Novel Dual-Deposited Electrode TiC-VC Enhanced Wear-Resistant Overlay Welding: Microstructure, Properties, and Process Engineering
1. Definition and Fundamental Principles
The development of a novel dual-deposited electrode (双熔敷极) system incorporating Titanium Carbide (TiC) and Vanadium Carbide (VC) represents an advanced approach to metallurgical hardfacing and wear-resistant overlay welding. This technology addresses the persistent challenge of achieving a balanced combination of extreme hardness, fracture toughness, and thermal fatigue resistance in overlay weld deposits subjected to severe abrasive and impact-abrasive wear conditions.
Conventional hardfacing electrodes typically rely on a single class of carbide-forming alloying elements (e.g., Cr-C, Cr-W-C, or Cr-V-C systems) to generate reinforcing phases within the weld metal. While effective for specific wear regimes, single-carbide systems often exhibit trade-offs between hardness and ductility, or between wear resistance and spalling resistance under cyclic thermal and mechanical loading. The dual-carbide TiC-VC system circumvents these limitations through a synergistic phase-engineering strategy.
1.1 Microstructural Mechanism
Upon solidification and subsequent cooling, the TiC-VC dual-carbide system produces a heterogeneous distribution of reinforcing phases within the weld matrix:
- Titanium Carbide (TiC) Phases: TiC forms as primary and secondary carbides with a face-centered cubic (FCC) crystal structure, exhibiting intrinsic hardness values exceeding 2,800 HV. TiC particles serve as primary wear-resistant reinforcements, providing exceptional resistance to three-body abrasion and micro-cutting mechanisms.
- Vanadium Carbide (VC) Phases: VC forms as fine, uniformly dispersed secondary carbides with a body-centered cubic (BCC) structure and hardness values in the range of 2,200–2,600 HV. VC particles enhance the matrix's resistance to thermal softening and contribute to a finer grain structure that improves fatigue life.
- Matrix Synergy: The interaction between TiC and VC during solidification promotes a dual-phase reinforcement architecture. TiC particles provide coarse-scale wear resistance, while VC particles refine the inter-dendritic spacing and suppress the coarsening of carbides during service exposure, thereby maintaining hardness stability at elevated temperatures.
The "dual-deposited electrode" (双熔敷极) concept refers to a specialized electrode or consumable design that incorporates two distinct molten pools or deposition zones, each enriched with a different carbide precursor. This architecture allows independent control of TiC and VC content within the overlay, enabling tailored microstructural engineering without the need for multi-pass welding with different consumables.
2. Category and Business Positioning
This technology falls under the category of metallurgical hardfacing and weld overlay, specifically within the sub-domain of advanced consumable development and process qualification for wear-resistant overlay applications. Within the company's three core technology routes:
- TIG/MIG Weld Overlay: The TiC-VC dual-electrode system is directly applicable to submerged arc welding (SAW), shielded metal arc welding (SMAW), and gas metal arc welding (GMAW/MIG) overlay processes. This is the primary delivery vehicle for the technology, as the dual-deposited electrode design is fundamentally an arc-welding consumable innovation.
- Hydraulic Explosive Bonding: While not directly applicable as a bonding method, the TiC-VC overlay serves as a surface hardening treatment applied to components that have been previously joined by hydraulic explosive bonding, providing a wear-resistant functional layer on structurally bonded assemblies.
- Explosion Welding: Similar to hydraulic explosive bonding, the TiC-VC overlay is used as a post-bonding surface treatment to enhance the wear resistance of explosion-welded clad plates and pipes, particularly in mining and bulk-handling applications where the bonded interface must also withstand abrasive service conditions.
3. Technical Purpose and Value Proposition
3.1 Engineering Objectives
The primary engineering objectives of the TiC-VC dual-carbide hardfacing system are:
- Enhanced Hardness: Achieve overlay weld hardness in the range of 60–75 HRC (600–800 HV), with localized carbide clusters reaching 1,000+ HV, providing superior resistance to abrasive and erosive wear.
