Abrasion-Erosion Performance of Novel Cr-Ni-Mo and Cr-Ni-Co Weld Overlay Alloys
1. Definition and Fundamental Principles
The study of abrasion-erosion performance for novel Cr-Ni-Mo and Cr-Ni-Co weld overlay alloys addresses one of the most demanding tribological challenges in industrial equipment protection. Abrasion-erosion (also termed cavitation erosion or erosion-abrasion) refers to the combined material removal mechanism where solid particles suspended in a fluid medium impact a surface at high velocity under conditions that may also induce microcavitation collapse. This dual-action degradation is far more severe than either erosion or abrasion alone, as the synergistic interaction between impact fatigue, cavitation bubble collapse, and particulate cutting accelerates surface failure by orders of magnitude.
The Cr-Ni-Mo alloy system leverages the hardening effect of molybdenum carbide (Mo₂C) precipitates within a Cr-Ni austenitic matrix, while the Cr-Ni-Co system benefits from cobalt's exceptional hot hardness retention, superior work-hardening capacity, and resistance to cavitation damage. Both alloy families are designed to deliver:
- High microhardness (typically 400–650 HV) achieved through solid solution strengthening and secondary carbide precipitation
- Excellent toughness to resist crack initiation under cyclic impact loading
- Corrosion resistance from the Cr-Ni austenitic base to prevent undercutting at crack tips
- Thermal stability maintaining hardness at elevated service temperatures (up to 600°C for Co-based variants)
The fundamental principle governing erosion-abrasion resistance is the balance between hardness (which resists particle cutting) and toughness (which resists fatigue crack propagation from repeated impacts). Neither extreme alone is sufficient; the optimal alloy must exhibit a hardness-to-toughness ratio that maximizes cumulative damage resistance under the specific particle size, velocity, and impact angle conditions of the service environment.
2. Category and Business Positioning
This technical entry falls squarely within the advanced weld overlay alloy development and qualification domain, representing the research-and-development arm of Cladding Technology Shanxi Co., Ltd.'s product portfolio. It bridges the gap between metallurgical research and production-ready overlay consumables, directly supporting the company's TIG/MIG weld overlay route as the primary delivery mechanism for these specialized alloys.
Within the company's business architecture, this capability serves three strategic functions:
- Consumable qualification — providing validated alloy formulations for custom overlay programs
- Technical authority — demonstrating deep metallurgical expertise to differentiate from commodity cladding suppliers
- Customer problem-solving — addressing applications where conventional Stellite or Cr-C-Ni overlays fail prematurely under severe erosion-abrasion conditions
The positioning of Cr-Ni-Mo and Cr-Ni-Co alloys as "next-generation" overlay materials reflects a deliberate strategy to move beyond standard UNS A-567/A-568/A-581 compositions toward proprietary or semi-proprietary formulations with demonstrably superior erosion-abrasion performance.
3. Technical Purpose and Value
3.1 Engineering Purpose
The primary purpose of this alloy development and qualification program is to extend service life of components subjected to combined erosion-abrasion-corrosion (EAC) degradation. In conventional applications using standard 309L, 310, or Stellite 6 overlays, service life under severe erosion-abrasion conditions may be limited to 6–18 months. The novel Cr-Ni-Mo and Cr-Ni-Co systems are designed to deliver 3–5× life extension in these demanding environments.
