Microstructure and Sliding Friction Wear Performance of High-Chromium Bimetal Wear-Resistant Plate Weld Overlay Layer
1. Definition and Fundamental Principles
High-chromium bimetal wear-resistant plates are composite steel structures consisting of a soft, ductile base plate (typically low-carbon structural steel) and a hard, wear-resistant overlay layer deposited on the working surface. The overlay layer is primarily composed of high-chromium white cast iron (Cr content typically 12–30 wt%), which forms a matrix of chromium carbides (Cr7C3, Cr3C, and Cr23C6) embedded in a martensitic or austenitic ferrite matrix. The term "bimetal" reflects the deliberate combination of two metals with complementary mechanical properties: the base plate provides formability, weldability, and structural toughness, while the overlay layer delivers exceptional hardness (HRC 58–68) and abrasion resistance.
The fundamental wear resistance mechanism of the high-chromium overlay relies on the formation of hard carbide phases during solidification. Chromium carbides, particularly Cr7C3 and Cr3C, exhibit extreme micro-hardness (HV 1800–2400), high thermal stability, and chemical inertness. Under sliding friction conditions, these carbide particles resist micro-ploughing, micro-cutting, and adhesive transfer, thereby dramatically reducing volumetric wear rates compared to conventional carbon steels. The microstructure of the overlay—carbide morphology, distribution density, matrix hardness, and grain orientation—directly governs the tribological performance.
The sliding friction wear behavior is typically evaluated using pin-on-disk or block-on-ring test configurations under dry or lubricated conditions, in compliance with ASTM G99 or GB/T 12444. Key performance metrics include specific wear rate (mm3/N·m), friction coefficient (COF), wear depth profile, and cross-sectional microstructural integrity after wear testing.
2. Category and Business Positioning
This technical entry falls under the category of weld overlay metallurgy research and process optimization, specifically addressing the microstructural characterization and tribological validation of high-chromium overlay consumables. Within Cladding Technology Shanxi Co., Ltd.'s capability portfolio, this work directly supports the TIG/MIG weld overlay route, where high-chromium hardfacing alloys are deposited via pulsed TIG or short-circuit MIG welding to produce bimetal wear-resistant plates, pipes, and custom-shaped components.
The business positioning of this competency is threefold:
- Qualification Building: Documented microstructural analysis and wear test data form the evidentiary basis for welding procedure specifications (WPS), welder performance qualifications (WPQ), and product certifications required by downstream customers in mining, cement, power generation, and material handling industries.
- Product Delivery Assurance: Understanding the relationship between welding parameters, cooling rates, and resulting carbide morphology enables consistent control of overlay hardness and wear life, reducing field failure rates and warranty claims.
- Customer Value Engineering: Quantitative wear performance data allows engineers to select the optimal overlay alloy and process for specific service conditions (abrasive vs. adhesive vs. erosive wear), extending component service life by 3–10× compared to unclad alternatives.
3. Technical Purpose and Engineering Value
The primary technical purpose of studying the microstructure and sliding friction wear performance of the high-chromium weld overlay is to establish a robust process-structure-property-performance (PSPP) correlation model. This model enables the following engineering outcomes:
- Consumable Selection Optimization: Identifying the chromium content, carbon equivalent, and alloy additions (Mo, V, W, Ni, Co) that produce the most wear-resistant carbide architecture for a given service environment.
- Welding Parameter Refinement: Determining optimal heat input ranges (kJ/mm), travel speeds, and interpass temperatures that minimize dilution, control solidification cooling rate, and promote fine, uniformly distributed carbide networks.
- Performance Prediction: Enabling pre-delivery performance forecasting so that customers receive components with guaranteed minimum hardness, carbide content, and estimated wear life.
- Failure Analysis Capability: Providing the metallurgical knowledge base to diagnose premature wear failures in the field and implement corrective process modifications.