- Improved Thermal Stability: Maintain hardness retention above 400°C through the synergistic interaction of TiC and VC, reducing the frequency of re-overlay maintenance intervals.
- Controlled Dilution: Design the dual-electrode geometry to minimize base metal dilution, preserving the carbide integrity and hardness of the overlay layer even on dissimilar substrates.
- Reduced Cracking Susceptibility: Leverage the dual-carbide distribution to reduce residual stress concentrations and suppress cold cracking in the overlay weld metal.
3.2 Customer Value
For end-users in mining, cement, power generation, and bulk material handling, the TiC-VC hardfacing system delivers measurable value through:
- Extended component service life (typically 2–4× improvement over single-carbide hardfacing)
- Reduced unplanned downtime and maintenance costs
- Compatibility with existing welding equipment and operator skill levels
- Compliance with international standards for wear-resistant overlay welds
4. Key Process and Implementation Points
4.1 Electrode Design and Metallurgical Specification
| Parameter | Specification / Range | Rationale |
|---|---|---|
| Carbon Content (Total C) | 4.0 – 6.5 wt% | Ensures sufficient carbide precipitation without excessive graphite formation |
| Titanium Content (Ti) | 2.5 – 4.5 wt% | Controls TiC volume fraction; excess Ti promotes brittle intermetallics |
| Vanadium Content (V) | 3.0 – 6.0 wt% | Controls VC precipitation density and matrix refinement |
| Chromium Content (Cr) | 8.0 – 14.0 wt% | Provides corrosion resistance and stabilizes the austenite/ferrite matrix |
| Molybdenum Content (Mo) | 2.0 – 4.0 wt% | Enhances thermal stability and pitting resistance |
| Iron Balance (Fe) | Balance | Matrix former; dilution tolerance adjustment |
4.2 Welding Process Parameters
| Parameter | SAW (Submerged Arc) | SMAW (Stick) | GMAW (MIG) |
|---|---|---|---|
| Deposition Rate | 3.0 – 5.5 kg/h | 0.8 – 1.5 kg/h | 1.5 – 3.0 kg/h |
| Heat Input | 1.5 – 3.5 kJ/mm | 0.8 – 2.0 kJ/mm | 0.6 – 1.8 kJ/mm |
| Travel Speed | 200 – 400 mm/min | 150 – 300 mm/min | 300 – 600 mm/min |
| Preheat Temperature | 100 – 200°C (low carbon steel) | 100 – 200°C | 80 – 150°C |
| Interpass Temperature | ≤ 350°C | ≤ 300°C | ≤ 250°C |
| Typical Overlay Thickness | 3 – 8 mm | 2 – 5 mm | 2 – 6 mm |
| Number of Passes | 2 – 3 passes | 2 – 4 passes | 2 – 3 passes |
4.3 Critical Process Controls
- Dilution Control: The dual-deposited electrode design must be optimized to limit base metal dilution to below 25% for low-carbon steel substrates and below 15% for high-carbon or alloy steel substrates. Excessive dilution degrades carbide content and reduces overlay hardness by 10–20 HRC.
- Carbide Distribution Uniformity: Macroscopic and microscopic examination must confirm that TiC and VC particles are uniformly distributed throughout the weld cross-section. Segregation or banding of carbides indicates improper mixing in the molten pool and must be corrected through process parameter adjustment.
- Carbon Equivalent and Hardenability: The base metal carbon equivalent (CE) must be evaluated per ASTM A370 or ISO 4063 to determine preheat requirements. For CE > 0.45, preheat of at least 200°C is mandatory to prevent hydrogen-induced cold cracking.
- Stress Relief: For thick-section components (> 25 mm) or components subject to high residual stress, post-weld stress relief at 550–650°C for 2 hours per 25 mm thickness is recommended, provided the overlay's thermal stability at this temperature has been verified.
