is the type of service the part will undergo. Get the wear mechanism wrong and no amount of hardness will save the deposit.
Beyond service conditions, weigh these factors:
- Machinability — Can you finish-machine the deposit after application, or must you grind it?
- Cost of the alloy — Does the material cost justify the performance gain for this part?
- Porosity of the deposit — Is a fully dense coating critical, or is slight porosity acceptable — even desirable, as in oil-retaining bearing surfaces?
- Appearance in use — Does the surface need to hold a polished or finished look?
- Ease of application — Can your shop deposit the material with existing equipment?
The Fundamental Rule
Generally, the greater the hardness of the facing material, the greater its resistance to abrasion and to shock or impact wear.
But hardness alone never tells the full story. Some alloys trade machinability for hardness. Others trade impact resistance for abrasion resistance. Selection is always a set of trade-offs — and the alloy guide below gives you the data to make those trade-offs deliberately rather than by guess.
The Hardenable Base Metals
Many hardenable materials can be used for hard facing: carbon steels, low-alloy steels, medium-alloy steels, and medium-high alloys.
None of these is outstanding for hard-facing service. They work as functional overlays where extreme wear resistance is not required, but for demanding duty you need one of the six specialized alloy families that follow.
Deep Dive: The Six Major Hard-Facing Alloy Families
This is the core of hard-facing material science. Each family occupies a distinct performance envelope defined by hardness, impact resistance, temperature capability, corrosion resistance, and machinability. Read each one against the failure mode you are fighting.
1. High-Speed Steels (RFe5 / EFe5)
Picture a production line where forming dies shape hot metal at temperatures approaching 1100°F. Ordinary tool-steel overlays soften and wear rapidly, the dies need regrinding every few shifts, and production stops each time. High-speed steels solve this by holding exceptional hardness at elevated temperature — the same property that makes them dominant in cutting-tool metallurgy.
Designations and forms
| Form | AWS Designation |
|---|---|
| Welding rod | RFe5 |
| Electrode | EFe5 |
Typical applications: cutting tools, shear blades, reamers, forming dies, shearing dies, guides, ingot tongs, broaches.
Hardness data
| Condition | Hardness (Rockwell C) |
|---|---|
| As-welded | 55–60 HRC |
| Annealed | 30 HRC |
| At 1100°F (service temperature) | 47 HRC (slow decline from 60 HRC) |
| At 1200°F | 30 HRC maximum |
The defining behavior: as-deposited hardness of 60 HRC falls off very slowly up to 1100°F, dropping only to 47 HRC. That retained hot hardness is what makes high-speed steels invaluable for elevated-temperature tooling overlays. Above 1200°F the advantage disappears as hardness collapses to 30 HRC.
Resistance properties
| Property | Rating |
|---|---|
| Impact resistance (as-deposited) | Medium |
| Impact resistance (tempered) | Appreciably increased |
| Oxidation resistance | Poor (high molybdenum content oxidizes readily) |
| Atmospheric corrosion resistance | Good |
| Liquid corrosive resistance | Not suitable |
Other characteristics: excellent metal-to-metal wear, especially at elevated temperature; outstanding hot-hardness retention (the family's signature); takes a high polish. For machining, the deposit must be annealed first; full hardness is then regained through subsequent heat treatment.
Where it fit — and where it didn't: High-speed steel was the wrong choice for Marcus's jaw crusher, which faced heavy impact, not heat. But Priya filed it away for another client running forming-die overlays at 900°F. At 55+ HRC retained at that temperature, die life tripled.
2. Austenitic Manganese Steels (EFeMn)
Marcus's jaw crusher plates took a literal pounding — impact from boulders dropping into the crushing chamber. This is the home territory of austenitic manganese steel, the one hard-facing family engineered specifically for high-impact, metal-to-metal wear.
Designations and forms
| Form | AWS Designation |
|---|---|
| Electrode | EFeMn |
Austenitic manganese steels are available primarily in electrode form for hard facing.
Typical applications: rock-crushing equipment, railway frogs and crossings, impact-wear surfaces, heavy-equipment buckets and teeth.
Hardness data
| Condition | Hardness |
|---|---|
| As-deposited | 170–230 BHN |
| Work-hardened (in service) | 450–550 BHN |
Here is the counter-intuitive part: as-deposited hardness is low — only 170 to 230 BHN. But austenitic manganese steels work-harden rapidly under impact. Every blow drives surface hardness upward, eventually reaching 450 to 550 BHN in service.
The work-hardening mechanism
<code>Surface hardness (in service) = f(Impact energy × Number of cycles)</code>
The yield strength of the deposited metal in compression starts low, but any compressive deformation rapidly raises it until plastic flow ceases. This self-strengthening behavior is an extraordinary asset in impact wear: the harder the service punishes the surface, the harder the surface becomes.
