Bimetallic Wear-Resistant Weld Overlay Plate: High-Chromium Flux-Cored Wire Overlay Technology for Mine and Cement Industry Life Extension
1. Definition and Fundamental Principles
Bimetallic wear-resistant weld overlay plate is a composite engineering component constructed by depositing a high-chromium hardfacing alloy onto a ductile base material (typically Q235, Q345, or similar carbon/low-alloy steel) through either open arc (GMAW/MAG) or submerged arc (SAW) welding processes using flux-cored wire. The resulting product exhibits a bimetallic structure in which the overlay layer achieves surface hardness in the range of HRC 58–65, while the substrate retains full structural toughness and weldability. This combination delivers exceptional abrasive and impact wear resistance without compromising the base plate's ability to withstand mechanical loads, thermal cycling, and fabrication demands.
The metallurgical principle underlying this technology relies on the formation of a high-volume fraction of hard carbides—predominantly Cr₇C₃ and Cr₂₃C₆—within a tough martensitic or austenitic matrix. Chromium content in the overlay alloy typically ranges from 15% to 35% by weight, depending on the specific flux-cored wire composition. The extremely hard carbide particles resist micro-cutting and ploughing mechanisms that dominate abrasive wear in mining and cement processing environments. The base metal provides a ductile backing that absorbs impact energy and prevents catastrophic brittle fracture propagation from the overlay layer.
The bonding between overlay and substrate is achieved through a metallurgical weld fusion mechanism, producing an integral joint with no interface delamination risk under normal service conditions. The dilution ratio between base metal and overlay alloy—typically controlled between 15% and 30%—is a critical parameter that directly influences the final hardness, toughness, and crack susceptibility of the composite plate.
2. Category and Business Positioning
Within the company's product portfolio, bimetallic wear-resistant weld overlay plates occupy a strategic position in the wear-resistant products category. This product line directly addresses the most economically significant pain point in mining and cement industries: the rapid degradation of wear-critical components due to abrasive particle impact and sliding wear. The technology bridges the gap between standard carbon steel components (which fail prematurely under abrasive service) and fully alloyed wear-resistant castings (which are prohibitively expensive and difficult to fabricate).
The business positioning of this product is characterized by three key value propositions:
- Cost efficiency: Utilizing low-cost base plate with high-value overlay layer achieves 60–70% cost reduction compared to monolithic high-chromium alloy castings while delivering comparable or superior wear performance.
- Fabrication flexibility: Unlike cast components, weld overlay plates can be cut, formed, drilled, and welded in the field to accommodate custom geometries and retrofit requirements.
- Service life extension: Typical field performance data demonstrates 3–8 times the service life of uncoated carbon steel components, directly translating to reduced downtime, lower spare parts inventory, and improved operational availability.
3. Technical Purpose and Value Creation
3.1 Mine Industry Applications
In mining operations, bimetallic overlay plates serve as critical wear protection for material handling systems that process abrasive ore, coal, and tailings. Chutes,溜槽 (chutes), and transfer hoppers experience severe sliding abrasion from angular mineral particles traveling at high velocity. The HRC 58–65 overlay layer resists micro-cutting wear mechanisms, extending component life from weeks to months or even years in moderate service conditions.
3.2 Cement Industry Applications
In cement manufacturing, the overlay technology protects classifier vanes (选粉机叶片), grinding mill liners, and material transfer hoppers (料斗) from the combined effects of abrasive cement clinker particles and high-temperature thermal cycling. Cement kiln dust and raw meal exhibit exceptional hardness (Mohs 6–7) and angularity, creating severe abrasive conditions that rapidly degrade unprotected steel components.
3.3 Quantifiable Value Metrics
| Value Metric | Typical Improvement | Measurement Basis |
|---|---|---|
| Service life extension | 3–8× vs. uncoated carbon steel | Field replacement interval comparison |
| Cost per ton of material processed | 40–60% reduction | Lifecycle cost analysis (LCA) |
| Unplanned downtime | 50–70% reduction | Equipment availability tracking |
| Spare parts inventory | 30–50% reduction | Stock rotation analysis |
| Installation labor | Comparable to standard steel | Field fabrication and welding time |
4. Key Process and Implementation Points
4.1 Base Plate Preparation
The base plate preparation is the foundation of overlay quality. The following requirements must be met:
- Material specification: Q235B, Q345B, or equivalent carbon/low-alloy steel conforming to GB/T 709 or GB/T 1591.