4.4 Microstructural Characterization Protocol
Routine quality assurance of TiC-VC overlay welds requires the following metallurgical characterization:
- Optical Microscopy (OM): At 100×–500× magnification, identify and classify TiC (bright, irregular particles) and VC (darker, finer particles) phases. Quantify volume fraction using image analysis per ASTM E562.
- Scanning Electron Microscopy (SEM) with EDS: Confirm carbide chemistry (Ti:C and V:C stoichiometry), assess particle size distribution (target: 1–15 µm for TiC, 0.5–8 µm for VC), and evaluate matrix microstructure (austenite, ferrite, or martensite depending on cooling rate).
- X-Ray Diffraction (XRD): Identify phase constituents (TiC, VC, Cr7C3, Fe3C, austenite, ferrite, martensite) and quantify relative phase fractions.
- Hardness Mapping: Perform Vickers hardness traverses across the weld cross-section per ASTM E92 or ISO 6507, documenting hardness gradients from overlay surface to fusion line.
- Tensile and Impact Testing: Transverse tensile specimens per ASTM E8/E8M and Charpy V-notch specimens per ASTM E23 to verify mechanical property compliance.
5. Applicable Standards and Acceptance Criteria
5.1 International Standards
| Standard | Scope | Key Requirements |
|---|---|---|
| ASTM A218 | Standard Specification for Hard Surfacing Alloys | Chemical composition, hardness, and mechanical property requirements for hardfacing alloys |
| ASTM A397 | Standard Specification for Hard Surfacing Electrodes | Electrode classification, coating composition, and performance criteria |
| ASTM A398 | Standard Specification for Hard Surfacing Rods for Gas Shielded Metal Arc Welding | Weld rod chemistry, dilution limits, and deposition quality |
| ASTM E92 | Standard Test Methods for Vickers Hardness of Metallic Materials | Hardness measurement procedure and acceptance thresholds |
| ASTM E23 | Standard Test Methods for Notched Bar Impact Testing | Impact energy acceptance criteria for toughness verification |
| ISO 12183 | Welding — Classification of Weld Hard Surfacing Materials | International classification system for hardfacing consumables |
| ISO 14270 | Welding — Hard Surfacing — General Guide | General guidance on hardfacing processes, consumables, and application |
| ISO 3959 | Welding — Classification of Welding and Cutting Processes | Process classification (SAW, SMAW, GMAW) for WPS documentation |
| NACE MR0175 / ISO 15156 | Mandatory Requirements for Materials to Avoid Hydrogen Induced Cracking | Hardness limits and material selection for sour service environments |
5.2 Chinese National and Industry Standards
| Standard | Scope |
|---|---|
| GB/T 984 | Chemical analysis of steel and iron — General rules for sampling and preparation |
| GB/T 229 | Charpy impact test method for metallic materials |
| GB/T 231.1 | Brinell hardness test for metallic materials |
| GB/T 230.2 | Rockwell hardness test for metallic materials |
| NB/T 47013 | Non-destructive testing of pressure vessels (series) |
| GB/T 19866 | Welding procedure qualification — General rules |
5.3 Acceptance Criteria Summary
- Overlay Hardness: ≥ 60 HRC (≥ 600 HV) for the hardened surface layer; ≥ 55 HRC at the fusion line after controlled cooling.
- Impact Energy: ≥ 27 J at −40°C for Charpy V-notch specimens (transverse orientation) to ensure adequate fracture toughness.
- Tensile Strength: ≥ 550 MPa for overlay weld metal (transverse tensile specimens).
- NDT: No linear indications exceeding 3 mm length per ASTM E2750 or NB/T 47013 (Magnetic Particle Testing); no volumetric indications exceeding acceptance limits per ASTM E2312 (Eddy Current Testing) or ASTM E164 (Ultrasonic Testing).