Resistance properties
| Property | Rating |
|---|---|
| Impact resistance | High — the defining property |
| Corrosion / oxidation resistance | Similar to ordinary carbon steels |
| Abrasion resistance (vs. hard abrasives like quartz) | Mediocre |
| Hot hardness | None — becomes brittle above 500–600°F |
Critical limitation: these steels have no practical hot hardness and turn brittle when reheated above 500 to 600°F. Hard facing with austenitic manganese steel must avoid overheating the deposit, and service temperatures must stay well below that threshold.
Machinability: difficult with ordinary tools — finished surfaces are usually ground. The work-hardened layer resists conventional cutting tools, the very property that makes the alloy excel in service.
Priya's call: This was the alloy for Marcus's crusher. Impact loading was severe, temperatures were ambient, and the self-hardening behavior meant the rebuilt plates would only get tougher. She deposited multiple passes of EFeMn electrode, building the worn faces back to original dimensions. Within a week the crusher was running. Within a month the surfaces had work-hardened to nearly 500 BHN — harder than the original plates had ever been new.
3. Austenitic High-Chromium Irons (RFeCr-A / EFeCr-A)
Not every wear problem involves impact. In agricultural equipment, coke chutes, steel-mill guides, sand-blasting cabinets, and brick-making machinery, the dominant failure mode is low-stress scratching abrasion — a constant grinding-away of surface material by hard particles sliding across it. Austenitic high-chromium irons are built for exactly this.
Designations and forms
| Form | AWS Designation |
|---|---|
| Welding rod | RFeCr-A |
| Electrode | EFeCr-A |
Typical applications: agricultural machinery parts, coke chutes, steel-mill guides, sand-blasting equipment, brick-making machinery.
Hardness data
| Condition | Hardness (Rockwell C) |
|---|---|
| As-welded | 51–62 HRC |
| At 900°F (instantaneous) | 43 HRC |
| At 900°F (3 minutes under load) | 37 HRC |
| At 1200°F (instantaneous) | 5 HRC |
| After cooling to ambient from hot test | Returns to approximately original hardness |
The hot-hardness profile reveals a hard design boundary. These alloys keep useful hardness up to roughly 800–900°F; above that, hardness degrades fast, hitting just 5 HRC instantaneous at 1200°F. The redeeming detail: the loss during hot testing is practically recovered on cooling — this is not the permanent softening most alloys suffer.
Resistance properties
| Property | Rating / Details |
|---|---|
| Impact resistance | Light impact only — deposits crack under heavy impact |
| Dynamic compression limit | 60,000 psi maximum — avoid higher stresses |
| Low-stress scratching abrasion | Outstanding — tied to hard carbide content |
| High-stress grinding abrasion | Mediocre — not suited to grinding service |
| Oxidation resistance | Good up to 1800°F |
| Hot wear resistance | Acceptable where hot plasticity is not objectionable |
| Liquid corrosion resistance | Poor — rusts in moist air |
| Stability vs. iron / steel | More stable than ordinary iron and steel |
The abrasion paradox — where engineers lose money: low-stress scratching resistance is outstanding, but high-stress grinding performance is only mediocre. The distinction is everything:
- Low-stress scratching — particles slide across the surface at low contact pressure (sand flowing through a chute, grain moving over a plow blade).
- High-stress grinding — particles are crushed between two surfaces at high contact pressure (crushing-chamber walls, ball-mill liners).
Specify high-chromium iron for a grinding application and the deposit will wear far faster than expected. The hard carbides that resist scratching cannot survive the fracture mechanics of high-stress grinding.
Mechanical properties
| Property | Value |
|---|---|
| Yield strength (0.1% offset, compression) | 80,000–140,000 psi |
| Ultimate strength (compression) | 150,000–280,000 psi |
| Tensile strength | Low — avoid tension loading in design |
Machinability: these deposits are considered commercially unmachinable and are also very difficult to grind. When grinding is required:
| Parameter | Recommendation |
|---|---|
| Abrasive type | Aluminum oxide |
| Grit size | 24 grit |
| Bond (off-hand, high speed) | Hard (Q), medium-spaced, resinoid |
| Bond (off-hand, low speed) | Slightly softer (P), vitrified |
4. Cobalt-Base Alloys (RCoCr / ECoCr)
At 1200°F and above, most hard-facing alloys have surrendered their hardness. Cobalt-base alloys are the exception, holding outstanding strength and hardness at elevated temperature where other materials fail.
