Weld Overlay Process for Composite Wear-Resistant Material Fabrication
1. Definition and Fundamental Principles
Weld overlay technology for composite wear-resistant materials involves the deposition of one or more layers of specialized alloy onto a base substrate through arc welding processes to create a metallurgically bonded, functionally graded composite structure. The resulting clad component combines the toughness and formability of the base material with the exceptional hardness, abrasion resistance, and erosion resistance of the overlay alloy, delivering a dual-property material system that neither constituent can achieve independently.
The fundamental metallurgical principles governing this process include:
- Metallurgical Bonding: Complete fusion between successive weld passes and between the overlay and base metal, achieved through controlled heat input, proper preheating, and optimized welding parameters to ensure a diffusion-bonded interface free of delamination, porosity, or incomplete fusion.
- Functionally Graded Microstructure: Deliberate control of dilution rates (typically 10–30% base metal dilution in the first pass) to create a transition zone with progressively changing hardness and toughness, preventing catastrophic brittle failure at the interface.
- Carbide and Phase Engineering: Selection of overlay alloys whose solidification behavior produces hard carbides (WC, Cr₃C₂, Cr₇C₃, TiC), martensitic structures, or austenitic-carbide composites capable of resisting abrasive and erosive wear mechanisms.
- Thermal Cycle Management: Control of peak temperature, cooling rate, and interpass temperature to manage residual stresses, minimize cracking susceptibility, and achieve target microstructure in the weld metal and heat-affected zone (HAZ).
2. Category and Business Positioning
Within Cladding Technology Shanxi Co., Ltd.'s technical portfolio, weld overlay fabrication of composite wear-resistant materials occupies a central position as the primary process route for delivering high-performance tribological surfaces. This capability falls under the TIG/MIG Weld Overlay technology branch and serves as a foundational qualification for the company's broader cladding and composite material manufacturing business.
The business positioning of this capability is threefold:
- Core Manufacturing Capability: Provides the primary production method for wear-resistant liners, sleeves, hammers, chutes, and custom-shaped components where geometric complexity precludes explosion welding or hydraulic bonding.
- Qualification Foundation: Establishes the WPS (Welding Procedure Specification) database, welder performance qualifications, and NDT competency that underpin all other cladding operations, including transition layer welding for explosion-welded clad plate.
- Customer Value Differentiation: Enables the company to offer engineering-designed overlay systems tailored to specific wear mechanisms (abrasive, erosive, adhesive, corrosive-abrasive), providing customers with extended component life and reduced maintenance downtime.
3. Technical Purpose and Value
3.1 Engineering Objectives
The primary technical purpose of weld overlay fabrication of composite wear-resistant materials is to extend the service life of critical components subjected to severe mechanical wear by 3–20 times compared to unclad base material, while maintaining structural integrity and dimensional accuracy. Specific engineering objectives include:
- Achieving surface hardness of HV 500–1200+ depending on alloy system (high-carbon martensitic, carbide-composite, or austenitic)
- Maintaining base metal toughness and weldability for subsequent fabrication operations (bending, machining, assembly)
- Ensuring overlay-to-base bond strength exceeding 200 MPa in shear and 350 MPa in tensile per relevant standards
- Controlling residual stress to prevent deformation during or after welding
- Achieving overlay thickness uniformity within ±0.5 mm across the clad surface
3.2 Economic and Operational Value