- Surface preparation: Grind or blast to Sa 2.5 per ISO 8501-1, removing rust, scale, oil, and moisture. Surface roughness should be 40–80 μm Ra to promote mechanical keying.
- Preheating: For plates thicker than 20 mm or in cold ambient conditions (below 5°C), preheat to 100–200°C per WPS requirements. For Q345 base materials, preheat to 150–250°C to minimize hydrogen-induced cracking risk.
- Geometry: Bevel the overlay edge at 30°–45° to ensure full penetration of the first overlay pass into the base material.
4.2 Flux-Cored Wire Selection and Classification
The flux-cored wire is the primary determinant of overlay performance. High-chromium flux-cored wires for this application are classified as follows:
| Wire Type | Cr Content (%) | C Content (%) | Achieved Hardness (HRC) | Matrix Structure | Typical Application |
|---|---|---|---|---|---|
| Type A (Medium Cr) | 15–20 | 2.0–2.8 | 58–62 | Martensitic | Sliding abrasion, moderate impact |
| Type B (High Cr) | 25–30 | 2.5–3.5 | 62–65 | Martensitic + Carbides | Severe sliding abrasion |
| Type C (Ultra-high Cr) | 30–35 | 3.0–4.0 | 63–65 | Martensitic + Cr₇C₃ | Extreme abrasion, impact loading |
4.3 Open Arc (GMAW/MAG) Overlay Parameters
Open arc welding using flux-cored wire in short-circuit or spray transfer mode is preferred for thin plates (6–25 mm) and complex geometries where positional flexibility is required.
| Parameter | Typical Range | Notes |
|---|---|---|
| Wire diameter | 1.2–2.0 mm | 1.6 mm most common for general overlay |
| Wire feed speed | 5–9 m/min | Depends on wire diameter and gas mixture |
| Shielding gas | CO₂ or Ar/CO₂ (80/20) | CO₂ provides deeper penetration; Ar/CO₂ reduces spatter |
| Travel speed | 200–400 mm/min | Slower speed = lower dilution, higher hardness |
| Interpass temperature | ≤ 200°C | Monitor with magnetic or infrared thermometer |
| Number of passes | 2–4 layers | Minimum 2 passes for uniform hardness |
| Overlay thickness | 2–5 mm per pass | Total overlay: 6–15 mm typical |
| Bead overlap | 30–50% | Ensure complete coverage, no gaps |
4.4 Submerged Arc (SAW) Overlay Parameters
Submerged arc welding is preferred for large-format plates, high production volumes, and maximum overlay thickness. The flux blanket provides excellent deoxidation and controlled cooling rates.
| Parameter | Typical Range | Notes |
|---|---|---|
| Wire diameter | 2.4–3.2 mm | Flux-cored or solid wire with consumable flux |
| Current | 350–600 A | DCEN polarity standard |
| Voltage | 28–36 V | Higher voltage = wider bead, lower profile |
| Travel speed | 150–300 mm/min | Slower speed for lower dilution |
| Flux coverage | Complete, uniform | Flux must fully cover arc zone |
| Number of passes | 2–5 layers | Build-up to required thickness |
| Interpass temperature | ≤ 250°C | Lower than GMAW to control grain growth |
4.5 Multi-Layer Overlay Strategy
A typical multi-layer overlay sequence for achieving HRC 58–65 is as follows:
- Transition layer (if required): One pass of 309L or 312 stainless steel wire to reduce dilution from base carbon content and prevent cracking at the interface. This layer is 1.5–2.5 mm thick.
- Fill overlay layers: 1–2 passes of high-chromium flux-cored wire at moderate travel speed. These layers build bulk thickness and gradually increase carbon/chromium content.
- Surface overlay layer: Final 1–2 passes of high-chromium flux-cored wire at slower travel speed to minimize dilution and achieve target hardness. This layer is 2–3 mm thick and directly exposed to wear.
The dilution decreases with each successive pass: typically 30–40% in the first pass, 15–25% in the second pass, and 10–15% in the final surface pass. This progressive dilution reduction ensures the top layer achieves the highest hardness.