Designations and forms
| Form | AWS Designation |
|---|---|
| Welding rod | RCoCr |
| Electrode | ECoCr |
Typical applications: exhaust-valve contact surfaces (aircraft, truck, and bus engines), valve trim in steam engines, pump shafts in combined corrosion-and-erosion service, high-temperature sliding-wear surfaces.
The three cobalt-chromium grades — running from impact-tolerant to maximum-hardness:
| Grade | Carbon Content | Primary Advantage |
|---|---|---|
| CoCr-A | Standard | Best impact resistance of the three; moderate hardness |
| CoCr-B | Higher | Greater hardness; reduced impact tolerance |
| CoCr-C | Highest | Maximum hardness and abrasion resistance; impact not expected |
Hardness data — gas-welded deposits
| Grade | Hardness (HRC) |
|---|---|
| CoCr-A | 38–47 |
| CoCr-B | 45–49 |
| CoCr-C | 48–58 |
Hardness data — arc-welded deposits
| Grade | Hardness (HRC) |
|---|---|
| CoCr-A | 23–47 |
| CoCr-B | 34–47 |
| CoCr-C | 43–58 |
Why the wider range for arc-welded deposits? The values depend primarily on base-metal dilution — the greater the dilution, the lower the hardness. Gas welding produces tighter ranges because it generally dilutes less than arc welding.
The exceptional hot-hardness property: many surfacing alloys are softened permanently by heating to elevated temperatures. Cobalt-base alloys are exceptional — they show lower hardness when hot, but return to their approximate original hardness on cooling. That reversibility is what makes them uniquely suited to thermal-cycling environments such as internal-combustion-engine exhaust valves.
Temperature service guidelines
| Temperature Range | Cobalt-Base Advantage |
|---|---|
| Below 1000°F | Other surfacing metals may prove better |
| 1000–1200°F | Advantages not definitely established |
| Above 1200°F | Considered advantageous — the sweet spot |
Resistance properties
| Property | Rating |
|---|---|
| Creep resistance (1000–1200°F) | Great |
| Scaling resistance (combustion products, incl. leaded fuels) | Excellent — chromium promotes a thin, adherent scale |
| Corrosion resistance (air, food, certain acids) | Good — field testing recommended |
| Metal-to-metal wear | Excellent — takes a high polish, low friction coefficient |
| Flow resistance and toughness | Inferior to tough martensitic steel deposits |
Machinability: CoCr-A is preferably machined with sintered-carbide tools; CoCr-B and CoCr-C become increasingly difficult as carbon content rises; CoCr-C deposits are finished by grinding, since machining is impractical.
5. Copper-Base Alloys
Not all hard facing chases extreme hardness. Bearing surfaces require a specific hardness relationship with their mating part; corrosion-resistant overlays need chemical stability. Copper-base alloys fill these roles with a range spanning soft bearing surfaces to hard wear plates.
Designations and forms — an extensive family of rods and electrodes:
- Rods: RCuAl-A2, RCuAl-B, RCuAl-C, RCuAl-D, RCuAl-E, RCuSi-A, RCuSn, RCuSn-D, RCuSn-E, RCuZn-E
- Electrodes: ECuAl-A2, ECuAl-B, ECuAl-C, ECuAl-D, ECuAl-E, ECuSi, ECuSn-A, ECuSn-C, ECuSn-E, ECuZn-E
Application guide by alloy group
| Alloy Group | Hardness (BHN) | Primary Applications |
|---|---|---|
| CuAl-A2 | 130–190 | Bearing surfaces, corrosion-resistant surfaces |
| CuAl-B, CuAl-C | 140–290 | Bearing surfaces (mid-range hardness) |
| CuAl-D, CuAl-E | 230–390 | Gears, cams, wear plates, dies — high-hardness bearings |
| CuSn (copper-tin) | Lower range | Corrosion-resistant surfaces, moderate wear resistance |
Hardness depends on the welding process and on how the metal is deposited:
| Welding Process | Relative Hardness | Reason |
|---|---|---|
| Inert-gas metal-arc (GMAW/GTAW) | Higher | Lower losses of Al, Sn, Si, Zn thanks to superior shielding from oxidation |
| Gas welding, metal-arc, carbon-arc | Lower | Greater oxidation losses reduce alloy content in the deposit |
Temperature limit: copper-base alloys are not recommended at elevated temperatures — hardness and mechanical properties decline steadily above 400°F.
Resistance properties
| Alloy | Impact Resistance | Notes |
|---|---|---|
| CuAl-A2 | Highest of all copper-base alloys | — |
| CuAl (increasing Al content) | Decreases markedly | Impact and aluminum content are inversely related |
| CuSi | Good | — |
| CuSn (as deposited) | Low | — |
| CuZn-E | Very low | — |
Corrosion resistance: except for CuSn-E and CuZn-E, copper-base alloys are widely used to resist many acids, mild alkalies, and salt water. The CuAl filler metals form a protective oxide on exposure to the atmosphere.