For customers in mining, cement, power generation, and material handling industries, the investment in weld-overlay-clad components typically yields:
- Reduction in component replacement frequency by 60–90%
- Decreased unplanned downtime through predictable service life
- Lower total cost of ownership through elimination of frequent replacement cycles
- Reduced material consumption by replacing full-alloy components with clad (base + overlay) designs
4. Key Process and Implementation Points
4.1 Overlay Alloy Selection Matrix
| Alloy Category | Typical Composition | Achieved Hardness (HV) | Primary Wear Mechanism | Representative Standards |
|---|---|---|---|---|
| High-Carbon Martensitic | C 2.0–4.5%, Cr 18–25%, Mo 1–3% | 550–750 | Abrasive (clean, dry) | GB/T 11365, ASTM A516 equivalent |
| Carbide-Composite (High Cr) | Cr 28–36%, C 1.5–3.0%, Mo 2–5% | 600–900 | Abrasive + Corrosive | GB/T 11365, ISO 3677 |
| WC-Reinforced | WC 40–60%, Cr 20–30%, Fe balance | 800–1200 | Severe Abrasive | GB/T 11365, ASTM B592 (WC) |
| Austenitic (High Alloy) | Ni 12–18%, Cr 20–30%, Mo 6–12% | 350–500 | Erosive-Corrosive | ASTM A335 Gr. 9, ISO 3506 |
| Hardfacing Nickel-Alloy | Ni 60–70%, Cr 10–20%, Mo 2–5% | 350–450 | Slurry Erosion | ASTM B412, ISO 3677 |
4.2 Welding Process Parameters
| Parameter | TIG (GTAW) Overlay | MIG (GMAW) Overlay | Submerged Arc (SAW) Overlay |
|---|---|---|---|
| Welding Current | 100–250 A | 150–400 A | 300–600 A |
| Travel Speed | 20–60 mm/min | 100–300 mm/min | 200–500 mm/min |
| Heat Input | 0.5–1.5 kJ/mm | 0.8–2.5 kJ/mm | 1.5–4.0 kJ/mm |
| Shielding Gas | Ar / Ar+2%H₂ | Ar / Ar+5%CO₂ / Ar+2%O₂ | Flux (rutile/basic) |
| Typical Pass Thickness | 1.0–2.0 mm | 1.5–3.0 mm | 3.0–6.0 mm |
| Interpass Temperature | ≤150°C (martensitic) / ≤200°C (austenitic) | ≤150°C / ≤200°C | ≤200°C |
| Productivity | Low (precision applications) | Medium (general production) | High (large flat surfaces) |
4.3 Critical Implementation Steps
- Substrate Preparation: Machining of cladding surface to remove mill scale, oil, and contamination. Surface roughness Ra ≤ 6.3 μm. Bevel preparation (V-groove or U-groove) for thick overlay requirements to ensure adequate penetration and bonding.
- Preheating: Application of preheat temperature based on base material carbon equivalent (CE) and overlay alloy cracking susceptibility. Typical range: 150–300°C for low-alloy steels, 250–400°C for high-Cr martensitic overlays on carbon steel.
- Transition Layer Deposition: For dissimilar material combinations (e.g., Cr26 overlay on Q235/Q345 base), a 1–2 pass transition layer of 309L/310 stainless steel or equivalent is deposited first to arrest carbon diffusion and prevent intergranular cracking in the base metal HAZ.
- Overlay Pass Sequencing: Multi-pass deposition following the approved WPS, with careful attention to weave pattern, overlap (minimum 50% of wire diameter), and pass-to-pass cooling. Stringer beads preferred for carbide-containing alloys to prevent carbide spheroidization.
- Post-Weld Heat Treatment (PWHT): Tempering at 550–650°C for 2 hours per 25 mm thickness for martensitic overlays to reduce hardness from as-welded HV 800–900 to target HV 550–700 while eliminating residual stresses. Austenitic overlays typically require no PWHT.
- Dimensional Verification: Post-PWHT measurement of overlay thickness, surface flatness, and dimensional tolerance to ensure conformance to drawing requirements.
4.4 Multi-Pass Overlay Strategy
For overlay thicknesses exceeding 3 mm, a multi-pass strategy is essential to manage dilution, residual stress, and microstructure. The typical approach involves:
- First pass (bonding pass): Higher dilution accepted (20–30%); focus on achieving complete fusion and metallurgical bond. May use a slightly more ductile alloy to reduce cracking risk.
- Intermediate passes: Dilution decreases to 10–20% as the previous pass provides a compatible substrate. Full hardfacing alloy used.
- Final (capping) pass: Dilution < 10%; full alloy composition achieved. Surface quality and hardness uniformity critical. Often finished with a smooth, uniform bead profile.