3.2 Quantifiable Value to Customer
- Reduced unplanned downtime — longer overlay life means fewer maintenance interventions in continuous-process industries
- Lower total cost of ownership — despite higher consumable cost per kilogram, the extended service interval reduces labor, production loss, and spare parts inventory
- Enabling of harsher service conditions — components can be designed for higher flow velocities or more abrasive slurries without proportional maintenance escalation
- Regulatory and safety compliance — failure of erosion-abrasion-critical components can lead to environmental releases or safety incidents; superior overlay performance mitigates this risk
4. Key Process and Implementation Points
4.1 Alloy Design Parameters
| Parameter | Cr-Ni-Mo System | Cr-Ni-Co System | Rationale |
|---|---|---|---|
| Base matrix | Cr 20–25%, Ni 20–25% | Cr 18–22%, Ni 12–16% | Austenitic stability for toughness |
| Hardness promoter | Mo 12–18% | Co 25–40% | Mo₂C precipitation vs. Co solid solution strengthening |
| Carbon content | 0.8–1.5% | 0.6–1.2% | Carbide formation without excessive brittleness |
| Titanium/Zirconium | Ti 0.5–1.5% | Zr 0.1–0.3% | Carbide control, grain refinement |
| Target as-welded hardness | 450–550 HV | 500–650 HV | Optimal erosion-abrasion resistance window |
| Target as-welded toughness | ≥ 10 J (Charpy V-notch) | ≥ 8 J (Charpy V-notch) | Crack resistance under impact cycling |
4.2 Weld Overlay Process Parameters
| Process Variable | TIG Overlay (GTAW) | MIG Overlay (GMAW) | Control Objective |
|---|---|---|---|
| Heat input | 0.8–1.5 kJ/mm | 1.0–2.0 kJ/mm | Prevent excessive dilution while ensuring full fusion |
| Travel speed | 40–80 mm/min | 60–120 mm/min | Control solidification rate for desired microstructure |
| Wire diameter | 2.4–3.2 mm | 1.6–2.4 mm | Match to deposit cross-section and layer thickness |
| Layer thickness | 3–6 mm per pass | 4–8 mm per pass | Minimize interpass dilution, maintain alloy integrity |
| Interpass temperature | ≤ 150°C | ≤ 200°C | Control grain growth, prevent sensitization |
| Shielding gas | Ar (99.99%) or Ar + 5% N₂ | Ar + 5–10% CO₂ or Ar + 2% O₂ | Stabilize arc, optimize wetting, control oxidation |
| Number of layers | 2–5 layers | 2–4 layers | Achieve target build-up with acceptable dilution profile |
4.3 Critical Implementation Considerations
- Dilution management — The first overlay layer typically experiences 30–50% base metal dilution, significantly reducing erosion-abrasion resistance. A minimum of 2 layers is required to achieve the specified alloy composition in the surface layer. For TIG processes, a pre-deposition of a transition layer (e.g., 309L) followed by 2–3 layers of the Cr-Ni-Mo or Cr-Ni-Co alloy is recommended.
- Microstructural control — The as-welded microstructure should be predominantly austenitic with fine, uniformly distributed carbides (Mo₂C in the Mo system; M₇C₃/M₆C in the Co system). Columnar grain structures oriented perpendicular to the surface are acceptable; equiaxed grain structures achieved through appropriate cooling rates are preferred for isotropic erosion resistance.
- Post-weld heat treatment — A solution treatment at 1050–1150°C followed by water quenching may be applied to homogenize the microstructure and dissolve coarse carbides. An optional aging treatment at 800–900°C for 2–4 hours precipitates fine secondary carbides for maximum hardness.
- Surface finish — Post-weld machining to Ra ≤ 1.6 μm is recommended for erosion-critical surfaces, as surface roughness accelerates cavitation initiation and particle cutting depth.
5. Applicable Standards and Acceptance Criteria
5.1 Material and Consumable Standards
- GB/T 13814 — Welding consumables for weld overlay (Chinese national standard for overlay consumable classification)
- ASTM A567 — Castings, cast weld overlays, and castings for repair, austenitic and austenitic-ferritic
- ASTM A568 — Castings, cast weld overlays, and castings for repair, cobalt-base
- ASTM A581 — Castings, cast weld overlays, and castings for repair, austenitic and austenitic-ferritic, cobalt-base, and nickel-base
- ISO 3677-1 — Welding consumables — Weld overlay consumables — Part 1: Specification for weld wires, rods, and electrodes
- GB/T 17493 — Welding consumables for weld overlay (Chinese standard for classification and specification)
5.2 Testing and Acceptance Standards
- ASTM G73 — Standard Practice for Laboratory Determination of Erosion Corrosion by Jet Impingement
- ASTM G74 — Standard Test Method for Determining the Abrasion Resistance of Metals by Dry Sand Rubber Wheel