Abrasion limit: copper-base deposits are not recommended where severe abrasion occurs. Their strength is metal-to-metal wear, bearing service, and corrosion protection — not resisting hard-particle abrasion.
Bearing-surface selection rule: metals chosen for bearing surfaces should run 50 to 75 BHN below the mating surface. This differential makes wear occur preferentially on the bearing surface — which can be rebuilt by hard facing — rather than on the more expensive shaft or housing. Slight porosity is acceptable here, because a porous deposit retains oil for lubrication, a deliberate design advantage.
Mechanical properties in compression
| Alloy | Elastic Limit (psi) | Ultimate Strength (psi) |
|---|---|---|
| CuAl | 25,000–65,000 | 120,000–171,000 |
| CuSi | 22,000 | 60,000 |
| CuZn-E | ~5,000 | ~20,000 |
Machinability: all copper-base deposits can be machined — a significant advantage over the austenitic high-chromium irons and the harder nickel-chromium-boron grades.
6. Nickel-Chromium-Boron Alloys (RNiCr / ENiCr)
When a cement plant needed to rebuild the screws on its slurry pumps, conventional alloys presented a dilemma. The screws faced three failures at once: metal-to-metal wear, abrasive scratching from suspended solid particles, and constant corrosion from alkaline cement slurry. No single family seemed to cover all three. Nickel-chromium-boron alloys answered — combining metal-to-metal wear resistance, scratch-abrasion resistance, corrosion resistance, and retained hardness at elevated temperature. This is the multi-threat family of the hard-facing world.
Designations and forms
| Form | AWS Designation |
|---|---|
| Welding rod | RNiCr |
| Electrode | ENiCr |
The three NiCr formulations
| Grade | Hardness (rod, HRC) | Hardness (electrode, HRC) |
|---|---|---|
| NiCr-A | 35–40 | 24–35 |
| NiCr-B | 45–50 | 30–45 |
| NiCr-C | 56–62 | 35–56 |
The lower values and wider ranges of electrode deposits trace to the dilution of deposit and base metals — the same effect seen across every family in this guide.
Typical applications: seal rings, cement-pump screws, valves, screw conveyors, cams.
Hot-hardness data (600°F → 1000°F)
| Grade | Source | 600°F → 1000°F |
|---|---|---|
| NiCr-A | Electrode | 30 → 19 HRC |
| NiCr-A | Rod | 34 → 24 HRC |
| NiCr-B | Electrode | 41 → 26 HRC |
| NiCr-B | Rod | 46 → 37 HRC |
| NiCr-C | Electrode | 49 → 31 HRC |
| NiCr-C | Rod | 55 → 40 HRC |
Rod deposits consistently beat electrode deposits in hot hardness because of the lower dilution inherent in rod (gas welding) work.
Resistance properties
| Property | Rating |
|---|---|
| Light impact | Fair — deposits withstand it well |
| Plastic-deformation cracking | NiCr-C most susceptible; NiCr-A and NiCr-B more resistant |
| Oxidation resistance | Good up to 1800°F |
| Maximum service temperature | 1750°F (fusion may begin near this point) |
| Atmospheric / steam corrosion | Completely resistant |
| Salt water / salt spray | Completely resistant |
| Mild acids and common corrosive chemicals | Completely resistant |
| High-stress grinding abrasion | Not recommended |
| Metal-to-metal wear | Good |
| Galling resistance | Particularly resistant — especially NiCr-C |
| Surface polish | Takes a high polish under wearing conditions |
The galling resistance of NiCr alloys — NiCr-C above all — is a standout. Where two metal surfaces slide under high load (seal rings, valve seats), galling can destroy components in hours. NiCr deposits resist this failure mode exceptionally well.
Mechanical properties (compression)
| Property | Value |
|---|---|
| Elastic limit | 42,000 psi |
| Yield strength (0.01% offset) | 92,000 psi |
| Yield strength (0.10% offset) | 150,000 psi |
| Yield strength (0.20% offset) | 210,000 psi |
Machinability: NiCr deposits may be machined with tungsten-carbide tools using slow speeds, light feeds, and heavy, rigid tool shanks. They are also finished by grinding with a soft-to-medium vitrified silicon-carbide wheel.