4. Key Process and Implementation Points
4.1 Overlay Composition Design
High-chromium weld overlay alloys used for bimetal wear-resistant plate fabrication are typically classified into the following families based on chromium content and matrix type:
| Alloy Family | Cr Content (wt%) | C Content (wt%) | Matrix Type | Typical Hardness (HRC) | Primary Carbides | Typical Application |
|---|---|---|---|---|---|---|
| High-Cr White Iron (Type I) | 12–16 | 2.5–3.5 | Martensite + Ferrite | 58–64 | Cr7C3, Cr3C | Chute linings, bucket teeth |
| High-Cr White Iron (Type II) | 20–25 | 2.0–3.0 | Martensite + M7C3 | 60–66 | Cr7C3, Cr3C | Conveyor idlers, mill liners |
| Stainless White Iron | 25–30 | 2.0–3.5 | Austenite + Martensite | 56–65 | Cr7C3, Cr23C6 | Corrosive + abrasive service |
| Ni-Cr Hardfacing | 15–25 | 2.5–4.0 | Austenite + Martensite | 58–66 | Cr7C3, Cr3C | Impact + abrasion (bucket teeth) |
4.2 Welding Process Parameters
For TIG (GTAW) overlay of high-chromium alloys on bimetal plates, the following parameter ranges are typically applied:
| Parameter | TIG (GTAW) Range | MIG (GMAW) Range | Influence on Microstructure |
|---|---|---|---|
| Welding Current | 80–180 A | 120–220 A | Higher current → coarser carbides, increased dilution |
| Travel Speed | 100–250 mm/min | 200–500 mm/min | Lower speed → higher heat input, larger grain size |
| Heat Input | 0.8–2.5 kJ/mm | 1.0–3.0 kJ/mm | Controls solidification rate and carbide morphology |
| Interpass Temperature | ≤ 150 °C | ≤ 150 °C | Excessive temperature → coarse carbides, reduced hardness |
| Shielding Gas | 100% Ar or Ar/He mix | Ar + 5–10% CO2 | Oxygen ingress → oxide inclusions, reduced toughness |
| Wire Diameter | 1.6–3.2 mm | 1.0–1.6 mm | Affects deposition rate and bead profile |
| Number of Passes | 2–6 layers | 2–8 layers | Multi-pass reduces dilution, refines final layer microstructure |
4.3 Microstructural Characterization Methods
Systematic microstructural analysis of the overlay layer is conducted using the following techniques:
- Optical Microscopy (OM): Grain size measurement, carbide distribution mapping, and dilution zone assessment at 100×–1000× magnification. Samples are prepared per ASTM E3 (polishing) and etched with 3–5% Nital or 10% picric acid in ethanol.
- Scanning Electron Microscopy (SEM) with EDS: Detailed carbide morphology (plate-like Cr7C3 vs. granular Cr3C), elemental mapping of Cr, C, Fe, and alloying additions, and identification of brittle intermetallic phases (e.g., Fe3C cementite) that may compromise impact toughness.
- X-Ray Diffraction (XRD): Phase identification and quantification of martensite, austenite, ferrite, and carbide phases. Diffraction patterns are analyzed per ASTM E975.
- Vickers Microhardness Profiling: Hardness traverses across the overlay/base interface at 0.5–1 mm intervals under 500–1000 g load per ASTM E92 / GB/T 6398.1. Typical target: ≥ HV 900 in overlay center, with controlled gradient at the transition zone.
- Carbide Content Quantification: Image analysis or gravimetric acid dissolution methods to determine volume fraction of chromium carbides (target: 25–40 vol%).