- ASTM G111 — Standard Practice for Accelerated Laboratory Evaluation of the Resistance of Metals to Erosion-Corrosion by Air-Entrained Water
- ASTM G165 — Standard Practice for Laboratory Evaluation of the Resistance of Metals to Erosion-Corrosion by Air-Entrained Water
- ASTM G179 — Standard Test Method for Laboratory Determination of Resistance of Metals to Erosion-Corrosion by Air-Entrained Water
- ASTM G178 — Standard Test Method for Determining the Resistance of Metals to Erosion-Corrosion by Air-Entrained Water
- GB/T 16490 — Metallic materials — Test methods for cavitation erosion resistance
- ASTM E10 — Standard Test Method for Vickers Hardness of Metallic Materials
- ASTM E23 — Standard Test Method for Notched Bar Impact Testing of Metallic Materials
5.3 Acceptance Criteria
| Property | Acceptance Threshold | Test Method |
|---|---|---|
| Surface hardness (as-welded) | ≥ 450 HV (Cr-Ni-Mo); ≥ 500 HV (Cr-Ni-Co) | ASTM E10 |
| Erosion-abrasion mass loss rate | ≤ 50% of baseline (Stellite 6) under ASTM G73 conditions | ASTM G73 | Cavitation erosion mass loss | ≤ 0.5 mg/cm²/h at 1.25 MHz, 20°C | GB/T 16490 |
| Impact toughness (as-welded) | ≥ 8 J at 25°C (Charpy V-notch) | ASTM E23 |
| Dilution in surface layer | ≤ 15% base metal content (Fe, Si, Mn) | Optical emission spectroscopy / XRF |
| Microstructure | ≥ 80% austenite; no continuous intergranular carbide network | ASTM E3 (metallographic examination) |
| Weld defects (surface layer) | No cracks, porosity ≤ 1% area fraction | GB/T 11345 / ASTM E164 |
6. Common Risks and Controls
6.1 Metallurgical Risks
| Risk | Mechanism | Mitigation Strategy |
|---|---|---|
| Hot cracking | Solidification cracking in high-Cr, high-CaC alloy layers due to low melting point eutectics at grain boundaries | Control heat input; ensure adequate preheating (100–200°C); use low-sulfur, low-phosphorus consumables; maintain C ≤ 1.5% |
| Excessive dilution | Base metal alloying elements dilute overlay composition, reducing hardness and erosion resistance | Use narrow groove preparation (V-groove with 60° included angle); increase number of overlay layers; use TIG for first layer to minimize dilution |
| Coarse carbide precipitation | Slow cooling rates or excessive carbon content lead to large M₇C₃ particles that are easily pulled out during erosion | Control interpass temperature; optimize C content; apply post-weld aging treatment to refine carbides |
| Phase instability | σ-phase or δ-ferrite formation at elevated temperatures reduces toughness | Limit Cr content to ≤ 25%; avoid prolonged exposure in 500–800°C range; solution treat after welding |
6.2 Process Risks
- Porosity — Hydrogen porosity from moisture contamination is the primary porosity mechanism. Control: bake consumables at 200°C for 2 hours prior to use; ensure clean, dry base metal; use high-purity shielding gas (≥ 99.99%).
- Undercut and incomplete fusion — Particularly at layer-to-layer boundaries. Control: optimize torch angle (75–85° from horizontal); maintain consistent travel speed; use pulsed TIG or short-circuit transfer for MIG.
- Geometric distortion — High heat input causes warping of thin-wall components. Control: back-plate clamping; low heat input; intermittent welding sequence; post-weld stress relief at 650°C for 2 hours.
- Inconsistent layer quality — Operator variability affects dilution, porosity, and geometry. Control: automated TIG/MIG where possible; documented WPS with strict parameter windows; first-piece approval for each production batch.
6.3 Testing and Qualification Risks
- Test-to-service correlation — Laboratory erosion-abrasion tests may not replicate actual service conditions. Control: conduct service-specific test coupons alongside standard tests; use actual service slurry composition and flow velocity in accelerated testing.
- Sample representativeness — Test specimens must replicate production welding parameters and heat treatment. Control: coupon qualification as part of WPS qualification; test specimens welded simultaneously with production components.
- Aging degradation — Erosion-abrasion properties may degrade with time at elevated temperature due to carbide coarsening or phase transformation. Control: include thermal aging simulation in qualification testing (e.g., 600°C × 1000 h exposure prior to erosion testing).
7. Application Scenarios Across Technology Routes
7.1 TIG/MIG Weld Overlay (Primary Route for These Alloys)
The Cr-Ni-Mo and Cr-Ni-Co alloys are primarily delivered through TIG and MIG weld overlay processes, as these routes provide the best control over dilution, layer geometry, and microstructural refinement required for erosion-abrasion-critical applications.