Master Comparison: All Six Alloy Families at a Glance
This is the table to print and hang in the shop. When a worn part lands on the bench, it tells you where to start.
| Property | High-Speed Steel | Austenitic Mn Steel | High-Cr Iron | Cobalt-Base | Copper-Base | NiCr-Boron |
|---|---|---|---|---|---|---|
| Max hardness | 55–60 HRC | 450–550 BHN (work-hardened) | 51–62 HRC | 48–58 HRC (CoCr-C) | 230–390 BHN | 56–62 HRC (NiCr-C) |
| Impact resistance | Medium | High | Light only | Moderate | Varies by alloy | Fair (light) |
| Hot hardness | Good to 1100°F | None (brittle >500°F) | Good to 800–900°F | Excellent (>1200°F) | Poor (>400°F) | Good to 1000°F |
| Abrasion (low-stress) | Good | Mediocre | Outstanding | Good | Poor | Good |
| Abrasion (high-stress) | Good | Good (work-hardened) | Mediocre | Moderate | Not suitable | Not recommended |
| Corrosion resistance | Atmospheric only | Like carbon steel | Rusts in moist air | Good (air, food, acids) | Many acids, salt water | Excellent (atm, steam, salt) |
| Metal-to-metal wear | Excellent (hot) | Good (impact) | Low tension | Excellent | Good (bearings) | Good (anti-galling) |
| Machinability | Anneal first | Grinding only | Unmachinable | Carbide tools (A); grind (C) | All machinable | Carbide tools, slow |
| Max service temp | 1100°F | 500°F | 1800°F (oxidation) | 1200°F+ | 400°F | 1750°F |
| Typical use | Cutting tools, dies | Crushers, railway | Agri, sand-blast | Engine valves, pumps | Bearings, corrosion | Seals, valves, cams |
Application Processes in Depth
Plasma Arc Surface Coating: The High-Volume Method
When production demands rapid deposition, or when the substrate cannot tolerate heavy heat input, plasma arc surface coating becomes the process of choice.
Transferred-arc process. The arc strikes between the electrode and the workpiece, producing a true metallurgical weld. Arc temperatures run 25,000 to 50,000°F, and deposition is fast:
| Feed Method | Deposition Rate |
|---|---|
| Powdered alloy | Up to 15 lb/h (6.8 kg/h) |
| Wire feed | Up to 28 lb/h (12.7 kg/h) |
Base-metal dilution can be held below 5% if required — a major edge over conventional arc welding.
Non-transferred-arc process (metal spraying). The arc strikes between the electrode and the torch nozzle and does not attach to the workpiece. It is used for building up surfaces for hard facing and for applying anticorrosion and barrier layers. Over 500 powder combinations are available, and deposition rates can reach up to 100 lb/h (45 kg/h).
High-velocity plasma systems. Advanced systems at higher voltage produce plasma arc lengths at temperatures over 10,000°F, plasma velocity of roughly 12,000 ft/s, extremely dense coatings with under 1% porosity, across current ranges of 30 to 500 amps.
Laser Cladding: The Precision Alternative
Laser cladding is the highest-precision way to apply hard-facing material. A shaped or defocused beam heats preplaced or gravity-fed powdered alloy, which melts, flows across the substrate, and rapidly solidifies when laser power is removed.
Process variables: laser power, beam or part travel speed, clad thickness, substrate thickness, powder feed rate, shielding gas.
Compatible alloys — many of the same materials used in plasma arc or MIG cladding work with laser cladding: Stellites (cobalt-base), Colmonoys (nickel-base), carbide-containing alloys, Inconel, Tribaloy, Fe-Cr-C-X alloys, and tungsten and titanium carbides.
The key advantage — minimal dilution:
| Process | Typical Dilution |
|---|---|
| Laser cladding | below 2% |
| Plasma arc | 5–15% |
| Stick electrode | 20–25% |
The result is a dense, homogeneous, nonporous clad layer metallurgically bonded to the substrate — in contrast to the mechanically bonded, more porous layer from spraying.
Chromium Plating: The Finishing Complement to Hard Facing
Hard facing and chromium plating are not competitors — they are complements. Hard facing rebuilds geometry and provides bulk wear resistance. Chromium plating adds a final surface layer of extreme hardness and corrosion protection.
What it is. Chromium plating is an electrolytic process that deposits chromium on metals, either as protection against corrosion or to increase surface-wearing qualities.
The proof case — gages. The value of chromium-plating plug and ring gages has been demonstrated more thoroughly than any other single application. Chromium-plated gages not only wear longer, but when worn the chromium can be stripped and the gage replated and reground to size — effectively immortal, recyclable through plating-and-grinding cycles indefinitely.
Performance across materials. Chromium-plated tools have greatly improved performance on nearly every class of work material — brass, bronze, copper, nickel, aluminum, cast iron, steel, plastics, and asbestos compositions.