4.6 Post-Weld Treatment
Post-weld treatment is optional but can be beneficial in specific service conditions:
- Controlled cooling: Allow natural air cooling for most applications. Avoid water quenching which increases crack susceptibility.
- Stress relief: For heavily loaded components or thick plates (>25 mm), stress relieve at 550–600°C for 2 hours per 25 mm thickness. Note: tempering above 650°C will reduce overlay hardness by 5–10 HRC.
- Surface finishing: Light grinding of the overlay surface to remove wire overlap and create a uniform wear surface. Do not grind below 50% of the designed overlay thickness.
5. Applicable Standards and Acceptance Criteria
5.1 Material Standards
- GB/T 24187-2009: Welding consumables for hardfacing — Classification and specifications (applies to flux-cored hardfacing wire)
- GB/T 1952-2008: Carbon steel plates and hot-rolled plates for general use (base plate specification)
- GB/T 1591-2018: Structural steel plates for low-alloy high-strength (Q345 base plate)
- ASTM A743: Castings, iron-cast, for special purposes (reference for high-chromium alloy composition)
- ISO 14272-1: Welding consumables — Classification of hardfacing electrodes and wires
5.2 Process Standards
- GB/T 985-2008: Welding symbols and supplementary symbols on technical drawings
- GB/T 19866-2005: Welding procedure qualification and performance qualification
- GB/T 3375-2017: Welding terms and definitions
- ASME Section IX: Qualification rules for welding, brazing, and fusion bonding (WPS/PQR qualification)
- ISO 15614-1: Qualification testing of welding procedures for metallic materials — Fusion welding
- NB/T 47014-2011: Qualification and examination of welding procedures for pressure vessels
5.3 Acceptance Criteria
| Acceptance Parameter | Requirement | Test Method | Standard Reference |
|---|---|---|---|
| Surface hardness | HRC 58–65 | Rockwell C indentation | GB/T 230.1 / ASTM A262 |
| Hardness uniformity | ±3 HRC variation across surface | Grid pattern testing (5×5 points) | Company WPS specification |
| Overlay thickness | ≥ 80% of nominal at any point | Magnetic thickness gauge or cross-section | GB/T 13895 |
| Overlay/base bond | No delamination at interface | Macrographic examination or bend test | ASTM A270 |
| Surface cracks | Permissible per WPS (see Section 6) | Visual + PT inspection | GB/T 11345 / ASTM E165 |
| Base plate hardness | Unchanged from original specification | Rockwell B or Brinell | GB/T 231 |
| Base plate impact (if required) | ≥ 27 J at -20°C (Q345) | Charpy V-notch | GB/T 229 / ASTM E23 |
5.4 Non-Destructive Testing (NDT) Requirements
- Visual examination (VT): 100% of overlay surface. Acceptable: uniform bead pattern, wire overlap, minor surface cracks (≤0.5 mm wide, ≤50 mm long). Reject: undercut >2 mm deep, slag inclusion >5 mm, porosity clusters.
- Magnetic particle testing (MT): 100% of overlay surface for critical applications. Acceptable: linear indications ≤3 mm length. Reject: linear indications >3 mm, clustered indications.
- Ultrasonic testing (UT): For thick overlays (>10 mm) or critical applications. Detects subsurface delamination and lack of fusion.
- Hardness mapping: Grid pattern (typically 5×5 or 10×10 points) to verify uniform hardness distribution across the overlay surface.
6. Common Risks and Controls
6.1 Surface Cracking — The Critical Process Characteristic
The technical description explicitly notes that surface cracks are a normal process characteristic (表面裂纹为正常工艺特征). This is a fundamental metallurgical reality of high-carbon, high-chromium martensitic overlay deposits. The formation of micro-cracks is driven by:
- Thermal contraction mismatch: The overlay layer contracts more than the base during cooling, creating tensile stresses at the surface.
- High carbon and chromium content: These elements promote hard, brittle martensitic structures with limited plastic deformation capacity.
- Carbide network formation: Continuous carbide networks at grain boundaries reduce crack initiation stress.
- Rapid cooling rates: Thin overlay layers cool rapidly, promoting high hardness but also high residual stress.