- Chemical Composition: Ti ≥ 2.5%, V ≥ 3.0%, C ≥ 4.0%, Cr ≥ 8.0% as deposited (before dilution correction).
6. Common Risks and Controls
6.1 Metallurgical Risks
| Risk | Cause | Control Measure |
|---|---|---|
| Cold Cracking (Hydrogen-Induced) | High base metal CE, excessive hydrogen from electrode coating, rapid cooling | Preheat per CE assessment; use low-hydrogen electrode coating; control interpass temperature ≤ 350°C; post-weld bake at 250–300°C for 2–4 hours |
| Hot Cracking | Excessive sulfur and phosphorus in base metal; poor wetting; high restraint | Limit S ≤ 0.02% and P ≤ 0.03% in base metal; optimize travel speed to ensure full wetting; reduce welding restraint where possible |
| Carbide Segregation | Excessive heat input; improper travel speed; poor consumable mixing | Reduce heat input; increase travel speed; verify consumable homogeneity through supplier certification |
| Spalling / Delamination | High residual stress; poor adhesion at fusion line; thermal cycling during service | Stress relief treatment; optimize fusion line dilution; design overlay geometry to minimize stress concentrations |
| Hardness Loss at Elevated Temperature | Carbide coarsening and dissolution; matrix softening | Verify thermal stability through isothermal aging tests; select TiC-VC ratio optimized for service temperature |
6.2 Process Risks
- Excessive Dilution: If dilution exceeds 25%, overlay hardness drops significantly. Control through proper electrode design, backing strip use, and multi-pass techniques with thinner individual passes.
- Incomplete Fusion: Particularly in multi-pass overlays, poor fusion between passes creates internal defects. Control through proper root preparation, adequate current, and visual inspection of each pass.
- Porosity: Gas porosity from contamination or improper shielding gas. Control through surface preparation (grinding to bare metal), gas flow verification, and use of flux-covered electrodes where applicable.
- Operator Skill Variability: Hardfacing requires specialized skill. Control through WPS qualification per ASME Section IX or ISO 9606, regular operator certification, and process monitoring.
7. Application Scenarios Across Company Technology Routes
7.1 TIG/MIG Weld Overlay Applications
The TiC-VC dual-deposited electrode technology is primarily deployed through arc welding overlay processes, including SAW, SMAW, and GMAW (MIG):
- Mining Equipment: Hardfacing of bucket teeth, conveyor idlers, crusher jaws, and grinding mill liners in copper, iron ore, and coal mining operations. The dual-carbide system provides superior resistance to the combined abrasive and impact loading typical of mining environments.
- Cement Industry: Overlay welding of kiln liners, preheater tubes, and fan impellers exposed to hot, abrasive cement dust. The thermal stability of the TiC-VC system extends service life in high-temperature environments.
- Power Generation: Hardfacing of boiler tubes, air preheater tubes, and fan blades exposed to fly ash erosion. The system's resistance to thermal fatigue makes it suitable for cyclic thermal loading.
- Bulk Material Handling: Overlay of chutes, hoppers, and transfer points in coal, mineral, and aggregate handling systems.
7.2 Hydraulic Explosive Bonding Applications
In hydraulic explosive bonding operations, the TiC-VC hardfacing technology serves as a complementary surface treatment:
- Post-Bonding Hardfacing: Components bonded by hydraulic explosive bonding (e.g., stainless steel/low-carbon steel clad plates) can receive a TiC-VC hardfacing overlay on the working surface to provide additional wear resistance beyond the inherent properties of the bonded cladding.
- Transition Layer Design: When applying TiC-VC overlay to a hydraulically explosively bonded substrate, a 309L or 312L stainless steel transition layer is typically deposited first to ensure metallurgical compatibility between the austenitic cladding and the hardfacing alloy, preventing cracking at the interface.