Tool types that benefit
| Tool Category | Examples |
|---|---|
| Cutting tools | Drills, taps, reamers, broaches, saws, thread chasers |
| Forming tools | Files, tool tips |
| Dies | Stamping, drawing, hot forging, die casting, plastics molding |
Preparation is decisive. Special care is essential in grinding and lapping tools before plating the cutting edges. The chromium deposit is influenced materially by the grain structure and hardness of the base metal; poor surface preparation leads to poor adhesion and premature flaking.
Plating thickness guidelines
| Application | Thickness Range |
|---|---|
| Standard tool plating | 0.0001–0.001 in. |
| Building up undersize tools (taps, reamers) | Up to 0.002 in. |
Step-by-Step Framework: Choosing the Right Hard-Facing Strategy
When a worn or new part arrives at the bench, work it through this sequence. The order matters — wear mechanism first, everything else after.
Worn or new part
↓
Step 1 — Identify the primary wear mechanism
↓
Step 2 — Evaluate secondary requirements (machining, corrosion, thermal cycling)
↓
Step 3 — Select the deposition method (control dilution)
↓
Step 4 — Specify post-processing (machine or grind)
↓
Return to service
Step 1 — Identify the Primary Wear Mechanism
| If the primary failure is... | Start with... |
|---|---|
| Heavy impact | Austenitic manganese steel (EFeMn) |
| Low-stress scratching abrasion | Austenitic high-chromium iron (RFeCr-A / EFeCr-A) |
| High-temperature wear (>1200°F) | Cobalt-base alloy (RCoCr / ECoCr) |
| Elevated-temperature tooling (<1100°F) | High-speed steel (RFe5 / EFe5) |
| Bearing surface / metal-to-metal wear | Copper-base alloy (select grade by hardness need) |
| Corrosion + wear + galling | Nickel-chromium-boron (RNiCr / ENiCr) |
Step 2 — Evaluate Secondary Requirements
- Must you machine after deposition? Eliminate high-chromium irons (unmachinable). Prefer copper-base (all machinable) or high-speed steels (machinable after annealing).
- Is the part in corrosive media? Eliminate high-speed and manganese steels. Prefer NiCr-boron (completely resistant to atmospheric, steam, and salt corrosion) or copper-base (resists acids, alkalies, salt water).
- Does the part thermally cycle? Cobalt-base alloys recover hardness on cooling; most others soften permanently. Austenitic high-chromium iron also recovers, within its lower temperature ceiling.
- Is dilution control critical? Use laser cladding (below 2%) or plasma arc surfacing (below 5%) rather than SMAW (20–25%).
Step 3 — Select the Deposition Method
| Priority | Recommended Method |
|---|---|
| Minimum dilution, maximum coating quality | Laser cladding |
| High volume, controlled dilution | Plasma arc surfacing (transferred arc) |
| Rapid large-area coverage, mechanical bond acceptable | Plasma arc spraying (non-transferred arc) |
| General-purpose, field-repairable | Shielded-metal arc welding (SMAW) |
| Precision deposits, small repair areas | Oxyacetylene gas welding |
| Superior shielding, minimum alloy loss | Inert-gas-shielded arc (GTAW/GMAW) |
Step 4 — Specify Post-Processing
| Alloy | Finishing Method |
|---|---|
| High-speed steel | Anneal → machine → heat treat to restore hardness |
| Austenitic manganese steel | Grind to finish (do not machine) |
| High-chromium iron | Grind only (Al₂O₃, 24-grit, hard bond) |
| Cobalt-base (CoCr-A) | Machine with sintered-carbide tools |
| Cobalt-base (CoCr-C) | Grind to finish |
| Copper-base (all) | Machine with standard tooling |
| NiCr-boron | Machine with WC tools (slow speed, light feed, rigid setup) or grind with SiC wheel |
Real-World Examples
The jaw crusher (heavy impact, ambient temperature). Marcus's manganese jaw plates were rebuilt with multiple passes of EFeMn electrode. The plates work-hardened toward 500 BHN in service and ran for fourteen months before needing attention again — longer than the originals had lasted, at roughly one-fifth of replacement cost, with downtime measured in days rather than weeks.
The forming die (elevated-temperature tooling). A second operation ran forming dies near 900°F. High-speed steel overlay (RFe5/EFe5) held 55+ HRC at temperature, tripling die life and removing the recurring regrind-and-stop cycle.
The cement-pump screw (combined wear, abrasion, and corrosion). Slurry-pump screws faced metal-to-metal wear, abrasive scratching, and alkaline corrosion simultaneously. Nickel-chromium-boron (RNiCr/ENiCr) covered all three failure modes at once, with NiCr-C's galling resistance protecting the sliding contact.
The recyclable gage (precision and corrosion). Plug and ring gages were chromium-plated; once worn, the chromium was stripped, the gage replated and reground to size, and returned to service — repeated indefinitely.