4.4 Sliding Friction Wear Testing Protocol
Wear performance is validated through standardized sliding friction tests:
| Test Parameter | Typical Configuration | Standard Reference |
|---|---|---|
| Test Machine | Pin-on-Disk or Block-on-Ring | ASTM G99 / GB/T 12444 |
| Counterface Material | GCr15 bearing steel pin (HRC 60–62) | ASTM G99 |
| Normal Load | 5–20 N (adjustable) | ASTM G99 |
| Sliding Distance | 1000–10000 mm | GB/T 12444 |
| Environment | Ambient (dry) or lubricated (ISO VG 68 oil) | ASTM G99 |
| Temperature | 20–25 °C (ambient) or elevated up to 300 °C | Custom |
| Measured Outputs | Friction coefficient (COF), wear volume loss, specific wear rate (mm3/N·m) | ASTM G99 |
Post-test analysis includes SEM examination of the wear track surface and cross-section to identify dominant wear mechanisms: abrasive wear (ploughing, cutting), adhesive wear (material transfer), oxidative wear (oxide scale formation), and fatigue wear (surface cracking). The overlay's carbide network should remain largely intact with minimal pull-out, indicating successful wear resistance.
5. Applicable Standards and Acceptance Criteria
5.1 Welding and Overlay Standards
- GB/T 11345-2013: Non-destructive testing of welds by magnetic particle testing (for surface crack detection in overlay).
- NB/T 47013.2-2015: Ultrasonic testing of welds in pressure equipment (applicable when overlay is on pressure vessels).
- ASTM A743 / A743M: Standard specification for castings, iron cast, for special purposes (reference for high-chromium cast iron composition and properties).
- ASTM A540: Standard specification for alloy steel castings for pressure vessels (base plate reference).
- GB/T 25677-2010: Welding consumables for hardfacing—classification and designation.
- ISO 16372: Welding consumables—classification for hardfacing electrodes and wires.
- ASME Section IX: Qualification of welding procedures and welders (WPS/WPQ framework).
- GB/T 985-2008: Welding procedure specification—content and preparation.
5.2 Microstructure and Properties Acceptance Criteria
| Property | Acceptance Criteria | Test Method |
|---|---|---|
| Overlay Hardness | ≥ HRC 58 (or HV ≥ 600) in overlay zone | ASTM E140 / GB/T 6398.1 |
| Transition Zone Dilution | ≤ 30% base metal dilution in first overlay pass | SEM-EDS / Spark-OES |
| Overlay Thickness | 3–10 mm (as specified per drawing) | Ultrasonic thickness gauge (GB/T 19624) |
| Surface Cracks | No cracks ≥ 0.3 mm length (MT) | GB/T 11345 / ASTM E709 |
| Porosity | No porosity clusters > 2 mm (UT/RT) | NB/T 47013.2 / GB/T 3323 |
| Carbide Volume Fraction | ≥ 25 vol% (target 30–40%) | Image analysis / acid dissolution |
| Specific Wear Rate | ≤ 1.0 × 10-6 mm3/N·m (dry sliding, 10 N) | ASTM G99 / GB/T 12444 |
| Impact Toughness (overlay) | ≥ 5 J (Charpy V-notch, 25 °C, if impact service) | GB/T 229 / ASTM E23 |
5.3 Industry-Specific Standards
- API 5L / API 5CT: When overlay is applied to casing, tubing, or line pipe for oil and gas service.
- NACE MR0175 / ISO 15156: Materials for H2S-containing environments (if overlay is used in sour service).
- ASTM B447 / B564: Reference for hardfacing alloy composition in copper-based systems (comparative).
- ISO 3320: Classification of wear types (abrasive, adhesive, erosive, fatigue) for wear testing documentation.
