Frequently Asked Questions About Hardfacing Welds
Many industries operate equipment with components exposed to various types of destructive wear. But there is a solution. Hardfacing is a low-cost, effective tool that minimizes wear and extends the service life of components.
At first glance, hardfacing may seem confusing or complex — but it’s not.
Understanding a few basic principles about hardfacing will give you greater confidence when selecting the right products for your hardfacing applications.
Postle Industries, a leading manufacturer of hardfacing products, has compiled the following 22 frequently asked questions, designed to help you choose the most suitable solutions for your specific needs.
Frequently Asked Questions about Hardfacing
1. What is Hardfacing?
Metal parts often fail not because they break, but due to wear caused by abrasion, impact, metal-to-metal contact, or other types of wear that result in loss of dimensions and functionality.
Hardfacing, also known as hard coating or wear-resistant overlay welding, is the process of applying wear-resistant or buildup welding to the surface of a part to extend its service life. The weld deposit can be applied as a solid surface or in patterns like waffles, herringbone, or buttons.
Hardfacing can be used to recondition worn parts or on new parts to increase wear life before service.
Its importance continues to grow across industries that rely on equipment exposed to high wear. Postle Industries manufactures hardfacing products for mining, dredging, recycling, agriculture, railways, earth moving, construction, cement, forestry, energy generation, oil drilling, steelmaking, and forging. By extending the life of wear parts, companies save thousands of dollars and improve productivity.
There are three main types of hardfacing applications:
Build-up or rebuilding
Hardfacing or overlay
A combination of both
2. What base metals can be hardfaced?
Carbon and low-alloy steels with less than 1% carbon content are ideal for hardfacing. Medium-carbon and low-alloy steels are common due to their better strength and abrasion resistance. High-carbon alloys may require a cushioning or buffer layer before hardfacing.
Common base metals suitable for hardfacing:
Stainless steel
Manganese steel
Carbon and alloy steels
Cast iron
Nickel-based alloys
Copper-based alloys
Carbon and low-alloy steels are magnetic and distinguishable from non-magnetic austenitic manganese steel. Proper identification is critical to determine correct pre- and post-weld heat treatments, especially as alloy content increases.
3. What is the most commonly used welding process for hardfacing?
Listed in order of popularity:
Flux-Cored Arc Welding (FCAW) (open arc or gas-shielded)
Gas Metal Arc Welding (GMAW)
Shielded Metal Arc Welding (SMAW)
Submerged Arc Welding (SAW)
Gas Tungsten Arc Welding (GTAW)
Oxy-Fuel Welding (OFW)
Others: Plasma transferred arc, laser welding, thermal spray, etc.
Semi-automatic welding (FCAW, GMAW) is preferred due to high deposition rates and efficiency. SMAW remains popular for on-site repairs due to equipment portability.
4. Which process is most economical?
Deposition rate determines cost-efficiency. See table:
| Process | Deposition Rate (lbs/hr) |
|---|---|
| FCAW | 8–25 |
| GMAW | 5–12 |
| SMAW | 3–5 |
| SAW | 8–25 |
| GTAW | 3–5 |
| OFW | 5–10 |
5. How is wear categorized?
Major wear types (estimated % of total wear):
Abrasive wear: 40–50%
Impact wear: 20%
Metal-to-metal (adhesive): 15%
Heat: 5%
Corrosion: 5%
Other: 5%
Most failures are due to a combination (e.g., impact + abrasion). Identifying the wear type is crucial to selecting the right hardfacing alloy.
6. How are hardfacing alloys categorized?
Iron-based alloys can be divided into:
A. Martensitic – Tool steel-like, 20–65 HRC. Ideal for abrasion and metal-to-metal wear.
B. Austenitic – Manganese or stainless steel, work-hardening, impact-resistant.
C. Metal carbides in soft matrix – Chromium or tungsten carbides in soft matrix for severe abrasion.
D. Metal carbides in hard matrix – Tool-steel matrix with vanadium, niobium, etc., crack-resistant.
7. Is cracking normal in some alloys?
Yes. Chromium carbide-based alloys (e.g., Postalloy 2834-SPL) commonly crack to relieve stress. Austenitic and martensitic alloys typically don’t crack if properly applied.
8. What is check-cracking?
Check-cracking is a controlled, stress-relief cracking in chromium carbide overlays. Cracks run perpendicular to the weld bead and stop at the base metal. Use buffer layers if the base metal is brittle.
9. What is a chromium carbide overlay?
Iron-based alloys with >15% chromium and >3% carbon. Cracks are normal and relieve stress. Low friction, high abrasion resistance. Limited to 2–3 layers.
10. What are complex carbides?
Chromium carbide-based alloys with additions of niobium, tungsten, molybdenum, or vanadium for enhanced abrasion resistance at high temperatures.
11. What are carbides in martensitic matrix?
Tool steel-like matrix with compact carbide particles. Similar wear resistance to chromium carbides but without cracking. Suitable for multiple layers.
12. What is MIG-CARBIDE (CARBITEC)?
Process where tungsten carbide particles are dropped into the molten pool, forming extremely abrasion-resistant overlays, e.g., bulldozer blades, dragline buckets, etc.
13. What is hardfacing patterning?
Pattern welding (parallel, perpendicular, button, waffle, etc.) improves wear resistance based on material flow direction (rocks, sand, clay, etc.).
14. Can hardness predict abrasion resistance?
Not always. Two alloys with the same HRC may behave differently. Microstructure is more reliable. Use hardness comparisons only within the same alloy family.
15. How is wear measured?
ASTM G65 (dry sand/rubber wheel test) is a standard for measuring abrasive wear. Results are expressed in grams or volume lost.
16. What gases are used in GMAW hardfacing?
Low penetration is desired. Argon, argon-oxygen, or argon-CO₂ mixes are preferred. Pure CO₂ increases spatter.
17. What is globular transfer and why does it matter?
Globular transfer (large molten drops) promotes low penetration, ideal for hardfacing. Spray transfer (fine drops) is better for structural welding.
18. Should parts be preheated before hardfacing?
Yes, especially for high-carbon or alloy steels to prevent HAZ cracking. Manganese and some stainless steels don’t need preheating; keep them below 260°C (500°F).
19. When are cobalt or nickel-based hardfacing alloys used?
Cobalt: For abrasion at high temperature and some corrosion resistance.
Nickel: For corrosive and high-temperature environments. Can also contain borides.
20. Why are some overlays limited to 2–3 layers?
Chromium or complex carbides are brittle and prone to stress cracking. Limit to 2–3 layers unless buffer layers or procedures permit more.
21. What is a buildup or buffer alloy?
Used to:
A. Restore worn dimensions before hardfacing.
B. Serve as a cushion layer to prevent cracking into the base metal.
Soft mild steels like 7018 are unsuitable as buffers. Use tough manganese or alloy steels.
22. Can cast iron be hardfaced?
Yes, with proper preheat/interpass temperatures. Use nickel or iron-nickel for buildup, then apply a wear-resistant layer like carbides if needed.