Common Mistakes
Confusing low-stress and high-stress abrasion. The most expensive error in hard facing. High-chromium iron is outstanding against sliding particles and only mediocre against crushed ones. Specify it for ball-mill liners or crushing-chamber walls and it wears out far faster than expected. Prevention: classify the abrasion mode before touching the alloy chart.
Treating hardness as the only spec. A 60 HRC deposit that cracks under impact, rusts in service, or can't be machined to tolerance is a failure regardless of its hardness. Prevention: read the resistance and machinability rows, not just the hardness row.
Ignoring dilution. Two shops can deposit the same electrode and get hardness 20 points apart purely from dilution. Quoting a deposit at its "as-welded" hardness while running a high-dilution SMAW process sets up a surprise. Prevention: match the process to the dilution you can tolerate, and verify hardness on the finished deposit, not from the datasheet.
Overheating manganese steel. Austenitic manganese steel embrittles above 500–600°F. Excessive interpass heat or grinding heat during rebuild can ruin the very toughness you deposited it for. Prevention: control heat input, keep deposits cool, and avoid heavy grinding passes.
Designing high-chromium iron in tension. Its tensile strength is low and it cracks under heavy impact. Using it where the part sees bending or shock loads invites fracture. Prevention: reserve it for compression-dominated, low-impact abrasion service.
Running copper-base or manganese steel hot. Copper-base properties fall off above 400°F; manganese steel has no hot hardness at all. Prevention: check the max-service-temperature row against the real operating temperature, including transient peaks.
Expert Insights
- Engineer the surface and the substrate separately. The deeper value of hard facing is decoupling. Use a cheap, tough base metal for structure and deposit exactly the alloy the surface needs. You are no longer forced to buy an expensive through-hardened part to get a hard surface.
- Let the service do your hardening for free. Austenitic manganese steel is the rare alloy that gets better the harder you hit it. In genuine high-impact duty, its low as-deposited hardness is a feature, not a weakness — the work-hardened skin forms over a tough core.
- Reversible hot hardness is worth more than peak hardness in thermal cycling. Cobalt-base alloys (and, within limits, high-chromium iron) recover their hardness on cooling. For valves and any component that heats and cools repeatedly, that recovery beats a higher cold hardness that softens permanently the first time it gets hot.
- Spend the dilution budget where it counts. If the deposited alloy's designed chemistry is critical to performance, the case for laser cladding or low-dilution plasma is strong even at higher process cost — you are paying to keep the alloy's properties intact. For rough build-up where bulk matters more than precise chemistry, high-dilution SMAW is perfectly economical.
- Stack hard facing and chromium plating for the toughest duty. Rebuild geometry and bulk wear resistance with hard facing, then add a thin chromium layer for surface hardness and corrosion protection. The two processes solve different parts of the same problem.
- Plan the finish before you weld. An unmachinable deposit on a tight-tolerance feature is a self-inflicted wound. Decide in advance whether the part will be machined or ground, and pick an alloy whose finishing method your shop can actually execute.
FAQ
What is hard facing?
Hard facing is a surface-engineering method that deposits a coating, edge, or point of a wear-resistant metal or alloy onto a component to resist abrasion, corrosion, heat, or impact. It applies to new parts (building in wear resistance from the start) and to worn parts (restoring and often upgrading them).
What is the difference between hard facing and chromium plating?
Hard facing rebuilds geometry and provides bulk wear resistance through a relatively thick deposited alloy layer. Chromium plating is a thin electrolytic surface layer that adds extreme surface hardness and corrosion protection. They are complementary — hard facing first, chromium plating as a finishing layer for the most demanding duty.
Which hard-facing alloy is best for impact wear?
Austenitic manganese steel (EFeMn). It deposits relatively soft at 170–230 BHN but work-hardens under impact to 450–550 BHN in service, making it the standard choice for crushers, railway frogs, and heavy-equipment teeth — provided service temperature stays below about 500°F.
What is dilution in hard facing, and why does it matter?
Dilution is the share of the deposited layer made up of melted base metal. The more base metal mixes in, the lower the hardness and the further the deposit drifts from its designed properties. Typical dilution runs below 2% for laser cladding, 5–15% for plasma arc, and 20–25% for stick electrode (SMAW).
What is the difference between low-stress and high-stress abrasion?
In low-stress scratching abrasion, particles slide across a surface at low contact pressure (sand in a chute, grain on a plow). In high-stress grinding abrasion, particles are crushed between two surfaces at high pressure (ball-mill liners, crushing chambers). They demand different alloys: high-chromium iron is outstanding for low-stress but only mediocre for high-stress.
Can hard-faced surfaces be machined?