Engineering control philosophy: Rather than eliminating all surface cracks (which would require reducing hardness below the target range), the industry standard approach is to control crack size, spacing, and morphology to ensure they do not compromise functional performance:
| Crack Parameter | Acceptable Limit | Control Measure |
|---|---|---|
| Crack width | ≤ 0.3–0.5 mm | Control interpass temperature, travel speed |
| Crack length | ≤ 50–80 mm | Optimize bead length, use back-step welding |
| Crack depth | ≤ 30% of overlay thickness | Multi-pass strategy, controlled dilution |
| Crack density | ≤ 3 cracks per 100 mm² | Process parameter optimization |
| Crack orientation | Random, non-directional | Varied welding sequence |
Crack control measures:
- Maintain interpass temperature between 100–200°C (not too hot, not too cold)
- Use back-step or interrupted welding sequences to distribute thermal input
- Employ slightly slower travel speed on the final surface pass to allow controlled grain growth
- Ensure proper wire stick-out (10–15 mm) for consistent arc stability
- Use dry, uncontaminated flux-cored wire stored at controlled humidity
- Apply controlled post-weld stress relief at 550–600°C if crack density is high
6.2 Other Common Risks and Controls
| Risk | Cause | Control Measure |
|---|---|---|
| Delamination at interface | Excessive dilution, contamination, inadequate preheat | Transition layer, clean base surface, proper preheat |
| Hardness below specification | Excessive base metal dilution, fast travel speed | Multi-pass strategy, slower travel speed, verify wire chemistry |
| Hardness above specification (excessive brittleness) | Very low dilution, rapid cooling | Control cooling rate, ensure minimum dilution |
| Base plate distortion | Excessive thermal input, asymmetric welding | Balance welding sequence, use backing plate, limit heat input |
| Hydrogen-induced cracking in base | Moisture in wire/flux, high carbon base, cold conditions | Preheat, dry consumables, post-weld heat treatment |
| Overlay spalling during service | Thermal fatigue, cyclic impact, insufficient overlay thickness | Ensure minimum overlay thickness, proper base preparation |
7. Application Scenarios Across Technology Routes
7.1 TIG/MIG Weld Overlay Route
The TIG (GTAW) and MIG (GMAW) weld overlay routes are the primary fabrication methods for bimetallic wear-resistant plates at Cladding Technology Shanxi Co., Ltd. This route offers maximum flexibility for:
- Custom geometries: Overlay on formed, bent, or complex-shaped base plates that cannot accommodate automated SAW equipment.
- Positional welding: Overlay in vertical, overhead, or angled positions for on-site repair and retrofit applications.
- Small batch production: Economical for short runs of specialized wear components.
- Transition layer deposition: TIG welding is ideal for the first transition pass (309L or 312) where precise arc control is needed.
- Flux-cored GMAW overlay: The primary production method for high-chromium overlay layers, combining high deposition rate with positional flexibility.
Typical implementation: TIG transition layer (1 pass, 1.5–2 mm) followed by 2–3 passes of flux-cored GMAW overlay at 1.6 mm wire diameter. Total overlay thickness: 8–12 mm. Achieved hardness: HRC 60–64.
7.2 Hydraulic Explosive Bonding Route
While bimetallic wear-resistant plates are primarily produced via weld overlay, the hydraulic explosive bonding (waterjet-assisted explosive welding) route can be applied in specific scenarios:
- Large-format wear plates: For plates exceeding 3000×2000 mm where weld distortion becomes problematic, explosive bonding can produce a metallurgical bond between a high-chromium overlay strip and a carbon steel base without thermal distortion.
- Multi-material combinations: When the overlay material is incompatible with welding (e.g., certain nickel-based or copper-based wear alloys), explosive bonding provides an alternative.
- Zero dilution requirement: In applications where absolute hardness consistency is required (no dilution variation), explosive bonding ensures 100% overlay composition in the surface layer.
Limitations: Explosive bonding requires precise velocity and angle control for metallurgical bonding of high-chromium alloys to carbon steel. The minimum practical overlay thickness is typically 2–3 mm, and surface roughness after bonding requires machining to achieve the final wear surface. This route is best suited for high-volume production of standardized plate sizes.
7.3 Explosion Welding Route
Explosion welding (airblast explosive welding) offers a production-scale alternative for bimetallic wear-resistant plate fabrication:
- High-volume production: For large quantities of standardized wear plates (e.g., 1000+ units per year), explosion welding provides consistent quality at lower per-unit cost.