5. Applicable Standards and Acceptance Criteria
5.1 Governing Standards
| Standard | Scope | Key Requirements |
|---|---|---|
| GB/T 11365-2008 | Welding consumables — Hardfacing electrodes | Chemical composition, hardness, impact toughness, dilution rate |
| GB/T 12469-2014 | Welded structures — General technical requirements | Weld quality, NDT requirements, documentation |
| NB/T 47014-2011 | Welding procedure qualification for pressure vessels | WPS qualification ranges, essential/non-essential variables |
| ASME Section IX | Welding, Brazing, Fusing and Bonding Qualifications | WPS/PQR qualification, welder performance qualification |
| ASTM A395 | Hardfacing electrodes and rods | Classification, chemistry, mechanical properties of deposit |
| ASTM E10 / E92 | Rockwell / Vickers hardness testing | Hardness verification methodology |
| ISO 9015-1 | Welding — Welding procedure qualification | Qualification parameters, essential variables |
| GB/T 3323-2005 | Non-destructive testing — Radiographic testing | RT acceptance criteria for weld overlay |
| GB/T 11345-2013 | Non-destructive testing — Ultrasonic testing | UT detection of lack of fusion, cracks |
| NACE MR0175/ISO 15156 | Materials for H₂S environments | Hardness limits, PWHT requirements for sour service |
5.2 Acceptance Criteria
- Visual Inspection (VT): No surface cracks, undercut > 0.5 mm, porosity clusters, or incomplete bead overlap. Surface appearance consistent with WPS requirements.
- Radiographic Testing (RT): Acceptance per GB/T 3323 Level B or ASME Section V Article 2. No linear indications (cracks, incomplete fusion) > 3 mm length. Porosity limited to 25% of weld area with individual pore diameter < 3 mm.
- Ultrasonic Testing (UT): Detection of subsurface lack of fusion and cracks per GB/T 11345. No reflections above 80% DAC at the bond line.
- Magnetic Particle Testing (MT): Surface and near-surface crack detection per GB/T 26955. No linear indications; round indications limited to 3 mm.
- Hardness Verification: Minimum 5 test points per 500 cm² of overlay area. Hardness within ±10% of specified value. For NACE MR0175 applications, maximum hardness ≤ 22 HRC (237 HB) in weld metal and HAZ.
- Bond Strength: Peel test or shear test demonstrating bond strength ≥ 200 MPa (per GB/T 11365 or customer specification).
- Impact Testing: Charpy V-notch impact energy ≥ 27 J at -20°C for transition layer (where specified for low-temperature service).
6. Common Risks and Controls
| Risk | Cause | Consequence | Control Measure |
|---|---|---|---|
| Hot Cracking in Overlay | Low melting point eutectics at grain boundaries; high sulfur/phosphorus in consumables | Surface cracks, overlay failure | Use low-S/P hardfacing consumables; optimize travel speed; maintain proper interpass temperature |
| Cold Cracking in HAZ | High CE base metal; hydrogen pickup; rapid cooling | HAZ cracking, structural failure | Preheat per CE-based calculation; use low-hydrogen consumables; controlled cooling rate |
| Lack of Fusion at Bond Line | Insufficient heat input; contamination; improper technique | Delamination in service; overlay spalling | WPS qualification with adequate heat input; thorough surface preparation; 100% UT/RT of bond line |
| Excessive Dilution | High heat input; large groove; improper wire/feed | Substandard hardness; reduced wear resistance | Control heat input per WPS; use multiple thin passes; verify hardness after each pass during qualification |
| Carbide Spheroidization | Repeated thermal cycles; excessive interpass temperature | Softening of overlay; loss of hardness | Stringer bead technique; control interpass temperature; limit number of passes over same area |
| Residual Stress and Distortion | High heat input; asymmetric cladding; no stress relief | Dimensional deviation; cracking in machining | Staggered welding sequence; back-step welding; PWHT; fixture design to restrain movement |
| Porosity | Contaminated surface; inadequate shielding; moisture in consumables | Reduced bond strength; NDT rejection | Surface cleaning to bare metal; adequate gas flow rate; consumable storage per manufacturer specification |
7. Application Across the Three Technology Routes
7.1 TIG/MIG Weld Overlay Route (Primary Application)
The weld overlay fabrication of composite wear-resistant materials is the flagship application of the TIG/MIG welding route. This route provides maximum flexibility in geometry, alloy selection, and thickness, making it suitable for:
- Complex-shaped components (cones, hoppers, chutes, curved liners)
- Repair and refurbishment of existing equipment
- Small-to-medium batch production with varying specifications
- Components requiring machinable overlay surfaces
- Multi-alloy layered systems (e.g., austenitic base + martensitic intermediate + WC-hardfacing cap)
The learning and mastery of weld overlay techniques for wear-resistant materials directly feeds into the company's TIG/MIG qualification portfolio, establishing WPS coverage for hardfacing applications per NB/T 47014 and ASME Section IX.