6. Common Risks and Controls
| Risk | Cause | Effect | Control Measure |
|---|---|---|---|
| Surface cracking in overlay | High carbon equivalent, rapid cooling, high restraint | Loss of wear protection, fatigue initiation | Preheat base plate to 150–250 °C; control heat input ≤ 2.0 kJ/mm; apply post-weld stress relief at 600–650 °C if permitted by alloy chemistry |
| Excessive dilution | High current, low travel speed, thin first pass | Reduced hardness, increased brittleness | Use low heat input first pass; apply multi-pass build-up; use consumable with higher Cr/C content in first pass |
| Coarse carbide morphology | Excessive heat input, slow cooling | Reduced wear resistance, increased pull-out during sliding | Maintain heat input 0.8–1.5 kJ/mm; use water quench or air cooling; increase travel speed |
| Porosity (gas inclusion) | Inadequate shielding, contaminated base/consumable | Reduced fatigue strength, surface roughness | Use high-purity Ar shielding; clean base surface to SA 2.5 (ISO 8501-1); apply back purging for pipe overlay |
| Heterogeneous hardness distribution | Inconsistent welding parameters, consumable lot variation | Non-uniform wear, premature localized failure | Implement SPC (Statistical Process Control) on hardness readings; certify consumable lots per ISO 16372; maintain welding parameter windows |
| Impact brittleness | Over-alloyed with Cr/C, high cooling rate martensite | Spalling under impact loading (e.g., bucket teeth) | Select Ni-Cr alloy family for impact service; temper overlay at 400–500 °C if impact toughness required; limit C content ≤ 3.0 wt% |
| Wear track delamination | Weak overlay/base bond, interfacial cracking | Catastrophic overlay loss in service | Ensure proper groove preparation (V-groove or bevel); verify wetting angle < 90°; perform bond strength test (ASTM A913) on witness coupons |
7. Application Scenarios Across Three Technology Routes
7.1 TIG/MIG Weld Overlay Route (Primary Application)
The high-chromium bimetal wear-resistant plate technology is most directly applicable through the TIG/MIG weld overlay route. This route is used for:
- Flat plate overlay: Production of wear-resistant lining plates (3–10 mm overlay thickness) for chute linings, hopper walls, and conveyor troughs in cement, mining, and power industries.
- Pipe and tube overlay: Internal or external overlay of high-chromium alloy on carbon steel pipes for slurry transport, pneumatic conveying, and cyclone wear linings.
- Custom-shaped component overlay: Bucket teeth, excavator wear plates, mill liners, and ball mill grinding bodies where the base geometry requires welding flexibility.
- Repair and restoration: Field repair of worn components by rebuilding the overlay layer to original dimensions, extending service life without component replacement.
In this route, the microstructural knowledge directly informs consumable selection (e.g., choosing a Type II high-Cr white iron wire for severe abrasion vs. a Ni-Cr alloy for impact-abrasion combined service) and welding parameter optimization to achieve target hardness and carbide morphology.
7.2 Hydraulic Explosive Bonding Route (Complementary Application)
While hydraulic explosive bonding (hydraulic explosion cladding) primarily produces bonded bimetallic plates through controlled fluid-driven collision, the high-chromium wear-resistant technology complements this route in the following ways:
- Overlay on bonded plate surfaces: After hydraulic explosive bonding produces a steel/copper or steel/stainless clad plate, a high-chromium weld overlay can be applied to the working surface to add wear resistance while retaining the corrosion or electrical conductivity of the bonded layer beneath.
- Multi-layer composite architecture: Base plate → explosive-bonded intermediate layer (for corrosion or thermal barrier) → TIG overlay of high-chromium alloy (for wear). This three-layer approach addresses multi-functional requirements in single components.
- Process qualification synergy: Microstructural data from weld overlay studies informs the design of transition layers between explosively bonded interfaces and subsequently welded overlay, ensuring metallurgical compatibility and avoiding brittle phase formation at multi-interface junctions.
7.3 Explosion Welding Route (Complementary Application)
Explosion welding (explosive cladding) produces high-strength metallurgical bonds between dissimilar metals at high collision velocities. The relationship to high-chromium wear-resistant technology includes:
- Explosively clad wear plates: Production of wear-resistant plates by explosion welding a high-chromium white cast iron sheet onto a ductile base plate. This method produces uniform overlay thickness and excellent bond strength without dilution, ideal for thick overlay requirements (5–25 mm) that would be impractical via welding.