- Thick overlay layers: Explosion welding can produce overlay layers of 3–8 mm without the dilution effects inherent to welding.
- Specialized overlay materials: Certain high-carbon, high-chromium alloys that are extremely difficult to weld (due to cracking sensitivity) can be bonded explosively and then machined to final geometry.
- Subsequent machining: The rough bonding surface is machined flat, providing a uniform overlay thickness and surface finish suitable for precision wear applications.
Process sequence for explosion-welded wear plate: Explode-bond high-chromium strip to carbon steel plate → Cut to size → Machine overlay surface to final thickness → Optional stress relief → Hardness verification → Deliver.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The bimetallic wear-resistant weld overlay plate technology contributes significantly to the company's qualification portfolio:
- WPS/PQR qualification: Each flux-cored wire type and process parameter combination requires a qualified Welding Procedure Specification (WPS) backed by a Procedure Qualification Record (PQR) per GB/T 19866 or ASME Section IX. The company maintains qualified WPS for multiple wire compositions, base plate grades, and thickness ranges.
- Process capability documentation: Hardness mapping data, dilution analysis, and crack control records establish traceable process capability for customer audits and specification compliance.
- Third-party certification: Product testing by accredited laboratories (CNAS-accredited) provides independent verification of hardness, microstructure, and wear resistance claims.
- Industry-specific approvals: Qualification for mining and cement industry procurement systems requires documented field performance data and compliance with specific OEM specifications (e.g., FL Smidth, Thiel, Metso for cement; Caterpillar, Komatsu for mining).
8.2 Product Delivery Excellence
The technical maturity of this product line enables reliable, repeatable delivery:
- Standardized product ranges: Pre-qualified overlay configurations for common plate sizes and thicknesses enable rapid quotation and short lead times (7–15 days for standard products).
- Custom engineering capability: The ability to customize overlay thickness, hardness range, and geometry for specific customer applications demonstrates engineering flexibility.
- Quality traceability: Each production batch is traceable to wire heat number, WPS number, operator qualification, and test results. This traceability meets the documentation requirements of major mining and cement OEMs.
- Field support: Technical support for on-site overlay repair, including WPS development for customer-specific conditions, adds value beyond product supply.
8.3 Customer Value Realization
The ultimate value proposition of bimetallic wear-resistant weld overlay plates is realized through measurable operational improvements at customer facilities:
- Reduced total cost of ownership (TCO): Despite higher initial cost compared to plain carbon steel, the 3–8× life extension results in significantly lower cost per ton of material processed over the component's service life.
- Improved equipment availability: Longer replacement intervals mean fewer shutdowns for wear component replacement, directly improving plant throughput.
- Simplified maintenance: Weld overlay plates can be re-overlay in the field when worn, extending service life further without complete replacement.
- Customization for specific wear mechanisms: Overlay composition can be tailored to the specific abrasive particle characteristics (hardness, angularity, size distribution) of the customer's material stream.
- Environmental benefit: Reduced component replacement frequency means less scrap generation, lower material consumption, and reduced carbon footprint per ton of product processed.
9. Summary and Technical Recommendations
The bimetallic wear-resistant weld overlay plate technology represents a mature, well-understood engineering solution for the most common wear challenge in mining and cement industries. The combination of high-chromium flux-cored wire overlay (HRC 58–65) on ductile carbon steel base provides an optimal balance of wear resistance, toughness, and fabricability.
Key recommendations for successful implementation:
- Always qualify the WPS/PQR for the specific base plate grade, overlay wire composition, and service conditions before production.
- Accept surface cracking as a normal process characteristic, but control crack dimensions per established acceptance criteria.
- Implement a multi-pass overlay strategy with a transition layer to minimize dilution and maximize surface hardness.
- Perform hardness mapping (grid pattern) on every production batch to verify uniform hardness distribution.
- Document all process parameters, consumable heat numbers, and test results for full quality traceability.
- Provide customers with field performance data and lifecycle cost analysis to substantiate the value proposition.
- Consider explosion welding or hydraulic explosive bonding for high-volume standardized products where zero dilution and dimensional precision are critical.
This technology entry (No. 102) represents a core product capability that directly addresses the highest-value wear protection needs in the company's target industries. Its successful execution demonstrates the company's technical competence in weld overlay metallurgy, process control, and quality management—capabilities that underpin the entire product portfolio.