7.2 Hydraulic Explosive Bonding Route (Complementary Application)
In hydraulic explosive bonding (hydroforming/cladding), weld overlay serves a complementary role:
- Transition Layer Welding: When explosion-bonded clad plate is fabricated into pressure vessels or structural components, TIG/MIG weld overlay is used to build up transition layers between the clad face and the base material at joints, per ASME Section VIII and NB/T 47014 requirements.
- Edge Preparation and Finish: After hydraulic bonding, weld overlay may be applied to edges and surfaces requiring additional thickness or specific tribological properties not achievable through bonding alone.
- Repair Cladding: For bonded plate that sustains damage during fabrication, weld overlay provides a repair method to restore the wear-resistant surface.
7.3 Explosion Welding Route (Integration Application)
In explosion welding, the relationship with weld overlay technology manifests as follows:
- Post-Weld Cladding Enhancement: Explosion-welded clad plate (e.g., Cr26 on Q345) may receive an additional weld overlay cap layer to achieve higher hardness or specific surface chemistry not attainable through the explosion process alone.
- Joint Fabrication: Components made from explosion-welded clad plate require weld overlay techniques for joining, with special WPS development to maintain clad integrity at weld locations.
- Qualification Synergy: Welder qualifications obtained for weld overlay hardfacing directly support the welding qualifications needed for fabrication of explosion-welded clad components, creating an integrated qualification system.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The systematic development and documentation of weld overlay processes for composite wear-resistant materials establishes a comprehensive qualification framework:
- WPS Database: Each qualified overlay procedure (per alloy combination, base material, thickness, and process) becomes a reusable WPS under NB/T 47014 and ASME Section IX, reducing future qualification costs and accelerating project delivery.
- Welder Performance Qualification (WPQ): Welders qualified for hardfacing overlay possess skills transferable to all cladding welding operations, building a skilled workforce.
- NDT Competency: The rigorous inspection requirements for weld overlay (100% RT/UT for bond lines) develop NDT capabilities applicable across all three technology routes.
- Material Qualification: Hardfacing consumable qualification (chemistry, mechanical properties, dilution behavior) creates a verified supply chain for overlay materials.
8.2 Product Delivery Enhancement
Mastery of weld overlay for wear-resistant materials directly accelerates product delivery through:
- Established WPS coverage for common alloy combinations, eliminating the need for new procedure qualification on routine orders
- Optimized welding sequences and parameters that maximize deposition rate while maintaining quality
- Standardized inspection protocols that reduce rework rates and accelerate NDT throughput
- Proven PWHT cycles that minimize post-weld processing time
8.3 Customer Value Creation
The technical depth achieved through systematic study of weld overlay fabrication for composite wear-resistant materials translates into direct customer value:
- Engineering Design Support: Ability to recommend optimal alloy systems, thickness, and process routes based on specific wear mechanism analysis
- Extended Service Life: Delivered components with verified hardness, bond strength, and metallurgical quality that perform reliably in the harshest service conditions
- Compliance Assurance: Full documentation package (WPS, PQR, WPQ, NDT reports, hardness certificates) meeting international standards for regulatory and customer audit requirements
- Cost Optimization: Right-sizing of overlay thickness and alloy selection to balance performance with material cost, avoiding over-engineering
- Technical Partnership: Ability to support customers through failure analysis, process optimization, and on-site technical assistance, building long-term relationships
9. Conclusion
The weld overlay process for fabricating composite wear-resistant materials represents a core competency that underpins Cladding Technology Shanxi Co., Ltd.'s entire technical ecosystem. Through rigorous process development, qualification, and continuous learning, the company positions itself as a technically authoritative partner for wear-resistant cladding solutions. The knowledge gained from mastering overlay techniques for wear-resistant applications directly strengthens the company's capabilities across all three technology routes, enhances qualification depth, accelerates product delivery, and delivers measurable value to customers through extended component life, reduced downtime, and total cost of ownership reduction. This systematic approach to technical capability development ensures that the company maintains competitive advantage in the demanding market for engineered composite materials.