- Microstructural comparison and process selection: The wear performance study data provides benchmarks for comparing explosively clad high-chromium plates against weld-overlaid equivalents, enabling process selection based on cost, thickness requirements, and performance equivalence.
- Post-explosion weld repair: When explosively clad plates require local repair or additional material build-up, TIG/MIG weld overlay is applied. Understanding the weld overlay microstructure ensures that repair welds do not degrade the existing explosive bond interface.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The systematic study of overlay microstructure and wear performance generates the technical documentation required for:
- WPS Qualification: Welding procedure qualification records (WPQR) per ASME Section IX or GB/T 19866, supported by hardness profiles, macro/microstructural photographs, and wear test data demonstrating the procedure produces acceptable results.
- Product Certification: Third-party certification bodies (e.g., TUV, DNV, CNAS-accredited labs) require documented microstructural evidence and performance test data to certify wear-resistant plate products. The study provides this evidentiary foundation.
- ISO 9001 / ISO 3834 Quality Management: The documented PSPP correlation model supports the "process control" and "product verification" clauses of quality management systems, enabling traceability from raw consumable to delivered product performance.
8.2 Product Delivery Assurance
- First-article inspection: Microstructural examination and hardness profiling of the first production batch establishes the baseline for ongoing production quality control.
- In-process monitoring: Hardness readings at each production lot (target ≥ HRC 58) serve as a rapid in-process indicator of microstructural quality, correlating with carbide content and morphology.
- Wear life prediction: Accelerated wear test data, combined with field service experience, enables delivery of estimated service life data with each product, reducing customer risk and supporting warranty terms.
8.3 Customer Value
- Extended Service Life: High-chromium overlay with properly controlled microstructure extends component service life by 3–10× compared to unclad carbon steel, reducing downtime and replacement costs for mining, cement, and power customers.
- Customized Performance: The ability to tailor alloy composition and welding parameters to specific wear conditions (abrasive vs. erosive vs. impact-abrasive) delivers optimized solutions rather than generic products.
- Technical Support and Engineering: The depth of microstructural and tribological knowledge enables the company to provide customers with engineering analysis, failure investigation, and application consulting—differentiating the company as a technical partner rather than a commodity supplier.
- Standard Compliance: Delivering products with documented compliance to GB/T 25677, ISO 16372, and relevant industry standards reduces customer procurement risk and accelerates qualification approval.
9. Conclusion and Forward-Looking Recommendations
The study of high-chromium bimetal wear-resistant plate weld overlay microstructure and sliding friction wear performance represents a core technical competency that underpins product quality, qualification certification, and customer trust. By systematically correlating welding parameters with microstructural features (carbide morphology, matrix type, hardness profile) and linking these to quantitative wear resistance metrics, the organization establishes a scientifically rigorous foundation for process control and product differentiation.
Recommended forward actions include:
- Expand wear testing matrix: Incorporate erosive wear (ASTM G74/G75), impact-abrasive wear (ASTM G81), and elevated-temperature sliding tests to cover the full spectrum of customer service conditions.
- Develop consumable library: Qualify and document at least 5–8 high-chromium alloy compositions across the TIG/MIG route, each with complete PSPP data, to enable rapid selection for diverse applications.
- Integrate with explosive bonding route: Conduct comparative wear studies between explosively clad and weld-overlaid high-chromium plates to establish process selection guidelines for thick overlay applications.
- Automate in-process hardness monitoring: Deploy portable hardness testers with data logging to create real-time production quality databases, supporting SPC and predictive maintenance of welding equipment.
- Pursue third-party certification: Submit representative products for independent wear testing and microstructural certification to accredited laboratories, providing customers with third-party verified performance data.
Through disciplined application of metallurgical science, standardized testing protocols, and systematic process control, the high-chromium bimetal wear-resistant plate technology positions Cladding Technology Shanxi Co., Ltd. as a technically competent provider of high-performance wear solutions across mining, cement, power, and material handling industries.