It depends on the alloy. Copper-base deposits machine with standard tooling. High-speed steel must be annealed first, then heat-treated to restore hardness. NiCr-boron machines with carbide tools at slow speeds and light feeds. Austenitic high-chromium iron is essentially unmachinable and is finished by grinding, as are work-hardened manganese steel and the hardest cobalt grades.
Which alloy handles the highest temperatures?
Cobalt-base alloys (RCoCr/ECoCr) are the high-temperature choice, considered advantageous above 1200°F and uniquely able to recover their hardness after heating and cooling — ideal for engine exhaust valves and other thermal-cycling parts. NiCr-boron serves to about 1750°F before fusion concerns, and high-chromium iron resists oxidation to 1800°F though its hardness fades much earlier.
Does hard facing only repair worn parts, or can it improve new ones?
Both. On worn parts it restores dimensions and frequently produces a surface harder than the original. On new parts it lets you engineer the wear surface independently of the base metal — a tough, inexpensive substrate carrying a precisely chosen wear-resistant overlay. In that sense hard facing is a design strategy, not just a repair technique.
Which process gives the lowest dilution and highest coating quality?
Laser cladding, at below 2% dilution, producing a dense, nonporous, metallurgically bonded layer. Transferred-arc plasma surfacing is the next step, holding dilution below 5% with high deposition rates for higher-volume work.
Final Takeaways
- Match the failure mechanism to the alloy. Impact → manganese steel. Low-stress abrasion → high-chromium iron. High-temperature wear → cobalt-base. Hot tooling → high-speed steel. Bearings and corrosion → copper-base. Combined wear, corrosion, and galling → NiCr-boron.
- Hardness is necessary but not sufficient. Impact tolerance, hot hardness, abrasion mode, corrosion exposure, and machinability all trade off. Read the whole row, not just the number.
- Control dilution to protect the alloy you chose. The deposition method largely decides whether the deposit performs at its rated hardness. Laser and plasma preserve chemistry; SMAW dilutes it.
- Use hard facing and chromium plating together for the most punishing service — bulk wear resistance from one, surface hardness and corrosion protection from the other.
- Treat hard facing as a design strategy. Decouple structure from surface: cheap, tough base metal carrying exactly the overlay the duty requires. Rebuilds become upgrades.
The six alloy families here cover the large majority of industrial wear scenarios; the application methods span manual field repair to precision laser cladding; the framework gives a systematic path from worn part to rebuilt asset. The metallurgy is proven and the processes are mature. The only remaining variable is whether you apply them.
Your Next Step
Pull one component from your current maintenance backlog — the part that wears out most often, costs the most to replace, or causes the most downtime when it fails. Run it through the framework above: identify the primary wear mechanism, match it to an alloy family, choose a deposition method that controls dilution, and get a quote from a qualified hard-facing shop.
That one rebuilt component will teach you more about hard facing than any reference manual — and once you see the cost and performance firsthand, you will never look at a worn part the same way again.
Suggested Internal Links
Map these anchor topics to existing or planned posts on your site:
- "low-stress vs. high-stress abrasion" → a dedicated explainer on abrasion mechanisms and wear testing.
- "weld dilution and how to control it" → a process-focused article on dilution across welding methods.
- "laser cladding" → a deep dive on laser cladding parameters and economics.
- "thermal spray coatings" → a companion guide to thermal/plasma spray processes.
- "chromium plating" → a standalone piece on electrolytic chromium plating and tool reconditioning.
- "austenitic manganese steel" → a metallurgy primer on work-hardening alloys.
- "selecting welding consumables" → a practical guide to AWS filler-metal designations.
Suggested External References
For authoritative, citable sources on the standards and data behind this guide:
- AWS A5.13/A5.13M — Specification for Surfacing Electrodes for Shielded Metal Arc Welding (American Welding Society). Defines the EFe5, EFeMn, EFeCr-A, ECoCr, ENiCr, and copper-base surfacing electrode classifications.
- AWS A5.21/A5.21M — Specification for Bare Electrodes and Rods for Surfacing (American Welding Society). Defines the RFe5, RFeCr-A, RCoCr, RNiCr, and copper-base surfacing rod classifications.
- ASM Handbook, Volume 6 — Welding, Brazing, and Soldering (ASM International). Includes the hardfacing and weld-cladding reference material.
- ASM Handbook, Volume 18 — Friction, Lubrication, and Wear Technology (ASM International). The standard reference on wear mechanisms and material selection for wear.
- ASM Handbook, Volume 5A — Thermal Spray Technology (ASM International). Background on plasma and thermal-spray coating processes.
- Manufacturer technical literature for proprietary alloy families referenced above — Stellite and Tribaloy (cobalt- and Laves-phase alloys) and Colmonoy (nickel-base) — for application-specific data sheets and selection guides.