Cobalt Based Welding Wires: Types, Selection Guide, Quality Standards & Buying Tips for Industrial Buyers

Cobalt based welding wires—also referred to as cobalt-chromium (Co-Cr-W) hardfacing filler metals—are specialized consumables used to overlay surfaces that must resist abrasive wear, metal-to-metal galling, corrosion, and high temperatures. Commonly specified to AWS A5.21/ ASME SFA-5.21, these wires are widely applied on valve seats, pump sleeves, turbine components, and processing equipment in the oil & gas, power generation, chemical, and heavy machinery industries.
This guide explains the common grades, how to select the right alloy, applicable quality standards, and what to check before placing an order.
1. Common Types of Cobalt Based Welding Wires (AWS A5.21)
The most widely used cobalt alloy welding wires are classified under AWS A5.21. Each grade differs in carbon and tungsten content, which determines hardness, wear mechanism, and crack sensitivity.
AWS Grade
Industry Reference
Typical Hardness (HRC)
Key Characteristics
Typical Applications
ERCoCr-A
Alloy 6 type
37–43
Balanced wear & impact resistance, good corrosion & heat resistance up to ~650°C
Valve seats (gate/ball/globe), pump sleeves, turbine blade shields
ERCoCr-B
Alloy 12 type
40–47
Higher C & W than ERCoCr-A → greater abrasion resistance, slightly less ductile
Hot shear knives, extrusion screws, high-pressure valve trim
ERCoCr-C
Alloy 1 type
50–58
Highest carbide content, extreme abrasion resistance, more crack-sensitive
Crusher hammers, mixer paddles, severe-erode valve trim
ERCoCr-E
Alloy 21 type
25–35 (work-hardens)
Low carbon + Mo, excellent cavitation & corrosion resistance, low crack tendency
Petrochemical valve trim, steam turbine parts, marine engine seats
"Alloy 6 / 12 / 1 / 21 type" refers to generic cobalt alloy families historically associated with the Stellite™ brand (Kennametal). Reputable suppliers offer chemically and mechanically equivalent alternatives that conform to AWS A5.21.
Available forms:
GTAW (TIG) bare rods – straight lengths, typically 1.6 / 2.4 / 3.2 mm
GMAW (MIG) continuous wires on spools – commonly 0.8 / 1.0 / 1.2 / 1.6 mm
Flux-cored cobalt wires for open-arc or gas-shielded hardfacing (less common but available)
2. How to Choose the Right Cobalt Welding Wire – 4 Key Criteria
Selecting the correct grade is about matching the dominant wear mechanism, not simply choosing the hardest option.
① Identify the Primary Wear Mode
Metal-to-metal sliding + moderate impact + corrosion → ERCoCr-A (Alloy 6 type) – the industry default for general-purpose hardfacing.
Severe abrasive particles / scratching / minimal impact → ERCoCr-C (Alloy 1 type) for maximum carbide reinforcement.
Abrasion + some impact, less corrosion concern → ERCoCr-B (Alloy 12 type) sits between A and C.
Cavitation, corrosion, thermal cycling, low crack tolerance needed → ERCoCr-E (Alloy 21 type).
② Consider Service Temperature
Cobalt alloys retain useful hardness at 600–800°C (1100–1470°F). For continuous high-heat service with oxidation concern, ERCoCr-A and ERCoCr-E are preferred.
③ Evaluate Base Material & Crack Sensitivity
Higher carbon grades (ERCoCr-C) have greater check-cracking tendency. Preheat (typically 300–400°C / 570–750°F) and controlled interpass temperature are often recommended, especially on carbon or low-alloy steels.
④ Match Welding Process
TIG (GTAW): Best for thin overlays, valve seat resurfacing, precise control.
MIG (GMAW): Faster, suited for larger areas; requires consistent travel speed.
Confirm your supplier offers the correct form (rod vs spooled wire) and diameter for your equipment.
3. Quality Standards & Compliance to Verify
When sourcing cobalt based welding wires internationally, ask suppliers to confirm:
Specification Compliance: Manufactured to AWS A5.21 / ASME SFA-5.21 (US) and/or EN ISO 24373 / DIN 8555 (Europe).
Chemical Certification: Mill Test Certificate (MTC) / Certificate of Compliance showing Co, Cr, W, C, Si, Mn, Fe, Ni per AWSlimits.
Typical All-Weld-Metal Hardness: Verified by Rockwell C-scale test on a minimum 2–3 layer deposit (single-layer readings can be misleading due to dilution).
Surface & Packaging Quality: Wire should be bright, oxide-free, evenly cast/spooled, moisture-protected. TIG rods should be straight, burr-free, and properly bundled.
Traceability: Heat / Lot number printed on label and cross-referenced on MTC.
 4. Practical Buying Tips for Overseas Procurement
Request a Data Sheet First – Compare the nominal chemistry and typical hardness with AWS A5.21ranges before requesting samples.
Ask for a Sample Weld Test – Especially for critical valve or turbine applications, verify bead appearance, slag behavior (if flux-cored), and dilution effect on your base metal.
Clarify Diameter & Pack Size – Common export packs are 5 kg / 10 kg boxes for TIG rods and 5 kg / 15 kg spools for MIG wires. Confirm before ordering.
Check Lead Time & MOQ – Some ERCoCr-E (Alloy 21 type) or special diameters may have longer production cycles.
Verify Export Documentation – CO (Certificate of Origin), MTC, commercial invoice, packing list – essential for customs clearance.
5. Quick-Grade Selection Summary
General-purpose valve / pump hardfacing: ERCoCr-A (Alloy 6 type)
Higher abrasion, edge retention: ERCoCr-B (Alloy 12 type)
Extreme grit / particle erosion: ERCoCr-C (Alloy 1 type)
Corrosion + cavitation + thermal shock: ERCoCr-E (Alloy 21 type)
Need technical data sheets or a cross-reference table for AWS grades vs. common industry alloy designations?
Contact our technical team — we supply cobalt based welding wires in ERCoCr-A / B / C / E grades, TIG rods and MIG spools, with full MTC and export documentation.