- Hydropower turbine components — Runner blades, guide vanes, and stay vanes in hydroelectric turbines exposed to water-sand mixtures at velocities of 10–25 m/s. TIG overlay with Cr-Ni-Mo alloy applied in 3–4 layers over existing Stellite or 310 overlay.
- Coal-fired boiler components — Air preheater tubes, cyclone separator liners, and ash handling chutes exposed to fly ash erosion at 800–1200 m/s gas velocities. MIG overlay for production efficiency on large tube arrays.
- Slurry pump and valve components — Impellers, diffusers, wear rings, and valve seats in mining, mineral processing, and dredging applications. TIG overlay for precision components requiring tight geometry control.
- Marine propeller and rudder surfaces — Cavitation erosion protection on propeller blades and rudder surfaces exposed to bubble collapse at 15–25 m/s flow velocities. Cr-Ni-Co alloy preferred for superior cavitation resistance.
- Pulp and paper industry components — Refiner discs, screen bars, and pump impellers exposed to abrasive wood fiber slurries. TIG overlay with Cr-Ni-Mo alloy on refiner disc faces.
- Cement industry kiln components — Kiln shells, cyclone separators, and preheater tubes exposed to hot cement dust erosion at 400–800°C. MIG overlay for large surface areas; Cr-Ni-Co alloy for high-temperature sections.
7.2 Hydraulic Explosive Bonding (Secondary Route — Alloy Development Support)
While hydraulic explosive bonding is not the primary delivery method for these overlay alloys, the metallurgical knowledge gained from the Cr-Ni-Mo and Cr-Ni-Co erosion-abrasion research directly supports hydraulic explosive bonding capability in the following ways:
- Base material selection for clad plate — Understanding of Cr-Ni-Mo and Cr-Ni-Co microstructure and properties enables informed selection of overlay-side materials for hydraulic explosive bonded clad plates used in erosion-critical applications.
- Post-bonding heat treatment protocols — The solution treatment and aging parameters developed for weld overlay alloys inform the post-bonding heat treatment of explosion-bonded clad plates to optimize the diffusion zone properties for erosion resistance.
- Interface characterization — The metallurgical examination techniques developed for overlay qualification (hardness traverse, carbide mapping, phase identification) are directly applicable to bonded interface quality assessment.
- Composite structure design — For applications requiring both corrosion resistance (base plate) and erosion-abrasion resistance (overlay), hydraulic explosive bonding provides a base clad plate that can then receive a TIG overlay of Cr-Ni-Mo or Cr-Ni-Co alloy for maximum performance.
7.3 Explosion Welding (Explosion Cladding) — Alloy System Extension
Explosion welding provides an alternative route for delivering Cr-Ni-Mo and Cr-Ni-Co overlay layers with the following specific advantages and applications:
- Thick overlay layers — Explosion welding can produce overlay layers of 5–25 mm thickness in a single pass, compared to 3–6 mm per pass for TIG. This is advantageous for components requiring substantial material build-up where the erosion-abrasion layer must be thick enough to survive extended service without through-thickness wear.
- Large area coverage — For large components such as turbine casings, vessel heads, or structural plates, explosion welding provides uniform overlay coverage over areas that would be impractical for TIG/MIG overlay.
- Microstructural advantage — The extreme deformation during explosion welding produces a highly refined, work-hardened microstructure at the interface with no intermetallic compound formation. This provides excellent mechanical bonding without the dilution concerns inherent in fusion welding.
- Composite erosion-abrasion/corrosion resistance — Explosion-welded clad plates combining a Cr-Ni-Co overlay on a duplex stainless steel or carbon steel base provide simultaneous erosion-abrasion resistance (surface) and corrosion resistance (base), suitable for chemical processing equipment handling abrasive corrosive slurries.
7.4 Route Selection Matrix
| Application Requirement | Recommended Route | Rationale |
|---|---|---|
| Small precision components (impellers, valves) | TIG overlay | Best geometric control, lowest dilution, highest surface quality |
| Large flat surfaces (cyclone liners, kiln shells) | MIG overlay | Higher deposition rate, suitable for large area coverage |
| Thick overlay layers (>10 mm) on large plates | Explosion welding | Single-pass thick layers, no dilution, excellent bonding |
| Repair of existing components (in-situ) | TIG overlay | Mobile applicability, precision targeting of worn areas |
| Composite structures (corrosion + erosion) | Hydraulic explosive bonding + TIG overlay | Hybrid approach: bonded base for corrosion, overlay for erosion |
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The Cr-Ni-Mo and Cr-Ni-Co alloy development and erosion-abrasion qualification program directly supports the company's qualification infrastructure in multiple dimensions:
- WPS qualification expansion — Each new alloy requires a complete WPS qualification package including procedure qualification (IQI), performance qualification (welder certification), and product testing. This builds the company's WPS library and demonstrates procedural competency.
