Transferred Arc Process
The transferred arc strikes between the electrode and the workpiece, producing a true metallurgical weld. Arc temperatures range from 25,000 to 50,000°F, and deposition occurs rapidly:
| 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) |
Dilution of the base metal can be held below 5% if required — a significant advantage over conventional arc welding methods.
Non-Transferred Arc Process (Metal Spraying)
In the non-transferred arc process, the arc strikes between the electrode and the torch nozzle — it does not attach to the workpiece. This process is used for:
- Building up surfaces for hard facing
- Application of anticorrosion and barrier layers
Over 500 different powder combinations are available, and deposition rates can reach up to 100 lb/h (45 kg/h).
High-Velocity Plasma Systems
Advanced systems operating at higher voltage settings produce:
- Plasma arc lengths at temperatures over 10,000°F
- Plasma velocity of approximately 12,000 ft/s
- Extremely dense coatings with less than 1% porosity
- Current ranges of 30 to 500 amps
Laser Cladding: The Precision Alternative
Laser cladding represents the highest-precision method for applying hard-facing materials. A shaped or defocused laser beam heats either preplaced or gravity-fed powdered alloys, which melt and flow across the substrate surface, rapidly solidifying 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 alloys currently used in plasma arc or metal inert gas cladding can be used with laser cladding:
- Stellites (cobalt-base)
- Colmonoys (nickel-base)
- Carbide-containing alloys
- Inconel
- Triballoy
- Fe-Cr-C-X alloys
- Tungsten and titanium carbides
The Key Technical Advantage: Minimal Dilution
| Process | Typical Dilution |
|---|---|
| Laser cladding | < 2% |
| Plasma arc | 5–15% |
| Stick electrode | 20–25% |
The result is a dense, homogeneous, nonporous clad layer that is metallurgically bonded to the substrate — in contrast to the mechanically bonded, more porous layer produced by spraying methods.
Chromium Plating: The Finishing Complement to Hard Facing
Hard facing and chromium plating are not competing processes — they are complementary. 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 of depositing chromium on metals either as a protection against corrosion or to increase the surface-wearing qualities.
The Gage Application: Proven Beyond Doubt
The value of chromium-plating plug and ring gages has been more thoroughly demonstrated than any other single application. Chromium-plated gages not only wear longer, but when worn, the chromium may be removed and the gage replated and reground to size. This makes the gage effectively immortal — it can be recycled through plating and grinding cycles indefinitely.
Performance Across Materials
Chromium-plated tools have given greatly improved performance on nearly all classes of materials:
- Brass, bronze, copper
- Nickel, aluminum
- Cast iron, steel
- Plastics, 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 |
Critical Preparation Requirements
Special care is essential in grinding and lapping tools preparatory to 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 of the chromium layer.
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. |
Decision Framework: Choosing the Right Hard-Facing Strategy
When a worn or new part arrives at your workbench, run through this decision tree:
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 exposed to corrosive media? Eliminate high-speed steels and manganese steels. Prefer NiCr-boron (completely resistant to atmospheric, steam, and salt corrosion) or copper-base alloys (resist acids, alkalies, salt water).
- Does the part experience thermal cycling? Cobalt-base alloys recover hardness on cooling. Most other alloys soften permanently.
- Is dilution control critical? Use laser cladding (<2%) or plasma arc surfacing (<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 |
The Universal Takeaway
the practitioner's rebuilt jaw crusher plates ran for fourteen months before needing attention again — longer than the original plates had lasted. The cost of hard facing was roughly one-fifth of full replacement. More importantly, the downtime was measured in days rather than weeks.
Hard facing is not a repair technique. It is a design strategy.
When you specify hard facing on new components, you are engineering the wear surface independently of the base metal. You can use inexpensive, tough base materials for structural strength and deposit exactly the alloy needed for surface performance. When you use hard facing for rebuilds, you are not merely restoring a part — you are upgrading it.
The six alloy families in this guide cover the vast majority of industrial wear scenarios. The application methods span from manual field repair to precision laser cladding. The decision framework gives you a systematic path from worn part to rebuilt asset.
Every worn surface is a decision point. Replace and spend, or rebuild and invest. The metallurgy is proven. The processes are mature. The only variable left is whether you apply them.
Your Next Step
Pull one component from your current maintenance backlog — the part that wears out most frequently, costs the most to replace, or causes the most downtime when it fails. Run it through the decision framework above. Identify the primary wear mechanism, match it to the right alloy family, and get a quote from a qualified hard-facing shop.
That single rebuilt component will teach you more about hard facing than any reference manual ever could. And once you see the cost savings and performance gains firsthand, you will never look at a worn part the same way again.
What is the most expensive wear problem in your operation right now — and which of these six alloy families would you use to solve it?