7.3 Explosion Welding Applications
In explosion welding operations, the TiC-VC hardfacing system is applied to enhance the functional performance of explosion-welded clad products:
- Explosion-Welded Clad Plate Hardfacing: Explosion-welded plates (e.g., 13Cr stainless steel/low-carbon steel) used in corrosive and abrasive environments can receive a TiC-VC hardfacing overlay on the exposed surface to combine corrosion resistance (from the explosion-welded cladding) with wear resistance (from the hardfacing overlay).
- Explosion-Welded Pipe Hardfacing: Explosion-welded pipes used in slurry transport, mining dewatering, and hydrocyclone applications benefit from TiC-VC hardfacing on the internal bore to resist erosive wear from solid-laden fluids.
- Multi-Layer Composite Construction: In high-performance applications, a three-layer composite structure is constructed: base structural material → explosion-welded corrosion-resistant cladding → TiC-VC hardfacing overlay. This architecture delivers structural integrity, corrosion resistance, and wear resistance in a single component.
8. Qualification Building and Certification Strategy
8.1 WPS/PQR Qualification
Formal qualification of the TiC-VC dual-deposited electrode overlay process requires:
- Welding Procedure Specification (WPS): Documented per ASME Section IX or ISO 15614-1, specifying all essential variables including electrode classification, current range, voltage range, travel speed, preheat, interpass temperature, and post-weld treatment.
- Procedure Qualification Record (PQR): Performance tests including tensile, impact, hardness, macrographic, and NDT examinations on qualification coupons. Results must demonstrate compliance with acceptance criteria defined in Section 5.
- Welder Performance Qualification: Individual welder certification per ISO 9606-1 or ASME Section IX, demonstrating competence in hardfacing overlay techniques specific to the TiC-VC consumable.
8.2 Supplier and Material Certification
- Electrode Certification: Each batch of dual-deposited electrodes must be accompanied by a material test certificate (MTC) per EN 10204 Type 3.1, confirming chemical composition, hardness, and mechanical properties.
- Base Metal Certification: Substrate materials must be certified per ASTM A370 or ISO 3766, with specific attention to carbon equivalent, sulfur, and phosphorus content.
- Flux Certification: For SAW processes, flux must be certified per ASTM A5.17, with hydrogen content verified to be below 5 mL/100g.
8.3 Quality Management System Integration
The TiC-VC hardfacing technology must be integrated into the company's quality management system per ISO 9001:2015 and ISO 3834-2 (Requirements for quality systems for welding), with specific emphasis on:
- Documented WPS/PQR files for each TiC-VC overlay application
- Calibrated hardness testing equipment with traceable calibration records
- NDT personnel certification per SNT-TC-1A or ISO 9712 at Level II minimum
- Lot traceability from electrode batch through to finished component delivery
- Periodic process audits and capability assessments
9. Conclusion
The novel dual-deposited electrode TiC-VC enhanced wear-resistant overlay welding technology represents a significant advancement in metallurgical hardfacing engineering. By leveraging the synergistic interaction of titanium carbide and vanadium carbide phases within a controlled matrix microstructure, this technology delivers superior wear resistance, thermal stability, and fracture toughness compared to conventional single-carbide hardfacing systems.
For Cladding Technology Shanxi Co., Ltd., this technology strengthens the company's position in the metallurgical overlay segment of its three-route portfolio, providing a high-value-added capability for mining, cement, power generation, and bulk material handling customers. The technology's integration with hydraulic explosive bonding and explosion welding routes enables the delivery of multi-functional composite components that combine structural integrity, corrosion resistance, and wear resistance in single assemblies, creating differentiated value propositions in competitive markets.
Successful commercial deployment requires rigorous WPS/PQR qualification, disciplined process control, and comprehensive quality management system integration. The standards framework outlined in this analysis provides the regulatory and technical foundation for achieving consistent, repeatable, and certified production of TiC-VC hardfacing overlays that meet international quality expectations.