- NDT capability development — Qualification of these alloys requires advanced NDT including ultrasonic testing (GB/T 11345 / ASTM E164), radiographic testing (GB/T 3323 / ASTM E94), and magnetic particle testing (GB/T 26952 / ASTM E709) to detect overlay-specific defects.
- Metallurgical testing infrastructure — The program requires investment in and utilization of metallographic preparation, optical emission spectroscopy, hardness testing, and impact testing capabilities that benefit all overlay programs.
- Customer qualification packages — Completed erosion-abrasion test data packages can be presented to end customers as part of product qualification, reducing their risk assessment burden and accelerating procurement decisions.
8.2 Product Delivery Enhancement
- Custom alloy formulation — The ability to tailor Cr-Ni-Mo and Cr-Ni-Co compositions to specific erosion-abrasion conditions (particle size, velocity, temperature, corrosivity) enables truly customized product delivery rather than one-size-fits-all solutions.
- Predictable service life — With validated erosion-abrasion test data, the company can provide customers with quantified service life predictions, enabling better maintenance planning and reducing the "unknown" that often delays procurement.
- Accelerated delivery — Pre-qualified WPS and consumable specifications for these alloys reduce the qualification lead time for new projects, enabling faster project execution.
8.3 Customer Value Proposition
"The Cr-Ni-Mo and Cr-Ni-Co overlay alloy program represents our commitment to delivering not just weld overlay services, but erosion-abrasion engineering solutions backed by rigorous metallurgical research and standardized testing. Every overlay we apply is supported by quantified performance data, enabling our customers to make informed decisions about maintenance intervals, production planning, and total cost of ownership."
The value proposition extends beyond the immediate overlay application to encompass:
- Risk reduction — Validated performance data reduces the risk of premature overlay failure and associated production losses
- Technical partnership — The depth of metallurgical expertise positions the company as a technical partner rather than a commodity service provider
- Regulatory compliance support — Complete test data packages support customer regulatory submissions for critical equipment (nuclear, pressure vessels, marine)
- Lifetime cost optimization — Even at higher consumable costs, the 3–5× life extension provides compelling ROI for high-value equipment
9. Future Development Directions
The erosion-abrasion research program on Cr-Ni-Mo and Cr-Ni-Co alloys provides a foundation for several future development initiatives:
- High-temperature erosion-abrasion alloys — Extension of the Cr-Ni-Co system with additional W and Ta to maintain hardness above 800°C for superheater tube applications
- Multi-layer gradient overlay design — Sequential application of Cr-Ni-Co (surface) over Cr-Ni-Mo (intermediate) over 309L (transition) to optimize hardness, toughness, and bonding simultaneously
- Computational alloy design — Integration of thermodynamic modeling (CALPHAD) and microstructure prediction (phase field) to accelerate alloy development and reduce trial-and-error testing
- Field monitoring integration — Development of embedded sensors or optical inspection protocols to monitor overlay thickness loss in-service and predict remaining life
- Green manufacturing — Development of low-emission, low-waste overlay processes for these alloys to meet increasing environmental compliance requirements
10. Conclusion
The novel Cr-Ni-Mo and Cr-Ni-Co weld overlay alloys represent a significant advancement in erosion-abrasion protection technology, combining the proven corrosion resistance of Cr-Ni austenitic systems with the superior tribological properties of Mo and Co additions. Through rigorous qualification against international standards (ASTM G73, ASTM G74, GB/T 16490, ASTM E10, ASTM E23), these alloys provide quantified performance data that directly translates into customer value through extended service life, reduced downtime, and optimized total cost of ownership. Delivered through TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding routes, these alloys enable Cladding Technology Shanxi Co., Ltd. to address the most demanding erosion-abrasion protection challenges across power generation, mining, marine, cement, and pulp/paper industries with technical authority and measurable results.